9th Class Science: The Fundamental Unit of Life

Question: How does fungi and bacteria can withstand much greater changes in the surrounding medium than animal cells?

Answer: The cell wall present in fungi and bacteria permits these cells to withstand very dilute external medium without bursting.

The cells take up water by osmosis, swells, and builds the pressure against the cell wall. The wall exerts an equal pressure against the swollen cell. It is because of the cell wall, such cells can withstand much greater changes in the surrounding medium than animal cells.

Question: Give the function of nuclear membrane.

Answer: The nuclear membrane present as outer covering in the nucleus allows the transfer of material inside and out of the nucleus to cytoplasm.

Question: Name the cell-organelles that have their own DNA and ribosomes.

Answer: The cell organelles with their own DNA and ribosomes are mitochondria and plastids.

Question: State the difference between smooth endoplasmic reticulum and rough endoplasmic reticulum.

Answer: Smooth Endoplamic Reticulum:

1. It looks smooth.
2. SER helps in the manufacture of fate molecules or lipids.

Rough Endoplasmic Reticulum:

1. It looks rough.
2. Ribosomes are attached to SER which synthesise proteins.

Question: What is endocytosis?

Answer: The cell membranes flexibility allows the cell engulf in food and other material from its external environment. This process is known as endocytosis. E.g., Amoeba acquires its food through such processes.

Question: What is the function of vacuoles?

Answer: Vacuoles are storage sacs for solid or liquid content. In plant cells it provides turgidity and rigidity to the cell. In single-celled organisms vacuoles store food, e.g., Amoeba.

Question: When we put raisins in water, why do they swell?

Answer: Raisins are dry with less water inside, when they are kept in water, osmosis takes place, water flows through the cell wall, cell membrane of the raisins and therefore it swells.

Question: Why are lysosomes called suicidal bags?

Answer: Lysosomes contain digestive enzymes in it and helps in the cleaning of cell by digesting any foreign materials entering the cell, such as bacteria, food and old cell organelles.

When the lysosomes burst, the digestive enzyme digest its own cell. Hence it is called as suicidal bag.

Question: What is nucleoid?

Answer: The nuclear region in some cells are poorly defined due to the absence of a nuclear membrane, it contains only nucleic acid. This undefined nuclear region with nucleic acid in it is called nucleoid.

Question: What is the role, of cell organelles in the cell?

Answer: Each kind of cell organelles performs a specific function such as making new material, clearing of the waste, transporting material, etc.

Question: Label the figure and answer the questions:

1. A – It is the packaging organelle
2. B – Provides energy
3. C – helps in the transport of material
4. D – Carries the information.

Answer:

1. A – Golgi body
2. B – Mitochondria
3. C – Endoplasmic reticulum
4. D – Nucleus

Question: What is the function of nucleus in a cell?

Answer: The nucleus plays a very important role in the reproduction of cells. It also helps the single cell to divide and form two new daughter cells.
It plays an important role in determining how the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of the cell.