All Free Biology MCQs with Answers

• A. Chromatids must lose their kinetochores
• B. Cohesin must attach the sister chromatids to each other
• C. Cohesin must be cleaved enzymatically
• D. Kinetochores must attach to the metaphase plate

Explanation: In order for anaphase to begin, the kinetochores must attach to the metaphase plate. During metaphase, replicated chromosomes align along the metaphase plate, and the spindle fibers attach to the kinetochores, which are protein structures located at the centromere of each chromosome. Once all chromosomes are properly aligned and attached, the cell proceeds to anaphase.

• A. To increase their potential energy
• B. To allow the chromosomes to move without becoming entangled and breaking
• C. To allow the chromosomes to fit within the nuclear envelope
• D. To provide for the structure of the centromere

Explanation: Chromosomes coil during mitosis primarily to facilitate their efficient segregation into daughter cells. This coiling, known as chromosome condensation, compacts the genetic material into a more manageable form, making it easier to distribute evenly during cell division.

• A. The chromosomes are "reeled in" by the contraction of spindle microtubules
• B. Motor proteins of the kinetochores move the chromosomes along the spindle microtubules
• C. Non-kinetochore spindle fibers serve to push chromosomes in the direction of the poles
• D. Both (A) and (B)

Explanation: During mitosis, motor proteins associated with the kinetochores of chromosomes interact with microtubules of the spindle apparatus. These motor proteins use energy from ATP hydrolysis to move chromosomes along the spindle microtubules towards the poles.During anaphase of mitosis, the sister chromatids separate and are pulled toward opposite poles of the cell by the shortening of spindle microtubules. Motor proteins attached to the kinetochores of the chromosomes walk along the microtubules, pulling the chromosomes toward the poles.

• A. The presence of the pathogen made the experiment too contaminated to trust the results
• B. Their tissue culture methods needed to be relearned
• C. Infection causes lymphocytes to divide more rapidly
• D. Infection causes cell cultures in general to reproduce more rapidly
• E. Infection causes lymphocyte cultures to skip some parts of the cell cycle

Explanation: Based on the described experiment where lymphocytes incorporated labeled nucleotides at a significantly higher level after a pathogen was introduced into the culture, the research team could reasonably conclude that infection causes lymphocytes to divide more rapidly. The incorporation of labeled nucleotides is often used as a marker for DNA synthesis, which is a hallmark of cell division. If lymphocytes are incorporating labeled nucleotides at a higher rate after exposure to a pathogen, it suggests that they are undergoing increased DNA synthesis, which is indicative of more rapid cell division.

• A. Move directly into telophase
• B. Complete the cycle and divide
• C. Exit the cycle and switch to a non-dividing state
• D. Complete cytokinesis and form new cell walls

Explanation: If mammalian cells receive a go-ahead signal at the G1 checkpoint, they will proceed with the cell cycle and divide. The G1 checkpoint, also known as the restriction point, is a critical control point where the cell assesses its readiness to proceed with DNA synthesis (S phase) and subsequent cell division. If conditions are favorable and the cell receives the necessary signals indicating that it has adequate resources and environmental conditions to proceed, it will progress through the cell cycle and divide.

• A. G0
• B. G2
• C. G1
• D. S

Explanation: Cells that are in a non-dividing state are typically in the G0 phase of the cell cycle. In this phase, cells exit the cell cycle and enter a quiescent state where they perform their specialized functions without actively preparing for division.

• A. G0
• B. G1
• C. M
• D. G2

Explanation: The shortest part of the cell cycle is typically mitosis itself, which consists of several sub-phases including prophase, metaphase, anaphase, and telophase. Mitosis is a relatively rapid process compared to the overall duration of the cell cycle, typically taking only a fraction of the time it takes for cells to complete a full round of division.

• A. G0
• B. G1
• C. S
• D. G2

Explanation: DNA is replicated during the S phase of the cell cycle. The cell cycle consists of several phases: interphase (G1, S, and G2 phases) and mitosis (M phase). During the S phase, DNA replication occurs. This is when the cell duplicates its entire genome, ensuring that each daughter cell receives an identical copy of the genetic material. After DNA replication in the S phase, the cell proceeds to the G2 phase, where it prepares for cell division.

• A. G0
• B. G1
• C. G2
• D. M

Explanation: The restriction point, also known as the G1 checkpoint, is a crucial control point in the cell cycle. It occurs late in the G1 phase, just before the cell commits to DNA synthesis (S phase), where the cell assesses external signals and internal conditions to decide whether to proceed with the cell cycle or enter a non-dividing state (G0 phase).

• A. G0
• B. G1
• C. S
• D. G2

Explanation: Nerve and muscle cells are typically in the G0 phase of the cell cycle. The G0 phase is a resting phase where cells exit the active cell cycle and temporarily or permanently cease dividing. Nerve cells (neurons) and muscle cells (muscle fibers) are both examples of cells that are specialized for their functions and have largely exited the cell cycle. They remain in the G0 phase for most of their lifespan, only re-entering the cell cycle under certain conditions, such as injury or tissue regeneration.