Download 10-1 Cell Growth

10-1
Cell Growth, Division, and
Reproduction
Key Questions:
1) What are some of the difficulties a cell
faces as it increases in size?
2) How do asexual and sexual reproduction
compare?
Limits to Cell Growth
• Why do cells divide rather
than continue to grow
indefinitely?
•
1. The larger a cell
becomes the more
demands the cell places
on its DNA.
– When a cell is small
the info stored in
DNA is able to meet
all the cell’s needs.
– As a cell increases in
size, it usually does
not make extra
copies of DNA.
– If the cell were to
increase without limit,
an info crisis would
occur.
Limits to Cell Growth
2. The cell has more
trouble moving
enough nutrients
and wastes across
the cell membrane.
– Food, Oxygen, and
water enter a cell
through its CM;
waste products leave
the same way.
Limits to Cell Growth
• The rate at which this
exchange takes place
depends on the surface
area of the cell & the total
area of the cell
membrane.
• The rate at which food
and oxygen are used up
& waste products are
produced depends on the
cell’s volume.
• The ratio of surface area
to volume allows us to
understand why cells
must divide.
SA/V Ratio
• If a cell gets too large,
it would be more
difficult to get
sufficient amounts of
oxygen & nutrients in
& waste products out.
• This is one reason
why cells do not grow
too large– they divide!
Surface Area/Volume Ratio
•
•
•
•
Surface area=length X width X number of sides (6).
Volume=length X width X height
SA/V Ratio=The surface area divided by the volume.
What happens to volume and surface area as a cell gets larger?
– The volume increases more rapidly than the surface
area.This causes the ratio of surface area to volume to
decrease.
– Ex: Street in a town that grows in size has more traffic.
• If a cell gets too large, it would be more difficult to get sufficient
amounts of oxygen & nutrients in & waste products out.
• This is one reason why cells do not grow too large– they divide!
Surface Area/Volume Ratio
Division of the Cell
• What is the name of
the process when
cells divide?
• What is produced in
cell division?
• It is called cell
division.
• Two new “daughter
cells.”
Before Cell Division
• What happens before cell
division?
• The cell replicates
(copies)all of its DNA.
• This solves the problem
of info storage because
each new daughter cell
gets one complete set of
genetic info.
• Cell division also solves
the problem of increasing
size by reducing cell
volume. Each new
daughter cell has an
increased SA/V ratio.
Cell Division and
Reproduction
– How do asexual and sexual reproduction
compare?
– The production of genetically identical offspring
from a single parent is known as asexual
reproduction.
Cell Division and
Reproduction
– How do asexual and sexual reproduction
compare?
– The production of genetically identical offspring
from a single parent is known as asexual
reproduction.
– Offspring produced by sexual reproduction
inherit some of their genetic information from
each parent.
Asexual Reproduction
–
In multicellular organisms, cell division leads to growth. It also
enables an organism to repair and maintain its body.
– In single-celled organisms, cell division is a form of
reproduction.
– Asexual reproduction is reproduction that involves a single
parent producing an offspring. The offspring produced are, in
most cases, genetically identical to the single cell that produced
them.
–
Asexual reproduction is a simple, efficient, and effective way
for an organism to produce a large number of offspring.
–
Both prokaryotic and eukaryotic single-celled organisms and
many multicellular organisms can reproduce asexually.
Sexual Reproduction
– In sexual reproduction, offspring are
produced by the fusion of two sex cells – one
from each of two parents. These fuse into a
single cell before the offspring can grow.
– The offspring produced inherit some genetic
information from both parents.
– Most animals and plants, and many singlecelled organisms, reproduce sexually.
Comparing Sexual and
Asexual Reproduction