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Why do cells divide?
1. Repair, or replace old or worn out cells
2. "Reproduction" some organisms reproduce by simple cell division (Asexual
Reproduction)
Mitosis: The process by which a cell reproduces to create two identical copies of
itself. The cells formed are known as "daughter cells".
Steps involved:
1. Genetic material must be copied
2. Organelles must be distributed
3. Cytoplasm splits in half
DNA replication:
when the DNA of each chromosome is copied.
Chromatin: thin filaments of
DNA. During most of Interphase
the DNA is in this form
Chromosomes: when thin
chromatin condenses to form thick rod like structures. During mitosis
the DNA is in this form
Interphase: the stage of the cell cycle between cell division.
DNA Replication: EACH STRAND OF THE DOUBLE HELIX SERVES AS A
TEMPLATE FOR THE FORMATION OF A COMPLIMENTARY STRAND.
How do cells increase in size?
MITOSIS: The process of
cell division which results in the production of two daughter cells from
a single parent cell. The nucleus divides to form 2 identical nuclei.
The daughter cells are identical
IPMAT:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase:
DNA is actively duplicating, organelles are
replicating and cell increase in size
Prophase:
Chromosomes are visible, nuclear membrane
disappear and centrioles move to opposite ends.
Metaphase:
Chromosomes line up at the middle of the cell
Spindle fibers attach to chromosomes at the
centromere.
Anaphase:
Spindle fibers pull chromosomes apart
The 2 strands (chromatids) move to each
daughter cell.
Telophase:
Animal Cell
Chromosomes/DNA spreads out
2 nuclei form
Cell membrane pinches in to form the 2 new
daughter cells
Plant Cell
New cell wall forms between the nuclei to form the 2 new daughter
cells
Asexual Reproduction
Offspring produced from one organism
Hereditary information is identical
Mitosis is one form of asexual reproduction
Types of Asexual Reproduction
 Budding
 Regeneration
 Fission: (Binary Fission)
Budding: New organism develops as an outgrowth of the parent and
then enlarges. Common in plants. Ex: yeast and hydra
Binary Fission: A one celled organism divides in half to form two
daughter cells Ex: Ameoba, paramecium, Bacteria.
Regeneration: The ability to replace lost or damaged body parts. It is a
common feature in invertebrates, like worms and starfish
Cancer: Out of control cell division
AIM: How do sexually reproducing organisms maintain their
chromosome number?
All the body cells of the individual have the full chromosome number of
the species Diploid (2n)
Gametes(sex cells): contain one half the number of chromosomes of
the species. Haploid (n)
EX: Human Sperm Cells and Egg Cells contain 23 chromosomes
Homologous/pair Chromosomes:
Chromosomes come in identical looking pairs. These chromosomes have
the same kind of genes along their length but the form of the gene
(allele) on each might be different.
Sexual Reproduction
Type of reproduction
Union of 2 sex cells:
Egg + sperm: join to form a zygote, which will develop into a new
organism with a unique identity.
The union of an egg and a sperm is called fertilization.
Meiosis is the type of cell division by which sex cells (eggs and sperm)
are produced.
One parent cell produces 4 daughter cells.
Daughter cells have 1/2 the number of chromosomes: Haploid
Meiosis is also called reduction division.
The nucleus divides twice. DNA replicates once
Meiosis I and Meiosis II
First Division of Meiosis
Prophase I: Duplicated chromosomes remain closely, These are called
sister chromatids.
Metaphase I: The pairs of duplicated chromosomes line up in the
center of the cell.
Anaphase I: Chromosome pairs separate with sister chromatids
remaining together.
Telophase I: Two daughter cells are formed with each daughter
containing only one chromosome of the chromosome pair.
Second Division of Meiosis
Prophase II: DNA does not replicate.
Metaphase II: Chromosomes line up at the center of the cell
Anaphase II: Centromeres divide and sister chromatids move
separately to each pole.
Telophase II: Cell division is complete.
Four haploid daughter cells are formed.
Mistakes can produce cells with too many or fewer chromosome
number.
Differences in mitosis and meiosis
Mitosis
Asexual
Cell divides once
2 daughter cells
Genetic information is identical
Meiosis
Sexual
Cell divides twice
4 haploid daughter cells
Genetic information is different]