Transcript Cells from Cells - Upper Grand District School Board

Cells from Cells
Cell Reproduction
• Process by which new cells are formed
– Recall the difference between cell reproduction
and the reproduction of a multicellular organism
• # of “parents” is different
• Body cells & single-celled organisms divide to produce
2 new daughter cells
• Sexual reproduction = 2 parents mate and offspring
receive ½ of their genes from each
This karyotype shows the 46 chromosomes present in
the nucleus of every cell in the body of a male human.
Cell Division
When you cut your skin, blood flows to the
area until a scab forms. This scab restores
the skin’s continuity, preventing bacteria
from entering the body. Then the skin cells
underneath can undergo cell division to
produce new cells that fill in the gap. Once
the skin layer is restored, the scab falls off.
• Process by which a
parent cell divides into
two daughter cells
• Main reproductive
process in single-celled
organisms
• Process by which a
fertilized egg becomes a
multicellular organism
with millions of cells
The Cell Membrane and Diffusion
• Cells also divide when they grow too large to
perform normal functions
– cell membrane has key role here – e.g. digestion
(nutrients into cell/waste out)
• Cell membrane acts as a barrier
– Most materials pass through via diffusion
– Water crosses through via osmosis
Diffusion is the movement of molecules from areas of high
concentration to areas of low concentration.
Moving from High
Concentrations to Low
Concentrations
•The cell membrane is
permeable to certain
substances
•Materials the cell needs (e.g.
oxygen) diffuse across the
membrane from outside the
cell (higher concentration) to
the inside (lower
concentration)
•Cell membrane is considered
selectively permeable
because not all materials can
cross it
•Water also moves from areas
of high to low concentration
Some examples
• A chicken egg as a cell...
• Wilted lettuce?
We’re all glorified Amoebas!
• What do I mean by that?
• Think about how you and the amoeba:
(a) get food,
(b) get water,
(c) exchange gases, &
(d) remove wastes.
Notice anything similar?
Growing Cells & Limiting Cell Size
• Surface of a cell must
be big enough to allow
for oxygen and
nutrients to pass
through
• Cells use nutrients and
produce more
organelles and more
cytosol  get bigger
• Cell then needs more
supplies/waste removal
• Every cell needs enough
S.A. to meet its volume
needs
• Large organisms have
less S.A. per unit of
volume than small
organisms
•  When a cell reaches
a certain size, it must
divide to produce
smaller cells
If an amoeba were as big as a human, critical substances,
such as oxygen, would take years to get through the
cell’s cytoplasm to reach the centre of the cell. This
would be far too long. In the meantime, the nucleus and
other organelles would not receive the nutrients they
need to function.
Questions...
1. Describe in your own words how substances
cross the cell membrane.
2. When a cell divides to produce daughter cells,
how similar are the daughters to the parent?
3. Why do the cells of multicellular organisms
divide?
4. Do you have to worry about seeing a headline
like “Giant Paramecium Threatens City”?
Explain your answer.