B2 revision

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  • Created by: Sophie
  • Created on: 29-12-12 11:28


Nucleus-controls all activites of the cell

Cytoplasm-where most chemical reactions take place

Cell membrane-controls the passage of substances in and out of the cell

Mitochondria-where most energy is released during respiration

Ribosomes-where protein synthesis occurs


Cell wall-made of cellulose, strengthens cell

chloroplasts-absorb light energy to make food for plants

permanent vacuole-filled with cell sap

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Specialised Cells

Root hair cell-large surface area to absorb water and minerals easily

Palisade cell-many chloroplasts for photosynthesis

White blood cell-can change shape to engulf microbes

Nerve cell- long nerve fibre to carry messages to other cells

Sperm cell- tall so it can swim

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The spreading of particles of a gas or substances in a solution that results in a movement from where there is a high concentration to a lower concentration

The greater the difference in concentration the faster the rate of diffusion

Oxygen that is required for respiration passes through the cell membranes by diffusion

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Digestive system

Glands e.g. pacreas and salivary glands produce digestive juices

The stomach and small intestines is where digestion occurs

The liver produces bile

The small intestine is where the absorption of soluble food occurs

Large intestine is where water is absorbed from the undigested foods and where faeces are produced

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Types of tissue

Muscular tissue-brings about movement

Glandular tissue-produces and releases substances such as hormones,saliva,milk and enzymes

Epithelial tissue-covers some parts of the body(can be smooth so it forms skin and can have cilia to help move substances along substances

In the stomach...

Muscular tissues helps to churn the contents in the stomach

Glandular tissue produce digestive juices

Epithelial tissue covers the outside and inside of the stomach

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Plant Tissues


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Plant Organs

Stem-helps support plant and carries water and food around the plant. The phloem carries food(f for food and f for phloem) The xylem carries water

Leaf-captures sunlight for photo synthesis, it happens in chloroplasts that contain chlorophyll

Flower-contains reproductive organs of the plant

Root-stores food products made during photosynthesis. Anchor plant in soil aborb water and minerals

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Photo=light synthesis=making of glucose

Word equation


Water+carbon dioxide------> Oxygen + glucose


Symbol equation- 6CO2+6H20------>C6H12O6+6O2

6 can be added to balance teh equation!

Where does it occur?

leaves! occurs mainly in mesophyll cells because they contain lots of chloroplasts that contain chlorophyll!

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Limiting factors of photosynthesis


Low temperatures will limit photosynthesis because the molecules will move less and so the reaction happens slower

Carbon Dioxide!

A shortage of carbon dioxide will limit the rate of phoosynthesis because it means that there isn't as much avaliable for the reaction as it is one of the reactants needed

Light intensity!

Sunlight is one of the conditions needed for photosynthesis to take place. Less sunlight means that there is less energy for the reaction

BUT if these factors are increased they will increase the rate of photosynthesis!

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Plants using up glucose

Glucose is produced during photosynthesis.  For storage it is converted into insoluble starch because glucose dissolves in water and starch doesn't.

Plants break down glucose using oxygen during photosynthesis to provide energy. It is used to:

  • Build up smaller molecules into larger ones(glucose to starch) As the starch in the cellulose which is used to make new cell walls.
  • Combine nutrients from the soil with sugars to prduce amino acids that can be built up to complex proteins
  • Build up fats and oils to make a food store in seeds.

In summer plants build up their starch reserve in their roots because in winter there is limited photosynthesis.

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Physical factors that affect organisms

Temperature:affects the rate of an organisms metabolism, some organisms can't maintain a constant high body temperature, Some may struggle to survive in extreme temperatures

Amount of light-plants need light for photosynthesis and low light intensities plants grow very slowly

Availability of water-ALL organisms need water!Needed for chemical reactions inside+outisde cells!

Availability of oxygen-needed for aerobic exercise, can become limited in soil so plant roots can't grow+absorb water and can become limited in aquatic organisms

Availability of carbon dioxide-essential for photosynthesis, can become limited in an environment that contains a small amount of plants which can reduce rate of growth in other plants

Availability of nutrients-nitrates are essential for growth

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Collecting quantitative data

Sampling! When studying the distibution of species you need to find out the size of the area you are studying, the number of organisms living there and where they live. BUT that would be time consuming, they may move and there may be too many to count.


They are square frames that can be used to mark off a certain area. They are used to survey the number or percentage of species in an area.

Random Sampling

Can be done by generating random numbers using a calculator and then throwing the transect there.

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Proteins, Catalysts and enzymes!

Proteins are made from amino acids. They have different shapes because they are made from different amino acids. They act as components of tissues such as muscle cells that interlink with protein fibres.

Some hormones are proteins such as insulin! they are released into the blood from glands and have speciific shapes that attach to molecules on the cell membrane of specific cells.

Catalysts! They speed up chemical reactions. eg iron platinum and yeast

Enzymes are biological catalysts, they are maed up of long chains of amino acids. The shape of an enzyme is important because it is a specific shape to do a certain job. At high temperatures enzymes denature as its shape changes. They are specific because of the active site.- the active site changes when it denatures!

Enzymes are proteins and catalysts!!!!

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Enzymes and digestion

Amylase is a carbohydrase produced by the salivary glands. Hydrochloric acid is found in the stomach and kills bacteria that could enter.

Enzymes and Ph...in the mouth enzymes work best in neutral conditions BUT in the stomach emzymes work best in acidic conditions because bile will neutralise the content of the stomach. Enzymes made in the pancreas and small intestine work best in alkalic or neutral conditions

Enzyme                 Breaks down           Into                         Produced

Carbohydrase      carbohydrate       simple sugar          mouth,small intestine+pancreas

Protease                   protein           amino acids           stomach,small intestine+pancreas

Lipase                fats/lipids          Fatty acids+glycerol      Small intestine+pancreas

1 enzyme, 1 enzyme SIP everything!

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In the mouth....food is chewed to create a larger surface area for the action of enzymes, saliva is released(contains amylase). The amylase digests starch into smaller sugars, food then enters oesophagus.................................................................

In the stomach...food enters the stomach from the oesophagus. The walls of the stomach produce digestive juices that contain protease and hydrochloric acid. It churns the food and after a few hours the proteins are digested. It then travels to the small intestine........

In the small intestine.... juices are produced!

Bile-produce in the live and stored in the gall bladder. It neutralises the stomach acid and convert the fat into smaller fats to give them a larger surface area-emulsification!!!

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Enzymes in industry

biological washpowder- contains enzymes! They react with stains to break down statins. They contain 3 enzymes and work best at 40oc so the enzyme doesn't denature!

Sports drinks: starch is converted into sugar syrup using carbohydrase to get glucose. 

Slimming foods: glucose is converted into fructose using isomerase. Fructose is a sweater than glucose and so less is needed to sweaten food so it contains less calories!

Baby food contains protease to break down protein so it is pre-digested so babies can eat the food. It is broken down into amino acids.

Advantages in industry...enable more chemical reactions to take place at lower temperatures. When enzymes are used the processes can be cheaper.

Disvantages...They are sensitve to temperature and pH changes and so they need to be monitored which can be expensive

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Aerobic respiration

Respiration is essential for survival. It happens in every living cell in the mitochondria. Aerobic respiration occurs when both glucose and oxygen are available which allows energy to be released, carbon dioxide and water are also given off as waste products.

Word Equation:

Glucose+ Oxygen-------> Carbon dioxide+ water+ energy

The energy released during respiration is used to:

Build up larger molecules using smaller molecules

 in animals to make muscles contract

 in mammals and birds to maintain a steady body temperature in cooler surroundings

in plants to build up into proteins.

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Effects of exercise

The heart rate and breathing rate increase, the more vigorous the exercise is the more the heart rate will increase. It increase because there is an increased blood flow to muscles so more oxygen is needed to be delivered to cells so more respiration can take place. More energy is produced because more enery is needed for exercise. Also because more respiration is carried out more carbon dioxide is produced and waste products are removed quicker. Breathing rate increases because more oxygen is needed so breathing becomes deeper.


Glucose can't be stored in the muscles as it is soluble so the glucose is converted into glygcogen for storage. It is broken down into glucose in the muscles.

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Anaerobic exercise

Anaerobic respiration is respiration without oxygen because the oxygen can't get to the working muscles quick enough. It is the incomplete break down of glucose, a small amount of energy is produced and the waste product is lactic acid!

Word equation:

Glucose------>lactic acid+energy

Cramp is the build up of lactic acid which causes a sharp pain in the muscles as there is a lack of oxygen in the muscles. To restore the blood supply you need to STOP working.

Muscle fatigue is caused by working anaerobically for long periods of time

Oxygen debt is caused when anaerobic respiration takes place. It is where oxygen needs to be paid back to the working muscles. It can be paid back by breathing in deeply to get oxygen to the muscles. The lactic acid reacts with the oxygen to oxidise the lactic acid into carbon dioxide and water

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Patterns of inheritance

In the nucleus there is 23 pairs of chromosomes(human). 23 chromosomes are inherited from each parent. Chromosomes are made from DNA. DNA consists of 2 strands that form a double helix

Alleles are different forms of the same gene. e.g. eye colour, different alleles can be brown, blue, green etc.

An allele which controls the development of a characteristic when it it present on only one chromosome is called a DOMINANT allele. Its represented as a captial letter

An allele which controls the development of a characteristic only if the dominant allele isn't present(there must be 2) is called a recessive allele.

If both chromosomes in the pair contain the same allele of the gene the individual is homozygous for that gene. If both chromosomes in the pair contain different alleles of the same gene is individual is hetrozygous for that gene.

A combination of 2 genes is called a genotype. Physical chacteristics is the phenotype

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In order for new body cells to be produced old ones must divide---MITOSIS! When mitosis occurs the new cells produced are genteically indentical to the original cell, this ensures that all cells in our body contain the same geneti information.

It allows us to produce new cells for growth repair, and replace.

Mitosis is asexual reproduction

Cell division occurs once and 2 new cells are produced.

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2 gametes must fuse together to create a new individual, the gametes contain only half the number of chromosomes of a normal body cell.

Each gamete that is produced is slightly different to the rest. This allows variation in species.

Meiosis is sexual reproduction.

Cell division occurs twice and produces 4 cells

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genetic disorders

Cystic fibrosis

Symptoms:extra mucus in the lungs caused by faulty cell membranes


Can be passed on by 2 parents that don't have the disorder but they may be carrying the ressive allele.


Symptoms: extra fingers or/and toes

Allele: dominant

At least one parent must have the dissorder, you can't be a carrier for polydactyl

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embryo screening

The good:

  • means that you can find out if your unborn child has a genetic disorder that they have inherited.
  • If your child has a genetic disorder it gives parents time to make preperations
  • Gives parents time to decide if they want to keep or terminate the baby
  • Saves NHS money because less money is spent on treatment
  • Removeds faulty genes in the population

The Bad:

  • More people may want abortions if they find out their child will have a disorder
  • can mean that the mother or can can get infected by the needle
  • embryo screening is expensive
  • goes against morals and makes parents more likely to terminate their child
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Stem Cells

Can be made to differentiate into many different types of cells, the cells can be taken from human embryos, adult bone marrow and umbilical cords

The good:

  • cells work better because they can be turned ino anything
  • saves lives and improved lives
  • grows tissues

The bad:

  • Takes away an embryos right to life
  • The embryo doesn't have a say
  • It's expensive
  • The long term effects are unknown
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Sex determination

Gametes contain 23 chromosomes because when 2 sex cells fuse together the full number of 46 is restored.

Eggs carry X chromosomes only

Sperm carry X or Y chromosomes

Boys will inherit XY chromosomes

Girls will inherit XX chromosomes

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