All Free Biology MCQs with Answers

• A. Centromere
• B. Chiasma
• C. Chromatid
• D. Synaptonemal complex

Explanation: The chiasma is the visible site where non-sister chromatids exchange genetic segments during crossing over.

• A. Pachytene
• B. Diplotene
• C. Diakinesis
• D. Zygotene

Explanation: Terminalization (movement of chiasmata toward chromosome ends) occurs in diakinesis, the final stage of Prophase I.

• A. Chromatids remain attached to one another until anaphase
• B. Metaphase chromosomes become aligned at the metaphase plate
• C. Chromosomes are grouped during telophase
• D. The nucleus is located prior to mitosis

Explanation: The centromere is a specialized region of a chromosome where two sister chromatids are held together until they separate during anaphase of cell division. During metaphase of mitosis or meiosis II, the sister chromatids are aligned at the metaphase plate, and the centromere acts as a point of attachment for microtubules from the spindle apparatus. These microtubules exert tension on the sister chromatids, ensuring that they are properly aligned. During anaphase, the proteins that hold the sister chromatids together at the centromere are degraded, allowing the sister chromatids to separate and move towards opposite poles of the cell. This ensures that each daughter cell receives the correct number of chromosomes.

• A. A chromosome in G1 of the cell cycle
• B. A replicate chromosome
• C. A chromosome found outside the nucleus
• D. A special region that holds two centromeres together

Explanation: In G1, each chromosome is a single chromatid. In G2, after DNA replication in S phase, as cell enter mitotic prophase, each chromosome consists of a pair of identical sister chromatids, where each chromatid contains a linear DNA molecule that is identical to the joined sister chromatid.

• A. 4
• B. 8
• C. 16
• D. 32

Explanation: Starting with a fertilized egg (zygote), a series of five cell divisions would result in a total of 32 cells in the early embryo.The number of cells at each division can be calculated using the formula:Total number of cells=2nwhere n is the number of cell divisions.For five cell divisions (n=5), the total number of cells would be:Total number of cells = 25 =32

• A. 10
• B. 20
• C. 30
• D. 40

Explanation: If there are 20 chromatids in a cell, it means that these chromatids are derived from 10 chromosomes. Each chromosome has two sister chromatids, so the total number of centromeres can be determined by dividing the total number of chromatids by 2.Number of centromeres = Total number of chromatids/2Number of centromeres = 20/2 = 10 So, if there are 20 chromatids in a cell, there are 10 centromeres.

• A. Binary fission would not allow for the formation of new organisms
• B. Cell division would allow for the orderly and efficient segregation of multiple linear chromosomes
• C. Cell division would be faster than binary fission
• D. Binary fision would not allow the organism to have complex cells

Explanation: Eukaryotic cell division is well-suited for organisms with multiple linear chromosomes, as it allows for the orderly segregation of these chromosomes into daughter cells. Each chromosome is condensed and organized into a distinct structure before being pulled apart during mitosis or meiosis, ensuring that each daughter cell receives the correct complement of chromosomes.

• A. The daughter cells have half the amount of cytoplasm and half the amount of DNA
• B. The daughter cells have half the number of chromosomes and half the amount of DNA
• C. The daughter cells have the same number of chromosomes and half the amount of DNA
• D. The daughter cells have the same number of chromosomes and the same amount of DNA

Explanation: At the end of mitosis and cytokinesis, the daughter cells produced are identical to each other and to the parent cell when it was in the G1 phase of the cell cycle in terms of the number of chromosomes and the amount of DNA. As the cell progresses through the cell cycle, it replicates its DNA during the S phase, resulting in the formation of identical sister chromatids for each chromosome. During mitosis, these sister chromatids are separated into two daughter cells, ensuring that each daughter cell receives a complete and identical set of chromosomes. Therefore, at the end of mitosis and cytokinesis, the daughter cells have the same number of chromosomes and the same amount of DNA as the parent cell in the G1 phase of the cell cycle. They are genetically identical to each other and to the original parent cell.

• A. A and B
• B. C and D
• C. E and A
• D. B and D

Explanation: Homologous chromosomes are chromosomes that are similar in size and shape. During metaphase of meiosis I, homologous pairs can be observed aligning next to each other at the metaphase plate, exhibiting similar size and shape.

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

Explanation: The term that describes centrioles beginning to move apart in animal cells is "prophase." During prophase of mitosis, the centrioles, which are located near the nucleus, start to move away from each other towards opposite poles of the cell. This movement is facilitated by microtubules and is essential for the formation of the mitotic spindle, which is responsible for separating sister chromatids during cell division.