Chapter 6: Sexual Reproduction in plants

Question 1

plants that are bisexual

Answer 1

Hermaphrodites

• lilies
• have both male and female reproductive organs within the same flower

Question 2

how to prevent self-pollination

Answer 2

• stigma higher than stamen

- stamen and stigma mature at different time

Question 3

Stamen

Answer 3

Male reproductive organ

• anther
• filament

Question 4

Carpel

Answer 4

Female reproductive organ

• stigma
• style
• ovary
• ovule

Question 5

formation of pollen grain in anther

Answer 5

anther - lobe - pollen sac - microspore mother cells - microspore cells - pollen grains - generative nucleus and tube nucleus

1. anther develop
2. Group of tissue grow inside each lobe to form 4 pollen sacs
3. Each pollen sacs contain hundreds of microspore mother cells (2n)
4. Microspore mother cells divide meiotically into 4 microspore cells (n) - tetrad
5. Each cell develops into a pollen grain
6. nucleus in pollen grain divides mitotically into 2 nuclei, generative and tube nucleus
7. when pollen grains mature, wall of pollen sac breaks
8. pollen grains are released

Question 6

pollination and double fertilisation

Answer 6

Pollination:

1. wall of anther dry, shrink and split.
2. pollen grain is released
3. pollination agent transfer pollen grain to stigma
4. pollen grain on stigma germinate to form pollen tube
5. end of the pollen tube secrete enzyme to digest style tissue and grow towards ovule
6. generative nucleus move along and divide mitotically into 2 male gametes (m)

Double Fertilisation:

1. Pollen tube penetrate the ovule through micropyle
2. tube nucleus degenarate
3. Both haploid male gametes enter the embryo sac
4. one male gamete fertilise with egg cell to produce zygote (2n)
5. one male gamete fuses with 2 polar nuclei to form triploid endosperm nucleus

Question 7

importance of double fertilisation

Answer 7

Zygote:

• genetic information is passed down
• restore diploid condition

Endosperm tissue

• used in development of embryo
• (eudicot) fully utilised for embryo development before seed mature
• (monocot) part is used for embryo development, part is stored in cotyledon for seed germination
• if conditions are not favourable, embryo is able to survive in seed for a long time

Question 8

formation of embryo sac in ovule

Answer 8

megaspore mother cells - megaspore cells - 3 antipodal, 2 polar nuclei, 2 synergid cells and 1 egg cell

1. one of the nucellus is megaspore mother cell
2. megaspore mother cell (2n) divides meiotically to produce 4 megaspore cell (n)
3. one megaspore cell develops and 3 degenerate
4. developed nucleus divide mitotically 3 times to produce 8 nuclei
   - 3 antipodal cells at the top
   - 2 polar nuclei at the centre
   - 1 egg cell at the bottom
   - 2 synergid cell beside egg cell

Question 9

development of seed

Answer 9

• triploid endosperm nucleus divide mitotically to form endosperm tissue
• to store food and provide nutrients to the embryo
• zygote divide mitotically into two cells, basal (larger) and terminal (smaller) cell
• basal cell develop into suspensor to anchor the embryo to wall of embryo sac
• terminal cell develop into embryo (plumule, cotyledon and radicle)

Question 10

development of fruits

Answer 10

1. ovule: seed
2. integument layer: 2 layer seed coat
3. ovary: fruit
4. ovary wall: pericarp (exo, meso, endo)
5. stigma and style: degenerate and leave a scar

Question 11

Adaptation of seeds for survival

Answer 11

• contain embryo germinate to form seedling
• endosperm tissue // cotyledon provide nutrient to supply energy for germination
• enclosed by testa (strong and water impermeable) to prevent spoiling
• can form a dormant structure to store for a long time
• special features (light, strong, spongy tissue) to be dispersd to another place to avoid competition