Biology Paper 1 AQA NEW SPEC

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Give two examples of eukaryotic cells. What do the

Plant and animal cells. They have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.

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Give an example of a prokaryotic cell. What do the

Bacterial cells are smaller than eukaryotic cells. They have cytoplasm and a cell membrane surrounded by a cell wall. It is a single DNA loop and there may be one or more small rings of DNA called plasmids instead of a nucleus.

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What do animal cells have?

Nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. 

Nucleus - controls the activity of the cell

Cytoplasm - where the reaction takes place, controlled by enzymes

Cell membrane - controls the movement of substances into and out of the cell

Mitochondria - where respiration takes place, energy is released here

Ribosomes - protein synthesis takes place

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What do plant cells have?

They are bigger than animal cells with a cell wall, chloroplasts, vacuole, nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. 

Cell wall - made up of cellulose which strengthens the cell

Choroplast - contains the green pigment chlorophyll which absorbs light energy for photosynthesis

Permanent vacuole - filled with cell sap to keep the cell turgid - swollen with water - and rigid. 

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What diseases are caused by fungi and protists?

Fungi - Rose black spot, trush and athlete's foot.

Protists - Malaria, African sleeping sickness and malaria.

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How does malaria spread?

Malaria is caused by a parasitic protist pathogen. It is transferred to humans by mosquitoes which act as vectors for the disease. Malaria causes fever and shaking as it destroys red blood cells. Spread is reduced by preventing the vectors from breeding and by using mosquito nets to prevent people from being bitten. Malarial parasites reproduce asexually in the human host but sexually in the mosquito.

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What is Gonorrhoea?

Gonorrhoea is a sexually transmitted disease (STD)

Symptoms = thick yellow or green discharge from the vagina or penis and pain on urinating.

It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom. 

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What is salmonella?

Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions.

In the UK, poultry are vaccinated against Salmonella to control the spread.

Symptoms: fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.

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What are measles?

Measles is a viral disease.

Symptoms of = fever and a red skin rash.

Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is spread by inhalation of droplets from sneezes and coughs.

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What is HIV?

HIV initially causes a flu-like illness.

Unless successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells.

Late stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.

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What is TMV?

Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes.

It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.

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What is rose black spot?

Rose black spot is a fungal disease.

Symptoms = purple or black spots develop on leaves, which often turn yellow and drop early.

It affects the growth of the plant as photosynthesis is reduced. It is spread in the environment by water or wind. Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.

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How are sperm cells specialised?

Function - Fertilises an egg cell - female gamete

Adaptation - a long tail whips from side to side to help move the sperm through water or the female reproductive system, the middle section is full of mitochondria, which is where respiration takes place and transfers the energy needed for the tail to work. The acrosome - head, which is also streamlined - stores digestive enzymes for breaking down the outer layers of the egg. A large nucleus contains the genetic information to be passed on.

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How are RBCs specialised?

Function - Contain haemoglobin to carry oxygen to the cells.

Adaptation - Thin outer membrane to let oxygen diffuse through easily. Biconcave shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin - a pigment that carries oxygen - and there is more space for oxygen to be carried. 

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How are muscle cells specialised?

Function - contract and relax

Adaptation - contain special proteins that slide over each other to make the fibre contract, they contain many mitochondria to transfer the energy needed for the chemical reactions to take place as the cells contract and relax. They can store glycogen, a chemical that can be broken down and used in cellular respiration by the mitochondria to transfer the energy needed for the fibres to contract.

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How are root hair cells specialised?

Function - absorb water and dissolved mineral ions from the soil. Mineral ions are moved into the root hair cells through active transport.

Adaptation - they greatly increase the surface area available for water to move into the cell. They have a large permanent vacuole that speeds up the movement of water by osmosis from the soil across the root hair cell. They have many mitochondria that transfer the energy needed for the active transport of mineral ions into the root hair cells.

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How are nerve cells specialised?

Function - to carry electrical signals around the body

Adaptation - lots of dendrites to make connections to other cells. An axon that carries the nerve impulse from one place to another can be very long. The nerve ending or synapses are adapted to pass the impulses to another cell or between a nerve cell and a muscle cell using special transmitter chemicals. They contain lots of mitochondria to provide the energy needed to make the transmitter chemicals.

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How is the xylem specialised?

Function - transport tissue in plants that carries water and mineral ions from the roots to the highest leaves and shoots. Supports the plant and it's stem.

Adaptation - xylem cells are alive when they are first formed but a special called called lignin builds up spirals in the cell walls. The cells die and form long, hollow tubes that allow water and mineral ions to move through them easily. The spirals and rings of lignin in the xylem cells make them very strong and help them withstand the pressure of the water moving up the plant. 

The movement of water from the roots through the xylem and out of the leaves is called transpiration. One direction. 

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How are the phloem cells specialised?

Function - specialised transport tissue that carries the food made by photosynthesis around the body of the plant. The phloem cells form tubes like xylem cells but unlike them, they do not become lignified and die.

Adaptations - The cell walls between the cells break down to form special sieve plates. These allow water carrying dissolved food to move freely up and down the tubes where it is needed. Phloem cells lose a lot of their internal structures by companion cells that help keep them alive. The mitochondria of the companion cells transfer the energy needed to move dissolved up and down the plants in the phloem.

The transport goes in both directions. This process is called translocation. Movement goes both ways.  

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How are photosynthetic cells specialised?

Adaptation - contain specialised green structures called chloroplasts containing chlorophyll that trap the light needed for photosynthesis. They are usually positioned in continuous layers in the leaves and outer layers of the stem of a plant so they absorb as much light as possible. They have a large permanent vacuole that helps keep the cell rigid as a result of osmosis. When lots of these rigid cells are arranged together to form photosynthetic tissue, they help support the cell. They also keep the leaf spread out so it can capture as much light as possible.

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What occurs as an organism develops?

Differentiation is the process by which a cell changes to become specialised for its job.

As an organism develops, cells differentiate to form different types of cells: Most types of animal cell differentiate at an early stage and many types of plant cells retain the ability to differentiate throughout life.

In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.

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Describe light microscopes and electron microscope

Light microscopes - they are relatively cheap and can be used almost everywhere. They use a beam of light to form the image of an object. They may magnify things several thousand times. 

Electron microscopes - use a beam of electrons to form an image and can magnify and image up to around 2 million times. Transmission electron microscopes give 2D images but very high magnification and resolution. Scanning electron microscopes give 3D images but lower magnifications.

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Why are electron microscopes better than light mic

An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

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What is the equation for magnification?

Magnification = size of image / size of real object

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How to convert between metres, centimetres, millim

m

↑ /1000 ↓ x1000

mm

↑ /1000 ↓ x1000

μm

↑ /1000 ↓ x1000

nm

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What is the difference between magnification and r

Magnification is the ability to make small objects seem larger, such as making a microscopic organism visible. Resolution is the ability to distinguish two objects from each other. Light microscopy has limits to both its resolution and its magnification.

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How do bacteria multiply?

Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature. Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate. Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.

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How does the process of binary fission occur?

1) The circular DNA and plasmids replicate.

2) The cell gets bigger and the circular DNA strands move to opposite 'poles' (ends) of the cell. 

3) The cytoplasm begins to divide and new cell walls begin to form.

4) The cytoplasm divides and two daughter cells are produced. Each daughter call has one copy of the circular DNA, but can have a variable number of copies of the plasmids.

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PRACTICAL - PREPARING SLIDE.

1) Add a drop of water to the middle of a clean slide.

2) Cut up an onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers.

3) Using the tweezers, place the epidermal tissue into the water on the slide.

4) Add a drop of iodine solution. Iodine solution is a stain. Stains are used to highlight objects in a cell by adding colour to them.

5) Place a cover slip (a square of thin, transparent plastic or glass) on top. To do this, stand the coer slip upright on the slide, next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubbles under there - they'll obstruct your view of the specimen.

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REQUIRED PRACTICAL - MICROSCOPY

1) Clip the slide you've prepared onto the stage.

2) Select the lowest-powered objective lens, the one that produces the lowest magnification.

3) Use the coarse adjustment knob to move the stage up to just below the objective lens.

4) Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus. 

5) Adjust the focus with the fine adjustment knob, until you get a clear image of whats's on the slide. 

6) If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocous.

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PRACTICAL - Where microorganisms are grown.

Bacteria are grown and cultured in a "culture medium", which contains the carbohydrates, minerals and vitamins they need to grow. They are grown on an agar plate. Bacteria grown on agar 'plates' will form visible colonies on the surface of the jelly, or will spread out to give an even covering of bacteria. In the lab at school, they are kept at 25°C because harmful pathogens are likely to grow above this temperature. In industrial conditions, cultures are incubated at higher temperatures so that they can grow a lot faster.

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PRACTICAL - Before the CULTURING experiment...

1) Petri dish must be sterilised before use to kill any unwanted microorganisms that may be lurking on them.

2) The inoculating loop must be sterilised by passing it through a flame.

3) After transferring the bacteria, the lid of the petri dish should be taped on, to prevent microorganisms from the air from entering.

4) The petri dish should be stored upside down - to stop drops of condensation falling onto the agar plate.

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REQUIRED PRACTICAL - EFFECT OF ANTIBIOTICS ON BACT

1) Place paper disks soaked in different types (or different concentrations) of antibiotics on an agair plate that has an even covering of bacteria. Leave some space between the discs.

2) The antibiotic should diffuse into the agar jelly. Antibiotic resistant bacteria will continue to grow on the agar around the paper discsm but non-resistant strains will die. A clear area will be left where the bacteria have died - this is called the inhibition zone.

3) Make sure you use a control. This is a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water. You can then be sure that any difference betwee the growth of the bacteria around the control disc and around one of the antibiotic discs is due to the effect of the antibiotic alone.

4) Leave the plate for 48 hours at 25°C.

5) The more effective the antibiotic is against the bacteria, the larger the inhibition zone.

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What does the nucleus contain?

The nucleus of a cell contains chromosomes made up of DNA molecules. Each chromosome carries a large number of genes. In the body the chromosomes are usually found in pairs. 23 pairs of chromosomes, 46 altogether. 

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Describe the process of mitosis.

Mitosis is asexual cell division in which two identical daughter cells are formed. Cells divide in a series of stages called the cell cycle. During the cell cycle the genetic material is doubled and then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis, the chromosomes line up at the centre of the cells and cell fibres pull them apart, the chromosomes are pulled to opposite ends. Membranes form around each set of chromosomes. The nucleus divides. Finally the cytoplasm and cell membranes divide to form two identical daughter cells who have the same DNA as the parent cell.

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What does Cytokinesis mean?

The dividing of the cell in the last stage of mitosis.

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What does chromosome mean?

Thread-like structure carrying genetic information.

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What are chromatids?

Duplicate chromosomes produced during mitosis.

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What does allele mean?

A version of a particular gene.

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What is mitosis need for?

New cells are needed for growth and to replace worn out cells. The new cells must have the same genetic information in them as the originals. Each cell has a nucleus containing the genes grouped together on chromosomes.

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What are stem cells?

An undifferentiated / unspecialised cell that can differentiate/ change into (many) other cell types.

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Advantages of using embryonic stem cells.

  • can create many embryos in a lab 
  • painless technique
  • can treat many diseases
  • stem cells are pluripotent / can become any type of cell (whereas bone marrow can treat a limited number) 
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Disadvantages of using embryonic stem cells.

  • harm / death to embryo
  • embryo rights / embryo cannot consent
  • unreliable technique / may not work 
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Advantages of using embryos from bone marrow.

  • no ethical issues / patient can give permission
  • can treat some diseases
  • procedure is (relatively) safe / doesn’t kill donor
  • tried and tested / reliable technique
  • patients recover quickly from procedure 
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Disadvantages of using embryos from bone marrow.

  • risk of infection from procedure
  • can only treat a few diseases
  • procedure can be painful 
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Advantage of using embryonic and bone marrow stem

  • can treat the disease / problem 
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Disadvantages of using embryonic and bone marrow s

  • risk of transfer of viral infection
  • some stem cells can grow out of control / become cancerous
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What is the function of stem cells in embryos?

To replace faulty cells in sick people.

For eg. You could make insulin-producing cells for people with diabetes and nerve cells for people paralysed by spinal injuries. 

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The function of stem cells in adults.

Medicine already uses adult stem cells to cure diseases.

For eg. stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient that recieves them. 

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The function of stem cells in meristems of plants.

In plants, stem cells are found in the meristems (parts of the plant where growth occurs). Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant. These stem cells can be used to produce clones (identical copies) of whole plants quickly and cheaply. They can be used to grow more plants of rare species - to prevent them being wiped out. Stem cells can also be used to grow crops of identical plants that have desired features for farmers, for example, disease resistance.

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What occurs in therapeutic cloning?

In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment.

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Define diffusion.

Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

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Give two examples of where diffusion takes place.

Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.

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Factors which affect the rate of diffusion are

  • the difference in concentrations (concentration gradient)
  • the temperature
  • the surface area of the membrane
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Difference in concentration gradient - diffusion

If there is a big difference in concentration between two areas, diffusion will take place very quickly. Many particles will move randomly towards the area of low concentration. 

However, if there is a small difference in concentration between two areas, the net movement by diffusion will be quite slow. The difference in concentration is called a concentration gradient. 

The bigger the difference, the steeper the concentration gradient and the faster the rate of diffusion.

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How does temperature affect diffusion?

An increase in temperature means the particles in a gas or a solution move around more quickly. This is because the particles have more energy so the random movement of the particles speeds up. Diffusion occurs quicker.

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Cell membranes and diffusion.

Cell membranes hold the cell together but also allows substances in and out as well. Dissolved substances move in and out of the cell in diffusion. These include simple sugars, such as glucose, gases, such as carbon dioxide and oxygen, and waste products such as urea from the breakdown of amino acids in your liver. The urea passes from the liver cells into the blood plasma and is excreted by the kidneys. Increasing the surface area of the cell membrane makes diffusion occur faster. By folding up the membrane of a cell, or the tissue lining an organ, the area over which diffusion can take place is greatly increased. 

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Oxygen and diffusion.

The oxygen required for respiration passes from the air in the lungs into the red blood cells through the cell membranes by diffusion. The oxygen moves down a concentration gradient from an area of high oxygen concentration to an area of low oxygen concentration. Oxygen also moves by diffusion down a concentration gradient from the red blood cells into the cells of the body where it is needed. Carbon dioxide moves out from the body cells into the red blood cells and then into the air in the lungs by diffusion down a concentration gradient. The diffusion of oxygen and carbon dioxide in opposite directions is called gas exchange.

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Exchange in the small intestine

Substances involved - digested food molecules

Moves from highly concentrated areas in the small intestine to areas that are less concentrated in the blood in villi capillaries. 

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How are villi adapted?

  • the folded villi greatly increase the surface area of the intestine which maximises the rate of diffusion
  • the villi are made of a single layer of thin cells so substances can diffuse across easily
  • beneath the villi is an extensive blood capillary network to distribute the absorbed food molecules and make the absorption quick
  • there are millions of them so diffusion occurs at a quick rate and this give it a large surface area as well
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How are the lungs adapted?

The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it. To do this, the lung contains millions of little air sacs called alveoli where the gas exchange takes place.

Alveoli are adapted because they have:

  • a large surface area
  • moist lining for dissolving gases
  • very thin walls
  • a good blood supply
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How are fish adapted?

The gills are the gas exchange surface in fish. Water containing oxygen enters the fish through its mouth and passes out through the gills. As this happens, oxygen diffuses from the blood into the gills and carbon dioxide diffuses from the blood into the water. Each gill is made up of lots of thin plates called gill filaments, which have a big surface area for gas exchange of gases. The gill filaments are covered in lots of tiny structures called lamellae, which incease the surface area even more. The lamellae have lots of blood capillaries to speed up diffusion. They also have a thin surface layer of cells to minimise the distance that the gases have to diffuse. Blood flows thhrough the lamellae in one direction and water flowers over in the opposite direction. This maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.

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How are leaves adapted?

Carbon dioxide diffuses into air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. The underneath of the leaf is a gas exchange surface, covered in stomata where the carbon dioxide diffuses in through. Oxygen produced in photosynthesis and water vapour also diffuse out through the stomata. The size of the stomata is controlled by guard cells which close the stomata if the plant is losing water faster than it is being replaced by the roots. Without these guard cells, the plant would wilt. The flattened shape of the leaf form another exchange surface so that it is more effective. The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increases the area of this surface so there's more carbon dioxide to get into the cells. The water vapour exaporats from the cells inside the leaf and escapes by diffusion because there's a lot of it inside the leaf and less of it in the air outside.

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How are the roots adapted?

  • Each branch of a root will be covered in millions of root hair cells which gives the plant a large surface area for absorbing water and mineral ions from the soil as it is needed for healthy growth.
  • The concentration of minerals is usually higher in the root hair cells than in the soil, so active transport takes place instead.
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How is the effectiveness of exchange surfaces incr

  • having a large surface area
  • a membrane that is thin, to provide a short diffusion path
  • (in animals) having an efficient blood supply
  • (in animals, for gaseous exchange) being ventilated
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Define osmosis.

Water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane. 

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Define cell isotonic to solution.

When the concentration of solutes in the solution outside the cell is the same as the concentration of solutes inside the cell.

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Define cell hypotonic to solution.

When the concentration of solutes in the solution outside the cell is higher than the concentration of solutes inside the cell. If a cell has a more concentrated solution inside it than outside it, then the overall movement of water is into the cell. In plant cells this causes the cell to begin to swell, and the cytoplasm and membrane push against the cell wall. The strong cell wall then resists further expansion, supporting the cell which becomes turged (fully inflated). More dilute solution outside the cell. 

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Define cell hypertonic to solution.

When the concentration of solutes in the solution outside the cell is lower than the concentration of solutes inside the cell. If a cell has a more dilute solution inside it than outside it, then the overall movement of water is out of the cell. In animal cells this would cause the cell to shrivel up, whilst in plant cells this would cause the membrane and cytoplasm to shrink away from the cell wall, causing the plant cell to become flaccid (limp) or plasmolysed. More concentrated solution outside of the cell. 

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PRACTICAL - OSMOSIS

1) Cut up a potato into identical cylinders and get some beakers with different sugar solutions in them. One should be pure water and another should be a very concentrated sugar solution. Then, have a few others with concentrations in between.

2) Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours. 

3) Then, take them out, dry them with a paper towel and measure their masses again.

4) If the cylinders have drawn in water by osmosis, they'll have increased in mass. If the water has been drawn out, they'll have decreased in mass. Calculate the percentage change in mass, then plot a graph.

Dependent variable: Chip mass

Independent variable: Concentration of sugar solutions

Control variable: Volume of solution, temperature, time, type of sugar used

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How can errors arise in Osmosis reaction?

They may occur when carrying out the method, for eg. if some potato cylinders were not fully dried, the excess water would give a higher mass, or if water evaporated from the beaker, the concentrations of the sugar solutions would change. You can reduce the effect of these errors by repeating the experiment and calculating a mean percentage change at each concentration.

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Define active transport.

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration.

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What does active transport allow?

Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.

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Difference between osmosis, active transport, diff

Diffusion is the movement of dissolved solutes or gases from an area of high concentration to an area of low concentration (down a concentration gradient). This is a passive process and so requires no energy in order to take place.

Osmosis is the movement of water down a concentration gradient (from high to low concentration) across a partially permeable membrane. Once again, this is a passive process and no energy is required.

Active transport is the movement of dissolved solutes across a membrane against a concentration gradient (moving from low to high concentration). This process requires a carrier protein, and energy in the form of ATP is required. 

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Define cells, tissues, organ, organ system.

  • Cells = basic building blocks of all living organisms.
  • A tissue = group of cells with a similar structure and function.
  • Organs = aggregations of tissues performing specific functions.
  • Organs are organised into organ systems, which work together to form organisms.
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What do muscular, glandular and epithelial tissue

Muscular tissue - contracts, moves the stomach wall to churn up the food

Glandular tissue - makes and secretes chemicals like enzymes and hormones, makes digestive juices to digest food

Epithelial tissue - covers parts of the body like the inside of the gut, covers the outside and inside of the stomach

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What organs are the digestive system made up of?

  • Glands - the pancreas (secretion of digestive enzymes) and salivary glands
  • Stoamach - digests food and it is the site of some protein digestion
  • Liver - produces bile
  • Small instestine - digests food and absorbs soluble food molecules
  • Large intestine - absorbs water from undigested food, leaving faeces
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Define catalyst.

A substance that increases the speed of a reaction without being changed or used up in the reaction.

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'Lock and key theory'.

Every enzyme has an active site with a unique shape that fits onto the substrate. They only catalyse one specific reaction. This is because for the enzyme to work, the substrate has to fit into the active site just like how a specific key is needed for certain doors. If the substrate doesn't fit into active site, the reaction will not be catalysed. In reality, the active site changes shape a little as the substrate binds to it to get a tigher fit. This is called the 'induced fit' model of enzyme action.

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What are enzymes?

They are biological catalysts and are made up of large proteins and all proteins are made up of chains of amino acids. These chains are folded into unique shapes, which enzymes need to do their job.

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What happens to enzymes if the temperature is too

If the temperature is too high, the enzyme will denature. This means that the active site will change shape and the substrate will no longer fit into the active site.

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What do digestive enzymes do?

Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.

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Give three examples of digestive enzymes.

  • Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch. Made in: salivary glands, pancreas and small intestine.
  • Proteases break down proteins to amino acids. Made in: stomach (pepsin), pancreas and small intestine.
  • Lipases break down lipids (fats) to glycerol and fatty acids. Made in: Pancreas and small intestine.

The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration. 

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Description of bile.

Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.

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How does pH affect enzymes?

If the pH is too high or too low, the pH inteferes with the bonds holding the enzymes together. This changes the shape of the active site and denatures the enzyme. All enzymes have an optimum pH that they work best at. It is often pH 7, but not always. For example, pepsin is an enzyme used to break down proteins in the stomach. It works best at pH 2, which means that it works best at acidic conditions.

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REQUIRED PRACTICAL - pH AND ENZYMES

1) Put a drop of iodine solution into every well of a spotting tile. Place a bunsen burner on a heat proof mat, and a tripod and gauze over the bunsen burner. Put a beaker of water on top of the tripod and heat the water until it is 35°C, make sure temperature is constant throughout.

3) Use a syringe to add 1 cm3  of amylase solution and cmof a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water and wait for 5 minutes.

4) Next, use a different syringe to add 5 cm3  of starch solution to the boiling tube. 

5) Immediately mix the contents of the boiling tube and start a stop clock.

6) Use continuous sampling to record how long it takes for the amylase to reak down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains browny-orange, starch is no longer present. 

7) Repeat the experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down. Remember to control any viariables like concentration and volume of amylase solution to make it a fair test.

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REQUIRED PRACTICAL - PREPARING FOOD SAMPLE

1) Get a piece of food and break it up using a pestle and mortar. 

2) Transfer the ground up food to a beaker and add some distilled water.

3) Give the mixture a good stir with a glass rod to dissolve some of the food.

4) Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food.

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Benedict's test for sugars.

1) Prepare a food sample and transfer 5 cm to a test tube.

2) Prepare a water bath so that it's set to 75°C.

3) Add Benedict's solution to the test tube (about 10 drops) using a pipette. 

4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure that the test tube is facing away from you.

5) If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick-red depending on how much sugar is in the food.

Turns brick red when on heating if sugar such as glucose is present.

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Iodine test for starch.

1) Make a food sample and transfer 5 cmof your sample to a test tube.

2) Then add a few drops of iodine solution and gently shake the tube to mix the contents. If the sample contains starch, the colour of the solution will change from browny-orange to black or blue-black.

Yellow-red iodine solution turns blue-black if starch is present.

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Biuret reagant for proteins.

1) Prepare a sample of your food and transfer 2 cmof your sample to a test tube.

2) Add 2 cmof biuret solution to the sample and mix the contents of the tube by gently shaking it. 

3) If the food sample contains protein, the solution will change from blue to pink or purple. If no protein is present, the solution will stay blue.

Blue biuret reagant turns purple if protein is present. Biuret solution is corrosive. Wear chemical and splash proof eye protection.

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Ethanol test for lipids.

Ethanol added to a solution gives a cloudy white layer if a lipid is present. Ethanol is highly flammable and harmful.

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How is the human circulatory system adapted?

Double circulatory system which means that it has a high blood pressure and a greater flow of blood to the tissues. The heart is made up of specialised cardiac muscle cells which have very long protein filaments that can slide past each other to shorten the cell, causing contractions for pumping the blood. Heart pumps blood o the lungs through pulmonary artery so that oxygenated blood diffuses into the blood from air in alveoli. Blood returns to the heart via the aorta to the rest of the body. Oxygen is carried by RBCs which have haemoglobin which binds to the oxygen and have no nucleus so there is more space for the oxygen to be carried. Arteries carry oxygenated blood to the tissues where capillaries deliver oxygen to cells for respiration and energy release. Thin walls allow for diffusion to cells. Large surface area of capillaries to maximise exchange. Waste products removed eg. Carbon dioxide diffuses from the cells into the blood plasma. Blood goes back to the heart through veins which have valves to prevent backflow. Cardiac output can vary according to demand and is affected by adrenalin.

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Blood flow.

Deoxygenated blood arrives at the left-hand side of the heart:

  1. It enters the heart through the vena cava.
  2. Blood flows into the right atrium.

  3. Blood is pumped into the right ventricle.

  4. Blood is pumped out of the heart, along the pulmonary artery, to the lungs.

Oxygenated blood arrives at the right-hand side of the heart:

  1. It enters the heart through the pulmonary vein.
  2. Blood flows into the left atrium.
  3. Blood is pumped into the left ventricle.
  4. Blood is pumped out of the heart, along the aorta to the rest of the body.
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Describe arteries.

  • Thick muscle and elastic fibres because high pressure blood travels through
  • Carries blood away from the heart
  • Small lumen
  • Thick walls
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Describe veins.

  • Carries blood to the heart
  • Contains valves to keep the blood flowing in the right direction and to prevent backflow
  • Large lumen
  • Low pressure blood
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Describe capillaries.

  • Walls are one cell thick which increases the rate of diffusion by decreasing the distance over which it occurs
  • Very narrow lumen 
  • Permeable walls so substances can diffuse in and out
  • Supply food and oxygen and take away waste such as carbon dioxide 
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What is the resting heart rate controlled by?

The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. These cells produce a small electrical impulse which spreads to the surrounding muscle cell, causing them to contract. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate. It produces an electric current to keep the heart beating regularly.

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Difference between artificial heart, pacemaker, tr

  • Artificial heart = a temporary mechanical heart
  • Artificial pacemaker = electrical device that corrects irregularities in the heart beat
  • Heart transplant = the transfer of a donor heart
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What are the four main components in blood?

1) Red blood cells - transports oxygen to the cells. They have a biconcave shape which gives it a large surface area for absorbing oxygen. Don't have a nucleus - more space to carry oxygen. Contain a red pigment called haemoglobin which binds to the oxygen to become oxyhaemoglobin in the lungs. In the body cells, the opposite happens and the oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen to the cells.

2) White blood cells - protects the body from infection. They engulf unwanted microorganisms through phagocytosis. Produce antibodies to fight microorganisms, as well as antitoxins to counteract the toxins released by the microorganism. Have a nucleus.

3) Platelets - helps to clot the blood. They are small fragments of cells and have no nucleus. They help blood clot at a wound to stop microorganisms from getting in. Lack of platelets can cause excessive bleeding and bruising.

4) Plasma - transports blood cells, carbon dioxide, and urea. Carries everything: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea from the kidneys, hormones, proteins, antibodies and antitoxings produced by the white blood cells.

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What builds up in coronary heart disease?

In coronary heart disease layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle which can result in a heart attack. Stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit.

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What do stents do?

Stents are tubes that are inserted inside arteries. They keep them open, making sure blood can pass through to the heart muscles. This keeps the person's heart beating. They are a way of lowering the risk of a heart attack in people with coronary heart disease. They are effective for a long time and the recovery time from the surgery is relatively quick. However, there is a risk of complications during the operation like heart attack from the surgery and a risk of infection. There is also the risk of patients developing a blood clot near the stent. This is called thrombosis. 

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What occurs when there are faulty valves?

In some people heart valves may become faulty, preventing the valve from opening fully, or the heart valve might develop a leak. Students should understand the consequences of faulty valves. Faulty heart valves can be replaced using biological or mechanical valves. Replacing a valve is a much less drastic procedure than a whole heart transplant, but fitting artificial valves is still major surgery, and there can still be problems with blood clots.

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What happens in case of heart failure?

In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery.

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What do statins do?

Statins are drugs that reduce cholesterol levels in the blood. Cholesterol is an essential lipid that your body produces and needs to function properly. However, too much cholesterol - LDL cholesterol - can cause health problems. Having too much cholesterol in the blood stream can cause fatty deposits to form inside arteries, which can lead to coronary heart disease. 

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Advantages of statins.

  • By reducing the amount of LDL (low density lipoprotein) in the blood, statins reduce the number of strokes, coronary heart disease and heart attacks
  • As well as reducing the amount of LDL, statins can increase the amount of beneficial type of cholesterol called HDL into the bloodstream. This type can remoe the LDL from the blood.
  • Some studies suggest that statins may also help prevent some other diseases
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Disadvantages of statins.

  • Statins are long term drugs that must be taken regularly. There's the risk that someone could forget to take them
  • Statins can sometimes cause negative side effects like headaches. Some of these side effects can be serious like kidney failure, liver damage and memory loss
  • The effect of statins isn't instant. It takes time for their effect to kick in
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What do artificial hearts do?

They are mechanical devices that pump blood for a person whose own heart has failed. They are usually only used as a temporary fix, to keep a person alive until a donor heart can be found or to help a person recover by allowing the heart to rest and heal. In some cases thoguh, they are used as a permanent fix, which reduces the need for a donor heart.

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Advantages of artificial hearts.

  • Less likely to be rejected by the body's immune system than a donor heart, no need to take immunosuppressant drugs
  • This is because they are made from metals or plastics, so the body doesn't recognise them as foreign and attack in the same way it does with living tissue
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Disadvantages of artificial hearts.

  • Surgery to fit an artificial heart can lead to bleeding and infection
  • Don't work as well as healthy ones, parts of the heart could wear out or the electrical motor could fail
  • Blood doesn't flow through artificial hearts as smoothly, which can cuase blood clots and lead to strokes
  • The patient has to take anticoagulants - blood thinners - to make sure that the blood doesn't clot which can cause problems with bleeding if they're hurt in an accident
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What does artificial blood do?

When someone loses a lot of blood, their heart can still pump the remaining red blood cells around (to get oxygen to their organs) as long as the volume of their blood can be topped up. Artificial blood is a blood substitute, eg a salt solution/saline, which is used to replace the lost volume of blood. It's safe (if no air bubbles get into the blood) and can keep people alive even if they lose two thirds of their red blood cells. If not, the patient will need a blood transfusion. Ideally, an artificial blood product would replace the function of the red blood cells, so that there's no need for a blood transfusion. 

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Define health.

Health is the state of physical and mental well-being. 

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What is responsible for causing ill health?

Diseases, both communicable and non-communicable, are major causes of ill health. Other factors including diet, stress and life situations may have a profound effect on both physical and mental health.

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Examples of different types of diseases interactin

  • Defects in the immune system mean that an individual is more likely to suffer from infectious diseases because their body is less likely to defend itself against the pathogen that causes the disease
  • Viruses living in cells can be the trigger for cancers. For example, infection with the hepititis virus can cause long term infections in the liver, where the virus lives in the cells. This can lead to an increased chance of developing liver cancer. HPV can cause cervical cancer in women
  • Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma
  • Severe physical ill health can lead to depression and other mental illness, particularly if they have an impact on the person's ability to carry out everyday activities or if they affect the person's life expectancy
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What other factors affect health?

  • Whether or not you have a good, balanced diet
  • The stress you are under
  • Life situation - if you have easy access to medicine, are able to buy healthy food, or access condoms to prevent the transmission of STDs.
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Human costs of non-communicable diseases.

  • Tens of millions of people around the world die from non-communicable diseases per year.
  • People with these diseases may have a lower quality of life or a shorter lifespan. This not only affects the diagnosed, but their loved ones too.
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Financial cost of non-communicable diseases.

  • The cost to the NHS of researching and treating the diseases is huge - same for other health services and organisations around the world.
  • Families may have to move or adapt their home to help a family member with a disease which can be costly.
  • Also, if the family member with the disease has to give up work or dies, the family's income will be reduced.
  • A reduction in the number of people able to work can also affect a country's economy.
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How are risk factors linked to disease?

Risk factors are linked to an increased rate of a disease.

They can be:

  • aspects of a person’s lifestyle - how much exercise they do
  • substances in the person’s body (asbestos fibres - asbestos was a material used in buildings until it was realised that the fibres could build up in airways and cause diseases such as cancer later on in life) or environment (pollution)

Many non-communicable diseases are caused by several different risk factors interacting with each other rather than one factor alone. Lifestyle factors can have different impacts locally, nationally and gobally. For eg. in developed countries, non-communicable diseases are more common as people have a higher income and can buy high fat food. Nationally, people in deprived areas are more likely to smoke, have a poor diet and not exercise. This means the incidence of cardiovascular disease, obesity and type 2 diabetes ias higher in those areas. Individual choices affect the incidence of disease.

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How can risk factors cause a disease directly?

  • The effects of diet, smoking and exercise on cardiovascular disease. Smoking has been proven to directly cause cardiovascular disease, lung disease and lung cancer. It damages the walls of arteries and the cells in the lining of the lungs.
  • Obesity as a risk factor for Type 2 diabetes. It is thought that obesity can directly cause Type 2 diabetes by making the body less sensitive or resistant to insulin, meaning that it struggles to control the concentration of glucose in the blood.
  • The effect of alcohol on the liver and brain function. Drinking too much alcohol has been shown to cause liver disease. The liver breaks down alcohol but the reaction can damage cells. Liver cells may damaged when toxic chemicals leak from the gut due to damage to the intestines caused by alcohol. Too much alcohol can affect brain function too. It can damage the nerve cells in the brain, causing the brain to lose volume.
  • The effect of smoking on lung disease and lung cancer.
  • The effects of smoking and alcohol on unborn babies. Smoking when pregnant reduces the amount of oxygen the baby recieves in the womb and can cause lots of health problems for unborn baby. Drinking alcohol has a similar effect, it can damage baby's cells affecting its development, causing a wide range of health issues.
  • Carcinogens, including ionising radiation, as risk factors in cancer which can be directly caused by exposure to certain substances or radiation. Carcinogens cause cancer and they work in different ways. For eg. some damage a cell's DNA in a way that makes the cell more likely to divide uncontrollably.
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How can risk factors be identified?

  • Risk factors are identified by scientists looking for correlations in data. However, correlation doesn't always equal cause.
  • Some risk factors aren't capable of directly causing a disease but are related to another risk factor that is.
  • For eg: A lack of exercise and a high fat diet are heavily linked to an increased chance of cardiovascular disease, but they don't cause the disease directly.
  • It's the resulting high blood pressure and high LDL levels that cause it.
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What is cancer caused by?

The result of changes in cells that lead to uncontrolled growth and division.

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What are benign tumours?

Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body. This is where the tumour grows until there is no more room. This type isn't normally dangerous, and the tumour isn't cancerous.

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What are malignant tumours?

Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours. Malignant tumours are dangerous and can be fatal - they are cancers.

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How do malignant and benign tumours differ?

  • (malignant tumours) invade / spread to other tissues via the blood (benign don’t)
  • (malignant tumours) form secondary tumours in other organs 
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How can risk factors be associated with lifestyle?

  • Smoking - smoking is linked to lung cancer, research has linked it to other types of cancer too like mouth, bowel, stomach and cervical cancer.
  • Obesity - linked to bowel and kidney cancer. Second biggest preventable cause of cancer after smoking.
  • UV exposure - people who are often exposed to UV radiation from the sun have an increased chance of developing skin cancer. People who live in sunny climates and people who spend a lot of time outside are at higher risk of developing skin cancer.
  • Viral infection - infection with some viruses has been shown to increase the chances of developing certain types of cancer. For eg. infection with hepatitis B and hepatitis C viruses can increase the risk of developing certain types of cancer. The likelihood of becoming infected with these viruses sometimes depend on lifestyle - for eg. they can be spread between people through unprotected sex or sharing needles.
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How can risk factors be associated with genetics?

Sometimes, someone can inherit faulty genes that make them more succeptible to cancer. For example: mutations in the BRCA genes have been linked to an increased likelihood of developing breast and ovarian cancer.

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Explain = structure linked to function in plants.

Plant tissues include:

  • epidermal tissues - this covers the whole plant
  • palisade mesophyll - this is the part of the leaf where most photosynthesis occurs
  • spongy mesophyll - this is also in the leaf, contains big air spaces to allow gases to diffuse in and out of cells
  • xylem and phloem - they transport things like water, mineral ions and food around the plant
  • meristem tissue found at the growing tips of shoots and roots - able to differentiate into lots of different types of plant cells, allowing the plant to grow. 
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What do xylem cells transport?

Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream. 

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What is the role of the stomata and guard cells?

The role of stomata and guard cells are to control gas exchange and water loss.

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What do phloem tissue transport?

Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation.

Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls.

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What is transpiration?

  • Transpiration is caused by the evaporation and diffusion of water from a plant's surface. Most transpiration happens at the leaves.
  • The evaporation creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
  • This in turn means more water is drawn up from the roots, and so there is a constant transpiration stream of water through the plant.
  • Transpiration is just a side-effect of the way leaves are adapted for photosynthesis. They have to have stomata in them so that gases can be exchanged easily. Because there's more water inside the plant than in the air outside, the water escapes the leaves through the stomata by diffusion.
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How does light intensity affect transpiration?

  • The brighter the light, the greater the transpiration rate.
  • Stomata begins to close as it gets darker. Photosynthesis can't happen in the dark, so they don't need to be open to let carbon dioxide in. When the stomata are closed, very little water can escape.
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How does temperature affect transpiration?

  • The warmer it is, the faster transpiration happens.
  • When it's warm, the water particles have more energy to evaporate and diffuse out of the stomata.
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How does air flow affect transpiration?

  • The better the air flow around a leaf, the greater the transpiration rate.
  • If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn't move away. This means there's a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn't happen as quickly.
  • If there's good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of high concentration to an area of lower concentration.
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How does humidity affect transpiration?

  • The drier the air around a leaf, the faster transpiration happens.
  • This is like what happens with air flow. If the air is humid, there's a lot of water in it already, so there's not much of a difference between the inside and the outside of a leaf.
  • Diffusion happens fastest if there's a really high concentration in one place, and a really low concentration in another.
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Why is water uptake is higher on a hot day than on

  • (on hot day) more water lost
  • more transpiration or more evaporation
  • so more water taken up (by roots) to replace (water) loss (from leaves) 
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The movement of potassium ions in leaves.

  • (potassium) ions increase the concentration of the solution (inside guard cells)
  • (potassium) ions make cell more concentrated / less dilute water moves into the (guard) cell by osmosis cell swells unevenly
  • (so stomata opens) as inner wall is less flexible than outer wall or thick part of the wall is less flexible than the thin part (of the wall) 
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How are guard cells adapted?

  • They have a kidney shape which opens and closes the stomata in a leaf.
  • When the plants of lots of water the guard cells fill with it and go plump and turgid. This makes the stomata open so gases can be exchanged for photosynthesis.
  • When the plant is short of water, the guard cells lose water and become flaccid, making the stomata close. This helps to stop too much water vapour from escaping.
  • Thin outer walls and thickened inner walls make the opening and closing work.
  • They're also sensitive to light and close at night to save water without losing out on photosynthesis.
  • More stomata is found on the undersides of leaves than on the top. The lower surface is shaded and cooler - so less water is lost through the stomata than if they were on the upper surface.
  • Guard cells are therefore adapted for gas exchange and controlling water loss within a leaf.
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How to estimate transpiration rate.

  • You can measure the rate of transpiration by measuring the uptake of water by plants.
  • This is because you can assume that water uptake by the plant is directly related to water loss through the leaves in transpiration.
  • Set up the apparatus as in the diagram, and then record the starting position of the air bubble.
  • Start a stopwatch and record the distance moved by the bubble per unit time.
  • Keep the conditions constant throughout the experiment.
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What are pathogens?

Microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and can be spread by direct contact, by water or by air.

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Dangers of bacteria and viruses.

  • Bacteria and viruses may reproduce rapidly inside the body.
  • Bacteria may produce poisons (toxins) that damage tissues and make us feel ill.
  • Viruses live and reproduce inside cells, causing cell damage.
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Human defence system.

  • Skin - sebum / oils to kill microbes, dead layer difficult to penetrate
  • Nose - hairs keep out dust and microbes
  • Trachea and bronchi - mucus traps microbes, cilia moves mucus
  • Stomach - (hydrochloric) acid kills bacteria
  • White Blood Cells - phagocytosis, antibody production, antitoxin production.

If a pathogen enters the body the immune system tries to destroy the pathogen.

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Oxygenated blood from the lungs to the body cells.

  • (blood) travels through (the) pulmonary vein (blood)
  • enters left atrium (blood)
  • enters (the) left ventricle
  • (blood) leaves the heart via / through (the) aorta
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Plant defence systems.

  • Mechanical:
  • cell wall - tough / difficult to penetrate, forms a physical barrier against pathogens that make it past the waxy cuticle.
  • waxy cuticle - tough / difficult to penetrate, provides a barrier to stop pathogens from entering.
  • dead cells / bark - fall off, taking pathogens with them
  • Chemical:
  • production of antibacterial chemicals - kill bacteria  
  • produce poisons which can deter herbivores like foxgloves, deadly nightshade etc.
  • Mechanical:
  • thorns and hairs - to stop animals from touching and eating them
  • other plants have leaves that droop or curl when something touches them, meaning that they can prevent themselves from being eaten otherwise known as mimicry
  • some plants mimic other organisms. Eg. the passion flower has bright yellow spots on its leaves which look like butterfly eggs. This stops other butterflies from laying their eggs there. Several species of plant in the 'ice plant family' in southern Africa look like stones and pebbles. This tricks other organisms into not eating them. 
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Fungi defence system.

  • antibiotic production - kill bacteria 
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What is injected in vaccination?

Vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.

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How can the spread of disease be reduced?

1) Being hygenic - washing hands before preparing food or after sneezing.

2) Destroying vectors - getting rid of the organisms that spread disease, vectors are insects that can be killed from insecticides of by destroying their habitat so they can no longer breed.

3) Isolating infected individuals.

4) Vaccination - in the UK, poultry is given a vaccination against Salmonella, to control the spread of the disease.

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Advantages to vaccination.

  • Have helped control lots of communicable diseases that were once common in the UK.
  • Because of vaccinations, smallpox no longer occurs at all, and polio infections have fallen by 99%
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Disadvantages to vaccinations.

  • Vaccines don't always work - sometimes they don't give you immunity.
  • You can sometimes have a bad reaction to a vaccine, but bad reactions are rare.
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What are antibiotics?

Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics. 

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What has antibiotics reduced?

The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. However, the emergence of strains resistant to antibiotics is of great concern. 

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What can antibiotics not do?

Antibiotics cannot kill viral pathogens. Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens. It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

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Why do bacteria become resistant to antibiotics?

  • Bacteria can mutate, sometimes the mutations can cause them to be resistant to an antibiotic. 
  • If you have an infection, some of the bacteria might be resistant to antibiotics.
  • This means that when the disease is treated, only the non-resistant strains of bacteria will be killed. 
  • The individual resistant strain of bacteria will survive and reproduce, and the population of the resistant strain will increase. This is an example of natural selection.
  • The resistant strain could cause a serious infection that can't be treated by antibiotics. Eg. MRSA causes serious wound infections and is resistant to the powerful antibiotic meticillin.
  • To slow down the rate of development of resistant strains, it's important for doctors to avoid over prescribing antibiotics. 
  • It's also important that you finish the whole course of antibiotics and not just stop once you feel better.
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Drugs originally came from plants...

Plants produce a variety of chemicals to defend themselves against pests and pathogens. Some of these chemicals can be used as drugs to treat human diseases or relieve symptoms. Traditionally drugs were extracted from plants and microorganisms: 

  • The heart drug digitalis originates from foxgloves. 
  • The painkiller aspirin originates from willow.
  • Penicillin was discovered by Alexander Fleming from the Penicillium mould. He was clearing out petri dishes containing bacteria when he noticed that one of the dishes of bacteria also had a mould on it and the area around the mould was free of the bacteria. He found that the mould on the petri dish was producing a substance that killed th bacteria - this substance was penicillin.

These days, drugs are made on a large scale in the pharmeceutical industry - they're synthesised by chemists in labs. However, the process still might start with a chemical extracted from a plant.

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Why do new medical drugs need to be tested?

New medical drugs have to be tested and trialled before being used to check that they are safe and effective. New drugs are extensively tested for toxicity, efficacy and dose. Preclinical testing is done in a laboratory using cells, tissues and live animals.

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Describe the first stage of drug testing.

  • In preclinical testing, drugs are tested on human cells and tissues in the lab.
  • However, you can't used human cells and tissues to test drugs that affect whole or multiple body systems. For eg. testing a drug for blood pressure must be done on a whole animal because it has an intact circulatory system. 
  • Very low doses of the drug are given at the start of the clinical trial.
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Second stage of drug testing.

  • This is when it is done on live animals.
  • This is to test efficacy (whether the drug works and produces the effect that you're looking for), to find out about its toxicity and to find the best optimum dosage (the concentration that should be given, and how often it should be given).
  • The law in Britain states that any new drug must be tested on two different live mammals. Some people think it's cruel to test on animals, but others believe it is the safest way to make sure a drug isn't dangerous before it's given to humans.
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Third stage of drug testing.

  • First, the drug is tested on healthy volunteers. This is to make sure that it doesn't have any harmful side effects when the body is working normally. At the start of the trial, a very low dose of the drug is given and this is gradually increased.
  • If the results of the test on healthy volunteers are good, the drugs can be tested on people suffering from the illness. The optimum dose is found - this is the dose of the drug that is the most effective and has few side effects.
  • To test how well the drug works, patients are randomly placed into two groups. One is given the new drug and the other is given a placebo - a substance that's like the drug being tested but doesn't do anything. This is so the doctor can see the actual difference the drug makes - it allows for the placebo effect (when the patient expects the treatment  to work and so feels better, even though the treatment isn't doing anything).
  • Clinical trials are blind - the patient in the study doesn't know whether they're getting the drug or the placebo. In fact, they're often double-blind trials, where neither the doctor nor the patient knows until all the results have been gathered. This is so the doctors monitoring the patients and analyzing the results aren't subconsciously influenced by their knowledge.
  • The results of drug testing and drug trials aren't published until they've been through peer review. This helps to prevent false claims.
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What is peer review?

When other scientists check that the work is valid and has been carried out vigorously.

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How are monoclonal antibodies produced?

Monoclonal antibodies are produced from a single clone of cells. The antibodies are specific to one binding site on one protein antigen and so are able to target a specific chemical or specific cells in the body.

They are produced by stimulating mouse lymphocytes to make a particular antibody. The lymphocytes are combined with a particular kind of tumour cell to make a cell called a hybridoma cell. The hybridoma cell can both divide and make the antibody. Single hybridoma cells are cloned to produce many identical cells that all produce the same antibody. A large amount of the antibody can be collected and purified.

Lymphocytes - produce antibodies but don't divide

Tumour cells - divides rapidly but doesn't produce antibodies

Hybridoma - makes antibodies and divides rapidly

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How are monoclonal antibodies used?

  • for diagnosis such as in pregnancy tests.
  • in laboratories to measure the levels of hormones and other chemicals in blood, or to detect pathogens.
  • in research to locate or identify specific molecules in a cell or tissue by binding to them with a fluorescent dye.
  • to treat some diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other cells in the body.
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How are monoclonal antibodies used in pregnancy te

  • A hormone called HCG is found in the urine of women only when they are pregnant.
  • The ***** that a woman urinates on has some antibodies to the hormone, with blue beads attached.
  • The test ***** (the bit that turns blue if you're pregnant) has some more antibodies to the hormones stuck onto it. 
  • If you're pregnant and you urinate on the *****: the hormone binds to the antibodies on the blue beads. The urine moves up the stick, carrying the hormones and the beads. The beads and hormones bind to the antibodies on the *****, so the blue beads get stuck onto the *****, turning it blue.
  • If you're not pregnant and you urinate on the *****: the urine still moves up the stick, carring the blue beads. But there's nothing to stick the blue beads onto the test *****, so it doesn't go blue.
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How can monoclonal antibodies treat diseases?

  • Different cells in the body have different antigens on their cell surface. Antigens are unqiue proteins on the surface of cells. You can make monoclonal antibodies that will bind to specific cells in the body.
  • Cancer cells have antigens on their cell membranes that aren't found on normal body cells. They're called tumour makers.
  • In the lab, you can make monoclonal antibodies that will bind to these tumour markers. An anti-cancer drugs can be attached to these monoclonal antibodies. This might be a radioactive substance, a toxic drug or a chemical which stops cancer cells from growing and dividing.
  • The antibodies target specific cells because they only bind to the tumour markers.
  • The drug kills the cancer cell but doesn't kill any normal body cells near the tumour.
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How are monoclonal antibodies used in research?

  • Monoclonal antibodies can be used to - bind to hormones and other chemicals in blood to measure their levels, test blood samples in laboratories for certain pathogens, and locate specific molecules on a cell or in a tissue:
  • First, monoclonal antibodies are made that will bind to the specific molecules you are looking for.
  • The antibodies are then bound to a flourescent dye.
  • If the molecules are present in the sample you're analysing, the monoclonal antibodies will attach to them, and they can be detected using the dye.
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Advantages of monoclonal antibodies.

  • Other cancer treatments can affect normal body cells as well as killing cancer cells, whereas monoclonal antibodies target specific target cells. 
  • This means that the side effect of an antibody-based drug are lower than for standard chemotherapy or radiotherapy.
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Disadvantages of monoclonal antibodies.

  • Monoclonal antibodies do cause more side effects than were originally expected for example, fever, vomiting and low blood pressure.
  • When they were first developed, scientists thought that because they targeted a very specific cell or molecule, they wouldn't create a lot of side effects.
  • This means that they are not widely used as treatments as scientists had originally thought they might be.
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Describe the structure of a leaf.

  • The epidermal tissues are covered with a waxy cuticle, which helps to reduce water loss by evaporation.
  • The upper epidermis is a transparent layer so that light can pass through it to the palisade layer.
  • The palisade layer has lots of chloroplasts. This means that they are near the top of the leaf where they can get the most light.
  • The xylem and phloem form a network of vascular bundles, which deliver water and othre nutrients to the entire leaf and take away glucose produced by photosynthesis. They also help support the structure. The tissues of the leaves are adapted for efficient gas exchange. The lower epidermis is full of stomata which allow carbon dioxide to diffuse directly into the leaf. 
  • The opening and closing of the stomata is controlled by guard cells in response to environmental conditions.
  • The air spaces in the spongy mesophyll tissue increase the rate of diffusion of gases.
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What can plant diseases be detected by?

  • stunted growth
  • spots on leaves
  • areas of decay (rot)
  • growths
  • malformed stems or leaves
  • discolouration
  • the presence of pests.
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Why do plants need mineral ions?

  • If there aren't enough mineral ions, plants will suffer deficiency symptoms.
  • Nitrates are needed to make proteins and therefore for growth. A lack of nitrates causes stunted growth.
  • Magnesium ions are needed for making chlorophyll, which is needed for photosynthesis. Plants without enough magnesium from chlorosis and have yellow leaves.
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What cause leads to crown galls?

Bacterial disease

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What cause leads to malformed stems and leaves?

Aphid infestation

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What causes stunted growth?

Nitrate deficiency

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What causes yellow leaves?

Magnesium deficiency

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What cause leads to mosaic patterns on leaves?

Tobacco mosaic virus.

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How can different signs of plants be identified?

  • Looking up the signs in a gardening manual or on a gardening website
  • Taking the infected plant to a laboratory, where scientists can identify the pathogen
  • Using testing kits that identify the pathogen using monoclonal antibodies
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What are aphids?

Insects that penetrate the plant phloem and feed on the dissolved food. They act as plant pathogens and are also vectors that carry pathogenic viruses, bacteria and fungi into healthy plant tissue.

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What is the equation for photosynthesis?

carbon dioxide + water → glucose + oxygen

Light is over 

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What type of a reaction is photosynthesis?

An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light so plants can make their own food. Energy is required in the form of light, which is absorbed by cholorphyll in the chloroplast. This energy is used to convert carbon dioxide and water into glucose. Oxygen is produced as a by-product.

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What are the 5 main ways that plants use glucose?

1) Respiration - transfers energy from glucose which enables the plants to convert the rest of the gluose into various other useful substances.

2) Making cellulose - glucose is converted into cellulose for making strong plant cell walls.

3) Making amino acids - glucose is combined with nitrate ions (from the soil) to make amino acids which are then made into proteins.

4) Stored as oils or fats - glucose is turned into lipds (fats and oils) for storing in seeds.

5) Stored as starch - glucose is turned into starch and stored in roots,stems and leaves, ready for use when photosynthesis isn't happening, like in winter. Starch is insoluble, which makes it better for storing that glucose - a cell with a lot of glucose in it would draw in lots of water and swell up, becoming turgid.

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What are the limiting factors of photosynthesis?

  • temperature
  • light intensity
  • carbon dioxide concentration
  • the amount of chlorophyll
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How can light intensity affect photosynthesis?

  • Light provides the energy needed for photosynthesis
  • As the light level is raised, the rate of photosynthesis increases steadily - up until a certain point
  • Beyond that point, no difference will be made because after this point, as light intensity increases, the rate of photosynthesis will no longer increase
  • This is because it is either temperature or the carbon dioxide level which is the limiting factor and not light
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How can carbon dioxide affect photosynthesis?

  • Too little carbon dioxide slows the rate of carbon dioxide down
  • As with light intensity, the amount of carbon dioxide will only increase the rate of photosynthesis up to a certain point
  • After this, the graph flattens out - as the amount of carbon dioxide increases, the rate no longer increases 
  • This shows that carbon dioxide is no longer a limiting factor
  • As long as light and carbon dioxide are in plentiful supply then the factor limiting photosynthesis must be temperature
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How can temperature affect photosynthesis?

  • Usually, if the temperature is the limiting factor it's because the temperature is too low - the enzymes needed for photosynthesis work more slowly at low temperatures
  • If the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be damaged and denatured
  • This will happen at about 45°C
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REQUIRED PRACTICAL - MEASURING RATE

1) A source of white light is placed at a specific distance from the pondweed.

2) The pondweed is left to photosynthesise for a set amount of time. As it photosynthesises,the oxygen released will collect in the capillary tube.

3) At the end of the experiment, the syringe is used to draw the gas bubbles in the tube  up alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of oxygen produced.

4) For this experiment, any variables that could affect the results should be controlled, eg. the temperature and the time.

5) The experiment is repeated twice with the light source at the same distance and the mean volume of oxygen produced is calculated.

6) Then the whole experiment is repeated with the light source at different distances from the pondweed.

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REQUIRED PRACTICAL - Altering apparatus.

  • The test tube of pondweed can be put into a water bath at a set temperature, or a measured amount of sodium hydrogencarbonate can be dissolved in the water which gives off carbon dioxide
  • The experiment can then be repeated with different temperatures of water/concentrations of sodium hydrogencarbonate
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What is the equation for light intensity?

Light intensity= 1/distance²

Inversely proportional

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What are hydroponics?

  • It is a system when plants are grown in water with a perfect balance of nutrients instead of soil to make sure nothing slows down their growth.
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Why are limiting factors important?

  • Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
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How to artificially create ideal conditions for fa

  • Greenhouses help trap the sun's heat, and make sure that the temperature doesn't become limiting. In winter, a farmer/gardener might use a heater as well to keep the temperature at the ideal level. In summer it could get too hot, so they might use shades and ventilation to cool things down.
  • Light is always needed for photosynthesis, so commercial farmers often supply artificial light after the sun goes down to give their plants more quality time for photosynthesis.
  • Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse by using a paraffin heater, and as the paraffin burns, carbon dioxide is produced as a by-product.
  • Keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases. The farmer can add fertilisers to the soil as well, to provide all the minerals needed for healthy growth.
  • Sorting this out costs money - but if the farmer can keep the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested much more often, which can then be sold. It's important that a farmer supplies just the right amount of heat, light, etc. - enough to make the plants grow well, but not more than the plants need, as this would just be wasting money.
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How to artificially create ideal conditions for fa

  • Greenhouses help trap the sun's heat, and make sure that the temperature doesn't become limiting. In winter, a farmer/gardener might use a heater as well to keep the temperature at the ideal level. In summer it could get too hot, so they might use shades and ventilation to cool things down.
  • Light is always needed for photosynthesis, so commercial farmers often supply artificial light after the sun goes down to give their plants more quality time for photosynthesis.
  • Farmers and gardeners can also increase the level of carbon dioxide in the greenhouse by using a paraffin heater, and as the paraffin burns, carbon dioxide is produced as a by-product.
  • Keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases. The farmer can add fertilisers to the soil as well, to provide all the minerals needed for healthy growth.
  • Sorting this out costs money - but if the farmer can keep the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested much more often, which can then be sold. It's important that a farmer supplies just the right amount of heat, light, etc. - enough to make the plants grow well, but not more than the plants need, as this would just be wasting money.
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What type of reaction is respiration?

Respiration is an exothermic reaction which is continuously occurring in living cells.

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What are the two types of respiration?

Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.

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What do organisms need energy for?

  • chemical reactions to build larger molecules
  • movement
  • keeping warm
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What is the equation for anaerobic respiration?

glucose + oxygen → carbon dioxide + water

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Anaerobic respiration in muscle cells?

Glucose → lactic acid

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Anaerobic respiration in plant and yeast cells.

Gucose → ethanol + carbon dioxide

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Why is less energy transferred in anaerobic respir

As the oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration.

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What is anaerobic respiration in yeast cells calle

Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcoholic drinks.

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What occurs during exercise?

During exercise the human body reacts to the increased demand for energy. The heart rate, breathing rate and breath volume increase during exercise to supply the muscles with more oxygenated blood.

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What will happen if insufficient oxygen is supplie

If insufficient oxygen is supplied anaerobic respiration takes place in muscles. The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt. During long periods of vigorous activity muscles become fatigued and stop contracting efficiently.

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What is oxygen debt?

Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells. Oxygen reacts with the lactic acid to from carbon dioxide and water. 

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When do the pulse and breathing rate stay high?

Whilst there are high levels of lactic acid and carbon dioxide.

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What occurs when you exercise more?

  • Muscles need energy from respiration to contract. When you exercise, some of your muscles contract more frequently than normal so you need more energy which comes from increased respiration. 
  • The increase in respiration in your cells means you need to get more oxygen to them.
  • Your breathing rate and breath volume increaases to get more oxygen to the blood, and your heart rate increases to get his oxygenated blood around the body faster. This removes carbon dioxide more quickly at the same time.
  • When you do really vigorous exercise, your body can't supply oxygen to your muscles quickly enough, so they start respiring anaerobically.
  • This isn't the best way to transfer energy from glucose because lactic acid builds up in the muscles, which gets painful.
  • Long periods of exercise also cause muscle fatigue - the muscles get tired and stop contracting efficiently.
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What is metabolism?

Metabolism is the sum of all the reactions in a cell or the body.

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What is the energy transferred by respiration used

The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.

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What does metabolism include?

  • conversion of glucose to starch, glycogen and cellulose
  • the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids
  • the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
  • respiration
  • breakdown of excess proteins to form urea for excretion.
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How are starch, glycogen and cellulose formed?

  • Lots of small glucose molecules are joined together in reactions to form starch (a storage molecule in plants), glycogen (a storage molecule in animal cells) and cellulose (a component of plant cell walls).
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What are lipids made from?

  • Lipid molecules are made from one molecule of glycerol and three molecules of fatty acids.
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What happens when glucose is combined with nitrate

  • Glucose is combined with nitrate ions to make amino acids, which are then made into proteins.
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What occurs when excess proteins are broken down?

  • Excess protein is broken down in a reaction to produce urea. Urea is then excreted in urine.
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What is the role of the liver?

  • detoxifying poisonous substances such as the ethanol from alcoholic drinks
  • passing the breakdown products into the blood so they can be excreted in the urine via the kidney
  • breaking down old, worn out blood cells and storing the iron until it is needed to synthesis more blood cells, which are produced in the bone marrow
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Give four examples of ionising radiation.

  • ultraviolet from the sun - this increases the risk of skin cancers such as melanoma (protection includes sunscreen and sensible clothing)
  • radioactive materials found in the soil, water and air (including radon gas in granite-rich areas such as Cornwall and the Pennines)
  • medical and dental X-rays
  • accidents in nuclear power generation, especially accidents such as the one in Chernobyl, Ukraine in 1986, can spread ionising radiation over wide areas
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What are the dangers of alcohol?

  • Alcohol can damage the liver and cause cirrhosis and liver cancer
  • Alcohol can cause brain damage and death
  • Can affect the development of unborn babies
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Describe the two ways we can treat cancer.

  • Radiotherapy - when the cancer cells are destroyed by targeted doses of radiation. This stops mitosis in the cancer cells but can also damage healthy cells. Methods of delivering different types of radiation in very targeted ways are improving cure rates.
  • Chemotherapy - chemicals are used to either stop the cancer cells dividing or to make them 'self-destruct'. There are many different types of chemotherapy and scientists are working to make them as specific to cancer cells as possible.
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What are the components in smoke?

  • Tar - a carcinogen and causes lung cancer, a sticky black chemical that accumulates in the lungs, turning them from pink to grey. Smokers are likely to develop bronchitis (inflammation and infection of the bronchi). The build up of tar in the delicate lung tissue can lead to a breakdown in the structure of the alveoli causing COPD. This reduces the surface area to volume ratio of the lungs, leading to severe breathlessness and eventually death
  • Carbon monoxide - haemoglobin binds to the carbon monoxide instead of the oxygen, leading to a shortage in oxygen which is why many smokers are usually breathless
  • Nicotine - addictive
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