Biology revision B7 - OCR 21st Century

notes on photosyntesis, respiration interdependence, blood, heart

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  • Created on: 12-06-12 17:42
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Plants use energy from sunlight to build up carbon dioxide and water into organic compounds such
as glucose. This process is photosynthesis.
Energy from sunlight is transferred into chemical energy in the new compounds.
Autotrophs ­ living things that can make their own food using sunlight
Heterotrophs ­ organisms that rely on other living things for food
Some plant materials pass to other organisms as they eat the plant. So the energy is passed along the
food chain. In this ecosystem some of the energy is lost through respiration. The energy warms the
air or water and eventually radiates back into space.
Plants only convert about 13% of the light energy
Carbon dioxide + water glucose +
6CO2 + 6H2O C6H12O6 + 6O2
A glucose molecule is made up of carbon, hydrogen and oxygen atoms, so glucose is a
Photosynthesis happens in chloroplast which contains chlorophyll. This absorbs light and uses
the energy to start photosynthesis.
The light energy splits water molecules into hydrogen and oxygen atoms.
The hydrogen combines with carbon dioxide from the air to make glucose.
The oxygen is released as a waste product.
Why are plants green?
Chlorophyll absorbs red and blue light because these are the most useful parts of the spectrum for
photosynthesis. Green light is not absorbed, it is reflected hence why leaves are green.
Making other chemicals needed for cell growth
Plant cells need carbohydrates as well as fats and proteins.
Two important carbohydrates in plants are cellulose and
starch which are polymers of glucose.

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Storing energy in starch molecules
Photosynthesis sometimes produces glucose faster than the plant needs. This extra glucose is
converted to starch and stored.
Releasing energy in respiration
Glucose is broken down and the stored energy in the molecules is released.
Glucose + oxygen carbon dioxide + water + ENERGY
This energy is used to power chemical reactions in the cells such as converting glucose to cellulose,
starch or proteins.…read more

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During summer, stomata close to prevent water diffusing out of the leaves and
this also reduces CO2 diffusing into the leaf.
At 0.04%, more light increases the rate of reaction up to a point until light is no
longer the limiting factor. Increasing CO2 level to 0.4% makes the rate of
reaction higher until another factor becomes short of supply.
CO2 levels ­ levels over about 1% are toxic to plants and animals. Greenhouses are kept at 0.1%.…read more

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Pyramid of biomass ­ shows the mass of organisms at each feeding level and how much food is
available to the next level.
When pyramids are a different shape
Some organisms are only present in the ecosystem for part of the year
Other organisms in an ecosystem may be eaten almost as fast as they are reproducing.
Living things contain different amounts of water so biomass can only be compared fairly if the
material is dried first.…read more

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They can be transferred by:
through the nose, mouth,, anus and genital and urinary tracts
insect bites
burrowing under the skin
Lives in the human gut ­ up to 9m long
Competes with the host for digested food
It does not enter the host's body tissues so symptoms are usually mild stomach aches
Tapeworms have a number of adaptations:
Heads have suckers and stickers to grip the gut wall when gut contracts prevents them being
squeezed out
Protected from digestion by a thick…read more

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The parasites have different markers on their cells at every stage of their life cycle. This makes it
hard for white blood cells to identify and attack them so they are protected from the immune
When one red blood cell is used up the parasites burst out and infects new cells.
Toxins are released from the used up cells causing dangerous fever
Sickle ­ cell anaemia
This is a genetic disorder.…read more

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It causes the milk they feed on to lump together. This slows the food down as it passes though the
gut, giving enzymes more time to digest the food and for molecules to be absorbed.
Growing microorganisms for food
Microbial cells contain carbohydrates, fats and proteins.
Some MOs provide a useful source of protein. Microbial cells are low in fat and high in fibre.
Microbial biomass grown for food is called single cell protein (SCP)
Quorn is made from fungus.…read more

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The bacteria that survive must have the plasmid so they will also make insulin
Large genes are too big to fit into plasmids. So bacteria are infected by viruses called
bacteriophages. These are used to carry larger genes but they are disabled before they used for
Anyone who wishes to introduce a GMO must apply to Defra. Each application is looked at by
ACRE.…read more

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Plasma is mainly water. It is a pale yellow fluid. It carries dissolved materials such as food
molecules, hormones, waste product and distributes heat around the body.
Red blood cells
They are made in bone marrows. 10% of CO2 is in the red blood cell in the form of carbonate. The
protein haemoglobin binds to oxygen as blood passes through the lungs. They contain iron.…read more

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Donor anti a and anti b antib antia none
antia and antib
If the wrong blood type is given then the red blood cells will clot together in the bloodstream. These
clots can block blood vessels stopping oxygen and glucose supply.
Agglutination ­ clumping
Haemolysis ­ cells leak haemoglobin so oxygen transport is affected
I.e.…read more


Nizbizzzz :)

hey thank you so much for these fantastic notes like this for chemistry? thank you again!

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