cell division when do cells divide? how do cells divide? what is meiosis? how do chromosomes combine...

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