B7 Revision

Revision cards for B7- Biology across the ecosystem


Heterotrophs- Rely on other living things for food.

e.g. eagle

Autotrophs- Produce their own food

eg. plants and algae

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                                   light energy
Carbon dioxide+water------------------> glucose+oxygen


-Glucose molecule is made up of carbon, hydrogen and oxygen, CARBOHYDRATE

-Photo.. happens in the chloroplast-contains green pigment called chlorophyll. Chlorophyll absorbs light and uses energy to kick-start photosynthesis.

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Using glucose

Cell growth-

glucose is converted into other chemicals needed for cell growth.

Cellulose- used for strengthening and building cell walls

Extra glucose is converted into starch. It is insoluable so will not disturb the osmotic balance of cells.Starch can be converted back into glucose when it cannot be produced.Special organs to store it, can be stored in leaf cells.

Starch- insoluable- turned into ammino acids---> proteins etc.
Glucose molecules are broken down, releasing energy stored in molecules.
This energy is used to power chemical reactions in the cells.

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Rate of photsynthesis

Can be affected by:

the amount of light- cannot photosythesise quickly if there is not enough light.

carbon dioxide levels- too low, cannot photosynthesise.

temperature- too hot it cannot photosynthesis, too cold it decreases the rate.

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Food chains...

Autotrophs(producers)------> heterotrophs (herbivores)-----> hetero...(carnivores).

Pyramid of numbers- number of consumers on each trophic level

Pyramid of biomass- Shows the situation more clearly, shows the total biomass of each trophic level.

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Parasites- one benefits and the other loses
eg. tapewom and humans

Mutualism- Both benefit from relationship
eg. Bacteria and tubeworm

Commensalism- One benefits but the other neither gains nor loses from relationship.
eg. sticky seed pods stuck to clothing.

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Genetic modification

Bacterial cells-

no nucleus, one large chromosome in their cytoplasm . 
most also have rings of DNA, which contain extra genes,these  DNA  rings are called plasmids.

Any cell can make a protein if it has the gene which codes for it.
Scientists can add a huan gene gto bacterial cells so that they can make the human protein.

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Genetic modification

Genetic modification is changing the genes of an organism.

Bacterial cells can be changed by adding genes from other microorganisms, plants or animals.

Many drugs are proteins that can be made using genetically modified bacteria. eg. human insulin.

Pig insulin used to be used for this, but there were harmful side effects. The G.M bacteria on the other hand did not cause these efffects.

It has also been used to modify crops, as 10% are lost to disease etc. by using GM, they can be given the codes for proteins to protect them from common diseases, and mainly give them resistance to them.

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Genetic modification

Genetic modification diagram.

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How to tell which cells have been modified

1. Make a modified PLASMID that contains the human insulin gene and also a gene for antibiotic resistance.

2. Add the modified plasmid to a bacteria population.

3. Treat the population with the specific antibiotic.

4. The bacteria which survive MUST contain the plasmid, so will also make insulin.

5. Grow these bacteria and harvest the insulin.


Attach a second gene to the plasmid. (eg. from a jellyfish, which codes for a green florescent protein which is easy to spot.)

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Technology behind genetic testing

1. Genetic tests are artificially made pieces of DNA called GENE PROBES. (Short piecec of single stranded DNA which has complimentary bases to the allele being tested for). So the probe will stick to this allele.

2. If the probe sticks to the person's DNA, they have the diseased allele.

To find out whether it has stuck:

UV- a fluorescent molecule is attached to the gene probe when it is made. These molecules glow under UV light.

Autoradiography- the gene probeis made from radioactive DNA bases. These blacken X-Ray film.

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DNA finger printing

1. Extract DNA from tissue sample- cut DNA at particular base sequences.

2. Cut the DNA up into pieces- 'Restriction enzymes'

3. Separate the fragments out- gel electrophoresis.

4. Make the pieces visible- add gene probe (fluorescent)

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