Cellular Organisation, Biomolecules, and Cell Division: MCQ Test
Test your comprehensive knowledge of cell structure, biomolecules, and cell division processes, suitable for competitive exams, based on the provided learning materials.
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Showing questions 61 - 80 of 80
61. The enzyme carbonic anhydrase accelerates the reaction of carbon dioxide and water to form carbonic acid by approximately how many times?
By using the enzyme present within the cytoplasm called carbonic anhydrase, the reaction speeds dramatically with about 600,000 molecules being formed every second, compared to 200 molecules per hour without the enzyme. This represents an acceleration of about 10 million times.
62. In an enzyme-catalysed reaction, the difference in average energy content of the substrate from that of the transition state is called the:
The difference in average energy content of ‘S’ from that of this transition state is called ‘activation energy’. Enzymes eventually bring down this energy barrier.
63. When an inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme by competing for the active site, it is known as a:
When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. Due to its close structural similarity with the substrate, the inhibitor competes with the substrate for the substrate-binding site of the enzyme.
64. Enzymes are classified into 6 classes. Which class of enzymes catalyzes the linking together of two compounds by forming bonds such as C-O, C-S, C-N, or P-O?
Ligases are enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds.
65. Co-factors are non-protein constituents bound to the apoenzyme to make it catalytically active. Which type of co-factor is an organic compound that is tightly bound to the apoenzyme, such as haem in peroxidase?
Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are tightly bound to the apoenzyme. For example, in peroxidase and catalase, haem is the prosthetic group and it is a part of the active site of the enzyme.
66. In a typical eukaryotic cell cycle, what percentage of the total duration does the interphase last?
In the 24 hour average duration of cell cycle of a human cell, cell division proper lasts for only about an hour. The interphase lasts more than 95% of the duration of cell cycle.
67. During the S phase of the cell cycle, DNA synthesis or replication takes place. If the initial amount of DNA is denoted as 2C, what will be the amount of DNA per cell after the S phase, and what happens to the chromosome number?
During S phase, the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. However, there is no increase in the chromosome number; if the cell had diploid or 2n number of chromosomes at G1, even after S phase the number of chromosomes remains the same, i.e., 2n.
68. Some cells in adult animals, such as heart cells, do not appear to exhibit division and exit the G1 phase to enter an inactive stage. What is this quiescent stage called?
These cells that do not divide further exit G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle.
69. Mitosis is also called 'equational division' because:
Since the number of chromosomes in the parent and progeny cells is the same, mitosis is also called as equational division.
70. At which stage of mitosis do the chromosomes condense to form compact mitotic chromosomes, and the centrosomes begin to move towards opposite poles?
Prophase is marked by the initiation of condensation of chromosomal material. The centrosome, which had undergone duplication during S phase, now begins to move towards opposite poles of the cell.
71. The complete disintegration of the nuclear envelope marks the start of which phase of mitosis, where chromosomes are spread through the cytoplasm and are most clearly visible for morphological study?
The complete disintegration of the nuclear envelope marks the start of the second phase of mitosis, Metaphase. By this stage, condensation of chromosomes is completed and they can be observed clearly under the microscope. This is the stage at which morphology of chromosomes is most easily studied.
72. In animal cells, cytokinesis is achieved by the appearance of a furrow in the plasma membrane. How does cytokinesis differ in plant cells?
In an animal cell, cytokinesis is achieved by the appearance of a furrow in the plasma membrane. Plant cells however, are enclosed by a relatively inextensible cell wall, therefore they undergo cytokinesis by a different mechanism. In plant cells, wall formation starts in the centre of the cell and grows outward to meet the existing lateral walls, beginning with the formation of a cell-plate.
73. What term describes the multinucleate condition that arises when karyokinesis is not followed by cytokinesis, such as in the liquid endosperm of coconut?
In some organisms karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises leading to the formation of syncytium (e.g., liquid endosperm in coconut).
74. Which of the following statements about meiosis is INCORRECT?
Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II but only a single cycle of DNA replication (before Meiosis I).
75. During Prophase I of meiosis, chromosomes start pairing together in a process called synapsis. The complex formed by a pair of synapsed homologous chromosomes is known as a:
During zygotene stage, chromosomes start pairing together and this process of association is called synapsis. The complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad.
76. Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during which stage of Prophase I of meiosis?
During pachytene stage, the four chromatids of each bivalent chromosomes becomes distinct and clearly appear as tetrads. This stage is characterised by the appearance of recombination nodules, the sites at which crossing over occurs between non-sister chromatids of the homologous chromosomes.
77. In meiosis, the X-shaped structures formed at the sites of crossovers between homologous chromosomes, which become visible during diplotene due to the dissolution of the synaptonemal complex, are called:
The beginning of diplotene is recognised by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers. These X-shaped structures, are called chiasmata.
78. During Anaphase I of meiosis, what separates and what remains associated?
In Anaphase I, the homologous chromosomes separate, while sister chromatids remain associated at their centromeres.
79. The stage between the two meiotic divisions (Meiosis I and Meiosis II) is called interkinesis. What is a key characteristic of this stage?
The stage between the two meiotic divisions is called interkinesis and is generally short lived. There is no replication of DNA during interkinesis.
80. Meiosis is significant for sexually reproducing organisms primarily due to two reasons. What are they?
Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms... It also increases the genetic variability in the population of organisms from one generation to the next.