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Learning out comes
Define mitosis and state its importance in
growth , development and asexual
reproduction.
Define meiosis and state its importance in
the formation of gametes and in producing
genetic variation.
How did we change from a baby
to adult?
What caused those changes?
How do we generate new cells?
Here are the answers ................
The cell division
New cells are produced by the
division of the old ones.
Before the cell divide the nucleus must divide.
As the nucleus is finishing its division in to two the cytoplasm divides.
The cell division
In animal cell a construction occurs
between the two nuclei to divide the cell in to two.
The cell division
In plant cell a new cell wall is formed between the nuclei.
The cell division
There are two ways in which nuclei divide
Mitosis: Is a type of nuclear division that occurs during growth and asexual reproduction.
Meiosis: Occurs in sex organs to form gametes the daughter cells are genetically identical.
Mitosis
Mitosis is used when a cell needs to produce exact copies of itself.
Everything in the cell is duplicated.
The two new cells have the same DNA, functions, and genetic code.
The original cell is called the mother cell and the two new cells are called daughter cells.
As a result of mitosis each daughter cell has the same chromosomal number as the original parent cell.
Mitosis
1. Chromosomes make
identical copies of
themselves.
2. They line up along the
centre.
3. They move apart.
4. Two daughter cells
form with identical
chromosomes to the
parent cell.
Some cells continually
divide all through life.
These are stem cells
E.g. Cells of bone
marrow.
They continually
produce red blood
cells and phagocytes .
Stem cells
A stem cell is
essentially
the building block
of the human body.
A stem cell is
pluripotent - When it
divides, it can make any
one of the 220 different
cells in the human
body.
Stem cells
Mitosis occurs in the following process
Growth: In animals this happens all over the
body , in plants it happens in special growing
areas such as the tips of stems and roots.
Repair of wounds: Your skin cells divide by
mitosis to repair damaged tissue and wounds.
Replacement of cells: That wear out and die
such as red blood cells which only live for a
short period.
Asexual reproduction: This occurs in fungi,
protists and in plants but is rare in animal
kingdom.
Mitosis occurs in the following process
Meiosis
Meiosis is the type of cell
division by which gametes (eggs
or sperm) are formed.
If human sperm cell and egg cell both had 46 chromosomes the zygote formed at fertilization would have 92 chromosomes.
If this continued generation after generation the number of chromosomes in the nuclei would double every generation.
This does not happen. Instead the number remains 46 This is because there is a different sort of
nuclear division producing gametes this type of nuclear division is meiosis.
Meiosis
Meiosis halves the number of
chromosomes so egg and sperm cells
only have 23 chromosomes each.
Meiosis
The zygote has 46 chromosomes , 23 from the
mother in the egg and 23 from the father in the
sperm.
In sexual reproduction the number of
chromosomes stays constant from generation
to generation.
Meiosis
Where does Meiosis occur?
Meiosis occurs in sex organs in human - the ovaries
and testis.
In flowering plants meiosis occurs in
anthers and in the ovules.
Where does Meiosis occur?
How are the daughter cells in meiosis
In meiosis daughter cells are not identical.
They are genetically different and this contributes to genetic variation that provides the raw material for selection and allow organisms to evolve in response to changing environments.
Mitosis vs. Meiosis
Diploid cells
Clone
Same genetic information in parent cell and daughter cell.
Haploid cells Daughter cells
different from parent cell and from each other.
Daughter cells have
½ the number of chromosomes as somatic cell.
Key points
Mitosis produces daughter cells genetically
identical and have same number of
chromosomes as parent cell.
Meiosis is involved in gamete production in
sex organs. It produces a halving of
chromosome number in cells from the diploid
to the haploid number.
Meiosis results in genetic variations so, unlike
mitosis the cells are not genetically identical.
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