Respiration and Photosynthesis

Question 1

Properties of ATP

Answer 1

• When hydrolysed, energy is released in small amounts
• Energy released in single-step reaction
• Soluble in water, where most chemical reactions occur
• Quickly broken down and resynthesised

Question 2

Functions of ATP

Answer 2

• Active transport
• Synthesis reactions
• Muscle contraction
• Cell division
• Light independent reactions of photosynthesis
• First stage of glycolysis

Question 3

Oxidation of amino acids

Answer 3

• Only used when all carbohydrate and lipid reserves have been used.
• Frst deaminated, and remaining keto acid can enter glycolysis or Krebs cycle, or be converted into a fatty acid which enters the Krebs cycle

Question 4

What occurs to pyruvate during anaerobic respiration and why is this significant?

Answer 4

It is reduced using the NADH produced during glycolysis. Enabling regeneration of NAD for reuse.

Question 5

Limitations of a respirometer

Answer 5

• Changes in T or atmospheric Pa can make gases expand or contract.
• These affect the distance the fluid moves, so measured distance isnt just affected by O2 volume.
• Chemicals used might alter composition of gases in the chamber.
• Volume change calculated using the diameter of the tube may be inaccurate.

Question 6

Photosynthesis

Answer 6

Autotrophic nutrition. Production of organic compounds, e.g. carbohydrates and lipids from the inorganic compounds CO2 and H2O using light energy.

Question 7

Product of light dependent reaction

Answer 7

• ATP
• NADPH plus H+ (H from photolysis of H2O
• Oxygen

Question 8

Uses of NADPH and ATP in light independent reaction

Answer 8

• Hydrogen from NADPH reduces GP forming TP

- ATP used as energy source for further synthesis reactions

Question 9

Products of non-cyclic phosphorylation

Answer 9

ATP, NADPH plus H+ and oxygen

Question 10

Products of cyclic phosphorylation

Answer 10

ATP

Question 11

What occurs to CO2 in calvin cycle?

Answer 11

It combines with RuBP in a reaction catalysed by Rubisco to form 2 GP.

Question 12

What occurs to GP in calvin cycle?

Answer 12

Reduced using NADPH to form TP, with energy supplied by ATP.

Question 13

What is TP used for in plants?

Answer 13

• Forms all photosynthetic products e.g. glucose, fatty acids, glycerol, amino acids
• Regenerates RuBP

Question 14

Action spectrum

Answer 14

Graph showing the effectiveness of different wavelengths of light in stimulating the process being investigated.

Question 15

Absorption spectrum

Answer 15

Graph of the relative amounts of light absorbed at different wavelengths for a pigment.

Question 16

What is the metabolic advantage of C4 plants to C3 plants?

Answer 16

• Not inhibited by oxygen

- CO2 acceptor, PEP has v high CO2 affinity, even in low concentrations

Question 17

What happens to CO2 in C4 plants?

Answer 17

1) CO2 is fixed in mesophyll cell then shuttled to bundle sheath cells for conventional C3 fixation
2) Carbon is shuttled as a 4C acid which releases CO2 and is fixed by RuBP.
3) Resulting 3C compound is shuttled back to mesophyll cells for conversion into PEP

Question 18

Adaptations of halophytes

Answer 18

• High transpiration rates & low water potential in root cells, greater water potential gradient
• Extensive root network providing anchorage and a large surface area for water and iron uptake
• Smaller plants able to store water when available
• Able to regulate salt content by excreting salt from glands at the margins of their leaves

Question 19

Adaptations of xerophytes

Answer 19

• A thickened waxy cuticle
• Reduced surface area of leaves.
• Curled leaves
• Hairs on leaf surface
• Stomata in ‘epidermal pits’ beneath leaf surface
• Extensive shallow root network and deep tap root

Question 20

How does a thickened waxy cuticle help prevent water loss?

Answer 20

Provides long diffusion pathway, reducing the rate of evaporation

Question 21

How do curled leaves help prevent water loss?

Answer 21

Reduces surface area for evaporation and increases humidity in air around stomata reducing transpiration.

Question 22

How do hairs on the leaf surface prevent water loss?

Answer 22

Trap layer of air, which becomes saturated with water vapour reducing water potential gradient for water loss.

Question 23

How does the location of stomata in epidermal pits help reduce water loss?

Answer 23

Reduce exposure to air currents which become saturated with water vapour & reduce the water potential gradient for evaporation.

Question 24

How does and extensive shallow root network and deep tap root help prevent water loss?

Answer 24

Maximises water uptake from just below the surface and from well below the sand level

Question 25

Adaptations of mesophytes

Answer 25

Presence of waxy cuticle, protected stomata (w/ regulatory diameters), variable leaf shape & abscission.

Question 26

Adaptations of hydrophytes

Answer 26

Cells become turgid & a point is reached where water potentials of surrounding water & plant cells are equal & there is no further net movement of water into cells.

Question 27

Adaptations of the xylem

Answer 27

• Tissue is dead, no cell contents, leaving hollow tubes so there is minimal resistance to flow of water & ions.
• Cell walls strengthened by lignin; making them more rigid providing support & impermeable to water.
• No cross-walls in xylem vessels allowing free flow. In tracheids the end walls have partially broken down.
• Bordered pits present allowing water and solutes to move laterally to adjacent vessels

Question 28

How does the endodermis control entry of substances into the xylem?

Answer 28

Casparian strip (made of suberin) is impermeable to water and ions, meaning they cannot pass through the apoplast pathway, only the symplast.

Question 29

How is root pressure produced?

Answer 29

• Active transport of ions into the xylem;
• By the endodermis;
• Lowers the water potential of the xylem;
• Water moves into the xylem by osmosis;
• Produces a positive hydrostatic pressure

Question 30

Explain how standard deviation helps in the interpretation of data

Answer 30

• Shows spread of the data
• Overlap = not significant;
• Low SD means results more reliable / repeatable

Question 31

Why is petroleum used as a control when measuring efficiency of biofuels

Answer 31

• Is widely/commonly used;
• Provides a standard amount of CO2 produced;
• Produces large amount of carbon dioxide;
• Could be replaced by biofuel

Question 32

Advantage of systemic herbicide over contact herbicide

Answer 32

• Absorbed / transported through tissues of plant
• Kills whole plant
• Less affected by light / rain

Question 33

Appropriate units for measuring energy transfer in a pyramid of energy

Answer 33

kJ m-2 yr-1

Question 34

Describe and explain how the stability of a community is related to the number of species it contains

Answer 34

• High stability with greater number of species
• More species linked to more food chains
• If one species dies others available as food

Question 35

Light independent reaction

Answer 35

• CO2 combines with RuBP, Catalysed by RUBISCO;
• Produce two molecules of GP, reduced to TP using NADPH and energy from ATP
• TP used to form glucose and resynthesize RuBP;