The Importance of Cell Division
Section 2.3
• We all started out as a single cell
– a fertilized egg called a zygote
• As adults, we have bodies consisting of
trillions of cells through the process of cell
division.
Purpose of Cell Division
1. Reproduction
2. Growth
3. Repair
Reproduction
• All cells, including single-celled organisms use
cell division to reproduce
• There are 2 basic kinds of reproduction:
– Sexual and asexual
Asexual Reproduction:
• Involves only 1 parent
dividing into two cells
• Offspring are
genetically identical to
parent cell.
Sexual Reproduction:
• Process of producing
offspring by the fusion of
two gametes (egg and
sperm cells)
– Gamete (sex cells)
• “half-cell” contains only
have of the DNA usually
found in a cell.
• Offspring have genetic
information from both
parents, and therefore
are NOT genetically
identical to their parents.
Growth
• As organisms grow, the number of cells increases.
OUT
IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUT
IN
waste
ammonia
salts
CO2
H2O
products
FOOD must be able to move into and throughout the cell quickly enough for
the proper function of the cell. WASTES also must be transported quickly out
of the cell.
How does material move in and out of
the cell?
• Diffusion
– Materials move from an area of higher
concentration to and area of lower concentration
• Concentration
– the amount of a substance (solute) in a given
volume of water
Osmosis is just diffusion of water
• Water is very important to life, so we talk
about water separately
• Osmosis
– Diffusion of water from HIGH concentration of
water to LOW concentration of water
– across a
semi-permeable
membrane
How to grow a gummy!
Cells do not substantially increase in size. Why?
• Food and nutrients have
less distance to travel to
organelles
• Food and nutrients take
too long to reach
organelles
Cells need to be efficient at getting food in
and wastes out!
Repair
• All organisms must repair
themselves to stay alive by the
division of the remaining cells
– Skin cells: millions replaced every
day
– Red blood cells: each red blood
cell is replaced every 120 days
– Broken bones, cuts and blisters:
new cells needed to fill in gaps
– Nerve cells: cannot regenerate!
Repair
Classwork/Homework
1. Read Lab: What is the ideal cell size?
2. Answer pre-lab questions (DUE WEDNESDAY)
3. Answer Q#1-6 on pg. 37