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How do Organisms Reproduce? - SEXUAL REPRODUCTION7.3 SEXUAL REPRODUCTION7.3 SEXUAL REPRODUCTION7.3 SEXUAL REPRODUCTION7.3 SEXUAL REPRODUCTION

Grade 10CBSE

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

🔑Concepts

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Sexual reproduction involves the fusion of two specialized cells called gametes (one from each parent) to form a single cell called a zygote.

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DNA copying mechanism is not absolutely accurate; the resultant errors are a source of variations in populations, which is important for the survival of species over time.

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To maintain a constant chromosome number in the offspring, specialized cells (germ-cells) are produced through meiosis, where the chromosome number is halved (nn).

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In flowering plants, the reproductive parts are located in the flower. The Stamen is the male reproductive part (produces pollen grains) and the Carpel/Pistil is the female reproductive part (contains the ovary, style, and stigma).

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Pollination is the transfer of pollen from the stamen to the stigma. It can be Self-pollination (same flower) or Cross-pollination (different flowers via wind, water, or animals).

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Double Fertilization: In plants, one male gamete fuses with the egg to form a zygote (2n2n), and another may fuse with polar nuclei (specific to higher plants study).

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Puberty in humans involves hormonal changes: Testosterone in males and Estrogen/Progesterone in females, leading to secondary sexual characteristics.

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The Male Reproductive System consists of testes (producing sperm and testosterone), scrotum (maintains lower temperature for sperm survival), vas deferens, and glands (prostate and seminal vesicles) that add fluid for nutrition and transport.

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The Female Reproductive System consists of ovaries (producing eggs), fallopian tubes (site of fertilization), uterus (site of implantation), and the cervix/vagina.

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The Placenta is a special disc-like tissue embedded in the uterine wall that provides a large surface area for the exchange of glucose and oxygen from the mother to the embryo and removal of waste (CO2CO_2 and nitrogenous waste) from the embryo.

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Menstruation occurs if the egg is not fertilized; the thick uterine lining breaks down and is expelled as blood and mucous roughly every 2828 days.

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Reproductive health involves mechanical barriers (condoms), chemical methods (pills), and surgical methods (vasectomy/tubectomy) to prevent STDs and manage population.

📐Formulae

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

Chromosome Number in Gamete=12×Chromosome Number in Somatic Cell\text{Chromosome Number in Gamete} = \frac{1}{2} \times \text{Chromosome Number in Somatic Cell}

Germination of Pollen:Pollen Grain+Stigma→Pollen Tube→Ovary\text{Germination of Pollen}: \text{Pollen Grain} + \text{Stigma} \rightarrow \text{Pollen Tube} \rightarrow \text{Ovary}

💡Examples

Problem 1:

If a human skin cell contains 4646 chromosomes, calculate the number of chromosomes present in a human sperm cell and the resulting zygote after fertilization.

Solution:

The sperm cell (gamete) contains 2323 chromosomes, and the zygote contains 4646 chromosomes.

Explanation:

Gametes are formed by meiosis, which halves the chromosome number: 462=23\frac{46}{2} = 23. Upon fertilization, the fusion of sperm (n=23n = 23) and egg (n=23n = 23) restores the diploid state: 23+23=4623 + 23 = 46.

Problem 2:

A flower has 1212 ovules in its ovary. If all ovules are successfully fertilized, how many male gametes are required, and how many seeds will be formed?

Solution:

1212 male gametes are required for the zygotes, and 1212 seeds will be formed.

Explanation:

Each ovule requires one male gamete to form a zygote. Since the ovule develops into a seed after fertilization, 1212 ovules will result in 1212 seeds. In a mathematical representation: Number of Seeds=Number of Fertilized Ovules\text{Number of Seeds} = \text{Number of Fertilized Ovules}.

Problem 3:

Calculate the duration of the menstrual cycle in days if the process repeats 1313 times in a year of 364364 days.

Solution:

28 days28 \text{ days}

Explanation:

The duration is calculated by dividing the total days by the number of cycles: 364/1328\begin{array}{r} 364 \\ / 13 \\ \hline 28 \end{array}