Transcript Homeostasis and Cellular Transport

Describe in detail the process that
is illustrated above. Include
details from each step , using
correct science terms.
Homeostasis and
Cellular Transport
 To
stay alive, a cell must
exchange materials such as
food and waste with its
environment.
 These
materials must cross
the cell membrane.
Passive Transport

Does not require the cell to use
energy
Diffusion
 Osmosis
 Facilitated diffusion

SimpleDiffusion

is the movement of molecules from an area
of higher concentration to an area of lower
concentration. (down its concentration
gradient)

concentration gradient - the difference in
the concentration of molecules across a
space
•

http://www.biologycorner.com/bio1/diffusion.html
Driven by kinetic energy
 energy of motion
Diffusion

Diffusion causes the concentration of
molecules to be the same throughout space

When molecules are dispersed evenly, there is
no longer any diffusion because there is no
longer a concentration gradient.

a state of equilibrium exists (balance)

http://www.brainpop.com/search/?keyword=diffusion
Rate of Diffusion

molecules diffuse faster at higher
temperatures than at lower temperatures

smaller molecules diffuse faster than
larger molecules

Type of molecule
Water and Diffusion
 The
diffusion of water across
a semipermeable membrane
is called osmosis.
 Osmosis
occurs in response
to the concentration of
solutes dissolved in water.
Diffusion of Water

 The
net direction of osmosis
depends on the
Hypertonic Solution
 In
a hypertonic solution, the
concentration of solute
molecules outside the cell is
higher than inside the cell.
 What
direction will the water
diffuse?
Water diffuses out of the cell
until equilibrium is reached.

What do you think will happen if the
cell loses too much water?
The cell will shrink and shrivel.
 plasmolysis

Hypotonic Solution

In a hypotonic solution, the
concentration of solutes outside the
cell is lower than the concentration
of solutes inside the cell.

What direction will the water
diffuse?
Water diffuses into the cell
until equilibrium is reached.

How does this affect the cell?
The cell will swell and possibly burst.
 Cytolysis

Isotonic Solution

In an isotonic solution, the
concentration of solutes outside and
inside the cell are equal.

How will the water diffuse across the
cellular membrane?
Water will diffuse in and out of
the cell at equal rates.
Red Blood Cell in different Solutions
http://www.coolschool.ca/lor/BI12/unit4/U04L06/rbc.html
http://www2.nl.edu/jste/osmosis.htm#Osmosis
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html

Facilitated Diffusion

To facilitate means to help.

Channel proteins and carrier
proteins
 Carrier
proteins change
shape when molecules
attach. The change in shape
of the carrier protein allows
the molecule to cross the
membrane.
Active Transport
 Movement
of molecules across
the membrane from an area of
low concentration to areas of
high concentration.
 This
requires the cell to expend
energy(ATP).

Cell Membrane Pumps

SODIUM-POTASSIUM PUMPS IN
ANIMAL CELLS PUMP SODIUM
IONS OUT, AND POTASSIUM IN,
UP THEIR CONCENTRATION
GRADIENT.

IMPORTANT FOR MUSCLE
CONTRACTIONS, and THE
TRANSMISSION OF NERVE IMPULSES
Endocytosis and
Exocytosis

Molecules that are too large to
cross the cell membrane are
packaged in membrane-bound sacs
(vesicles) and moved across the
membrane
Endocytosis
 Endocytosis
TWO TYPES ON ENDOCYTOSIS

PINOCYTOSIS – uptake of
liquids “cell drinking”

PHAGOCYTOSIS - uptake of
solids “cell eating”
Exocytosis
 Exocytosis
.

Think: Apply what you have learned!

In plants, cells that transport water
against the concentration gradient are
found to contain many more mitochondria
than do some other plant cells. Give a
possible explanation for this?