Based on the information given above, indicate which phase of mitosis is occurring in the following onion cells: Prophase Interphase Telophase Prometaphase Metaphase
The Correct Answer and Explanation is:
To identify which phase of mitosis is occurring in onion cells, we need to consider the specific characteristics of each phase. Here’s a breakdown of the phases:
- Interphase: This is the phase where the cell prepares for mitosis. It consists of three sub-stages: G1, S, and G2. During interphase, the cell is not dividing, and the chromatin (the material that will condense into chromosomes) is not yet visible under the microscope. The nucleus is well-defined, and the cell is metabolically active.
- Prophase: This is the first phase of mitosis. In prophase, the chromatin condenses into visible chromosomes, which are two sister chromatids joined at the centromere. The nuclear membrane starts to break down, and the mitotic spindle begins to form. In plant cells, like onion cells, the spindle apparatus is made up of microtubules that stretch across the cell.
- Prometaphase: During prometaphase, the nuclear membrane completely dissolves. The chromosomes become more distinct, and microtubules from the spindle attach to the centromere of the chromosomes at specialized regions called kinetochores.
- Metaphase: In metaphase, the chromosomes align along the metaphase plate, which is an imaginary line equidistant from the two poles of the cell. This alignment is due to the forces exerted by the spindle fibers attached to the kinetochores.
- Anaphase: This phase is characterized by the separation of sister chromatids. The chromatids are pulled toward opposite poles of the cell by the spindle fibers.
- Telophase: During telophase, the chromatids reach the poles, and the nuclear membrane re-forms around the separated chromosomes. The cell is preparing to divide into two.
To determine which phase is occurring in the onion cells, you would look for specific markers, such as the appearance or disappearance of the nuclear membrane, the alignment of chromosomes, or the condensation of chromatin. The presence of distinct chromosomes and the breakdown of the nuclear membrane indicates prophase or prometaphase, while chromosome alignment along the center of the cell suggests metaphase.
