Cell Division

•When do cells divide?•How do cells divide?•What is Meiosis?•How do Chromosomes combine and form new chromosomes?

Cell Size

• All living organism have same size cells

• The size of the animal does not affect the size of the cell

• Mouse cell size = elephant cell size

Eukaryotic Cell Size

• Cell membrane determines cell size• Why? Allows nutrients to enter or

exit• Larger cells require a larger cell

membrane

Is there a limit to a cell’s size?

• You must look at surface area and volume

Surface Area

• The sum of all the areas of all the shapes that cover the surface of the object.

Volume

• The amount of space occupied by a three-dimensional object or region of space, expressed in cubic units.

Surface Area and Volume : Cube

Surface Area = 6 sides x H x W

Volume = L x W x H

Ratio

• Ratio • The comparison between 2 numbers

How do you write a ratio of 4 to 8?• 4:8• 4/8• Surface Area : Volume

Smaller cells are better!

Bigger is Not Better

• Cells need to remain small to survive• Larger cells have a small SA : V ratio• Makes it difficult to transport

materials into or out of the cell

• Nucleus controls the cells size

Cell Division

• Cells divide when they reach their maximum size

• Cell division = one cell split and becomes

2 cells

Why do cells divide?

Essential for Three Life Processes• Growth • Repair• Reproduction

Growth

• Cells divide to increase the size of the organism

• Differentiation: cells develop specialized shapes and functions

• Ex. Nerve cells, heart cells, intestine cells, intestine cell

• Each cell has a unique function

Repair

• Repairs tissue• Mending of skin, blood vessels, and

bone• Regeneration of old skin cells

• Regeneration: ability to replace a missing body part, like a starfish or worm

Reproduction• Asexual reproduction: one parent

produces an offspring• Offspring is genetically IDENTICAL

to parent

• Sexual Reproduction: 2 parents produce an offspring

• Offspring has a combination of genetic material

Asexual Reproduction

• Fission• Spores• Budding• Bacteria, fungi,

plants, ocean animals

Sexual Reproduction

• Gamete = reproductive cell; sperm or egg

• Two gametes fuse to form a zygote

Gametes

zygote

Zygote

• Divides millions x • Becomes an individual• Humans, some plants, animals

http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4ADSA_enUS400US400&q=zygote+dividing+animation#hl=en&rlz=1T4ADSA_enUS400US400&q=zygote+dividing&um=1&ie=UTF-8&tbo=u&tbs=vid:1&source=og&sa=N&tab=wv&fp=f80ab3ca3ad412a3

Technology

• Human Growth Hormone (HGR) • controls the rate of cell division• pituitary gland

Pituitary Gland Malfunction

• Does not make enough HGR

• Dwarfism: person never reaches adult height or weight

• 1985 – Genetic engineers discovered a way to obtain HGR to