5A - Photosynthesis and Respiration

Question 1

What is the equation of photosynthesis?

Answer 1

• Carbon dioxide + water + energy -> glucose + oxygen

Question 2

What is the equation for respiration?

Answer 2

• glucose + oxygen -> carbon dioxide + water + energy

Question 3

What specific properties does ATP have that makes it a good energy source?

Answer 3

• stores and releases only small amounts of energy, no energy is wasted
• small, soluble molecule - easily transported
• easily broken down
• can be quickly re-made
• can make other molecules more reactive by transferring a phosphate group
• can’t pass out of a cell, cell always has immediate source of energy

Question 4

What is the coenzyme used in photosynthesis?

Answer 4

• NADP

- transfers hydrogen from one molecule to another (reduction or oxidation)

Question 5

What are coenzymes used in respiration?

Answer 5

• NAD, FAD and Coenzyme A
• NAD and FAD either reduce or oxidise a molecule
• Coenzyme A transfers acetate between molecules

Question 6

Where does photosynthesis take place?

Answer 6

• chloroplasts

Question 7

What are thylakoids?

Answer 7

• fluid-filled sacs stacked up into grana

Question 8

What are grana linked together by?

Answer 8

• lamellae

Question 9

What are photosynthetic pigments and what are the 3 types?

Answer 9

• coloured substances that absorb light energy

- chlorophyll a, chlorophyll b and carotene

Question 10

What wavelength does Photosystem I absorb light best?

Answer 10

• 700nm

Question 11

What wavelength does Photosystem II absorb light best?

Answer 11

• 680nm

Question 12

What is the stroma?

Answer 12

• gel-like substance which contains enzymes, sugars and organic acids

Question 13

What is the first stage of the light-dependent reaction?

Answer 13

• light energy is absorbed by chlorophyll in photosystems

- light energy excites electrons in chlorophyll, leading to eventual release (photoionisation)

Question 14

What is the second stage of the light-dependent reaction?

Answer 14

• some of the energy from released electrons is used to add phosphate group to ADP to form ATP, and some is used to form reduced NADP
• H2O is oxidised to O2

Question 15

The energy resulting from photoionisation in chlorophyll is used for what three things?

Answer 15

• photophosphorylation (ADP + Pi = ATP)
• making reduced NADP from NADP
• photolysis (splitting water into protons, electrons and oxygen)

Question 16

What happens during the first stage of non-cyclic phosphorylation?

Answer 16

• light energy is absorbed by PSII
• light energy excites electrons in chlorophyll
• electrons move to higher energy level
• electrons are released from chlorophyll and move down electron transport chain to PSI

Question 17

What happens during the second stage of non-cyclic phosphorylation?

Answer 17

• light energy splits water into protons, electrons and oxygen (photolysis)
• to replace the released electrons

Question 18

What happens during the third stage of non-cyclic phosphorylation?

Answer 18

• excited electrons lose energy as they move down the electron transport chain
• energy is used to transport protons into thylakoid, so thylakoid has higher concentration of protons than the stroma
• proton gradient is formed across thylakoid membrane
• protons move down gradient into stroma via ATP synthase. Energy from this movement makes ATP.

Question 19

What is the fourth stage of non-cyclic phosphorylation?

Answer 19

• light energy is absorbed by PSI, exciting electrons again to an even higher energy level
• electrons are transferred to NADP along with a proton to form reduced NADP

Question 20

What is ‘cyclic phosphorylation’?

Answer 20

• electrons are passed back to PSI via electron carriers rather than being passed to NADP
• only produces small amounts of ATP

Question 21

What is the first stage of the light-independent reaction?

Answer 21

• CO2 enters leaf through stomata and diffuses into stroma
• combines w/ ribulose biphosphate (RuBP), reaction is catalysed by rubisco
• gives unstable 6-carbon compound, which quickly breaks down into 2 glycerate 3-phosphate (GP)

Question 22

What is the second stage of the light-independent reaction?

Answer 22

• hydrolysis of ATP from light-dependent reaction provides energy to turn GP into triose phosphate (TP)
• reaction also requires H ions, which come from reduced NADP. Reduced NADP is recycled to NADP.
• some TP is then converted into useful organic substances and some regenerates RuBP

Question 23

What is the third stage of the light-independent reaction?

Answer 23

• 5/6 molecules of TP produced in the cycle is used to regenerate RuBP
• regenerating RuBP uses the rest of ATP produced by light-dependent reaction

Question 24

What are the three limiting factors of photosynthesis?

Answer 24

• light intensity
• CO2 concentration
• temperature

Question 25

What is the first stage of glycolysis?

Answer 25

- glucose is phosphorylated using a phosphate from ATP - creates 1 glucose phosphate and 1 ADP - ATP adds another phosphate, forming hexose bisphosphate - hexose bisphosphate is then split into 2 triose phosphate

Question 26

What is the second stage of glycolysis?

Answer 26

- triose phosphate is oxidised, forming two pyruvates - NAD collects hydrogen ions, forming 2 reduced NAD - 4 ATP are produced, but 2 were used up in the first stage, so net gain is 2 ATP

Question 27

What happens to the pyruvate in anaerobic respiration?

Answer 27

- converted to ethanol or lactate | - regenerates oxidised NAD, means glycolysis can continue even when there isn't much O2 around

Question 28

What happens first in the link reaction?

Answer 28

- pyruvate is decarboxylated (one carbon atom is removed in the form of CO2

Question 29

What happens second in the link reaction?

Answer 29

- pyruvate is oxidised to form acetate | - NAD is reduced to form reduced NAD

Question 30

What happens third in link reaction?

Answer 30

- acetate is combined with coenzyme A to form acetyl coenzyme A

Question 31

Is ATP produced in the link reaction?

Answer 31

- No

Question 32

What happens in the first stage of the Krebs Cycle?

Answer 32

- acetyl CoA from link reaction combines with 4-carbon molecule to form 6-carbon molecule - coenzyme A goes back to link reaction to be used again

Question 33

What happens in the second stage of the Krebs Cycle?

Answer 33

- 6C citrate molecule converted to 5C molecule - decarboxylation occurs, CO2 removed - dehydrogenation also occurs, H removed - hydrogen used to produce reduced NAD from NAD.

Question 34

What happens in the third stage of the Krebs Cycle?

Answer 34

- 5C molecule converted to 4C molecule - decarboxylation and dehydrogenation occur, producing 1 molecule of reduced FAD and 2 reduced NAD - ATP is produced by direct transfer of phosphate group from an intermediate compound to ADP - citrate is now converted into oxaloacetate

Question 35

What happens first in oxidative phosphorylation?

Answer 35

- hydrogen atoms are released from reduced NAD and reduced FAD as they're oxidised to NAD and FAD - H atoms split into protons and electrons

Question 36

What happens second in oxidative phosphorylation?

Answer 36

- electrons move down transport chain, losing energy at each carrier - energy is used to pump protons from mitochondrial matrix into the intermembrane space - concentration of protons is now higher in intermembrane space than the matrix - forms electrohemical gradient

Question 37

What happens third in oxidative phosphorylation?

Answer 37

- protons move down electrochemical gradient via ATP synthase - ATP is synthesised from ADP and P

Question 38

What happens fourth in oxidative phosphorylation?

Answer 38

- in the mitochondrial matrix, protons, electrons and O2 combine to form water - oxygen is the final electron acceptor

Question 39

What is the process of ATP production being driven by the movement of H+ ions across a membrane called?

Answer 39

- chemiosmosis