final:fertilisation

Question 1

Describe the process of fertilisation in mammals (4)

Answer 1

1. Acrosin is released from the acrosome cap of the sperm
2. Acrosin disperse follicle cells and digests the glycoprotein jelly of zona pellucida 3. Sperm head touches the egg cell membrane
3. Sperm head and egg cell cell membrane fuses, triggering the cortical reaction
4. Egg releases cortical granules which cause the cross linking of glycoproteins, thus the hardening of zona pellucida, preventing polyspermy
5. Fusion of the haploid sperm nucleus with the haploid egg nucleus to form a diploid zygote

Question 2

Acrosome reaction

Answer 2

1. Acrosin is released from the acrosin cap
2. On contact of the sperm head with the zona pellucida

Question 3

Preventing polyspermy

Answer 3

1. Ion channels in the plasma membrane of the ovum open and close
2. Such that the inside of the cell changes from electrically negative to positive 3. Blocking the entry of any further sperm

Question 4

Cortical reaction

Answer 4

1. The cortical reaction is triggered
2. When the sperm cell fuses with the egg cell membrane
3. Causing small vesicles called cortical granules to be released by exocytosis from the oocyte
4. The cortical granules move to the plasma membrane and fuse with it
5. Releasing enzymes by exocytosis into the zona pellucida
6. The enzymes cause the cross-linking of the glycoproteins in the zona pellucida
7. Making it hard and preventing polyspermy

Question 5

Asexual VS Sexual reproduction
Advantages of being able to do both

Answer 5

Sexual reproduction
1. Results in genetic variation
2. More likely for (animal) to survive and reduce chances that all (animal) will be killed by a single change in the environment, ie. disease, change in temperature

Asexual reproduction
1. Produces genetically identical (animal)
2. Hydra will be suited to existing conditions
3. Number of (animal) increases rapidly.

Question 6

Importance of fertilisation in sexual reproduction

Answer 6

1. Combines the chromosomes from the two parents
2. Restoring the diploid number of chromosomes
3. Produce genetically varied offspring

Question 7

Importance of mitosis in pollen tube growth

Answer 7

1. Mitosis in nucleus results in two haploid nuclei
2. Leading to double fertilisation
3. One male nucleus is needed to fuse with the egg cell to form the zygote
4. The other male nucleus is needed to fuse with the two polar nuclei to produce a triploid endosperm nucleus.

Question 8

Why several divisions of mitosis are involved in the production of sperm cells

Answer 8

1. Increase the number of primary spermatocytes
2. To increase the number of sperm produced

Question 9

How meiosis gives rise to genetic variation in gametes

Answer 9

1. Crossing over between non-sister chromatids at the chiasmata
2. Involves swapping sections of chromatids, forming recombinants
3. Independent assortment of homologous chromosomes
4. Gives rise to new combinations of paternal and maternal chromosomes

Question 10

Importance of meiosis in plants

Answer 10

1. Halves the chromosome number, forming a haploid nucleus
2. Allows for genetic variation in plant s
3. Increased survival chances of the species

Question 11

Structure of pollen grain VS Sperm cell

Answer 11

1. Sperm cells have flagella
2. Sperm cells have acrosome cap containing acrosin
3. Pollen grain has more nuclei
4. Pollen grain has a cell wall

Question 12

Process of fertilisation in flowering plants

Answer 12

1. Generative nucleus divides to form two male gametes, by mitosis
2. Tip of the pollen tube reaches the ovule and grows through the micropyle into the embryo sac in the ovule
3. The pollen tube degenerates and bursts, releasing two male nuclei into the ovule
4. Leading to double fertilisation
5. One male nucleus fuses with the egg cell nucleus to form a diploid zygote
6. The zygote develops into the plant embryo
7. The other male nucleus fuses with the two polar nuclei to produce a triploid endosperm nucleus
8. The endosperm is involved with supplying the embryo with food for germination

Question 13

How pollen is involved in the fertilisation of a flower

Answer 13

1. Pollen grain reaches the stigma of a flower and germinates to develop a pollen tube
2. The tip of the pollen tube secretes hydrolytic enzymes which digest the stigma and style to
3. Pollen tube grows down towards the ovary and pollen tube nucleus and generative nucleus travels down along the pollen tube
4. Generative nucleus divides by mitosis as it moves down the pollen tube forming the two male nuclei.
5. Tip of the pollen tube reaches the ovule in the ovary and grows through the micropyle into embryo sac in ovule
6. Pollen tube nucleus degenerates and bursts, releasing the two male nuclei into the ovule

Question 14

How pollen tube is involved in the fertilisation of flower

Answer 14

1. Pollen tube grows through the style the ovary and transports the generative nucleus and pollen tube nucleus to the ovule
2. Tip of the pollen tube secretes hydrolytic enzymes which digest the stigma and style to aid the growth of tube to the ovule
3. Pollen tube degenerates and bursts, releasing the two male nuclei into the ovule for double fertilisation
4. One male nucleus fuses with the two polar nuclei to form a triploid endosperm nucleus
5. The other male nucleus fuses with the egg cell to form a diploid zygote

Question 15

How pollen tubes grow through the style of the flower (2)

Answer 15

1. Tip of pollen tube secretes hydrolytic enzymes
2. Which digest the stigma and style
3. Pollen tube grows down the towards the ovary and the pollen tube nucleus travels down along the pollen tube, forming a pathway

Question 16

Role of digestive enzymes in the growth of pollen tube (3)

Answer 16

1. Hydrolytic enzymes digest the style
2. Breaking down the protein, pectin and middle lamella by hydrolysis
3. This makes it easier for the pollen tube to grow as there is reduced resistance
4. Supplying nutrients and energy for pollen tube growth.