Transcript Unit 7 Plasma membrane

The Cell Membrane or
Plasma Membrane
Homeostasis – Maintaining
a Balance
 The
cell/plasma membrane is
selectively permeable – it will
allow some things to pass through,
while blocking other things.
 Water,
nutrients in
 Wastes (CO2) out
Structure of the Plasma
Membrane

Lipid bilayer – two sheets of lipids
(phospholipids).
Found around the cell, the nucleus,
vacuoles, mitochondria, and
chloroplasts.
Embedded with proteins and
strengthened with cholesterol
molecules.
What’s a Phospholipid?

It’s a pair of fatty acid chains and
a phosphate group attached to a
glycerol backbone.
–Polar (water-soluble) heads face
out and the nonpolar fatty acids
hang inside.
Membrane Proteins

1. Determine what particles can pass
through the membrane.
Act as markers that are recognize
chemicals and molecules outside the
cell ( bouncer at the door of a club)
Cellular Transport

Diffusion – movement of particles from
an area of high concentration to an area
of low concentration.
– Continues until an equilibrium is
reached (no gradient).
– Dynamic equilibrium – particles move
freely and are evenly distributed.
2 Types of Cellular Transport

1) Passive transport

2) Active Transport

Passive transport – no energy is
needed to move particles.
1) Diffusion
2) Facilitated diffusion –
embedded proteins act as tunnels
allowing particles to “fall” through.

Active transport – energy is needed
to move particles.
Carrier proteins – embedded proteins
change shape to open and close
passages across the membrane.
1. Endocytosis – taking something into
the cell.
2. Exocytosis – expelling something
from the cell.
Osmosis

Diffusion of water across a selectively
permeable membrane.

Occurs until water is balanced on both
sides of the membrane.

A Solution is -A homogeneous mixture
of two or more substances (can be
solids, liquids, or gases)

A Solute is - A substance dissolved in
another substance.

A solvent is -A substance in which
another substance is dissolved in.

Example
Salt that is dissolved in water
Solution – salt water
Solute – salt
Solvent - water
Cell Concentrations

Hypertonic solutions – more
dissolved solute. Water will leave the
cell. The Cell shrinks

Hypotonic solutions – less dissolved
solute. Water enters the cell and the
cell will swell.

Isotonic solutions – the same
dissolved solute. Cell is unchanged
Overcoming Osmosis

Contractile vacuoles – expel
excess water from bacterial cells
that live in water.

Turgor pressure – water
pressure in a plant cell. Loss of
turgor pressure causes wilting
(plasmolysis).
Diffusion Demonstration

Data table
Temperature
of water
Cold water
Hot water
Time for food
coloring to
diffuse
Diffusion Demo Questions
1. What is Diffusion
2. Explain why diffusion is passive or
active transport.
3. Explain what equilibrium means? (use
food coloring to explain this)
4. Which beaker of water did the food
coloring diffuse the fastest through and
why??