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Title: Chapter 3 AQA Biology A2 Unit 4
Description: There are comprehensive notes for all of chapter 3 in unit 4 biology, AQA A2. They cover every learning objective with detailed diagrams and explanations of all features within this section of the course. Being highly in-depth, these are suitable for any ability student studying A2 biology.
Description: There are comprehensive notes for all of chapter 3 in unit 4 biology, AQA A2. They cover every learning objective with detailed diagrams and explanations of all features within this section of the course. Being highly in-depth, these are suitable for any ability student studying A2 biology.
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Chapter 3 – Photosynthesis
How is the plant leaf adapted to carry out photosynthesis?
Large surface area – greater area to catch
light
Arrangement of leaves which minimises
overlap
Transparent cuticle to allow light through
to the mesophyll cells
Mesophyll cells packed with chloroplasts
Numerous stomata for gaseous exchange
Air spaces in the lower mesophyll to
allow diffusion of oxygen and carbon
dioxide
Xylem networks which carry water to the leaf cells and phloem to carry away sugars
to the rest of the plant
What are the main stages of photosynthesis?
1
...
Light-dependent reaction – light energy used in photolysis of water and to excite
electrons in chlorophyll – produces reduced NAPD, ATP and oxygen
3
...
Reduction is the gain of electrons, gain of hydrogen or loss of oxygen
...
One water molecule absorbs light energy to be
split into protons, electrons and oxygen:
𝐻2 𝑂 → 2𝐻+ + 2𝑒 − +
1
𝑂
2 2
The electrons are donated to the chlorophyll molecule to replace the lost excited electrons,
the protons are taken up by NAPD to form reduced NADP and the oxygen is given out as a
waste product or used in respiration
...
As the products of the light dependent reaction can be released directly into the
stroma, the reactions can take place alongside one another
...
g
...
Changing the rates of other intervening factors will have no effect without changing the
limiting factor
...
It is important to
remember that CO2 is produced and O2 is used in respiration
...
As light intensity increases, O 2
output and CO2 intake increase until the levels are counteracted by those taken in/given out
by respiration (light compensation point)
...
Increasing the concentration of carbon dioxide increases the rate of photosynthesis
...
Increasing the temperature increases the rate of photosynthesis to a point, after which
the rate of photosynthesis declines
...
Title: Chapter 3 AQA Biology A2 Unit 4
Description: There are comprehensive notes for all of chapter 3 in unit 4 biology, AQA A2. They cover every learning objective with detailed diagrams and explanations of all features within this section of the course. Being highly in-depth, these are suitable for any ability student studying A2 biology.
Description: There are comprehensive notes for all of chapter 3 in unit 4 biology, AQA A2. They cover every learning objective with detailed diagrams and explanations of all features within this section of the course. Being highly in-depth, these are suitable for any ability student studying A2 biology.