Core T - Crop Plants

Question 0

Explain the meaning of the term self-pollination. (2)

Answer 0

• Transfer of pollen from anther to a stigma

* On the same flower / plant

Question 1

Explain the advantages to a plant species of cross-pollination compared to self-pollination. (3)

Answer 1

• Genetic variation
• Increased heterozygosity
• Hybrid vigour
• Able to adapt to changing conditions
• Some individuals surviving
• Reduced risk of harmful recessive alleles

Question 2

Suggest how the flowering habit of maize encourages wind pollination. (3)

Answer 2

• Anthers versatile / loosely attached
• Anthers on long filaments (hang out of plant)
• Anthers above leaves (high up)
• Stigmas hang out of plant / flower
• Stigmas have large surface area / hairy / feathery / long (to catch pollen)
• No petals allow access to wind

Question 3

Explain why at the same temperature, the rate of photosynthesis between wheat and maize are different. (3)

Answer 3

• Maize greater rate
• Maize is C4
• PEP carboxylase more efficient at higher temperatures than rubisco
• Photorespiration occurs in wheat
• Oxygen instead of carbon dioxide combines with RuBP
• Less fixation of carbon dioxide
• Calvin cycle slows down
• Kranz Anatomy

Question 4

Explain how rice plans are adapted for growth with the roots submerged in water. (3)

Answer 4

• Low oxygen in the water results in anaerobic respiration
• Anaerobic respiration produces alcohol
• Rice tolerant to alcohol
• Because rice has high levels of alcohol dehydrogenase (enzyme that breaks down alcohol)
• Presence of aerenchyma
• Allows oxygen to reach roots from aerial tissues

Question 5

Maize does not cope well with drought as well as some other crops.
Young seedlings were uprooted and left in dry air for varying periods of time to reduce the water potential of their tissues.
Explain why this treatment reduced the water potential of maize seedling tissues. (2)

Answer 5

• Water lost by transpiration

* No water uptake by roots

Question 6

Described two ways in which sorghum plants are adapted to prevent the development of low water potential in their tissues during drought conditions. (2)

Answer 6

• Extensive / deep roots
• Leaves have small surface area
• Leaves are curled / waxy / have bulliform / hinged cells
• Reduced stomata numbers / sunken in pits

Question 7

The roots of rice plants are highly tolerant of alcohol.

Explain how this helps them survive when the fields are flooded. (2)

Answer 7

• Oxygen availability is low when fields are flooded
• Plants carry out anaerobic respiration
• Produces ethanol
• Continues to respire

Question 8

Describe the function of the endosperm. (2)

Answer 8

• Store of nutrients

* For germination

Question 9

Explain why the grains of cereals such as rice are staple foods in many parts of the world. (2)

Answer 9

• Cheap source of food
• Rich in carbohydrate
• Grains store well
• Because they contain very little water
• High energy value / fibre content
• Contain wide range of nutrients