Chapter 7 - How do organisms reproduce Class 10 Notes (Science)
Chapter 7 How do organisms reproduce Class 10 Notes (Science)
Updated Solution 2024-2025 Updated Solution 2024-2025
NCERT Solutions for (Science) Chapter 7- How do organisms reproduce Class 10 Notes, Question/Answers, Activity, Experiments & Projects
Chapter 7 How do organisms reproduce?
Questions
Q 1. What is the importance of DNA copying in reproduction?
Ans 1: Importance of DNA Copying in Reproduction:
- Genetic Continuity: DNA copying ensures that offspring inherit genetic information from their parents, maintaining the species’ traits.
- Genetic Variety: In sexual reproduction, copying of DNA results in a mix of genes from both parents, promoting diversity.
- Cell Division: DNA replication is crucial for creating new cells during growth, repair, and reproduction.
- Accurate Information Transfer: Proper DNA copying guarantees that genetic information is accurately passed on, avoiding mutations or diseases.
- Evolution: It allows small changes in DNA over generations, leading to evolution and adaptation to new environments.
Q 2. Why is variation beneficial to the species but not necessarily for the individual?
Ans 2: Variation is beneficial to a species because it increases the chances of survival in changing environments. When individuals in a species have different traits, some may be better suited to new challenges like climate change or disease. This helps the species as a whole continue to thrive. However, for an individual, having variations in traits doesn’t always guarantee survival or success, as it depends on the specific environment and circumstances they face. So, while variation benefits the species over time, it may not always directly help each individual.
Activity 7.1
- Dissolve about 10 gm of sugar in 100 mL of water.
- Take 20 mL of this solution in a test tube and add a pinch of yeast granules to it.
- Put a cotton plug on the mouth of the test tube and keep it in a warm place.
- After 1 or 2 hours, put a small drop of yeast culture from the test tube on a slide and cover it with a coverslip.
- Observe the slide under a microscope.
Ans: Activity 7.1 students do yourself with the help of teacher
[Hint solution of this Experiment]:
Activity 7.1 describes an experiment to observe the fermentation process carried out by yeast. Here’s a summary of the steps and what you might observe:
Materials Needed:
- 10 gm of sugar
- 100 mL of water
- 20 mL of the sugar-water solution
- Yeast granules
- Test tube
- Cotton plug
- Microscope and slide
Procedure:
- Prepare sugar solution: Dissolve about 10 gm of sugar in 100 mL of water to create a sugar solution.
- Yeast culture: Take 20 mL of the sugar solution and add a pinch of yeast granules. Yeast cells will use the sugar as a food source and begin fermentation.
- Set up fermentation: Cover the test tube with a cotton plug and place it in a warm environment for 1-2 hours. The warmth will encourage yeast activity and fermentation.
- Microscopic observation: After 1 or 2 hours, take a small drop of the liquid from the test tube and place it on a slide. Cover it with a coverslip and observe under the microscope.
Expected Observations:
- Under the microscope: You should observe yeast cells under the microscope. Yeast cells are unicellular fungi, and they may appear as small oval or round cells. In a fermentation setup, you might also see bubbles or gas pockets as a result of carbon dioxide being released during fermentation.
Yeast performs fermentation, converting sugar into ethanol and carbon dioxide. The presence of gas bubbles indicates that fermentation is occurring. The yeast cells themselves might appear as small, round or oval-shaped cells, and you may observe budding (a process where new yeast cells are formed) under the microscope.
What This Demonstrates:
- This activity demonstrates the process of fermentation where yeast converts sugar into alcohol (ethanol) and carbon dioxide in the absence of oxygen, a form of anaerobic respiration. It shows how living organisms like yeast can metabolize sugars and produce gas, which is used in baking and alcohol fermentation.
Q 1. Observe the slide under a microscope.
Ans 1: Observations:
- Under the microscope: You should observe yeast cells under the microscope. Yeast cells are unicellular fungi, and they may appear as small oval or round cells. In a fermentation setup, you might also see bubbles or gas pockets as a result of carbon dioxide being released during fermentation.
Yeast performs fermentation, converting sugar into ethanol and carbon dioxide. The presence of gas bubbles indicates that fermentation is occurring. The yeast cells themselves might appear as small, round or oval-shaped cells, and you may observe budding (a process where new yeast cells are formed) under the microscope
Activity 7.2
- Wet a slice of bread, and keep it in a cool, moist and dark place.
- Observe the surface of the slice with a magnifying glass.
- Record your observations for a week.
Ans: Activity 7.2: This activity helps demonstrate the growth of microorganisms, particularly mold, in a favorable environment. Here’s how you can record your observations:
Day 1 (Setup Day):
- Action: Wet the bread slice and place it in a cool, moist, and dark place (e.g., a closed container with a bit of water).
- Observation: The bread appears normal; no visible changes.
Day 2:
- Observation: Small white or gray spots might appear on the surface of the bread. These are initial signs of mold spores beginning to grow.
Day 3:
- Observation: The spots grow larger, and you may notice a fine white, green, or black fuzzy appearance on the surface.
Day 4:
- Observation: The mold becomes more prominent, with an increase in color variation (green, black, or yellow shades). The bread may also begin to emit a musty odor.
Day 5:
- Observation: Mold growth is widespread across the bread slice. The texture becomes more fuzzy or slimy depending on the moisture content.
Day 6:
- Observation: Mold continues to spread and thicken. The colors may darken or intensify.
Day 7:
- Observation: The entire surface is likely covered with mold. The bread may appear deteriorated, and the odor is more intense.
Conclusions:
- Mold thrives in moist, dark, and cool environments.
- Mold growth is visible within 24–48 hours in such conditions.
- Mold species vary in color and texture, depending on environmental conditions.
Safety Note: Avoid touching the mold with bare hands and dispose of the bread carefully after completing your observations. Mold spores can be allergenic or harmful when inhaled.
Activity 7.3
- Observe a permanent slide of Amoeba under a microscope.
Ans: Observation 1: Permanent Slide of Amoeba
- Appearance: The Amoeba appears as an irregular, jelly-like structure. Its shape is constantly changing because it moves using pseudopodia (temporary extensions of its cytoplasm).
- Visible Features:
- The nucleus (a darker circular or oval structure) is prominent.
- The cytoplasm appears as a clear, granular fluid.
- Pseudopodia are seen extending outward, helping in movement and capturing food.
- Similarly observe another permanent slide of Amoeba showing binary fission.
Ans: Observation 2: Permanent Slide of Amoeba Undergoing Binary Fission
- Appearance: The Amoeba looks as though it is dividing into two parts. This is because it is undergoing binary fission, a method of asexual reproduction.
- Visible Features:
- The nucleus is splitting into two, and the cytoplasm is also dividing.
- Two nearly identical halves are forming, each becoming a new Amoeba.
- The overall structure appears elongated as the organism prepares for complete division.
- Now, compare the observations of both the slides.
Ans: Comparison of Both Slides
| Feature | Normal Amoeba | Amoeba Undergoing Binary Fission |
| Shape | Irregular, constantly changing shape | Elongated, preparing to divide |
| Nucleus | Single, prominent nucleus | Splitting into two nuclei |
| Cytoplasm | Uniform and granular | Dividing along with the nucleus |
| Activity | Engaged in movement or feeding | Focused on reproduction |
Key Differences:
- In the first slide, the Amoeba is in its normal state, while in the second, it is actively reproducing.
- The splitting of the nucleus and cytoplasm is a defining feature of the second slide, indicating binary fission.
This comparison helps us understand how Amoeba reproduces through binary fission, ensuring its survival and population growth.
Activity 7.4
- Collect water from a lake or pond that appears dark green and contains filamentous structures.
- Put one or two filaments on a slide.
- Put a drop of glycerin on these filaments and cover it with a coverslip.
- Observe the slide under a microscope.
Ans: When you observe the slide under a microscope, you will see the following key features of Spirogyra:
- Filamentous Structure: Long, unbranched filaments composed of cylindrical cells arranged end to end.
- Cell Wall:
- A distinct double-layered structure.
- The outer layer appears slimy due to its pectic composition, while the inner layer is made of cellulose.
- Spiral Chloroplasts: The most defining feature of Spirogyra. The chloroplasts are arranged in a spiral shape, often containing small pyrenoids.
- Cytoplasm and Nucleus:
- The cytoplasm lines the cell walls.
- The nucleus is visible, suspended in the center by strands of cytoplasm.
- Absence of Differentiated Tissues: The cells lack specialization seen in higher plants, emphasizing their simpler structure.
These observations illustrate the unique structural simplicity and efficiency of Spirogyra as a photosynthetic organism.
- Can you identify different tissues in the Spirogyra filaments?
Ans: No, Spirogyra filaments do not have differentiated tissues. Each filament is composed of identical, cylindrical cells arranged end to end. These cells are specialized for basic functions such as photosynthesis and growth but do not exhibit tissue-level differentiation like higher plants.
Activity 7.5
- Take a potato and observe its surface. Can notches be seen?
- Cut the potato into small pieces such that some pieces contain a notch or bud and some do not.
- Spread some cotton on a tray and wet it. Place the potato pieces on this cotton. Note where the pieces with the buds are placed.
- Observe changes taking place in these potato pieces over the next few days. Make sure that the cotton is kept moistened.
Ans: Observing Changes in Potato Pieces
Observations Over the Next Few Days:
- Potato Pieces with Buds:
- Green shoots will begin to emerge from the buds within 3-5 days.
- Small roots may also start to grow downward into the moist cotton.
- The buds show clear signs of growth, indicating active cellular activity.
- Potato Pieces without Buds:
- No visible changes or growth occur.
- The pieces remain the same, indicating that they lack the structures (buds) necessary for sprouting.
Importance of Keeping Cotton Moistened:
- Moist cotton ensures that the potato pieces remain hydrated, which is essential for the buds to sprout.
- Without adequate moisture, the process of vegetative propagation would be hindered as the buds would dry out and fail to grow.
Regular monitoring and maintaining the moisture level are crucial for the success of this activity.
- Which are the potato pieces that give rise to fresh green shoots and roots?
Ans: The potato pieces that give rise to fresh green shoots and roots are those that contain buds, also known as “eyes.” These buds contain meristematic cells that promote growth and regeneration.
Activity 7.6
- Select a money-plant.
- Cut some pieces such that they contain at least one leaf.
- Cut out some other portions between two leaves.
- Dip one end of all the pieces in water and observe over the next few days.
Q 1: Which ones grow and give rise to fresh leaves?
Ans 1: The cuttings that have at least one leaf are more likely to grow and give rise to fresh leaves. The presence of leaves allows the cutting to produce energy through photosynthesis, which supports root development and the growth of new shoots.
Q 2: What can you conclude from your observations?
Ans 2: From the observations, it can be concluded that the cuttings with at least one leaf are more likely to propagate successfully, as the leaves provide essential energy for the plant through photosynthesis. This energy helps the cuttings to develop roots and eventually sprout new leaves. On the other hand, the stem cuttings without leaves are less likely to root or grow, as they lack the energy produced by photosynthesis, which is crucial for the growth process. Therefore, for better propagation success, it’s important to include leaves on the cuttings.
Questions
Q 1. How does binary fission differ from multiple fission?
Ans 1: Binary fission and multiple fission are both ways organisms reproduce, but they happen a little differently:
- Binary fission: One single cell splits into two identical cells. This happens in simpler organisms like bacteria and amoebas. It’s like a cell making a copy of itself and then dividing into two.
- Multiple fission: One cell splits into many smaller cells at once. This is common in some single-celled organisms like plasmodium (which causes malaria). It’s like one cell splitting into several parts, all at the same time.
So, the key difference is that binary fission creates two cells, while multiple fission produces many cells in one go!
Q 2. How will an organism be benefited if it reproduces through spores?
Ans 2: Reproducing through spores helps an organism in several ways! Spores are tiny, lightweight, and can travel long distances, so the organism can spread to new places easily. They don’t need a mate to reproduce, which makes reproduction faster. Spores can also survive in tough conditions like drought or extreme temperatures, allowing the organism to keep going even in harsh environments. This way, the organism has a better chance of thriving and spreading.
Q 3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Ans 3: More complex organisms, like humans or animals, can’t regenerate new individuals because their cells are specialized for specific jobs (like muscle cells, nerve cells, etc.). Unlike simpler organisms, which have less specialized cells that can turn into any type of cell, complex organisms have different body parts that work together. So, if one part is lost or damaged, the body can heal it, but it can’t grow a whole new individual from scratch. Regeneration in complex organisms is limited to repairing or replacing damaged parts, not creating a whole new organism.
Q 4. Why is vegetative propagation practised for growing some types of plants?
Ans 4: Vegetative propagation is used to grow certain plants because it allows for quicker and more reliable reproduction. Instead of growing from seeds, new plants are produced from parts of the parent plant, like stems, roots, or leaves. This method ensures that the new plants have the same traits as the parent, which is important for plants that need specific characteristics (like fruit quality). It’s also useful for plants that don’t grow well from seeds or have a long germination time. This method is faster and more efficient for farmers and gardeners.
Q 5. Why is DNA copying an essential part of the process of reproduction?
Ans 5: DNA copying is essential in reproduction because it ensures that the offspring inherit genetic information from their parents. When organisms reproduce, their cells divide to create new ones. During this process, DNA is copied so that each new cell has the same instructions (genes) as the parent cell. This allows the offspring to grow and develop with the traits passed down, making DNA copying crucial for life to continue in a similar form from one generation to the next.
Chapter 7 – How do organisms reproduce Class 10 Notes, Question/Answer, Activity & Projects
Updated Solutions 2024-2025
Activity 7.7
- Soak a few seeds of Bengal gram (chana) and keep them overnight.
- Drain the excess water and cover the seeds with a wet cloth and leave them for a day. Make sure that the seeds do not become dry.
- Cut open the seeds carefully and observe the different parts.
- Compare your observations with the Fig. 7.9 and see if you can identify all the parts.
Ans: (Activity 7.7)
Activity 7.7 is a practical exploration of seed structure and germination, commonly included in biology lessons for understanding the anatomy and physiology of seeds. Here’s a step-by-step breakdown:
Steps in Activity:
- Soaking the Seeds:
- Take a few seeds of Bengal gram (chana) and soak them in water overnight to soften the seed coat and initiate germination.
- Draining and Wrapping:
- The next day, drain the excess water.
- Wrap the seeds in a wet cloth, ensuring the cloth stays moist but not waterlogged.
- Leave them for another day in a warm, ventilated spot.
- Cutting Open the Seeds:
- After this period, carefully cut open the softened seeds lengthwise using a blade or knife.
- Observing the Parts:
- Observe the seed’s internal structure.
- Compare your observations with Fig. 7.9 (typically a diagram of a seed in a textbook). Key parts to identify include:
- Seed coat: The outer protective covering.
- Cotyledons: The seed leaves, often large and storing nutrients.
- Embryo: The developing plant, comprising:
- Radicle: The part that develops into the root.
- Plumule: The part that develops into the shoot.
Expected Observations:
- The seed coat will be the thin, outer layer you peel off.
- Inside, you’ll find the cotyledons, which are fleshy and store food for the growing plant.
- The radicle and plumule will be tiny, with the radicle pointing downward and the plumule upward.
Questions
Q 1. How is the process of pollination different from fertilizations?
Ans 1: Pollination vs. Fertilization
- Pollination: It is the transfer of pollen grains from the male part (anther) of a flower to the female part (stigma). This is usually done by wind, water, or animals.
- Fertilization: It happens after pollination, when the male cell from the pollen combines with the female egg in the ovule to form a seed.
In short, pollination is about transferring pollen, while fertilization is about the actual union of male and female cells to create new life.
Q 2. What is the role of the seminal vesicles and the prostate gland?
Ans 2: The seminal vesicles and prostate gland are key players in the male reproductive system.
- Seminal Vesicles: These glands produce a sugary fluid that provides energy for sperm to move and survive. This fluid makes up a large part of semen.
- Prostate Gland: It produces a milky fluid that helps protect and nourish sperm, making it easier for them to swim effectively.
Together, they create a supportive environment for sperm to fertilize an egg.
Q 3. What are the changes seen in girls at the time of puberty?
Ans 3: During puberty, girls experience physical and emotional changes as their bodies mature. Here are the key changes:
- Breast development – Breasts begin to grow.
- Body shape changes – Hips widen, and body fat increases in areas like hips and thighs.
- Growth spurt – A rapid increase in height and weight.
- Hair growth – Hair appears under the arms and in the pubic area.
- Menstruation starts – Monthly periods begin, indicating reproductive maturity.
- Skin changes – Oily skin and pimples may occur.
- Emotional changes – Mood swings and increased sensitivity due to hormonal changes.
Q 4. How does the embryo get nourishment inside the mother’s body?
Ans 4: The embryo gets nourishment inside the mother’s body through the placenta. The placenta is an organ that forms during pregnancy and connects the mother’s blood supply to the embryo. It allows the transfer of nutrients, oxygen, and waste products between the mother and the developing baby. The mother’s blood carries food and oxygen, which pass through the placenta to the embryo, helping it grow. At the same time, the placenta removes waste products from the embryo’s blood and sends them back to the mother’s body to be eliminated.
Q 5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Ans 5: No, using a copper-T (intrauterine device or IUD) does not protect against sexually transmitted diseases (STDs). It only helps in preventing pregnancy. To reduce the risk of STDs, condoms should be used along with the copper-T.
Exercise
Q 1. Asexual reproduction takes place through budding in:
(a). Amoeba
(b). Yeast
(c). Plasmodium
(d). Leishmania
Ans 1: (b) Yeast: Asexual reproduction through budding is a process where a new individual develops from an outgrowth or bud on the parent organism. This is commonly observed in yeast, a unicellular fungus. The bud grows, matures, and eventually detaches to form a new organism.
Q 2. 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
Ans 2: (c). Vas deferens: Part of the male reproductive system, responsible for carrying sperm from the testes to the urethra.
Q 3. The anther contains:
(a)sepals
(b)ovules
(c)pistil
(d)pollen grains
Ans 3: (d) pollen grains: The anther is the part of the stamen (male reproductive organ of a flower) that produces and contains pollen grains, which are the male gametophytes responsible for fertilization.
Q 4. What are the advantages of sexual reproduction over asexual reproduction?
Ans 4: Advantages of Sexual Reproduction over Asexual Reproduction:
- Genetic Diversity: Sexual reproduction mixes genes from two parents, creating unique offspring. This helps populations adapt better to changing environments.
- Improved Survival: Genetic variation reduces the risk of entire populations being wiped out by diseases or environmental changes.
- Elimination of Harmful Mutations: Harmful traits are less likely to persist over generations due to gene reshuffling.
- Better Adaptation: Over time, it supports evolution, helping species develop traits that improve survival and reproduction.
Q 5. What are the functions performed by the testis in human beings?
Ans 5: The testes in human beings have two main functions:
- Sperm Production: The testes produce sperm, which are the male reproductive cells needed for fertilizing the female egg.
- Hormone Production: They also produce testosterone, the primary male hormone, which is responsible for the development of male characteristics like muscle mass, body hair, and deep voice.
Q 6. Why does menstruation occur?
Ans 6: Menstruation happens because the body is preparing for a possible pregnancy each month. The uterus builds up a lining to support a fertilized egg. If no egg is fertilized, the body sheds this lining, which leaves the body as blood through the vagina. This process is a natural part of the menstrual cycle and typically lasts 3-7 days. It helps keep the reproductive system healthy and ready for pregnancy if it happens.
Q 7. Draw a labelled diagram of the longitudinal section of a flower.
Ans 7:
Q 8. What are the different methods of contraception?
Ans 8: Contraception methods are ways to prevent pregnancy. Here are the main types:
- Barrier methods: These block sperm from reaching the egg. Examples include condoms, diaphragms, and cervical caps.
- Hormonal methods: These use hormones to regulate or stop ovulation. Examples include birth control pills, patches, injections, and implants.
- Intrauterine Devices (IUDs): These are small devices placed in the uterus to prevent pregnancy. There are hormonal and copper IUDs.
- Permanent methods: These are surgical options like sterilization, where the reproductive organs are permanently altered to prevent pregnancy.
- Natural methods: These involve tracking fertility and avoiding sex during fertile times, such as the rhythm method or withdrawal.
- Emergency contraception: These pills can be used after unprotected sex to prevent pregnancy.
Q 9. How are the modes for reproduction different in unicellular and multicellular organisms?
Ans 9: In unicellular organisms, reproduction usually happens through a process called asexual reproduction, like binary fission, where the single cell divides to create two identical cells.
In multicellular organisms, reproduction can be asexual (like in plants or some animals through processes like budding) or sexual (involving the combination of male and female cells, such as sperm and egg, to create offspring with a mix of both parents’ traits).
So, unicellular organisms mainly reproduce by dividing into two, while multicellular organisms have more varied ways, including both asexual and sexual methods.
Q 10. How does reproduction help in providing stability to populations of species?
Ans 10: Reproduction helps maintain stability in populations by ensuring that new individuals are born to replace those that die. This continuous cycle allows species to survive even when environmental conditions change. If a species didn’t reproduce, it could eventually go extinct. By reproducing, species can adapt to their surroundings and keep their population numbers balanced, which helps sustain the ecosystem.
Q 11. What could be the reasons for adopting contraceptive methods?
Ans 11: Adopting contraceptive methods can be influenced by several factors, such as:
- Family Planning: Couples may want to control the number and timing of their children.
- Health Reasons: Contraceptives can help avoid pregnancy-related health risks.
- Financial Stability: Raising children can be expensive, and contraception allows for better financial planning.
- Personal Choice: Individuals may want to focus on career, education, or personal goals before starting a family.
- Preventing Unwanted Pregnancies: Contraceptives help avoid accidental pregnancies.
- Health Benefits: Some methods can help with medical conditions like irregular periods or endometriosis.
Chapter 7 – How do organisms reproduce Class 10 Notes, Question/Answer, Activity & Projects
Updated Solution 2024-2025
This complete solution is prepared as per the latest syllabus of 2024-25. If you have any further queries, feel free to ask! 