ppt why cells divide ii #1 1

General Biology

ReproductionReproductionTwo typesTwo types

Types of Reproduction

Asexual Reproduction Asexual Reproduction:One parent gives rise to two offspringCells:One parent cell gives rise to two daughter cells

The daughter cells have identical DNA as the parent!

Sexual ReproductionThe process of sexual

reproduction begins after the sperm

fertilizes an egg.

Human Reproduction

• Terminology

• Why cells divide.

• How Cells Divide (Cell Cycle)

Our Focus in the First Part of this Lengthy Unit is Going to be on

CELL DIVISION

CELL DIVISION - Terminology

Mother Cell

Daughter Cells

Chromosomes

CHROMATIN

• A strand of DNA in the nucleus

• Long & stringy during normal cell activity

• Contains genes

DNA (Chromatin) Replicated

Gene

Chromosome

• Condensed CHROMATIN

Why do cells divide?1. DNA Overload

2. Efficiency

3. Growth

4. Repair and Replace

DNA Overload• Cell becomes too large for the DNA

to control. It has to divide!

To be more EFFICIENT!• Cell becomes too large the volume

increases faster than the surface area.

• The cell membrane is no longer efficient at allowing nutrients and waste to pass through it.

Growth• We start as a single cell and become

a person because cells divide!

Repair and Replace damaged or worn out cells!

• Cell becomes too large for the DNA to control. It has to divide!

Which has more cells?

Or

Which Has Bigger Cells?

or

Cell Sizes

There is a nerve cell in the leg of the giraffe that is nearly two meters

long.

What Limits Cell Size?

All needed cell materials are absorbed through the surface

of the cell.

These materials are used by the entire volume of the cells “living stuff”.

Cell A Cell B

1 cm

3cm

Lets compare surface area to volume ratios

1 cm

3cmSA = 6 cm2

Volume = 1cm3

SA = 54 cmSA = 54 cm22

Volume = 27 cmVolume = 27 cm336:1 Ratio

2:1 Ratio

What Limits Cell Size?

The Surface Area of the Cell The Surface Area of the Cell Becomes to Becomes to Small Small to Support theto Support the

VolumeVolume

That is why cells divide ! !

How do cells divide ? ? ?

Surface Area & Volume

When cells get too large it is more difficult for them to transfer sufficient amounts of O2 and nutrients in & waste product out

• Volume increases more rapidly than surface area when cells grow, causing the ratio of surface area to volume to decrease

Calculations

• SURFACE AREA=

Length x width x # of sides

• Volume =• length x width x height

Practice Problems

• Find surface area & volume of a cube that is 4cm on all sides:

• Surface area= ____cm x ____cm x ___ = ______cm

• Volume = ____cm x _____cm x _____cm = _______cm• Ratio of surface area to volume is = surface area = • volume

Ratio = 1.5:1

CELL CYCLE

Homework Tonight deals with the Cell cycle

Lab tomorrow deals with

Why Cells Divide?

That’s All From Here For

Today