Ncert Questions
Question 1. What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
Answer: Mesosomes are special membranous structure formed by the extension of plasma membrane. These extensions are in the form of vesicles, tubules, and lamella Functions (1) They help in the formation of cell wall (2) They take part in the replication of and distribution DNA to the daughter cells. (3) Mesosomes help in respiration, and secretion processes. (4) They increase the surface area of the plasma membrane and enzymatic content.
Question 2. How do neutral solutes move across the plasma membrane? Can the polarmolecules also move across it in the same way? If not, then how are thesetransported across the membrane?
Answer: Neutral solutes move across the membrane by the process of simple diffusion along the concentration gradient which is from higher concentration to lower concentration. Polar molecules cannot move across the membrane in the same way. They require a carrier protein of the membrane to facilitate their transport.
Question 3. What are the characteristics of prokaryotic cells.
Answer: (1) Prokaryotes have cell wall surrounding the cell membrane. (2) They do not have a well defined nucleus. (3) The genetic material is not covered by a nuclear membrane. (4) Extra chromosomal DNA called plasmids is present in the cytoplasm. (5) Prokaryotes do not have membrane bound organelles.
Question 4. Multi cellular organisms have division of labour. Explain.
Answer: Multi cellular organisms have different types of cells and each of these cells have different functions to perform. For e.g. red blood cells helps in the transport of oxygen, white blood cells help in protection of the body against pathogens, nerve cells for bodily co-ordination etc. A group of cells, which are of the same type, perform the same function like the cells of the kidney helping in excretion, the cells of the respiratory system helping in respiration, the cells in the digestive system helping in nutrition etc. Thus we can see that in multi cellular organisms each function is performed by each system, which exhibits division of labour.
Question 5. Cell is the basic unit of life. Discuss in brief.
Answer: All living organisms are composed of small, tiny structures or compartments called cells. These cells are called the ‘building blocks’ of life.The cells in a true sense are considered as the basic unit of life because all the life processes, i.e., metabolism, responsiveness and reproduction are carried out by the cells. Cells are the seat of all metabolic processes. Respiration, nutrition and release of energy are carried out within the cells. Even the animals and plants reproduce because the cells reproduce individually. Growth occurs because cells grow and multiply.Let us take the example of amoeba, a unicellular organism. In amoeba, all the life processes are performed within the boundaries of the single cell. On the other hand, the body of a multi cellular organism is made up of many cells. In these organisms, the cells do not behave independently, but get organized into tissues. Each tissue is specialized to perform specific functions. Different tissues then get organized into organs, which perform certain specific functions. Different organs are finally organized to form organ systems. These tissues, organs and organ systems of the organisms work because the cells work.On account of the above discussion, it can be said that cells are the structural and functional unit of living beings. Hence it is the basic unit of life.
Question 6. What are nuclear pores? State their function.
Answer: The minute pores formed by the fusion of the two nuclear membranes which envelopes the nucleus is called as the nuclear pores. FunctionIt forms the passage for the movement of RNA and proteins in both the directions between the nucleus and the cytoplasm.
Question 7. Both lysosomes and vacuoles are endo membrane structures, yet they differ in terms of their functions. Comment.
Answer: Lysosomes are membrane bound vesicular structure, which contains all types of hydrolytic enzymes. The main function of these enzymes is the digestion of carbohydrates, proteins, lipids, and nucleic acids. Vacuoles are membrane bound space found in the cytoplasm, which contain water, sap, excretory products, and other materials not necessary for the cell. Its helps in the excretion of unwanted waste products. In some organisms like amoeba it forms food vacuole for digestion of food and also contractile vacuole for excretion of waste.