Cell Cycle and Cell Division (SAQs)

Botany-1 | 11. Cell Cycle And Cell Division – SAQs:
Welcome to SAQs in Chapter 11: Cell Cycle And Cell Division. This page includes the most important FAQs from previous exams. Each answer is provided in simple English, followed by a Telugu explanation, and presented in the exam format. This approach helps you prepare effectively and aim for top marks in your final exams.

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SAQ-1 : Which division is necessary to maintain constant chromosome number in all body cells of multicellular organism and why?

Introduction:

In multicellular organisms, it’s crucial to keep the number of chromosomes the same in all body cells to ensure the proper functioning and development of the organism. The process that makes this possible is called mitosis.

Mitosis Maintains Constant Chromosome Number:

Mitosis is a type of cell division that ensures each new cell gets an exact copy of the chromosomes from the parent cell. During this process, a single cell divides into two identical daughter cells, each with the same chromosome number as the parent cell. This consistency is important because it keeps the genetic information the same across all body cells, allowing the organism to grow and develop correctly.

Cell Growth, Wound Healing, and Regeneration:

Mitosis isn’t just about maintaining chromosome numbers—it’s also crucial for the body’s growth and repair. For example, when a multicellular organism grows, cells multiply through mitosis, increasing the total number of cells. Similarly, when the body needs to heal a wound, mitosis helps create new cells to replace the damaged ones, allowing the body to recover. This process is also vital for regeneration, helping organisms restore tissues and maintain their health.

Restoring Surface-to-Volume Ratio:

As cells grow, their volume increases faster than their surface area, which can lead to inefficiencies in nutrient exchange and waste removal. Mitosis helps solve this problem by dividing large cells into smaller ones, thereby restoring a balanced surface-to-volume ratio. This balance is essential for cells to function effectively, ensuring they can absorb nutrients and expel waste efficiently.

Summary:

Mitosis is necessary to maintain a constant chromosome number in all body cells of multicellular organisms. By ensuring that daughter cells inherit the same genetic information as the parent cell, mitosis supports proper growth, healing, and tissue regeneration. Additionally, it helps restore the surface-to-volume ratio in growing cells, ensuring they remain efficient in their functions.al.

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SAQ-2 : Though redundantly described as a resting phase, interphase does not really involve rest. Comment.

Introduction:

Interphase is often mistakenly called a “resting phase,” but this term is misleading. Instead of resting, the cell is actually very busy during interphase, carrying out vital processes that prepare it for the next stages of cell division.

Misconception of “Resting Phase”:

The idea that interphase is a period of rest is a common misconception. The term “resting phase” might make it seem like the cell is taking a break, but that’s far from the truth. In reality, interphase is a time of intense activity where the cell is actively growing and getting ready for division. It’s like the cell is getting all its supplies in order before a big project, rather than taking a break.

Key Activities During Interphase:

During interphase, the cell goes through several important stages:

G1 Phase (First Gap Phase):

In the G1 phase, the cell is like a factory in full swing. It grows larger and produces all the proteins and enzymes it will need later. This phase is crucial because the cell is building the tools it will use to copy its DNA and grow.

S Phase (Synthesis Phase):

Next, in the S phase, the cell focuses on copying its DNA. Imagine it as making a backup of all its important data so that when it divides, both new cells will have the same information. Each chromosome is carefully duplicated, ensuring that the future cells have the correct genetic material.

G2 Phase (Second Gap Phase):

Finally, in the G2 phase, the cell does some last-minute preparations. It grows a bit more, checks for any errors, and produces the proteins and organelles needed for the final stage of division, called mitosis. It’s like double-checking everything before starting a big task to make sure everything is in place.

Summary:

Interphase is far from a resting phase; it is a time of crucial activity where the cell grows, duplicates its DNA, and gets ready for division. Understanding this phase is essential because it lays the groundwork for how cells function, grow, and eventually divide. Without the busy work of interphase, the process of cell division couldn’t happen smoothly, and the organism’s growth and repair processes would be disrupted.

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SAQ-3 : Explain prophase I of meiosis

Introduction:

Prophase I is an essential stage in Meiosis I, which is a type of cell division important for producing reproductive cells like sperm and eggs. Unlike the simpler prophase in mitosis, prophase I of meiosis is more complex and takes longer. It is divided into five distinct phases, each with specific changes happening to the chromosomes.

Phases of Prophase I:

1. Leptotene: In the Leptotene phase, the cell’s nucleus grows as it absorbs water. The chromatin, which is the material that makes up chromosomes, starts to condense and become visible. It’s like starting to pack up clothes into boxes for a move—the chromosomes begin to take shape and are easier to see under a microscope.
2. Zygotene: During the Zygotene phase, the chromosomes get shorter and thicker. They begin to find their matching partners (homologous chromosomes) and pair up. This pairing is called synapsis. The paired chromosomes are now known as bivalents. Imagine each chromosome finding its twin to work together—this pairing is essential for the next steps.
3. Pachytene: In the Pachytene stage, the paired chromosomes become clearly visible as tetrads—a group of four chromatids. This is when crossing over happens. Crossing over is like swapping pieces of a puzzle between the paired chromosomes. This process exchanges genetic material and increases genetic diversity, making sure that the offspring have a mix of traits from both parents.
4. Diplotene: During the Diplotene phase, the structure holding the paired chromosomes together, known as the synaptonemal complex, begins to break down. The chromosomes start to separate, but they stay connected at the points where crossing over occurred. These connection points are called chiasmata, and they hold the chromosomes together at specific spots.
5. Diakinesis: Diakinesis is the final phase of prophase I. In this stage, the chromosomes become even more condensed and the chiasmata reach their maximum level of condensation. The nucleolus disappears, and the nuclear envelope breaks down, preparing the cell for the next stages of meiosis.

Summary:

Prophase I of Meiosis I is a complex and detailed process. Each phase plays a crucial role in organizing the chromosomes, ensuring that genetic material is exchanged through crossing over, and setting up the cell for the next steps in meiosis. This stage is essential for creating reproductive cells with unique genetic combinations, which is important for the diversity of offspring.

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SAQ-4 : How does cytokinesis in plant cells differ from that in animal cells?

Introduction:

Cytokinesis is the final step of cell division, where the cell’s cytoplasm splits to create two new daughter cells. The way this happens is different in plant and animal cells because of their unique structures.

Cytokinesis in Animal Cells:

In animal cells, cytokinesis starts with the formation of a cleavage furrow. Imagine this furrow as a belt tightening around the middle of the cell. This belt is made up of proteins called actin and myosin, which pull the cell membrane inward. As the furrow deepens, it pinches the cell membrane until the cell splits into two separate daughter cells. It’s similar to how you might use a drawstring to tighten a bag and separate it into two parts.

Cytokinesis in Plant Cells:

In plant cells, cytokinesis works a bit differently due to the presence of a cell wall. Instead of pinching in, the cell forms a cell plate right in the middle. Think of the cell plate as a new wall being built in the center of the cell. This plate is made from materials like cellulose and pectin, which are delivered by tiny transport vehicles called vesicles from the Golgi apparatus. These vesicles come together in the middle of the cell and start forming the new wall. Once the cell plate reaches the edges of the cell, it fuses with the existing cell walls, creating two separate daughter cells. It’s like constructing a new wall inside a room that divides it into two separate spaces.

Summary:

So, the way cytokinesis happens is quite different in plant and animal cells. In animal cells, a cleavage furrow forms and tightens to split the cell. In plant cells, a cell plate forms in the middle and turns into a new cell wall to separate the cell. These differences are due to the unique structures of plant and animal cells, with plant cells having a rigid cell wall that requires a different method for division.