Biology - Energy Transfer - Topic 11 & 12

Outline the Light Dependent Reaction

1. Chlorophyll absorbs light and electrons become excited

2. Electron transport chain accepts excited electrons and they move down chain releasing energy

3. Photolysis of water occurs, producing electrons, protons and oxygen

4. Energy is used to pump protons from stroma to thylakoid membrane 

5. H⁺ ions to facilitated diffuse through ATP synthase, causing it to catalyse ADP + Pi, forming ATP

6. Electrons reduce NADP forming NADPH

Describe the role of electron transport chains in LDR (6)

• Electron transport chains accept excited electrons from chlorophyll

• Electrons move down electron transport chain releasing energy

• Energy is used to pump H⁺ from stroma to thylakoid membrane

• Allows H⁺ ions to facilitatedly diffuse through ATP synthase which catalyses ADP+Pi forming ATP

• Electrons reduce NADP to NADPH

Outline the Light Independent Reaction

• CO₂ combines with RuBP, catalysed by rubisco

• forms GP

• GP reduced by NADPH using energy from ATP

• forming triose phosphate

• 1/6 triose phosphate forms hexose sugar

• 5/6 triose phosphate forms RuBP using ATP so all RuBP is reformed

One of the products produced from TP is hexose sugars. Give two uses for hexose sugars in plant cells. (2)

• cellulose strengthens cell walls

• respiration for ATP

• conversion of starch for storage

Outline glycolysis

• (1st stage of respiration, in cytoplasm)

• Glucose is phosphorylated using 2 ATP

• unstable intermediate forms, then splits into 2 triose phosphate

• triose phosphate is phosphorylated then dephosphorylated

• 2 ATP form per triose phosphate, 4 per glucose

• triose phosphate is oxidised, forming reduced NAD and pyruvate

what is the end result of glycolysis

• net gain of 2 ATP

• 2 pyruvate

• 2 reduced NAD

Outline the Link Reaction

• (in matrix)

• pyruvate is oxidised forming acetate and releasing CO₂

• NAD is reduced forming reduced NAD

• coenzyme A combines with acetate forming acetyl coenzyme A

Outline Krebs Cycle

• (matrix)

• 2C Acetyl CoA combines with 4C oxaloacetate making 6C citrate

• citrate is dehydrogenated, reducing NAD to NADH & decarboxylated releasing CO₂ forming 5C intermediate compound

• 5C is dephosphorylated making ATP, dehydrogenated forming 2 NADH and 1 FADH₂ and decarboxylated releasing CO₂ and forming 4C oxaloacetate

Outline Oxidative Phosphorylation

• (inner mitochondrial membrane)

• FADH₂ and NADH are oxidised forming FAD and NAD, releasing H⁺ ions and electrons

• ETC accept electrons and they release energy as they move down

• Energy is used to pump H⁺ ions from matrix to intermembrane space

• H⁺ ions facilitatedly diffuse down electrochemical gradient via ATP synthase which catalysed ADP+Pi to ATP

• Oxygen is the final electron acceptor 

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion

• oxygen oxidises NADH and FADH₂

• ATP is formed as electrons move down transport chains

• oxygen is the final electron acceptor

Outline anaerobic respiration in mammals

• (lactate fermentation)

• glycolysis occurs

• pyruvate is reduced by NADH from glycolysis forming lactate

• NAD regenerates which allows glycolysis to continue

Outline anaerobic respiration in plant cells and yeast

• (ethanol fermentation)

• glycolysis occurs

• pyruvate is decarboxylated, releasing CO₂ and forming ethanal 

• ethanal is reduced by NADH from glycolysis forming ethanol 

• NAD regenerates which allows glycolysis to continue

Using a respirometer

• oxygen diffuses into respiring maggots in aerobic respiration

• CO₂ produced and is absorbed by soda lime

• this decreases volume and pressure so liquid moves left