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Movement of particles
Diffusion: is the net movement of molecules and ions from a
region of their higher concentration to a region of their
lower concentration down a concentration gradient, as a
result of their random movement
...

Substances can move into and out of cells by diffusion with
or without the cell membrane
...


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Solutes (liquids):
•
•

•

•

(plants) Dissolved salts diffuse through root hair cell
...

Some digested food material is absorbed by diffusion from
the small intestine to the blood
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Water as a solvent

•

•

•

Plants cannot obtain minerals unless they are dissolved in
water
Enzymes and hormones cannot be secreted unless they are
dissolved in water
Excretory products cannot be excreted unless they are
dissolved in water
...

Factors that influenced the rate of diffusion:

•

•

Surface area of the membrane– The larger the surface area
of the exchange membrane the faster particles diffuse
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•

•

•

Concentration gradient – The steeper the gradient the
faster the particles diffuse
...

The size of the molecules- small sized molecules will diffuse
faster than large sized molecules
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Figure 2
(a)The sugar solution in the bag is more concentrated than
the water outside the bag
...

(c)The sugar solution in the bag is of the same concentration
as that of the solution outside the bag
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Hypotonic solution: the concentration of the solute is low
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Hypertonic solution: the concentration of the solute is high
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Isotonic solution: the concentration of the solute is equal to
the solvent
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Solute: is a substance dissolved in another substance
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the cell swells
up and becomes turgid (firm) but it will never burst because
plant cells are surrounded by cell walls, which are made of
cellulose and is elastic, it will stretch but never break
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Turgor pressure: is the force within the cell that pushes
the plasma membrane against the cell wall
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First, the cell shrinks slightly and becomes flaccid
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The importance of osmosis:

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Plants gain water through osmosis in their roots from the
soil
...
Plant cells contain vacuoles, which, if not
full with water, will cause the cell to become flaccid
...
Plant cells
therefore need water to remain turgid and keep firm
...

Osmosis and animals:
If an animal cell surrounded with a high water potential,
osmosis will take place, and if the water is not expelled
some way or another, the cell will burst (a process
called haemolysis in red blood cells)
...

If an animal cell is surrounded with low water potential, the
water in the cytoplasm will diffuse outwards, causing the
cell to shrink (crenated)
Cytolysis: also known as osmotic lysis, occurs when a cell
bursts and releases its contents into the extracellular
environment due to a great entry of water into the cell
...

Active Transport: The movement of molecules and ions in and
out of a cell through the cell membrane from an area of
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lower concentration to an area of higher concentration
(against a concentration gradient) by using energy from
respiration
...
This includes the absorption of:
•
•

Dissolved mineral salts by the root hairs,
Glucose and amino acids by cells in the small intestine of
humans

Fig
...
4 Active transport-molecules diffuse against the
concentration gradient from B to A
...

Notes: Active transport:
Þ Consume energy from respiration
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Þ A transport protein (enzyme) is essential to allow the
movement of molecules through the cell (in or out of
the cell)
...

Overview:
* uptake of water takes place by the process of osmosis
which is a passive process (doesn’t need energy)
...

* Uptake of some minerals and some digested food takes
place by the process of active transport which is an
active process (need and consume energy)
...


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Diffusion

Active transport

Osmosis

Passive (No energy is
consumed)

Active (Consumed energy)

Passive (No energy is
consumed)

Moves – gases and solutes

Moves – solutes only

Moves – water only

With or without a membrane

Through a membrane

Through a partially permeable
membrane

Importance: 1
...

2
...
Absorption of
mineral ions from soil to
plants
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Absorption of digested food
from small intestine to blood in
animals
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Absorption of
water from soil to plants
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Enters sap vacuole, makes
cell turgid à supports plants
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movement of water in & out
of cells

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