Reproduction In Plants

Question 1

What is asexual reproduction?

Answer 1

Involves only one parent

Question 2

What is sexual reproduction?

Answer 2

Involves the union of 2 sex cells

Question 3

What are gametes?

Answer 3

Haploid cells capable of fusion

Question 4

What is the function of the receptacle?

Answer 4

Supports floral parts

Question 5

What is the function of the sepals?

Answer 5

Protects flower when it is a bud

Question 6

What is the function of the petals?

Answer 6

Attract animals

Question 7

What is a stamen?

Answer 7

Male part of flower

Question 8

What is a carpel?

Answer 8

Female part of plant

Question 9

What is the function of the anther?

Answer 9

Produce pollen grains by meiosis

Question 10

How is the male gamete formed?

Answer 10

1. Cells lining inside of anther are diploid
2. Meiosis takes place to make pollen grains
3. Pollen grains divide by mitosis to form gametes
4. When pollen grains fully developed, the anther splits leaving them exposed

Question 11

How does a pollen grain develop?

Answer 11

1. Anther consists of 4 chambers called pollen sacs.
2. Pollen sac enclosed by protective epidermis and fibrous layer
3. Tapetum is a layer of cells just inside the fibrous layer. It is a food source for energy for cell division
4. Number of diploid microspore mother cells in each pollen sac
5. These cells divide by meiosis to make a cluster of 4 haploid cells called a tetrad.
6. Tetrad breaks up to form 4 separate haploid pollen grains
7. Pollen grain coated with thick outer wall called an exine for protection. The intine is a thin inner coat on pollen grain.
8. Pollen may divide by mitosis to form the tube and generative nuclei.

Question 12

How does a female gamete form?

Answer 12

1. Each ovule has a number of diploid cells.
2. One divides by meiosis to form a single haploid cell
3. Cell undergoes mitosis 3 times to form embryo sac
4. Embryo sac contains egg cell and 2 polar nuclei

Question 13

How does the embryo sac develop?

Answer 13

1. Each ovary has 1 or more ovules. Ovules have 2 walls called integuments
2. Integuments have small opening, the micropyle, which pollen enters
3. Most of ovules is diploid nucellus cells that supply nutrients for later growth
4. 1 cell low down in ovule called megaspore mother cell, divides by meiosis to form 4 haploid cells
5. 3 of these cells degenerate. Remaining cell called embryo sac.
6. Haploid nucleus in embryo sac divides by mitosis 3x to make 8 haploid cells
7. They are contained in embryo sac which swells using food supply from nucellus.
8. 5 nuclei degenerate. 3 remainders form gametes
9. 2 gametes form polar nuclei in embryo sac. Remaining gamete forms a thin wall and becomes the egg cell.

Question 14

What is pollination?

Answer 14

Transfer of pollen from an anther to a stigma of a flower from the same species

Question 15

What is self pollination?

Answer 15

Involves the transfer of pollen from an anther to a stigma on the same plant

Question 16

What is cross-pollination?

Answer 16

Involves the transfer of pollen from an anther to a stigma on a different plant of the same species.

Question 17

What is fertilisation?

Answer 17

The union of the male and female gametes to form a diploid zygote.

Question 18

How does fertilisation occur?

Answer 18

1. Pollen lands on stigma and is stimulated to grow by sugars on stigma.
2. Pollen tube grows down style to ovule
3. Growth of pollen tube controlled by nucleus which degenerates when reaches micropyle.
4. Pollen tube grows towards chemicals released from ovule. Example of chemotropism
5. Haploid generative nucleus divides by mitosis and move down pollen tube. 2 haploid sperm nuclei formed.
6. They move down pollen tube
7. Presence of pollen tube means male gametes dont need external water to move to egg- adaption to life on dry land.

Question 19

Give an account of double fertilisation

Answer 19

1. 1 sperm nucleus joins with the egg nucleus to form diploid zygote. This zygote will develop into embryo
2. 2nd sperm nucleus joins with the 2 polar nuclei to form a triploid endosperm nucleus.

Question 20

How do seeds form?

Answer 20

1. Fertilised ovule becomes seed
2. Integuments dry up and become testa
3. Zygote grows repeatedly by mitosis. It forms group of cells that become embryo
4. Embryo consists of radicle, plumule.
5. Some embryos grow to form the seed leaves (cotyledons). These are simple leaves which may become swollen with stored food, especially in dicots.
6. At the same time the endosperm nucleus divides repeatedly by mitosis to produce many endosperm cells.
7. These expands and absorb nucellus. The endosperm acts as a food source. The main foods stored in seeds are fats and starch.

Question 21

What is a non-endospermic seed?

Answer 21

A seed that has no endosperm when fully formed.

Question 22

What is an endospermic seed?

Answer 22

A seed that contains some endosperm when fully formed.

Question 23

What does the ovule develop into?

Answer 23

Seed

Question 24

What does the integuments develop into?

Answer 24

Testa

Question 25

What does the nucellus develop into?

Answer 25

Endosperm–> cotyledon(s)

Question 26

What does the egg develop into?

Answer 26

Zygote–> embryo

Question 27

What does the polar nuclei develop into?

Answer 27

Endosperm

Question 28

What does the ovary develop into?

Answer 28

Fruit

Question 29

What does the ovary wall develop into?

Answer 29

Pericarp

Question 30

How does fruit form?

Answer 30

1. As seed develops the surrounding ovary becomes fruit.
2. Fruit formation stimulated by auxins produced by seeds
3. Wall of ovary becomes wall of fruit. Fruits are designed to protect seed(s) and help disperse them.
4. Once the fruit forms the rest of the flower parts die and fall away.

Question 31

Why are grains considered fruits?

Answer 31

They have an internal seed and the fruit wall is attached to seed wall.

Question 32

Give an account of false fruits.

Answer 32

1. False fruits develop from other parts of the plant besides the ovary.
2. Apple is a false fruit as it develops when the flower parts at the base of the flower and join together and swell with stored food. Core of apple derives from ovary.

Question 33

What is dispersal?

Answer 33

Transfer of a seed or fruit away from the parent plant.

Question 34

Why is dispersal necessary?

Answer 34

1. Avoid large numbers of seeds competing with each other and parent plant.
2. Increase chance of survival for plant
3. Find new areas for growth.
4. Increase number of species.

Question 35

How are seedless fruit formed?

Answer 35

1. Genetic breeding programmes

2. Treating flowers with auxins

Question 36

What is dormancy?

Answer 36

Resting period when seeds undergo no growth and have reduced cell activity.

Question 37

How is dormancy brought about?

Answer 37

1. Growth inhibitors (abscisic acid) present in outer seed. They inhibit growth until broke down by water, cold or decay
2. Testa may be impermeable to water or oxygen. Eventually testa decays allowing water and oxygen to enter.
3. Testa may be too tough for embryo to emerge.
4. Lack of suitable growth regulator needed to stimulate growth. Regulator may be produced due to increased light or temp.

Question 38

What are the advantages of dormancy?

Answer 38

1. Allows plant to avoid harsh conditions of winter
2. Gives embryo time to fully develop
3. Provides time for seed to be dispersed.
4. Maximises growing season

Question 39

What is germination?

Answer 39

The growth of the embryo after a period of dormancy if the environmental conditions are suitable.

Question 40

Give an account of the events in germination

Answer 40

1. Seeds store food as oils, starch and proteins
2. Germination begins when seeds absorbs water. Water absorbed through tiny hole called micropyle and through the testa. Water activates enzymes
3. Oils are digested to fatty acids and glycerol, starch to glucose and proteins to amino acids
4. Products of digestion moved to growing embryo
5. Glucose and amino acids are used to make new structures like cell walls and enzymes.
6. Fats and glucose used for respiration for energy
7. Dry weight of seed falls due to food used in respiration
8. Weight of food stores falls, weight if embryo increases
9. Radicle bursts through testa
10. Plumule emerges above ground and leaves form
11. Leaves start to photosynthesis, dry weight of seedling increases

Question 41

Give the stages of seedling growth if cotyledons remain below soil.

Answer 41

1. Seeds absorb water, enzymes become active and radicle begins to grow
2. Radical bursts out through testa and grows down.
3. Plumule emerges and region between cotyledon and plumule grows
4. Plumule grows up through soil and its leaves protected by plumule being hooked over.
5. Cotyledons shrivel as food transferred from them.
6. Radical develops into primary root which forms lateral roots.
7. Once above ground plumule straightens and produces first true leaves. Soon become green and start photosynthesis.

Question 42

Give the stages of seedling growth when cots move above soil.

Answer 42

1. Region between emerging radical and cot grows. This causes cot to be carried above soil.
2. Once above soil, fruit wall falls to ground. Cots open out and become green and photosynthetic. Plumule emerges from between cit and forms the first foliage leaves.