Biology MCQs
Topic Notes: Biology
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
21
Mitotic chromosomes are formed by the coiling of a large cylindrical fiber known as what?
Answer:
Unit fibre
In the context of chromosome structure models, the 'unit fiber' refers to the fundamental chromatin fiber that undergoes hierarchical coiling and folding to form the highly condensed mitotic chromosome. This structural organization allows the long DNA molecule to be packed efficiently within the cell nucleus during cell division.
22
How does the chromosome number of an individual change over its lifespan?
Answer:
is constant
The chromosome number is a characteristic feature of a species and remains constant in the somatic cells of an individual throughout its entire life. While cells may divide or die, the genetic material within the nuclei of diploid cells remains stable, ensuring the continuity of the organism's genetic identity regardless of age or body weight.
23
When chromatid ends break, they exhibit 'stickiness' and fuse together; what structure is formed as a result of this fusion?
Answer:
Dicentric chromatid
When two broken chromatid ends fuse, they create a single chromatid containing two centromeres, known as a dicentric chromatid. This often occurs during chromosomal breakage-fusion-bridge cycles, leading to instability during cell division. The presence of two centromeres causes the chromosome to be pulled toward opposite poles during anaphase, resulting in further breakage.
24
Evaluate the following assertion and reason: Assertion (A): Reproduction is the process by which living organisms produce offspring. Reason (R): Male and female sex organs are mandatory for reproduction.
Answer:
A is true, but R is false
The assertion is true as it defines the biological purpose of reproduction. However, the reason is false because reproduction can occur through asexual means (e.g., binary fission, budding, fragmentation), which do not require specialized male and female sex organs. Therefore, sex organs are not mandatory for all forms of reproduction.
25
During cell division, what is the term for the alignment of chromosomes along the central plane of the cell?
Answer:
metaphase plate
The metaphase plate is an imaginary plane located at the equator of the cell where chromosomes align during the metaphase stage of mitosis or meiosis. This alignment is critical for ensuring that each daughter cell receives an identical and complete set of chromosomes when they are pulled apart during anaphase.
26
Which protein complexes are responsible for maintaining the cohesion between sister chromatids during cell division?
Answer:
Cohesins
Cohesins are specialized protein complexes that hold sister chromatids together from the time of DNA replication until the onset of anaphase. This physical linkage is essential for ensuring that each daughter cell receives an identical set of chromosomes during mitosis and meiosis, preventing premature separation.
27
During the early stages of embryonic development, at which specific phase does a fluid-filled cavity first emerge?
Answer:
Blastula
The blastula stage is defined by the formation of the blastocoel, a central fluid-filled cavity. This stage follows the morula phase and precedes gastrulation, representing a critical transition where the embryo organizes into a hollow sphere of cells known as blastomeres.
28
At which stage of mitosis are identical sister chromatids separated into distinct chromosomes?
Answer:
end of anaphase
During anaphase, the centromeres split and the sister chromatids are pulled toward opposite poles of the cell by spindle fibers. By the end of anaphase, these chromatids are officially considered individual chromosomes, ensuring each daughter cell receives an identical set.
29
Cytokinesis is defined as the physical division of which cellular component?
Answer:
cytoplasm
Cytokinesis is the final stage of cell division, following mitosis or meiosis, where the cytoplasm of a single eukaryotic cell divides into two distinct daughter cells. This process ensures that each new cell receives a complete set of organelles and cellular machinery.
30
What is the name given to the set of spindle fibers that form during the prophase stage of cell division?
Answer:
mitotic spindle
The mitotic spindle is a structure composed of microtubules that forms during prophase. It is essential for segregating chromosomes into the daughter cells during the later stages of mitosis.