5th Grade ScienceUnit A - Chapter 3

Lesson 1: How Do Animals Grow and Reproduce?

How Organisms Grow: Cell DivisionChromosomes: threadlike strands of DNA inside a cell’s nucleus

Mitosis - The process of Cell Division5 Phases of Mitosis:

PROPHASE: Gets everything ready to divide● Duplicate DNA● Centrioles get in right

position● Prepare cell for division

Mitosis - The process of Cell Division5 Phases of Mitosis:

PROMETAPHASE: separates duplicated genetic material● Nuclear envelope breaks

down● Mitotic spindle completed● Sister chromatids move

towards center of cell

Mitosis - The process of Cell Division (continued)5 Phases of Mitosis:

METAPHASE: pieces align for division● DNA lines up along central

axis● Centrioles send out tubules

that connect to DNA● DNA condensed into 2

chromosome strands connected with centromere

Mitosis - The process of Cell Division (continued)5 Phases of Mitosis:

ANAPHASE: separation begins● Half of chromosomes go

to one side of cell● Other half go to other

side

Mitosis - The process of Cell Division (continued)5 Phases of Mitosis:

TELOPHASE: division finishes up● Cell membrane closes in

and splits cell into two pieces

● 2 separate cells each with half of original cell’s DNA

Mitosis - The process of Cell Division (continued)CYTOKINESIS: process of cell actually dividing into two cells● Cytoplasm splits● Cell pinches off● Two new cells form

Mitosis - The process of Cell Division (continued)INTERPHASE: normal state of the cell● Known as the “resting

state”● goes about its normal

business until next cell division

Regeneration● Provides organisms with a means of replacing lost or damaged tissues

and organs (through the process of mitosis)

In Humans:

● Heals wounds and replaces damaged tissue

In Plants and Some Animals:

● Can regenerate major body parts● Planaria - a type of freshwater flatworm

that can regenerate most of its body

Asexual Reproduction● The production of new organisms without the joining of male and female

cells (through the process of mitosis)

Two Ways Organisms Reproduce Asexually:

● Fission ○ simple cell division

● Budding○ tiny bud forms on parent cell ○ copy of parent chromosomes enter bud○ when bud is fully grown, it separates from parent cell

Sexual Reproduction● Cells from two parent cells unite to form one cell called a ZYGOTE

○ Contains chromosomes from both female and male○ Human body cells have 46 chromosomes○ Zygote can’t have 92 chromosomes○ Reproductive cells only have 23 chromosomes

● Meiosis ○ the process that reduces the number of chromosomes in reproductive

cells

Meiosis

Stages of Meiosis8 Stages of Meiosis

1. PROPHASE I- The chromosomes condense, and the nuclear membrane breaks down,

crossing-over occurs.

2. METAPHASE I- Pairs of similar chromosomes move to the middle of the cell.

3. ANAPHASE I- Similar chromosomes move to opposite poles of the cell.

4. TELOPHASE I and CYTOKINESIS- Chromosomes gather at the poles of the cell; cytoplasm divides

Stages of Meiosis (continued)8 Stages of Meiosis

5. PROPHASE II- A new spindle forms around the chromosomes

6. METAPHASE II- Chromosomes lines up in the middle

7. ANAPHASE II- Centromeres divide, chromatids move to opposite side of the cell

8. TELOPHASE II and CYTOKINESIS- A nuclear membrane forms around each new set of chromatids, the

cytoplasm divides

Stages of Meiosis(continued)

Meiosis results in the formation of four new cells called GAMETES.

- They have only 23 chromosomes