Activity Answer Microorganisms Friend or foe

Activity Answer Microorganisms Friend or foe Chapter 2 Class 8 Science

Activity 2.1

This activity asks us to make a microscopic slide of organisms present in soil and observe it under the microscope.

Procedure:

• Put some soil in a test-tube
• Add some water in it
• Shake the test tube and allow it to settle.
• pick up a  drop of water using a pipette and put it into the slide.
• put the coverslip on the slide
• observe it under a simple microscope.

Observation:

We see numerous organisms moving inside the slide.

Explanation:

Soil is a natural harbour of microorganisms. Many organisms live there. It becomes visible when we observe it under a microscope. Above is a  sample of soil under a microscope. There are many organisms. Those with tail swim and those who do not have tails are non-motile.

The moving organism here is Chlamydomonas.

Inference:

Soil is home to many microorganisms. Always wash your hand properly with soap after you come in contact with the oil.

Activity 2.2

Activity 2.2 asks us to see the slide of pond water just like we did in activity 2.1.

Observation:

We see numerous green filamentous organism along with other organisms.

Explanation:

Pond water is stagnant water. It harbours many microorganisms just like the soil.

Here a green filamentous fungi spirogyra is common.

Inference: Pond water contains numerous microorganisms.

Activity 2.2

Activity 2.2 asks us to add some yeast to atta or maida.

Procedure:

• Take lukewarm water.
• Add a spoonful of sugar.
• Add some yeast to the solution.
• mix the solution with the flour.
• wait for a 2 hour.

Observation:

Flour swells and increases its size like a balloon.

Explanation:

Yeast is a microorganism. It usage sugar to multiply in number and produces carbon dioxide gas. This gas gets trapped into the floor. As a result, dough raises.

Inference:

Dough and sugar act as a food source to microorganisms.

Facts:

Bakes raised dough is soft and crispier. So, Bakery shop uses this in making bread, pizza base, cakes etc.

Activity 2.4

Activity 2.4 asks us to add some yeast sugar solution and observe the smell after a few hours.

Observation:

We see foul smell coming from the solution. The solution looks pale and untidy.

Explanation:

Sugar acts as a food source to yeast. Yeast decomposes it and forms alcohol and carbon dioxide through the process called Fermentation.

As a result, the solution smells.

Inference:

Yeast fermentate sugar and produces alcohol.

Application:

Fermentation is a widely used application in the food industry. Pickles, vinegar, dosa batter are products of fermentation.

See also: Activity solution Chapter 1.

Microorganisms Friend or foe MCQ

 

Activity Answer Microorganisms Friend or foe Chapter 2 Class 8 Science

 

Ref: Ch2.