Science Class Nine     Class 9 Subject List

Cell: Fundamental Unit of Life

Solution of NCERT Exercise

In text questions:

Page 59

1. Who discovered cells and how?

Answer: It was Robert Hooke who discovered cells. He observed the cells in thin slices of cork. They appeared like small compartments when viewed through the microscope.

2. Why is the cell called structural and functional unit of life?

Answer: A cell is capable of carrying out all the life functions; such as nutrition, excretion, respiration, etc. Hence a cell is called the functional unit of life. Additionally, the cell is the smallest unit of life and all the living beings are made up of cells. Hence a cell is called the structural unit of life.

Page 61

1. How do substances like CO2 and water move in and out of the cell? Discuss.

Answer: Substances move in and out of the cell because of diffusion. Diffusion is the random movement of particles in order to attain concentration equilibrium. The movement of water through a semi-permeable membrane is called osmosis. It is important to note that plasma membrane is a semi-permeable membrane. Water always moves from high water concentration to low water concentration.

2. Why is the plasma membrane called a selectively permeable membrane?

Answer: Plasma membrane allows passage to some selected substances. Hence it is called a selectively permeable or semi-permeable membrane.

Page 65

1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: Mitochondria and Chloroplast contain their own genetic material.

2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: Various parts of a cell are responsible for various functions. They work in tandem to continue life in the cell. In case, the organization of a cell is destroyed due to some physical or chemical influence, the cell will die.

3. Why are lysosomes known as suicide bags?

Answer: Lysosomes contain digestive enzymes. In case of a rupture in lysosome, the enzymes are released in the cytoplasm and end up digesting the contents of the cell. This results in cell death. Due to this, lysosome is also known as suicide bags of cells.

4. Where are proteins synthesized inside the cell?

Answer: Proteins are synthesized in ribosome.

Exercise Questions

1. Make a comparison and write down ways in which plant cells are different from animal cells.


plant cell animal cell comparison

2. How is a prokaryotic cell different from a eukaryotic cell?


prokaryote eukaryote comparison

3. What would happen if the plasma membrane ruptures or breaks down?

Answer: Plasma membrane provides a container for the cell organelles and cytoplasm. Moreover, plasma membrane also protects the contents of a cell from external environment. In case the plasma membrane ruptures or breaks down, the cell contents would be exposed to the external environment. This would prove lethal for the cell and the cell would cease to exist.

4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Golgi apparatus plays the important role of packaging various substances for further use or for storage. If there was no Golgi apparatus, various substances would not be in a position to be transformed in proper forms for further use. Certain substances; like protein and lipid are important for the formation of plasma membrane and hence absence of Golgi apparatus will hamper the formation of new cells during cell division.

5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondrion is known as the powerhouse of the cell. The reason for this is the fact that cellular respiration takes place in mitochondria and the energy released after that gets stored in mitochondria; in the form of ATP. These ATP molecules are utilized on an SOS basis.

6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: Lipids are synthesized in the endoplasmic reticulum. Protein is synthesized in ribosomes which are usually present on the rough ER.

7. How does an Amoeba obtain its food?

Answer: Amoeba obtains its food through a process called phagocytosis. The cell membrane of amoeba is projected into numerous finger-like outgrowths; called pseudopodia. Amoeba surrounds a food particle by pseudopodia and makes a food vacuole; after engulfing the food.

8. What is osmosis?

Answer: The movement of water from high concentration to low concentration through a semi-permeable membrane is called osmosis.

Cell: Fundamental Unit of Life: Class note


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