All Free Biology MCQs with Answers

• A. Telophase
• B. Anaphase
• C. Metaphase
• D. Interphase

Explanation: Interphase is the longest stage of the cell cycle, encompassing the period between cell divisions. During interphase, the cell grows, carries out its normal functions, and replicates its DNA in preparation for cell division. Interphase can be further divided into three sub-phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2). During G1, the cell grows and carries out its normal functions. In the S phase, DNA replication occurs, resulting in the synthesis of two identical copies of each chromosome. Finally, during G2, the cell continues to grow and prepares for cell division by synthesizing proteins necessary for mitosis or meiosis.

• A. Telophase
• B. Anaphase
• C. Prometaphase
• D. Metaphase

Explanation: The term that describes centromeres uncoupling, sister chromatids separating, and the two new chromosomes moving to opposite poles of the cell is "anaphase." Anaphase is the stage of mitosis or meiosis where the sister chromatids separate and move to opposite ends of the cell due to the shortening of the microtubules attached to the centromeres. This movement ensures that each daughter cell receives a complete set of chromosomes.

• A. Anaphase
• B. Prophase
• C. Telophase
• D. Metaphase

Explanation: Colchicine is a drug that interferes with the assembly of microtubules, which are crucial for the formation of the mitotic spindle. Without a functional spindle, the separation of chromosomes cannot occur properly. Therefore, cells treated with colchicine will typically be arrested in metaphase. During metaphase, the chromosomes are aligned along the metaphase plate, attached to the spindle fibers, and awaiting the signal for separation. Since colchicine prevents the proper formation of the spindle fibers, the chromosomes cannot segregate to opposite poles of the cell, leading to arrest at this stage.

• A. 16
• B. 23
• C. 46
• D. 92

Explanation: In mitosis, the number of chromosomes in the daughter cells is identical to the number of chromosomes in the parent cell. During metaphase of mitosis, each chromosome is composed of two sister chromatids, so if a cell contains 92 chromatids at metaphase, it means it has 46 chromosomes (since each chromosome consists of two sister chromatids). At the completion of mitosis, each daughter cell will receive an equal number of chromosomes. Therefore, each daughter cell would contain 46 chromosomes.

• A. Cell membrane synthesis
• B. Spindle fiber formation
• C. Nuclear envelope breakdown
• D. Formation of telophase nuclei

Explanation: Formation of telophase nuclei occurs after anaphase in both mitosis and meiosis. In anaphase, the sister chromatids separate and move to opposite poles of the cell. Following anaphase, the cell progresses into telophase.

• A. 10
• B. 20
• C. 30
• D. 40

Explanation: If there are 20 centromeres in a cell at anaphase, it indicates that the chromosomes have already undergone separation and are moving towards opposite poles of the cell. Anaphase is the stage of mitosis or meiosis where sister chromatids (each with one centromere) are pulled apart. Since each centromere corresponds to one chromosome (or chromatid), and during anaphase, each chromatid moves to opposite poles, we can infer that there are 20 chromosomes total in the cell at anaphase. Following cytokinesis, each daughter cell receives a portion of the chromosomes. Therefore, each daughter cell would receive half of the total number of chromosomes present in the parent cell at anaphase. So, each daughter cell would have 20/2 = 10 chromosomes.

• A. Centromere
• B. Centrosome
• C. Centriole
• D. Chromatid

Explanation: During mitosis in both plant and animal cells, the microtubules of the spindle originate from structures called centrosomes (also known as microtubule-organizing centers or MTOCs). In animal cells, centrosomes consist of a pair of centrioles surrounded by pericentriolar material. The centrosomes duplicate during the cell cycle, and each pair of centrosomes migrates to opposite poles of the cell during prophase. From these centrosomes, microtubules radiate outward, forming the mitotic spindle.

• A. 2
• B. 4
• C. 8
• D. 16

Explanation: During anaphase of mitosis, the sister chromatids separate and move towards opposite poles of the cell. Each chromatid is considered a chromosome. So if a cell has 8 chromosomes (each consisting of 2 sister chromatids) at metaphase, during anaphase, each sister chromatid will be pulled apart. Therefore, the cell will have 16 chromosomes during anaphase.

• A. A single large nucleus
• B. High concentrations of actin and myosin
• C. Two abnormally small nuclei
• D. Two nuclei

Explanation: If a cell completes mitosis but not cytokinesis, the result would be a cell with two nuclei. This condition is known as "cellular multinucleation." Essentially, the genetic material has been segregated into two separate nuclei, but the cytoplasm has not been divided into two distinct daughter cells. As a result, the cell will have multiple nuclei within a single cytoplasmic compartment. This can be observed in certain types of cells, such as muscle cells and some fungi.

• A. The spindles contain microfibrils in addition to microtubules, whereas animal spindles do not contain microfibrils
• B. Sister chromatids are identical, but they differ from one another in animals
• C. A cell plate begins to form at telophase, whereas in animals a cleavage furrow is initiated at that stage
• D. Chromosomes become attached to the spindle at prophase, whereas in animals chromosomes do not become attached until anaphase

Explanation: One key difference between mitosis and cytokinesis in higher plants and animals is the process by which cytokinesis occurs. In animals, cytokinesis typically involves the formation of a cleavage furrow, which is a constriction around the cell equator formed by a contractile ring of actin and myosin filaments. This furrow deepens until the cell is pinched into two daughter cells. In higher plants, however, cytokinesis occurs differently due to the presence of a cell wall. During cytokinesis in plant cells, a structure called the cell plate forms. This cell plate develops in the middle of the dividing cell, and it consists of vesicles containing cell wall materials and other components. These vesicles fuse together, gradually forming a new cell wall that separates the two daughter cells.