THE CELL
FILL IN THE BLANKS
Q.01: Fill in the blanks:
(i) In eukaryotic cell, chromatin material is bounded by ________. (nuclear membrane)
(ii) A group of ribosomes attached to mRNA is known as ________. (polysome)
(iii) ________ is the place on chromosomes where spindle fibres are attached during cell division. (centromere)
(iv) The endoplasmic reticulum with attached ribosomes is known as ________. (rough endoplasmic reticulum)
(v) The soluble part of the cytoplasm is called ________. (sol)
TRUE/FALSE
Q.02: Write whether the statement is ‘true’ or ‘false’ and write the correct statement if it is false.
(i) Cell membrane is present in all eukaryotic cells. (TRUE)
(ii) Chloroplast and mitochondria do not have hereditary material. (FALSE)
CORRECT: Chloroplast and mitochondria have hereditary material.
(iii) Centriole is involved in cell secretions. (FALSE)
CORRECT: Centriole is involved in cell division.
(iv) Sometimes many ribosomes get attached to the same stretch of mRNA forming a structure called the cytosome. (FALSE)
CORRECT: Sometimes many ribosomes get attached to the same stretch of mRNA forming a structure called the polysome.
(v) Mitochondria are very important organelles of the eukaryotic cells. (TRUE)
MULTIPLE CHOICE QUESTIONS
Q.03: Multiple choice questions.
(i) Which statement about the nuclear envelope is not true?
(a) It has pores.
(b) It is a double membrane structure.
(c) Its inner membrane bears ribosomes.
(d) RNA and some proteins pass through it.
ANSWER: (c) Its inner membrane bears ribosomes.
EXPLANATION: Ribosomes are formed and assembled in the nucleolus, and then pass through nuclear pores into cytoplasm. They are not attached to the inner nuclear membrane.
(ii) Which statement about plastids is true?
(a) They are surrounded by a single membrane.
(b) They are the power house of cell.
(c) They are found in all organisms.
(d) They contain DNA and ribosomes.
ANSWER: (d) They contain DNA and ribosomes.
EXPLANATION: Stroma of the chloroplasts contains proteins, some ribosomes and a small circular DNA. This is because some proteins required for photosynthesis are synthesized here. Furthermore, chloroplast is also a self-replicating organelle.
(iii) Which type of cell would probably be most appropriate to study lysosomes?
(a) Phagocytic white blood cells
(b) Mesophyll cell of leaf
(c) Nerve cell
(d) Muscle cell
ANSWER: (a) Phagocytic white blood cells
EXPLANATION: Phagocytic white blood cells are involved in phagocytic activity in which any foreign particles or germs are engulfed and digested by the enzymes secreted by lysosomes. So, white blood cells are the best choice for observing the role of lysosomes.
(iv) Which of the following pairs of structure-function is mismatched?
(a) Ribosomes; Protein synthesis
(b) Nucleolus; ribosomes production
(c) Golgi; muscle contraction
(d) Lysosomes; intracellular digestion
ANSWER: (c) Golgi; muscle contraction
EXPLANATION: Golgi bodies are involved in cell secretions which are synthesized on RER and then further processed in Golgi apparatus and then transported as primary lysosomes. So, Golgi bodies are nothing to do with muscle contraction.
(v) Which of the following statements about bound ribosomes is correct?
(a) They are structurally different from free ribosomes.
(b) They are enclosed in their own membrane.
(c) They are concentrated in the cisternal space of rough ER.
(d) They are attached to cisternal surface.
ANSWER: (d) They are attached to cisternal surface.
EXPLANATION: The ribosomes present on rough endoplasmic reticulum are attached to the surface tubular membranes called cisternae.
Q.04: SHORT QUESTIONS
(i) Describe various movements involved in the transport of materials across the cell membrane.
ANSWER:
Following types of movements are involved in the transport of materials across the cell membrane:
(1) Non-Facilitated Transport: The non-polar or lipid soluble substances easily cross lipid bilayer in plasma membrane. This is called non-facilitated transport.
(2) Facilitated Transport: Polar molecules move through membrane with the help of special transport proteins. This is called facilitated transport.
(3) Passive Transport: Many small molecules constantly leave or enter the cell by passive transport, which is the movement of substances from higher to lower concentration. This may be:
(a) Diffusion: The movement of solute from higher to lwer concentration.
(b) Osmosis: The movement of water (solvent) across a membrane from an area of higher solvent concentration to an area of lower solvent concentration.
(4) Active Transport: Some substances move against the concentration gradient, i.e., from an area of low concentration to an area of high concentration. This uphill movement of materials requires energy that is provided by ATP. This is termed as active transport.
(5) Endocytosis: In many animal cells, the cell membrane helps to take in materials by infolding in the form of vacuoles. This type of intake is termed as endocytosis, which can either be phagocytosis (to engulf solid particles) or pinocytosis (to take in liquid material).
(ii) State various structural modifications in a cell involved in secretions.
ANSWER:
Structural Modifications In Cell Involved In Secretions:
(1) Cell secretionsare initially proteins, synthesized within the cell on ribosomes, and then pushed into the channels of endoplasmic reticulum.
(2) From endoplasmic reticulum, they transported to the Golgi Apparatus as blebs or transport vesicles.
(3) The blebs fuse at the forming face of the Golgi complex and move towards maturing face. Here, they are converted into the finished products (glycoproteins).
(4) From maturing face, the secretions are pinched off as secretory granules or transport vesicles that merge with the plasma membrane to release the secretions out of the cell.
(iii) List the processes blocked by mitochondrial failure in a cell.
ANSWER:
Following processes will be blocked in the cell as a result of mitochondrial failure:
(1) Kreb’s cycle
(2) Electron transport chain
(3) Fatty acid metabolism
(iv) What will happen if a chromosome loses its centromere?
ANSWER:
Autophagy: “Autophagy is the self-eating of a cell or its components by its own lysosomes.” In this process, some old worn out parts of the cell, such as mitochondria, are engulfed by the primary lysosomes and digested to generate energy. In this way, the materials of the cell are recycled and cell may be renewed.
Autophagy helps in converting a tadpole larva into an adult amphibian. The tadpole larva of an amphibian has a tail. During development, the number and the activity of lysosomes in tail cells increase. The lysosomal enzymes start digesting tail cells, and finally, the whole tail is degenerated.
(v) How does autophagy help in converting a tadpole larva into an adult amphibian?
ANSWER:
Although bacterial and plant cell walls are totally different, yet they have a few similarities. For example:
(1) The bacterial cell wall is composed of polysaccharide chains bound covalently to shorter chains of amino acids. The plant cell wall is also composed of a polysaccharide, cellulose, though is differently structured.
(2) Both provide shape and protection to the cell.
(vi) Is there any similarity between bacterial and plant cell wall?
ANSWER:
Although bacterial and plant cell walls are totally different, yet they have a few similarities. For example:
(1) The bacterial cell wall is composed of polysaccharide chains bound covalently to shorter chains of amino acids. The plant cell wall is also composed of a polysaccharide, cellulose, though is differently structured.
(2) Both provide shape and protection to the cell.
Q.05: EXTENSIVE QUESTIONS
(i) Compare structure and function of chloroplasts and mitochondria.
ANSWER:
Consult textbook at page 59 — 61.
(ii) State ‘Cell Theory’ and discuss its emergence.
ANSWER:
Consult textbook at page 46 — 48.
(iii) Write notes on: (a) Cytoskeleton (b) Peroxisomes & Glyoxysomes
ANSWER:
Consult textbook at page 57 — 58.
(iv) What might happen if some lysosomal enzymes are absent? Explain with examples.
ANSWER:
The absence of some lysosomal enzymes may result in certain congenital disease which are caused by the accumulation of substances such as glycogen or various glycolipids, within the cell.
These are also called storage diseases and are produced by a mutation that effect one of the lysosomal enzymes involved in the catabolism of a certain substance.
For example, in glycogenosis type II disease, the liver and muscle appear filled with glycogen within membrane bound organelles. In this disease, an enzyme that degrades glycogen to glucose, is absent.
About twenty such diseases are known these days, which are because of absence of a particular enzyme. For example, Tay-Sach’s disease is because of absence of an enzyme that is involved in the catabolism of lipids. Accumulation of lipids in brain cells lead to mental retardation and even death.
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