animal, plant & soil science lesson b2-2 cell division

Animal, Plant & Soil Science

Lesson B2-2

Cell Division

Interest Approach

Ask students if they have ever had a cut or injury that has healed. Ask students if they know how their body created the new cells that healed the injury. We know that we received half of our genetic code from each parent. Ask students if they can explain how cells can grow, reproduce, and create reproductive cells.

Objectives

Define cell theory and examine the importance of mitosis.

Identify and describe the five stages of mitosis.

Identify and describe the stages of meiosis I and II.

Objectives

Analyze the role of meiosis in spermatogenesis and oogenesis.

Compare and contrast mitosis and meiosis.

Terms anaphase centromere chromatids cytokinesis gametes haploid number haploid cells homologous

interphase meiosis metaphase mitosis ova prophase spermatozoa telophase

What is cell theory, and why is mitosis important?

Cell theory states that cells are the basic structural unit of all living things.

This theory also states that cells are created by other living cells through cellular division.

Mitosis is a sequential process of cell division.


At the conclusion of mitosis, what was formerly one cell becomes two.

This process is repeated over and over during the life of the organism.


A. Mitosis is cell division for growth and repair. This process involves the division of cells

that make up the plant body, which consists of the roots, stem, leaves, and flower parts.


B. This process is continually occurring. It is extremely important because this is how

organisms grow and repair damaged parts. Without mitosis, plant growth could not

occur.

What are the five stages of mitosis?

Mitosis is divided into five stages or steps.

A. The first stage of mitosis is called interphase. Interphase is thought of as the resting stage

for the cell. During interphase, the cell is growing and

producing proteins and organelles that will be needed for division.


B. Prophase, the second stage, is the stage of chromosome replication. The chromosome contains

the genetic information for the cell.


C. Metaphase, the third stage, involves the chromosomes (formed in prophase) moving to the middle of the cell. These chromosomes

line up along the equator of the cell and prepare to divide.


D. In the fourth stage, anaphase, the chromosomes separate and move to opposite sides of the cell. Shortening spindle

fibers separate the chromosomes.


E. In the final stage, telophase, the nucleus reforms and a membrane appears between each mass of chromosomes. This newly formed membrane divides the

cytoplasm. Once this stage is completed, the two

separate cells begin to repeat the process.

What are the stages of meiosis I and II?

Meiosis occurs in two stages, meiosis I and meiosis II, with each stage containing four steps.

A. Meiosis I is very similar to mitosis. The four steps of meiosis I are:


1. In prophase I, thread-like fibers form. Homologous, or corresponding,

chromosome pairs are located together and DNA, which was replicated at the end of interphase, is present.


2. Metaphase I is the step during which chromosomes align at the equator of the cell, with the spindle fibers attached from the centromere to the poles of the cell. The centromere is the point at which two

chromatids are attached. Chromatids are strands of identical DNA

that join to form a chromosome.


3. In anaphase I, the centromere does not duplicate. The shortening spindle

fibers pull the paired chromosomes into two pieces to the poles of the cell.

This separated chromosome contains half of the cell’s genetic information.


4. The fourth and final step of meiosis I is telophase I. In this step, the chromosomes are still

joined and contain the haploid number, or half the original chromosome number.

Two daughter cells are produced when the nucleus reforms.


B. After the four steps of meiosis I, meiosis II begins.

The four steps of meiosis II are:

1. The first step is prophase II. In this step, spindle fiber formation begins. The main difference between prophase I

and prophase II is that DNA does not replicate before prophase II.


2. Prophase II is followed by metaphase II. In metaphase II, chromatids align at the

equator of the cell with spindle fibers attached.


3. The duplication of the centromere signals the beginning of anaphase II. This divides the chromosomes so that each

half is pulled to a pole by the spindle fibers.


4. In telophase II, a cell membrane forms between the developing nuclei. Cytokinesis, the division of the cytoplasm,

occurs, and four daughter cells are formed containing the haploid number of chromosomes.

What is the role of meiosis in spermatogenesis and oogenesis?

Meiosis is the division of cells in the reproductive process.

A. Haploid cells are cells that are produced as a result of meiosis. These cells have only single chromosomes

rather than a homologous, or matching, pair.

These cells are known as gametes. Male gametes are called spermatozoa. Female gametes are known as ova.


B. Meiosis is a very important and necessary process. During this process, the sex cells for the

organism are produced. Without these sex cells, the organism could

not reproduce. If an organism cannot reproduce, the

species will become extinct.

How do the processes of mitosis and meiosis differ?

The cellular division processes of mitosis and meiosis differ in several ways.

A. In mitosis, the division of the mother cell results in two daughter cells, whereas in meiosis the division of the mother cell results in four daughter cells.

B. In mitosis, the mother cell can be either haploid or diploid, whereas in meiosis the mother cell is always diploid.


C. In mitosis, the number of chromosomes remains the same after division, whereas in meiosis each daughter cell contains half the original chromosomes.

D. In mitosis, there is normally no pairing of homologous chromosomes, whereas in meiosis there is always pairing of all homologous chromosomes.


E. In mitosis, there is normally no exchange of DNA between chromosomes, whereas in meiosis there is at least one exchange of DNA per pair of homologous chromosomes.

F. In mitosis, the centromeres are split during anaphase, whereas in meiosis the centromeres do not split until anaphase II.


G. In mitosis, the daughter cells will be genetically identical to the mother cell, whereas in meiosis each daughter cell contains only half the genetic information of the mother cell (giving variation in offspring).

Review


What are the five stages of mitosis? What are the stages of meiosis I and

II?

Review



animal, plant & soil science lesson b2-2 cell division

Documents

stages of mitosis

stage of mitosis

cell division slide

mitosis important

importance of mitosis

contrast mitosis

conclusion of mitosis

stages of meiosis