5 - Energy Transfers

AQA A-LEVEL BIOLOGY PAPER 2 TOPIC 5

What is photosynthesis?

A reaction in which light energy is used to produce glucose in plants.

What are the required compounds of photosynthesis?

carbon dioxide and water

What are the products of photsynthesis?

glucose and oxygen

Where does photosynthesis take place?

The chloroplasts

How many stages of photosynthesis are there?

2

What are the 2 stages of photosynthesis?

Light dependent reaction
Light independent reaction

Name 3 factors that may affect the rate of photosynthesis.

Carbon dioxide concentration, light intensity, temperature

What is the Light Dependent Reaction?

the first stage of photosynthesis

Where does the LDR take place?

The thylakoid membranes or the grana

What happens overall in the LDR?

Light energy and water are used to create ATP and reduced NADP, which are needed for the light independent reaction.

List the chemicals required for the LDR.

NADP
ADP 
Pi
Water

What are the 4 key stages of the LDR?

Photoionisation of Chloropyll

Photolysis

Chemiosmosis

Production of ATP and reduced NADP

Describe the process of the photoionisation of chlorophyll during the LDR.

chlorophyll molecules inside the PSII absorb light

the light excites the electrons in the chlorophyll.

Electrons are lost, and the chlorophyll becomes positively charged

Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis.

Describe the process of the photolysis of water in the LDR.

light energy is absorbed by the chlorophyll, splitting water into Oxygen, protons and electrons.

Describe the process of chemiosmosis during the LDR.

The electrons that were excited by the light energy and left the chlorophyll move along an electron transfer chain, releasing energy.

Some of this energy is used to pump the protons across the chloroplast membrane.

An electrochemical gradient of protons is established; the protons pass through the enzyme ATP synthase, which results in the production of ATP.

The protons combine with the co-enzyme NADP to become reduced NADP.

What type of reaction is the LIR of photosynthesis?

A cycle

What is the term used to describe the cycle that takes place during the LIR?

The calvin cycle

Where does the calvin cycle take place?

the stroma

What enzyme does the stroma of the chloroplast contain that is used in the calvin cycle?

RuBisCo

What is the purpose of RuBisCo in the Calvin Cycle?

It catalyses the reaction

Why is the Calvin Cycle temperature sensitive?

Due to the presence of the enzyme RuBisCo in the stroma of the chloroplasts.

What is hydrolysed to provide energy for the calvin cycle?

ATP

Describe the process of the Calvin Cycle.

Carbon dioxide reacts with Ribulose Biphosphate RuBP to form 2 molecules of glycerate-3-phosphate (GP). This is catalysed by rubisco.

GP is then reduced to Triose Phosphate (TP) using energy from ATP and by accepting an H from reduced NADP.

Some carbon atoms from TP leave the cycle to be converted into organic substances such as glucose.

The rest of the carbon from TP is used to regenerate RuBP with the energy from ATP.

What happens to the carbon atoms from TP that leave the cycle?

They are converted into organic substances such as glucose