Transcript Cell boundaries

Cell boundaries
Objectives
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Identify the main functions of the cell
membrane and the cell wall
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Describe what happens during diffusion
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Explain the processes of osmosis, facilitated
diffusion, and active transport
The cell membrane
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The cell membrane is a thin, flexible barrier that
regulates what enters and leaves the cell
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The cell membrane is made up of a double
layered sheet, called a lipid bilayer
Model of a cell membrane
Diffusion
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Diffusion is the tendency of particles to move
from an area of high concentration, to an area of
low
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Diffusion relies on random particle movement,
therefore, diffusion requires no energy
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This process will continue until the system
reaches what is called equilibrium – The
concentration of the solute is the same through
out the system
Osmosis
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What is osmosis?
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Osmosis is simply diffusion of water through a
selectively permeable membrane
A membrane is considered selectively
permeable if it some things can pass through
it but not others
All biological membranes are selectively
permeable
Does osmosis require energy?
Concentration
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The concentration of a solution is the mass of
a solute in a given volume, or mass/volume
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A solution is made up of 2 parts, a solute and
a solvent
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Solute is the substance that is being dissolved
Solvent is the substance that is doing the
dissolving
Isotonic solutions
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When talking about equilibrium within a cell,
we say the concentrations of the solute are
the same within the cell, as they are outside
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In this case, the solutions are said to be
isotonic, or “same strength”
Hypertonic vs hypotonic solutions
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While a solute is diffusing across a membrane,
that solute is moving from an area of high
concentration to an area of low
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The solution containing the greater
concentration is called hypertonic, or “above
strength” and the solution containing the lower
concentration is called hypotonic
Facilitated diffusion
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This is the movement of specific molecules across a
cell membrane using protein channels (transport
proteins)
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This is a fast and specific form of diffusion, but it is
still diffusion – therefore it must follow the rules of
diffusion ([high]>[low]) and doesn’t require energy
Glucose
molecules
Facilitated diffusion
High
Concentration
Cell
Membrane
Low
Concentration
Protein
channel
Active transport
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When a cell needs something, but cannot use diffusion, it must
use energy
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2 of the ways this energy is used are:
1 – Small molecules are “pumped” across a membrane by transport
proteins
2 – Larger molecules are moved across the membrane using
endocytosis and exocytosis
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A large part of the energy a cell has is used in supporting these
forms of transport
Endocytosis
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Endocytosis – This is the process of bringing
material into the cell using infoldings or pockets of
the cell membrane and forming a vacuole within
the cell
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There are 2 forms of endocytosis
1.
2.
Phagocytosis
Pinocytosis
Exocytosis
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In this type of active transport, use of energy
to remove material from the cell
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A contractile vacuole is an example of this
Pinocytosis
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In this form of endocytosis, pockets of liquid
form along the cell membrane – They then
“pinch” off within the cell to form a vacuole
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This is also known as cell drinking
Phagocytosis
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This process can be thought of as “cell eating”
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It happens when a cell engulfs a particle and
packages it within a vacuole
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Amoebas use this form of transport to acquire food
Terminology
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cell membrane
cell wall
concentration
lipid bilayer
diffusion
equilibrium
osmosis isotonic
hypertonic
hypotonic
facilitated diffusion
endocytosis
phagocytosis
pinocytosis
exocytosis