Class 10 Science Chapter 7 – How Do Organisms Reproduce?

Key Concept: Complexity and Reproduction, DNA Control

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] The assertion correctly states that meiosis produces gametes with half the chromosome number, thus maintaining a stable chromosome count across generations when fertilization occurs. The reason is also true; meiosis leads to genetic variation through mechanisms like crossing over and independent assortment. However, while both statements are true, the process described in the reason (genetic variation) does not directly explain the prevention of chromosome doubling, which is explicitly addressed by the halving of chromosome number in gametes.

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Key Concepts: DNA and Proteins

b) Different proteins are synthesized.

[Solution Description] An alteration in the DNA sequence can change the information required for protein synthesis. This may lead to different proteins being formed, as the sequence of amino acids in a protein is determined by the order of nucleotides in DNA.

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Key Concept: Variation Accumulation Impact, Reproductive Strategy

b) They create novel combinations of traits, aiding adaptation
[Solution Description] In sexual reproduction, each generation inherits a combination of genetic variants from both parents, accumulating variations over time. This accumulation leads to increased genetic diversity across generations, allowing populations to adapt to new challenges such as environmental changes or diseases. The varied genetic makeup enhances resilience against extinction threats, thereby playing a critical role in evolutionary success.

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Key Concept: Comparative Analysis, Real-world Application

d) Condoms
[Solution Description]
Given the need to address both pregnancy prevention and STI protection, we must choose a method that provides an effective barrier against infections while also preventing fertilization. Condoms are the only contraceptive method that serves as a physical barrier, thereby reducing the risk of STIs along with preventing pregnancy. They do not require medical intervention for use, making them accessible even in resource-limited settings.

Notes

Reproduction methods vary among organisms, categorized into asexual and sexual reproduction. Asexual reproduction (e.g., binary fission, budding) is rapid, requires a single parent, and produces genetically identical offspring, suitable for stable environments. Sexual reproduction involves two parents, combining genetic material to create diverse offspring, advantageous in changing environments.

In real life, understanding reproduction aids in agriculture, cloning, and genetic research. For instance, artificial vegetative propagation enhances crop yields, while knowledge of human reproduction informs family planning and fertility treatments. Additionally, controlling the reproduction of pests and endangered species helps balance ecosystems and conserve biodiversity.

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Key Concept: Comparative Evolution, Structural Role

c) Regeneration in Planaria showcases advanced cellular differentiation while Hydra’s budding emphasizes rapid reproduction.
[Solution Description] In Planaria, regeneration involves complex reorganization where specialized cells can form new tissues and organs, an example of higher cellular complexity and adaptability, allowing survival through severe injuries. Hydra’s budding is simpler, using localized growth at one site, showing less cellular complexity, but still offers rapid reproduction advantages. Evolutionarily, both processes illustrate adaptations to environmental challenges, yet Planaria shows more advanced regenerative capabilities compared to Hydra’s simpler budding method.

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Key Concept: Real-world Application, Pollination Efficiency

c) Introduce bee colonies to promote effective pollen transfer.
[Solution Description]
To maximize fruit production, the farmer must ensure effective cross-pollination. Introducing bees can significantly enhance this process, as bees are efficient pollinators that facilitate pollen transfer between flowers, improving fertilization rates. Additionally, planting compatible varieties nearby can increase pollination chances.

– Optimizing Yield: Employ pollinators like bees for enhanced pollen transfer.
– Consideration: Encourage biodiversity with compatible plant varieties.

Options must present logical solutions addressing both pollination efficiency and possible impediments.

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Key Concept: Basic Definition

a) Budding
[Solution Description] The process where a new individual grows as an outgrowth in Hydra is known as budding. It involves repeated cell division at a specific site, leading to the formation of a bud that eventually detaches to become an independent organism.

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Key Concept: Critical Analysis, Genetic Implications

d) Uniform genetic makeup can increase susceptibility to specific pathogens affecting the entire population.
[Solution Description] Although tissue culture allows rapid and disease-free production, the key drawback is genetic uniformity among propagated plants. This poses risks such as vulnerability to pests or diseases that can affect all clones similarly. Over-reliance on genetically identical plants reduces resilience to environmental stresses and might lead to significant crop losses if an unforeseen pathogen emerges.

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Key Concept: Hormonal Influence, Environmental Conditions

b) Auxins; Controlled environment prevents bacterial contamination.
[Solution Description] In tissue culture, auxins play a critical role in promoting cell division and growth. Specific environmental conditions such as temperature, humidity, and light intensity must be carefully controlled to ensure successful differentiation and growth of plantlets. Variations in these conditions can hinder or alter the intended outcomes of the tissue culture process.

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Key Concept: In-Depth Process Analysis, Advanced Reasoning

a) Regenerative cells divide and form a mass that forms a bud at a specific site
[Solution Description] The budding process in Hydra involves the development of a bud from regenerative cells at a specific site. These cells undergo repeated cell division to form a small outgrowth. As the cells proliferate, they differentiate into tissues required for the new organism, eventually detaching and growing independently as a mature Hydra.

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Key Concept: Fertilisation Pathway, Seed and Fruit Advantages

c) A pollen tube grows through the style to the ovule; seeds protect the embryo and aid in dispersal.
[Solution Description] After pollination, the pollen grain lands on the stigma of the flower. A pollen tube grows from the pollen grain through the style and reaches the ovary where it enters an ovule, facilitating fertilisation by allowing the male gamete to fuse with the female gamete. The formation of seeds provides several advantages: they protect the embryo, enable dormancy during unfavorable conditions, and facilitate dispersal to new locations, thus ensuring species survival and colonization.

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Key Concept: Basic Definition

b) Budding
[Solution Description] In Hydra, reproduction occurs through a process known as budding. During this process, a bud forms on the body of the parent organism. This bud develops into a small individual, which eventually detaches from the parent and grows into an independent organism. This is a form of asexual reproduction.

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Key Concept: Ethical Dilemmas

b) Balancing effectiveness with personal health impacts
[Solution Description] Individuals using contraceptives that alter hormonal balance may face ethical dilemmas related to potential side effects versus their benefits. Decisions must weigh health risks against preventing unintended pregnancies.

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Key Concept: Advanced Contraceptive Methods, Disease Transmission

b) By creating a physical barrier preventing sperm and disease pathogen exchange
[Solution Description] Condoms act as a barrier method of contraception by physically blocking sperm from entering the uterus, thus preventing pregnancy. Additionally, they create a protective layer that reduces skin-to-skin contact during intercourse, thereby decreasing the transmission risk of sexually transmitted infections (STIs), including bacterial and viral pathogens.

Notes

Key Concept: Ethical Considerations, Real-World Application

b) Increased agricultural yield at the expense of ecosystem balance.
[Solution Description] Spore formation in Rhizopus presents several ethical considerations when applied commercially. One concern is the potential for genetically modified spores to escape into the wild and potentially disrupt local ecosystems, which may threaten biodiversity. Additionally, the large-scale cultivation may lead to resource allocation issues, where resources could otherwise support more sustainable practices. These concerns must be weighed against the benefits Rhizopus provides in industrial fermentation and enzyme production.

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Key Concept: Real-World Application, Regeneration

b) In a fluctuating environment with frequent predation and physical damage.
[Solution Description] Regeneration, like that observed in organisms such as Hydra and Planaria, allows individuals to recover from physical injuries by regrowing lost parts, effectively creating new individuals if needed. In an environment with frequent disturbances or predators, this ability can ensure survival and continuity of the species even when individuals are partially consumed or damaged.

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Key Concept: Advanced Comparison, Critical Evaluation

d) Grafting offers greater genetic uniformity and is generally quicker.
[Solution Description] Grafting will offer higher genetic uniformity because it attaches the desired rose variety onto a rootstock, ensuring that the scion’s characteristics dominate. Layering may take longer as it involves rooting stems still attached to the mother plant, possibly introducing more variability. Therefore, grafting is quicker and maintains genetic uniformity better than layering.

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Key Concept: Real-World Application, Long-Term Evolution

c) Natural selection favors birds with strong beaks; these traits become prevalent over generations.
[Solution Description]

With the shift in available food resources from insects to seeds, birds with traits suited to seed consumption will have a survival advantage. Birds possessing stronger beaks capable of cracking seeds are more likely to survive and reproduce.

– Step 1: Note the environmental change impacting food availability (from insects to seeds).
– Step 2: Identify necessary trait changes such as beak strength to exploit new food resources.
– Step 3: Birds with stronger beaks would be naturally selected for survival and reproduction.
– Step 4: Over many generations, the frequency of strong-beaked individuals increases, illustrating evolution driven by natural selection.

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Key Concept: Concept Integration, Critical Thinking

b) By halving the chromosome number in gametes before they unite.
[Solution Description] Meiosis is a specialized form of cell division that reduces the number of chromosomes by half, producing gametes (sperm and egg cells) with only one set of chromosomes each. When these gametes fuse during fertilisation, the resultant zygote has two sets of chromosomes, re-establishing the organism’s characteristic chromosome number without doubling it. This mechanism prevents the continuous doubling of DNA content across generations.

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Key Concept: Detailed Process Analysis, Advanced Reasoning

b) It helps in converting proliferating cells into different cell types necessary for forming tissues and organs.
[Solution Description] After initial cell proliferation at the site of injury in Planaria, specialized cells undergo a process called differentiation where these undifferentiated cells transform into various types of functional cells needed to reconstruct the missing body parts. This is crucial because it allows the mass of proliferating cells (blastema) to form specific tissues and organs required for complete organismal regeneration.

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Key Concepts: Health Consequences

c) HIV/AIDS

[Solution Description] Condoms are effective in preventing many sexually transmitted diseases (STDs), such as HIV/AIDS, gonorrhea, and chlamydia, by creating a barrier that reduces exposure.

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Key Concept: Societal Impact, Ethical Dilemmas

c) By promoting family planning awareness and legal safeguards
[Solution Description] Societal pressure such as the expectation to have children or avoid them due to governmental policies can affect contraceptive choices. Ethical dilemmas arise in cases like sex-selective abortions where contraception misuse occurs. Legal measures, like banning prenatal gender tests, aim to maintain gender ratios, showing societal impact.
The solution indicates that both social norms and ethical considerations would heavily sway people’s decisions on whether to use contraceptives and how they choose among them.

Notes

Advancements in reproductive technologies, such as in vitro fertilization (IVF), cloning, and genetic engineering, have transformed reproductive health and practices. These innovations allow individuals and couples facing infertility to have children and offer potential solutions for genetic disorders. However, they raise significant ethical dilemmas, including concerns over genetic manipulation, cloning, and the morality of creating “designer babies.” There is a debate over the societal implications, including the potential for exploitation, inequality, and loss of genetic diversity. Ethical questions also focus on the rights of children born through assisted reproductive technologies and the long-term impact on society.

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Key Concept: Hormonal Regulation, Uterine Changes

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the menstrual cycle is regulated by hormones from the ovaries, which include estrogen and progesterone, while also involving changes in the uterine structure. This is accurate because these hormones play a crucial role in coordinating the various steps of the menstrual cycle, including egg maturation and release, as well as preparing the uterus for possible pregnancy.

The reason asserts that estrogen specifically causes the uterine lining to thicken. This is also true; during the follicular phase of the menstrual cycle, rising levels of estrogen lead to the proliferation of the endometrial tissue, thus thickening the uterine lining.

Therefore, both the assertion and the reason are true, and the reason correctly explains why the assertion is valid. The reasoning provided fits the context of hormonal regulation and its effect on uterine changes during the menstrual cycle.

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Key Concept: Real-World Application, Comparative Lifecycle

b) Maintaining low humidity prevents Rhizopus but not yeast growth.
[Solution Description] Controlling mold growth, like that of Rhizopus, relies on understanding spore formation. Rhizopus forms spores that remain dormant until favorable moisture conditions exist. In comparison to yeast which reproduces via budding, Rhizopus requires environmental triggers for spore germination. Control measures typically involve keeping storage areas dry to prevent spore activation. Understanding these differences allows for targeted approaches in managing fungal infestations in various settings.

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Key Concept: Evolutionary Advantage, Genetic Implications

b) It introduces genetic variations that enhance adaptability and survival in changing environments.
[Solution Description] Sexual reproduction offers significant evolutionary advantages due to its ability to increase genetic variation within a population. This increased variability provides a broader range of traits for natural selection to act upon, thus improving a species’ adaptability to changing environments and resilience to diseases or adverse conditions. In contrast, asexual reproduction produces genetically identical offspring, limiting the potential for adaptation.

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Key Concept: Reproductive Systems: Tests knowledge of male and female reproductive systems

c) Fallopian Tubes
[Solution Description] Fertilization in humans occurs in the fallopian tubes. After sperm is introduced into the vagina, it travels through the cervix and uterus to reach the fallopian tube where it meets the egg for fertilization.

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Key Concept: Evolutionary Advantage, Menstrual Cycle Disorders

c) It prepares the body for pregnancy; dysmenorrhea reflects intense uterine contractions.
[Solution Description] Menstruation allows for the shedding of the uterine lining when pregnancy doesn’t occur, preparing the body for future fertilization opportunities. Dysmenorrhea, painful periods, can be linked to prostaglandin production that aids in contracting the uterus to shed its lining, though excessive contractions cause pain.

Notes

Reproduction is essential for the continuation of a species. Sexual reproduction, involving the fusion of male and female gametes, provides genetic diversity, which increases the chances of survival in changing environments. This diversity offers an evolutionary advantage as it allows populations to adapt to new challenges, such as diseases or climate changes, ensuring the survival of the species.

Menstrual Cycle Disorders
Menstrual cycle disorders include irregular periods, excessive bleeding, or absence of menstruation. Common causes are hormonal imbalances, stress, PCOS (Polycystic Ovary Syndrome), or thyroid issues. Treatment varies depending on the cause, ranging from lifestyle changes to medications like hormonal therapy or surgical options in severe cases.

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Key Concept: Reproductive Organ Differences, Pollination Mechanisms

c) Results in specialized organ structures coordinating effective pollination strategies.
[Solution Description] Specialized male and female gametes necessitate adaptations in reproductive organs and pollination strategies. Male organs develop traits to facilitate pollen dispersal, while female organs evolve to optimize pollen reception and fertilization, often leading to diverse flower structures and various pollination methods such as wind or animal assistance.

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Key Concept: Real-World Application, Advanced Conceptual Understanding

c) Grafted plants flower and fruit sooner than seed-grown ones, providing quicker agricultural yields.
[Solution Description] Vegetative propagation offers several advantages over seed germination. Grafting allows farmers to produce plants that mature faster and bear fruit earlier than those grown from seeds due to bypassing juvenile growth stages. Additionally, grafted plants are genetically identical to the parent plant, ensuring uniformity in crop quality and characteristics, which is beneficial for commercial farming. This technique also aids in propagating plants that do not reproduce effectively through seeds.

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Key Concept: Concept Understanding

b) Disease-free growth
[Solution Description] Tissue culture allows for the clonal propagation of plants under controlled disease-free conditions, leading to rapid production of large numbers of identical plants.

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Key Concept: Reproduction and Stability

c) By passing genes to future generations, allowing adaptation.
[Solution Description] Reproduction contributes to population stability by ensuring the continuous presence of individuals within a species. Through both sexual and asexual reproduction, genetic material is passed on to successive generations, enabling adaptation to environmental changes and promoting genetic diversity, which aids in survival over long periods.

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Key Concept: Comparative Regeneration, Regeneration Mechanism

b) Planaria’s reliance on neoblasts for rebuilding tissue architecture
[Solution Description] While both Hydra and Planaria exhibit regeneration, Planaria’s process involves highly organized cell proliferation and differentiation into complex structures, making it more intricate than Hydra, whose budding relies on simpler regenerative cells.

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Key Concept: Structural Integration

d) Urethra
[Solution Description] In the male reproductive system, the urethra serves as a common channel for both urine and sperm to exit the body. It connects to the bladder and also receives sperm from the vas deferens.

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