Name Class Date
Skills Worksheet
CH10.1 Active Reading
Section: Cell Reproduction
Read the passage below. Then answer the questions that follow.
A gene is a segment of DNA that codes for RNA and protein. A single molecule of DNA has thousands of genes lined up like the cars of a train. When genes are being used, the strand of DNA is stretched out so that the information it contains can be decoded and used to direct the synthesis of proteins needed by the cell.
As a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome. Before the DNA coils up, however, the DNA is copied. The two exact copies of DNA that make up each chromosome are called chromatids. In the chromatids, the DNA is very condensed. The two chromatids, which become separated during cell division and are placed into each new cell, ensure that each new cell has the same genetic information as the original cell.
Skill: Reading Effectively
Read each question, and write your answer in the space provided.
1. How are genes and DNA related?
2. What occurs to a DNA strand as its genes are being used?
3. How are chromatids and chromosomes related?
An analogy is a comparison. In the space provided, write the letter of the term that best completes the analogy.
4. A train is to cars as a molecule of DNA is to
a. chromatids.
b. genes.
c. proteins.
d. RNA.
Skills Worksheet
CH10.2 Active Reading
Section: Mitosis
Read the passage below. Then answer the questions that follow.
During its lifetime, a cell goes through a repeating sequence of cellular growth and division. This repeating sequence is called the cell cycle. A cell spends 90 percent of its time in the first three phases of the cycle, which are collectively called interphase. A cell will enter the last two phases of the cell cycle only if it is about to divide.
The five phases of the cell cycle are as follows:
First gap (G1) phase: During the G1 phase, a cell grows rapidly and carries out its routine functions. This phase occupies the major portion of the cell’s life in most organisms.
Synthesis (S) phase: A cell’s DNA is copied during this phase. At the end of this phase, each individual chromosome consists of two sister chromatids attached at the centromere.
Second gap (G2) phase: In the G2 phase, preparations are made for the nucleus to divide. Mitochondria and other organelles replicate. Hollow protein fibers called microtubules are assembled. The microtubules are used to move the sister chromatids during mitosis.
Mitosis: The process during cell division in which the nucleus of a cell is divided into two nuclei is called mitosis, each with a complete set of the cell’s chromosomes.
Cytokinesis: The process during cell division in which the cytoplasm divides is called cytokinesis. In this process, each daughter cell receives about half of the original organelles in a cell.
Skill: Reading Effectively
Read each question, and write your answer in the space provided.
1. Identify and define the two Key Terms in the first paragraph of this passage.
2. A cell viewed under a high-powered microscope appears to be in the fourth phase of the cell cycle. What does this indicate about the cell?
Active Reading continued
Skill: Sequencing Information
Match each statement with the phase of the cell cycle it describes. Write the letter of the correct phase in the space provided. Some choices may be used more than once.
3. The nucleus divides.
4. It makes up a major portion of
most cells’ lives.
5. The cytoplasm divides.
6. The mitochondria replicate.
7. The cell grows rapidly.
8. Two identical nuclei are produced.
9. DNA is copied.
10. Microtubules are assembled.
11. Sister chromatids form and become attached at the centromere.
12. The cell carries out its routine functions.
13. Microtubules move sister chromatids.
Read the question, and write your answer in the space provided.
14. How are mitosis and cytokinesis alike? How do they differ?
An analogy is a comparison. In the space provided, write the letter of the term that best completes the analogy.
15. G2 phase is to mitochondria as S phase is to
a. chromatids.
b. centromere.
c. microtubules.
d. DNA.
Skills Worksheet
CH10.3 Active Reading
Section: Regulation
Read the passage below. Then answer the questions that follow.
The cell cycle has checkpoints. These are mechanisms the cell uses to make sure it is ready to go on to the next phase. There are three main checkpoints in the cell cycle.
The first checkpoint comes during the first gap phase. It is called the G1 checkpoint. Its purpose is to check the cell and its surroundings before cell division begins. The cell needs to be large enough and healthy enough to undergo cell division. It needs to have adequate nutrients and oxygen to sustain the process. If conditions are not favorable, the cell goes into a resting phase. If conditions are favorable, the cell enters the synthesis phase.
The second checkpoint comes during the second gap phase. It is called the G2 checkpoint. Its purpose is to ensure that the cell is ready for mitosis. As with the G1 checkpoint, the cell must still be large enough and healthy enough to continue cell division. The copied DNA must be identical to the original DNA. If there are mistakes in the copied DNA, enzymes correct the mistakes. If the cell is not large enough, the cell continues growing until it reaches the optimal size. When conditions are favorable, mitosis begins.
The third checkpoint comes during metaphase in mitosis. It is called the mitosis checkpoint. Its purpose is to check that the genetic material will divide properly into the two daughter cells. During the mitosis checkpoint, the cell makes sure that all the chromosomes have lined up properly at the cell equator. It checks to make sure that each chromosome is properly attached to the spindle. If chromosomes need rearranging or attaching or reattaching to the spindle, the cell makes these adjustments. When conditions are favorable, mitosis continues.
Skill: Reading Effectively
Read each question, and write your answer in the space provided.
1. What is the general purpose of the checkpoints related to the cell cycle?
2. Why are checkpoints important to the health of cells?
Active Reading continued
3. When does the G1 checkpoint occur? What does the cell check?
4. What happens if a cell does not pass the G1 checkpoint?
5. What happens if a cell passes the G1 checkpoint?
6. When does the G2 checkpoint occur? What does the cell check?
7. What happens if a cell does not pass the G2 checkpoint?
8. What happens if a cell passes the G2 checkpoint?
9. When does the mitosis checkpoint occur? What does the cell check?
10. What happens if a cell does not pass the mitosis checkpoint?
11. What happens if a cell passes the mitosis checkpoint?
Write the letter of the term that best answers the question.
12. Which graphic could you use to best show the checkpoints in the cell cycle?
a. line graph
b. bar graph
c. flowchart
d. map
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Biology 12 Cell Growth and Division