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In this chapter

(^1717)

Cell Division

chapter

Cell Division

Exploration: Observing

Daphnia

Investigation 17.1:

Frequency of Cell Division

Mini Investigation:

Cloning from a Plant

Cutting

Explore an Issue: The

Ethics of Stem Cell

Research

Web Activity: Stem Cell

Cord Blood

Investigation 17.2:

Identification of a

Cancer Cell

Mini Investigation:

Gamete Formation in

Grasshoppers

Investigation 17.3:

Comparing Mitosis and

Meiosis

Web Activity: Comparing

Life Cycles of Plants

Web Activity: Dr. Renée

Martin

Web Activity: Modelling

Mitosis and Meiosis

All life depends on the ability to grow and reproduce. Both these processes involve cell

division. Organisms that reproduce asexually produce offspring that are identical to the

parents. Sexually reproducing organisms exchange genetic information, so that the off-

spring have a unique combination of traits. The genetic material determines the proteins

that make up cells, which ultimately give rise to physical traits.

Daphnia(Figure 1, next page) is a truly remarkable animal. Females can produce off-

spring without a mate since they can produce eggs that require no fertilization. Upon

development, these eggs become females, which in turn produce females, all of which are

identical to each other and to the parent. Then, in response to some environmental cue,

Daphniabegin producing eggs that develop as either males or females. The males and

females produce sex cells. Sexual reproduction occurs when the sperm cells fertilize the

egg cells, producing many offspring with a variety of traits. Asexual reproduction occurs

when food is plentiful, while sexual reproduction is triggered during times of environ-

mental stress.

All of the cells in Daphniaarise from one single cell. To develop into the complex

organism in Figure 1, that single cell must divide many times. In this chapter, you will

explore the events that occur during cell division in order to produce cells of the body

and specialized cells involved in reproduction.

556 Chapter 17 NEL

Answer these questions as best you can with your current knowledge. Then, using

the concepts and skills you have learned, you will revise your answers at the end of

the chapter.

1. Make a list of the advantages of being multicellular.
   2.Suggest possible advantages of reproducing
   (a) asexually
   (b) sexually
   3.If 22 chromosomes are found in the muscle cell of a mouse, predict the number of
   chromosomes found in each cell of the following types:
   (a) brain cell
   (b) sperm cell
   (c) fertilized egg cell
   Explain your predictions.

STARTING Points

Career Connection:

Geneticist