9.3 Reproduction in Angiospermophytes

Question 1

Define pollination

Answer 1

The transfer of pollen grains from the mature anther to the receptive stigma (usually of another plant) often facilitated by animals, wind or water movement

Question 2

Define fertilisation

Answer 2

Fusion of the male gamete in the pollen grain with the female gamete in the ovule to form a zygote

Question 3

Outline seed dispersal

Answer 3

Fertilised ovules form seeds which move away from the parental plant before germination, reducing competition for resources. Seed dispersal mechanisms include fruit, wind, water and animals

Question 4

Define germination

Answer 4

The process by which a seed emerges from a period of dormancy and starts to sprout

Question 5

Outline three factors which a seed requires for germination

Answer 5

• Temperature for the optimal function of enzymes
  * Oxygen for aerobic respiration (seed needs ATP to grow)
  
  • Water to metabolically activate the cells

(TOW)

Question 6

Outline the metabolic processes during germination of a starchy seed

Answer 6

• Water is absorbed, which causes the formation of gibberellin in the embryo’s cotyledon
  
  • Gibberellin stimulates the production of amylase, which catalyses the breakdown of starch to maltose
  • Maltose is transported to the embryo, where it is either hydrolysed to glucose (for energy) or polymerised to cellulose (for cell wall formation)

Question 7

Explain how flowering is controlled in long day and short day plants

Answer 7

• Flowing is affected by light
  
  • Phytochrome exists in two forms, Pr which absorbs red light and Pfr which absorbs far-red light
  • Pfr is active form, Pr is inactive form
  • Daylight converts Pr to Pfr
  • In darkness, Pfr gradually reverts back to Pr
  • Pfr acts as promoter of flowering in long-day plants
  • In long day plants, flowing induced by dark periods shorter than a critical length because enough Pfr remains at the end of short nights to stimulate flowering
  • Pfr acts as inhibitor of flowering in short-day plants
  • Short-day plants induced to flower by dark periods longer than a critical length because at end of long nights enough Pfr has been converted to Pr to allow flowering to occur