Chapter 8 Sexual Reproduction In Plants Flashcards Preview

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Flashcards in Chapter 8 Sexual Reproduction In Plants Deck (42)
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1
Q

What are flowering plants called?

A

Angiosperms

2
Q

What are the male gametes in plants called?

A

Pollen grains

3
Q

What are the female gametes in plants called?

A

Embryo sacs

4
Q

Where are pollen grains produced?

A

Anthers

5
Q

Where are embryo sacs produced?

A

Ovule

6
Q

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

A

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

7
Q

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

A

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)

8
Q

Define pollination

A

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

9
Q

Define self-pollination

A

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

10
Q

Define cross pollination

A

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

11
Q

What 2 ways can pollination occur?

A

By wind or insects(animals)

12
Q

What are the advantages of self-pollination?

A

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

13
Q

What are the disadvantages of self-pollination?

A

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

14
Q

What are the advantages of cross-pollination?

A

Greater genetic variation

Reduces the chances of harmful allele combinations

15
Q

What methods are used to ensure cross-pollination?

A

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

16
Q

What are the characteristics of insect pollinated flowers?

A

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

17
Q

What are the characteristics of wind pollinated flowers?

A

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

18
Q

How does the male gamete develop?

A

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.

19
Q

What is the tapetum?

A

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.

20
Q

How does the female gamete develop?

A

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.

21
Q

What is the nucellus?

A

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.

22
Q

What are the functions of synergids and antipodals?

A

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

23
Q

Outline the process of double fertilisation

A

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.

24
Q

What is a fruit?

A

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

25
Q

What is a seed?

A

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

26
Q

Outline how the fruit and seeds develop

A

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.

27
Q

What are the characteristics of monocotyledons

A

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

28
Q

What are the characteristics of dicotyledons

A
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
29
Q

Define dormant

A

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

30
Q

How do seeds disperse by wind?

A

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

31
Q

How do seeds disperse by transport?

A

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

32
Q

How do seeds disperse by rolling?

A

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

33
Q

How do seeds disperse by bursting?

A

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

34
Q

How do seeds disperse by water?

A

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.

35
Q

How do seeds disperse by carrying?

A

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

36
Q

How are seeds adapted for survival?

A

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

37
Q

Define germination

A

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

38
Q

What 3 main requirements are needed for germination?

A

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

39
Q

Outline the process of germination

A

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

40
Q

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

A

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.

41
Q

Describe the effects of gibberellic acid produced by embryos?

A

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.

42
Q

What happens when germinating seeds are placed on malt agar?

A

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