Biology-Unit 2a

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  • Created by: Zoe
  • Created on: 12-04-13 12:07

2.1 Animal and Plant cells

In Plant and Animal cells

  •  Cell membrane – has tiny pores. These allow small molecules like water and gases to diffuse through, but keep large molecules inside the cell. 
  •  Cytoplasm – where many of the chemical reactions in the cell occur. These reactions are catalysed by enzymes. 
  • Nucleus – controls the activities of the cell. It contains genetic information for making proteins. This has a membrane extending from it onto which ribosomes are attached.
  • Mitochrondrion – where energy stored in sugars is released by respiration in the cell.
  • Ribosomes – where protein synthesis occurs. A copy of the genetic information needed to produce a protein is made from the DNA in the nucleus. This copy becomes attached to a ribosome. Enzymes then use this information to join amino acids in the correct sequence to produce the protein.
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2.1 Animals and Plant cells

Extra parts that are in a plant cell

  • Chloroplasts – contain a green pigment called chlorophyll. This absorbs light energy. Chloroplasts convert this light energy into chemical energy into carbohydrates. 
  • Vacuole – is filled with a solution of ions called cell sap. When it is full the vacuole supports the cell. 
  • Cell wall – made up of tiny fibres. Together these are very strong, so the cell wall supports the cell.
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2.1 Specialised cells- Leaf cells

Cells may be specialised for a particular function. Their structure will allow them to carry this function out.

cross section through a leaf cell (

Leaf Cells- absorbs light energy for photosynthesis – packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.


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2.1 Specialised cells- Root hair cells

root hair cell - has a head and tail (

Root hair cell-Absorbs water and mineral ions from the soil - Long 'finger-like' process with very thin wall, which gives a large surface area.

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2.1 Specialised cells- Sperm cells

sperm cell - has a head and tail (

Sperm cells- Fertilises an egg cell - The head contains genetic information and an enzyme to help penetrate the egg cell membrane. The middle section is packed with mitochondria for energy. The tail moves the sperm to the egg.


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2.1 Specialised cells

Xylem – hollow, dead (no cytoplasm) 

Nerve – long slender axons 

Egg – big and carry food reserves 

White blood – can change cell shape to engulf microbes

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2.2 Movement in and out of cells-Diffusion


Diffusion is the movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration.

Diffusion happens when the particles are free to move. Particles continue to move from a high to a low concentration while there is a concentration gradient. The higher the concentration gradient, the faster the rate of diffusion.

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2.2 Movement in and out of cells- Osmosis


Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

Eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels.

Osmosis is important to plants. They gain water by osmosis through their roots.

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2.3 Photosynthesis

Photosynthesis is the process in which green plants use sunlight, water and carbon dioxide to produce carbohydrates (and oxygen as a by-product). The reaction requires light energy, which is absorbed by a green substance called chlorophyll.

Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration.

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2.3 Photosynthesis-limiting factors

Three factors can limit the speed of photosynthesis - light intensity, carbon dioxide concentration and temperature.

  •  Light intensity – high intensity, high rate. However, past a certain point, it has no effect. 
  • Carbon dioxide concentration – high concentration, high rate. However, at a certain point it has no effect. 
  • Temperature – high temperature, high rate. However, at 45ºC, enzymes are denatured and the rate drops to 0.
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2.3 Photsynthesis 2

Plants get hydrogen and oxygen from water in the soil, and carbon and oxygen from the atmosphere. Water and carbon dioxide are used to synthesise food during photosynthesis. Oxygen is used to release energy from food during respiration.

In addition to these three elements, plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. Two important mineral ions needed by plants are:

  •  Nitrate → Amino acids → Proteins → Growth 
  •  Magnesium→ Chlorophyll→ Colour of leaves + photosynthesis
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2.3 Photosynthesis in farming

Farmers artificially manipulate the environment in which they grow plants. 

They grow plants in greenhouses or in polythene tunnels

They can control the temperature in greenhouses using heaters and ventilation

They can artificially increase the carbon dioxide levels.

They can control the light using fluorescent lamps.

By doing all of this, their plants grow faster and certain plants can be grown out of their natural growth season. 

Therefore, farmers can increase their profits

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2.4 Energy flow in ecosystems

A food chain shows what eats what in a particular habitat. The Sun is the ultimate source of energy for most communities of living things. Green plants absorb some of the Sun’s light energy to make their own food by photosynthesis. The other organisms in a food chain are consumers.

Energy is transferred along food chains from one stage to the next. But not all of the energy available to organisms at one stage can be absorbed by organisms at the next one. The amount of available energy decreases from one stage to the next.

Most food chains are pretty short. There are rarely more than four stages, because a lot of energy is lost at each stage.

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2.4 Biomass

Biomass means the mass of living material at a stage in a food chain. A pyramid of biomass is a chart, drawn to scale, showing the biomass at each stage in a food chain. It is always pyramid shaped.

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2.4 Efficiency of food production

The efficiency of food production can be improved by reducing the amount of energy lost to the surroundings. This can be done by:

  • preventing animals moving around too much 
  • keeping their surroundings warm
  • Advantages:
  • Cheap 
  • Own many animals 
  •  Earn money 
  •  Doesn’t take up lots of space Quick

Disadvantages: 

  • Poor conditions 
  •  Many die 
  • Health problems 
  •  Ethics
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2.5 Recycling of waste- carbon cycle

Carbon cycle

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2.5 Carbon cycle

Removing carbon dioxide from the atmosphere

Green plants remove carbon dioxide from the atmosphere by photosynthesis. The carbon becomes part of complex molecules such as proteins, fats and carbohydrates in the plants.

Returning carbon dioxide to the atmosphere

Organisms return carbon dioxide to the atmosphere by respiration. It is not just animals that respire. Plants and microorganisms do, too.
Passing carbon from one organism to the next

When an animal eats a plant, carbon from the plant becomes part of the fats and proteins in the animal. Microorganisms and some animals feed on waste material from animals, and the remains of dead animals and plants. The carbon then becomes part of these microorganisms.

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2.6 enzymes

Enzymes are biological catalysts. Enzymes are also proteins that are folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.

They can be denatured by high temperatures or extremes of pH. The enzyme activity gradually increases with temperature until around 37ºC, or body temperature. Then, as the temperature continues to rise, the rate of reaction falls rapidly, as heat energy denatures the enzyme.

Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, a stomach enzyme would work best in acidic conditions. A mouth enzyme would work best in neutral conditions.

Enzymes reduce the activation energy needed for a chemical reaction to take place.

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2.6 Enzymes in aerobic respiration

Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in the mitochondria. The inner surface of the mitochondria is highly folded in order to increase surface area.

This is the equation for aerobic respiration:
glucose + oxygen    →    carbon dioxide + water (+ energy)

The energy released by respiration is used:

  • Molecules – making larger molecules from smaller ones
  • Muscles – making muscles contract for movement
  • Maintaining heat – keeping a constant temperature
  • Making proteins – in plant
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2.6 Enzymes in digestion

Enzymes in digestion Digestion is the breakdown of large molecules into smaller, soluble molecules that can be absorbed into the body. Digestion happens inside the gut, and relies on enzymes.

  • Amalyse:
  • reaction catalysed:Starch → sugars
  • produced in:salivary glands, pancreas, small intestine
  • Used in the mouth and small intestine.
  • Protease:
  • Reaction catalysed: Proteins → amino acids
  • Produced in:stomach, pancreas, small intestine
  • Used in the stomach and small intestine
  • Lipase:
  • Reaction catalysed:Lipids → fatty acids + glycerol
  • Produced in: pancreas, small intestine
  • Used in the small intestine
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2.6 Enzymes in the stomach and small intestine

Enzymes in the stomach

The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions - in other words, at a low pH.

Enzymes in the small intestine
After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. Bile is produced in the liver and neutralises the acid to provide the alkaline conditions needed in the small intestine. It also emulsifies fat droplets to produce a larger surface area for enzymes to work.

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2.6 Enzymes uses

Enzymes allow certain industrial processes to be carried out at normal temperatures and pressures, thereby reducing the amount of energy and expensive equipment needed.

  • Protease: used to pre-digest proteins during the manufacture of baby foods
  • Lipase:used - together with protease - in biological detergents to break down - digest - the substances in stains into smaller, water soluble substances
  • carbohydrase:used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinks
  • isomerase:used to convert glucose syrup into fructose syrup - fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods
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2.6 Enzyme uses- pro's and con's


  • Used over and over again 
  •  Speeds up reactions 
  • No need for high temperatures 
  • Easily grown 
  •  Tried and tested
  • Varied Applications


  • Allergies 
  •  Costly 
  •  Idea of microorganisms in food may not be accepted
  • Soluble, so may be difficult to reclaim from liquid
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2.7 Homeostasis

Waste products

Waste products must be removed from the body. If they are not, they will increase in concentration and may interfere with chemical reactions or damage cells.

Waste product. Why is it produced? How is it removed?

  • C02: it is a product of aerobic respiration. Through the lungs when we breathe out
  • Urea: it is produced in the liver when excess amino acids are broken down. the kidneys remove it from the blood and make urine, which is stored in the bladder temporarily
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2.7 Water and ions (osmoregulation)

Water and ions enter the body through food and drink. Water is also a product of aerobic respiration in cells. If the amount of water or ions in the body is wrong, cells can be damaged because too much water enters or leaves them. The kidneys control the water content of the blood.

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2.7 Temperature (Thermoregulation)

Human enzymes work best at 37ºC, so the body’s temperature is controlled. A part of the brain called the thermoregulatory centre monitors and controls body temperature.

  • When we get too hot:
    • Sweat glands in the skin release more sweat. This evaporates, removing heat energy from the skin.
  • Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.
  • When we get too cold:
    • Muscles contract rapidly - we shiver. These contractions need energy from respiration, and some of this is released as heat.
  • Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body.
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2.7 Controlling glucose

The pancreas monitors and controls the concentration of glucose in the blood. It produces a hormone called insulin. Insulin causes glucose to move from the blood into cells. It lowers the blood glucose concentration if it has become too high. This can happen after eating a meal that is rich in carbohydrates

Blood glucose too high → Pancreas produces insulin → Glucose is converted into glycogen in the liver → Glucose removed from blood → Blood glucose is normal

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2.7 Diabetes

Diabetes is a disease where the concentration of glucose in the blood is not controlled properly by the body. In Type 1 diabetes, the pancreas does not produce enough insulin. This can lead to high levels of glucose in the blood, which can be fatal.

Diabetes treatment

  • There are two types of treatment for diabetes:
    • Careful monitoring of food intake, with particular care taken over carbohydrates - which are digested into glucose. (Type 1 and 2)
  • Injecting insulin into the blood before meals. The extra insulin causes glucose to be taken up by the liver and other tissues. Cells get the glucose they need for respiration, and the blood glucose concentration stays normal. (Type 1)
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2.8 Inheritance-Cell division

DNA (deoxyribose nucleic acid) molecules are large and complex. They carry the genetic code that determines the characteristics of a living thing.
Genes: A gene is a short section of DNA. Each gene codes for a specific protein by specifying the order in which amino acids must be joined together.
Chromosomes: The cell’s nucleus contains chromosomes made from long DNA moleculeschromosome, showing gene as section of DNA (

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2.8 Mitosis

The chromosomes contain the cell’s genetic information. They are normally found in pairs in body cells. Body cells divide by a process called mitosis. When a body cell divides by mitosis:

  1. The genetic material is copied
  2. The cell divides once to form two genetically identical body cellsThe six stages of mitosis (
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2.8 mitosis 2

parent cell 

chromosomes make identical copies of themselves 

they line up along the centre 

they move apart 

two daughter cells form with identical chromosomes to the parent cell

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2.8 stem cells

Stem cells are cells that have yet to differentiate. Stem cells can be made to differentiate into many different types of cells. Stem cells are found in human embryos, adult bone marrow and umbilical cords. Treatment with these cells may help cure conditions such as paralysis.


  • Only a few days old – only ‘ball of cells’
  • Useful
  •  Repairs damaged tissues
  •  Treat many diseases in the future


  •  Unethical 
  • Morally wrong 
  •  Can turn cancerous 
  • Could turn into human life
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2.8 gender

Human body cells have 23 pairs of chromosomes in the nucleus. One of these pairs controls the inheritance of gender - whether offspring are male or female:

  •  In males, the two sex chromosomes are different. They are XY.
  • In females, the two sex chromosomes are the same. They are **.

Fertilisation is the joining or fusion of a male gamete and a female gamete (producing a zygote). The new cell that is formed divides over and over again by mitosis. This creates the many cells that eventually form a new individual.

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2.8 Meiosis

The cells that are formed by meiosis have half as many chromosomes as the cell that formed them. Human body cells contain 23 pairs of chromosomes, while human gametes contain 23 single chromosomes.

The main features of meiosis are:

  • the chromosomes are copied 
  •  the cell divides twice, forming four gametes
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2.8 Mendel

Mendel was a monk in the 19th century. He studied inheritance in pea plants. He noticed that certain characteristics that were shown by 2 pea plants were not always shown in their offspring. However, when he crossed these offspring together, the characteristics sometimes reappeared in the next generation. He proposed the idea of units of inheritance. However, his discoveries were not recognised until after his death, because he published his work in an obscure journal, DNA, chromosomes and genes were not discovered and people could not accept the link between plants and humans

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2.8 Alleles

Different forms of the same gene are called alleles. Alleles are dominant or recessive:

  • the characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair
  • the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair
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2.8 Huntingtons disease

Huntington’s disease is an inherited disorder that affects the nervous system. It is caused by a dominant allele. This means it can be passed on by just one parent if they have the disorder.

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2.8 Cystic fibrosis

Cystic fibrosis is an inherited disorder that affects the cell membranes, causing the production of thick and sticky mucus. It is caused by a recessive allele. This means that it must be inherited from both parents. Offspring with Ff are labelled 'carriers'. A carrier has one copy of the faulty allele, but does not have the disorder themselves. It is possible to screen embryos to see if they carry alleles for genetic disorders

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2.8 cystic fibrosis 2

The cystic fibrosis allele is represented by f. The normal allele is F. Suppose one parent is FF and the other is a carrier, Ff. The possible combinations of alleles in the children are FF, FF, FF and Ff. So the parents cannot produce children with cystic fibrosis (ff). But they can produce children with alleles Ff, who will be carriers (

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2.8 Polydactyly

Polydactyly is an inherited condition in which a person has extra fingers or toes. It is caused by a dominant allele of a gene. This means it can be passed on by just one parent if they have the disorder.

Offspring need to carry just one dominant allele from their parents to inherit the polydactyl condition. 50% chance

 The disorder is caused by a dominant allele. 'D' and so can be inherited if just one parent carries the defective allele

The parent that has the defective allele will be a sufferer

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2.8 Polydacatyly diagram

Polydactyly allele chart (

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2.8 Embryo Screening

People in families with previous history of certain genetic disorders can have a genetic test to see if they carry the allele for the disease. If they do carry the allele, their embryos can be screened to see if it is affected. They can then decide whether to have an abortion.


  • Detect illness
  • Prepare parents
  • Parents can make an informed decisions


  • Abortions
  • Choice on Children
  • Lead to designer babies
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