Class 9 Science : Chapter 5 The Fundamental Unit of Life

 

Chapter 5 The Fundamental Unit of Life

Question 1:

Who discovered cells and how?

Answer: Robert Hooke discovered the cell in 1665. He examined a thin slice of cork through a self designed primitive microscope and saw that the cork resembled the structure of a honey comb consisting of many tiny compartments. He called these tiny compartment as cells . 

Question 2:

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

Answer: A living organism is made up of one or more cells. Therefore, cell is structural unit of life.A cell is capable of independently carrying out all necessary activities of life. So, they are called  functional unit of life.

Question 3:

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

Answer:

CO2 moves in and out of the cells by the process of diffusion which involves movement of molecules from higher concentration to lower concentration across the cell membrane.

Water moves in and out of the cells by osmosis. Osmosis is the movement of water or solvent through a semi-permeable membrane from a solution of lower concentration of solutes to a solution of higher concentration of solutes.

Question 4:

Why is the plasma membrane called a selectively permeable membrane?

Answer: Plasma membrane called a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

Question 5:

Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer: The differences between prokaryotic cell and eukaryotic cell are as follows:

Question 6: Can you name the two organelles, we have studied that contain their own genetic material ?

Answer: The two organelles which have their own genetic material are:
1. Mitochondria 2. Plastids

Question 7: If the organization of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: If the organization of a cell is destroyed due to some physical or chemical influence then cell will not be able to perform the basic functions like respiration, nutrition, excretion etc. This may stop all the life activities and may result in its death.

Question 8: Why are lysosomes known as suicide bags?

Answer:Lysosomes contain digestive enzymes that are capable of  breaking down any foreign food particle or microbes entering the cell . During breakdown of cell structure, when the cell gets damaged, lysosomes digest their own cells by releasing own enzymes. Therefore, they are known as suicide bags of a cell.

Question 9: Where are proteins synthesized inside the cell?

Answer: The ribosomes attached to the endoplasmic reticulum as well as present freely in the cytoplasm of all active cells are the site for the synthesis of proteins.

Question 10: Make a comparison and write down ways in which plant cells are different from animal cells.

Answer:

Animal cell	Plant cell
Animal cells are generally small in size.	Plants cells are usually larger than animal cells.
Cell wall is absent.	Cell wall is present.
Except the protozoan Euglena, no animal cell possesses plastids.	Plastids (chromoplasts and leucoplasts) are present.
Vacuoles are smaller in size.	Vacuoles are larger in size.

Question 11: What would happen if the plasma membrane ruptures or breaks down?

Answer: If the plasma membrane of a cell is ruptured, then the cell will die. The plasma membrane regulates the movement of substances in and out of the cell by diffusion or osmosis. Thus, if the plasma membrane is ruptured, then the cell might leak out its contents.

Question 12: What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Golgi apparatus has the function of storage modification and packaging of the products. If there is no Golgi apparatus, then the packaging and transporting of materials synthesized by cell will not happen.

Question 13: Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria is known as powerhouse of the cell because it releases the energy required for different activities of life in the form of ATP .

Question 14: Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: a) Lipids are synthesized in Smooth endoplasmic reticulum (SER)

b) proteins are synthesized in rough endoplasmic reticulum (RER).

Question 15: How does an Amoeba obtain its food?

Answer: Amoeba takes in food using temporary finger-like extensions of the cell surface called pseudopodia which fuse over the food particle forming a food-vacuole  . Inside the food vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.