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Reproduction - Compare asexual and sexual reproduction with examples in plants and animals

Grade 9CBSE

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

🔑Concepts

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Asexual reproduction involves a single parent and results in offspring that are genetically identical to the parent, often referred to as clones. No fusion of gametes occurs.

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Sexual reproduction involves two parents (male and female) and the fusion of specialized germ cells called gametes (sperm and egg) to form a zygote (2n2n).

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Asexual methods in plants include vegetative propagation (e.g., via roots, stems like PotatoPotato tubers, or leaves like BryophyllumBryophyllum).

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Asexual methods in animals include binary fission in AmoebaAmoeba, budding in HydraHydra, and fragmentation in PlanariaPlanaria.

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Sexual reproduction promotes genetic variation due to the recombination of DNA from two different individuals, which is essential for species survival and evolution.

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The chromosome number in gametes is haploid (nn), which restores to diploid (2n2n) after fertilization.

📐Formulae

Male Gamete (n)+Female Gamete (n)→FertilizationZygote (2n)\text{Male Gamete } (n) + \text{Female Gamete } (n) \xrightarrow{\text{Fertilization}} \text{Zygote } (2n)

N=2nN = 2^n (where NN is the number of individuals produced via binary fission after nn generations)

Variation∝Complexity of Reproduction (Sexual > Asexual)\text{Variation} \propto \text{Complexity of Reproduction (Sexual > Asexual)}

💡Examples

Problem 1:

Identify the mode of reproduction in a PotatoPotato tuber and a HumanHuman being, and compare the genetic similarity of the offspring to the parent.

Solution:

The PotatoPotato reproduces asexually via vegetative propagation (eyes/buds), while HumansHumans reproduce sexually.

Explanation:

In PotatoPotato, the offspring is a clone, meaning genetic similarity is 100%100\%. In HumansHumans, offspring inherit 50%50\% DNA from each parent, leading to significant genetic variation.

Problem 2:

If a single AmoebaAmoeba cell undergoes binary fission every 3030 minutes, how many cells will be present after 22 hours?

Solution:

24=162^4 = 16 cells.

Explanation:

In 22 hours (total 120120 minutes), the number of generations nn is calculated as: 120 minutes30 minutes=4\frac{120 \text{ minutes}}{30 \text{ minutes}} = 4. Using the formula for binary fission N=2nN = 2^n, we get 24=162^4 = 16.

Problem 3:

In a flowering plant, if the pollen grain has 1212 chromosomes, what will be the chromosome number in the leaf cell and the zygote?

Solution:

Leaf cell = 2424; Zygote = 2424.

Explanation:

The pollen grain is a gamete (n=12n = 12). Leaf cells are somatic cells (2n2n), so 2×12=242 \times 12 = 24. The zygote is formed by the fusion of two gametes (n+nn + n), so 12+12=2412 + 12 = 24.