CBSE/NCERT/NCERT Biology Activities/Class 8 Science Activities

Class 8 Science Activities

NCERT Biology Activities for Class 8 Science.

Class 08 Science - How Nature Works in Harmony

NCERT Biology Activities for Class 08 Science - How Nature Works in Harmony - Class_08_Science

Created by Titas Mallick

Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner

CBSE/NCERT/NCERT Biology Activities/Class 8 Science Activities

Class 08 Science - The Invisible Living World: Beyond Our Naked Eye

NCERT Biology Activities for Class 08 Science - The Invisible Living World: Beyond Our Naked Eye - Class_08_Science

Class 08 Science - The Invisible Living World: Beyond Our Naked Eye

Activities

Activity 2.1: Demonstration of Magnification

Aim/Objective: To understand the concept of magnification using a simple water-filled flask.

Materials Required:

1x 500 mL Round-bottom glass flask.
450 mL Clean water (to fill the flask).
1x Rubber or cork stopper.
Printed text (a book with standard 10-12 pt font).

Procedure:

Fill the round-bottom flask completely with water until it reaches the neck and secure it with a cork.
Place the flask directly on top of a page of a book.
Move the flask slowly across the text for 2-3 minutes and observe the letters through the central part of the flask.

A curved transparent surface filled with a medium of higher refractive index than air (like water) acts as a convex lens. It converges light rays, creating a magnified virtual image of the text behind it.

Handle the glass flask with care. If it breaks, do not pick up the glass shards with bare hands. Use a brush and dustpan.

For the best magnification effect, ensure the flask is perfectly spherical and the water is clear of any air bubbles or suspended particles.

Observation:

The letters appear significantly larger (approx. 2x to 3x magnification) and clearer when viewed through the water-filled flask.

Conclusion:

Simple optical properties of curved surfaces can be used to create magnification tools, which are the basis for microscopes.

Activity 2.2: Study of Plant Cells (Onion Peel)

Aim/Objective: To observe the structure of plant cells using a light microscope.

Materials Required:

1x Medium-sized Onion bulb.
1x Pair of Forceps and 1x Fine camel hair brush.
2 mL Safranin stain (dilute).
1 mL Glycerin.
1x Glass slide and 1x Square coverslip.
1x Compound Microscope (10x and 45x objectives).

Procedure:

Peeling: Use forceps to remove a thin, transparent layer (epidermal peel) from the concave inner surface of an onion fleshy leaf.
Staining: Place the peel in a watch glass with water, then transfer it to a drop of Safranin stain for exactly 30 seconds.
Mounting: Rinse the extra stain with water using the brush. Place the peel flat on a clean slide. Add 1 drop of glycerin over it.
Sealing: Gently lower the coverslip at a 45-degree angle to avoid trapping air bubbles.
Observation: View under low power (10x) first, then switch to high power (45x).

The cell wall is a rigid outer layer made of cellulose. Safranin specifically stains the cell walls and the nucleus, making the cellular boundaries clearly visible under the microscope.

Be careful while using the needle or forceps to lower the coverslip. Do not press too hard on the coverslip as it is very fragile and can break.

To avoid air bubbles, use a mounting needle to support the coverslip and lower it very slowly onto the specimen.

Observation:

Large numbers of rectangular, box-like cells are seen arranged closely together. Each cell has a distinct cell wall, a dark nucleus, and a large central vacuole.

Conclusion:

All plants are composed of basic units called cells, which possess a rigid cell wall providing structural integrity.

Activity 2.3: Study of Animal Cells (Human Cheek Cells)

Aim/Objective: To observe the structure of animal cells and compare them with plant cells.

Materials Required:

1x Sterile Toothpick (blunt end) or a clean plastic spatula.
2 mL Methylene blue stain.
1 mL Glycerin.
1x Glass slide and 1x Coverslip.
1x Compound Microscope.

Procedure:

Collection: Gently scrape the inside of your cheek with the blunt end of a clean toothpick for 10-15 seconds.
Transfer: Spread the scraped material onto the center of a glass slide.
Staining: Add 1 drop of Methylene blue stain and let it sit for exactly 1 minute.
Final Step: Add 1 drop of glycerin, cover with a coverslip, and observe under the microscope.

Animal cells lack a cell wall and a large central vacuole. Methylene blue is a basic dye that binds to acidic components like DNA, making the nucleus appear dark blue against the lighter blue cytoplasm.

Do not scrape your cheek too hard; a very light touch is sufficient to collect thousands of cells. Always use a new, sterile toothpick and dispose of it immediately after use.

If the cells are too crowded, add another drop of water before placing the coverslip to spread them out for better individual cell visualization.

Observation:

Irregularly shaped, polygon-like cells are seen. They have a thin cell membrane, a prominent central nucleus, and granulated cytoplasm but lack a rigid cell wall.

Conclusion:

Animal bodies are made of cells that are structurally flexible due to the absence of a cell wall.

Activity 2.4: Observing Microorganisms in Pond Water

Aim/Objective: To identify living microorganisms in a natural water source.

Materials Required:

100 mL Pond or stagnant water (collected from near the edges with some green scum).
1x Glass dropper.
1x Glass slide and 1x Coverslip.
1x Compound Microscope.

Procedure:

Collect a sample of stagnant pond water in a clean jar.
Use the dropper to take a tiny drop from the bottom or near the floating green patches.
Place the drop on a slide and cover it with a coverslip.
Scan the slide under the microscope for 10-15 minutes at different magnifications.

Pond water contains various Protozoa (like Amoeba and Paramecium) which move using cilia or pseudopodia, and Algae (like Spirogyra) which are autotrophic and contain chlorophyll.

Wash your hands thoroughly with soap after handling pond water, as it may contain harmful bacteria or parasites.

To slow down fast-moving organisms like Paramecium for better viewing, add a few strands of cotton wool to the water drop before placing the coverslip.

Observation:

Various tiny, moving organisms of different shapes are seen. Some are green and filamentous (Algae), while others are transparent and move rapidly (Protozoa).

Conclusion:

Natural water bodies host a diverse world of unicellular and multicellular microorganisms.

Activity 2.5: Observing Microorganisms in Soil Suspension

Aim/Objective: To demonstrate the presence of microbial life in soil.

Materials Required:

50g Moist garden soil.
100 mL Distilled or clean water.
1x 250 mL Glass beaker.
1x Glass dropper, 1x Slide, and 1x Coverslip.

Procedure:

Mix 50g of moist soil with 100 mL of water in a beaker and stir vigorously for 1 minute.
Let the beaker stand undisturbed for 30 minutes to allow the heavy soil particles to settle.
Take a drop of the relatively clear water from the top (supernatant) using a dropper.
Place the drop on a slide, cover, and observe under high power.

Soil is a biologically active medium. A single gram of garden soil can contain millions of bacteria, fungi, and actinomycetes that are vital for nutrient cycling.

Ensure the soil is free from sharp objects like broken glass or metal. Use gloves if the soil is collected from a public area.

For best results, collect soil from near the roots of a plant (rhizosphere), as microbial activity is highest in this zone.

Observation:

Tiny moving specks (bacteria) and long, thread-like structures (fungal hyphae) are often visible at high magnification.

Conclusion:

Soil is a living reservoir containing a vast population of microorganisms essential for ecological balance.

Activity 2.7: Making Manure from Kitchen Waste

Aim/Objective: To observe the process of biological decomposition by microorganisms.

Materials Required:

1x 5L Plastic container or a small pit in the garden.
2 kg Garden soil.
500g Kitchen waste (vegetable peels, fruit scraps, eggshells).
200 mL Water (for periodic moistening).

Procedure:

Layering: Fill the container halfway with 1 kg of soil.
Adding Waste: Add the 500g of kitchen waste and mix it slightly with the top layer of soil.
Capping: Cover the waste completely with the remaining 1 kg of soil.
Maintenance: Keep the soil moist by adding 50 mL of water every 3 days.
Observation: Leave it for exactly 21 days (3 weeks). Dig up the waste to observe changes.

Decomposition is an aerobic process where microbes break down complex organic matter into Humus. Humus is a dark, organic substance that improves soil structure and provides nutrients to plants.

Do not add meat, dairy products, or oily food to the container, as these attract pests and produce foul odors during anaerobic decay.

Turn the soil and waste every 3-4 days using a small trowel to provide oxygen to the aerobic bacteria, which speeds up the composting process.

Observation:

The kitchen waste has largely disappeared, replaced by a dark, crumbly, earthy-smelling substance (manure).

Conclusion:

Microorganisms act as "nature's recyclers," converting waste into valuable nutrients.

Activity 2.8: Role of Yeast in Baking

Aim/Objective: To observe the effect of yeast fermentation on dough volume.

Materials Required:

250g All-purpose flour (Maida) or Wheat flour.
20g Granulated sugar.
100 mL Warm water (approx. $37^\circ C$ ).
5g Active dry yeast powder.
2x Identical glass bowls (labeled A and B).

Procedure:

Bowl A (Test): Mix 125g flour, 10g sugar, and 5g yeast. Add 50 mL warm water and knead into a soft dough.
Bowl B (Control): Mix 125g flour and 10g sugar (no yeast). Add 50 mL warm water and knead into a soft dough.
Incubation: Place both bowls in a warm, draft-free place for exactly 2 hours.
Observation: Compare the size and texture of the two doughs.

Yeast performs anaerobic fermentation, breaking down sugar into energy and releasing Carbon Dioxide ( $CO_2$ ) gas. The $CO_2$ gets trapped in the gluten network of the flour, causing the dough to rise (leavening).

Ensure the water is only lukewarm ( $35$ - $40^\circ C$ ). If the water is too hot (above $50^\circ C$ ), it will kill the yeast cells and the experiment will fail.

To check if your yeast is active before starting, mix it with a little warm water and sugar; if it doesn't foam within 10 minutes, the yeast is dead.

Observation:

The dough in Bowl A increases to nearly double its original volume and feels spongy. The dough in Bowl B remains the same size and is dense.

Conclusion:

Yeast is a vital microorganism in the food industry that causes aeration and leavening of dough through fermentation.

Activity 2.9: Curd Formation using Lactobacillus

Aim/Objective: To investigate the thermal conditions required for the conversion of milk to curd.

Materials Required:

500 mL Full-cream Milk (divided into two equal parts).
20g Fresh curd (to be used as a starter/inoculum).
2x Clean glass bowls (labeled A and B).
1x Thermometer (optional).

Procedure:

Preparation: Heat 250 mL of milk until it is lukewarm (approx. $40^\circ C$ ) and pour into Bowl A. Keep the other 250 mL of milk cold ( $5$ - $10^\circ C$ ) and pour into Bowl B.
Inoculation: Add 10g (one tablespoon) of curd to each bowl and stir gently for 30 seconds.
Setting: Keep Bowl A in a warm corner of the kitchen and Bowl B in the refrigerator.
Observation: Check the consistency of the milk after 6-8 hours.

Curd contains Lactobacillus bacteria. These microbes ferment the milk sugar (lactose) into lactic acid, which lowers the pH and causes the milk protein (casein) to denature and coagulate into a semi-solid state.

Use clean, sterilized bowls and spoons to avoid contamination by unwanted bacteria which can cause the milk to spoil rather than curdle.

Do not disturb or stir the milk in Bowl A while it is setting, as this can break the protein chains and result in a watery, inconsistent curd.

Observation:

The milk in Bowl A has set into a thick, uniform curd. The milk in Bowl B remains liquid with the starter curd settled at the bottom.

Conclusion:

Successful curdling requires specific beneficial bacteria (Lactobacillus) and an optimal warm environment for their multiplication.

location:

/CBSE/NCERT/Activities/Class_08_Science/Chapter_02_The_Invisible_Living_World.mdx

Class 8 Science Activities

NCERT Biology Activities for Class 8 Science.

Class 08 Science - How Nature Works in Harmony

NCERT Biology Activities for Class 08 Science - How Nature Works in Harmony - Class_08_Science

On this page

Class 08 Science - The Invisible Living World: Beyond Our Naked Eye Activities Activity 2.1: Demonstration of Magnification Activity 2.2: Study of Plant Cells (Onion Peel)Activity 2.3: Study of Animal Cells (Human Cheek Cells)Activity 2.4: Observing Microorganisms in Pond Water Activity 2.5: Observing Microorganisms in Soil Suspension Activity 2.7: Making Manure from Kitchen Waste Activity 2.8: Role of Yeast in Baking Activity 2.9: Curd Formation using Lactobacillus