OCR Biology B7 Revision Notes

Summary of the Unit 7 section of OCR's GCSE Biology. 

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  • Created on: 30-05-12 21:18
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B7 Revision Notes
· Life depends on solar energy absorbed during photosynthesis and
stored in chemicals like starch.
· Autotrophs make food from minerals, carbon dioxide and water but
heterotrophs need ready-made food.
· Chlorophyll absorbs light for photosynthesis. The equation is: carbon
dioxide + water glucose + oxygen
· Some glucose is used for respiration and to make cellulose, protein,
starch and chlorophyll.
· Nitrates are absorbed and added to glucose to make proteins.
· They are absorbed by active transport in the roots.
· Starch has little effect on the osmotic balance of the cell, so it is used
for energy storage.
· Photosynthesis may be limited by low temperatures and low carbon
dioxide or light levels.
· Human activity is increasing atmospheric carbon dioxide levels.
· Compensation points occur when respiration make as much carbon
dioxide as photosynthesis uses.
· Energy is transferred when living things are eaten or broken down by
· Pyramids of biomass show the food available to the herbivores and
carnivores in an ecosystem.
· Only about 10% of the energy in biomass is passed on at each stage in
a food chain. The rest is lost to decomposers or as waste heat.
· Soil contains living organisms, decaying material, sand, clay, air, water
and dissolved materials.
Further up the food chain
· Mutualistic relationships benefit partner species; commensalism
benefits one without harming the other; and parasitism harms the
· Parasites cause human disease and reduce farmers' yields.
· Parasites evolved with their hosts, so they can evade the host's
immune system. For example, malaria parasites hide in red blood cells.
They produce large numbers of offspring to ensure transfer to new
· Sickle-cell anaemia is caused by a faulty recessive allele. It makes red
cells jam in small capillaries, causing pain, organ damage and early
· Natural selection has increased the allele's frequency where malaria
exists because having one copy of the allele protects you.
New technologies
· Bacteria have a cell wall, cell membrane, circular DNA chromosome,
and plasmids.

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Bacteria and fungi are grown in fermenters to produce antibiotics,
single-cell protein, and enzymes like rennin.
· Genetic modification involves isolating and copying genes and putting
them in new cells.
· This is done by adding a virus or plasmid as a vector.
· GM bacteria make drugs, and hormones such as insulin. GM plants have
added characteristics like disease resistance which lead to higher
· Economic, social and ethical implications have to be considered before
genetically modified organisms are released.…read more

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Vertebrate skeletons support the body and allow movement.
· Bones are held together by slightly elastic ligaments.
· Tough inelastic tendons attach muscles to bone.
· Layers of cartilage and synovial fluid reduce friction at joints.
· Muscles operate in antagonistic pairs because they can only contract.
· Health information is needed before medical treatment or an exercise
regime starts.
· Regular contact with health or fitness practitioners and accurate
records are essential.
· These records may be needed by other practitioners.…read more



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