Transcript 10-1 2014 Why Cells Divide

Bellwork: Thurs. Oct. 22, 2015: (1st BELLWORK
for new unit!!)
Main reasons why cells divide:
1. more demands are put on its DNA when it
becomes larger.
2. The cell has more trouble moving enough
nutrients and wastes across the cell membrane.
when it becomes larger.
Mitosis
Meiosis
Notes 5
Notes: 10 – 1 Cell Growth
Imagine: What if all classes at IRHS were held in
the gym…at the same time?
Think of few problems that this would cause.
What if instead of having
more than one vending
machine on campus,
there was only one
vending machine for all of
IRHS?
OMG… no more junk food!
What if IRHS had a room filled with vending
machines but only a single door in and out?
Why would this be a problem?
Students Trampled in Vending Machine
Frenzy for Last Poptart
DNA Overload
The information controlling cell function is stored in
the DNA molecule
When a cell is small, the information stored in
that DNA is able to meet all of the cell's
needs. But as a cell increases in size, it
usually does not make extra copies of DNA.
If a cell were to grow without limit, an
“information crisis” would occur.
https://www.youtube.com/watch?v=wuXSEOKNxN8
Ratio of Surface Area to Volume
Surface area = length × width × number of sides
Volume = length × width × height
Ratio = surface area / volume
A bigger ratio of surface area to volume is better for
exchange!
Exchange of Materials
Food, oxygen, and water enter a cell through its
cell membrane .
Waste products leave/exit in the same way.
rate of exchange depends on cell surface area which is the total area of its cell membrane.
BUT… rate at which food and oxygen are used up and waste products
are produced depends on the cell's volume.
How does a
whale stay warm
in freezing
water?
A low surface
area to volume
ratio!
As an animal increases in size, its volume increases
more rapidly than its surface area. This means that there
is less surface area, skin, exposed to the freezing water in
comparison to the volume.
Where do you think this rabbit (Sylvilagus audubonii)
lives and how can you tell?
The desert! Note the surface area to volume ratio of
the ears.
When a living thing grows, what happens to its cells?
Does an animal get larger because each cell increases
in size or because it produces more of them?
In most cases, living
things grow by
producing more cells.
On average, the cells of
an adult animal are no
larger than those of a
young animal—there
are just more of them.
So how do we go from this…
…to this?
Cell Growth and Division!
Process by which cells divide into two new
daughter cells is called________________
Mitosis
https://www.youtube.com/watch?v=Cg4ASxSKH2o
Q1. As a cell increases in size, which increases more
rapidly, its surface area or its volume?
A.Surface Area
B.Volume
C.They increase at the same rate.
Q1. Which do you want for better exchange of
materials across the cell membrane?
A.Low surface area to volume ratio, i.e. 2:1
B.Equal surface area to volume ratio, i.e. 1:1
C.High surface area to volume ratio, i.e. 6:1
Q3. Which of the following is a reason why cells
divide?
A.All of the DNA can’t fit within a single cell.
B.DNA becomes diluted as a cell increases in size.
C.The larger a cell becomes, the more demands the
cell places on its DNA.
D.DNA doesn’t increase in size fast enough to keep
up with a cell’s growth.
Q4. Which of the following is another reason why
cells divide?
A.As a cell gets larger, it becomes more susceptible
to attack.
B.The cell has more trouble moving enough
nutrients and wastes across the cell membrane.
C.There isn’t enough room in the organism to
accommodate larger cells.
D.As a cell gets larger, its membrane gets weaker
until it bursts.
What are the two main reasons why cells divide?
1. The larger a cell becomes, the more demands
the cell places on its DNA.
2. In addition, the cell has more trouble moving
enough nutrients and wastes across the cell
membrane.
Process by which cells divides into two new
daughter is called Mitosis
1-3 p. 274
5 p. 275