Class 10 Biology - How do Organisms Reproduce

Activities

Activity 7.1: Growth of Yeast and Bread Mould

Aim/Objective: To observe and compare the modes of asexual reproduction in yeast and bread mould.

Materials Required:

• Sugar, Water, Yeast granules
• Test tube, Slide, Coverslip, Microscope
• Slice of bread, Magnifying glass, Cool moist dark place

Procedure:

1. Dissolve 10g sugar in 100mL water and add yeast granules to 20mL of this solution in a test tube.
2. Plug the test tube with cotton and keep it in a warm place for 1-2 hours.
3. Observe a drop of the yeast culture under a microscope.
4. Moisten a bread slice and keep it in a cool, moist, and dark place for a few days.
5. Observe the surface of the bread with a magnifying glass daily for a week.

Observation:

• In the yeast culture, tiny tiny bulb-like projections (buds) are seen coming out of the yeast cells.
• On the bread, thread-like structures (hyphae) and tiny blobs (sporangia) are observed.

Explanation:

• Yeast reproduces asexually through budding. A small bud develops on the parent cell, which grows and eventually detaches to form a new individual. This process is rapid and efficient for unicellular organisms.
• Bread mould (Rhizopus) reproduces asexually through spore formation. Spores are produced within sporangia and are protected by thick walls. These spores are dispersed by air and germinate on contact with a suitable moist surface.

Conclusion:

• Yeast and bread mould use different asexual methods (budding and spore formation) to reproduce rapidly in favourable conditions.

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Activity 7.3: Binary Fission in Amoeba

Aim/Objective: To observe the process of binary fission in a unicellular organism.

Materials Required:

• Permanent slides of Amoeba and Amoeba showing binary fission
• Compound microscope

Procedure:

1. Observe a slide of a normal Amoeba cell under the microscope.
2. Switch the slide to one showing Amoeba in the process of binary fission.
3. Compare the two slides, noting the changes in the nucleus and cytoplasm.

Observation:

• In the binary fission slide, the nucleus appears elongated or divided into two. The cell membrane shows a constriction at the centre, dividing the cytoplasm.

Explanation:

• Binary fission is a type of asexual reproduction where a single parent cell divides into two equal halves.
• The process begins with karyokinesis (nuclear division), where the DNA is replicated and the nucleus splits. This is followed by cytokinesis (division of cytoplasm). Each daughter cell receives one nucleus and becomes a new independent organism.

Conclusion:

• Binary fission is an efficient method of reproduction for simple unicellular organisms like Amoeba.

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Activity 7.4: Identification of Spirogyra Filaments

Aim/Objective: To observe fragmentation in multicellular organisms with simple organization.

Materials Required:

• Pond/lake water containing green filaments
• Microscope, Slide, Glycerine, Coverslip

Procedure:

1. Collect filamentous green structures from a pond.
2. Place a few filaments on a slide with a drop of glycerine and cover with a coverslip.
3. Observe under the microscope and look for individual cells and tissues.

Observation:

• Long green filamentous structures are seen, which consist of individual cells joined end-to-end. There is little differentiation of tissues.

Explanation:

• Spirogyra is a multicellular alga that reproduces by fragmentation.
• When the filament reaches maturity, it simply breaks into smaller pieces or fragments. Each fragment then grows into a new individual by repeated cell division. This method is possible because each cell in the filament is capable of living and growing independently.

Conclusion:

• Fragmentation allows organisms with simple body designs to multiply effectively.

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Activity 7.5: Vegetative Propagation in Potato

Aim/Objective: To demonstrate that certain plant parts can grow into new plants under appropriate conditions.

Materials Required:

• A potato with "eyes" (buds)
• Tray, Wet cotton, Knife

Procedure:

1. Observe the surface of a potato for "eyes" or notches.
2. Cut the potato into pieces, ensuring some pieces have a bud and some do not.
3. Place all pieces on wet cotton in a tray and keep them moist for several days.
4. Note which pieces show new growth.

Observation:

• Only the pieces that contained an "eye" or bud develop fresh green shoots and roots.

Explanation:

• This is a form of vegetative propagation using tubers. The "eyes" of a potato are actually vegetative buds that contain meristematic tissue capable of growing into a new plant.
• The pieces without buds lack the necessary tissues to initiate growth, proving that reproduction depends on specialized reproductive structures, even in vegetative parts.

Conclusion:

• Vegetative propagation can be used to grow new plants from non-reproductive organs like stems (tubers) if buds are present.

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Activity 7.6: Vegetative Propagation in Money Plant

Aim/Objective: To show the requirement of at least one node for the growth of a money plant from cuttings.

Materials Required:

• Money plant
• Knife, Beakers with water

Procedure:

1. Cut a money plant into pieces, ensuring some pieces have at least one leaf (and therefore a node) and some are just the stem portion between leaves (internodes).
2. Place the ends of all pieces in water and observe for a few days.
3. Note which pieces develop roots and fresh leaves.

Observation:

• Only the cuttings that contained a leaf (and its associated node/bud) grow and produce new leaves.

Explanation:

• In money plants, roots and new shoots emerge from the nodes (the point on the stem where a leaf is attached). The internodal region lacks the dormant buds required to initiate growth.
• This highlights the importance of using cuttings that include at least one functional node for successful vegetative propagation.

Conclusion:

• Successful vegetative propagation via stem cuttings requires the presence of a node with a vegetative bud.

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Activity 7.7: Germination of Bengal Gram Seeds

Aim/Objective: To observe the structure of a seed and the process of germination.

Materials Required:

• Bengal gram (chana) seeds
• Water, Beaker, Wet cloth

Procedure:

1. Soak Bengal gram seeds in water overnight.
2. Drain the water, wrap the seeds in a wet cloth, and leave them for a day to initiate germination.
3. Carefully cut open the seeds and identify the embryo, cotyledons, plumule, and radicle.

Observation:

• The seed coat softens and peels away. Inside, two large cotyledons are visible. Between them is the embryo, with a small upward-pointing plumule and a downward-pointing radicle.

Explanation:

• Germination is the process by which an embryo within a seed becomes active and begins to grow into a seedling.
• The radicle develops into the root system, and the plumule develops into the shoot system. The cotyledons store food for the developing embryo until it can perform photosynthesis on its own.

Conclusion:

• A seed contains a dormant embryo and a food supply, ready to develop into a new plant when favourable conditions (water, air, warmth) are met.