4. Random fertilisation and unusual life cycles

Question 1

Meiosis produces genetically unique gametes

Answer 1

Which randomly come together in fertilisation – resulting in yet more different combinations of alleles and more genetic diversity.

Question 2

Fertilisation restores the diploid number of chromosomes

Answer 2

Question 3

Lifecycles

Answer 3

Sexual reproduction requires the production of gametes by meiosis and then fertilisation to restore the diploid number of chromosomes, followed by mitosis for growth.

In the exam you could be given an unfamiliar lifecycle and asked to label the stages involving haploid & diploid cells, meiosis, mitosis and fertilisation – don’t panic just look for the gametes – formed by meiosis

Question 4

Plant lifecycles

Generations

Sporophytes

Answer 4

Plants reproduce both sexually (produce gametes) and asexually (spores). A sexually reproducing plant will make a plant that reproduces asexually, and then the asexually reproducing plant will make a sexually reproducing plant, and the circle goes round and round.

Each reproductive event produces a new generation, and they alternate the types of reproduction, thus the name alternation of generations.

A sporophyte is a plant that produces spores and, a gametophyte is a plant that produces gametes.

Question 5

Lifecycle of moss

1. What do the term haploid and diploid mean?
2. What do the term (n) and (2n) stand for?
3. Using the terms (n) and (2n) describe what happens in meiosis.
4. Using the terms (n and (2n ) describe what happens in fertilisation.
5. Name 3 haploid structures in the moss lifecycle.
6. Name 2 diploid structures in the moss lifecycle.

Answer 5

1. What do the term haploid and diploid mean? HAPLOID – 1 CHROMOSOME OF EACH TYPE (AHALF SET OF CHROMOSOMES), DIPLOID -2 OF EACH CHROMOSOME
2. What do the term (n) and (2n) stand for? n=HAPLOID, 2n= DIPLOID
3. Using the terms (n) and (2n) describe what happens in meiosis. 2n -> n
4. Using the terms (n and (2n ) describe what happens in fertilisation. n+n -> 2n
5. Name 3 haploid structures in the moss lifecycle. SPORE GAMETOPHYTE & GAMETES
6. Name 2 diploid structures in the moss lifecycle. ZYGOTE & SPOROPHYTE

Question 6

Lifecycle of Babesia
1. How many organisms feature in this lifecycle?

2. How is the Babesia parasite transmitted from one organism to another?
3. Which type of cell division results in the formation of the merozoite?
4. In which organism does fertilisation take place?
5. Which type of cell division produces sporozoites?
6. Suggest a way in which the spread of Lyme disease could be reduced.

Answer 6

1. How many organisms feature in this lifecycle? 3
2. How is the Babesia parasite transmitted from one organism to another? TICK Biting and FEEDING ON COW
3. Which type of cell division results in the formation of the merozoite? MITOSIS
4. In which organism does fertilisation take place? TICK
5. Which type of cell division produces sporozoites? MITOSIS
6. Suggest a way in which the spread of Lyme disease could be reduced. REDUCING THE NUMBER OF TICKS/PHYSICALLY REMOVING TICKS

Question 7

Lifecycle of Ferns

Answer 7

1. Is the fern plant that we are used to seeing in the wild haploid or diploid?
2. Are fern spores haploid or diploid? Explain your answer.
3. What type of cell division takes place when the spore develops into a young gametophyte?
4. Which organs in the gametophyte produced the sperm and the eggs?
5. Does meiosis take place in these organs?
6. Suggest an advantage of alternate generation lifecycles

Question 8

Lifecycle of Malaria
1. During its lifecycle the malaria parasite lives in 2 organisms - which ones?

2. In which organism does The parasite undergo meiosis?
3. In which organism are the malaria gametes fertilised?
4. Suggest how the malaria parasite passes from one organism to the other.
5. Are the sporozoites haploid or diploid?
6. What is the function of the gametocyte?

Answer 8

1. During its lifecycle the malaria parasite lives in 2 organisms - which ones? MOSQUITO AND HUMAN
2. In which organism does The parasite undergo meiosis? HUMAN
3. In which organism are the malaria gametes fertilised? MOSQUITO
4. Suggest how the malaria parasite passes from one organism to the other. WHEN MOSQUIT FEEDS ON HUMAN BLOOD
5. Are the sporozoites haploid or diploid? DIPLOID
6. What is the function of the gametocyte? TO PRODUCE GAMETES

Question 9

Answer the following

Answer 9

(a) (1) 22;

(ii) 1. Odd number of chromosomes/33 chromosomes (In leaf cell);

2. Chromosomes cannot pair/cannot undergo melosis/would result in half chromosomes/cannot form haploid cells;

(b) (i) Fast growth/produces crop fast/produces large crop:
(ii) Leaves less likely to break/higher breaking strength:

Question 10

Banana growers can only grow new variety B plants from suckers. Suckers grow from cells at the base of the stem of the parent plant.

Use your knowledge of cell division to explain how growing variety B on a large scale will affect the genetic diversity of bananas.

Answer 10

Low genetic diversity because they are produced by mitosis;

Will all have the same DNA/genes/alleles/will be genetically Identical/will be clones;

OR

Low genetic diversity because they are not produced by melosis;

No crossing ovenindependent segregation/will not be genetically different;