1. Lesson 1: How does cell division affect growth?
Chapter 4: Animal Growth and Heredity
Lesson 1: How does cell division affect growth?

2. Vocabulary
Life cycle- the stages that a living thing passes through as it grows and changes.
Mitosis- the process by which most cells divide.
Chromosome- A threadlike structure in the nucleus, made up of DNA.

3. Growth and Development
All organisms star life as a single cell; the same cell divides and forms two cells, and so on. By the time a plant or an animal is complete, the body is made up of trillions of cells.
(1, 2,4,8,16…………… trillions of cells)
Even in a complete organism cells continue dividing.

4. Growth and Development
Sometimes the changes are noticeable, for example you get taller as you grow. Sometimes you cannot see the changes for example, the ones that happen inside you body.

5. Cell Division
During cell division each type of cell makes a copy of themselves.
Bone cells make more bone cells, muscle cells make more muscle cells, nerve cells make new nerve cells. This enables the organs and system to function properly as you grow.

6. Chick Development Begins life as a single cell in a fertilized egg.
After 7 days blood vessels begin to form.
After day 14 the skeleton and most organs have formed.
By day 21 the chick is fully developed.

7. Life Cycle
A life cycle begins with a fertilized egg. Some animals develop inside their mother’s bodies, other inside an egg, and others like bacteria and protist are mature as soon as they are formed.

8. Life cycle Starts as a fertilized egg. The organism grows and matures.
The organism reproduces.
A new life cycle begins.

9. Growing and Maturing
Some animals spend months or years growing and developing before reaching maturity.
Some animals such as butterflies, change a great deal before they mature. The changes they undergo is called metamorphosis.
Other animals such as mammals, reptiles, bids, and most fish do not change much during their lives.

10. Cell Division (MITOSIS)
The process by which most cells divide is called mitosis.
The nucleus contains threadlike structures called chromosomes which are made up of a complex chemical called DNA (deoxyribonucleic acid)
The DNA carries a code in its structure with all the information that directs how a cell functions, including when to divide.

11. Cell Division
Before mitosis begins, an exact copy of each chromosome is made, producing a pair.
During mitosis, the identical chromosome pair separate resulting in two sets identical to the original chromosome.
The sets pull apart and then the cell membrane pinches in the middle, forming two new cells. Each cell is like the parent cell.

12. Regeneration
Have you ever skinned your knee? Cells in the area form to replace lost tissue, soon the scrape disappears and your skin is smooth again.
In humans regeneration is limited to heal wounds. But in some animals like sea stars and lizards, regeneration can replace entire body parts.

13. Asexual Reproduction
You know that some organisms have only one cell. When the cell divides, the whole organism reproduces. For example yeast, protist, bacteria.

14. Functions of Mitosis
Growth
Regeneration
Asexual Reproduction

15. Reproduction
Most multicellular organisms reproduce by the joining of cells from two different individuals. This is called sexual reproduction.
Cells from each parent joins to form a zygote (fertilized egg). A zygote receives chromosomes from each parent. It is important to receive the right number of chromosomes. The cells from every organism have a specific number of chromosomes. If they have too many or too few cells don’t work properly.

16. Reproduction
Organisms that reproduce sexually have two types of cells– body cells and reproductive cells or gametes.
Gametes contain only half the number of chromosomes of body cells. When two gametes join, the zygote has the same number of chromosomes as body cells.

17. Meiosis
During meiosis, the number of chromosomes in a cell divides in half. For example human body cells have 46 chromosomes, each gamete has 23 chromosomes.

18. Meiosis
Meiosis occurs in two stages, during the first stage the chromosomes are copied and the cell divides. In the second stage, the two new cells divide again without copying their chromosomes. So each four new cells have half the number of chromosomes that body cells have.

19. Make Connections Activity
Writing
Suppose you are a science writer for a newspaper. Write a descriptive article detailing the process of mitosis.
Math
Use the library or internet resources to find out the number of chromosomes in the body cells of at least 5 animals. Make a bar graph to compare the numbers. Which animal has the most? The least?

20. Lesson Review When a chick begins life, how many cells does it have?
How does cell division help organisms grow?
How do animals change as they mature?
What are some of the ways in which different kinds of organisms begin their life cycle?
How does the appearance of an adult butterfly compare with its form during its other stages of their life?

21. Lesson Review
Before an animal cell divides, what happens to its chromosomes?
When do the chromosomes makes copies of themselves?
What happens to the nuclear membrane as mitosis begins?
When does a new nuclear membrane form?
What is asexual reproduction? What is one way organisms reproduce asexually?

22. Lesson Review
How does the number of chromosomes of a zygote compare with the number of chromosomes in a gamete?
How does the number of chromosomes in a zygote compares to the number of chromosomes in a body cell?
What is formed during meiosis?

23. Lesson Review Workbook p. 22-23
Why must gametes contain half the number of chromosomes that body cells have?
During mitosis, which part of the cell pinches in to make a new cell?
If an organism has 12 chromosomes in its body cells, how many chromosomes do its gametes and zygote have?
Workbook p