Topic 5A: Photosynthesis and Respiration

Question 1

Photosynthesis

Answer 1

A process where energy from light is used to make glucose from water and carbon dioxide.

6(CO2)+6(H2O)+energy->(C6H12O6)+(602)

1) Light dependent reaction (Photophosphorylation)
2) Light independent reaction (The Calvin Cycle)

Question 2

Aerobic Respiration

Answer 2

A process where energy is released from glucose using oxygen.

(C6H12O6)+6(02)->6(CO2)+6(H20)+energy

1) Glycolysis
2) Link Reaction
3) Kreb’s cycle
4) Oxidative phosphorylation

Question 3

Structure of ATP

Answer 3

ATP is made from the nucleotide base adenine, a ribose sugar and 3 phosphate groups.

Question 4

Phosphorylation

Answer 4

When ATP is synthesised via a condensation reaction between ADP+Pi, with the use of energy. It is catalysed by ATP synthase.

Question 5

Properties of ATP

Answer 5

Release small, manageable amounts of energy so none is wasted as heat.

Easily broken down so it can be used instantaneously.

Question 6

Compensation point

Answer 6

The light intensity at which the rate of photosynthesis is equal to the rate of respiration so the net oxygen production is zero.

Question 7

Anaerobic respiration

Answer 7

A process where energy is released from glucose without using oxygen, producing lactic acid as a waste product.

1) Glycolysis
2) Fermentation

Question 8

Photosynthesis: Light dependent Reaction (Non-cyclic photophosphorylation)

Answer 8

1) Light energy is absorbed by photosystem II, and excites electrons to a higher energy level.
(replaced through photolysis of water)

2) They then move down the electron transport chain to photosystem 1, losing energy as they do so.
3) This energy is used to transport H+ ions into the thylakoid, creating a higher concentration of H+ ions than in the stroma.
4) The H+ ions move down the gradient, into the Stroma via ATP Synthase.
5) The energy from this is used to combine ADP + Pi to form ATP.
6) At photosystem I, light energy is absorbed once again, exciting electrons to an even higher level.
7) The electrons are then transferred to NADP, along with a H+ ion to form reduced NADP.

Question 9

Photosynthesis: Light dependent Reaction (Cyclic photophosphorylation)

Answer 9

Electrons from the chlorophyll molecule are passed back to photosystem I meaning electrons aren’t recycled.

This process doesn’t produce reduced NADP or oxygen, and only small amounts of ATP.

Question 10

Photosynthesis: Light independent Reaction (The Calvin Cycle)

Answer 10

1) Carbon Dioxide and RuBP combine (carbon fixation) in a reaction catalysed by rubisco to create an unstable 6-carbon compound.
2) This compound eventually breaks down into two GP molecules.
3) Energy from the hydrolysis of ATP is used to reduce the two GP molecules into two TP molecules by using H+ ions from reduced NADP.
4) Some TP is converted into useful organic compounds.
5) 5/6 TP molecules are used to regenerate RuBP, by using energy released from the hydrolysis of ATP.

Question 11

Limiting factors of photosynthesis

Answer 11

• Light intensity
• Temperature
• Carbon dioxide concentration

The more energy the molecules have, the more collisions there are and therefore more ES complexes are formed.

Question 12

Aerobic / Anaerobic respiration: Glycolysis

Answer 12

A process which occurs in the cytoplasm to convert glucose into pyruvate.

1) Glucose is phosphorylated using an inorganic phosphate from ATP, to produce GP.
2) Another inorganic phosphate from a different ATP molecule is added to produce Hexose bisphosphate.
3) This then splits into two TP molecules.
4) These TP molecules are oxidised to form two pyruvate molecules.
5) The H+ ions released here combine with NAD to form reduced NAD, and the energy released forms 4x ATP molecules.

Question 13

Aerobic respiration: Link reaction

Answer 13

A process which occurs in the matrix of the mitochondria to produce acetyl coenzyme A from pyruvate.

1) A carbon dioxide molecule and H+ ion are removed from pyruvate to form acetate. This H+ ion is used to produce reduced NAD.
2) Acetate then combines with coenzyme A to form acetyl coenzyme A.

Question 14

Aerobic respiration: Kreb’s Cycle

Answer 14

Occurs in the matrix of the mitochondria.

1) Acetyl coenzyme A combines with oxaloacetate to form citrate. (Coenzyme A goes back to the link reaction to be reused)
2) Carbon dioxide is then removed from the citrate molecule to form a 5-carbon molecule. Hydrogen is also removed to produce reduced NAD.
3) This 5-carbon molecule is then regenerated back into oxaloacetate by removing a carbon dioxide molecule.
4) During this process, one molecule of reduced FAD and two molecules of reduced NAD are formed. The energy released also forms ATP from ADP + Pi.

Question 15

Aerobic respiration: Oxidative phosphorylation

Answer 15

The process where energy carried by electrons is used to produce ATP.

1) Hydrogen atoms released during the oxidation of reduced NAD/FAD split into H+ ions and electrons.
2) The electrons move down the electron transport chain, releasing energy to pump H+ ions from the matrix into the membrane, to produce a concentration gradient.
3) H+ ions then move back down the gradient via ATP Synthase, which produces ATP from ADP + Pi.
4) The H+ ions then combine with the electrons and oxygen to form water.

Question 16

Anaerobic respiration: Fermentation

Answer 16

Pyruvate produces in glycolysis is converted into ethanol or lactate using reduced NAD. This regenerates oxidised NAD meaning glycolysis can continue even without oxygen.

Alcoholic Fermentation:
Occurs in plants.
Pyruvate->Ethanal->Ethanol

Lactate Fermentation:
Occurs in animal cells/bacteria.
Pyruvate -> Lactate

Question 17

Why is oxygen required in oxidative phosphorylation?

Answer 17

It acts as the final electron acceptor and combines with electrons and hydrogen ions to form water.