Unit 5 - Energy transfers in and between organisms

Question 1

What are the two reactions in photosynthesis?

Answer 1

light-dependent reaction, light-independent reaction

Question 2

Where does the light-dependent reaction take place?

Answer 2

in the thylakoid membrane

Question 3

Where does the light-independent reaction take place?

Answer 3

in the stroma

Question 4

Which chemicals are needed for the light-independent reaction?

Answer 4

NADP, ADP, Pi and water

Question 5

What happens during photoionisation?

Answer 5

chlorophyll absorbs light and electrons are lost

Question 6

How does the light-dependent reaction generate ATP?

Answer 6

Chlorophyll absorbs light energy which excites the electrons
Electrons pass down the electron transport chain in the thylakoid membrane and lose energy
Energy used to pump H+ into thylakoid lumen from stroma
Chemiosmosis - H+ moves down the electrochemical gradient by facilitated diffusion through ATP synthase
ADP + Pi –> ATP

Question 7

How is NADPH made in the light-dependent reaction of photosynthesis?

Answer 7

light energy is absorbed by chlorophyll
excites electrons
electrons pass down electron transport chain
electrons lose energy
electrons accepted by chlorophyll
light energy excites electrons
electron accepted by NADP —–> NADPH

Question 8

What is photolysis?

Answer 8

splitting of water using light energy
2H2O —-> O2 + 4H+ +4e-

Question 9

Describe the light-independent reaction of photosynthesis? (Calvin cycle)

Answer 9

CO2 and RuBP binds to Rubisco enzyme
2x GP is produced
GP is reduced to Triose phosphate using reduced NADP and energy from ATP
2x triose phosphate forms hexose sugars
triose phosphate is used to regenerate RuBP using energy from ATP

Question 10

What are the properties of ATP?

Answer 10

• stores or releases only a small amount of energy so no energy wasted as heat
• small, soluble molecule so easily transported around the cell
• easily broken down so energy can be released instantly
• it can be quickly remade
• can make other molecules more reactive by phosphorylation
• can’t pass out of the cell so the cell always has an energy supply

Question 11

What are the stages of aerobic respiration?

Answer 11

glycolysis, link reaction, kreb’s cycle, oxidative phosphorylation and the electron transport chain

Question 12

What happens during glycolysis?

Answer 12

phosphorylation of glucose using ATP, phosphorylate glucose is converted to 2x triose phosphate, oxidation of triose phosphate to pyruvate, net gain of ATP, NAD reduced

Question 13

Where does glycolysis take place?

Answer 13

cytoplasm

Question 14

What happens during the Link reaction?

Answer 14

pyruvate actively transported from the cytoplasm into the matrix of mitochondria
pyruvate is oxidised to acetate
NAD reduced and CO2 lost
acetate and co-enzyme A combine to form acetyl co-enzyme A

Question 15

What happens during the Kreb’s cycle?

Answer 15

Acetyl CoA combines with a 4 carbon compound called oxaloacetate. This reaction releases the CoA enzyme allowing it to be re-used. The now 6 carbon compound (citric acid) releases Co2 leaving a 5 carbon compound. This reaction also produces NADH, reduced FAD and ATP

Question 16

What are the four stages of the nitrogen cycle?

Answer 16

ammonification, nitrification, nitrogen fixation, denitrification

Question 17

What is nitrogen fixation?

Answer 17

converting nitrogen gas into a nitrogen containing compound

Question 18

How is nitrogen fixation done in legumes?

Answer 18

• in legumes, bacteria in root nodules converts nitrogen gas into ammonium or nitrates

Question 19

What is ammonification?

Answer 19

nitrogen-fixing bacteria in soil converts nitrogen gas into ammonium

Question 20

What are the two stages of nitrification?

Answer 20

• nitrifying bacteria converts ammonium into nitrites
• nitrifying bacteria converts nitrites into nitrates

Question 21

How do nitrates get into plants?

Answer 21

absorbed by active transport

Question 22

What does saprobiotic bacteria do?

Answer 22

digest the proteins in dead animals/ plants into other nitrogen containing compounds

Question 23

What is denitrifcation?

Answer 23

denitrifying bacteria converts nitrates into nitrogen gas

Question 24

What conditions are needed for dentifrying bacteria?

Answer 24

anaerobic

Question 25

What is the last stages of aerobic respiration?

Answer 25

oxidative phosphorylation

Question 26

Explain the process of oxidative phosphorylation

Answer 26

• NADH and reduced FAD are oxidised to NAD and FAD, hydrogen atoms are released which split into H+ and e-
• electrons move down the electron transport chain and lose energy
• this energy is used by the electron carriers to pump protons from the matrix into the intermembrane space
• the H+ concentration is now higher in the intermembrane space than in the matrix forming an electrochemical gradient
• H+ moves down the electrochemical gradient into the matrix via ATP synthase which drives the synthesis of ATP from ADP and Pi in a condensation reaction
• in the matrix, at the end of the electron transport chain, H+ , e- and oxygen from the blood combine to form water. Oxygen is the final electron acceptor