Section 8Cellular Reproduction

Biology I and

Science Skills and Reasoning

I. The Cell Cycle

A. All living things must be able to grow and reproduce.

B. They grow and reproduce during the cell cycle

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I. The Cell Cycle

C. Diagram of a Chromosome:

Sister chromatids

centromere

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I. The Cell Cycle

A. Two Parts of the Cell Cycle1. Interphase

• G1 stage (1st growth phase) – Normal cell growth

• S phase – Chromosomes replicate in the nucleus to form a new set of identical chromosomes.

• G2 phase – (2nd growth phase) – The cell is getting ready for division. RNA and proteins are made. Organelles are duplicated

I. The Cell Cycle

I. The Cell Cycle

2. M Phase (M stands for Mitosis) a. This is mitosis (nuclear division) b. Mitosis is responsible for tissue

repair. It heals the cut.

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I. The Cell Cycle

There are 4 stages of Mitosis1. Prophase

a. Chromosomes coil up, thicken, and become visible.

b. Nuclear membrane dissolvesc. Spindle forms from the centrioles

I. The Cell Cycle

2. Metaphasea. Chromosomes are pulled

to the equator of the cell and line up.

b. Meta means “middle.”

I. The Cell Cycle

3. Anaphasea. The chromosomes (in pairs)

are pulled apart by the spindle fibers.

b. Looks like an “X” that has been pulled apart.

I. The Cell Cycle

1. Telophasea. Opposite of prophaseb. Everything done in prophase is undone in telophase.

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I. The Cell CycleAt the end of telophase the cell undergoes

cytokinesis (cyto means cell; kinese means to cut).a. The cell splits.b. The G1 phase begins at the end of cytokinesis.c. Plant cells form a cell plate between the two new cells which will become the new cell wall between the cells.d. In animal cells the cell separates when it’s “pinched” in half by the cytoskeleton. This indentention is called the cleavage furrow.

REMEMBER

PMAT

ProphaseMetaphaseAnaphaseTelophase

II. Sexual Reproduction and Meiosis

A. Organisms using sexual reproduction have 2 types of cells

1. Somatic cells – Body Cells2. Gametes – Sex cells

B. Sex cells reproduce by a process called MEIOSIS

II. Sexual Reproduction and Meiosis

A. MEIOSIS = SEX!!!1. Anytime you see the word

meiosis thing “SEX.”2. Meiosis is the process whereby

your body makes sex cells.

II. Sexual Reproduction and Meiosis

1. Male cells are called sperm cellsa. Sperm cells are produced in the testes and

are released through the penis.b. Sperm begins production at puberty and

continues until death.c. It takes 72 days for a sperm to reach

maturity.d. 400-500 Million sperm are released every

ejaculation.

II. Sexual Reproduction and Meiosis

1. Male cells …..(continued)a. Sperm can build up over time and must be

released. Some dribble out and are released during urination. Some may be reabsorbed into the body.

b. Sperm require a temperature about 5 degrees cooler than the body. That’s why the testes hang outside the body.

c. A change in temp. will cause the testes to draw closer to the body for warmth or get really lose when it gets hot.

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II. Sexual Reproduction and Meiosis

1. Female sex cells are called eggs.a. Eggs are produced in the ovaries.b. Egg production begins at birth in females but the eggs are not released until the onset of menstruation.c. Egg production stops at menopaused. Ovaries contain thousands of eggs.e. Only one egg is released each month in humans.

II. Sexual Reproduction and Meiosis1. Female sex cells….(continued)

f. Before ovulation (releasing an egg) the uterus swells with blood and become a nice thick pillow for the prospective baby.g. When fertilization doesn’t take place, the lining of the uterus, the egg, and all the extra blood must be removed from the body. This takes place during the menstrual cycle.

II. Sexual Reproduction and Meiosis

A. Chromosome number1. The normal number of chromosomes an

organism is suppose to have is referred to as diploid (2n).

2. Haploid (n) is half the number of chromosomes.

3. Sex cells are haploid and body cells are always diploid.

II. Sexual Reproduction and MeiosisA. Chromosome number (continued)

1. Chromosomes exist in pairs (homologous chromosomes). Humans have 23 pairs of chromosomes which equals 46.

2. The diploid number for human body cells is 46.

3. The haploid number for human sex cells is 23.a. Eggs have 23 chromosomesb. Sperm cells have 23 chromosomesc. Skin cells have 46 chromosomes

II. Sexual Reproduction and Meiosis

A. Chromosome number…continued1. Meiosis therefore produces haploid

cells.2. Meiosis adds genetic variation3. Chromosomes separate randomly and

get “mixed up” therefore it adds variation to the way organisms look. For example you and your siblings were made by the same 2 parents but are genetically different.

II. Sexual Reproduction and MeiosisA. Stages of Meiosis

• Meiosis is divided into 2 parts.a. Meiosis I

1. It is very similar to mitosis2. Meiosis I results in 2 identical cells.3. 4 parts of meiosis I are prophase I,

metaphase I, anaphase I, and telophase I.

b. Meiosis II1. End product is 4 cells with half the

number of chromosomes2. Stages of meiosis II are prophase II,

metaphase II, anaphase II, and telophase II.

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A.Comparing Mitosis to meiosis

Occurs only in organisms that perform sexual reproduction

Occurs in most all living things

2 divisions1 division

Makes haploid cellsMakes diploid cells

Makes sex cellsMakes body cells

MeiosisMitosis

Comparing Mitosis to Meiosis

III. Types of Reproduction

A. Reproduction is an essential part of the characteristics of life.

B. Assures the continuation of the speciesC. An organism adaptations and drives are

for one purpose: reproduction.D. An organism is only successful if it is

able to reproduce

III. Types of Reproduction

A. Two Types of Reproduction1. Sexual Reproduction

a. Egg and sperm (haploid) meet and create a new organism (diploid)

b. Pollen fertilizing and eggc. Female frog lays eggs in the

water and the male sprays sperm over them (external fertilization)

d. Sperm is deposited into the female’s vagina by the penis (internal fertilization)

III. Types of ReproductionA. Two types of reproduction (continued)

1. Asexual reproductiona. Comes from 1 parentb. Produces genetically identical offspring (clones)c. There is NO halving of the chromosomes.d. Binary fission – a single cell splits in half.

Common in bacteria and some protists.e. Budding – small area of cells that begin to grow

into a new, separate organism. Used by fungi and simple animals.

f. Vegetative propagation – plants send out runners that grow into a new plant or cuttings can be taken from a plant and grown.