MODULE 5: Energy for Biological Processes !!

Question 1

Equation for photosynthesis:

Answer 1

C₆H₁₂O₆ + 6O₂ –> 6CO₂ + 6H₂O

- reverse is respiration

Question 2

Photosynthesis and respiration:

Answer 2

Interrelated reactions, as the reactants for one equation are the products of another

Question 3

Structure of chloroplast: (7)

Answer 3

Inner and outer membrane, lamellae, grana, thylakoid, stoma and DNA

Question 4

Thylakoid:

Answer 4

Flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation. Location of light dependent phase, membrane contains photosystems I and II, as well as ATP synthase

Question 5

Stroma:

Answer 5

Central cavity that contains appropriate enzymes and pH for the Calvin cycle to occur. Contains starch, lipids, ribosomes and chloroplast DNA

Question 6

Grana:

Answer 6

Stacks of thylakoids to increase SA:V of thylakoid membrane

Question 7

Lamellae:

Answer 7

Connects and separates grana to maximise photosynthetic efficiency

Question 8

Purpose of pigments in photosynthesis:

Answer 8

Absorb different wavelengths of light to transfer energy to the reaction centre

Question 9

Primary pigment:

Answer 9

Chlorophyll A

Question 10

Accessory pigments:

Answer 10

Chlorophyll B, xanophylls, carotenoids

Question 11

Why do chloroplasts have several pigments?

Answer 11

Create a light harvesting system, as certain pigments absorb some wavelengths of light and reflect others (causing their colour.) This maximises absorption of light

Question 12

Photosystem:

Answer 12

Light harvesting system and reaction center

Question 13

Thin layer chromatography in photosynthetic pigments:

Answer 13

• Mobile phase = solution containing mixture of pigments
• Stationary phase = thin layer of silica gel (on glass)
• Different solubilities of pigments = different distances moved, hence different Rf values

Question 14

Rf equation:

Answer 14

Distance travelled by component / distance travelled by solvent

Question 15

Two phases of photosynthesis:

Answer 15

Light dependent phase and light independent phase (Calvin cycle)

Question 16

Light dependent phase brief summary:

Answer 16

Energy from sunlight is used to form ATP, and photolysis of water allows NADP to be reduced into NADPH

Question 17

Light independent phase brief summary:

Answer 17

Products from light dependent phase are used to produce glucose, lipids and amino acids; ATP supplies the energy, whilst NADPH and CO₂ are converted into organic molecules

Question 18

Non cyclic vs cyclic photophosphorylation:

Answer 18

Non cyclic = uses photosystems I and II

Cyclic = uses photosystem I only

Question 19

Photophosphorylation:

Answer 19

Transducing light energy into chemical energy, so ADP can be phosphorylated into ATP

Question 20

Chemiosmosis:

Answer 20

Diffusion of protons from a region of high concentration to an area of low concentration

Question 21

Two methods of exciting electrons:

Answer 21

• breaking of chemical bonds (electrons present in respiratory substrates)
• absorbing light from the sun (electrons present in pigments)

Question 22

Electron transport chain: (ETC)

Answer 22

• series of electrons carriers
• progressively less energy (less excited due to loss of energy moving between carriers)
• released energy is used to pump protons across the membrane
• creates a gradient, which is maintains as the membrane is impermeable to protons
• protons can only re enter the thylakoid via hydrophilic protein channels, which is linked to the enzyme ATP synthase
• flow of proteins through the channel allows the enzyme to catalyse the formation of ATP from ADP and inorganic phosphate

Question 23

ATP formation from chemiosmosis and ETC:

Answer 23

• protons move out of thylakoid due to energy released from ETC
• creates a proton gradient
• protons move back into the thylakoid by chemiosmosis via the hydrophilic channel protein that is linked to ATP synthase
• movement of protons through the channel allows the enzyme (ATP synthase) to catalyse the formation of ATP from ADP and inorganic phosphate

Question 24

Photolysis:

Answer 24

H₂O –> 2H⁺ + 0.5O₂ + 2e⁻

• energy from the sun splits water into hydrogen ions, oxygen and electrons.
• electrons released from this process replace the lost electrons from reaction center of PSII.
• catalysed by oxygen-evolving complex enzyme in PSII