4.1 sexual reproduction in plants

Question 1

What are 5 features of insect pollinated flowers?

Answer 1

Receptacle, calyx, corolla, stamen, carpel, nectaries.

Question 2

What’s the function of the receptacle?

Answer 2

The top of the flower stalk from which the different parts of the flower develop.

Question 3

What’s the function of the calyx?

Answer 3

The first set of modified leaves called the sepals - these protect the flower while it’s still forming and before the flower bud opens.

Question 4

What’s the function of the corolla?

Answer 4

This is the layer of modified leaves called petals - these are often large, coloured and patterned to attract insects; some of the colours, e.g. UV are not visible to humans - only to insects.

Question 5

What’s the function of the stamen?

Answer 5

This is made of the filament and anther. This is the male reproductive organ of a flower - the site of meiosis and mitosis to produce the male gametes.

Question 6

What’s the carpel?

Answer 6

Composed of the ovary, style and stigma, this is the female reproductive organ of a flower. The ovary is the site of meiosis to produce the female gametes contained within the ovules.

Question 7

What’s the function of the nectaries?

Answer 7

These secrete a sweet substance - nectar - that attracts many insects and other animals that carry pollen from one flower to another.

Question 8

What are other features that distinguish an insect pollinated flower?

Answer 8

• A smell may be produced to attract insects,
• anthers and stigma are generally enclosed within the petals,
• pollen is often large and sticky/spiky, - only a small quantity of pollen is produced.

Question 9

What are features of a wind pollinated flower?

Answer 9

-Petals are absent,
- no scent is produced,
- nectaries are absent,
- anthers and stigma hang outside the flower,
- anther is loosely attached,
- stigma is usually feathery,
- pollen is small and light, and very large quantities of pollen are produced.

Question 10

Define self pollination.

Answer 10

Self-pollination occurs when a plant’s own pollen lands on the stigma of the same flower.

Question 11

What are advantages of self pollination?

Answer 11

1. Rapid pollination with a high chance of success.
2. Reduced genetic variation.
3. Good genomes are preserved.

Question 12

What are disadvantages of self pollination?

Answer 12

Reduced genetic variation makes plants equally susceptible to diseases and environmental changes.

Question 13

Define cross pollination.

Answer 13

Cross-pollination occurs when a stigma receives pollen from a different plant of the same species.

Question 14

What’s the main advantage of cross pollination?

Answer 14

Increased genetic variation, enhancing the chance of species survival.

Question 15

What are the disadvantages of cross pollination?

Answer 15

Good combinations of alleles can be lost due to crossing over and random fertilisation.

Question 16

What are some adaptations of plants to ensure cross pollination occurs?

Answer 16

-Chemical self-incompatibility,
-flower structure,
-development of anther and stigma, separate male and female flowers.

Question 17

How does chemical incompatibility increase cross pollination?

Answer 17

Stigma chemicals inhibit pollen from the same plant, promoting cross-pollination.

Question 18

How does flower structure promote cross pollination?

Answer 18

Irregular structures force insects to enter and leave the flower in a way that reduces self-pollination.

Question 19

How does the development of anthers/stigmas promote cross pollination?

Answer 19

Either the anthers mature before the stigmas or vice versa, preventing simultaneous presence.

Question 20

What do pollen grains contain?

Answer 20

Pollen grains contain the male gametes of flowering plants.

Question 21

What is the tapetum?

Answer 21

A specialised layer of nutritive cells found within the anther, important for the nutrition and development of pollen grains.

Question 22

Describe the development of pollen.

Answer 22

Pollen mother cells develop
by mitosis.
- Meiosis occurs to produce
a tetrad of 4 haploid cells.
-In each haploid, pollen
grain mitotic division of the
nucleus forms a generative
nucleus (that mitotically
divides to produce 2 male
nuclei) and a tube nucleus.

Question 23

Describe the development of an ovule.

Answer 23

1. Diploid Megaspore mother cell undergoes meiosis to form 4 haploid megaspores
2. Three megaspores disintegrate.
3. The 1 functional megaspore develops into the embryo sac.
4. It undergoes 3 mitotic divisions producing eight haploid nuclei.
5. 2 nuclei move to centre of cell (polar nuclei), 3 antipodal cells and 2 synergids

Question 24

What is double fertilisation?

Answer 24

Fertilisation of female gamete to form a diploid zygote and fertilisation of polar nuclei to form triploid endosperm nucleus.

Question 25

What occurs during double fertilisation?

Answer 25

1. Pollen grain lands on stigma. 2. Pollen tube grows down the style. 3. Generative nucleus divides to form two male gametes. 4. Pollen tube enters through micropyle. 5. Fertilization occurs.

Question 26

What forms when the zygote divides by mitosis?

Answer 26

Forms the embryo which contains the embryo root (radicle) and embryo shoot (plumule).

Question 27

What does the primary endosperm nucleus form?

Answer 27

Divides by mitosis to form food storage tissue.

Question 28

What do the integuments form?

Answer 28

Fuse to form testa and seed coat.

Question 29

What does the ovary form?

Answer 29

Forms fruit wall and encloses the seeds.

Question 30

What do ovules form?

Answer 30

Seeds.

Question 31

Describe the role of organelles in the passage of the pollen tubes through the style.

Answer 31

1. Secretory vesicle releases enzymes. 2. Enzymes digest a path through the style. 3. Mitochondria provide ATP. 4. Rough ER synthesizes enzymes. 5. Golgi bodies process and package proteins.

Question 32

What is a dicotyledonous plant?

Answer 32

A plant with 2 seed leaves or cotyledons which act as food stores.

Question 33

What is a monocotyledon?

Answer 33

A plant with one seed leaf or cotyledon, where the main food store is the endosperm.

Question 34

What are the requirements of germination?

Answer 34

Seeds absorb water and oxygen, require a warm temperature, and some need light to trigger germination.

Question 35

What's an endospermic seed?

Answer 35

Seeds which use endosperm as their food store, e.g., maize.

Question 36

Describe the process of germination in endospermic seeds.

Answer 36

1. Water is absorbed. 2. Gibberellins are mobilised. 3. DNA is transcribed into mRNA. 4. Hydrolytic enzymes are produced. 5. Amylase hydrolyses starch to glucose.

Question 37

What's a non-endospermic seed?

Answer 37

Seeds which don't use endosperm as their food store, e.g., broad bean.

Question 38

Describe the process of germination in non-endospermic seeds.

Answer 38

1. Water is imbibed. 2. Cotyledon swells and testa splits. 3. Food reserves from cotyledons are mobilised.