Cell Cycle And Cell Division

The question asks which statement about the G1 checkpoint of the eukaryotic cell division cycle is incorrect. To answer this question, we should first understand the role of the G1 checkpoint.

The G1 checkpoint, also known as the Restriction Point, is key in determining whether a cell proceeds through the cell cycle. It checks for:

1. Favorable Extracellular Environment: The cell ensures that the conditions outside are suitable for cell division, such as the availability of nutrients and proper growth signals.
2. DNA Damage: The cell checks for any damage to the DNA. If DNA damage is detected, the cell cycle is halted for repairs, preventing the propagation of damaged DNA.
3. Cell Size: The cell confirms adequate growth to support division.

Examining the given options:

• Cell assures the existence of favorable extracellular environment: This is correct, as explained above.
• Cell assures the DNA has no damage: This is correct. DNA damage detection is a crucial function of the G1 checkpoint.
• Cell assures the damaged DNAs are directed for repair mechanism: This is correct. If the checkpoint detects DNA damage, it initiates repair mechanisms.
• Cell assures complete replication of DNA: This option is incorrect for the G1 checkpoint. The replication of DNA is actually checked at the G2 checkpoint, not G1. The G2 checkpoint ensures that DNA replication is complete and that the replicated DNA is not damaged before the cell proceeds to mitosis.

Therefore, the statement "Cell assures complete replication of DNA" is the incorrect statement about the G1 checkpoint in the context of eukaryotic cell division.

The question requires us to identify the correct statements about the phase of mitosis known as telophase. Let's analyze each statement in the context of telophase:

1. Daughter chromosomes are yet to form: This statement is incorrect. By the time telophase occurs, daughter chromosomes have already formed during anaphase, where the sister chromatids are separated and pulled to opposite poles of the cell.
2. New nuclear envelop starts to reassemble: This statement is correct. Telophase involves the reformation of the nuclear envelope around the sets of chromosomes at each pole of the cell. This marks the near end of nuclear division.
3. Division of cytoplasm begins: This statement is correct. Cytokinesis, the division of the cell's cytoplasm, often begins during telophase, further aligning with this description.
4. Nuclear membrane disappears: This statement is incorrect. The disappearance of the nuclear membrane occurs during prophase, not telophase. During telophase, the nuclear membrane reappears, encapsulating the chromosomes.

Based on the explanation above, the correct statements about telophase are:

• New nuclear envelop starts to reassemble
• Division of cytoplasm begins

This understanding of telophase aligns with the widely accepted description of the mitotic process in cellular biology.

Apoptosis, also known as programmed cell death, is a highly regulated process in which cells undergo an orderly sequence of events leading to their own death. This mechanism is crucial for maintaining cellular homeostasis and development in multicellular organisms. During apoptosis, cells exhibit distinct morphological changes that can be used to identify them. Let's go through these changes to determine the correct answers:

1. Formation of blebs on cell surface: One of the characteristic features of apoptosis is the formation of blebs or small blisters on the surface of the cell. These blebs occur when the cytoskeleton collapses and the cell membrane detaches from underlying cytoskeletal proteins, leading to bubble-like protrusions. Therefore, this option is correct.
2. Swelling and bursting of cells: This is typically observed in necrosis rather than apoptosis. In necrosis, cells swell and burst, releasing their contents, which can trigger inflammation. Therefore, this option is incorrect for apoptosis.
3. Collapse of the cytoskeleton: During apoptosis, the cytoskeletal structure breaks down, which contributes to the cell shrinking and bleb formation. The collapse of the cytoskeleton is indeed a hallmark of apoptosis, making this option correct.
4. Condensation and fragmentation of nuclear chromatin: Another key feature of apoptosis is the condensation of chromatin within the nucleus, followed by its fragmentation. This is an important step in the apoptotic process, ensuring the orderly packaging and disposal of nuclear material. Therefore, this option is correct.

To summarize, the correct morphological changes during apoptosis are the formation of blebs on the cell surface, collapse of the cytoskeleton, and condensation and fragmentation of nuclear chromatin.