Chapter 9 – Cellular Growthpp. 244-246

Sizes of Different Cells Red blood cell – 8 um Nerve cell (large animals) – 1um Largest known cell – ostrich egg yolk

(8 cm diameter) Most cells are between 2 and 200 um in

diameter

um = micrometer

Cell Size Limits Cells can metabolize only as quickly as

they can diffuse nutrients, oxygen and wastes.

Diffusion is fast and efficient over short distances, but becomes slow and inefficient as the distances become larger.

Affects the ability of the cell to communicate instructions for cellular functions.

Surface Area-to-Volume Ratio

As a cell’s size increases, its volume increases much faster than its surface area.

Surface-to-Volume Ratio in Cells

Cell Size (cm) 1 x 1 x 1 2 x 2 x 2 4 x 4 x 4

Volume 1cm3 8 cm3 64 cm3

Surface Area 6 cm2 24 cm2 96 cm2

Surface-to-Volume Ratio 6 3 1.5

When cell size doubles:• Cell requires 8 times more nutrients.• Has 8 times more waste to excrete• Surface area only increases by 4 times so the

plasma membrane would not have enough surface area through which O2 and nutrients could diffuse.

• The cell would either starve or be poisoned from the buildup of waste products. To prevent this, the cell divides.

When Do Cells Divide?

• Many of the cells in your body are growing, dividing, and dying.

• Cuts and bruises are healing.

• Intestines are producing millions of new cells each second.

Chromosomes‘Chroma’ means colored.

‘Soma’ means body.

Chromosome Structure

• A rod-shaped structure that forms when a single DNA molecule and its proteins coil tightly before cell division.

• If DNA did not coil, a single strand of DNA would be about 5 cm long (2 inches).

Number of Chromosomes Penicillium 1-4

Mosquito 6

Carrot 18

Garden pea 20

Frog 26

Cat 32

Earthworm 36

Human 46

Chimpanzee 48

Gorilla 48

Orangutan 48

Amoeba 50

Sand Dollar 52

Horse 64

Dog 78

Adder’s tongue fern

1262

Adder’s Tongue Fern