Download SOLVING REAL WORLD PROBLEMS-

BIOLOGY Ch 4 Cells and their Environment
Concentration of substances __________________ __________
Organisms maintain homeostasis by the movement of substances across the cell
membrane. Cells may or may not use energy to move substances across the
membrane.
PASSIVE TRANSPORT
It is the movement across the membrane that does not need energy
Concentration gradient – is the difference in the concentration of a substance across
space
e.g. Two rooms with a door in between and balls being released from one room to the
other
Equilibrium – is the condition in which the concentration of a substance is the same
across the space
Diffusion – is the movement of a substance from a higher to lower concentration
e.g. many molecules or ions dissolved in the cytoplasm or in the fluid outside cells
enter or leave cells by diffusing across the cell membrane
Types of membranes
 Permeable membranes – allow substances to pass through
 Impermeable membranes – do not allow substances to pass through
 Semi permeable membranes – allow only some substances to pass through
Osmosis – is the diffusion of water through a semi permeable membrane
Types of solutions



Hypertonic
Hypotonic
Isotonic
(Refer to picture at end of packet)
CROSSING THE CELL MEMBRANE
Transport proteins called channels provide polar passageways through which ions and
polar molecules can move across the cell membrane.
Diffusion through ion channels
(Refer to picture at end of packet)
Ion channels allow certain ions to pass through the cell membrane. They have gates
which may open or close in response to some stimuli e.g. stretching of cell
membrane, change in electrical charge, or binding of specific molecules to the ion
channel
e.g. Na +, Cl –
Electrical charge and ion transport
The inside of a cell is typically ______________________.
Opposite charges ________________, Like charges ____________________.
Facilitated diffusion
(Refer to picture at end of packet)
It is a type of passive transport
Cell membrane has some _________________________ in channels that allow
certain substances to be carried inside cell e..g _____________, _______________
ACTIVE TRANSPORT
Cell moves materials in opposite direction against the concentration gradient and
needs energy (i.e. from an area of low concentration to an area of higher
concentration)
Some carrier proteins are involved in active transport and they act as ____________
that move substances against their concentration gradients.
e.g. Movement of Ca, K, Na ions
Sodium Potassium Pump
(Refer to picture at end of packet)
Usually uses ATP to transports 3 sodium ions out of a cell and 2 potassium ions into a
cell
Why is the pump useful?
Movement in Vesicles
(Refer to picture at end of packet)
Endocytosis – taking material into cells by means of infoldings or pockets of cell
membrane
e.g. proteins, polysaccharides
Phagocytosis –
Pinocytosis –
Exocytosis- membrane surrounds material, fuses with the cell and forces content out
of cell
e.g. some proteins modified by golgi apparatus are exported in this way
Membrane receptor proteins
A Receptor protein is a protein that binds to a specific signal molecule and controls
the opening and closing of ion channels
Second messengers
When they are activated, they act as signal molecules in the cytoplasm; they amplify
the signal of the original signal molecule and also change the functioning of the cell
in different ways e.g. activating enzymes, triggering some biochemical reactions in
cell etc.