AQA A Level Biology - Photosynthesis

What are the two stages of photosynthesis called>

The Light Dependent reaction

The Light Independent reaction (The calvin cycle)

What is the purpose of photosynthesis?

To energy from light is used to make glucose

What is the general equation for photosynthesis ?

6H2O + 6CO2 + energy --> C6H12O6 + 6O2

What are the x stages of the light dependent reaction ?

1. Photoionisation of PSII

2. Photolysis of water

3. Photoionisation of PSI

4. Active transport of H+ ions

5. Oxidative phosphorylation

6. Reducing NADP

Describe what happens during photoionisation of PSII

Chlorophyll absorbs light

Electrons excited and move to higher energy level

Electrons move down electron transport chain to PSI

Describe what happens during photolysis of water

Light energy splits water molecules into H+, e- and oxygen

The electrons replace those lost from PSII during photoionisation

Explain how H+ ions are moved across the thylakoid membrane

The excited electrons from photoionisation lose energy as they move down the electron transport chain

The energy is used to actively transport H+ into the chloroplast

Explain how H+ are involved in the synthesis of ATP in chloroplasts

H+ move down their concentration gradient into the stroma

This is via ATP synthase in the thylakoid membrane

The energy synthesises ATP from ADP and Pi

Explain why the photoionisation of PSI is important

The excited eletrons are transferred to NADP with H+ to form reduced NADP

This is needed for the light-independent reaction

What is chemiosmosis ?

Electrons move down the electron transport chain and creating a proton gradient

This drived ATP synthesis

Which molecules from the light-dependent reaction are needed in the light-independent reaction?

ATP

reduced NADP

Where does the light dependent reaction take place?

(acrodd) thylakoid membranes of chloroplasts

Where does the light-independent reaction take place?

Stroma of chloroplasts

What are the 3 stages of the light-independent reaction?

1. Formation of glycerate 3-phosphate

2. Formation of triose phosphate

3. Regeneration of ribulose bisphosphate

Explain how glycerate 3-phosphate (GP) is formed

Ribulose bisphosphate (RuBP) combines with CO2

Forms unstable 6 carbon compound which breaks down to give 2 molecules of glycerate 3-phosphate

Catalysed by Rubisco

How does CO2 enter the stroma from the atmosphere?

Diffusion through the stomata

Difussion into the stroma

Which enzyme catalyses the reaction of CO2 with ribulose bisphosphate (RuBP) ?

Rubisco

How many molecules of glycerate 3-phosphate (GP) are produced from 1 molecule of CO2 and 1 molecule of ribulose bisphosphate (RuBP) ?

2

How many carbon atoms are in ribulose bisphosphate ?

5

How many carbon atoms are in glycerate 3-phosphate (GP) ?

3

Explain how triose phosphate (TP) is formed from glycerate 3-phosphate (GP)

Glycerate 3-phosphate (GP) is reduced to triose phosphate (TP) using H+ ions

How is glycerate 3-phosphate (GP) reduced to triose phosphate (TP) ?

Hydrolysis ATP from the light dependent reaction provide energy

reduced NADP releases H+ to form NADP

What two things can triose phosphate (TP) be used for?

1. regenerating ribulose bisphosphate (RuBP)

2. Converted to useful organic substances

How many of the carbon atoms in 2 molecules of triose phosphate (TP) are used to regenerate ribulose bisphosphate (RuBP) ?

5/6 carbon atoms

How many of the carbon atoms in 2 molecules of triose phosphate (TP) are converted to useful organic substances?

1/6

Which two stages in the light independent reaction is ATP hydrolysed ?

Reduction of glycerate 3-phosphate (GP) to triose phosphate (TP)

Regeneration of ribulose bisphosphate (RuBP)

Which 3 factors can limit the rate of photosynthesis?

1. Light Intensity

2. Temperature

3. CO2 concentration

Why is it important that ribulose bisphosphate (RuBP) is regenerated?

So that glycerate 3-phosphate (GP) is formed and the light-independent reaction can continue

Photosynthesis can continnue

What are the 4 optimum conditions for photosythesis ?

1. High light intensity of a certain wavelength (red and blue for chlorophyll a/b )

2. 25 C

3. 0.4% CO2

4. Water of the right volume

What 5 things will happen at a higher light intensity to cause faster growth of the plant?

Faster production of ATP and NADP in LDR

Faster light independent reaction

More sugars produced/synthesis of new materials

Sugars used for respiration

More energy for growth

Why is chlorophyll green?

Chlorophyll does not absorb green light well

What is the saturation point on a limiting factor/rate of photosynthesis graph ?

The point where increasing the limiting factor has no effect on the rate of photosynthesis

What does the saturation point indicate ?

That another factor is limiting the rate of photosynthesis

How do growers of plants create optimum conditions ?

Using glasshouses

How might plant growers control the CO2 concentration?

Burning propane

How might plant growers control the light intensity ?

Use lamps

How might plant growers control the temperature ? (3 ways)

Glasshouses trap heat energy

Heating/cooling systems

Air circulation systems

REQUIRED PRACTICALS

What is a photosynthetic pigment?

Coloured substances which absorb the light energy needed for photosynthesis

What does the stroma contain?

Enzymes, sugars, organic acids , starch grains

Where are carbohydrates produced in the light-independent reaction stored?

Starch grains in the stroma

What is a coenzyme?

A molecule that aids the function of an enzyme e.g. NADP transfers H+ between molecules

Give 3 examples of organic substances which can be produced in the Calvin Cycle

Carbohydrates

Lipids

Protein

What is a limiting factor ?

A factor which can slow down the rate of photosynthesis (or any reaction)

Why does keeping limiting factors at their optimum encourage a high yield ?

The rate of photosynthesis is at its optimum

The rate of production of organic products is high

Organic products are needed for plant growth

e.g. glucose can be respired to produce ATP needed to provide energy for protein synthesis