9 what are the checkpoints for cells, where in the cell cycle can they be found, and what are they checking for?
10. cancer is caused by?
changes(mutation) to the
dna within cells.
11 what is the cell cycle?
a series of events that takes place in a cell as it
grows and divides.
12 what are the parts of interphase and what occurs in each step?
13. what are the functions of the cell cycle?
14. what is mitosis?
15. how is mitosis related to genetic continuity (continuity means he same \)?

Question

9 what are the checkpoints for cells, where in the cell cycle can they be found, and what are they checking for?
10. cancer is caused by?
changes(mutation) to the
dna within cells.
11 what is the cell cycle?
a series of events that takes place in a cell as it
grows and divides.
12 what are the parts of interphase and what occurs in each step?
13. what are the functions of the cell cycle?
14. what is mitosis?
15. how is mitosis related to genetic continuity (continuity means 	he same \)?

Accepted Answer

### Question 9 (Cell Cycle Checkpoints)
#### Brief Explanations:
Cell cycle checkpoints ensure accurate cell division. There are three main checkpoints: G₁ (before S phase), G₂ (before M phase), and M (during mitosis).
- **G₁ Checkpoint**: Located at the end of G₁ phase. Checks if the cell has enough resources (nutrients, growth factors), if the DNA is undamaged, and if the cell size is adequate for division. If conditions are met, the cell enters S phase; otherwise, it may enter G₀ (resting) or undergo repair/apoptosis.
- **G₂ Checkpoint**: At the end of G₂ phase. Verifies that DNA replication in S phase was accurate and complete, and that the cell has enough proteins/organelles for mitosis. If DNA is damaged or replication is incomplete, the cell pauses to repair or is eliminated.
- **M Checkpoint (Spindle Checkpoint)**: During metaphase of mitosis. Checks if all sister chromatids are properly attached to the mitotic spindle fibers at the kinetochores. If attached correctly, anaphase (sister chromatid separation) proceeds; otherwise, mitosis is paused.

#### Answer (Table Completion):
| Ck point | Location | checking for... |
|----------|----------|-----------------|
| G₁ Checkpoint | End of G₁ phase (before S phase) | Adequate nutrients, growth factors, undamaged DNA, proper cell size |
| G₂ Checkpoint | End of G₂ phase (before M phase) | Accurate DNA replication, sufficient cell components for mitosis |
| M Checkpoint (Spindle Checkpoint) | Metaphase of mitosis | Proper attachment of all sister chromatids to spindle fibers |

### Question 10 (Cause of Cancer)
#### Brief Explanations:
Cancer arises from **uncontrolled cell division** due to mutations (changes) in genes that regulate the cell cycle (e.g., tumor suppressor genes like *p53*, or proto - oncogenes that become oncogenes). These mutations disrupt normal cell cycle checkpoints, allowing cells to divide uncontrollably, evade apoptosis (cell death), and form tumors. Environmental factors (carcinogens like UV, tobacco), genetic predisposition, or viral infections can trigger these mutations.

#### Answer:
Cancer is caused by **mutations (changes) in genes** that control the cell cycle, leading to uncontrolled cell growth and division. These mutations can be caused by carcinogens (e.g., UV radiation, chemicals), genetic factors, or viral infections, disrupting normal cell cycle regulation (e.g., inactivating tumor suppressors or activating oncogenes).

### Question 11 (What is the Cell Cycle?)
#### Brief Explanations:
The cell cycle is a **series of ordered events** that a cell undergoes as it grows, replicates its DNA, and divides to produce two daughter cells. It includes interphase (G₁, S, G₂ phases, where the cell grows and prepares for division) and the mitotic (M) phase (where cell division occurs, including mitosis and cytokinesis). The cycle ensures cells reproduce accurately for growth, repair, and (in some organisms) asexual reproduction.

#### Answer:
The cell cycle is a **series of events** that occur in a cell as it grows and divides. It includes interphase (G₁: cell growth, S: DNA replication, G₂: preparation for division) and the mitotic (M) phase (mitosis and cytokinesis, where the cell divides into two daughter cells). It regulates cell growth, repair, and reproduction.

### Question 12 (Parts of Interphase and Their Events)
#### Brief Explanations:
Interphase is the non - dividing phase of the cell cycle (about 90% of the cycle) and has three sub - phases:
- **G₁ (Gap 1) Phase**: The cell grows in size, synthesizes proteins and organelles needed for normal cell functions, and prepares for DNA replication. If conditions are right, it moves to S phase; otherwise, it may enter G₀ (a resting state).
- **S (Synthesis) Phase**: The cell replicates its DNA. Each chromosome is duplicated to form two sister chromatids, ensuring each daughter cell gets a complete set of genetic material.
- **G₂ (Gap 2) Phase**: The cell continues to grow, synthesizes proteins (like those for mitosis, e.g., tubulin for spindle fibers), and checks the accuracy of DNA replication. It prepares for mitosis (M phase).

#### Answer:
Interphase has three parts:
1. **G₁ (Gap 1) Phase**: Cell grows, produces proteins/organelles, and prepares for DNA replication.
2. **S (Synthesis) Phase**: DNA is replicated (chromosomes duplicate into sister chromatids).
3. **G₂ (Gap 2) Phase**: Cell grows further, synthesizes mitosis - related proteins, and checks DNA replication accuracy.

### Question 13 (Functions of the Cell Cycle)
#### Brief Explanations:
The cell cycle serves multiple key functions:
- **Growth**: Multicellular organisms grow by increasing cell number (e.g., a zygote divides to form an embryo, then a fetus, and finally a mature organism).
- **Repair**: Replaces damaged or dead cells (e.g., skin cells after a cut, liver cells after injury).
- **Asexual Reproduction**: Single - celled organisms (e.g., bacteria, yeast) reproduce by cell division (binary fission or budding, part of their cell cycle) to produce new individuals.
- **Development**: In multicellular organisms, the cell cycle drives embryonic development (e.g., differentiation of stem cells into various tissues).

#### Answer:
The cell cycle functions include:
- **Growth**: Increasing cell number for organismal growth (e.g., from embryo to adult).
- **Repair**: Replacing damaged/dead cells (e.g., in wounds or damaged organs).
- **Asexual Reproduction**: Producing new individuals in single - celled organisms (e.g., bacteria dividing).
- **Development**: Driving embryonic development and tissue differentiation.

### Question 14 (What is Mitosis?)
#### Brief Explanations:
Mitosis is the **nuclear division** stage of the cell cycle (part of M phase) that produces two daughter nuclei with the **same number and type of chromosomes** as the parent nucleus (diploid → diploid in somatic cells). It consists of four main stages: prophase, metaphase, anaphase, and telophase, followed by cytokinesis (cytoplasmic division) to form two genetically identical daughter cells. Mitosis is essential for growth, repair, and asexual reproduction (in some organisms).

#### Answer:
Mitosis is the process of **nuclear division** in eukaryotic cells (during the M phase of the cell cycle) that results in two daughter nuclei, each with the same number and genetic content as the parent nucleus. It occurs in four stages (prophase, metaphase, anaphase, telophase) and, with cytokinesis, produces two genetically identical daughter cells. It functions in growth, repair, and asexual reproduction.

### Question 15 (Mitosis and Genetic Continuity)
#### Brief Explanations:
Genetic continuity means passing on the same genetic information. During mitosis, the parent cell’s replicated chromosomes (sister chromatids) are **equally separated** into two daughter cells. In S phase (before mitosis), DNA is replicated, so each chromosome has two identical sister chromatids. During anaphase of mitosis, these sister chromatids are pulled to opposite poles and become chromosomes of the daughter cells. Thus, each daughter cell receives a **genetically identical set of chromosomes** (same number and genes) as the parent cell, ensuring genetic continuity (the “same” genetic information is passed to daughter cells).

#### Answer:
Mitosis ensures genetic continuity because it produces daughter cells with the **same genetic material** as the parent cell. During S phase, DNA replicates (each chromosome has two identical sister chromatids). In mitosis, these sister chromatids are separated and distributed equally to the two daughter cells. So, each daughter cell inherits the same number and type of chromosomes (and thus the same genes) as the parent, maintaining genetic continuity (the “same” genetic information is passed on).

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QUESTION IMAGE

Question

Explanation:

Question 9 (Cell Cycle Checkpoints)

Answer:

Question 10 (Cause of Cancer)

Ck point	Location	checking for...
G₂ Checkpoint	End of G₂ phase (before M phase)	Accurate DNA replication, sufficient cell components for mitosis
M Checkpoint (Spindle Checkpoint)	Metaphase of mitosis	Proper attachment of all sister chromatids to spindle fibers