Cell-The Basic Unit of Life
Short Questions and Answers
One Mark Questions with Answers
1. The new cells originate
(a) by bacterial fermentation
(b) from abiotic materials
(c) from pre-existing cells
(d) through regeneration of old cells
Answer: (c) from pre-existing cells
2. Nucleus was discovered by
(a) Robert Koch
(b) Leeuwenhoek
(c) Robert Brown
(d) Robert Hooke
Answer: (c) Robert Brown
3. Schleiden and Schwann are connected with
(a) Theory of cell lineage
(b) Cell theory
(c) Protoplasm is basis of life
(d) Nuclear control of cell
Answer: (b) Cell theory
4. Which one is an exception to cell theory?
(a) Virus
(b) Mycoplasma
(c) Alga
(d) All the above
Answer: (a) Virus
5. Cell theory was proposed by
(a) Watson and Crick
(b) Mendel and Morgan
(c) Schleiden and Schwann
(d) Robert Hooke
Answer: (c) Schleiden and Schwann
6. According to cell theory
(a) all cells are living
(b) all cells have nuclei
(c) cells reproduce by mitosis and meiosis
(d) cell are structural units of organisms
Answer: (d) cell are structural units of organisms
7. Cellular totipotency is related to
(a) synthesis of new cells
(b) formation of new plant
(c) capability of a cell to from whole organism
(d) formation of new species
Answer: (c) capability of a cell to from whole organism
8. Longest cell in our body is nerve fibre. The smallest is of
(a) human egg
(b) eye
(c) kidney and intestine
(d) blood
Answer: (d) blood
Two Marks Questions with Answers
1. Mention three advantages of unicellularity.
Answer: (1) The single cell in unicellular organisms performs all the functions of life.
(2) The single cell perceives all types of sensations and responds to the same.
(3) Regeneration is present still the fragment contains the nucleus.
2. Mention three disadvantages of unicellularity.
Answer: (1) In unicellular organisms a single cell has to perform all the activities of life.
(2) The different cells have little coordination. There cannot be any division of labour.
(3) Death of the cell will kill the organism.
3. Mention any two advantages of multicellularity.
Answer: In multicellular organism cell performs dual function one for themselves and the other for the whole organism. Secondly, despite performing dual functions a cell of a multicellular organism have lesser workload due to reduction in certain activities like protection contractibility, movement, etc.
4. Mention any two disadvantages of multicellularity.
Answer: (1) Loss of structure and function: Organisation at a higher level always results in loss of some structure and function of the lower level. This also happens in case of a multicellular organism.
(2) Power of division: Specialised cells often lose the power of division so that injury is not repaired, for example, nerve cells.
5. Differentiate between unicellular and multicellular organisms.
Answer: The body of the unicellular organism is made of a single cell while the body of multicellular organism has a large number of cells. In case of unicellular organism all the functions of the organism are performed by the same cell whereas in case of multicellular organism the cells have dual functions, one for themselves and other for the whole organism. In case of unicellular organism the cell processes power of division in case of multicellular organism all the cells do not have the power of division.
6. What is the significance of modern cell theory?
Answer: (a) there is structural similarity in cells belonging to diverse groups of organisms.
(b) all the cells perform similar metabolic activities.
(c) life exists only in the form of cells.
(d) life passes from one generation to the next as cells.
(e) all living beings are descendents of a primitive cell that developed on earth as the first eukaryote and prior to that as the first prokaryotes.
Three Marks Questions with Answers
1. What do you mean by cellular totipotency?
Answer: Cellular totipotency is the ability of a living somatic nucleated cell to form the complete organism. Cellular totipotency was first proposed by German botanist Haberlandt in 1902.
Theoritically all somatic should be totipotent since they carry the full gene complement of the individual. However, during their maturation the cells undergo differentiation and are able to return to their undifferentiated status. They, however, do so under special circumstances. The phenomenon is called the dedifferentiation. The differentiated cells can undergo division ultimately from the whole individual or a part of it. Totipotency can be easily demonstrated in plant cells. However, nucleus taken from any living somatic cell of frog can be shown to have complete genetic information and hence totipotent.
2. What does the cell theory state?
Answer: The cell theory states that the bodies of all organisms are made up of cells and their products so that cells are units of both structure and function of living organisms. This theory was jointly put forward by Schleiden and Schwann (1839).Development of cell theory illustrates how scientific methodology operates. It involves observation, hypothesis, formulation of theory and its modification. Schleiden found that all plant tissues were made of one or the other kind of cells. Therefore Schleiden concluded that cells constitute the ultimate units of all plant tissues. Schwann found that animal cells lack a cell wall instead they are covered by a membrane. Otherwise cells of both plants and animals are similar. Schwann defined a cell as membrane enlocked, nucleus containing structure.
3. What are the fundamental features of the cell theory?
Answer: Following are the five fundamental observation of the cell theory:
(a) Organisms are composed of cell and their products.
(b) Each cell is made of a small mass of protoplasm containing a nucleus in its inside and a plasma membrane with or without a cell wall on its outside.
(c) New cells arise from pre-existing cells.
(d) All cells are basically alike in the chemistry and physiology.
(e) Activities of an organism are the sum total of activities and interactions of its constituent cells.
4. What does the cell doctrine or modern cell theory or cell principal state?
Answer: Some of the observations of modern cell theory are as follows:
(a) the bodies of all living beings are made up of cells and their products.
(b) cells are units of structure in the body of living organisms.
(c) every cell is made up of a small mass of protoplasm having a number of organelles and a covering membrane.
(d) while a cell can survive independently its organelles cannot do so.
(e) the cells belonging to diverse organisms and different regions of the same organism has a fundamentally similarity in their structure, chemical composition and metabolism.
(f) life exists only in cells because all the activities of life are performed by cells.
5. What are the objections of modern cell theory?
Answer: (a) viruses do not have a cellular machinery. Even then they are considered to be organisms.
(b) in some organisms, the body is not differentiated into cells though it may have numerous nuclei.
(c) protozoans and many thallophytes have a uninucleate differentiated body which cannot be divided into cells. They are acellular.
(c) bacteria and cyanobacteria do not possess a nucleus. Many cell organelle are also absent.
(d) RBCs and sieve tube cells continue to live without nucleus and other vital organelles.
(e) Protoplasm is replaced by nonliving materials in the surface cells of skin and cork.
(f) connective tissue contains a lot of intracellular material or matrix in which the living cells are embedded.
6. Mention some methods where cellular totipotency is being extensively used.
Answer: (1) Rapid multiplication of desired plants.
(2) Multiplication of rare plants which reproduce through seeds with great difficulty.
(3) Embryos which failed to reach maturity.
(4) Production of virus free plants.
(5) Multiplication of sterile hybrids.
(6) Multiplication of products of protoplast fusion.
(7) Development of resistance to chemicals like weedicides.
(8) Induction and selection of mutants.