The Fundamental Unit Of Life
Q42. Name the parts which
(a) determines the function and development of the cell
(b) packages materials coming from the endoplasmic reticulum
(c) provides resistance to microbes to withstand hypotonic external media without bursting
(d) is site for many biochemical reactions necessary to sustain life.
(e) is a fluid contained inside the nucleus.
Ans. (a) Nucleus
(b) Golgi apparatus
(c) Cell wall
Q43. Which of the following can be made into crystal?
(a) A bacterium
(b) An Amoeba
(c) A virus
(d) A sperm
Ans. (c) A virus
Viruses lack any membranes and hence do not show characteristics of life until they enter a living body and use its cell machinery to multiply. Viruses can be made into crystals. A virus crystal is a collection of thousands of viruses and is used for chemical studies.
Q44. Plasmolysis in a plant cell is defined as
(a) breakdown (lysis) of plasma membrane in hypotonic medium
(b) shrinkage of cytoplasm in hypertonic medium
(c) shrinkage of nucleoplasm
(d) none of them
Ans. (b) shrinkage of cytoplasm in hypertonic medium
When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.
Q45. Which of these options are not functions of ribosomes?
(i) It helps in manufacture of protein molecules.
(ii) It helps in manufacture of enzymes.
(iii) It helps in manufacture of hormones.
(iv) It helps in manufacture of starch molecules.
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)
Ans. (c) (iii) and (iv)
The ribosomes, which are present in all active cells, are the sites of protein manufacture. Enzymes are proteins. Hormones and starch are not produced in ribosomes.
Q46. A person takes concentrated solution of salt, after some time, he starts vomiting. What is the phenomenon responsible for such situation? Explain.
Ans. Concentrated salt is a hypertonic solution. When a person drinks concentrated salt solution, water comes out of the cells of the alimentary canal by the process of exosmosis causing a loss of water in the cells. This results in dehydration and vomiting.
Q47. What is Golgi apparatus?
Ans. The Golgi apparatus consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cisterns. These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.
Q48. Draw a neat labelled diagram of a prokaryotic cell.
Image from NCERT
Q49. Find out the correct sentence.
(a) Enzymes packed in lysosomes are made through RER (rough endoplasmic reticulum).
(b) Rough endoplasmic reticulum and smooth endoplasmic reticulum produce lipid and protein respectively.
(c) Endoplasmic reticulum is related with the destruction of plasma membrane.
(d) Nucleoid is present inside the nucleoplasm of eukaryotic nucleus.
Ans. (a) Enzymes packed in lysosomes are made through RER (rough endoplasmic reticulum).
Digestive enzymes of lysosomes are produced by rough ER. Any enzyme which is meant for the lysosomes is synthesized on the ribosomes attached to the surface of rough ER.
Q50. Why does the skin of your finger shrink when you wash clothes for a long time?
Ans. The soap solution is hypertonic. We know that, when the cell is immersed in a hypertonic solution, water diffuse out of the cells by exosmosis, due to lower concentration of water outside the cell. As a result, the cell shrinks. Similarly, while washing clothes for a long time, exosmosis occurs in the skin cells resulting in the shrinkage of skin cells of our fingers.
Q51. Why do plant cells possess large sized vacuole?
Ans. Vacuoles are small sized in animal cells while plant cells have very large vacuoles. The central vacuole of some plant cells may occupy 50-90% of the cell volume. In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell. Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids, sugars, various organic acids and some proteins.
Q52. Which organelle is known as the powerhouse of the cell? Why?
Ans. Mitochondria are known as the powerhouses of the cell. It is because the energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphopshate) molecules. ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work.
Q53. Which cell organelle controls most of the activities of the cell?
Ans. Nucleus controls most of the activities of the cell (such as cellular metabolism, reproduction etc.) because it contains chromosomes. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells.
Q54. The undefined nuclear region of prokaryotes are also known as
(c) nucleic acid
Ans. (d) nucleoid
In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane. Such an undefined nuclear region containing only nucleic acids is called a nucleoid. Such organisms, whose cells lack a nuclear membrane, are called prokaryotes.
Q55. Why is the cell called the structural and functional unit of life?
Ans. Each cell acquires its structure and ability to function because of the organization of its membrane and organelles in specific ways. The cell thus has a basic structural organisation. This helps the cells to perform functions like respiration, obtaining nutrition, and clearing of waste material, or forming new proteins. Thus, the cell is the fundamental structural unit of living organisms. It is also the basic functional unit of life.
Q56. Cell theory was given by
(a) Schleiden and Schwann
Ans. (a) Schleiden and Schwann
The cell theory, that all the plants and animals are composed of cells and that the cell is the basic unit of life, was presented by two biologists, Schleiden (1838) and Schwann (1839). The cell theory was further expanded by Virchow (1855) by suggesting that all cells arise from pre-existing cells.