Topic 9.3 Reproduction in Angiospermophytes

Question 1

9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower.

Answer 1

• Stamen (male reproductive part)
  
  • filament (stem part under anther)
  • anther (tip)
• Carpel/Pistil (female reproductive part)
  
  • stigma (tip)
  • style (connects stigma to ovary)
  • ovary (base)
• Ovule (inside ovary)
• Petal
• Receptacle (base of flower)

Question 2

9.3.2 Distinguish between pollination, fertilization and seed dispersal.

Answer 2

Pollination

Transferring of pollen (containing male sex cells) onto female stigma by means of vector transport (including wind, insect, bird, water & other animals).

• Flowers of plants adapt to attract insect/animal pollinators (e.g. by colour, scent).
• 2 types: self-pollination & cross-pollination

Fertilization

Occurs after pollination, when male gamete (in pollen grain) unites with female gamete (in ovules) to form a diploid zygote.

Seed Dispersal

Fertilized ovules move far from parent plant, reducing competition for limited resources. Fruits (mature ovaries containing seeds) adopt a number of adaptations for successful seed dispersal by wind, water & animals.

Question 3

9.3.3 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed.

Answer 3

Runner bean

• scar where seed was attached to ovary
• seed coat (testa)
• plumule (embryo shoot)
• radicle (embryo root)
• cotyledon (seed leaves)

Question 4

9.3.4 Explain the conditions needed for germination of a typical seed.

Answer 4

• Water to rehydrate dried seed tissues
• Oxygen for aerobic cellular respiration & ATP
• Temperature at appropriate level for successful enzyme action
  
  • without adequate conditions, seed may stay dormant

Question 5

9.3.5 Outline the metabolic processes during germination of a starchy seed.

Answer 5

1. Uptake of water causes gibberellin to be released
2. Gibberellin, the plant growth hormone, triggers production of amylase
3. Amylase causes hydrolysis of starch into maltose, which is present in the endosperm or food reserve of seed
4. Maltose is further hydrolysed into glucose (used in cell respiration) or converted into cellulose (necessary for production of cell walls in new cells) by condensation reactions

Question 6

9.3.6 Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.

Answer 6

Phytochrome: pigment that controls flowering in long-day & short-day plants

Long-day plants: bloom when days = longest, nights = shortest

Short-day plants: bloom when days = shortest, nights = longest

• Phytochrome exists as P_r (inactive) & P_fr (active)
• Conversion between the two in darkness allows plant to time the dark period (the controlling factor for flowering)
  
  • when red light (wavelength 660 nm) is present, P_r converts to P_fr
  • when far-red light (wavelength 730 nm) is present, P_fr converts to P_r
• Short dark period = more P_fr; long dark period = less P_fr
• P_fr promotes flowering in long-day plants
  
  • flowering occurs when dark period is less than critical night length & P_fr levels are high
• P_fr form inhibits flowering in short-day plants
  
  • ​flowering occurs when dark period is more than critical night length & P_fr levels are low