Download Detailed Notes with Basic Practice 1

Danyal Education
Movement of Substances Notes 1
UNIT 2
M()UEMENT ()F SUBSIANCES
Learning Objectives:
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Definitionofdffision
Definition of osmosis
Osmotic changes in cells may have drastic consequences.
. Plant cells may undergo plasmolysis or become turgid
. Animal cells may undergo crenation or haemolysis
Definition ofwater potential
Defnition and examples of active transport in living cells
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DIFFUSION
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Diffusion is the movement of molecules from a region of their higher concentration to a region of
their lower concentration, down a concentration gradient.
lt is a passive kind of transport because energy, in a form of ATB is not required for the movement
of molecules from one place to another.
When the molecules have been spread evenly between the two regions, the concentration
gradient is no longer present. As a result, there will be no net movement of molecules between
these regions anymore.
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after some time
direction of movement
of particles
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particles are evenly
distributed
lmportant role of ditfusion in living organisms
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Diffusion enables living organisms, unicellular or multicellular, to survive by allowing the exchange
of nutrients, gases and waste substances between them and the surroundings.
Unicellular organisms such as amoeba and paramecium take in oxygen and excrete waste
substances through simple diffusion.
Plants and animals require energy to survive. The living cells use up oxygen during aerobic
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respiration. This process causes the concentration of oxygen in the cells to decrease. As a result,
oxygen molecules are able to diffuse into the cells from the surroundings down their concentration
gradient. The cells can obtain fresh oxygen molecules to carry out this important process again.
Diffusion also plays an important role in the uptake of nutrients in animals and plants.
During the process of digestion, soluble digested substances diffuse into the bloodstream
from the lumen of the small intestine due to the presence of concentration gradient of the
nutrients between these two regions.
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Minerals and nutrients are absorbed into the root hairs through diffusion when the
concentration of these substances are higher in the surroundings than in the root hair cells.
Diffusion allows living organisms to remove the metabolic waste substances, such as ammonia,
excess water and mineral salts, in the tissues. They diffuse out of the tissues into the bloodstream
and are transported to the respective excretory organs.
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REVISION
7. (a) Define diffusion
Explain what is meant by concentration gradient of a substance.
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(b)
Answer True or False for each of the following statements given below.
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(a)
Diffusion of a substance is affected by the presence of another type of substance
(b)
The particles of a substance stop moving between two regions when equilibrium
is reached.
(c)
The steeper the concentration gradient for a substance, the faster the rate of
diffusion.
(d)
A permeable membrane restricts the movement of certain substances across it.
(e)
Complex substances cannot pass through the cell membrane due to its size
(f)
The gaseous exchange taking place in plant cells and animal cells involves
diffusion only.
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membrane.
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Osmosis is the movement of water molecules from a region of their higher concentration (higher water
potential) to a region of their lower concentration (lower water potential), through a partially permeable
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higher solute
concentration
(lower water
concentration)
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lower solute
concentration
(higher water
concentration)
after some time
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solute molecules
i.i:i: water molecules
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Oartially permeable membrane
:
equal solute
concentration
level of water on right
side has decreased and that
on left side has increased
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osmosis is a passive transport as well because it does not consume energy.
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WATER POTENTIAL
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Water potential is the measure of the tendency of water to move from one place to another.
A dilute solution has more water molecules per unit volume than a concentrated solution.
Hence it has higher water potential.
Water always moves from an area of higher water potential to a lower one.
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Cell membrane is a partially permeable membrane that allows some substances to pass
through but not others.
The concentration of dissolved substances is usually higher inside the cell than outside. This
allows water to enter by osmosis.
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Application to living cells
water enters!
lower concentration of
dissolved su
outside the cell
-+ higher water
outside the cell
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concentration of
dissolved substances
inside the cell
-+ thus lower water potential
inside the cell
Leaf cell
(An example of
plant cells)
Effect in concentrated solution
Etfect in dilute solution
Plasmolysis occurs when cells
Turgor pressure results when cells
are placed
are placed in a dilute solution.
Water enters the cell
Vacuole increases in size
Cellulose cell wall prevents over
in a
concentrated
solution.
Water leaves the cell
Vacuole decreases in size
Cytoplasm shrinks away from the
cell wall
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Type of cells
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tflect ol osmotic chonges in cells
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concentrated
solution
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expansion of the cell membrane by
exerting an opposing pressure.
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When cell is fully turgid, further
entry of water is prevented.
in dilute
solution
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cell becomes
plasmolysed
cell becomes
turgid
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Haemolysis occurs when cells are
placed in a dilute solution.
solution.
Water leaves the cell
Membrane of the cell forms little
Water enters the cell
spikes
of the cell membrane
Cell bursts
. Cell shrinks and
dehyd rated
. Cell dies
Red blood cell
(An example of
animal cells)
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concentrated
solution
+
becomes
Animal cells do not have cell
walls to prevent over expansion
Cell dies
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Crenation occurs when cells
are placed in a concentration
in dilute
solution
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haemolysis
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REVISION
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Diffusion is a result of the random movement of (a)
from a region of their
(b)........
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cell undergoes
cell undergoes
crenation
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The net movement is
...... concentration to a region of their (c)
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concentration, down a concentration gradient. The particles continue to (d).......
even when they are evenly spread throughout.
Osmosis is the diffusion of
(e).....
......... molecules. When
a
(0.......
permeable membrane like a cell membrane separates two solutions of different concentrations, a
concentration gradient is set up. Water molecules move in both directions, but the (g). ...............
(a) Define osmosis.
3.
A dilute solution and a concentrated solution has different water potential. what is meant by
water potential?
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(b)
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movement of water is from a dilute solution to a concentrated solution.
The diagram below shows a beaker containing two different liquids. They are separated by a semipermeable membrane. The beaker is left undisturbed for one hour.
A
B
semi-permeab
membrane
10% starch
solution
20
distilled water
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(a) (i)
Explain your answer.
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(ii)
What would happen to the liquid levels in regions A and B after one hour?
(b) (i)
(ii)
4.
starch solution is replaced by lOo/o glucose solution, what would you expect to
happen to the liquid levels in regions A and B?
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Explain your answer.
The diagram below shows how osmosis affects plant cells when they are placed in different
concentrations of solution.
Diagram
after one hour
in solution Y
after one hour
in solution X
+
--f
Which region
has higher
water potential
Changes of
cell after one
hour
Explanation
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BIOLOGY
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Level Conceptual Learning I
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5.
The diagram below shows how osmosis affects animal cells when they are placed in different
concentrations of solution.
Diagram
after one hour
in solution Q
after one hour
in solution P
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Which region
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has higher
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water potential
Changes of
cell after one
Explanation
An animal cell and a plant cell were both placed in distilled water. After one hour, they were examined
again under an optical microscope. Only fragments of cell membrane were observed in animal cell
while the plant cell has increased in size.
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hour
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Explain why the results are different in both types of cells.
ACTIVE TRANSPORT
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Active transport is the movement of substances across a cell membrane against
gradient, using energy from respiration.
a concentration
Examples
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The cells lining the gut take up glucose molecules into the blood, which already contains a relatively
high amount of glucose.
Mineral ions are absorbed by the root hair cells even though the concentration is much lower in the
surrounding soil particles than in the root hair cells.
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glucose molecules or
@REVISI0l'l
1,. (a)
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mineral ions enter!
(dissolved substances enter the cell
against their concentration gradient)
higher concentration of dissolved
substances such as glucose or
mineral ions inside the cell
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lower concentration of
dissolved substances
such as glucose or mineral
ions outside the cell
Define active transport.
(b) Name the cell organelle
that will be present in a greater amount in a cell if the cell carries
out active transport constantly. Explain your answer.
2.
State two examples of active transport taking place in living organisms.
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The surface area to volume ratio is the amount of surface area per unit volume of an object.
ln living organisms, it is an important factor that affects the rate of diffusion of substances across
the cell membrane. Nutrients, oxygen and waste substances need to diffuse through the cell
membrane in order to enter or leave the cells.
Cells with a large surface area to volume ratio enable nutrients and oxygen to diffuse into the cell
quickly and allow waste to diffuse out of the cell quickly. lf the cells have a small surface area to
volume ratio, the nutrients and oxygen will take longer time to diffuse into the cell. As a result,
the cell would not be able to survive.
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SURFACE AREA TO UOLUME RATIO
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Even though larger cells have more surface area than smaller ones, they have less surface area
for every unit volume of protoplasm. Hence their rate of intake of nutrients per unit volume
is
slower than smaller cells.
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Calculation of surface area to volume ratio
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1,
L
1
Height, H (m)
1
Width, W (m)
1
1
Surface area,
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Volume,LxHxW(ms)
Surface
a
rea/Vol ume ratio
2
3
2
3
4
9
24
54
27
8
1
(6/1):6,
1
(2418)=3:l
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The smaller the size of an object, the greater the surface
area to volume ratio, hence the faster the movement of
substances in and out of the object.
Conclusion
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[Note: There are a total of 6 sides
in each cube.l
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3
2
Surface area of one side,
6xLxH(m'z)
2
2
Length, L (m)
LxHh2)
3
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Cube
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ln living organisms, the exchanges of nutrients, gases and wastes occur through the surface area
of the cells, which is the cell membrane. The surface area is a critical interface between the cell
and its environment. The greater the surface area to volume ratio, the faster the rate of diffusion of
a substance for a given concentration gradient. The diagram below shows how the surface area to
volume ratio can be calculated and how exactly it changes with changing size.
2cm
4cm
3cm
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Surface area
Volume
Surface area
to volume ratio
(4nr3)13 respective ly. Take
[The equations for: surface area = 4nr2 and volume =
24
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as 3.14.1
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(a) Calculate the surface area, volume and surface area to volume ratio for each sphere
(c)
The sphere can be used to represent the three-dimensional structure of a cell. Why does the
surface area to volume ratio decreases when a cell grows?
For a single-celled organism or a cell in a multicellular organism's body, exchange of materials
often occurs through the process of diffusion which is a passive process.
Why is diffusion said to be a passive process?
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(b)
(ii)
Why is the surface area to volume ratio important for the survival of a cell?
The diagram below shows the outline of a root hair cell
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2.
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(i)
highly elongated
and protrusion
Explain why the root hair cell is highly elongated and protrudes from the root surface
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(a)
(b) State two more examples of cells in the living organisms that have similar adaptation to perform
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their functions more efficiently.
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