Sexual reproduction in plants

Question 1

Where does meiosis takes place?

Answer 1

The anther to produce the male spores or pollen grans which contain haploid gametes

Question 2

What are the female spores?

Answer 2

The ovules which are made in the ovary. The female gametes develop inside the ovule.

Question 3

Adaption to pollen grain

Answer 3

Tough resistant wall to prevent it from drying out during this transfer.

Question 4

What’s fertilisation?

Answer 4

The proves where a male and female gametes fuses with a female gamete to produce a zygote.

Question 5

Adaptions to insect-pollinated flowers and wind -pollinated flowers.

Answer 5

Insect-pollinated- bright colours and scents

wind-pollinated- green no scent, light

Question 6

The structure of an insect-pollinated flower

Answer 6

1) the outermost ring of the structures is the sepals. They are usually green and protect flower bud
2) Inside sepals, there are rings of petals. They are brightly coloured, produce a scent and nectar to attract insects.
3) Inside the petals are the male parts of the plant, the stamens. Each stamen consist of a long filament at the end called anthers which produce pollen grains. As well as supporting the anther the filament contains vascular tissue which transports food materials necessary for the formation of pollen grains. The anther is usually made up of 4 pollen sacs arranged in two pairs side by side. When mature the pollen sacs split to release the pollen.
4) In the centre of the flower are one or more carpels which are the female part of the flower. Each carpel has a closed structure inside which one or more embryos develop. The lower part of the carpel (surround ovule) is called the ovary and bears the apex (stalk like structure) ending in a receptive surface called the stigma.

Question 7

What is pollination?

Answer 7

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

Question 8

Why is pollination necessary?

Answer 8

So that the pollen grains containing the male gametes are brought into contact with the female parts of the female part of the flower so that fertilisation can be achieved.

Question 9

What are the 2 types of pollination?

Answer 9

1) Self-pollination- the pollen from the anthers need only to be transported to the stigma of the same flower or another flower of the same species
2) Cross-pollination- pollen is transferred from the anthers of one flower to the stigma of another on another plant of the same species.

Question 10

What are the differences of in genetic consequences of self and cross pollination?

Answer 10

1) self-pollination leads to self-fertilisation whereas cross-pollination leads to cross-fertilisation
2) Self-fertilised species depend on the random assortment and crossing over during meiosis, and on mutation to bring about variation in the genomes of male and female gametes.
3) Self-fertilised species display less genetic variation then cross-fertilised species that are produced from gametes from two different individuals
4) outbreeding is of greater evolutionary significance because in the struggle for survival some genomes are more successful than others

Question 11

What happens in insect pollination?

Answer 11

Bees feed on the sugary nectar using their long tongues to reach the nectar at the base of the female part of the flower. As the bee enters the flower the anthers rub against the bee leaving the sticky pollen behind. When the bee enters another flower it brushes some of the pollen against the ripe stigma and cross pollination has taken place.

Question 12

What happens in wind-pollination?

Answer 12

(grass) The anthers hang outside the flower so that the wind can blow away the small, smooth and light pollen. The feathery stigmas hang outside the flowers and provide a large surface area for catching pollen grains that are blown into their path.

Question 13

Comparison of insect-pollinated and wind-pollinated

Answer 13

IP have colourful petals, scent and nectar whereas WP are small, green and inconspicuous, no scent, petals usually absent
IP anthers are within flower whereas WP anthers hang outside flower
IP stigma is within the flower whereas WP has a large feathery stigma
IP have small quantities of sticky pollen whereas WP have large quantities of small, smooth, light pollen.

Question 14

What enables a pollen grain to be transferred from one flower to another without drying out?

Answer 14

Pollen grain is surrounded by a tough wall that is resistant to desiccation.

Question 15

How are pollen grains created?

Answer 15

In the anther, diploid cells undergo meiosis to produce haploid pollen grains

Question 16

Inside the pollen grains what does the haploid nucleus do and produce?

Answer 16

Undergoes mitosis to produce two nuclei, a generative nucleus (later produces two male nuclei) and a tube nucleus.

Question 17

How are pollen grains exposed?

Answer 17

When pollen grains mature the outer layers of anther dry out and tensions are set up in lateral grooves. Eventually dehiscence occurs and the edges of pollen sacs curl away.

Question 18

How are the female gametes produced?

Answer 18

The ovules are produced in the ovary with the female gamete or egg nucleus developing inside the ovule. In the ovule a mother cell undergoes meiosis to produce a haploid embryo sac within which eight nuclei form by mitosis. The ovule is contained within the ovule.

Question 19

How does fertilisation occur?

Answer 19

1) When a compatible pollen grain lands on the stigma, the stigma produces a sugary solution in which the pollen grain germinates, producing a pollen tube
2) The pollen tube grows down the style and secretes enzymes as it goes, digesting its way through the tissues of the styles.
3) The pollen tube nucleus is positioned at the tip of the tube with the two male nuclei, derived by mitosis from the generative nucleus in the pollen grains close behind.
4) The pollen grains grow through the gap at the tip between the integuments (micropyle) and passes into the embryo sac
5) The pollen tube nucleus disintegrates
6) The tip of the pollen tube bursts open releasing the male gametes into the embryo sac and the two male nuclei enter.
7) One of the male gametes fuses with the female nucleus to form a zygote
8) the other male gamete fuses with both polar nuclei to form a triploid endosperm nucleus
9) Thus, a double fertilisation occurs.

Question 20

When does the production of a seed or flower take place?

Answer 20

After fertilisation

Question 21

How are fruit and seeds developed?

Answer 21

1) The diploid zygote divides by mitosis to form the embryo consisting of a plumule (developing shoot), a radicle (developing root) and one or two seed leaves or cotyledons.
2) The triploid endosperm nucleus develops into food store to provide reserves for the developing embryo
3) The integuments become the seed coat or testa
4) The ovule becomes the seed
5) The ovary becomes the fruit

Question 22

What’s the structure of a seed?

Answer 22

Broad bean is classed as a dicotyledon as it has two seed leaves or cotyledons whereas the maize is classed as a monocotyledon as it has only one cotyledon. In broad bean food store has been absorbed into cotyledons but in maize (cereal grains) the food store surrounds leaves.

Question 23

What are the requirements of germination?

Answer 23

1) A suitable temperature- optimum temp is the same as optimum for enzymes- varies from species
2) Water- Needed for mobilisation of enzymes, vacuolation of cells and for transport
3) Oxygen- respiration releases energy, in the form of ATP available for metabolism and growth.

Question 24

Mobilisation of food reserves during germination

Answer 24

1) Food reserves in seeds are insoluble in water and can’t be transported in seedling
2) Reserves must be broken down into relatively simple soluble substances which dissolve in water and are transported to the growing apices of the plumule and radicle.
3) The seed coat ruptures as the radicle pushes its way through first. The radicle will grow downwards and the plumule upwards
4) During germination the cotyledons of broad bean remain underground.

Question 25

How is the tip protected from damage by soil abrasion?

Answer 25

The plumule is bent over in the shape of a hook

Question 26

What do the enzymes do in germination?

Answer 26

The enzymes (amylase) hydrolyses starch into maltose, protease convert proteins to amino acids, The soluble products are transported into growing points

Question 27

What causes the tissues to swell and mobilisation of enzymes?

Answer 27

Water taken up in seed rapidly in initial stages