Transcript 2.4 Membranes - Rufus King Biology

Biology Journal 12/12/2013
What does “concentration” mean?
How can we use it to describe something?
2.4 Membranes
Assessment statement
2.4.1
Draw and label a diagram to show the structure of membranes. The diagram should
show: phospholipid bilayer, cholesterol, glycoproteins, integral proteins,, (embedded in
the phospholipid of the membrane), peripheral proteins (attached to the plasma
membrane surface), Use the term plasma membrane for the membrane surrounding the
cytoplasm.
2.4.2
Explain how the hydrophobic and hydrophilic properties of phospholipids help to
maintain the structure of cell membranes.
2.4.3
List the functions of membrane proteins: hormone binding sites, immobilized enzymes,
cell adhesion, cell-to-cell communication, channels for passive transport, pumps for
active transport
2.4.4
Define diffusion and osmosis.
2.4.5
Explain passive transport across membranes by simple diffusion and facilitated diffusion.
2.4.6
Explain the role of protein pumps and ATP in active transport across membranes.
2.4.7
Explain how vesicles are used to transport materials within a cell between the rough
endoplasmic reticulum, Golgi apparatus and plasma membrane.
2.4.8
Describe how the fluidity of the membrane allows it to change shape, break and re-form
during endocytosis and exocytosis.
Cell Membranes and Cell Transport
Diffusion is the passive net movement of
molecules from a region of high
concentration to a region of low
concentration.
Diffusion continues until equilibrium: when
all of the concentrations are the same.
Where is the high
concentration? Where is
the low concentration?
Diffusion requires no energy from the cell
(its passive).
These
molecules pass
through the
cell membrane
automatically.
Water is
55% to 75%
of our body
weight*
*People that are more lean have more water
than people who have more fat because muscle
cells hold more water than fat cells.
Osmosis is the diffusion of water
Water diffuses so much in the
bodies of living things that they
give it a special name: osmosis.
Diffusion happens across the cell
membrane.
You can cause osmosis to happen to
cells by adding solutes that can’t
diffuse across the cell membrane
Leaf cells, before salt
Leaf cells after adding salt
In the Third Punic War (it took 3
tries) the Roman Army invaded the city
of Carthage in 146 BC. They enslaved
or killed everyone there and salted the
Earth…
Why salt the
Earth?
Why do your fingers get
wrinkly in a bathtub?
• Think about concentrations and osmosis…
The cell membrane is made out of
a special lipid called a phospholipid
Phospholipids arrange themselves so that the
hydrophobic parts are not touching water
and the hydrophilic parts are touching
water.
The hydrophobic parts are not touching
water and the hydrophilic parts are touching
water.
A solution
consists of a
solute
dissolved into a
solvent.
What’s the solvent? What’s the
solute? What’s the solution?
Salt can pass through
the membrane. Will it
diffuse to the left or to
the right?
The solute (salt) moves
from high concentration
to low concentration
Passive transport: diffusion, it is automatic (passive)
Active transport: against diffusion, against the
“concentration gradient,” requires energy
Which type is in this picture?
With or “down”
the concentration
gradient
(facilitated diffusion)
Against the
concentration
gradient
At the end of 10 hour, when the bell rings, is
that more like active or passive transport?
Why?
A 9 year old kid is told by her parents to put
away all the toys into her toy box. Is that
more like active or passive transport? Why?
Exocytosis: Packaging up molecules in a vesicle
and sending them outside the cell
• Vesicles are made by the Golgi complex
It’s kind of like taking out the garbage
But, not everything released through
exocytosis is garbage!
Brain cells release dopamine from vesicles.
This makes you feel happy when good things
happen…
Endocytosis: Taking in molecules from the
outside and packaging them up in a vesicle.
Phagocytosis is when a cell
engulfs or “eats” another cell.
A white blood
cell engulfing
some bacteria.
Where might
the bacteria
be sent to
once inside the
cell?