Edexcel Biology Unit 4 Common Markscheme Answers

Biology Unit 4 Common Markscheme Answers

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  • Created on: 04-01-13 19:51
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Biology ­ Common Mark Scheme Answers
Light hitting leaf is not used by chloroplasts ­
Due to reflection
Incorrect wavelength
It is transmitted, not hitting the chloroplasts
Structures in a chloroplast involved in light dependent reactions
Made of membranes
Arranged as stacks of grana
Contains chlorophyll
Oxygen from Light dependent reactions
Energy from light
Photolysis occurs
Of water
Produces oxygen
Energy from light is made available in ATP molecules for synthesis
Thylakoid membrane
In Granum
Electrons become excited due to increase in light
Electrons released from chlorophyll
Taken by an electron carrier
Series of redox reactions occurs
Photophosphorylation occurs
Synthesis of ATP from ADP + P
Electrons from photolysis replace those which have been lost
Role of microorganisms in the recycling of the carbon from these
Releases CO2 for photosynthesis
Methane is released in anaerobic respiration
Site of carbon fixation is the Stroma of a chloroplast
Carbon Fixation
Produces GP
GP is converted into starch
Faster carbon fixation means faster production of starch
Increased GPP of crop
Net primary productivity
Rate of production of energy incorporated into biomass

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Losses in respiration in plants
Explain what is meant by the term NICHE:
Of an organism
It is predator ­ controls prey population/it is prey ­ provides food for
other animals
Provides shelter for some animals
Global Warming ­
Less greenhouse gases such as carbon dioxide & methane
Greenhouse gases cause greenhouse effect
Absorb/trap infrared radiation
Reflected from the earth
Decrease in greenhouse gases means decrease in greenhouse effect
Temp of earth's surface is less likely to rise
Reduced…read more

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Two species from a single population
Original population spreading to a wider diversity of habitats
Mutations may occur
Reproductive isolation may occur
Restriction in gene flow between extremes in populations
Different environmental factors in each region
Plants adapt to the region
Change in allele frequency over time
Genetic Mutation
Change in nucleotides
Causing a change in the sequence of amino acids
Plants growth
Pioneer communities
Able to grow in little/no soil
Break up rock fragments to form thin soil
Plants with short roots…read more

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Drop in body temp. is linked to time after death
Factors affect the temp.…read more

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DNA profiling
Assumes every individuals DNA is unique
apart from identical twins
DNA profiling analyses non-coding blocks
There is a large number of non-coding blocks
Many combinations at each locus
HYDROLYSIS - type of chemical reaction involved in the digestion of
cellulose by enzymes.
GLUCOSE - most likely product of the digestion of cellulose by the bacteria.…read more

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Specific response
Antigens are specific to each bacteria
Antibodies need to be complementary to antigens
So binding can take place
Antibodies already present from passive immunity/breast feeding
How organisms are taken up by macrophages
Bacterium recognises it as nonself
Phagocytosis occurs
Vacuole is formed
advantage of using monoclonal antibodies, rather than polyclonal
specific antigen
specific monoclonal antibody
specific treatment can be given
more likely to be effective
Active immunity ­
Vaccine contains the antigen
Activates specific lymphocyte
B memory cells are produced
Body can…read more

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On membrane of lymphocytes
Viral RNA enters the lymphocytes
And is used to produce Viral DNA
Using reverse transcriptase
T killer cells destroy T helper cells
HIV enters through T cells and phagocytic cells
Binds to CD4 receptors
On cells
Fusion of virus with cell membrane
Phagocytosis ­ macrophage…read more


Ricky Rozay


Katie Hamiton

Do you have Unit 5 by any chance?

Former Member



you guys are so cute


i love hanging out with you



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