Tiêu đề Ex-1 Cell The unit of life Reviewed.pdf ✅

30 CELL THE UNIT OF LIFE EXERCISE – 1: Basic Objective Questions Introduction to Cells 1. Unicellular microscopic organisms were first studied by (a) Robert Hooke (b) Priestley (c) Pasteur (d) Leeuwenhoek Ans. (d) Sol. Leeuwenhoek, the Dutch scientist was the first to study unicellular organisms like bacteria and protozoa. He also studied animal cells. Robert Hooke coined the term "cell". Pasteur discovered the process of pasteurisation. Priestley discovered oxygen gas. 2. Cell theory is not applicable for (a) Bacteria (b) Fungus (c) Algae (d) Virus Ans. (d) Sol. The Cell theory states that “All living organisms are formed of one or more cells. New cells arise from pre-existing cells by cell division. Cell is the fundamental unit of structure and function in living organism.” Viruses are an exception to the cell theory because they lack protoplasm and are only made up of a protein coat (Capsid) and have either DNA or RNA. Bacteria, fungi and algae all have a cell membrane and a protoplasm. 3. The most likely method, used to determine the ultrastructure of a cell organelle is (a) Autoradiography (b) Microdissection (c) Electron microscopy (d) Phase contrast microscopy Ans. (c) Sol. An electron microscope can provide higher magnification and resolution than autoradiography, microdissection and phase contrast microscope since the wavelength of its electrons are shorter than the wavelength of light. 4. Omnis cellula-e cellula i.e., new cells arise from pre-existing cells; this statement was given by (a) Schleiden and Schwann (b) Rudolf Virchow (c) Robert Brown (d) Robert Hooke Ans. (b) Sol. Omnis cellula-e cellula was given by Rudolf Virchow and it means that new cells arise from pre- existing cells. 5. Cell theory was formulated by (a) Schleiden and Schwann (b) Robert Hooke (c) Leeuwenhoek (d) Marcello Malpighi Ans. (a) Sol. Cell theory was formulated by Schleiden and Schwann which states that living organisms are made of cells and substances produced by cells. Robert Hooke was the first person to use the term "cell". Leeuwenhoek is known as the "father of microbiology". Marcello Malpighi discovered capillaries using primitive microscopes. 6. Golgi apparatus is absent in (a) Higher plants (b) Yeast (c) Bacteria and blue green algae (d) Liver cells Ans. (c) Sol. Golgi apparatus is a membrane-bound organelle that specializes in protein packaging. It is only seen in eukaryotes. It is absent in primitive cells like bacteria and blue-green algae. 8. Which of the following features is common to prokaryotes and many eukaryotes ? (a) Chromatin material present
CELL THE UNIT OF LIFE 31 (b) Cell wall present (c) Nuclear membrane present (d) Membrane-bound subcellular organelles present Ans. (b) Sol. With a few exceptions like Mycoplasma, almost all prokaryotes have cell walls. Amongst eukaryotes, the cell wall is seen in some protists and all fungi and plant cells. Nuclear membranes, membrane-bound organelles and chromatin are distinguishing features of eukaryotes. 9. Match the columns I and II, and choose the correct combination from the options given : Column I Column II (Cell) (Size) (i) Mycoplasma K 3 to 5 μm (ii) RBCs L 10 to 20 μm (iii) Bacteria M 7 μm (iv) Typical eukaryotic cell N 0.3μm (a) i–N, ii–L, iii–K, iv–M (b) i–K, ii–M, iii–N, iv–L (c) i–N, ii–M, iii–K, iv–L (d) i–K, ii–L, iii–N, iv–M Ans. (c) Sol. Mycoplasma is the smallest bacterium with a size of 0.3μm as it lacks a cell wall. A typical bacterial cell measures 3-5μm in length. Erythrocytes or red blood cells are 7μm in diameter. Typical eukaryotic cells are within the range of 10-20 microns. 10. Assertion: Rudolf Virchow modified the hypothesis of cell theory given by Schleiden and Schwann. Reason: Cell theory says that all cells arise from preexisting cells. (a) If both assertion and reason are true and reason is the correct explanation of assertion. (b) If both assertion and reason are true but reason is not the correct explanation of assertion. (c) If assertion is true but reason is false. (d) If both assertion and reason are false. Ans. (b) Sol. Schleiden and Schwann theory proposed the cell in 1838-39 but did not tell about how cells were formed. Rudolf Virchow gave omnis cellula e cellula in 1858. He stated that pre-existing cells divide and form new cells by multiplication. This way a new shape was given to the cell theory by Virchow. As per the cell theory: - Every living organism present on earth is made up of cells. - The cell is the basic unit of life. - All cells arise from pre-existing cells. Prokaryotic Cells 11. Prokaryotic cells are generally _____ and multiply _____ than the eukaryotic cells. (a) smaller, slower (b) larger, slower (c) smaller, faster (d) larger, faster Ans. (c) Sol. 0.1 to 5.0 μm in size, prokaryotic cells are significantly smaller than eukaryotic cells, which have sizes ranging from 10 to 100 μm. Prokaryotic cells multiply more rapidly, since their mode of reproduction is not so complex as compared to eukaryotic cells. 12. Which layer of the cell envelope determines the shape of the cell and provides a strong structural support to prevent the bacterium from bursting or collapsing ? (a) Cell wall (b) Cell membrane (c) Glycocalyx (d) Capsule Ans. (a) Sol. The bacterial cell has different structures for the gram-negative and gram-positive bacteria but a common feature is that it is mostly composed of peptidoglycan. This strong molecule is the reason why the cell wall determines the shape of the bacterium and also provides strong structural support. 13. Gas vacuoles are found in (a) Blue green algae / Cyanobacteria (b) Purple and green photosynthetic bacteria (c) Both a and b (d) All bacteria Ans. (c)
32 CELL THE UNIT OF LIFE Sol. Vacuoles are structures which are used to store food materials in the cells. Gas vacuoles, which are found in blue-green, purple and green photosynthetic bacteria, are hollow cylindrical structures and are made up of gas vesicles. These vacuoles inflate and deflate to provide buoyancy and help in floating. 14. Which one does not differ in E. coli and Chlamydomonas? (a) Ribosome (b) Cell wall (c) Cell membrane (d) Chromosomal organisation Ans. (c) Sol. The cell membrane which is also known as the plasma membrane has essentially the same structure in both E.coli which is a bacterium (prokaryote) and Chlamydomonas which is an alga (eukaryote). Prokaryotes and eukaryotes have different ribosomal structure, cell wall structure and chromosomal organisation. 15. Extension of plasma membrane in prokaryotic cell is (a) Mesosome (b) Glycocalyx (c) Ribosome (d) Pili Ans. (a) Sol. Mesosomes, also known as chondroid, are invaginations of the plasma membrane in prokaryotic cells. They aid the process of respiration by increasing the surface area of the cell. 16. Choose the wrong statements regarding bacterial cell A. Glycocalyx is the outermost envelope in bacteria. B. Glycocalyx could be a loose sheath called capsule. C. Glycocalyx may be thick and tough called slime layer. D. A special structure formed by the plasma membrane is called mesosome. E. Small bristle-like fibers sprouting out of the cell are called fimbriae. (a) A and E are wrong (b) D and E are wrong (c) B and C are wrong (d) A and D are wrong Ans. (c) Sol. The Glycocalyx is an outer layer present particularly in bacteria. When present as a loose sheath, it is termed the slime layer. When the glycocalyx is thick and tough, it is termed the capsule. It is a combination of glycoprotein and glycolipid. 17. Bacteria show a range in the number of arrangement of flagella. Bacterial flagellum is composed of (a) Two parts – pili and fimbriae (b) Three parts – filament, hook and basement membrane (c) Three parts – filament, shaft and basal body (d) Three parts – filament, hook and basal body Ans. (d) Sol. The flagellum is a whip-like structure that helps with bacterial motility. It consists of 3 parts. The filament is the long helical structure made of the protein flagellin. The basal body functions as the motor while the hook connects the filament to the basal body. 18. Reserve material in prokaryotic cells are stored in the cytoplasm in the form of (a) Pyrenoids (b) Paramylon bodies (c) Inclusion bodies which are bounded by single membrane (d) Inclusion bodies which are not bounded by any membrane system Ans. (d) Sol. In prokaryotes, nutrients and other reserve materials are stored in the cytoplasm in the form of cell inclusion bodies. These are not bounded by any membrane system which is a characteristic feature of prokaryotic cells. Pyrenoids are found in the chloroplasts in algae and hornworts to promote photosynthetic carbon dioxide fixation. Paramylon bodies are structures which reserve food in Euglena. 19. What is true about genetic material of a prokaryotic cell ? (a) Lacks histones (b) Not enveloped by nuclear membrane (c) Composed of a single circular DNA molecule (d) All of these Ans. (d)
CELL THE UNIT OF LIFE 33 Sol. The genetic material in prokaryotic cells is carried on a single circular DNA molecule which is in direct contact with the cytoplasm, since the nucleus is not enveloped by a nuclear membrane. The DNA strand lack histones, so there is no true nucleus but a compact DNA structure called the nucleoid. 20. _____ are self-replicating, extrachromosomal segments of double stranded circular and naked DNA, present in a bacterial cell. (a) Plasmids (b) Nucleoid (c) Mesosomes (d) Bacteriophages Ans. (a) Sol. Plasmids are extrachromosomal segments of double- stranded circular and naked DNA that are separated from the chromosomal DNA and hence are capable of replicating on their own. The genes carried in plasmids may also provide bacteria with genetic advantages, such as antibiotic resistance. They are naturally present in bacterial cells and may also occur in some eukaryotes. 21. Mesosomes are the infoldings of cell membrane, which (i) are present in both prokaryotic and eukaryotic cells (ii) help in cell wall formation, DNA replication and respiration (iii) increase the surface area of plasma membrane. (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iii) (d) (i), (ii) and (iii) Ans. (b) Sol. Mesosomes are usually found in association with the site of cell division or the nucleus, hence it helps in DNA replication. It comprises of vesicles tubules and whorls, which help in the cell wall formation and respiration. Since, they are the invaginations of the cell membrane, they increase its surface area. Statement (I) is incorrect as Mesosomes are absent in eukaryotes. 22. Correct sequence of layers of bacterial cell envelope from outward to inward is (a) Cell wall  Glycocalyx  Cell membrane (b) Cell membrane  Glycocalyx  Cell wall (c) Glycocalyx  Cell wall  Cell membrane (d) Glycocalyx  Cell membrane  Cell wall Ans. (c) Sol. Glycocalyx is the extra coating of macromolecules outside the cell wall forming a protective layer. The cell wall is a strong and rigid structure which determines the shape of the bacterium and also provides a strong structural support. The cell membrane is the innermost phospholipid bilayer which is semi-permeable in nature. 23. Prokaryotic ribosome has sedimentation coefficient of (a) 80S (b) 70S (c) 40S (d) 60S Ans. (b) Sol. The sedimentation coefficient is known as the amount of time it would take the particle to reach its terminal velocity under the given acceleration if there were no drag. The sedimentation coefficient of prokaryotic ribosomes (made up of the 50S and 30S) is 70S. The Svedberg (S) is the unit used to measure the sedimentation coefficient. The sedimentation coefficient of eukaryotic ribosomes is 80 S (made up of 60S and 40S subunits). 24. Polyribosomes are aggregation of (a) Ribosomes and rRNA (b) Peroxisomes (c) Several ribosomes held together by a string of mRNA (d) rRNA Ans. (c) Sol. During the translation phase of protein synthesis, several ribosomes become attached to a single mRNA molecule. This structure is called as polyribosome. They serve to convert the information contained in mRNA into protein. In eukaryotes, polyribosomes are attached to the surface of the rough endoplasmic reticulum (RER), while in bacteria, they are found free in the cytoplasm. 25. Assertion: The cells that have membrane bound organelles are called eukaryotic. Reason: The cells that lack membrane bound organelles are called prokaryotic.