Chapter 8 - Sexual Reproduction in Plants.

Question 1

What is the general name for the female parts of the flower and what does it consist of?

Answer 1

Carpel. Consists of…

• Stigma.
• Style.
• Ovary.
• Ovule.
• Embryo sac.

Question 2

What is the general name for the male part of the flower and what does it consist of?

Answer 2

Stamen. Consists of…

• Anther.
• Filament.

Question 3

What are the features of insect-pollinated flowers?

Answer 3

• Colourful petals, sometimes with nectar guides
• Scent and nectar (mainly sucrose).
• Anthers within the flower.
• Stigma within the flower.
• Small quantities of sticky, sculptured pollen.
• Produces larger pollen grains.

Question 4

What are the features of wind-pollinated flowers?

Answer 4

• Petals are usually absent or small, green and inconspicuous.
• No scent or nectar.
• Anthers hanging outside the flower.
• Large, feathery stigmas hang outside flower (provide a large surface area for catching pollen grains).
• Large quantities of smooth pollen.
• Produces smaller pollen grains.

Question 5

In the pollen sacs, what goes under meiosis and what do they form?

Answer 5

Diploid pollen mother cells undergo meiosis, each forming a tetrad containing 4 haploid cells which become 4 pollen grains.

Question 6

What provides nutrients and regulatory molecules to the developing pollen grains?

Answer 6

The tapetum.

Question 7

What happens to the haploid nucleus inside the pollen grain?

Answer 7

The haploid nucleus undergoes mitosis to produce 2 nuclei, a generative nucleus and a tube nucleus.

Question 8

What are the 2 nuclei formed in the pollen grain and what are their roles?

Answer 8

• Generative nucleus, produces 2 male nuclei by mitosis.

- Tube nucleus, creates a tube for the nuclei to pass down in the stigma and style to the ovary.

Question 9

What is dehiscence?

Answer 9

The opening of the anther, releasing mature pollen grains.

Question 10

How does the female gamete develop?

Answer 10

• The ovary will contain one or more ovules.
• In each ovule, a megaspore mother cell, surrounded by cells of the nucellus, undergoes meiosis making 4 haploid cells.
• 3 disintegrate.
• The remaining cell undergoes 3 rounds of mitosis producing 8 haploid nuclei.
• 2 of the haploid nuclei fuse to make a diploid nucleus called the polar nucleus.

Question 11

What does the embryo sac in a mature ovule contain?

Answer 11

• 3 antipodals (haploid).
• 1 polar nucleus (diploid).
• 1 oosphere (haploid and the female gamete).
• 2 synergids (haploid).

Question 12

What is the structure of an ovule?

Answer 12

• Nuclei in an embryo sac.
• Embryo sac surrounded by nucellus which provide nutrients.
• Integuments surrounding the nucellus.
• A gap in the integuments called the micropyle.

Question 13

What is pollination?

Answer 13

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

Question 14

What is protandry?

Answer 14

The stamens of a flower ripen before the stigmas to prevent self pollination.

Question 15

What are the 2 types of pollination?

Answer 15

• Self-pollination, the pollen from the anthers of a flower is transferred to the mature stigma of the same flower or another flower on the same plant.
• Cross-pollination, most Angiosperms transfer pollen from the anthers of one flower to the mature stigma of another flower on another plant of the same species.

Question 16

What are the advantages and disadvantages of self-pollination?

Answer 16

• Self fertilised species show less genetic variation.
• There is a greater chance of two potentially harmful recessive alleles being brought together.
• It can preserve those successful genomes that are suited to a stable environment.

Question 17

What are the advantages of cross-breeding?

Answer 17

• It combines gametes from 2 individuals so it creates more genetic variation.
• It reduces the chance of producing harmful allele combination.
• Some genomes are more successful than others so it allows a species to survive in a changing environment.

Question 18

How do flowering plants ensure that cross-pollination takes place?

Answer 18

• Protandry, the stamen and stigma ripen at different times.
• The anther is below the stigma so pollen can’t fall on to it.
• Genetic incompatibility.
• Separate male and female flowers on the same plant.
• Separate male and female plants.

Question 19

How does double fertilisation happen?

Answer 19

• Pollen grain lands on the stigma and germinates and produces a pollen tube.
• Pollen tube grows out the pit in cell wall and down the style.
• Pollen tube grown through the gap in the integuments, the micropyle and passes into the embryo sac.
• Pollen tube disintegrates.
• The tip of the pollen tube opens and releases the two male gametes that have undergone mitosis.
• One of the male gametes fuses with the female gamete to form a diploid zygote.
• The other male gamete fuses with the diploid polar nucleus to form a triploid nucleus, this generates the endosperm tissue which provides nutrients.

Question 20

How does the fruit and seed develop?

Answer 20

• Diploid zygote divides by mitosis becoming an embryo which consists of a plumule (shoot) and a radicle (root) and cotyledons.
• Endosperm develops into a food store.
• The outer integument becomes the testa.
• The ovule becomes the seed.
• The ovary becomes the fruit.

Question 21

What is a dicotyledon?

Answer 21

It means its seeds have 2 seed laves/cotlyedons with the embryo lying between them.

Question 22

What does it mean if a seed is dormant?

Answer 22

It describes a seed when its active growth is suspended. Germination will only occur when specific conditions are met.

Question 23

What are the different methods of dispersing seeds?

Answer 23

• Wind.
• Transport through animals.
• Rolling.
• Bursting.
• Water e.g. coconuts.
• Carrying, on animals.

Question 24

How have seeds evolved so that that Angiosperms are successful?

Answer 24

• Dormant seeds have a low metabolic rate so they survive very cold weather.
• Testa is chemically resistant.
• Water content is majorly reduced to survive dry conditions.
• Testa can physically protect the embryo.
• Endosperm/cotyledons provide a supply of nutrients.
• Seeds can be dispersed long distances.
• Dispersal allows the colonisation of new habitats.

Question 25

What is germination?

Answer 25

The biochemical and physiological processes through which a seed becomes a photosynthesising plant.

Question 26

What are the sequences of germination?

Answer 26

• Seed imbibes water.
• Testa splits.
• Radicle emerges.
• Plumule emerges.
• Elongation pushes shoot above ground.

Question 27

What are the three main requirements for successful germination?

Answer 27

• A suitable temperature.
• Water, to mobilise enzymes.
• Oxygen.

Question 28

What does it mean if the radicle is positively geotropic and negatively phototropic?

Answer 28

It means it grows downward.

Question 29

What effect does gibberellins have on barley?

Answer 29

• The embryo secretes giberellic acid which diffuses to the alurone layer.
• This switches on genes in the cells in the aleurone layer producing enzymes including protease and amylase.
• Proteases hydrolyse protein to amino acid, to make amylase.
• Amylase diffuses into the endosperm and hydrolyses the starch.
• The maltose and glucose diffuse back through the endosperm to the plumule and radicle of the embryo.
• These are respired for energy which brings the seed out of dormancy.