Transcript Cell Size and Membrane Transport

Cell Size and Membrane Transport
Georgia Performance Standards:
•Explain the role of cell organelles for both prokaryotic and
eukaryotic cells, including the cell membrane, in maintaining
homeostasis and cell reproduction.
Essential Questions:
EQ: Why do cells divide?
EQ: What limits the size of a Cell?
EQ: Why are cells small?
EQ: How does cell division help maintain homeostasis for the cell?
EQ: Why is mitosis necessary in cell reproduction?
EQ: What happens when mitosis goes wrong?
Cell Growth
• 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 (Cell Division)
Cell Growth & Division
• Why do cells divide instead of growing
bigger and bigger? (Two main reasons)
• When cells become large:
1. The cell places more demands on its DNA
2. It’s more difficult for cells to move enough
nutrients and wastes across the cell
membrane
Ratio of Surface Area to Volume
• Imagine a cell that is shaped like a cube with each side
having a length of 1 cm
• The surface area = length × width × number of sides
1 cm × 1 cm × 6 = 6 cm2).
• The volume of the cell = length × width × height
1 cm × 1 cm × 1 cm = 1 cm3
• To obtain the ratio of surface area to volume, divide
the surface area by the volume.
– The ratio of surface area to volume would be 6 / 1, or 6 : 1.
Ratio of Surface Area to Volume
• If the length of the cell
doubled, what would happen
to the cell’s surface area
compared to its volume?
• The cell’s surface area =
2 cm × 2 cm × 6 = 24 cm2
• The volume =
2 cm × 2 cm × 2 cm =8 cm3
• The cell’s ratio of surface area
to volume = 24 / 8 or 3:1
• What would happen if the
length of the cell triples?
• The cell’s surface area =
3 cm × 3 cm × 6=54 cm2
• The volume =
3 cm × 3 cm × 3 cm=27 cm3
• The ratio of surface area to
volume = 54 / 27 or 2 : 1
The ratio of surface area to volume decreased.
You have less surface area (Not Good)
Ratio of Surface Area to Volume in Cells
• As the length of a cell increases, its volume
increases faster than its surface area.
• The resulting decrease in the cell’s ratio of
surface area to volume makes it more difficult for
the cell to move needed materials in and waste
products out.
• How do cells fix this problem? They divide,
which allows them to stay small.
Checkpoint Questions:
1. Give two reasons why cells divide.
2. What is the solution to the problems
caused by cell growth?
3. As a cell increases in size, which
increases more rapidly, its surface area
or its volume?
4. Select two organelles and describe how
their functions might be impaired if the
cell were to become too large.
Section 10-1
Ratio of Surface Area
to Volume in Cells
Cell Size
Surface Area
(length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume
Go to
Section:
Review: The larger a cell becomes, the more demands the
cell places on its DNA and the more trouble the cell has
moving enough nutrients and wastes across the cell
membrane.
• Every cell must first copy its genetic
information before cell division begins.
• Each daughter cell then gets a
complete copy of that information.
• Cell division is called mitosis
• Each cell has identical DNA
Cell Division
• In eukaryotic cells,
the genetic
information is carried
by chromosomes.
• At the beginning of
cell division, each
chromosome consists
of two identical
“sister” chromatids.
• Chromosomes are
made up of DNA and
protein.
• Each pair of
chromatids is
attached at an area
called the
centromere.
Chapter 9
Cellular Reproduction
The Cell Cycle
 Cell division prevents the cell from
becoming too large.
 The cell reproduces so that you grow and
heal certain injuries.
 Cells reproduce by a cycle of growing and
dividing called the cell cycle.
The Cell Cycle
• During the cell cycle, a cell grows,
prepares for division, and divides
to form two daughter cells, each of
which then begins the cycle again.
The Cell Cycle
• During the cell cycle, a
cell grows, prepares for
division, and divides to
form two daughter
cells, each of which
then begins the cycle
again.
• During the M phase,
mitosis (cell division) of
the cell nucleus and
cytokinesis takes place.
• The other important phase—
the S phase —is the copying
of the chromosomes, making
a duplicate set of DNA.
• Between the M and S phases
are G1 and G2.
• The G in the names of these
phases stands for “gap,” but
the G1 and G2 are definitely
not periods when nothing
takes place. They are actually
periods of intense growth and
activity.
Chapter 9
Cellular Reproduction
9.1 Cellular Growth
 Interphase is the stage during which the
cell grows, carries out cellular functions,
and replicates.
 Mitosis is the stage of the cell cycle
during which the cell’s nucleus and
nuclear material divide.
 Cytokinesis is the method by which a cell’s
cytoplasm divides, creating a new cell.
The Cell Cycle
Section 10-2
G1 phase
M phase
S phase
G2 phase
Go to
Section:
Chapter 9
Cellular Reproduction
9.1 Cellular Growth
The Stages of Interphase
 The first stage of interphase, G1
 The cell is growing, carrying out normal
cell functions, and preparing to replicate
DNA.
Chapter 9
Cellular Reproduction
9.1 Cellular Growth
The Second Stage of Interphase, S
 The cell copies its DNA in preparation
for cell division.
Chapter 9
Cellular Reproduction
9.1 Cellular Growth
The Third Stage of Interphase, G2
 The cell prepares for the division of its
nucleus.
Mitosis: Four Stages
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Chapter 9
Cellular Reproduction
9.2 Mitosis and Cytokinesis
The Stages of Mitosis
 Prophase
 The cell’s chromatin tightens.
 Sister chromatids are attached at
the centromere.
 Spindle fibers form in the cytoplasm.
Chapter 9
Cellular Reproduction
9.2 Mitosis and Cytokinesis
 The nuclear
envelope seems
to disappear.
 Spindle fibers
attach to the
sister chromatids.
Chapter 9
Cellular Reproduction
9.2 Mitosis and Cytokinesis
Metaphase
 Sister chromatids
are pulled along
the spindle
apparatus toward
the center of the
cell.
 They line up in the
middle of the cell.
Chapter 9
Cellular Reproduction
9.2 Mitosis and Cytokinesis
Anaphase
 The microtubules of the spindle apparatus
begin to shorten.
 The sister chromatids separate.
 The chromosomes move toward the
poles of the cell.
Chapter 9
Cellular Reproduction
9.2 Mitosis and Cytokinesis
Telophase
 The chromosomes arrive at the poles and
begin to relax.
 Two new nuclear membranes begin to
form and the nucleoli reappear.
 The spindle apparatus disassembles.
Cytokinesis
• As a result of mitosis, two nuclei—each with
a duplicate set of chromosomes—are
formed, usually within the cytoplasm of a
single cell.
• Cytokinesis: the division of the cytoplasm
itself, ends mitosis.
• Cytokinesis usually occurs at the same time as
telophase.
Cytokinesis
• In most animal cells
– the cell membrane
is drawn inward
until the cytoplasm
is pinched into two
nearly equal parts.
– Each part contains
its own nucleus
and cytoplasmic
organelles.
• In plants cells
– a structure known as
the cell plate forms
midway between the
divided nuclei
– The cell plate
gradually develops
into a separating
membrane.
– A cell wall then begins
to appear in the cell
plate.
Chapter 9
Cellular Reproduction
Section 10-2
Concept Map
Cell Cycle
includes
G1 phase
Go to
Section:
Interphase
M phase
(Mitosis)
is divided into
is divided into
S phase
G2 phase
Prophase
Metaphase
Anaphase
Cytokinesis
Telophase
Bacteria and Viruses
Prokaryote (Bacteria) Structure
 Prokaryotes are
microscopic,
unicellular
organisms.
 They have some characteristics of all cells,
such as DNA and ribosomes.
 Lack a nuclear membrane and other
membrane-bound organelles
Cell Division
• In prokaryotes, the cell first replicates its
genetic information before cell division
begins. Then the cell splits into two parts.
Bacteria and Viruses
Reproduction of Prokaryotes: 2 Types
 Binary Fission: Division of
a cell into two genetically
identical cells
 Conjugation: Two
prokaryotes attach to
each other and exchange
genetic information.
Mitosis Summary
• Every cell must first
copy its genetic
• Mitosis produces
information before cell
two genetically
division begins.
identical daughter
cells with 2 sets of
chromosomes
• Cell division is called
(diploid)
mitosis
Checkpoint Questions
1. Name the 3 main events of the cell cycle.
2. Describe what happens during each of the four phases of mitosis.
3. Describe what happens during interphase.
4. What are chromosomes made of?
5. Compare and contrast how prokaryotic and eukaryotic cells divide?
6. Compare and contrast cytokenesis in plant and animal cells.
What happens
when mitosis
goes wrong?
Chapter 9
Cellular Reproduction
Normal Cell Cycle
 Different cyclin/CDK
combinations signal
other activities,
including DNA
replication, protein
synthesis, and
nuclear division
throughout the cell
cycle.
Chapter 9
Cellular Reproduction
Quality Control Checkpoints
 The cell cycle has built-in checkpoints that
monitor the cycle and can stop it if
something goes wrong.
 Spindle checkpoints also have been
identified in mitosis.
Chapter 9
9.3 Cell Cycle Regulation
Abnormal Cell Cycle: Cancer
 Cancer is the
uncontrolled
growth and division
of cells.
 Cancer cells can kill
an organism by
crowding out normal
cells, resulting in the loss of tissue function.
Chapter 9
Cellular Reproduction
Causes of Cancer
 The changes that occur in the regulation of
cell growth and division of cancer cells are
due to mutations.
 Various environmental factors can affect
the occurrence of cancer cells.
Chapter 9
Cellular Reproduction
Apoptosis
 Programmed cell death
 Cells going through apoptosis actually shrink
and shrivel in a controlled process.
Chapter 9
Cellular Reproduction
9.3 Cell Cycle Regulation
Stem Cells
 Unspecialized cells
that can develop into
specialized cells
when under the right
conditions
Chapter 9
Cellular Reproduction
Embryonic Stem Cells
 After fertilization, the resulting mass of cells
divides repeatedly until there are about
100–150 cells. These cells have not
become specialized.
Chapter 9
Cellular Reproduction
Adult Stem Cells
 Found in various tissues in the body and
might be used to maintain and repair the
same kind of tissue
 Less controversial because the adult stem
cells can be obtained with the consent of
their donor
Stem Cell Movie:
http://learn.genetics.utah.edu/content/tech/stemcells/sctypes/