NCERT Solutions for Class 9 Science Chapter 5
1. Why is a cell called the structural and functional unit of life?
Answer: A cell is the basic unit of life. Every cell in our body can perform certain basic functions that support our living. Cells perform these life functions with the help of cell organelles. There are various cell organelles, with the help of which, a cell can carry out oxidation, clears up waste materials, synthesizes proteins, and so on. Some important cell organelles are ribosomes, lysosomes, mitochondria, Golgi apparatus, and endoplasmic reticulum. In a certain way, all the cells contribute to our living, hence cells are called the structural and functional unit of life.
2. What do you understand by plasma membrane of a cell?
Answer: The plasma membrane of a cell is commonly called the cell membrane. It is a semi-permeable membrane that allows the movement of specific substances in and out of the cell. The plasma membrane regulates the movement of various important substances in the cell. It prevents unwanted substances from entering the cell.
The plasma membrane is different from the cell membrane in terms of permeability and functions.
3. What do you understand by osmosis and diffusion?
Answer: Osmosis: When two solutions of different concentrations are separated by a semi-permeable, the water molecules move from the solution with its higher concentration to the solution with its lower concentration, through the membrane, till a state of equilibrium is attained. This process is called osmosis.
Diffusion: In the process of diffusion, substances move from the region of a higher concentration to the region of a lower concentration, until the state of equilibrium is reached.
4. Why are mitochondria called the powerhouse of a cell?
Answer: Mitochondria are called the powerhouse of a cell as they provide the energy required by the body. They provide the energy in the form of ATP and the body utilizes this energy to carry out various chemical functions and the body performs mechanical work with the help of the energy in ATP.