Cell division through mitosis and meiosis is essential for growth, development, and reproduction in organisms. Mitosis produces two identical daughter cells during normal growth and tissue repair. Meiosis produces gametes like sperm and egg cells that have half the number of chromosomes, allowing sexual reproduction to create offspring with a full set of chromosomes from both parents. DNA is replicated and passed on to new cells through these cell division processes to ensure genetic continuity.

1. Chapter
CELL CYCLE

2. Why Is Cell Division Important
What do you, an octopus, and an oak tree
all have in common?
You are all made of many cells, trillions of
them!
Many multi-celled organisms start off as just
one single cell. And this single divides to
become 2 cells which divide to become 4
cells and then 8 and 16 and so forth.

3. Why Is Cell Division Important
Many celled organisms are able to grow
and develop because cell division
increases the total number of cells in an
organism.
Even after we stop growing cell division is
very important.
Everyday billions of red blood cells are
replaced by new ones through cell
division.

4. Why Is Cell Division Important
Cell division is not just important to multi-
celled organisms. It is also important to
single celled organisms, like bacteria and
algae.
All cells go through cell division in what is
called the cell cycle or the cell life cycle.
The cell cycle begins with the formation of
a cell of an organism.
This formation is followed by growth and
finally ends in the death of the cell.

5. Cell Cycle
There are 3
stages of the cell
cycle. And they
are:
1) Interphase
2) Mitosis
3) Cytokenesis.

6. Cell Cycle
1) Interphase- during this first stage of the
cell cycle, the cell grows and duplicates
its organelles and chromosomes in order
to prepare for mitosis.
2) Mitosis- Is stage 2 of the cell cycle. And
mitosis is the way that all of our cell go
through cell division.
3) The third stage of the cell cycle is called
cytokenesis. Here the cytoplasm of the
parent cell is evenly distributed into the
two new daughter cells or offspring.

7. Interphase
Most of the life of any cell is spent in Interphase, in
which the cell grows and develops.
Also, during the later part of interphase the cell
duplicates all of its chromosomes, which hold all of our
genetic material and prepares to undergo a form of
cell division called mitosis.
When chromosomes duplicate they form 2
chromatids.
You are able to grow and develop because of mitosis,
the process in which one cell splits its nuclei and its
DNA to produce two exact genetic copies of itself.
The cells want to duplicate or copy its chromosomes
before mitosis so that the two new cells that are going
to be made have an equal amount of chromosomes in

9. Cell Division or Mitosis
Cells go through mitosis in order to
assure that each new cell receives
exactly the same information as the
cell it came from.
Also, cells go through mitosis in order
to grow and replace dead or
damaged cells, like when you get a
cut, or break a bone.

10. 5 Stages of Mitosis.
Mitosis occurs in 5 stages, and they are
called:
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase

11. Mitosis
1) Prophase- Here, the chromatids
become visible because the nucleus is
breaking down and the spindle
apparatus, which is used to separate
the chromosomes is formed.
- The spindle apparatus is a set of thread
like fibers that are made by an organelle
called a centriole.
And it is used to pull the duplicated
chromatids apart so that each new cell
can have an equal amount of
chromosomes.

12. Prophase

13. Mitosis
2) Metaphase- The
chromatids line up in
the middle of the cell
and begin to be pulled
apart from one
another by the spindle
apparatus, which is
attached to the
centromere of the
chromatid, or where
the chromatids are
attached.

14. Metaphase

15. Mitosis
3) Anaphase- In anaphase all of the
chromatids that were lined up in the
middle of the cell are completely pulled
apart from on another by the spindle
apparatus.
This leaves two sets of equal numbers of
chromosomes on each end of the cell.

16. Anaphase

17. Mitosis
4) Telophase- here the
cell wall or cell
membrane of the cell
begins to pinch in and
the cells divide into
two cells of equal size
with the same genetic
material.
Also here the spindle
starts to disappear
and a new nucleus
forms.

18. Stage 3 of the Cell Cycle:
Cytokenesis
In animal cells, the cell membrane pinches
and the cytoplasm of the parent cell is
divided into the two new cells.
In plant cells, after telophase a cell plate
is formed in order to allow the proper
formation of the cell wall.
The presence of the cell plate tells you
that the cell is in the stage of cytokenesis.

19. Results of Mitosis
You should remember 2 important facts
about mitosis:
1) It is the division of the nucleus.
2) It produces 2 new nuclei that are
identical to each other and also identical
to the original parent cell.

20. Reproduction
The method in which an organism can produce
a new organism from one parent is called, what?
Asexual reproduction
In asexual reproduction, all the DNA in the new
organism comes from only one parent.
A potato uses asexual reproduction, so every
potato that comes from one parent potato will
have the same DNA as that parent.

21. There are 2 ways in which
reproduction from one parent
occurs.
1) By Splitting-bacteria and other single
celled organisms divide in half,
forming two new cells.
When the cell divides, each new cell gets
an exact copy of the parents DNA.
Now the two new cells are exactly alike
and the parent cell no longer exists.

22. There are 2 ways in which reproduction from
one parent occurs.
2) Buddingout and
breaking up- Many
mushrooms, plants,
and some animals
use budding as a
form of asexual
reproduction.
Here a new cell will
bud off of the parent
cell, break away and
live on its own.

23. Budding & Regeneration
Ex: If you cut a piece of ivy, that piece that
you cut can be planted and grow to a new
plant.
In a process called regeneration some
organisms are able to replace body parts
that have been lost because of injury.

24. Sexual Reproduction
In sexual reproduction- a new organism is
produced from two parents.
During this process, DNA from both parents
combine to form a new individual with its own
DNA.
In Chapter 3 we spoke of how there are
different cells for different function in the human
body.
For sexual reproduction have cells called sex
cells.

25. Sex cells
There are two types of sex cells:
1) Sperm- a male sex cells that form in male
reproductive organs.
2) Ova or egg- a female sex cell which will
form within the female reproductive organs.
Body cells or non sex cells in your body have
46 chromosomes and are called diploid
because each chromosome has a pair.
And when they divide the new cells gets all 46
chromosomes that the original had, and we
said that this process was called mitosis.

26. Sex Cells
Sex cells are a little different. They go
through a process called meiosis, which is
the formation of sex cells.
Sex cells only contain 23 chromosomes and
are called haploid.
These cells have half the amount that a
normal non-sex cell would have.
So when they divide only 23 chromosomes
are given to the new cell.

27. Sex Cells
So, each sperm and egg have 23 chromosomes
and when they join in a process called
fertilization, the result or offspring has a full set
of 46 chromosomes.
After these sex cells combine and fertilization
occurs the resulting cell that is formed is called a
zygote.
As soon as the zygote is formed, it then begins
to go through cell division.

28. Meiosis
Meiosis only occurs with respect to sex cells.
And meiosis produces more haploid sex cells.
Meiosis ensures that the offspring between 2
organisms will result in an offspring that has the
same amount of chromosomes, 46, as the
original parents had.
During Meiosis 2 divisions of the nucleus occurs.
These two divisions are called Meiosis I and
Meiosis II

29. Meiosis I & II
Meiosis I is very similar to mitosis.
It starts with one diploid cell. They have the
same steps ( Interphase I, prophase I,
metaphase I, telophase I.
However, in Meiosis I the duplicated
chromosomes in the cells all have chromatids
that do not separate at all during the division of
the cell.
The end result here is that 2 new diploid cells
are formed and both have the same genetic
material as the original parent cell.

30. Meiosis I

31. Meiosis II
The 2 new diploid cells produced by
Meiosis I are now ready to go through
Meiosis II.
Again these 2 cells go through
Interphase II, Prophase II, etc.
However, here the chromatids are
separated from the centromere by the
spindle apparatus.
This separation of the chromatids in these
2 cells produces 4 new sex cells that only
contain 23 chromosomes.

32. Mistakes in Meiosis
Sometimes mistakes occur during
meiosis.
One mistake could be that a cell might be
produced with too many or too few
chromosomes.
If this cell becomes fertilized it might not
survive and if it does the organism that
forms may not develop or grow properly.

33. DNA
DNA- Deoxyribonucleic acid contains all
the information that an organism needs to
grow and develop.
DNA, as we know, is contained inside all
cells in their nuclei. And when a cell
divides, DNA is copied and passed on to
the new cells, or daughter, cells that are
formed.
Cells do this to ensure that all new cells
receive the same coded information that
was in the original cell.

34. Discovery of DNA
In the 1800’s scientists knew that inside the
nucleus of all cells were large molecules called
nucleic acids, however they did not know what
they were used for.
In the 1950’s, scientists identified what the
nucleic acids were and named them Adenine,
Thymine, Guanine, and Cytosine. But they still
didn’t know how they were arranged or put
together.
In 1952, a scientist named Rosalind Franklin
discovered that DNA was composed of 2 chains
of molecules in a spiral shape or a twisted
ladder shape.
This twisted ladder or spiral staircase shape is
called a helix. And DNA, since it has 2 chains is
called a double helix.

35. Discovery of DNA
In 1953, two scientists
named James
Watson and Francis
Crick created the first
3-D model of a DNA
molecule.

36. DNA Structure

37. DNA Model
Each side of the DNA ladder is made up of
a 5 carbon sugar molecule with a
phosphate molecule attached to it.
Because of this, we call the sides of the
ladder the sugar-phosphate backbone of
DNA.
The sugar here in the backbone is a
deoxyribose sugar. Meaning it has 2
oxygen molecules and a ribose sugar.

38. DNA Model
The rungs of this ladder that connect the
two sides are the nucleic acids Adenine,
guanine, cytosine, and thymine.
Another name for a nucleic acid is
nitrogenous base, because all 4 of them
contain nitrogen.
When these nitrogen bases interact they
are called base pairs.

39. DNA Model
These nucleic acids are very specific when it
comes to binding.
Adenine will only bind to Thymine
Guanine will only bind to Cytosine
A-T & G-C We now this because when
scientists measured the amounts of these
nucleic acids they found that in every cell the
amount of Adenine was always the same as the
amount of thymine.
And the amount of Guanine was always equal
to the amount of cytosine

41. Copying DNA
We said that before mitosis, in interphase,
chromosomes inside the nucleus are
duplicated.
The Watson and Crick model shows that
when this happens each side of the DNA
unwind from each other.
Now the two separate sides each become
a template for a new piece of DNA to be
made from.

42. DNA Replication

43. Genes
The nucleic acids in our DNA are used to
make proteins.
Genes are the specific instructions for
making specific proteins.
And proteins are made of hundreds of
thousands of things called amino acids.
The genes tells what amino acids to make
and in what order to make them in.

44. Ribonucleic acid
RNA is made in the nucleus on a DNA pattern.
It is very similar to DNA, but instead of looking
like a ladder, it looks like half a ladder. And
instead of deoxyribose it has a ribose sugar.
There is also one other major chemical
difference. Instead of having thymine like DNA.
RNA has a nucleic acid called Uracil.
So in RNA A binds to U not to T.
G will always bind to C, even in RNA

45. Main types of RNA
mRNA- messenger RNA
rRNA- ribosomal RNA
tRNA- transverse RNA

46. How Proteins are Made
Proteins are made in a couple of steps:
1) First, tRNA makes a copy of the DNA section that is
needed for the production of a protein, in the form of
mRNA. ( this occurs inside the nucleus)
2) Next, the mRNA, which is an exact copy of the DNA,
is shipped to a ribosome in the cytoplasm.
3) The mRNA attaches to the ribosome, which is made
of rRNA. The ribosome now reads the mRNA and
begins to make the amino acids that the nucleic
acids tell it to make.
4) Lastly, tRNA takes the amino acids made by the
ribosome and puts them together in the order in
which the ribosome made them.

47. Protein production

48. Mutations
Mutations a source of trait variation.
A mutation is a permanent change in a gene or
a chromosome due to some error during cell
division.
Some mutations could be caused from outside
sources like UV light from the sun or smoking.
Some mutations occur because they are
present on the parent DNA and it is passed
down to the offspring. Or, the DNA is not
copied correctly during cell division.
Not all mutations are of the negative variety.
Some are good. Like a 4 leaf clover. Normally it
will have 3 leaves but due to a mutation it has
4. This is good because the extra leaf can trap
more sunlight for photosynthesis.

49. H.W
& Look though your notes and
see if you have any questions
about the Chapter.

50. Test on Chapter 4 in one
Week!!!!!