Chapter 11

Question 1

Metabolic pathway

Answer 1

A series of small reactions controlled by enymes

Question 2

Phosphorylation

Answer 2

Adding phosphate to a molecule

Question 3

Photophosphorylation

Answer 3

Addding phosphate to a molecule using light

Question 4

Photolysis

Answer 4

The splitting of a molecule using light

Question 5

Photoionisation

Answer 5

When light energy excites electrons in an atom giving them more energy causing them to be released, meaning the substance becomes a positively charged ion.

Question 6

Hydrolysis

Answer 6

The splitting of a substance using water

Question 7

Decarboxylation

Answer 7

The removal of CO2

Question 8

Dehydrogenation

Answer 8

Removal of hydrogen

Question 9

What specific properties makes ATP a good energy source

Answer 9

ATP stores or releases small manageable amout of energy at once so none is wasted as heat
Easily broken down so readily available.
Can be quickly re made.
ATP cant pass out of a cell so the cell always has an immediate source of energy.

Question 10

What is a coenzyme?

Answer 10

Aids the function of an enzyme, they work by transfering a chemical group from one molecule to another.
NADP transfers hydrogen.

Question 11

How is the structure of the leaf adapted for gas exchange?

Answer 11

• Large surface area: for sunlight absorption
• Arrangement of leaves minimises overlapping: prevents shadowing
• Thin: Diffusion distance kept short
• Transparent cuticle and epidermis: let light through to the photosynthetic mesophyll cells beneath.
• Long narrow upper mesophyll cells packed with sunlight: collect sunlight
• Numerous stomata: for gaseous exchange so all mesophyll are a short diffuison distance away.
• Stomata: open and close in response to light intensity
• Many air spaces in the lower mesophyll: allow rapid diffuision
• Extensive network of xylem: brings water to the leaf cells

Question 12

Photolysis of water

Answer 12

2 H2O = 4 H+ + O2 + 4 e

Question 13

NADP reduction

Answer 13

NADP + H + e = NADPH

Question 14

Atp production equation

Answer 14

ADP + Pi = ATP (light)

Question 15

Site of light dependant reaction

Answer 15

thylakoid membrane

Question 16

Site of light independant reaction

Answer 16

stroma

Question 17

Describe what happens during the light-dependant reaction?

Answer 17

1. Sunlight is absorbed by chlorphyll found in photosystem 2
2. Light energy exites the electrons and they move to a higher energy level.
3. The excited electrons along with H+ ions from the photolysis of water causes an electron carrier protein to be produced.
4. The excited electrons move down the electron transport chain through a series of redox reactions, with gradually decreasing energy levels.
5. Each time oxidation occurs a proton moves into the thylakoid.
6. NADPH is the final electron acceptor to be reduced
7. The buildup of protons in the thylakoid space causes photophosphorylation. The protons move down the concentartion gradient into the stroma via ATP synthase which is embedded in the thylakoid membrane in the process of chemiosmosis.
8. ADP + Pi = ATP
9. This is sustained by the photolysis of water as electrons formed replaces the lost electrons from the chlorophyll.

Question 18

Describe what happens during the light independant reaction?

Answer 18

1. A molecule of CO2 diffuses into the stroma and combines with ribulose biphosphae to produce an unstable 6 carbon compound in carbon fixation.
2. This is catalysed by rubisco
3. Two glycerate 3-phosphate moelcules are formed.
4. Glycerate 3-phosphate is then reduced to triose phospahte in a redox reaction where NADPH is oxidised.
5. This also requires energy from ATP released by ATP hydrolysis
6. NADPH and ATP are both from the light dependant stage of reaction
7. Triose phosphate is used to make useful organic substances like carbohydrates, lipids and amino acids
8. Spun six times to make one hexose sugar
9. Rubp is regenrated by a series of reactions requiring energy from ATP hydrolysis.
10. This is known as the calvin cycle

Question 19

Describe how you would investigate the activity of dehydrogenase in chloroplats?

Answer 19

In PS1 during the light dependant stage NADP acts as an electron acceptor and is reduced. This is catalysed by dehydrogenase. DCPIP acts as an electron acceptor and gets reduced by the dehydrogenase in the chloroplasts . As the dye gets reduced it turns from dark blue to colourless. Dehydrogenase activity can be measured by the rate that DCPIP loses it’s blue colour.

Question 20

How is the chloroplast adapted to to carrying out the light independant reaction?

Answer 20

1. The fluid of the stroma contains all the enzymes needed to carry out the reaction. Stromal fluid is membrane bound in the chloroplast meaning a chemical environment that has a high concentration of enzymes and substrates can be maintained within it.
2. The stroma fluid surrounds the grana and so the products of the light dependant reaction can easily diffuse into the stroma.
3. Contains DNA and ribosomes so can quickly and easily manufacture the proteins involved in the light dependant reaction.