reproduction in plants

Question 1

Sepals (func.)

Answer 1

enclose and protects the flower bud

Question 2

Petals (func.)

Answer 2

are often colourful and fragrant, serves to attract insects and other pollinators to the flower

Question 3

Stamen (func.)

Answer 3

consists of a stalk (filament) tipped by an anther

Question 4

Anther (func.)

Answer 4

sacs where meiosis occurs and pollen grains develop; pollen grains house the cells that develop into sperm

Question 5

Carpel (func.)

Answer 5

consists of a long slender neck (style) with a sticky stigma at its tip; at the base of the carpel is the ovary

Question 6

Ovary (func.)

Answer 6

contains reproductive structures called ovules; each containing one developing egg and the cells that support it

Question 7

Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation

Answer 7

1. Pollen grains on the stigma germinate in response to the sugary fluid produced by the mature stigma.
2. A pollen tube grows out from the pollen grain and the male gamete forms in the tube.
3. As the pollen tube grows, it secretes enzymes to digest the tissue of the stigma and style. The pollen tube grows down the style.
4. The pollen tube enters the ovule through an opening in the ovule wall called the micropyle.
5. Within the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the two male gametes.
6. The nucleus of one of the male gamete fuses with the nucleus of the ovum to form the zygote. This is fertilisation.

Question 8

Fertilisation

Answer 8

Requires the production of gametes
Pollen grain: essential for pollination and produces sperm (male gamete)
Female gamete is the ovum (inside the ovule)

Question 9

Pollination (def.)

Answer 9

transfer of pollen grains from an anther to a stigma

Question 10

Self-pollination (def.)

Answer 10

transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant

Question 11

Cross-pollination (def.)

Answer 11

transfer of pollen grains from one plant to the stigma of another plant of the same species

Question 12

Insect-pollinated flower (features)

Answer 12

• Petals are large brightly coloured
• Nectar is present
• Flowers are fragrant or sweet-smelling
• Stigmas are small, compact and do not protrude out of the flower
• Stamens are small, compact and do not protrude out of the flower
• Pollen is fairly abundant; pollen grains are usually larger with rough surfaces so that they can cling onto the body of insect
• Nectar guide may be present on the petals to guide insects towards the nectar

Question 13

Wind-pollinated flower (features)

Answer 13

• Petals are small or without petals; dull-coloured petals
• Nectar is absent
• Flowers are odourless/scentless
• Stigmas are large, feathery and usually protrude out of the flower to provide large surface area to trap pollen
• Stamens have long pendulous filaments and protruding anthers; pollen grains are easily shaken out from the anthers
• Pollen is more abundant; pollen grains have smooth surfaces and are tiny and light so that they are easily blown about by wind
• Nectar guide is absent

Question 14

How flowers ensure cross-pollination?

Answer 14

Ripen male and female structures at different times, anthers release pollen first then stigma opens
Plants can be unisex (containing only male of female reproductive structures) or dioecious (different male/female flowers on the same plant)
The male part can be covering the female part and will only allow pollination after its own pollen sacs are removed by pollinators
Self-incompatibility → stigma is able to recognise its own pollen grains and therefore does not allow germination