The Fundamental Unit Of Life

Q25. Cell wall of which one of these is not made up of cellulose?

(a) Bacteria

(b) Hydrilla

(c) Mango tree

(d) Cactus

Ans. (a) Bacteria

Explanation:

The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants.

Q26. What is the purpose of the large central vacuole in plant cells?

Or

What role does the central vacuole in a plant cell have?

Ans. Most mature plant cells have a large central vacuole that helps to maintain the turgidity of the cell and stores important substances including wastes.

Q27. Write a short note on prokaryotic cells.

Ans. Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles.

Q28. How does an Amoeba obtain its food? 

Ans. The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment. Such processes are known as endocytosis. Amoeba acquires its food through such processes.

Q29. Amoeba acquires its food through a process, termed

(a) exocytosis

(b) endocytosis

(c) plasmolysis

(d) exocytosis and endocytosis both.

Ans. (b) endocytosis

The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment. Such processes are known as endocytosis.

Q30. We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, amino acids, fatty acids, glycerol etc. What mechanisms are involved in absorption of digested food and water?

Ans. The mechanisms involved in absorption of digested food and water are:

1. Glucose, amino acids and some ions – Active Transport

2. Fatty acids, glycerol – Diffusion

3. Water – Osmosis.

Q31. If you are provided with some vegetables to cook, you generally add salt into the vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?

Ans. The mechanism responsible for this process is exosmosis. On adding salt, vegetable release water due to exosmosis. Exosmosis occurs whenever the external medium is hypertonic as compared to the osmotic concentration inside living cells.

Q32. Which cell organelle plays a crucial role in detoxifying many poisons and drugs in a cell?

(a) Golgi apparatus

(b) Lysosomes

(c) Smooth endoplasmic reticulum

(d) Vacuoles

Ans. (c) Smooth endoplasmic reticulum

Explanation:

In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying many poisons and drugs.

Q33. Lipid molecules in the cell are sythesised by

(a) smooth endoplasmic reticulum

(b) rough endoplasmic reticulum

(c) Golgi apparatus

(d) plastids.

Ans. (a) smooth endoplasmic reticulum

Explanation:

The SER helps in the manufacture of fat molecules, or lipids, important for cell function.

Q34. Organelle without a cell membrane is

(a) ribosome

(b) Golgi apparatus

(c) chloroplast

(d) nucleus.

Ans. (a) ribosome

Explanation:

Golgi apparatus, chloroplast and nucleus are all double membrane bound cell organelles. Ribosomes are not surrounded by any membrane.

Q35. Do you agree that “a cell is a building unit of an organism”. If yes, explain why?

Ans. Yes, “a cell is a building unit of an organism” because all organisms that we observe around are made up of cells.  The cell is the fundamental structural unit of living organisms. It is also the basic functional unit of life.

Q36. Why is the plasma membrane called a selectively permeable membrane? 

Ans. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The plasma membrane, therefore, is called a selectively permeable membrane.

Q37. Who discovered cells, and how? 

Ans. Robert Hooke discovered cells in 1965. While examining a thin slice of cork, he saw that the cork resembled the structure of a honeycomb consisting of many little compartments. He made this chance observation through a self-designed microscope. He called these boxes cells. Cell is a Latin word for ‘a little room’.

Q38. Find out the false sentences.

(a) Golgi apparatus is involved with the formation of lysosomes.

(b) Nucleus, mitochondria and plastid have DNA; hence they are able to make their own structural proteins.

(c) Mitochondria is said to be the power house of the cell as ATP is generated in them.

(d) Cytoplasm is called as protoplasm.

Ans. (d) Cytoplasm is called as protoplasm.

Explanation:

Cytoplasm is a part of protoplasm of the cell. The protoplasm is bound by plasma membrane whereas cytoplasm is that part of protoplasm which surrounds the nucleus.

Q39. The only cell organelle seen in prokaryotic cell is

(a) mitochondria

(b) ribosomes

(c) plastids

(d) lysosomes.

Ans. (b) ribosomes

Explanation:

Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles.

Q40. The proteins and lipids, essential for building the cell membrane, are manufactured by

(a) rough endoplasmic reticulum

(b) Golgi apparatus

(c) plasma membrane

(d) mitochondria.

Ans. None

Explanation:

The ribosomes, which are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on need, using the ER. The SER helps in the manufacture of fat molecules, or lipids, important for cell function.

Q41. Select the odd one out.

(a) The movement of water across a semi- permeable membrane is affected by the amount of substances dissolved in it.

(b) Membranes are made of organic molecules like proteins and lipids.

(c) Molecules soluble in organic solvents can easily pass through the membrane.

(d) Plasma membranes contain chitin sugar in plants.

Ans. (d) Plasma membranes contain chitin sugar in plants.

Explanation:

Plasma membrane is a living, thin, elastic, selectively permeable membrane which chemically consists of lipids, proteins, carbohydrates and water. Chitin sugar is not present in the plasma membrane of plants.