Chapter 8 Sexual Reproduction In Plants

Question 1

What are flowering plants called?

Answer 1

Angiosperms

Question 2

What are the male gametes in plants called?

Answer 2

Pollen grains

Question 3

What are the female gametes in plants called?

Answer 3

Embryo sacs

Question 4

Where are pollen grains produced?

Answer 4

Anthers

Question 5

Where are embryo sacs produced?

Answer 5

Ovule

Question 6

What is the structure and functions of the male reproductive system in angiosperms?

Answer 6

The stamen consists of:
Anthers (where meiosis occurs producing pollen)
Filaments (vascular tissue transporting sucrose/minerals/water to pollen grains)

Question 7

What is the structure and functions of the female reproductive system in angiosperms?

Answer 7

Gynaecium consists of the carpel. The carpel has 3 parts, the stigma (receives pollen from anther), style (provides pathway for pollen to ovary), and ovary (where meiosis occurs to produce haploid ovules)

Question 8

Define pollination

Answer 8

The transfer of pollen from a mature anther to a receptive stigma of a flower of the same species.

Question 9

Define self-pollination

Answer 9

Where the pollen comes from anthers in the same flower or flower of the Same plant.

Question 10

Define cross pollination

Answer 10

Where the pollen comes from a different plant of the same species.

Question 11

What 2 ways can pollination occur?

Answer 11

By wind or insects(animals)

Question 12

What are the advantages of self-pollination?

Answer 12

Preserves successful genomes that are suited to a relatively stable environment.

Question 13

What are the disadvantages of self-pollination?

Answer 13

Less genetic variation as it only relies on independent assortment and crossing over during meiosis
Greater chance of potentially harmful recessive alleles being brought together at fertilisation

Question 14

What are the advantages of cross-pollination?

Answer 14

Greater genetic variation

Reduces the chances of harmful allele combinations

Question 15

What methods are used to ensure cross-pollination?

Answer 15

Dichogamy - stamen and style ripening at different times
Genetic incompatibility - pollen cannot fertilise the stigma of the flower which it was produced
Separate male and female plants

Question 16

What are the characteristics of insect pollinated flowers?

Answer 16

Colourful petals, scents, nectar, anthers and stigma within flower, sticky pollen, not much pollen required(less wastage)

Question 17

What are the characteristics of wind pollinated flowers?

Answer 17

Absent or small green petals, no scent, no nectar, anthers and stigma hang outside of flower, smooth pollen

Question 18

How does the male gamete develop?

Answer 18

In the pollen sac of the anther, the diploid pollen mother cell undergoes meiosis. Each forms a tetrad, containing 4 haploid cells, which become 4 pollen grains. Inside the pollen grains the haploid nucleus undergoes mitosis to produce 2 nuclei, a generative nucleus which produces 2 nuclei and tube nucleus. Eventually the outer layers of the anthers dry out and the tension pulls on the lateral grooves pulling the walls of the anther apart. This allows the pollen grain to be released.

Question 19

What is the tapetum?

Answer 19

A layer of cells surrounding the pollen grains in the anthers. It provides nutrients to the developing pollen grains as well as protect them from mutation as the cells are resistant to chemicals and ultraviolet light.

Question 20

How does the female gamete develop?

Answer 20

In the ovules, a megaspore mother cell, surrounded by cells of the nucellus, undergoes meiosis, making 4 haploid cells. 3 die and the remaining cell undergoes mitosis 3 times. This produces 8 haploid nuclei. 2 of theses nuclei fuse to form a diploid polar nucleus, 3 become antipodals, 2 become synergids and 1 becomes an oosphere.

Question 21

What is the nucellus?

Answer 21

Layer of cells surrounding embryo sac. The nucellus is surrounded by integuments with gaps called micropyles. The micropyles provide a pathway for the pollen tube to enter the embryo sac.

Question 22

What are the functions of synergids and antipodals?

Answer 22

Synergids produce enzymes which enable passage of the pollen tube end into the embryo sac.
Antipodals provide nutrients.

Question 23

Outline the process of double fertilisation

Answer 23

When a pollen grain lands on the stigma, a pollen tube grows from the tube nucleus up a gradient of chemoattractants. This is a chemical response from GABA made in the ovule. The pollen tube passes through the micropyles and passes into the embryo sac. The 2 male nuclei produced by the generative nucleus are released. One fuses with the oospehere forming a zygote. The other fuses with the polar nucleus forming a Triploid endosperm which provides nutrients to the growing embryo.

Question 24

What is a fruit?

Answer 24

A structure developing from the ovary wall, containing one or more seeds.

Question 25

What is a seed?

Answer 25

Structure developed from a fertilised ovule, containing an embryo and food store enclosed within a testa

Question 26

Outline how the fruit and seeds develop

Answer 26

The zygote divides by mitosis becoming an embryo consisting of a plumule (shoot), a radicle (root) and one or two cotyledons (seed leaves). The Tripolid endosperm develops into a food store for the embryo. The outer integument dries out and hardens becoming the testa (seed coat). The ovule comprising these components becomes the seed. The ovary becomes the fruit.

Question 27

What are the characteristics of monocotyledons

Answer 27

One seed leaf
Leaf veins are parallel
Sepals, petals and stamens in multiples of 3
Vascular bundles scattered in stems and roots
Example - maize

Question 28

What are the characteristics of dicotyledons

Answer 28

Two seed leaves 
Leaf veins form a network
Sepals, petals and stamens in multiples of 4 or 5
Vascular bundles in a ring in stems
Vascular bundles in the centre of roots

Question 29

Define dormant

Answer 29

Describes a seed when it’s active growth is suspended. Germination will only occur when specific conditions are met

Question 30

How do seeds disperse by wind?

Answer 30

Ash fruits have sails and dandelion fruits have stiff hairs which allow the fruit to be carried away when blown by wind

Question 31

How do seeds disperse by transport?

Answer 31

Animals especially birds eat seeds that pass through their digestive system and are dispersed in the faeces. In a process called scarification the digestive system weakens the testa by acid and enzymes which in some species can cause germination

Question 32

How do seeds disperse by rolling?

Answer 32

When the fruit of the horse chestnut tree breaks open, the Conker falls to the ground and rolls away from the parent tree.

Question 33

How do seeds disperse by bursting?

Answer 33

When legume pods dry, they split and the seeds scatter. The pods rotate as they burst open, sending seeds in many different directions.

Question 34

How do seeds disperse by water?

Answer 34

Air cavities in seeds make them buoyant and are carried away when they fall in water from parent plants. For example, coconut palms grow by water and the coconuts (fruit/seeds) usually fall in and are carried away.

Question 35

How do seeds disperse by carrying?

Answer 35

Hooked seeds attach to animals coats and are carried away. For example, burdock

Question 36

How are seeds adapted for survival?

Answer 36

Dormant seeds have low metabolic rates and so can survive very cold weather
Testa are chemically resistant
Endosperm and cotyledons provide nutrients until the seedling can photosynthesise adequately
Dispersal allows colonisation of new habitats

Question 37

Define germination

Answer 37

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

Question 38

What 3 main requirements are needed for germination?

Answer 38

Suitable temperature (between 5°C - 30°C)
Water
Oxygen

Question 39

Outline the process of germination

Answer 39

When conditions are suitable, water is imbibed (taken up) rapidly by the seed through the micropyle. Amylase hydrolyses starch into maltose and proteases hydrolyses proteins into amino acids. The soluble products are transported to the embryo and carried in the phloem to the apical meristems of the plumule and radicle, where rapid cell division occurs. The Swollen tissues rupture the testa and the radicle emerges from the seed. It is positively geotropic and negatively phototropic so it grows downwards. The plumule emerges and grows upwards for the opposite reason. Elongation pushes the shoot upward out of the soil it will now be able to photosynthesise

Question 40

Describe the relative changes in the dry mass of the embryo, seedling and endosperm/cotyledons during germination

Answer 40

The dry mass of the embryo as it develops into a seedling increases whilst the dry mass of the endosperm/cotyledons, providing its food decreases.

Question 41

Describe the effects of gibberellic acid produced by embryos?

Answer 41

The barley embryo secretes gibberellic acid which diffuses through the endosperm to the aleurone layer (layer of cells towards the outside of the seed). It switches on genes in the aleurone layer producing enzymes such as amylase. The amylase diffuses our of the aleurone layer and hydrolyses the starch in the endosperm cells. The maltose and glucose produced are used for respiration.

Question 42

What happens when germinating seeds are placed on malt agar?

Answer 42

During germination, amylase enzymes are synthesised. In this experiment, the Amylase digests starch in the agar plate resulting in areas that lack starch. This can be shown by iodine solution failing to turn blue-black in these areas