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

What does respiration produce?

ATP

What are the 4 key stages of aerobic respiration

Glycolysis

Link Reaction

Krebs Cycle

Oxidative Phosphorylation 

Where does glycolysis occur? (Respiration)

The cytoplasm

Where does the link reaction occur? (Respiration)

mitochondrial matrix

Where does the krebs cycle occur?

The mitochondrial matrix

Where does oxidative phosphorylation occur?

Mitochondrial cristae

Is glycolysis an aerobic or anaerobic process?

anaerobic

Describe the process of glycolysis in respiration.

Phosphorylation of glucose to glucose phosphate using ATP

The production of two triose phosphate (3C) by the splitting of glucose phosphate

Oxidation of triose phosphate to pyruvate

There is a net gain of ATP, an NAD is reduced

What are the products of glycolysis during respiration?

2X Pyruvate

Net gain of 2 ATP

2X NADH

Describe the process of the link reaction in respiration?

The pyruvate made in glycolysis is oxidised to acetate

NAD picks up the hydrogen and becomes reduced NAD

Acetate combines with coenzyme A to produce acetylcoenzyme A

How many times does the link reaction occur for every glucose molecule?

twice

What are the products of the link reaction during respiration?

2X Acetylcoenzyme A,

2X CO2 released,

2 reduced NAD.

Describe the process of the krebs cycle.

Acetyl CoA combines with a 4 carbon  molecule, releasing coenzyme A and producing a 6 carbon compound.

 The 6 carbon compound is decarboxylated into a 5 carbon compound.

A hydrogen is removed from NAD to produce reduced NAD

The 5 carbon molecule is now converted into a 4 carbon molecule.

2X NAD are reduced to reduced NAD, 1 ATP is produced and 1 FAD is reduced into reduced FAD.

What are the products per cycle of the krebs cycle?

3X Reduced NAD

1X Reduced FAD

1X ATP

2X CO2

What are the products per glucose molecule for the krebs cycle?

6X reduced NAD
2X reduced FAD

2X ATP

1X CO2