Structure of Cell
Short Questions and Answers
One Mark Questions with Answers
1. Ribosome is centre of
(a) fat synthesis
(b) protein synthesis
(d) synthesis of RNA
Answer: (b) protein synthesis
2. Rough endoplasmic reticulum is well developed in cells engaged in active
(a) lipid synthesis
(b) secretory function
(c) nucleotide synthesis
(d) protein synthesis
Answer: (d) protein synthesis
3. Ribosomes are attached to ER through
(d) hydrophobic interaction
Answer: (a) Ribophorins
4. Eukaryote 80s ribosome have two subunits of
Answer: (b) 60S+40S
5. In nature the ribosomes of plastids, mitochondria, bacteria and other prokaryotes are
Answer: (a) 70S
6. Peroxisomes are associated with
Answer: (a) photorespiration
7. Organelle having flattened cisternae near the nucleus is
(d) Golgi apparatus
Answer: (d) Golgi apparatus
8. Nucleolus takes part in synthesis of
(c) t RNA
Answer: (d) rRNA
9. Organelle connected with proteins synthesis is
Answer: (b) ribosome
10. The term thylakoidwas coined by
Answer: (a) Menke
11. Thylakoids are found inside
(a) endoplasmic reticulum
(c) Golgi apparatus
Answer: (b) chloroplast
12. Membrane covering vacuole is
(c) cell membrane
(d) middle lamella
Answer: (b) tonoplast
Two Marks Questions with Answers
1. Differentiate between pili and fimbriae.
Answer: Pili occur only in gram-negative bacteria while fimbriae are found in both gram positive and gram negative bacteria. Pili are longer and broader while fimbriae are shorter and narrower. Pili help in conjugation while fimbriae take part in adhesion. The number of pili per cell is 1-4 while the number of fimbriae is 300 to 400. Formation of pili is controlled by fertility factor while formation of fimbriae is controlled by a nucleoid gene.
2. Differentiate between gram positive and gram negative bacteria.
Answer: Gram positive bacteria remain coloured blue or purple with gram stain even after washing with absolute alcohol while gram negative bacteria do not retain the stain when washed with absolute alcohol. In case of gram positive bacteria the wall is single layered and the outer membrane is absent whereas in gram negative bacteria the wall is two layered with the presence of outer membrane. The thickness of wall in gram positive bacteria is 20-80 nm while the thickness of wall in gram negative bacteria is 8-12 nm.
3. What are thylakoids?
Answer: Thylakoids are membrane membrane lined flattened sacs which run throughout the stroma or matrix of the chloroplast. Since they take part in photosynthesis they are also called photosynthetic thylakoids. Thylakoids are thus the structural elements of the chloroplast. In the chloroplast of higher plants, thylakoids are stacked at places to form grana. Each granum has to 2-100 thylakoids. Thylakoid membranes possess photosynthetic pigments and coupling factors. The coupling factors are involved in ATP synthesis.
4. Differentiate between the outer mitochondrial membrane and the inner mitochondrial membrane.
Answer: Outer mitochondrial membrane is smooth whereas the inner mitochondrial membrane contains a large number of particles. The outer mitochondrial membrane bears porins or protein lined channels where as these are absent in inner mitochondrial membrane. Enzymes are fewer in outer mitochondria membrane as compared to the inner mitochondrial membrane. Foldings are absent in outer mitochondrial membrane where the inner mitochondrial membrane develops a large number of folding is called cristae.
5. What do you mean by autolysis?
Answer: It is self destruction of a cell, tissue or organ with the help of lysosomes. Lysosomes performing autolysis do not enclose the structures to be broken down. Instead they themselves burst to release the digestive enzymes. Autolysis occurs in aeging, dead and diseased cells. The disappearance of larval organs during metamorphosis is also due to autolysis.
Three Marks Questions with Answers
1. Mention some of the functions of mitochondria.
Answer: Mitochondria are miniature biochemical factories where food stuffs or respiratory substrates are completely oxidized to carbon dioxide and water. The energy liberated in the process is initially stored in the form of reduced coenzymes and reduced prosthetic groups. The latter soon undergo oxidation and form energy rich ATP. Because of the formation of ATP, the mitochondria are called power houses of the cell. Mitochondria provide important intermediates for the synthesis of several biochemicals like chlorophyll, cytochromes, pyrimidine, steroids, alkaloids etc. The matrix or inner chamber of mitochondria has enzymes for the synthesis of fatty acids. Enzymes required for the elongation of fatty acids have been reported in the outer mitochondrial membrane.
2. Differentiate between leucoplast and chromoplast.
Answer: Leucoplast are colourless plastids. Chromoplast are orange-red plastids. Leucoplast usually occur in unexposed parts of the plants. Chromoplasts are commonly found in exposed parts like flowers and fruits. The shape of leucoplast is more regular mostly rounded while the shape of chromoplast is irregular and having angles due to crystallisation of pigments. Leucoplast do not attract animals as they are colourless while chromoplast attract animals for pollination and dispersal.
3. What are cisternae, vesicles and tubules?
Answer: Cisternae are flat interconnected sac like parts of the endoplasmic reticulum which are 40-50 nm in diameter. The cisternae are found in bundles where they lie parallel to one another. They occur in the cells actively involved in synthetic activity. Vesicles are oval or rounded sacs of 25-500 nm in diameter. The vesicles appear as small vacuoles isolated in the cytoplasm. Vesicles are also called microsomes. Tubules are tube like extensions which may be connected with cisternae or vesicles to form a reticular system. The tubules can be a regular or irregular, branched or unbranched with a diameter of 50-100 nm.
4. Mention the functions of Golgi bodies.
Answer: All glandular cells depend upon Golgi complex for concentrating and pouring their secretion to the outside. Secretion vesicles of the glands usually contain zymogen granules. Protein synthesized by the rough endoplasmic reticulum reach the cisternae of the Golgi apparatus. Here, they combine with carbohydrates to form glycoproteins. Most of the complex carbohydrates, other than glycogen and starch, are synthesised inside the Golgi complex, example, pectic compounds, mucopolysaccharides,etc. Fatty acid and glycerol absorbed by intestinal epithelium are transferred as fat to lacteal through Golgi complex. It helps in the formation of acrosome.
5. What are the functions of ribosomes?
Answer: Ribosomes are sites for polypeptide or protein synthesis. Free ribosomes synthesize structural and enzymatic proteins for use inside the cell. The attached ribosomes synthesise proteins for transport. Ribosomes provide enzymes and factors for condensation of amino acids to form polypeptide. Newly synthesized polypeptide is provided protection from cytoplasmic enzymes by enclosing it in the groove of larger subunit of ribosome till it attains secondary structure.