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Biology B Cell Reproduction
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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