1. Cells: Why do they divide?
Doing Life’s Work

2. animal cells plant cells
bacteria cells
Types of cells
Prokaryote
no organelles
no nucleus
animal cells
Eukaryotes
Organelles
nucleus
plant cells

3. Why study cells? Cells  Tissues  Organs  Bodies
bodies are made up of cells
cells do all the work of life!

4. The Work of Life Jobs that cells do to keep an organism alive…
“breathe”
O2 in and CO2 out
Eat
make energy
build molecules
remove wastes
control internal conditions
respond to external environment
build more cells
growth, repair, reproduction & development

5. Cells have 3 main jobs make energy make proteins make more cells
need energy for all activities
need to clean up waste produced while making energy
make proteins
proteins do all the work in a cell, so we need lots of them
make more cells
for growth
to replace damaged or diseased cells

6. Cells have to work to live!
They need to make more cells for
growth
repair
reproduction
To reproduce, repair & grow, the cell must…
copy their DNA
make extra organelles
divide the new DNA & new organelles between 2 new “daughter” cells

7. What does Cell Division Repair?
Dead/ injured cells
Your body sheds millions of cells daily! All of these need to be replaced
Broken bones, blisters, cuts. You need new cells to heal the break

8. Cell lifespans
Not all cells are created equal, they all have a predetermined self-destruct time!
red blood cells live 120 days
liver cells live 200 days
intestine lining cells live 3 days
skin cells live 20 days
stomach lining cells live 2 days
brain cells live years

9. Cell Division for: REPRODUCTION
Cell Reproduction
Asexual reproduction: involves only one parent, and the offspring all have identical DNA to the parent and each other
Occurs in many single celled organisms, and ALL of your body cells except sex cells

10. Offspring are NOT identical
REPRODUCTION
Sexual Reproduction: sex cells called gametes contain only half of the DNA.
DNA from two parents join to create offspring with characteristics from both parents
Offspring are NOT identical

11. QUESTIONS - For you to answer:
A cleaning product claims to kill 99.9% of all bacteria. Will a cleaned surface stay bacteria free forever? Explain your reasoning.
What is the major difference between sexual and asexual reproduction?
Why do cells divide instead of just getting bigger as organisms grow?
Provide some evidence that suggest that not all cells in your body divide at the same rate (speed).
At one time, Dr.’s transfused blood from younger individuals into the elderly. They believe that the younger blood would provide the elderly with more energy. Do older people have older blood?