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3.1 MOVEMENT OF SUBSTANCES
ACROSS THE PLASMA MEMBRANE
3.1 THE MOVEMENT OF SUBSTANCES ACROSS
THE PLASMA
3.1.1 Substances Required by Cells and
Substances Eliminated from Cells
3.1.2 The Necessity for Movement of Substances
Across the Plasma Membrane3.1.3 The Structure of The Plasma Membrane
3.1.4 Permeability of The Plasma Membrane
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3.1.1 Substances Required by Cells
and Substances Eliminated from Cells
1. All living cells carry out metabolism to stay alive.
2. Metabolism refers to all the chemical activities takingplace in the cell.
3. Metabolism consist of two processes:
a. Anabolism, which is building up of molecules.Examples are the syntheses of proteins and
ATPs, which a cell needs.
b. Catabolism, which is the breaking down of large
molecules to smaller; simpler molecules. Anexample is the oxidation of glucose in the cellrespiration.
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4. A cell takes in raw substances for
anabolism from its external environment.
5. Wastes from catabolism and excess
substances are removed from the cell.
6. Also, water and various salts are either
brought into, or are taken out of the cell.
7. Table 3.1 and Table 3.2 show some
substances that leave the cell and some
that enter the cell respectively.
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Table 3.1
Substances that leave the cell
SUBSTANCE REASON OF REMOVAL
Carbon dioxide
(animal cell)
A waste product of respiration
Oxygen (plant cell) A waste product ofphotosynthesis
Secretions
Are cellular products for use in
order parts of the bodyNitrogenous waste
Are waste products from
breakdown of excess proteins
Excess water Osmoregulation
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Table 3.2
Substance that enter the cell
SUBSTANCE REASON OF REMOVAL
Oxygen
(animal cell)
For cell respiration
Carbon dioxide(plant cell)
As a raw materials for proteinsynthesis
Glucose For cell repsiration
Amino Acids As aw materials for proteinsynthesis
Ionic Salts
For cell metabolism and
osmoregulation
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1. All movements of substances go through thecell membrane, which is also known as theplasma membrane
2. The necessities for the movement of
substances across a plasma membrane are:a) Cells need nutrients and oxygen. These pass
through the plasma membrane from the externalenvironment.
b) Cells produce waste products which exit throughthe plasma membrane.
c) The plasma membrane can control the types andthe amounts of substances needed by the cell atany time.
3.1.2 The Necessity for Movement of
Substance Across The Plasma Membrane
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plasma
membrane
cytoplasm
cell
nucleus
Movement of
substances into
the cell
Movement of
substances out
the cell
External Environment
THE NECESSITY FOR MOVEMENT OF SUBSTANCES ACROSS
THE PLASMA MEMBRANE
Figure 3.1 Movement of substances in and out of a cell
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A MODEL OF PLASMA
MEMBRANE
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To understand the concept of the plasma
membrane, we shall look ata) Basic unit of the plasma membrane
b) Formation of the plasma membrane
c) Other molecules present in the plasmamembrane.
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The Structure of Plasma
Membrane
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The basic unit of the plasma membrane
is the phospholipid molecule.
The phospholipid molecule consists of:
a. A polar phosphate molecule head which is
hydrophilic and
b. Two non-polar fatty acid tails which are
hydrophobic.
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Permeability of The Plasma
Membrane
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Permeability of The Plasma Membrane
Permeable means allowing something to
pass through
The proteins and the phospholipids of the
plasma membrane affect the permeability
of the plasma membrane.
The phospholipid bilayer is permeable to:
Small non-polar (hydrophobic)
Small uncharged molecules