CBSE Class 9 Science Advanced Biology Fundamental Unit of Life Very Short Answer Questions Set 01

Very Short Answer Type

Question 1. Who discovered cell and how ?
Answer:
Robert Hooke discovered the cell in 1665.
He examined a thin slice of dead cork under a simple microscope and saw many tiny, box-like compartments that looked like the rooms of a honeycomb. He named them cells and described them in his book Micrographia.
In simple words: Robert Hooke saw the cells of cork under a microscope and gave them the name 'cell'.

Teacher's Note:
1. Remember three facts together: Hooke, cork, 1665.
2. The cells he saw were dead; A. V. Leeuwenhoek was the first to see living cells.

Question 2. Who proposed cell theory ?
Answer:
The cell theory was proposed by the botanist M. J. Schleiden and the zoologist Theodor Schwann.
In simple words: Schleiden and Schwann gave the cell theory.

Teacher's Note:
1. Schleiden worked on plants and Schwann on animals.
2. Rudolf Virchow later extended the theory.

Question 3. Who expanded cell theory and why ?
Answer:
Rudolf Virchow expanded the cell theory.
Schleiden and Schwann had said only that organisms are made of cells. Virchow added that every new cell arises from a pre-existing cell (omnis cellula e cellula), which explained how cells increase in number and ruled out the idea that cells form from non-living matter.
In simple words: Virchow added that all cells come from existing cells.

Teacher's Note:
1. Link Virchow with the third point of the cell theory.
2. The Latin phrase means 'every cell from a cell'.

Question 4. What is nucleoid ?
Answer:
The nucleoid is the irregular region in the cytoplasm of a prokaryotic cell where the naked, circular DNA lies.
It is not surrounded by a nuclear membrane, and there is no nucleolus. It is also called the incipient (primitive) nucleus.
In simple words: A nucleoid is the nucleus-like area of a bacterium that has DNA but no membrane around it.

Teacher's Note:
1. The chapter does not define this term, so learn it from this answer.
2. A nucleoid has no membrane, while a true nucleus has a double membrane.

Question 5. Define plasmid.
Answer:
A plasmid is a small, circular DNA molecule found in many bacteria in addition to the main DNA loop.
It can copy itself independently and often carries useful genes, such as those for resistance to antibiotics.
In simple words: A plasmid is an extra small ring of DNA in a bacterium.

Teacher's Note:
1. Plasmids are not part of the main chromosome.
2. They are used as carriers of genes in genetic engineering.

Question 6. Which is the longest cell ?
Answer:
In animals the longest cell is the nerve cell (it can be a metre or more long). In plants the longest cell is the hemp fibre.
In simple words: The nerve cell is the longest animal cell.

Teacher's Note:
1. The largest cell, in contrast, is the egg of an ostrich.
2. Do not mix up longest and largest.

Question 7. Give name of smallest cell.
Answer:
The smallest cells known are the PPLOs (pleuropneumonia-like organisms), such as Mycoplasma, which is about 0.1 µm across.
In simple words: Mycoplasma (a PPLO) is the smallest cell.

Teacher's Note:
1. PPLO stands for pleuropneumonia-like organism.
2. Compare with a typical cell, which is 20 to 30 µm.

Question 8. Can you name the two organelles we have studied that contain their own genetic material ?
Answer:
Mitochondria and chloroplasts (plastids). Each has its own circular DNA, and also its own ribosomes, so each can make some of its own proteins.
In simple words: Mitochondria and chloroplasts have their own DNA.

Teacher's Note:
1. Because of this they are called semi-autonomous organelles.
2. Their ribosomes are of the 70S type.

Question 9. Why are lysosomes known as suicide bags ?
Answer:
Lysosomes contain strong digestive enzymes (hydrolases).
When the cell is damaged or its metabolism is disturbed, the lysosomes burst and release the enzymes, which digest the cell itself. So the cell destroys itself, and the lysosomes are called suicide bags.
In simple words: Lysosomes burst when a cell is damaged and digest their own cell.

Teacher's Note:
1. The enzymes inside are normally kept safely inside the lysosome membrane.
2. Their normal work is to digest food and worn-out parts.

Question 10. Where are proteins synthesised inside the cell ?
Answer:
Proteins are made on the ribosomes. Some ribosomes lie free in the cytoplasm and others are attached to the rough endoplasmic reticulum.
In simple words: Ribosomes are the protein-making sites.

Teacher's Note:
1. Ribosomes are called protein factories.
2. Proteins made on the rough ER are usually sent out of the cell.

Question 11. What is the use of stage clip in microscope ?
Answer:
The two stage clips hold the slide firmly in position on the stage so that it does not move while it is being observed.
In simple words: Stage clips keep the slide steady.

Teacher's Note:
1. They are fixed on the stage of the microscope.
2. A slide that moves would be out of focus.

Question 12. Write down the function of fine adjuster ?
Answer:
The fine adjustment is the smaller screw of the microscope. It moves the body tube only slightly and is used for the final, exact focusing so that the image becomes sharp and clear.
In simple words: The fine adjustment screw gives the last, sharp focus.

Teacher's Note:
1. Use the coarse screw first and the fine screw next.
2. The coarse screw is the larger one.

Question 13. Why are lysosomes known as 'suicide-bags' of a cell ?
Answer:
Lysosomes hold powerful digestive enzymes. If the cell is damaged, the lysosomes burst and the enzymes spill into the cytoplasm and digest the whole cell, so the cell is killed by its own enzymes. Hence they are called suicide bags.
In simple words: They burst and digest their own cell when it is damaged.

Teacher's Note:
1. Link the name to what happens: self-destruction.
2. In a healthy cell the enzymes stay enclosed.

Question 14. Do you agree that "A cell is a building unit of an organism". If yes, explain why ?
Answer:
Yes, I agree.
All living organisms are made of cells, which is the first statement of the cell theory. A unicellular organism such as an amoeba is a single cell, while the body of a multicellular organism is built from millions of cells. Similar cells join to form tissues, tissues form organs, organs form organ systems and organ systems form the organism.
The organism also grows by increasing the number of its cells, since new cells arise from existing cells.
In simple words: Yes, just as a building is made of bricks, a living body is made of cells.

Teacher's Note:
1. Use the cell theory as your reason.
2. Mention both unicellular and multicellular organisms.

Question 15. Why does the skin of your finger shrink when you wash clothes for a long time ?
Answer:
Washing involves keeping the hands in a strong detergent solution for a long time.
This solution is more concentrated than the fluid in the skin cells (it is hypertonic). Water therefore moves out of the skin cells by osmosis (exosmosis), the cells lose water and the skin of the finger shrinks and wrinkles.
In simple words: Water leaves the skin cells by osmosis into the strong soap solution, so the skin shrinks.

Teacher's Note:
1. The same idea explains why salted raw mango pieces shrink.
2. Remember: hypertonic outside means water goes out of the cell.

Question 16. Why is endocytosis found in animals only ?
Answer:
Endocytosis needs the plasma membrane to fold inwards and wrap around a large particle or a drop of liquid to form a vesicle.
The cells of animals have only a soft, flexible plasma membrane, so they can do this. Plant cells have a rigid cell wall outside the membrane, which stops it from folding and engulfing material. Hence endocytosis (phagocytosis and pinocytosis) is found only in animals.
In simple words: Animal cells have no hard cell wall, so their membrane can engulf particles.

Teacher's Note:
1. Plant cells take in material through the wall by diffusion and osmosis.
2. Amoeba's way of feeding is a good example.