B6

Question 1

What is photosynthesis?

Answer 1

• An endothermic chemical reaction that takes place inside photosynthetic organisms (plants, algae etc)
• converts light energy into chemical energy

Question 2

What is the symbol equation for photosynthesis?

Answer 2

6CO₂ + 6H₂O ———> C₆H₁₂O₆ + 6O₂

Question 3

Why is photosynthesis important?

Answer 3

It produces glucose which:
- used in respiration to release energy
- converted to starch and stored, then broken down when required
- used to make complex organic molecules used for growth and making up an animal’s biomass (to be transferred through food chains)

Question 4

What does chlorophyll do?

Answer 4

Absorbs light

Question 5

Give the two main stages of photosynthesis

Answer 5

1) Chlorophyll absorbs light energy, used to split water into oxygen and hydrogen ions

2) Carbon dioxide combines with hydrogen ions to form glucose

Question 6

What factors affect rate of photosynthesis?

Answer 6

• temperature (provide KE for enzymes (25º)
• light intensity (they’re directly proportional)
• carbon dioxide concentration

Question 7

Why does the rate of photosynthesis decrease as the distance from a light source increases?

Answer 7

Light intensity is inversely proportional to the distance square from the light source. Thus, as distance increases, light intensity decreases, causing rate of photosynthesis to, too, decrease

Question 8

What is the formula for light intensity?

Answer 8

Light intensity = 1/distance²

Question 9

Why do plants require water?

Answer 9

• photosynthesis
• keep turgid (for structure)
• cooling effect

Question 10

Why do plants require mineral ions?

Answer 10

For growth eg. nitrates required to produce proteins

Question 11

How are root hair cells adapted to absorb nutrients and mineral ions?

Answer 11

• big surface area
• many mitochondria which produce ATP for active transport

Question 12

What is the function of the xylem?

Answer 12

Transports water and minerals up the plant via transpiration

Question 13

How is the xylem adapted?

Answer 13

• dead cells to form long, hollow tube
• no end walls (little resistance)
• thick wall strengthened by lignin

Question 14

What is the function of the phloem?

Answer 14

Transports sugars up and down the plant via translocation
- from photosynthetic tissues (green leaves)
- to non-photosynthetic tissues (seeds)

Question 15

How is the phloem adapted to its function?

Answer 15

• sieve tube elements
  -> long, thin
  -> perforated end-plate for flow of sugars
  -> no nucleus, small cytoplasm (allows easy flow)
• companion cells (adjacent to sieve cell) that provide energy for processes in both of cells
  -> dense cytoplasm, nucleus, mitochondria

Question 16

Describe the process of transpiration?

Answer 16

• water evaporates from mesothelioma cells out of stomata
• water molecules and dissolved mineral ions are drawn up the xylem to replace lost water
• hence, more water molecules and absorbed mineral ions are absorbed from the soil

Question 17

How do the stomata open and close?

Answer 17

• to open them, water is drawn into the guard cells, making stomata open
• to close them, water is evaporated out of guard cells, allowing the stomata to close

Question 18

What factors affect rate of transpiration?

Answer 18

• light intensity (increase rate: stomata open which increases rate of photosynthesis. More water needed for the photosynthesis so more is taken up)
• temperature (increases rate: more KE to water molecules for diffusion. Also photosynthesis increases
• air movement (increases rate: higher water concentration gradient maintained between air spaces in leaf and atmosphere)

Question 19

What apparatus used to measure rate of transpiration?

Answer 19

Potometer

Question 20

What’s assumed when measuring rate of transpiration with a potometer?

Answer 20

Rate of water uptake ≈ rate of transpiration

Question 21

How can rate of transpiration be measured using a potometer?

Answer 21

Rate of transpiration = distance moved my bubble/time taken

Question 22

Describe how tissues of the leaves of the leaves are adapted for photosynthesis and gas exchange?

Answer 22

Upper epidermis: transparent, allows light to reach palisade layer

Palisade mesophyll layer: receives most light so contains greatest concentration of chloroplasts

Spongy mesophyll layer: air space increase the rate of diffusion

Lower epidermis: contains many stomata for gas exchange

Question 23

What are plant tropisms?

Answer 23

The growth of a plant in response to a stimulus

Question 24

What are auxins?

Answer 24

• group of plant hormones involved in tropisms
• control growth in plant roots and shoot tips

Question 25

How do auxins move through a plant?

Answer 25

They diffuse through the plant in solution

Question 26

Explain how tropisms increase chance of survival?

Answer 26

• Shoot growth towards sunlight to. Maximise light absorption
• Root growth towards ground to maximise mineral absorption

Question 27

What are gibberellins?

Answer 27

Plant hormone that control germination and flowering

Question 28

Describe the role of gibberellins in commercial plant cultivation

Answer 28

• Initiate germination at an unnatural time of year
• Increase yield by producing flowers in irregular conditions
• Produce seedless fruit by stimulating unpollinated flowers

Question 29

How do gibberellins trigger germination?

Answer 29

In presence of water, they break seed dormancy

Question 30

Why is ethane important in commercial plant cultivation?

Answer 30

• stimulates enzymes that control fruit ripening
• enables fruits to be picked while they unripe, to ripen in transportation