Know this information for the AIR test.

1. Introduction to
Cell Division
Notes

2. Cell Division
 Where do new cells come from?
 Other cells… skin cells make skin
cells, muscle cells make muscle
cells and so on.
 A skin cell can not make a muscle
cell, only another skin cell.
 The process of one cell making
another cell is called cell division.

3. Cell Division
 What is cell
division?
 how a cell
reproduces, makes
a copy of itself.
 how living things
grow (Mitosis) and
make sex cells
(Meiosis).

4. Why do we need new cells?
 Need new cells to:
 Grow
 Repair scratches and
tears (scars)

5. Prokaryotic vs. Eukaryotic??
• What is the difference?
• Do both have a cell membrane?
• YES!!!!
• Eukaryotic cells have a nucleus and
organelles with membranes and
Prokaryotic cells do NOT have a
nucleus!!

7. Cell Division
 Cell Divison for:
 1. Prokaryotes (like
bacteria cells)
 Binary Fission (unicellular
organisms)  DNA copied,
cell grows, cell splits in two.
 Unicellular organisms- this is
how they reproduce.

8. Cell Division
 2. Eukaryotes –
(plant/animal cells)
 Mitosis (multicellular
organisms)  DNA copied,
cell grows, cell splits in two.
 new cells have identical
genetic material; produces
clones.
 Mitosis is about the division of
the nucleus.

9. Nucleus
 Nucleus is important for:
 1. Stores hereditary
information in its DNA.
 2. DNA makes RNA
 3. Contains the nucleolus
(where DNA is in
nucleus, dark circle)

10. Nucleic Acids
 Function of DNA –
 Store and transmit hereditary information
 DNA – stands for Deoxyribose Nucleic Acid

12. Cell Division: Mitosis
 Before a cell can divide it must organize its
DNA and form chromosomes, so it copies and
divides DNA accurately.

13. Making Chromosomes
 How DNA condenses to form chromosomes:
 1.Strands of DNA wrap around proteins called
Histones.
 2. This then forms a
molecule called chromatin.
 Chromatin is found in the
nucleus and is how DNA
spends the majority of its life.

14. Chromosomes
 Chromatin continues to condense and
eventually it forms chromosomes.
 Chromosomes – tightly coiled packages of
DNA held together by proteins.

15. Chromosomes
 Chromatid – half of a
chromosome; forms as
DNA copies itself before
cell division
 Centromere – holds the
chromatids together until
they separate

16. Chromosomes
 Each species has a unique number of chromosomes
 How many chromosomes do humans have?
 46 chromosomes or 23 pairs.

17. Chromosomes
 2 Types of Chromosomes:
 1. Sex Chromosomes – are the chromosomes
that determine the sex of an organism.
 Female: XX
 Male: XY
 2. Autosomes – all other chromosomes
 Humans: 44 autosomal chromosomes

18. Chromosomes
 Karyotype – is a picture
of the chromosomes in
a dividing cell.
 22 homologous
pairs of autosomes.
 2 sex chromosomes

20. Chromosomes
 Homologous
chromosomes – two copies
of each autosome (maternal
and paternal)
 Homologous chromosomes
are the same size, shape,
and carry genes for the same
trait.

22. Chromosomes
 Diploid Cells (2n)– are
cells that have 46
chromosomes.
 All cells in your body are
diploid except sex cells
 Haploid Cells (n)– cells
that only have 23
chromosomes
 Ex. Gametes (sex cells)

23. Chromosomes
 Examples of haploid
cells?
 Gametes - sperm
and egg cells; they
have 23
chromosomes
 Fertilization 23 in
sperm + 23 in egg =
46