Transcript Cell Growth and Reproduction

Cell Growth
and
Reproduction
Cell Size Limitations
Cell Size Limitations

Although it is the smallest unit of life, a
cell still has all of the characteristics of
life. A cell is able to grow, but it is limited
in how big it can grow because of the
necessary functions it carries
out…Remember organelles???
Cell Size Limitations

The plasma membrane lets nutrients into
the cell and allows wastes to leave.
Inside the cell, nutrients and wastes
move by diffusion. Diffusion limits cell
size because it is a fast and efficient
process only over short distances.
Cell Size Limitations

Remember, a cell has a lot of cell parts
or organelles to perform specialized
functions. In order for them to work
together quickly and efficiently, they
need to be able to transport things
VERY QUICKLY therefore they have to
be VERY small.
Let’s take a look at our example…
Cell Size Limitations
Cell Size Limitations

Because a cell’s size can slow down
the rate of diffusion, cells have to
have a way of limiting their growth.
Cells divide before they become too
big and therefore unable to function
well:

The cell would either starve to death or
be poisoned from the buildup of waste
products.
Why Divide???

Cells divide in organisms for:
1.
2.
3.
Cell repair
Cell replacement
Growth (lengthening of bones, etc)
Cell Reproduction

When cells divide, new cells are produced
from one cell. Remember the cell theory?
Part 3 of the cell theory stated that all
cells come from pre-existing cells.
Cell Reproduction
-
Cell division is the process by which
new cells are produced from one cell.
- Cell division results in two cells that
are identical to the original, called a
parent cell. The two new cells are
called the daughter cells. When exact
copies are made of “body” cells, this
is called MITOSIS.
Cell Reproduction-Important Structures

Organisms could not grow or function
properly if the genetic material encoded
in DNA was not passed from cell to cell.
So when cells reproduce by dividing, they
also pass along their DNA. But how???
Cell Reproduction-Important Structures

Chromosome: the carrier of the
genetic material that is copied and
passed from generation to generation
of cells



Formed during cell division, it is only
seen right before and right after cell
division
It has to be accurate (mistakes =
mutations)
It is a rod-shaped structure made of
tightly coiled DNA and protein
Cell Reproduction-Important Structures

Chromatin: long strands of DNA coiled
in a ball in the nucleus

for most of a cell’s lifetime, chromosomes are
found in this form
Cell Reproduction-Important Structures

Chromatid: half of the chromosome
(individual sides).

each part is called a sister chromatid
Cell Reproduction-Important Structures

Centromere: a part of the chromosome
that holds sister chromatids together;
helps move the chromosome during cell
division
Centromere
Sister
chromatids
Chromosome
Supercoil
within
chromosome
Continued
coiling within
supercoil
Histone
DNA
Cell Reproduction-Important Structures
Chromosome
centromere
sister chromatids
The Cell Cycle (in Eukaryotes)


The cell cycle is the sequence of growth
and division of a cell. Cell division is ONE
stage. A cell will divide many times in its
lifetime before it dies and is replaced by a
new cell.
There are three stages of the cell cycle:
1. The time BETWEEN cell divisions is called
interphase.
2. The time OF cell division is called mitosis.
3. When the cytoplasm divides and you officially have
2 new cells, it is called cytokinesis.
The Cell Cycle
Growth
Division
2 New Cells
The Cell Cycle (in Eukaryotes)
IPeedMadlyAtTheCrapper-
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
The cell cycle and Mitosis (in Eukaryotes)
Cell division occurs in a series of
stages, or phases.
The cell cycle and Mitosis (in Eukaryotes)
1st: Interphase
Chromosomes are copied
Chromosomes are in the
form of threadlike coils
(chromatin)
***Interphase is the longest and busiest
phase of the cell cycle.
The cell cycle and Mitosis (in Eukaryotes)
2nd: Prophase
Mitosis begins (cells start to divide)
spindle fibers
Chromatin condenses to form
chromosomes
Centrioles (pole-like organelles) appear
Spindle fibers form between the poles
**Chromatin condenses to form chromosomes so
this is where chromosomes become visible under
a microscope**
The cell cycle and Mitosis (in Eukaryotes)
3rd: Metaphase
Chromatids (or pairs of chromosomes)
attach to the spindle fibers
The chromosomes line up in the
middle of the cell
spindles
The cell cycle and Mitosis (in Eukaryotes)
4th: Anaphase
What happens:
Centromeres at the center of the chromosome split
and sister chromatids are pulled apart to the
opposite sides of the cell.
The cell cycle and Mitosis (in Eukaryotes)
5th: Telophase
Chromosomes loosen up to
become chromatin again
Mitosis ends
What happens:
Two new nuclei are formed and a double membrane
begins to form around them.
The cell cycle and Mitosis (in Eukaryotes)
6th: Cytokinesis
Cell membrane moves inward and the cytoplasm
divides
Two daughter cells are
created – each with its own
nucleus (with identical chromosomes)
What happens:
The cell’s cytoplasm divides and separates into two
new identical cells.
Mitosis in a Plant Cell
The Results of Mitosis
= Organization
Cells working
together for
the same
function are
called tissues
Similar
tissues
will form
an organ
Several organs
working together
make up an
organ system
The results of mitosis: Cancer
• Cancer is cell reproduction gone wrong:
- It occurs when a cell loses control of its
division and starts making cells even if they are
not needed
• Cancer can be caused by 3 major things:
1. UV radiation & radiation (too much sun,
radiation exposure)
2. Environmental influences (ex. air pollution,
smoking)
3. Viruses (a viral infection can damage genes)
Cancer Prevention
• Diets low in fat and high in fiber
• Daily exercise
• Not using tobacco
Question 1
The stringy structures in the cell nucleus that
contain DNA are __________.
A. centromeres
B. chromosomes
C. genes
D. chlorophylls
Question 2
Look at the diagram and identify the stage of
mitosis that is depicted.
Centromere
Sister
chromatids
A. prophase
C. anaphase
B. metaphase
D. telophase
Question 3
What is the process by which a cell's cytoplasm
divides?
A. cytokinesis
B. telekinesis
C. meiosis
D. mitosis
Question 4
In multicellular organisms, groups of cells that
work together to perform a specific function are
called __________.
A. organ systems
B. organs
C. tissues
D. cell cycles
Question 5
Magnification of a plant cell reveals centromeres
that have split and sister chromatids being pulled
to opposite poles of the cell. This cell is in which
phase of mitosis?
A. prophase
B. metaphase
C. anaphase
D. telophase
Question 6
Which phase of mitosis is depicted in this
diagram?
Spindle Fibers
Doubled
chromosome
Disappearing
nuclear envelope
A. prophase
C. anaphase
B. metaphase
D. telophase
Question 7
What is the term used for the period of the cell
cycle represented by the red arrow in this graph?
A. prophase
B. metaphase
C. centrophase
D. interphase
DNA synthesis
and replication
Centrioles
replicate; cell
prepares for
division
Rapid growth
and metabolic
activity
Mitosis
Cytokinesis