7.3-Sexual Reproduction

7.3-Sexual Reproduction Important Formulae

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Grade 10 → Science → How Do Organisms Reproduce? → 7.3-Sexual Reproduction

Sexual reproduction is a mode of reproduction that involves the combination of genetic material from two parent organisms, resulting in offspring that are genetically diverse. This process is fundamental to the evolution and adaptation of species. Sexual reproduction is characterized by several key components, including gamete formation, fertilization, and development of the offspring.

Gametes and Gametogenesis

Gametes are specialized reproductive cells involved in sexual reproduction. In animals, there are two types of gametes:

  • Sperm: The male gamete, which is typically small and motile, produced in the testes through a process called spermatogenesis.
  • Ova (Eggs): The female gamete, which is usually larger and non-motile, produced in the ovaries through a process called oogenesis.

The process of gametogenesis involves meiosis, a type of cell division that reduces the chromosome number by half, producing haploid gametes. This ensures genetic diversity and maintains the chromosome number in the offspring.

Fertilization

Fertilization is the process by which a sperm and an egg unite to form a zygote. It can occur in two main ways:

  • External Fertilization: This occurs outside the female's body, commonly seen in aquatic animals like fish and amphibians. In this method, females release eggs into the water, and males release sperm simultaneously, increasing the chances of fertilization.
  • Internal Fertilization: This occurs inside the female's body, typical of terrestrial animals. The sperm is deposited into the female reproductive tract, leading to fertilization. This method provides better protection for the developing zygote.
Development of Offspring

After fertilization, the zygote undergoes a series of divisions and differentiations to develop into a mature organism. The development can occur in different ways:

  • Oviparous Development: In this mode, eggs are laid outside the body, where they develop into young ones. Examples include birds and reptiles.
  • Viviparous Development: In this mode, the young develop inside the female's body and are born live. This is common in mammals.
  • Ovoviviparous Development: In this case, eggs develop inside the female’s body, but the young are nourished by the yolk rather than through a placenta, as seen in some species of sharks and reptiles.
Genetic Variation

One of the key advantages of sexual reproduction is the introduction of genetic variation among offspring. This variation arises due to:

  • Independent Assortment: During meiosis, the chromosomes are randomly distributed into gametes, leading to different combinations of genes.
  • Crossing Over: During meiosis, homologous chromosomes can exchange segments of DNA, further increasing genetic diversity.
  • Fertilization: The random combination of gametes from two parents results in unique genetic combinations in the offspring.
Reproductive Strategies

Different organisms have evolved various reproductive strategies to enhance their reproductive success. These include:

  • R-Strategists: These organisms produce a large number of offspring with low parental investment, like many fish and insects. They rely on external fertilization.
  • K-Strategists: These organisms produce fewer offspring but invest more time and resources in nurturing them, typical of mammals.
Role of Hormones

Hormones play a significant role in regulating sexual reproduction. They control the development of gametes, mating behaviors, and reproductive cycles. In mammals, hormones such as testosterone and estrogen are crucial for the development of secondary sexual characteristics and reproductive functions.

7.3-लैंगिक प्रजनन (Sexual Reproduction)

लैंगिक प्रजनन वह प्रक्रिया है जिसमें दो विशिष्ट लिंगों (पुरुष और महिला) से उत्पन्न युग्मज (गैमीट्स) का मिलन होता है। यह प्रजनन जीवों के आनुवंशिक गुणसूत्रों के मिश्रण से नई संतति का निर्माण करता है। इस प्रक्रिया में दो अभिभावकों के डीएनए का मिलाजुला होता है, जिससे संतति में आनुवंशिक विविधता उत्पन्न होती है।

लैंगिक प्रजनन की विशेषताएँ

लैंगिक प्रजनन में दो मुख्य प्रकार के युग्मज होते हैं:

  • पुरुष युग्मज (Sperm): यह पुरुष का युग्मज है, जो नर प्रजनन अंगों (अंडकोष) में उत्पन्न होता है।
  • महिला युग्मज (Egg): यह महिला का युग्मज है, जो मादा प्रजनन अंगों (अंडाशय) में उत्पन्न होता है।

जब ये दोनों युग्मज मिलकर निषेचन (fertilization) करते हैं, तो एक नई कोशिका (जैसे अंडाणु) का निर्माण होता है, जिसे युग्मज (zygote) कहते हैं। यह युग्मज धीरे-धीरे विभाजन के द्वारा एक नया जीव बनाता है।

निषेचन (Fertilization)

निषेचन वह प्रक्रिया है जिसमें पुरुष युग्मज और महिला युग्मज मिलकर युग्मज का निर्माण करते हैं। निषेचन के बाद, युग्मज में डीएनए का मिश्रण होता है और यह नए जीवन की शुरुआत करता है। निषेचन दो प्रकार का होता है:

  • बाहरी निषेचन (External Fertilization): इसमें निषेचन बाहरी वातावरण में होता है। यह आमतौर पर जलजन्तुओं (जैसे मछली, मेंढ़क) में पाया जाता है।
  • आंतरिक निषेचन (Internal Fertilization): इसमें निषेचन जीव के शरीर के अंदर होता है। यह प्रजनन पद्धति स्तनधारियों, पक्षियों, और रेप्टाइल्स में सामान्य है।
नवीन जीवन का विकास

निषेचन के बाद, युग्मज (zygote) विभाजन प्रक्रिया से कई कोशिकाओं में बदल जाता है। यह विभाजन प्रक्रिया क्रमशः दो, चार, आठ, और अधिक कोशिकाओं में होती है। इसके बाद ये कोशिकाएँ एक विशेष रूप में विकसित होती हैं, जिससे नया जीव बनता है। उदाहरण के तौर पर, इंसान में युग्मज का विभाजन और विकास भ्रूण (embryo) में होता है, जो धीरे-धीरे विकसित होकर एक नवजात शिशु (newborn) बनता है।

लैंगिक प्रजनन में गुणसूत्रों की संख्या

लैंगिक प्रजनन में युग्मजों के गुणसूत्रों की संख्या आधी होती है। उदाहरण के लिए, मानव में सामान्य गुणसूत्रों की संख्या 46 होती है। जब यह युग्मज मिलते हैं, तो उनकी कुल संख्या 46 हो जाती है। यदि हम इसे गणितीय रूप से व्यक्त करें, तो इसे निम्नलिखित प्रकार से लिखा जा सकता है:

गुणसूत्रों की संख्या = $2n$ (यहाँ $n$ गुणसूत्रों की संख्या है जो प्रत्येक युग्मज में होता है)

युग्मज मिलकर पुनः सामान्य गुणसूत्र संख्या $2n$ बनाते हैं।

लैंगिक प्रजनन में आनुवंशिक विविधता

लैंगिक प्रजनन में आनुवंशिक विविधता उत्पन्न होती है, क्योंकि यह गुणसूत्रों का मिश्रण करता है। जब दो विभिन्न व्यक्तियों के युग्मज मिलते हैं, तो संतति में आनुवंशिक गुणसूत्रों का मिश्रण होता है, जो उन्हें उनके माता-पिता से भिन्न बनाता है। इस प्रकार लैंगिक प्रजनन प्रकृति में विविधता और विकास का कारण बनता है।

How is the process of pollination different from fertilisation?

Solution:

Difference Between Pollination and Fertilisation

Pollination is the transfer of pollen grains from the male anther of a flower to the female stigma. It can occur through wind, water, or animals. This process is crucial for the reproduction of flowering plants. In contrast, fertilisation is the fusion of male and female gametes, which occurs after pollination. During fertilisation, the sperm cell from the pollen grain unites with the ovule, leading to the formation of a zygote. While pollination is an external process, fertilisation happens internally within the ovary of the flower.

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What is the role of the seminal vesicles and the prostate gland?

Solution:

Role of Seminal Vesicles and Prostate Gland

Seminal vesicles and the prostate gland play crucial roles in the male reproductive system. Seminal vesicles produce a fluid rich in sugars, proteins, and other substances, which nourish sperm and help form semen. This fluid makes up a significant portion of the semen volume. The prostate gland contributes additional fluids that enhance sperm motility and protect sperm from acidic environments. It also helps to expel semen during ejaculation. Together, these glands ensure optimal conditions for sperm viability and transport during reproduction.

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What are the changes seen in girls at the time of puberty?

Solution:

Changes in Girls at Puberty

During puberty, girls experience various physical and emotional changes. Physically, they develop breasts, and their hips widen, leading to a more adult body shape. Menstruation begins, marking the onset of the menstrual cycle. Additionally, there is an increase in body hair, including underarm and pubic hair. Hormonal changes can cause mood swings and emotional fluctuations. Skin may become oilier, and some may experience acne. Overall, these changes are part of the transition from childhood to adulthood, preparing girls for reproductive capability and maturity.

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How does the embryo get nourishment inside the mother’s body?

Solution:

Nourishment of Embryo in the Mother's Body

The embryo receives nourishment through the placenta, a specialized organ that forms during pregnancy. The placenta develops from the tissue of the embryo and attaches to the uterine wall. It facilitates the exchange of nutrients, gases, and waste products between the mother and the embryo. Maternal blood flows through the placenta, allowing nutrients like glucose, amino acids, and vitamins to pass to the embryo while removing waste materials like carbon dioxide. This exchange occurs through diffusion and active transport, ensuring the embryo’s growth and development throughout gestation.

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If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Solution:

Copper-T and Protection Against STDs

The Copper-T, a type of intrauterine device (IUD), is primarily used for contraception. It works by preventing sperm from fertilizing an egg and altering the uterine lining. However, it does not provide protection against sexually transmitted diseases (STDs). Unlike condoms, which create a barrier against pathogens, the Copper-T only prevents pregnancy. For effective protection against STDs, using barrier methods such as condoms in conjunction with the Copper-T is advisable. Regular health check-ups and discussions with a healthcare provider are essential for overall sexual health.

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