krit.club logo

Reproduction - Asexual and sexual reproduction

Grade 11IGCSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Asexual reproduction is a process resulting in the production of genetically identical offspring from one parent, involving the process of mitosismitosis.

•

Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other and the parents.

•

The fusion of haploid (nn) nuclei is known as fertilization, which restores the diploid (2n2n) number of chromosomes.

•

Gametes are produced through meiosismeiosis, a type of cell division that halves the chromosome number from 2n2n to nn.

•

Advantages of asexual reproduction include being faster than sexual reproduction and requiring only one parent, which is beneficial in stable environments.

•

Advantages of sexual reproduction include increased genetic variation, allowing species to adapt to changing environments and resist diseases.

•

In humans, the diploid number is 2n=462n = 46 and the haploid number found in gametes (sperm and egg) is n=23n = 23.

📐Formulae

Gamete (n)+Gamete (n)→Zygote (2n)\text{Gamete } (n) + \text{Gamete } (n) \rightarrow \text{Zygote } (2n)

Mitosis: 2n→2n\text{Mitosis: } 2n \rightarrow 2n

Meiosis: 2n→n\text{Meiosis: } 2n \rightarrow n

Total Chromosomes=2×n\text{Total Chromosomes} = 2 \times n

💡Examples

Problem 1:

If the somatic (body) cell of a certain plant species contains 2424 chromosomes, determine the number of chromosomes found in its pollen grain and the resulting zygote after fertilization.

Solution:

Pollen grain = 1212 chromosomes; Zygote = 2424 chromosomes.

Explanation:

The pollen grain is a male gamete and is therefore haploid (nn). If 2n=242n = 24, then n=242=12n = \frac{24}{2} = 12. The zygote is formed by the fusion of two haploid nuclei (n+nn + n), returning the chromosome count to the diploid state (2n=242n = 24).

Problem 2:

A bacteria colony reproduces asexually every 2020 minutes. If there is 11 bacterium at t=0t=0, how many bacteria will be present after 22 hours?

Solution:

26=642^6 = 64 bacteria.

Explanation:

Asexual reproduction in bacteria (binary fission) involves doubling the population each generation. In 22 hours (120120 minutes), there are 120/20=6120 / 20 = 6 generations. The formula for the number of individuals is 2n2^n, where nn is the number of generations: 26=642^6 = 64.

Problem 3:

Explain the genetic outcome of a strawberry plant producing runners versus a strawberry plant grown from seeds.

Solution:

Runners produce 100%100\% genetically identical clones; Seeds produce genetically unique offspring.

Explanation:

Runners are a form of asexual reproduction involving mitosismitosis, so the offspring have the same DNADNA as the parent. Seeds are the product of sexual reproduction (pollination and fertilization), leading to a recombination of alleles and genetic variation.

Asexual and sexual reproduction - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology