5.1 Photosynthesis

Question 1

Photosynthesis and energy

Answer 1

The process where energy from light is used to make glucose from water and carbon dioxide. Photosynthesis an example of a metabolic pathway

Question 2

ATP

Answer 2

ADP phosphorylated to ATP, ATP hydrolysed to ADP

Question 3

ATP properties

Answer 3

Stores only a small, manageable amount of energy, no energy wasted as heat. Small, soluble molecule so easily transported. Easily broken down, energy released instantaneously. Quickly remade. Can phosphorylate molecules. Can’t pass out of cell, cell always has immediate supply of energy

Question 4

Compensation point

Answer 4

Particular light intensity at which the rate of photosynthesis matches rate of respiration

Question 5

Chloroplasts

Answer 5

Contain photosynthetic pigments (e.g. chlorophyll a/b, carotene) found in thylakoid membranes, create a photosystem when attached to protein

Question 6

Stroma

Answer 6

Contains enzymes, sugars and organic acids. Starch grains store carbohydrates in stroma

Question 7

Redox reactions

Answer 7

Reactions that involve reduction and oxidation. Oxidation is loss of electrons, reduction is gain of electrons

Question 8

Coenzymes

Answer 8

A molecule that aids the function of an enzyme, transfer a chemical group from one molecule to another

Question 9

NADP

Answer 9

NADP coenzyme transfers hydrogen from one molecule to another. Reduces by giving hydrogen, oxidises by taking hydrogen

Question 10

Light-dependent reaction

Answer 10

Photophosphorylation of ADP to ATP, making reduced NADP from NADP, splitting water into protons. Photolysis splits water into protons, electrons and oxygen

Question 11

Non-cyclic photophosphorylation (Light-dependent) Step 1

Answer 11

Light energy absorbed by PSII. Electrons move to higher energy level, they are released from chlorophyll and move down ETC to PSI

Question 12

Electron carriers

Answer 12

Proteins that transfer electrons. Photosystems and electron carriers form an electron transport chain

Question 13

Non-cyclic photophosphorylation (Light-dependent) Step 2

Answer 13

Photolysis replaces the electrons lost from PSII

Question 14

Non-cyclic photophosphorylation (Light-dependent) Step 3

Answer 14

Electrons lose energy as they move down ETC, energy used to transport protons into thylakoid so proton gradient across thylakoid membrane. Protons move down ATP synthase into stroma, forming ATP

Question 15

Non-cyclic photophosphorylation (Light-dependent) Step 4

Answer 15

Light energy absorbed by PSI, exciting electrons. Electrons transferred to NADP along with proton from stroma. Forms reduced NADP

Question 16

Chemiosmotic theory

Answer 16

Process of electrons flowing down ETC and creating proton gradient to form ATP

Question 17

Cyclic photophosphorylation (Light-dependent)

Answer 17

Produces ATP only using PSI. Electrons recycled to PSI via electron carriers. Only produces small amounts of ATP, no NADPH or oxygen

Question 18

Calvin Cycle (Light-independent)

Answer 18

Takes place in stroma of chloroplasts. Makes triose phosphate which can be used to make glucose or other useful organic substances

Question 19

Calvin Cycle Step 1

Answer 19

CO2 enters leaf through stomata and diffuses into stroma. Combined with RuBP and catalysed by rubisco. Unstable compound breaks down to glycerate 3-phosphate

Question 20

Calvin Cycle Step 2

Answer 20

Hydrolysis of ATP reduces GP to triose phosphate with H ions from NADPH

Question 21

Calvin Cycle Step 3

Answer 21

Five out of every 6 molecules of TP used to regenerate RuBP, which uses rest of ATP from light-dependent reaction

Question 22

Hexose sugars

Answer 22

Used to make larger carbohydrates. Calvin cycle happens six times to make one hexose sugar from 2 TP. Requires 18 ATP and 12 reduced NADP

Question 23

Light intensity optimum

Answer 23

Higher light intensity, more energy provided. Photosynthetic pigments only absorb red and blue wavelengths

Question 24

Temperature optimum

Answer 24

Temperatures around 25 degrees Celsius optimum. At high temperatures enzymes denature and stomata close to prevent too much loss of water, so less CO2 enters leaf which slows down photosynthesis

Question 25

Carbon dioxide optimum

Answer 25

Optimum at 0.4% CO2. If any higher, stomata will begin to close

Question 26

Water optimum

Answer 26

Too little and photosynthesis stops, too much and soil becomes waterlogged which reduces uptake of minerals needed to produce photosynthetic pigments. (E.g. magnesium for chlorophyll a)