Biology Chapter 10

2. b) As a cell increases in size, which increases more rapidly, its surface area or its volume?

As a cell increases in size the volume of the cell increases more rapidly than the surface area.

2. c) How is a cell's potential growth affected by its ratio of surface area to volume?

As the cell increases in size the volume of the cell increases more rapidly than the surface area which causes a decrease in the cell's ratio of surface area to volume and makes it more difficult for the cell to move needed materials in and waste products out. If a cell gets too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out, so the cell has to stop growing before this happens.

15. b) Explain how cancer cells are different from other cells.

Cancer cells do not respond to signals that regulate growth in the cells. Many cancer cells have a defect in the p53 gene, which normally stops the cell cycle intil the chromosomes are properly replicated.

3. Describe how cell division solves the problems of cell growth.

Cell division solves the problems of cell growth because cell division keeps the cells from getting too large but allows the organism enough cells to survive. Because of cell division the cells that die can me made up for and the cells work more efficiently.

2. a) Describe what is meant by each of the following terms: cell volume, cell surface area, ratio of surface area to volume

Cell volume is the amount of space the cell occupies and is found by multiplying the length of the cell by the width and by the height fo the cell. Cell surface area is the area of all the sides of the cell added together. It is the total area of the outside of the cell. The ratio of surface area to volume is the division of the surface area of the cell by the volume of the cell. If a cell had a volume of eight and a surface arfea of 24 then the ratio of surface area to volume ratio would be 24/8 or 3.

12. Identify a factor that can stop cells from growing.

Cells grow until they reach other cells or the sides of their container. When an injury occurs, cells at the edges of the injury are stimulated to start mitosis, which starts the process of healing. When the healing process nears completion the rate of cell division slows and controls on growth are restored and everything returns to normal.

13. b) How do they work?

Cyclins are proteins that begin the process of mitosis. When cytoplasm from a cell in mitosis is injected into another cell, the second cell enters mitosis.

13. a) What chemicals regulate the cell cycle?

Cyclins are the proteins that seem to regulate the cell cycle. Cyclins regulate the timing of the cell cycle in eukaryotic cells and they also seem to control the development of parts needed for mitosis. Cyclins were discovered in the early 1980's by several scientists, including Tim Hunt of Great Britain and Mark Kirschner of the U.S., who discovered that cells in mitosis contained a protein that when injected into nondividing cells would cause a mitotic spindle to form.

9. c) What is cytokinesis?

Cytokinesis is the separation of the cytoplasm when the cell membrane pinches inward at the end of telophase.

8. Explain how the following terms are related to one another: DNA centromere chromosome chromatid

DNA is an organism's genetic information. Chromosomes are threadlike structures within the nucleus that are condensed chromatin and contain the DNA. Chromatids are the two identical parts of a chromosome. Centromeres are the center of a chromosome that separates during mitosis, therefore separating the chromatids. All four terms have to do with the genetic information in a cell.

7. Summarize what happens during interphase.

During interphase cells grow and prepare for the cell cycle. The cell grows and makes new proteins and organelles, chromosomes are replicated to make another copy of the DNA, and many organelles and molecules required for cell division are produced.

9. e) How do chromosome numbers before mitosis compare to chromosome numbers after mitosis?

Each daughter cell has the same number of chromosomes as the original cell.

4. Summarize what happens during the process of cell division.

In cell division, a cell copies its DNA, divides the nucleus, separates the sister chromatids, and then splits into two daughter cells.

9. d) How is cytokinesis different in plants and animals?

In most animal cells, cytokinesis takes place when the cell membrane pinches inward. In plants, a structure known as the cell plate forms midway between the divided nuclei and then a cell wall begins to appear within the cell plate, which forms two separate cells.

11. Answer an application question on the life spans of human cells.

In the human body, most muscle cells and nerve cells do not divide at all once they have developed. The cells fo the skin and digestive tract, and cells in the bone marrow that make blood cells, grow and divide rapidly throughout life.

14. Describe the difference between internal regulators and external regulators.

Internal repulators allow the cell cycle to proceed only when certain processes have occured within the cell. External regulators (such as growth factors) direct cells to speed up or slow down the cell cycle.

5. What is the relationship between interphase and cell division?

Interphase is the time between cell divisions during which growth and preparation for division occurs. Interphase happens between every cell division and is not a part of the actual splitting of the cell.

9. b) Describe the major characteristics of the four phases of mitosis.

Prophase is when chromatin begin to condense into chromosomes, the centrioles separate and move toward opposite poles, a spindle begins to form across the cytoplasm, the nuclear envelope starts to break down, and chromosomes coil more tightly. Metaphase is when the chromosomes line up across the equator, or center, of the cell and microtubles connect the centromere of each chromosome to the two poles of the spindle. Anaphase is when the sister chromatids separate into the individual chromosomes and are moved apart. Telophase is the phase in which the chromosomes begin to gather at the opposite ends of the cell and disperse, the nuclear envelope reforms around each cluster of chromosomes, the spindle begins to break apart, and a nucleolus becomes visible in each daughter nucleus.

9. a) List the events of mitosis in order.

Prophase, metaphase, anaphase, and then telophase.

16. What are stem cells?

Stem cells are cells which have the potential to differentiate into other types of cells. They are "blank" cells that can become any type of cell.

1. Explain the problems that growth causes for cells

The lardger a cell becomes, the more demands the cell places on its DNA. As a cell increases in size, it usually does not make extra copies of DNA. If a cell became too large, an "information crisis" would occur. The cell has more trouble moving enough nutrients and wastes across the cell membrane. The rate at which food, oxygen, and water enter the cell, as well as wast products leave the cell, depends on the surface area of the cell and the cell's volume. If a cell gets too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out.

6. Name the main events of the cell cycle and discuss the relative length of the major events.

The main events of the cell cycle are G1 phase, S phase, G2 phase, (these are all parts of interphase) prophase, metaphase, anaphase, telophase, and cytokinesis (these last five are M phase). Prophase, metaphase, anaphase, and telophase are all in mitosis. Interphase is the longest part of the cell cycle; cell division is only a small part. S phase is the longest phase of interphase and G2 phase is the shortest of the three phases of interphase. The longest phase of mitosis is prophase and it takes up 50 to 60% of the total time required to complete mitosis. Metaphase only lasts a few minutes.

15. a) Why is it important that cell growth in a multicellular organism be regulated so carefully?

When cell growth in a multicellular organism can't be regulated carefully then the cells can grow out of control and form masses of cells. The masses are tumors. Cancer is a disorder in which some of hte body's own cells lose the ability to control or regulate growth. Cancer tumors are very harmful because they can damage the surrounding tissues, disrupt normal activities, and cause serious health problems or death.

10. What is the role of each of the following during mitosis: a) centriole b) spindle

a) Centrioles lie in a region called the centrosome that helps to organize the spindle and during prophase, the centrioles separate to opposite poles of the cell so the spindles form correctly. b) The spindle is made up of fibers that chromosomes become attached to at is centromere during prophase. The spindle helps to separate the chromosomes.