How do Organisms Reproduce-Exercise
Biology - Exercise
Q1. Asexual reproduction takes place through budding in
(a) Amoeba
(b) Yeast
(c) Plasmodium
(d) Leishmania
Asexual reproduction refers to the process where new organisms are produced from a single parent without the involvement of gamete fusion or sexual processes. One of the most common methods of asexual reproduction is budding.
Budding is a process in which a small part of the parent’s body grows out as a bud, gradually develops into a new individual, and eventually detaches to live independently. This form of reproduction is typically seen in organisms such as yeast.
Among the given options, yeast reproduces by budding. During this process, a small bulge appears on the yeast cell, enlarges, and separates as a new cell. The rest of the organisms mentioned, like Amoeba, Plasmodium, and Leishmania, use other methods of asexual reproduction such as binary fission or multiple fission.
Correct answer: (b) Yeast
Q2. Which of the following is not a part of the female reproductive system in human
beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
Answer:
The female reproductive system in humans consists of several organs responsible for the production of ova (egg cells), fertilization, and nurturing the developing embryo. Key parts of this system include the ovaries, uterus, and fallopian tubes.
- Ovary: Produces eggs and female hormones.
- Uterus: Provides a site for the growth and development of the embryo and fetus.
- Fallopian Tube: Transports eggs from the ovary to the uterus and is the site of fertilization.
On the other hand, the vas deferens is not a part of the female reproductive system. It is actually found in males, where it serves as the duct that carries sperm from the testes towards the urethra during ejaculation.
Correct answer: (c) Vas deferens
Q3. The anther contains
(a) sepals
(b) ovules
(c) pistil
(d) pollen grains
Answer:
In the flower of a plant, the anther is the part of the stamen which is responsible for producing and storing pollen. Pollen grains are the male reproductive cells needed for fertilization.
- Sepals: are the outermost part of the flower, protecting the bud before it opens.
- Ovules: are present within the ovary, which is a part of the pistil (female reproductive organ).
- Pistil: is the central female part of the flower, comprising ovary, style, and stigma.
Pollen grains are found inside the anther, which is a component of the stamen (male reproductive
organ).
Therefore, among the options, the correct answer is that the anther contains pollen grains.
Correct answer: (d) Pollen grains
Q4. What are the advantages of sexual reproduction over asexual reproduction?
Answer:
Sexual reproduction provides several important advantages compared to asexual reproduction:
- Genetic Variation: Sexual reproduction combines genetic material from two parents, resulting in offspring with unique traits and greater genetic diversity.
- Greater Adaptability: Increased genetic diversity enables populations to better adapt to diseases, environmental changes, and other threats.
- Evolutionary Advancement: Genetic recombination during sexual reproduction leads to new gene combinations, helping species evolve more rapidly.
- Reduced Risk of Harmful Mutations: Mixing genes from two parents lowers the chance of offspring inheriting disadvantageous traits in double dose.
- Dynamic Offspring: Offspring produced sexually are not identical copies, promoting diversity and innovation for long-term species survival.
In summary, sexual reproduction enhances species’ adaptability, evolution, and long-term health by increasing genetic diversity and minimizing the impact of harmful mutations.
Q5. What are the functions performed by the testis in human beings?
Answer:
In human beings, the testis is a vital organ of the male reproductive system. It performs two main functions:
- Production of Sperm: The testis is responsible for producing male gametes, called sperm, through a process known as spermatogenesis. Sperm are necessary for fertilizing the female egg during reproduction.
- Secretion of Testosterone: The testis also produces and releases the hormone testosterone. Testosterone controls the development of male secondary sexual characteristics, such as deepening of the voice, growth of facial and body hair, increased muscle mass, and maturation of reproductive organs. It also maintains male sex drive and supports sperm production.
In summary, the testis produces sperm for reproduction and secretes testosterone for the development and regulation of male features and reproductive health.
Q6. Why does menstruation occur?
Answer:
Menstruation occurs as a natural part of the female reproductive cycle. Every month, the uterus prepares itself to receive a fertilized egg by building up a thick, nutrient-rich lining called the endometrium. If fertilization does not happen—meaning no sperm meets the egg—there is no need for this extra lining.
As a result, the body breaks down and sheds the unused endometrial tissue along with blood and mucus through the vagina. This monthly process is called menstruation or a “period.” It usually lasts for a few days and marks the beginning of a new reproductive cycle.
In summary, menstruation occurs because the prepared uterine lining is not needed for pregnancy and is removed by the body so that a fresh cycle can begin the next month.
Q7. Draw a labelled diagram of the longitudinal section of a flower.
Answer:
- Petal: Brightly colored part that attracts pollinators.
- Anther: Produces pollen grains (male gametes).
- Filament: Supports the anther.
- Stigma: Receives pollen during pollination.
- Style: Connects stigma to ovary.
- Ovary: Contains ovules; site of fertilization.
- Ovule: Develops into seeds after fertilization.
- Sepal: Protects the flower bud.
Q8. What are the different methods of contraception?
Answer:
Contraception refers to the deliberate methods used to prevent pregnancy. The different methods include:
- Barrier Methods: Physically block sperm from reaching the egg, e.g., condoms, diaphragms, cervical caps.
- Hormonal Methods: Alter hormone levels to prevent ovulation or fertilization, e.g., oral contraceptive pills, patches, injections, implants.
- Intrauterine Devices (IUDs): Small devices like Copper-T placed in the uterus to prevent implantation of the fertilized egg.
- Surgical Methods (Sterilization): Permanent surgical procedures such as vasectomy (males) or tubectomy (females).
- Natural Methods: Avoiding intercourse during the fertile period or withdrawal before ejaculation, e.g., rhythm method, withdrawal method.
- Chemical Methods (Spermicides): Use of chemicals that kill or disable sperm before fertilization.
In summary, contraception can be achieved using barrier, hormonal, intrauterine, surgical, natural, or chemical methods. Some also help protect against sexually transmitted diseases.
Q9. How are the modes for reproduction different in unicellular and multicellular organisms?
Answer:
The modes of reproduction differ significantly between unicellular and multicellular organisms due to their level of organization and complexity:
- Unicellular Organisms: These are made of a single cell. Reproduction usually takes place by simple methods such as binary fission, budding, or multiple fission. The organism divides or develops a bud directly to produce offspring. Examples include bacteria (binary fission) and yeast (budding).
- Multicellular Organisms: These are made up of many
specialized cells.
Reproduction can be:
- Asexual: Methods like vegetative propagation, fragmentation, or spore formation. New individuals are formed from parts of the parent without gamete formation. Example: plants growing from cuttings.
- Sexual: Specialized cells called gametes (sperm and egg) are formed and fused together, leading to offspring with genetic variation. This process is more complex and ensures diversity.
In summary, unicellular organisms reproduce by simple cell division or budding, while multicellular organisms use both asexual and sexual reproduction, involving more specialized structures and processes.
Q10. How does reproduction help in providing stability to populations of species?
Answer:
Reproduction plays a crucial role in ensuring stability within populations of species. By allowing living organisms to produce new individuals, reproduction maintains the population size over time.
If organisms only lived out their lifespan without reproducing, their numbers would quickly decline, leading to the possible extinction of the species. Reproduction replenishes the population by replacing individuals lost due to death, disease, or predation.
Moreover, reproduction makes sure that the essential genetic traits and adaptations are passed on to new generations, helping species survive and thrive in changing environments. In this way, reproduction not only maintains population numbers but also supports the long-term survival and stability of species in nature.
Q11. What could be the reasons for adopting contraceptive methods?
Answer:
Contraceptive methods are adopted for several important reasons:
- Preventing Unwanted Pregnancy: To avoid unplanned pregnancies and have children when parents are ready.
- Controlling Family Size: Helps families plan the number and spacing of their children according to their resources and desires.
- Protecting Reproductive Health: Some methods, like condoms, protect against sexually transmitted diseases (STDs).
- Reducing Health Risks: Prevents frequent pregnancies, reducing complications and risks for mothers.
- Promoting Women's Well-being: Empowers women to make choices about their bodies, education, and careers.
- Population Control: Helps manage population growth, reducing pressure on resources like food, water, housing, and healthcare.
In summary, contraceptive methods prevent unwanted pregnancies, support responsible parenthood, protect against diseases, and promote social and economic well-being.
