The Fundamental Unit of Life

Activity 5.5

Question: Find out about electron microscopes from resources in the school library or through the internet. Discuss it with your teacher.

Answer

An electron microscope is a device used to see microscopic objects. An electron microscope works on the principle asserted by French physicist Louis de Broglie in 1924 for which he got the Noble Prize.

In an electron microscope electron beam is used to magnify the object while in a simple compound microscope, light beam is used.

An electron microscope can 10 × 10⁷ times magnification while a simple microscope can magnify only up to 2000 times.

With the invention of the electron microscope, it becomes possible to see cells and other many microscopic objects with very high magnification.

Activity 5.6

Mount the peel of a Rhoeo leaf in water on a slide and examine cells under the high power of a microscope. Note the small green granules, called chloroplasts. They contain a green substance called chlorophyll. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe under a microscope.

Question (1) What do we see?

Answer

The granules of chloroplasts get shrunk. This happens because sugar or salt solution has more concentration than that of green granules resulting in liquid from granules of chloroplasts passing out due to deplasmolysis.

• Now place some Rhoeo leaves in boiling water for a few minutes. This kills the cells. Then mount one leaf on a slide and observe it under a microscope. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe it again.

Question (2) What do we find?

Answer

After boiling Rhoeo leaves, there is no effect seen on the granules of chloroplasts when the leaf is seen under a microscope. This happens because boiling Rhoeo leaves kills the cells of the leaves. And plasmolysis or deplasmolysis occurs only with living cells.

Question (3) Did plasmolysis occur now?

Answer

Plasmolysis does not occur in this case. This is because boiling kills the cells of Rhoeo leaves', and plasmolysis or deplasmolysis does not take place in a dead cell.

Question (4) What do we infer from this activity?

Answer

From this activity following conclusions are drawn:

(1) Swelling of cells because of absorbing water or shrinkage of the cell because of loss of water through a process called osmosis occurs only in living cells.

The swelling of cells because of absorbing water is called plasmolysis and the shrinkage of cells because of loss of water is called deplasmolysis or cytolysis.

(2) Plasmolysis or deplasmolysis does not take place in dead cells.

Activity 5.7

• Let us take a glass slide with a drop of water on it. Using an ice cream spoon gently scrape the inside surface of the cheek.

Question: Does any material get stuck on the spoon?

Answer:

Yes, some sticky material gets stuck on the spoon.

This material is the epidermis of our chick wall.

• With the help of a needle we can transfer this material and spread it evenly on the glass slide kept ready for this. To colour the material we can put a drop of methylene blue solution on it. Now the material is ready for observation under the microscope. Do not forget to put a cover slip on it!

Question (1) What do we observe?

Answer

The structure similar to a honeycomb has been seen.

These are the cells found in the cheek of a human.

Question (2) What is the shape of the cells we see?

Cheek's Cells have rectangular to oval shapes.

Draw it on the observation sheet.

Figure: Human Cheek Cell¹

Reference: MaryViennePascual, CC BY-SA 4.0, via Wikimedia Commons

Question: Was there a darkly coloured, spherical or oval, dot-like structure near the centre of each cell?

Answer

Yes. There is a darkly coloured spherical or dot-like structure near the centre of each cell. These structures are the nucleus of the cell. This structure is called the nucleus.

Question: Were there similar structures in onion peel cells?

Answer

Yes. These structures of the nucleus are similar to those found in the cells of the onion peel.