Problem 29 - Objective Biology for NEET

Question

Cell which divides by mitosis is (a) Upper layer of epidermis (b) Cells lining gut (c) Stem cells (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these. All these cells divide by mitosis as it is essential for growth, development, and repair of the body.

Step 1: Understand Mitosis

Recognize that mitosis is a process of cell division where a parent cell divides into two identical daughter cells each having the same number and kind of chromosomes as the parent nucleus. This is typical of ordinary tissue growth in multicellular organisms.

Step 2: Identify where mitosis occurs

Know that mitosis takes place in all tissues for growth and repair, which means it happens in all type of cells including the upper layer of the epidermis, cells lining the gut and stem cells.

Step 3: Examining each option

a) The upper layer of the epidermis - the epidermis constantly undergoes mitosis to replace dead or lost skin cells. Thus, mitosis occurs here. b) Cells lining the gut - The lining of our gut is constantly being damaged and replaced, so mitosis must occur here as well. c) Stem cells - These are unique cells that have the potential to become any type of cell in the body. Mitosis occurs here as they divide and differentiate into other cell types.

Key Concepts

Cell Cycle and Division

The cell cycle is the complex sequence of events by which cells grow and divide. It is essential for the survival and growth of all living organisms. Within the cell cycle, a vital stage known as mitosis is responsible for the production of two identical daughter cells from a single parent cell. This phase is crucial for both growth and maintenance in multicellular organisms.

Mitosis includes several steps: prophase, metaphase, anaphase, and telophase, followed by cytokinesis. Here's a simplified breakdown:

• In prophase, chromosomes condense and become visible.
• During metaphase, chromosomes align at the cell's equator.
• In anaphase, chromosomes separate to opposite sides of the cell.
• Finally, during telophase, two new nuclei form around these separated chromosomes.

Cytokinesis then divides the cytoplasm, completing the formation of two cells. This process is tightly regulated to ensure that cells do not divide uncontrollably, which can lead to cancer.

Growth and Repair in Multicellular Organisms

Multicellular organisms rely on cell division for growth, development, and repair. Mitosis enables these organisms to expand in size by adding cells in a controlled manner. For instance, the upper layer of the epidermis renews itself through mitosis to protect us from external environmental factors and heal wounds.

Similarly, the cells lining the gut are subject to constant wear and tear due to the passage of food. They are renewed every few days entirely via mitosis, allowing for the gut to maintain its function and integrity. Furthermore, when a bone breaks, cells at the edge of the injury site will divide to fill in the gap. This regeneration highlights how mitosis is not only about growth but also essential in routine bodily maintenance and repair.

Stem Cell Differentiation

Stem cells are the keystones of development and repair. They have the remarkable potential to differentiate into various cell types in the body. Stem cell differentiation is a process that involves a stem cell turning into a more specialized cell, such as a muscle cell, a red blood cell, or a neuron.

The process begins with a stem cell that has to divide. Through mitosis, one of the two daughter cells remains a stem cell, ensuring a continual supply, while the other daughter cell becomes a progenitor cell, which can differentiate into a specific type of cell. This remarkable ability is why stem cells are central to regenerative medicine, holding the promise for repairing damaged tissues and organs.