Sexual Reproduction in Plants

Question 1

What are the male sex organs called

Answer 1

Stamen consisting of filament and anther

Question 2

What are the female sex organs called

Answer 2

Carpel consisting of ovule, ovary, style and stigma

Question 3

How are wind pollinated plants adapted

Answer 3

Feathery stigmas which hang out of flower
No petals
Vast numbers of smooth, lightweight pollen grains

Question 4

How are insect pollinated plants adapted

Answer 4

Colourful petals with guidelines
Produces nectar
Sticky stigma
Large pollen grains with spiky surface

Question 5

Describe the formation of pollen

Answer 5

A mother cell undergoes meiosis to form a tetrad which then undergoes mitosis to create a pollen grain with two haploid nuclei. This then matures to form a generative nucleus and a tube nucleus

Question 6

Describe the development of an ovule

Answer 6

The megaspore mother cell undergoes meiosis and forms 4 megaspore haploid cells. Three of these degenerate and one matures into the embryo sac. 3 mitotic divisions occur and eight haploid nuclei form.
Three form antipodal cells that have no further use, two form synergids which degenerate later, 1 forms the egg cell, and the other two fuse and form a diploid polar nucleus.

Question 7

Describe cross-pollination

Answer 7

Transfer of pollen from the flower of one plant onto the flower of a different plant. Allows for genetic variation

Question 8

Describe self pollination

Answer 8

Transfer of pollen from the flower of a plant onto the same flower or another flower of the same plant. Decreases variation, only allows for crossing over.

Question 9

How do plants try and prevent self pollination

Answer 9

Dichogamy - anthers and stigmas mature at different times
Have separate male and female flowers
Have separate male and female plants

Question 10

Describe the process of double fertilisation

Answer 10

The pollen lands on the stigma, and the tube nucleus begins to burrow down into the style by digesting the tissue. The generative nucleus splits by mitosis forming two haploid nuclei. Once the pollen tube has entered the embryo sac it degenerates. One of the generative nuclei fuses with the egg cell, the other with the polar nucleus to form the endosperm which will nourish the embryo.

Question 11

What happens to the endosperm in monocots and dicots

Answer 11

Monocots - the endosperm remains and only one cotyledon forms
Dicots - the endosperm is absorbed and stored in two cotyledons

Question 12

What becomes of the following after fertilisation
Ovule
Integuments
Micropyle
Ovary wall
Ovary

Answer 12

Seed
Seed coat
Pore
Fruit coat (skin)
Fruit

Question 13

Describe dormancy in seeds

Answer 13

Seeds can remain dormant for many years and will only germinate if there is water, oxygen, and a suitable temperature

Question 14

Describe the germination process in a dicotyledon

Answer 14

Water is imbibed through the micropyle.
The cotyledons swell and the seed coat splits allowing entry of more water and oxygen for aerobic
respiration.
Starch and protein reserves in the cotyledons are hydrolysed.
Products of hydrolysis are used as:
• a source of energy for respiration,
• growth of the plumule and radicle.

Question 15

Describe the germination process in a monocotyledon

Answer 15

Following the imbibing of water, gibberellin is released by the embryo. The gibberellin diffuses to the aleurone layer which contains
protein. Gibberellin induces the production of hydrolytic enzymes, e.g. amylase.
The hydrolytic enzymes diffuse into the inner layer of the endosperm and catalyse the
breakdown of stored nutrients, e.g. starch.
Glucose and other breakdown products of the stored nutrients diffuse into the embryo where
they are used for aerobic respiration and growth.