Edexcel Biology Unit 4 Notes

These are my personal notes and include most of the information you need to know. Please message me if there are any mistakes or anything could be added.

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Biology Notes
Photosynthesis ­ 6CO2 + 6H20 + (Energy/ATP) C6H12O6 + 6O2
Autotrophic organisms make their own food e.g. by photosynthesis.
Heterotrophic organisms eat other organisms as their source of food.

ATP ­ Adenosine triphosphate
ATP is the molecule that provides the energy that is needed within an organism to…

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Stroma contains all the enzymes etc. for light independent reaction to take place.
Lots of ATPase is present in the thylakoid membranes to produce ATP.

Light dependent reaction - first step in the production of glucose ­ takes
place on thylakoid membranes. These contain photosynthetic pigments
such as chlorophyll a,…

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2. This breaks down into 2 molecules of glycerate-3-phosphate almost immediately.
3. Glycerate-3-phosphate is reduced to glyceraldehyde 3-phosphate (a 3 carbon sugar) by
NADPH. Energy for this reaction is provided by ATP.
4. The sugar is then used to produce organic molecules such as glucose.
5. Glucose can then be…

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Since more plants are present, there is a higher plant biodiversity and the plants are able to provide
for more animals hence the biodiversity of animals in the habitat also increases.

Secondary succession
Secondary succession is when succession occurs on land that already has soil but the previous habitat
was…

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Biotic factors
Predation ­ predators kill prey hence increased predators will cause a decrease in prey but if
the predator numbers increase too much they will compete (intraspecific competition) and
their numbers will decrease due to lack of food.
Finding a mate ­ if a male can't find a female…

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Investigating populations and abiotic factors
Abundance ­ the number of individuals of one species in an area. This can be measured by counting
the number of organisms of a species or by using percentage cover (for plants) i.e. the percentage of
area they cover.

Distribution ­ where the species is…

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Carbon sinks ­ these are places where carbon is removed from the
atmosphere and locked up

Oceans ­ These are carbon sinks and they store a large proportion of the earth's CO2.
Phytoplanktons use the CO2 to photosynthesise and crustaceans use it to make their shells.
This means there is…

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3. If the rings are wide, this suggests that the year was particularly warm and vice versa for thin
rings. However, temperature isn't the only thing that affects tree ring growth. If the ring is
wide, this could suggest better rainfall, CO2 levels, more sunlight etc. Not ONLY temperature.

Pollen…

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Preventing increased carbon emissions

Biofuels ­ these are fuels made from renewable biological resources (biomass). They are
carbon neutral as they only release the carbon the plants took in during photosynthesis
when the fuels are burned. However, CO2 is released when the biofuels are transported
hence they aren't completely carbon…

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Different types of sympatric speciation ­ pre-zygotic

Mechanical isolation ­ this is when the physical reproductive organs of two sets of
organisms is different hence they no longer fit together so reproduction is not possible.

Temporal isolation (time) ­ organisms may be fertile during different seasons. These
seasons may not…

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