15 — modes of reproduction

Question 1

Asexual reproduction

Answer 1

Asexual reproduction is the process that results in the production of genetically identical offspring from one parent by mitosis, without the fusion of nuclei of gametes.

Examples: rhizome, runner, stem tube

Question 2

Offspring

Answer 2

refers to children or the next generation.

Question 3

Gametes

Answer 3

Gametes are reproductive cells (e.g. sperm and ovum) containing haploid number of chromosomes (23 chromosomes) and are produced by the reproductive organs (e.g. testes and ovaries)

Question 4

Mitosis

Answer 4

Mitosis is a type of cell division giving rise to genetically identical cells in which the daughter cells nuclei contain the same number of chromosomes as the parent cell nucleus.

Question 5

Sister chromatids

Answer 5

Each chromosome consist of two
identical DNA molecules known as
sister chromatids.

Question 6

Centromere

Answer 6

The point where sister chromatids are joined

Question 7

Importance of mitosis

Answer 7

• Asexual reproduction
• Growth in multicellular organisms
• Repair of damaged tissues

Question 8

Advantages and disadvantages of asexual reproduction

Answer 8

A:
1. Only 1 parent required
2. Fusion of gametes not required
3. All the beneficial qualities r passed on to the offspring
4. Faster than sexual reproduction

D:
1. No genetic variation in offspring -> species r not well-adapted to changes in the env (and may go extinct by natural select.)

Question 9

Define Sexual reproduction [3]

Answer 9

Sexual reproduction is the process involving the fusion of haploid nucleus of a male gamete and haploid nucleus of a female gamete [1] to form a diploid zygote which is genetically dissimilar from its parents [1] through fertilisation. The male and female gametes are produced by meiosis in the gonads. [1]

Question 10

Meiosis

Answer 10

Meiosis is a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number in daughter cells nuclei is half of the parent cell nucleus due to the separation of homologous chromosomes.

Question 11

Mitosis vs meiosis

Answer 11

Similarities:
1. Parent cell has 23 pairs of homologous chromosomes.
2. Parent cell undergoes DNA replication first

Differences:
Mitosis:
Two daughter cells obtained
Meiosis:
Four daughter cells obtained

Mitosis:
Each daughter cell has 23 pairs of
homologous chromosomes. It is diploid.
Meiosis:
Each daughter cell has 23 chromosomes. It is haploid.

Mitosis:
Daughter cells are genetically identical to each other and to the parent cell.
Meiosis:
Daughter cells are genetically dissimilar to one another and to the parent cell.

Question 12

Advantages and disadvantages of sexual reproduction

Answer 12

Advantages:
1. Offspring may inherit beneficial qualities from both parents
2. There is greater genetic variation in the offspring. This leads to species that r better-adapted to changes in the env

Disadvantages:
1. 2 parents r required (uses more energy)
2. Fusion of nuclei of gametes is required (uses more energy)
3. Method of reproduction is slower

Question 13

Differences betw asexual and sexual reproduction

Answer 13

A: does not involve fusion of nuclei of gametes
S: involves the fusion between haploid nuclei of male gamete and female gamete to form a diploid zygote

A: only 1 parent required
S: requires 2 parents

A: offspring r genetically identical;
S: offspring r genetically diff

A: relatively quicker method to produce offspring
S: slower method to produce offspring

A: involves mitosis
S: involves meiosis in production of haploid gametes

Question 14

Tissue culture of plants

Answer 14

New plantlets are grown from
same plant tissues in a special
growth medium via asexual reproduction

Question 15

Define fertilisation

Answer 15

Fertilisation - fusion of haploid nucleus of a male gamete and haploid nucleus of a female gamete [1] to form a diploid zygote. [1]

Question 16

Meiosis and fertilisation can lead to variation.
Describe 3 ways that meiosis and fertilisation can lead to variation. [3]

Answer 16

Random fertilisation involves the fusion of nuclei of a random haploid male gamete and female haploid gamete, sperm and egg respectively, allowing variation to occur as new combinations of chromosomes in the zygote. [1]
Random and independent assortment of homologous chromosomes occur during meiosis, resulting in new combination of chromosomes, leading to variation. [1]
Crossing over of homologous chromosomes during meiosis results in new combinations of alleles, leading to variation. [1]

Question 17

A new disease breaks out amongst 2 plant populations. Population A are all asexual, and population B are all sexual. It is observed that population A failed to survive, while population B survived. Explain why. [4]

Answer 17

Population A are all asexual hence are all genetically identical.
They have the same level of susceptibility to the disease, hence had a high chance of being wiped out all at once.

Population B are all sexual hence they have genetic variation between individuals.
Some of them had resistance to the disease and were able to survive and reproduce, hence the population was not wiped out.

Question 18

Determine the haploid number of the plant species [3]

Answer 18

Haploid number = 3 [1]
The cell has diploid number of chromosomes which is 6. [1]
Haploid number is half the number of chromosomes as in the parent cell. [1]

Question 19

Body cell vs gamete [2]

Answer 19

Body cell is diploid and will contain homologous chromosomes, one from each parent [1] while a gamete is haploid and does not contain homologous chromosomes and only contain one chromosome from each homologous pair. [1]

Question 20

Haploid

Answer 20

A condition of cells that contain half the number of chromosomes (n) of the parent cell

Question 21

Diploid

Answer 21

A condition of cells that contain the full number of chromosomes (2n) as in the normal body cell