Analyzing Data

The Rise and Fall of Cyclins

Scientists measured cyclin levels in clam egg cells as the cells went through their first mitotic divisions after fertilization. The data are shown in the graph.

Cyclins are continually produced and destroyed within cells. Cyclin production signals cells to enter mitosis, while cyclin destruction signals cells to stop dividing and enter interphase.

A curved graph demonstrating rise and fall of cyclin levels in different stages of cell division.d

  1. Interpret Graphs How long does cyclin production last during a typical cell cycle in fertilized clam eggs?

  2. Infer During which part of the cell cycle does cyclin production begin? How quickly is cyclin destroyed?

  3. Predict Suppose that the regulators that control cyclin production are no longer produced. What are two possible outcomes?

Apoptosis Just as new cells are produced every day in a multicellular organism, many other cells die. Cells end their life cycle in one of two ways. A cell may die by accident due to damage or injury, or a cell may actually be “programmed” to die. Apoptosis (AYP up TOH sis) is a process of programmed cell death. Once apoptosis is triggered, a cell undergoes a series of controlled steps leading to its self-destruction. First, the cell and its chromatin shrink, and then parts of the cell's membranes break off. Neighboring cells then quickly clean up the cell's remains.

Apoptosis plays a key role in development by shaping the structure of tissues and organs in plants and animals. For example, look at the photos of a mouse foot in Figure 10–15. Each foot of a mouse is shaped the way it is partly because cells between the toes die by apoptosis during tissue development. When apoptosis does not occur as it should, a number of diseases can result. For example, the cell loss seen in AIDS and Parkinson's disease can result if too much apoptosis occurs.

Two mice. An inset image is a micrograph of embryonic foot.

FIGURE 10–15 Apoptosis The cells between a mouse's toes undergo apoptosis during a late stage of development. Predict What is one way the pattern of apoptosis would differ in foot development for a duck?

End ofPage 288

Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q, R
S
T
U
V
W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Credits
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