Download Cell Specialization and Size

Cell Specialization
Unicellular Organism – consists of only one
cell
- that one cell carries out all functions
required to maintain the life of the organism
Multicellular Organism – consists of more
than one cell
- Cells are specialized to perform certain
functions (cell specialization/differentiation)
Examples of Cell Specialization
1. Neuron (nerve cell)
- sends info from one part of the body to
another
- very long and thin
Examples of Cell Specialization
2. Red Blood Cells
- carry oxygen throughout body
- flattened disks so that they can easily
flow through blood vessels
Examples of Cell Specialization
3. Sperm Cell
- fertilizes egg
- strong tail for quick swimming, distinct
head for entering egg cell
Cell differentiation is a result of
different gene expression.
• Most cells in your body
have the same DNA
• Cells use only the DNA
that they need; the rest
is inactive
• For example, skin cells
use the DNA that codes
for melanin (a skin
pigment that protects
from UV light)
• Heart cells do not need
melanin, so it is “turned
off” in heart cells
Stem Cell Research
• stem cells – cells of humans that can develop
into different cell types
• 2 kinds: embryonic and adult
• some researchers believe that they can be
a source of replacement cells to treat
disorders (ex. Parkinson’s disease and
burn injuries)
Embryonic stem cells
Adult stem cells
Cell Communication
- Cells communicate with one another by
secreting and receiving chemicals
- Chemicals released by one cell can
influence the activity of another cell
http://learn.genetics.utah.edu/content/begin/cells/cellcom/
Example of Cell Communication
- Sensory cells to nerve cells to muscle cells
Cell Communication (cont.)
Hormone – communication chemicals that travel
through the blood (ex. insulin, estrogen)
- Secreted by endocrine glands
- Acts much slower than nerve impulses but
effects last much longer
- Only influence the action of target cells
that have specific receptors
Two Hormone Mechanisms
1.
Negative Feedback – the end product
stops the production of the hormone
Negative Feedback
2. Positive Feedback – the last step
triggers more release of the initial
hormone or other hormones
- triggers a series of events
• Cell Growth and Size Limitations
– Most cells are 2 – 200 micrometers
(largest cell is the ostrich egg – 8 cm)
http://www.cellsalive.com/howbig.htm
Cells cannot get very big
because …
1. Volume increases faster than surface
area.
- a bigger cell means that you have more
nutrient demand with limited surface
area for diffusion
Cells cannot get very big
because …
2. Diffusion is a SLOW process.
- Organelles might not get the nutrients
they need in time.
Cells cannot get very big
because …
3. A bigger cell needs
more proteins.
- DNA is used to make
proteins, and cells have
a limited amount of DNA.
- Therefore, when a
cell starts to get too
big, it must divide.