Biology Plant reproduction

Question 1

What is the tapetum

Answer 1

Inner wall of cells that provide nutrients to the developing pollen grains

Question 2

Function of the area of dehiscence

Answer 2

When the pollen grains are mature, the outer layers of the anther dry out. Tension in the lateral grooves causes dehiscence - anther walls pull apart releasing the pollen grains

Question 3

Formation of pollen

Answer 3

2n microspore mother cell (meiosis) -> n tetrad (4 immature pollen cells) (mitosis) -> n pollen grain with 2 nuclei (cell wall thickens) -> mature pollen grain

Question 4

Components of a mature pollen grain

Answer 4

Generative nucleus, tube nucleus, cell wall (intine and exine)

Question 5

Components of an ovule

Answer 5

The ovule contains a mass of cells called the nucellus surrounded by two protective integuments. The ovule is carried on a short stalk called the funicle.

Question 6

Formation of an ovule

Answer 6

2n megaspore mother cell (meiosis) -> n 4 megaspores -> 3 degenerate and one divides by mitosis to form embryo sac (3 mitosis) -> 8 nuclei formed

Question 7

What happens to the 8 haploid nuclei formed in an ovule

Answer 7

2 move to the centre to form the polar nuclei, 3 form antipodal cells, 1 nearest micropyle develops into the female gamete, 2 form synergids that degenerate after fertilisation

Question 8

Define pollination

Answer 8

The transfer of pollen grains from the anther to the mature stigma of the same species.

Question 9

What is genetic variation dependent on in self pollination

Answer 9

• crossing over during prophase I of meiosis, • independent assortment during metaphase I of meiosis, • mutation.

Question 10

What is genetic variation dependent on in cross pollination

Answer 10

Same factors as self-pollination plus the combining genotypes of gametes from two different individuals.

Question 11

Advantage and 2 disadvantages of self pollination

Answer 11

Successful genomes are preserved, Greater chance of two potentially harmful recessive alleles combining, Population is less adaptable to changes in the environment

Question 12

Name 2 ways plants have adapted to promote cross-pollination

Answer 12

Chemical self-incompatibility - gametes from the same parent plant are unable to fuse and form a zygote, Dichogamy - anthers and stigmas mature at different times

Question 13

Define double fertilisation

Answer 13

Double fertilisation involves two male gametes in two separate fertilisation events. • Fertilisation of female gamete to form a diploid zygote, • Fertilisation of the polar nuclei to form a triploid endosperm nucleus.

Question 14

Describe the role of the pollen tube in double fertilisation

Answer 14

Pollen grain lands on stigma and absorbs water. If pollen grain and stigma are compatible, the pollen tube will germinate and grows down through the style (controled by the tube nucleus - hydrolase enzymes to digest through the style). Pollen tube grows through a gap in the integuments (the micropyle) and passes into the embryo sac.

Question 15

Why is the growth of the pollen tube described as a positive
chemotrophic response

Answer 15

The pollen tube grows towards chemicals secreted by the embryo sac.

Question 16

What happens to the generative nucleus during double fertilisation

Answer 16

Divides by mitosis to form 2 male nuclei (n); the gametes.

Question 17

What happens to the zygote following fertilisation

Answer 17

Divides by mitosis to form the diploid embryo which then differentiates into a young shoot (the plumule), young root (the radicle) and one or two seed leaves (the cotyledons).

Question 18

What happens to the triploid endosperm following fertilisation

Answer 18

Divides by mitosis to form endosperm tissue which forms the food source for the growing embryo.

Question 19

What does the ovule become after fertilisation

Answer 19

The seed

Question 20

What do the integuments become after fertilisation

Answer 20

Testa (seed coat)

Question 21

What does the content of the ovary become after fertilisation

Answer 21

Fruit

Question 22

What does the attachment point of funicle to ovule become after fertilisation

Answer 22

Hilum

Question 23

What conditions are required for seeds to come out of dormancy and begin germination

Answer 23

• water to mobilise enzymes; for transport; and to vacuolate cells to make them turgid, • oxygen for aerobic respiration, • suitable temperature for enzymes to operate

Question 24

Describe the 4 steps of germination in a non-endospermic seed

Answer 24

1. Water is absorbed through the micropyle. 2. The cotyledons swell and the testa splits allowing entry of more water and oxygen for aerobic respiration. 3. Starch and protein reserves in the cotyledons are hydrolysed. 4. Products of hydrolysis are used for respiration and growth of the plumule and radicle.

Question 25

Describe the 5 steps of germination in an endospermic seed

Answer 25

1. Following the absorption of water, gibberellin is released by the embryo. 2. The gibberellin diffuses to the aleurone layer which contains protein. 3. Gibberellin induces the production of hydrolytic enzymes, e.g. amylase. 4. The hydrolytic enzymes diffuse into the inner layer of the endosperm and catalyse the breakdown of stored nutrients, e.g. starch. 5. Glucose and other products diffuse into the embryo where they are used for aerobic respiration and growth.