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Transport Systems in Living Things
Diffusion, Osmosis and Active transport
Diffusion is the spreading out of one substance through another due to the random
motion of particles. Diffusion is the net movement of molecules or ions in response to a
concentration gradient by moving from the region of higher concentration to a region
of lower concentration.
(Concentration - Number of molecules or ions per unit volume. Concentration gradient
- Difference in concentration between adjoining regions of fluid.)
The rate of diffusion depends on five factors:
1. Size. It takes more energy to move a large molecule than it does to move a small
one. Thus, smaller molecules diffuse more quickly than larger ones.
2. Temperature. Molecules move faster at higher temperature, so they collide more
often. Thus, the higher the temperature, the faster the diffusion.
3. Steepness of the concentration gradient. The rate of diffusion is higher with
steeper gradients, because molecules collide more often in a region of greater
concentration.
4. Charge can affect the rate and direction of diffusion between two regions. Each ion
or charged molecule in a fluid contributes to the fluid’s overall electric charge. A
difference in charge between two regions can affect the rate and direction of diffusion
between them. For example, positively charged substances, such as sodium ions,
diffuse toward a region with an overall negative charge.
5. Pressure. Diffusion may be affected by a difference in pressure between two
adjoining regions. Pressure squeezes molecules together, and molecules that are
more crowded collide and rebound more frequently. Thus, diffusion occurs faster at
higher pressures.
Figure 1A
Figure 1A can help to visualize diffusion across a membrane. Figure 1A shows a
solution of green dye separated from pure water by a membrane. Assume that this
membrane has microscopic pores through which dye molecules can move. Thus, we
say it is permeable to the dye. Although each molecule moves randomly, there will be
a net movement from the side of the membrane where dye molecules are more
concentrated to the side where they are less concentrated. Put another way, the dye
diffuses down its concentration gradient.
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Eventually, the solutions on both sides will have equal concentrations of dye. At this
dynamic equilibrium, molecules still move back and forth, but there is no net change in
concentration on either side of the membrane.
Figure 1B
Figure 1B illustrates the important point that two or more substances diffuse
independently of each other; that is, each diffuses down its own concentration gradient.
Diffusion in Cells
Diffusion is an important means by which materials are exchanged between a cell and
its environment. For example, cells constantly use oxygen in various chemical
reactions. Consequently, the oxygen concentration in cells always remains low. The
cells, then, contain a lower concentration of oxygen than does the environment outside
the cells. This creates a concentration gradient, and the oxygen molecules diffuse from
the outside of the cell to the inside.
Diffusion can take place only as long as there are no barriers to the free movement of
molecules. In the case of a cell, the plasma membrane surrounds the cell and serves
as a partial barrier to the movement of molecules through it. If a molecule is able to
pass through the membrane, the membrane is permeable to the molecules. Because
the plasma membrane allows only certain molecules to pass through it, it is selectively
permeable. A molecule’s ability to pass through the membrane depends on its size,
electrical charge, and solubility in the plasma membrane. In certain cases, the
membrane differentiates on the basis of molecular size; that is, the membrane allows
small molecules, such as oxygen or water, to pass through but prevents the passage
of larger molecules. The membrane may also regulate the passage of ions. If a
particular portion of the membrane has a large number of positive ions on its surface,
positively charged ions in the environment will be repelled and prevented from crossing
the membrane.
Because a cell does not have to do work when molecules diffuse across its membrane,
such movement across a membrane is called passive transport. Much of the traffic
across cell membranes occurs by diffusion.
Diffusion in living things
In living organisms, many organs have specialised features to improve the efficiency of
diffusion of materials. These specialised features are mainly developed to increase the
surface area so that they can carry out their functions more efficiently.
Some examples of important diffusion of substances in living things:
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- Gases exchange between the lungs and blood capillaries
- Absorption of simple food substances in the small intestine
- Gases exchange between the stomata and the atmosphere
Osmosis is the diffusion of water across a membrane
Osmosis is the movement of water molecules from the region of higher water
concentration to a region of lower water concentration through a partially permeable
membrane.
Partially permeable membrane is a membrane that only allows certain substances to
pass through but not the other. It restricts the movement of substances based on their
size. Substances of larger size such as starch cannot pass through it.
The partially permeable membrane can be divided into two groups:
Natural: Cell membrane found in plant cells and animal cells
Artificial: Visking tubing and cellophane bag
A dilute solution has a higher water concentration than a concentrated solution. The
concentration of water molecules is higher in a dilute solution. Therefore, water
molecules move from the dilute solution into the concentrated solution.
Figure 2.The
selectively
permeable
membrane
dividing this Ushaped tube
permits water but
not solutes to
pass. Water
diffuses from the
left side (low
solute
concentration)
toward the right
side (high solute
concentration). At
equilibrium, water
flow is equal in
both directions,
and the solute
concentrations
will be equal on
both sides of the
membrane.
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Osmosis affects the size and the mass of the living cells. When water enters a potato
strip, it causes the length of the strip to increase due to the expansion in the size of the
cells inside it. The mass of the strip increases as well due to net gain of water
molecules.
Some examples of osmosis in living things:
— Uptake of water molecules from the soil by the root hair cells
— Absorption of water molecules in human large intestine
Effect of osmosis on living cells
The term tonicity refers to the
ability of a surrounding solution to
cause a cell to gain or lose water.
The tonicity of a solution mainly
depends on its concentration of
solutes that cannot cross the
plasma membrane relative to the
concentration of solutes inside the
cell.
Figure 3 illustrates how the
principles of osmosis and tonicity
apply to cells. The effects of
placing an animal cell in solutions
of various tonicities are shown in
the top row of the illustration; the
effects of the same solutions on a
plant cell are shown in the bottom
row.
When the overall solute
concentrations of the two fluids
differ, the fluid with the lower
overall concentration of solutes is
Figure 3
said to be hypotonic.
The other one, with the higher overall solute concentration, is hypertonic. Fluids that
are isotonic have the same overall solute concentration.
When an animal cell is immersed in a solution that is isotonic to the cell, the cell’s
volume remains constant. The solute concentration of a cell and its isotonic
environment are essentially equal, and the cell gains water at the same rate that it
loses it. In your body, red blood cells are transported in the isotonic plasma of the
blood.
What happens when an animal cell is placed in a hypotonic solution, a solution with a
solute concentration lower than that of the cell. (Can you figure out in which direction
osmosis will occur? Where are there more free water molecules available to move?)
The cell gains water, swells, and may burst (lyse) like an over-filled balloon.
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The upper right shows the opposite case — an animal cell placed in a hypertonic
solution (hyper, above), a solution with a higher solute concentration. The cell shrivels
and can die from water loss.
For an animal to survive in a hypotonic or hypertonic environment, it must have a way
to prevent excessive uptake or excessive loss of water. The control of water balance is
called osmoregulation. For example, a freshwater fish, which lives in a hypotonic
environment, has kidneys and gills that work constantly to prevent an excessive
buildup of water in the body.
Figure 3, a plant cell immersed in an isotonic solution is flaccid (limp). In contrast, a
plant cell is turgid (very firm), which is the healthy state for most plant cells, in a
hypotonic environment. To become turgid, a plant cell needs a net inflow of water.
Although the somewhat elastic cell wall expands a bit, the pressure it exerts prevents
the cell from taking in too much water and bursting, as an animal cell would in a hypotonic environment. Plants that are not woody, such as most house-plants, depend on
their turgid cells for mechanical support.
In a hypertonic environment (bottom right), a plant cell is no better off than an animal
cell. As a plant cell loses water, it shrivels, and its plasma membrane pulls away from
the cell wall. This process, called plasmolysis, causes the plant to wilt and can be
lethal to the cell and the plant. The walled cells of bacteria and fungi also plasmolyse in
hypertonic environments. Thus, meats and other foods can be preserved with
concentrated salt solutions because the cells of food-spoiling bacteria or fungi become
plasmolysed and eventually die.
Simple diffusion gets rid of an existing concentration gradient. Often, however, a cell
needs to do the opposite: create and maintain a concentration gradient. A plant’s root
cell, for example, may need to absorb nutrients from soil water that is much more dilute
than the cell’s interior. In active transport, a cell uses a transport protein to move a
substance against its concentration gradient—from where it is less concentrated to
where it is more concentrated (Figure 4). Because a gradient represents a form of
potential energy, the cell must expend energy to create it. Energy for active transport
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often comes from ATP. Cells must contain high concentrations of K+ and low
concentrations of Na+ to perform many functions. In animals, for example, sodium and
potassium ion gradients are essential for nerve and muscle function. One active
transport system in the membranes of most animal cells is a protein called the sodium–
potassium pump (Figure 5 ), which uses ATP as an energy source to expel three
sodium ions (Na+ ) for every two potassium ions (K+ ) it admits. Maintaining these ion
gradients is costly: the million or more sodium–potassium pumps embedded in a cell’s
membrane use some 25% of the cell’s ATP.
Figure 5. The Sodium–Potassium Pump. This ―pump‖ is a protein embedded in the cell
membrane. It uses energy released in ATP hydrolysis to move potassium ions (K+)
into the cell and sodium ions (Na+) out of the cell. In each case, the ions move from
where they are less concentrated to where they are more concentrated.
MCQ
1. A root hair cell absorbs water through__________because the cell sap of the root
hair cell has a__________water potential than the water in the soil.
A. osmosis; higher
B. osmosis; lower
C. diffusion; higher
D. diffusion; lower
2. Which of the following represents the reason why glucose molecules can pass
through the Visking tubing?
A. Glucose molecules are very heavy.
B. Glucose molecules are very large.
C. Glucose molecules are very small.
D. Glucose molecules are very light.
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3. Which of the following is an example of diffusion in a plant?
A. Carbon dioxide from the air moving into a photosynthesizing leaf
B. Nitrate ions moving into root hairs against a concentration gradient
C. Sugars in the phloem moving from leaves to roots
D. Water in the xylem moving from roots to leaves
4. Which of the following processes involves osmosis?
A. Circulation of blood in the blood vessels
B. Conduction of water up the xylem
C. Absorption of water in the large intestines of humans
D. Uptake of oxygen in the alveoli
5. Red blood cells were placed in water and in three salt solutions of different
concentrations.
Cells from each solution were examined under the microscope. Which diagram shows
the appearance of a cell in pure water?
(B)
6. The diagrams show a mixture of water and sugar solution at two different times
By what process has the two liquids been mixed?
A. Absorption
B. Conduction
C. Diffusion
7. The apparatus shown in the
diagram was set up. After one
hour, the water in the beaker
turned red.
What is the most likely reason
for this colour change?
A. Molecules of red ink move through the membrane by diffusion.
B. Molecules of red ink move through the membrane by osmosis.
C. Molecules of water move through the membrane by diffusion.
D. Molecules of water move through the membrane by osmosis.
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D. Osmosis
8. Which of the following are examples of osmosis?
(1) The absorption of water by root hairs
(2) The absorption of mineral salts by root hairs
(3) The absorption of water by dry cotton wool
(4) The absorption of water by the large intestines
(5) The movement of water across the surface of the floor
A. (1) and (2) only B. (3) and (5) only
C. (1) and (4) only D. (1), (4) and (5) only
9. The diagram below shows an experimental set-up to investigate osmosis.
Which of the following combinations of liquids would cause X to rise to the highest level
in the glass tube after three hours?
Liquid X
Liquid Y
A
Concentrated sucrose solution
Dilute sucrose solution
B
Concentrated sucrose solution
Water
C
Dilute sucrose solution
Concentrated sucrose solution
D
Water
Concentrated sucrose solution
For questions 10 and 11, refer to the following diagram of four plant cells.
10. Which of the cells shown above have low water potential?
A. P and Q
B. Q and S
C. P and R
D. R and S
11. If the cells remain in contact as shown, which of the following shows the direction
of movement of water molecules?
A. R to Q and Q to P
B. Q to S and R to Q
C. P to Q and R to S
D. Q to P and S to R
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For questions 12 and 13, refer to the following diagram which represents an
experiment that is used to investigate movement of substances in potato tissue.
12. Which diagram shows the result after twenty-four hours?
(B)
13. Which of the following processes are shown in the above experiment?
A. Photosynthesis
B. Osmosis
C. Respiration
D. Diffusion
14. An experiment was set up as shown in
the diagram below. After some time has
elapsed, the Visking tube containing liquid X
collapsed while the tubing containing liquid Y
was firm and hard.
Which of the following could be a correct
description of the liquids at the start of the
experiment?
Liquid X
Liquid Y
A
concentrated sucrose
water
solution
B
dilute sucrose solution
concentrated sucrose
solution
C
water
concentrated sucrose
solution
D
water
dilute sucrose solution
Liquid Z
dilute sucrose solution
water
dilute sucrose solution
concentrated sucrose
solution
15. A cube of fresh potato is weighed. It is then placed in a test tube containing a dilute
solution of sucrose. After a day, its mass has increased. Which process has occurred
and what has happened to the concentration of the solution in the test tube?
process occurred
concentration of solution
A
diffusion of sucrose molecules
decreased
B
diffusion of sucrose molecules
increased
C
osmosis of water molecules
decreased
D
osmosis of water molecules
increased
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16. The diagram below shows an
apparatus used to investigate osmosis.
After a few hours, which changes in levels
will occur and which substances will move
across the membrane?
Level M Level N Substance
A.
Fall
Rise
Starch
B.
Fall
Rise
Water
C.
Rise
Fall
Starch
D.
Rise
Fall
Water
Questions 17 and 18 refer to
the diagram below. It shows a
typical plant cell after being
placed in beaker of salt
solution for 10 minutes.
17. What could be the
concentration of the salt
solution in the beaker?
A. 5% salt solution B. 15% salt solution
C. 20% salt solution D. 25% salt solution
18. Which process is involved to cause this observation of the cell?
A. Osmosis
B. Diffusion
C. Expansion
D. Active transport
19. The diagram below shows an
experiment to investigate the
movement of substances.
Which of the following most likely
will not happen to the respective
regions 1, 2 and 3 at the end of the
experiment?
A. Region 1 increases in volume.
B. There are same number of
glucose molecules in these three
regions.
C. Regions 2 and 3 have equal
volume.
D. Blue-black observed in region 3 when two drops of iodine is added to it.
20. The diagram below shows the effect of solution Y on a red blood cell after half an
hour.
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Which statement is not correct from this observation?
A. Solution Y contains a higher concentration of solute than in the red blood cell
B. The cell membrane of this red blood cell eventually will break apart.
C. The red blood cell is said to be dehydrated.
D. The red blood decreases in its volume and becomes soft.
Short Structured Questions
1(a) Define 'diffusion'.
(b) Define 'osmosis’.
(c) Compare and contrast diffusion and osmosis using the table below.
diffusion
osmosis
particles involved
movement of
particles
involvement of
membrane
(d) State two examples in living things where diffusion and osmosis occur.
particles involved
movement of
particles
involvement of
membrane
diffusion
Small particles such as glucose
and ions
High to low concentration
osmosis
Only water
molecules
High to low water potential
no
Partially permeable
membrane
(d) Diffusion: absorption of glucose in the small intestines, entry of carbon dioxide
through stomata
Osmosis: absorption of water by root hair cells and the large intestines
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2. Study the diagram carefully.
(a) The apparatus is left standing for a few hours. What will happen to the level of
sucrose solution in the capillary tube? Explain your answer.
(b) With the help of the key provided, draw the movement of particles in the movement
in the space provided.
(c) The sucrose solution in the Visking tube was replaced with glucose solution. With
the help of the key provided, draw the movement of particles in the experiment in the
space provided.
(d) What does this experiment show you about the size of the two sugar molecules and
their ability to cross the partially permeable membrane of the Visking tube?
(e) Other than size of molecules, state two other factors that affect the movement of
substances across a partially permeable membrane.
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(a) The sucrose solution level will increase. The water potential in water is higher
compared to sucrose solution. Hence osmosis of water molecules into the sucrose
solution, across the partially permeable Visking tube occurs.
(d) Glucose molecules are smaller than sucrose molecules and hence can cross the
partially permeable membrane. Sucrose molecules are too big to cross.
(e) Size of membrane pore; temperature.
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3. As shown in the diagram below, cell X was placed in a beaker of solution A for 20
minutes and showed no visible difference, cell X was then placed in solution B. After
20 minutes in solution B, it was noticed that cell X had become bloated.
(a)(i) Identify cell X.
(ii) Explain why there was no visible difference in cell X after being placed in solution A
(b)(i) Explain the appearance of cell X after being placed in solution B.
(ii) Describe how cell X is adapted for its function of water absorption
(a)(i) Root hair cell
(ii) No difference in water potential. No net movement of water molecules by osmosis
(b)(i) Difference in water potential. There was net movement of water molecules from
solution B into the cell by osmosis.
(ii) Protrusion increases surface area to volume ratio for efficient absorption of water by
osmosis. Concentrated cell sap keeps internal water potential low, so osmosis of water
molecules into the cell is possible.
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4 The picture below shows a plant cell that was placed in a concentrated sucrose
solution.
(a) State the condition of the plant cell.
(b) Explain the appearance of the cell.
(c) What does the part labelled Y contain? Explain the reason for your answer.
(d) The same cell was then placed in pure water. The following diagram shows the
appearance of the cell after the treatment in pure water.
(i) State the condition of the plant cell above.
(ii) Explain the appearance of the cell.
(iii) Explain why the cell did not burst.
(e) Describe and explain the effects of placing a red blood cell in
(i) concentrated sucrose solution.
(ii) pure water.
(a) Plasmolysed
(b) There was higher water potential in the cell sap compared to the sucrose solution.
Water molecules move out of the cell sap by osmosis, causing the cell membrane to
detach from the cell wall.
(c) Sucrose solution. The cell membrane has detached. The cell wall is fully
permeable, thus allowing sucrose molecules to enter.
(d) (i) Turgid
(ii) There was higher water potential in the pure water compared to the cell sap. Hence
water molecules move into the cell sap by osmosis, causing the cell to become turgid.
(iii) The cell wall exerts an opposing force to prevent the cell from bursting.
(e) (i) There is higher water potential in the cytoplasm of the red blood cell compared to
the sucrose solution. Water molecules move out of the cytoplasm by osmosis, causing
the cell to form spikes or become crenate.
(ii) There is higher water potential in the pure water compared to the cytoplasm of the
red blood cell. Hence water molecules move into the cytoplasm of the red blood cell by
osmosis, causing the cell to swell and eventually lyse.
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5. The figure shows the experiment set up using Visking tubings.
The solution in the beaker turns blue at the end of the experiment. When two drops of
iodine are added into the beaker, no blue-black colour is observed.
(a)(i) Suggest the final concentration of blue dye solution, greater than 10% lesser than
10% or remaining as 10%, in the Visking tubing A. [1]
(ii) Explain how you derive your answer. [3]
(b) From what evidence can you conclude that Visking tubing is a partially permeable
membrane? Explain your answer. [2]
(c)(i) What would happen to mass of the Visking tubing B, increase, decrease or
remain the same, at the end of experiment? [1]
(ii) Explain your answer. [2]
(d) Would you expect the content of Visking tubing B to turn blue at the end of the
experiment? Explain your answer. [2]
(a)(i) Less than 10%
(ii) Blue dye particle can pass through the Visking tubing. Therefore, they will move
from a region of high concentration in the Visking tubing to a region of low
concentration in the beaker until both sides have equal concentration.
(b) It prevents starch to move across it but allows blue dye particles and water to move
through.
(c)(i) Increase
(ii) The concentration of water molecules is higher in the beaker than in the tubing, so
water molecules diffuse into the tubing from the beaker by osmosis.
(d) Yes. Since blue dye can pass through the Visking tubing, it will enter Visking tubing
B since there is a low concentration of blue dye particles.
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Transport in Plants
There are two separate systems to
transport water, mineral salts and
nutrients:
1. Xylem vessels
2. Phloem tissues
Water and dissolved mineral salts are
transported inside the xylem vessels in
an upward direction.
Food substances made in the leaves are
transported in the plant by phloem
tissues in all directions.
Xylem and phloem tissues are grouped
together to form vascular bundles.
Uptake of water
Roots have many root hairs to increase the
surface area by developing an elongated
structure, so water can be absorbed in a
faster rate.
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The solution inside the root hair cell is more
concentrated than in the soil particles. As a
result, the concentration of water molecules
is lower in the cell than in the soil. Thus,
water enters the root hair cells by osmosis.
Once inside the root hair cell, the water
dilutes the solution in the cytoplasm, it is
now less concentrated compared to the
root cell next to it. Water moves to that root
cell by osmosis.
The process of osmosis continues
throughout the root cells until it reaches the
xylem vessel.
When water evaporates in leaves, it
creates a pulling force that move the water
up the stem to the leaves.
Xylem Transport. Transpiration of water from
leaves pulls water up a plant’s stem from the
roots. The cohesiveness of water makes xylem
transport possible.
Uptake of mineral salts
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Soil water contains high concentration of dissolved mineral salts compared to the
solution in the root hair cells.
Mineral salts enter root hair cells by diffusion.
Sometimes soil water has a lower concentration of dissolved mineral salts compared to
the cytoplasm and the vacuole of root hair cells. In this case, mineral salts enter the
root hair cells by active transport.
Active transport is a process when a substance moves from its region of low
concentration to its region of high concentration. Energy is involved.
A plant’s root cell, for example, may need to absorb nutrients from soil water that is
much more dilute than the cell’s interior. In active transport, a cell uses a transport
protein to move a substance against its concentration gradient—from where it is less
concentrated to where it is more concentrated. Because a gradient represents a form
of potential energy, the cell must expend energy to create it.
Transport of food
Food made in the leaves is needed by all the cells in the plant.
Phloem tissue transports the food to all parts of the plants upwardly and downwardly.
Multiple-Choices Questions
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1. What is the process by which large amount of water is lost from the stomata in
leaves?
A. Diffusion
B. Osmosis
C. Respiration
D.
Transpiration
2. Anita bought a bunch of blue flowers from the market. In order to find out whether
the colour was artificially introduced or not, she prepared a section of the stem and
observed it under the microscope. Which of the following correctly shows the condition
of the section of the colour if the flowers were artificially introduced? The dark area is
the place where the colour is present.
(B)
3. A piece of a plant with a
transparent stem was placed in a
beaker containing a blue dye and
then examined 5 hours later.
Which of the following explains
the change in appearance?
A Blue dye diffuses through the stem.
B Blue dye moves up the stem by osmosis.
C Blue dye moves up through the xylem due to transpiration.
D Blue dye moves up through the phloem due to transpiration
4. Which of the following situations would cause a plant to wilt?
Water loss
Water uptake
A
High
High
C
Low
High
Water loss
Water uptake
B
High
Low
D
Low
low
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5. Four similar plants are growing under different conditions of temperature and
humidity.
Which plant is likely to wilt first?
Temperature
Humidity
A
High
High
C
Low
High
Temperature
Humidity
B
High
Low
D
Low
low
Extra info:
Humidity is the amount of water vapor in the air. A hygrometer is an instrument used
for measuring humidity or the moisture content in the environment. Humidity
measurement instruments usually rely on measurements of some other quantity such
as temperature, pressure, mass or a mechanical or electrical change in a substance as
moisture is absorbed. By calibration and calculation, these measured quantities can
lead to a measurement of humidity.
A psychrometer measures relative humidity, using the cooling effect of evaporation.
Psychrometer
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6. The roots of a plant were placed in a coloured dye. The diagrams below show the
transverse sections of its leaf, stem and root after one day.
Which of the numbered tissues of the leaf, stem and root would be most heavily
stained by the dye?
A 1, 3, 5
B 1, 3, 6
C 1, 4, 5
7. The diagram below shows a section of a plant stem.
Which tissue would show radioactivity when the plant is
exposed to radioactive carbon dioxide during
photosynthesis?
(B)
8. The diagram shows an experiment.
Which of the following affects the amount of water
droplets formed in the bell jar?
A The humidity of the air surrounding the bell jar
B The size of the bell jar
C The temperature of the air surrounding the bell
jar
D The velocity of the air movement outside the bell jar
9. The photomicrograph below shows part of a section of a
young root. Which type of cells does not respire?
(C)
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D 2, 3, 6
10. What are the possible functions of water in plants?
(1) As a requirement for respiration
(2) As raw material for photosynthesis
(3) As a medium for food transport
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and
(3)
11. Which of the following instruments is often used to measure the rate of water
uptake in plants?
A Potometer
B Photometer
C Respirometer
Potometer
The diagram shown in question 12 is a potometer, too.
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D Data logger
12. The diagram shows an experimental set-up
to investigate the rate of transpiration.
Under which of the following environmental
conditions would the air bubbles in the capillary
tube move at the fastest rate?
A Cold, dry and windy
B Cold, humid and windy
C Warm, dry and windy
D Warm, humid and without wind
13. Miss Daisy carried out marcotting on her balsam plant.
What causes the swelling seen above the removed ring?
A Accumulation of salts and water due to interruption of the
phloem tissue
B Accumulation of salts and water due to interruption of the
xylem tissue
C Accumulation of food materials due to interruption of the phloem tissue
D Entry of bacteria from the atmosphere due to removal of the bark
How a marcotted part look like.
If you want to know more about marcotting, go to the following website.
http://www.cropsreview.com/marcotting.html
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14. The diagram below shows a tree whose bark at the base of the stem has been
scraped away by wild forest dogs.
Why did the tree die after several weeks?
A. The xylem had been destroyed.
B. Microorganisms attacked the tree.
C. The root lacked the supply of organic foods.
D. Water had been lost at the wound.
15. The graph below shows the changes in the transpiration rate of a plant during a
dry, hot, sunny day
Which of the following could be the reason
for the sudden drop in the transpiration rate
at 1400 hour?
A The sky became cloudy temporarily.
B The temperature rose.
C There was more carbon dioxide in the air.
D The stomata closed.
Question 16 and 17 refer to diagram in the right which
shows cross-section of the stem of a green plant.
16. Which part is responsible for transporting water and
mineral salts?
(B)
17. Which part most likely contains the substance which gives a positive result with
Benedict's test?
(A)
Benedict's solution is used to test for the presence of sugar eg glucose.
25
A negative test (left) and a positive test (right)
The presence of glucose is indicated by the formation of orange-red precipitate as
shown on the right diagram.
To test for sucrose, a few drops of dilute hydrochloric acid + a few drops of Benedict's
solution is used. If sucrose is present, orange-red precipitate is observed.
26
Structured Questions
1. The diagram below shows sections of a young plant. X and Y represent tissues
which carry substances within the plant
(a)(i) Name the sections A and B of the plant.
(ii) Name the substances carried by X and Y.
(iii) Describe the structure of X and explain how it is adapted to carry out its functions.
(b) Describe briefly a simple method to show that substances move through tissue X.
(c) Suggest one way in which the movement of substances in plants differs from that in
animals.
(d) Explain why tissue X is located towards the centre of the plant.
(a)(i) A : stem; B: root
(ii) X: water and mineral salts Y: manufactured food / sucrose and amino acids
(iii) X is hollow for continuous flow of water; reinforced with lignin to prevent collapse
and for mechanical support of the plant.
(b) Place the stem in coloured water for a few hours. Cut a cross section and observe
which vessels the dye travelled through.
(c) Movement of substances in animals occurs at high pressure due to presence of
muscular pump (heart). There is no muscular pump in plants, so transport is at lower
pressure. / Animals' transport does not rely on external environmental factors. Plants,
transport is affected by external environmental factors such as temperature and air
movement.
(d) This is to ensure that the plants do not collapse and is kept upright by being
supported in the centre.
2. Melanie placed three stalks of celery under the conditions indicated in the diagram
below, with their stalks dipping into a coloured dye.
27
(a) State what she would see, after 24 hours, inside the plastic bag that is wrapped
around P.
(b) Give an explanation for your answer in (a)
(c) In which of the plants, P, Q or R, would the dye move furthest up the stalk? Explain
your answer.
(a) Water droplets
(b) Transpiration occurred. Water vapour evaporated from the stomata and condensed
on the plastic bag.
(c) R.
For plant P, the movement of the dye solution is limited by the humidity or amount of
water vapor in the air within the plastic bag.
For Q, there is no leaf to cause transpiration to occur.
For R, transpiration can occur continuously, resulting in the furthest movement of the
dye solution.
28
3. Mr Wong set up an experiment to investigate water loss by two young shoots. The
two shoots were kept under conditions which varied but were always the same for both
shoots. The volume of water remaining in each tube was observed each day, for three
days.
The results he obtained are shown in the table below.
Water level (cm)
Time (day)
Tube A
Tube B
0
10.0
10.0
1
8.8
9.1
2
7.4
8.5
3
5.8
7.5
(a) Name the process which caused the loss of water from the shoots
(b) Which tube, A or B lost more water?
(c) On which day was the most water lost by the shoots?
(d) Suggest an explanation for more water being lost on this day than on the other two
(a) Transpiration
(b) A
(c) Day 3
(d) Higher temperature / low humidity / windy on Day 3 compared to Day 1 and 2.
29
4. Gilbert carried out an experiment to study the impact of girdling on plants. Diagram 1
shows the girdling of a woody shoot by removal of a ring of bark, leaving the xylem
intact. The girdled region is smeared with Vaseline.
Diagram 2 shows the appearance of this shoot four weeks after the girdling treatment.
(a)(i) Which vascular tissue is removed in the girdling treatment of the woody shoot?
(ii) What is the purpose of covering the girdled region with Vaseline?
(b) Describe and explain the resulting appearance of the woody shoot above the
girdled region.
(c) What will be the fate of this tree? Explain your answer.
(d) If the girdling action removed all the vascular tissues, what would be the resulting
appearance of the leaves present at region X one week after the girdling treatment?
Explain your answer.
(a) (i) Phloem tissue
(ii) To prevent evaporation of water from the xylem tissue (core of stem)
(b) The base of the upper section of shoot above the girdled region becomes swollen.
Phloem tissue is removed, food manufactured in the leaves cannot be transported
across the girdled region to the lower regions of the shoot, hence it accumulates at the
base of the upper section, which becomes swollen.
(c) The tree will die after a while.
The manufactured food cannot be transported down to the lower parts of the tree,
especially the roots.
Absorption of water and dissolved mineral salts will be affected if cells around the roots
die from lack of nutrients.
(d) The leaves will wilt.
30
Xylem tissue is removed, water absorbed by the roots cannot be transported up to the
leaves.
The water lost by leaves cannot be replaced, resulting in wilting.
Photosynthesis cannot occur. The leaves and eventually the tree die.
5. A plant was placed in a beaker containing red dye solution as shown in Diagram A.
One hour later, thin slice was cut from the stem and the result was shown in Diagram
B.
(a)(i) Name the tissue X which has been stained with red dye solution.
(ii) Explain why that tissue X was stained with red dye solution.
(b) Through what process do red dye particles enter the root hairs of the plant?
(c) What could most likely the objective of this investigation be?
(a) (i) Xylem
(ii) Xylem is responsible for transporting water. Water contains red dye, so it is
transported together with the red dye by the xylem.
(b) Diffusion
(c) To show that xylem tissues are responsible for transporting water in the plant
transport system.
31
Transport System in Humans
The human transport system is called the circulatory system.
The circulatory system can be divided into three major parts:
 Heart
 Blood vessels
 Blood
The circulatory system is responsible for transporting substances throughout the entire
body.
1. Bringing nutrients, water, oxygen and other substances to the body cells
2. Removing waste substances such as carbon dioxide from the body cells
Double Circulatory system in humans
Pulmonary Circulation : Blood is pumped out of the right side of the heart and travels
to the lungs. In the lungs blood picks up oxygen and becomes oxygenated at the
same time carbon dioxide is removed. The oxygenated blood then travels back to the
left side of the heart.
32
Systemic Circulation : The oxygenated blood is pumped by the left side of the heart
to the rest of the body. It delivers oxygen to the body’s cells and becomes
deoxygenated. It also picks up Carbon dioxide and other waste products. This
deoxygenated blood then makes it way back to the right side of the heart where the
cycle is repeated.
Heart
The human heart is a four-chambered muscular pump which pumps blood around the
circulatory system. The pumping action is as follows:
 When the heart muscles contract (systole phase), blood is forced out.
 When the heart muscles relax (diastole phase), blood is pulled in.
33
Left ventricle has a thicker muscular wall because it needs to pump blood at a higher
pressure as the blood needs to travel a greater distance to all parts of the body from
the heart.
Right ventricle has a thinner muscular wall because it pumps blood at a lower pressure
as the blood only needs to travel to the lungs which is a shorter distance from the
heart.
There are valves in the heart to make sure that blood flows in one direction only.
Blood vessels
34
Arteries
Veins
Capillaries
Function carry blood away from carry blood towards the allow exchange of
the heart
heart
substances between
blood and the body
cells
Structure Thick,
elastic
and Thin, less elastic and One-cell thick to allow
muscular wall
less muscular wall
substances
can
diffuse to and from the
cells
Valves
Absent
Present
Absent
Blood
Very fast as blood is Slow as under low Slow as under low
flow
under high pressure
pressure
pressure
In spurts
Smooth flow
Size of
Small
Large
Very narrow
lumen
35
Let’s follow the flow of blood through the human circulatory system. Starting in the right
ventricle in the figure above, we trace the pulmonary circuit first.
 The right ventricle pumps oxygen-poor blood to the lungs via  the pulmonary
arteries.
As blood flows through capillaries in the lungs, it takes up oxygen and unloads
carbon dioxide.
Oxygen-rich blood flows back through  the pulmonary veins to  the left atrium.
Next, the oxygen-rich blood flows from the left atrium into  the left ventricle.
The figure shows, the left ventricle pumps oxygen-rich blood into  the aorta. The
aorta is our largest blood vessel, with a diameter of about 2.5 cm. The first branches
36
from the aorta are the coronary arteries (not shown), which supply blood to the heart
muscle itself. Next there are large branches leading to  the head, chest, and arms,
and the abdominal regions and legs. For simplicity, the figure does not show the
individual organs, but within each organ, arteries lead to arterioles that branch into
capillaries. The capillaries rejoin as venules, which lead to veins.  Oxygen-poor blood
from the upper part of the body is channeled into a large vein called the superior vena
cava, and from the lower part of the body it flows through the inferior vena cava. The
two venae cavae empty into  the right atrium. As the blood flows from the right atrium
into the right ventricle, we complete our journey, only to start the pulmonary circuit
again at the right ventricle.
Remember that the path of any single red blood cell is always heart to lung capillaries
to heart to body tissue capillaries and back to heart. In one systemic circuit, a blood
cell may travel to the brain; in the next (after a pulmonary circuit), it may travel to the
legs. A red blood cell never travels from the brain to the legs without first returning to
the heart and being pumped to the lungs to be recharged with oxygen.
Blood
A healthy adult has about five litres
of blood in their vessels.
Blood is known as the fluid of life. It
is a fluid tissue which consists of
the following components:
 Red blood cells
 White blood cells
 Platelets
 Plasma
Blood acts as a transport medium
in the human body.
1. It transports the following
substances to the body cells:
 Oxygen (for respiration)
 Hormones (important chemical substances for various chemical activities)
 Nutrients (such as glucose, amino acids, fatty acid, glycerol and vitamins)
2. It transports the following substances from the body cells:
 Carbon dioxide (waste from the respiration)
37
 Waste products from other processes (such as excess water and urea)
38
Component
Red blood cells
(Erythrocytes)
Description and function
Transport oxygen from the lungs to all cells in the body. Oxygen
combines with a red pigment knows haemoglobins in the cell to be
transported.
Transport oxygen from lungs to aerobically respiring cells and
facilitate movement of carbon dioxide to the lungs.
Red blood cells lose their nucleus and other organelles as they
develop.
Mature red blood cells are flexible disks with a depression at their
center. Their flexibility allows them to slip easily through narrow
blood vessels, and their flattened shape facilitates gas exchange.
Haemoglobin fills the interior of the mature red blood cell.
Most oxygen that enters the blood travels to the tissues while bound
to the haemoglobin.
A mature red blood cell has enough stored sugars, RNAs, and other
molecules to live about 120 days.
White blood cells They form part of the immune system.
Destroy foreign substances, initiate inflammation, fight infection.
Five types of white blood cells.
The cells differ in their size, nuclear shape, and staining traits, as
well as function.
These cells participate in many immune responses. Some secrete
signaling molecules that provoke inflammation, whereas others
destroy microbes or produce antibodies.
1.Neutrophils, the most abundant white cells, are phagocytes that
engulf bacteria and debris.
2. Eosinophils attack larger parasites, such as worms.
3. Basophils secrete chemicals that have a role in inflammation.
4. Monocytes are white cells that circulate in the blood for a few
days, then move into the tissues, where they develop into
phagocytic cells known as macrophages. Macrophages interact with
lymphocytes to bring about immune responses. There are two types
39
Platelets
Plasma
of lymphocytes, B cells and T cells. B cells mature in bone, whereas
T cells mature in the thymus. Both protect the body against specific
threats
Stop bleeding by clotting the blood flow when blood vessels are cut.
Platelets are small, colorless cell fragments that initiate blood
clotting.
When a vessel is injured, it constricts (narrows), reducing blood
loss. Platelets adhere to the injured site and release substances
that attract more platelets. Plasma proteins convert blood to a gel
and form a clot. During clot formation, fibrinogen, a soluble plasma
protein, is converted to insoluble threads of fibrin. Fibrinforms a
mesh that traps cells and platelets
Dissolves and transports materials around the body, for example
digested food, carbon dioxide and waste substances.
The fluid portion of the blood, known as the plasma, constitutes
about 50 to 60 percent of the blood volume.
Plasma is mostly water with hundreds of different plasma proteins
dissolved in it. Some plasma proteins transport lipids and fat-soluble
vitamins; others have a role in blood clotting or immunity.
Dissolved sugars, amino acids, vitamins, and some gases travel
through the bloodstream in plasma.
Blood clotting
In a healthy circulatory system, platelets travel freely within the vessels. Sometimes,
however, a wound nicks a blood vessel, or the blood vessel’s inner lining may become
obstructed.
Platelets then ―catch‖ on the obstacle and shatter, releasing biochemicals that combine
with plasma proteins called clotting factors.
The resulting complex series of reactions ends with the formation of a blood clot ‒ a
plug of solidified blood.
40
(a) A cut blood vessel immediately constricts. Platelets aggregate at the injured site.
Proteins called clotting factors participate in a cascade of reactions, producing a
meshwork of protein threads. (b) Red blood cells trapped by protein threads in a clot.
Blood that clots too slowly can lead to severe blood loss. Hemophilias, for example,
are inherited bleeding disorders caused by absent or abnormal clotting factors.
Deficiencies of vitamins C or K can also slow clotting and wound healing. Blood that
clots too readily is also extremely dangerous. In atheroscle-rosis, platelets may snag
on rough spots in blood vessel linings.
The resulting clot may stay in place or travel in the bloodstream to another location;
either way, the obstruction may cut off circulation and sometimes even cause death.
41
MCQ
1. Which of the following shows the thickness of the walls of blood vessels in
ascending order?
A. Capillaries, veins, arteries
B. Arteries, veins, capillaries
C. Veins, arteries, capillaries
D. Arteries, capillaries, veins
2. What is the function of blood plasma?
A Formation of clots
B Transport of oxygen
C Production of antibodies
D Transport of dissolved nutrients and waste products
3. The diagrams show the crosssections of three different types of
blood vessels P, Q and R.
Which shows the correct type of
blood vessels?
P
A
Artery
B
Artery
C
Vein
D
Capillary
Q
Vein
Capillary
Capillary
Artery
4. Which of the following statements about arteries is/are correct?
(i) All arteries do not contain any valves.
(ii) All arteries transport blood away from the heart.
(iii) All arteries transport blood under high pressure.
(iv) All arteries transport oxygenated blood.
A. (ii) only
B. (iii) only
C. (i) and (ii) only
D. (ii) and (iii) only
(D)
42
R
Capillary
Vein
Artery
Vein
5. Which of the following shows the correct routes for blood to travel from the leg to the
brain in the human body?
A. Leg  lungs  heart  lungs  brain
B. Leg  heart  lungs  heart  brain
C. Leg  arm  lungs  liver  brain
D. Leg  liver  heart  lungs  brain
6. The diagram shows a human blood sample in a
blood vessel. Where is carbon dioxide found?
(B)
7. The bar chart shows the concentration of
carbon dioxide in blood samples taken from
four different places in the human circulatory
system. Which blood sample was taken from
the pulmonary vein?
(B)
8. The following graph shows how the
concentration of oxygen changes when
the blood flows in the blood vessels.
What could most likely take place in
region X which causes the concentration
of oxygen to increase abruptly?
43
A. Red blood cells in the blood pick up oxygen from the alveoli when it reaches region
X.
B. The body cells in region X return the excess oxygen to the blood.
C. The body cells in region X carry out chemical reactions which produce large quantity
of oxygen.
D. Haemoglobins in the red blood cells lose the ability to carry oxygen abruptly in
region X.
9. Which of the following exerts the highest pressure during the beating of the
mammalian heart?
A. Left atrium
B. Left ventricle
C. Right atrium
D. Right ventricle
10. Cholesterol plague is formed by the accumulation of cholesterol on the wall of
arteries. Which of the following is the reason why a heart attack may occur if the
coronary artery is blocked by cholesterol plague?
A. The rate of heartbeat increases.
B. Less blood is pumped out from the heart.
C. The heart muscle breaks down.
D. Less blood is supplied to the heart muscle.
11. The table shows the characteristics of the blood in one blood vessel in the body.
Oxygen concentration
Carbon dioxide concentration
Pressure
Low
High
High
Which blood vessel contains blood with these characteristics?
A. Aorta
B. Pulmonary artery
C. Pulmonary vein
D. Vena cava
12. Which of the following components of the blood can destroy bacteria that have
entered the body?
(1) Antibodies
(2) Phagocytes
(3) Blood platelets
A. (1) & (2) only
B. (1) & (3) only
C. (2) & (3) only
D. (1), (2) & (3)
44
13. The photomicrograph below shows the
transverse section of two blood vessels connecting
the heart and the lungs.
Which heart chamber is connected to vessel Q?
A. Left atrium
B. Left ventricle
C. Right atrium
D. Right ventricle
14. The diagram below shows a human heart and its
attached vessels.
Which of the following correctly describes the conditions of
the blood in the different vessels?
P
Q
R
A
Oxygenated,
Deoxygenated,
Deoxygenated,
high pressure
low pressure
high pressure
B
Oxygenated,
Deoxygenated,
Deoxygenated,
high pressure
high pressure
low pressure
C
Deoxygenated,
Deoxygenated,
Oxygenated,
low pressure
low pressure
high pressure
D
Deoxygenated,
Deoxygenated,
Oxygenated,
high pressure
low pressure
high pressure
45
S
Oxygenated,
high pressure
Deoxygenated,
low pressure
Oxygenated,
high pressure
Oxygenated,
high pressure
15. Which statement explains why white blood cells are produced in larger quantities
when there is a wound on the skin?
A. To stop the bleeding of blood by clotting
B. To transport more oxygen to the cells nearby for respiration
C. To prevent any unwanted foreign entities from entering the blood
D. To facilitate platelets to form clot
46
Structured Questions
1. The figure below represents some blood cells.
(a) In the figure above, label the cells X, Y and Z.
(b) Describe the structure of X and what it contains.
(c) State the function of cell Y.
(d) State the function of cell Z
(e) Explain why the number of cells Y and Z increase in numbers when a person has
an influenza infection.
(f) What is the fluid that surrounds the cells above?
(a) X: red blood cell;
Y: phagocyte;
Z: lymphocyte
(b) It has a biconcave disc shape to increase surface area to volume ratio for efficient
transportation of oxygen. It contains haemoglobin to transport oxygen. It has no
nucleus so that more space is available to transport oxygen.
(c) To engulf foreign bodies
(d) To produce antibodies
(e) To destroy the influenza virus by producing antibodies and/or engulfing the virus
(f) Plasma
47
2.(a) State the meaning of the followings:
(i) an artery
(ii) a vein
(b) Capillaries have very thin walls surrounded by the body cells. What is the
advantage of having thin walls?
(c) Name two other substances, besides oxygen, which can pass through the wall of
capillaries.
(a)
(ii)
(b)
(c)
(i) An artery is the blood vessel which carries blood away from the heart.
A vein is the blood vessel which carries blood towards the heart.
So that diffusion of substances is easier between the blood and the body cells
Carbon dioxide, glucose
48
3. The diagram below shows a vertical section of human heart
(a) Using the letters provided in the diagram, state all the part(s) which
(i) carry/carries oxygenated blood under low pressure.
(ii) return(s) blood to the heart
(iii) deliver(s) blood to the lungs
(b) Explain why the muscular wall G is thicker than that of F
(c) (i) Name structure E.
(ii) Explain the role of structure E.
(d) Explain the effects on a person if X and Y are faulty.
(e) Complete the following table to indicate the characteristics of blood flow in regions
A, B, C and D.
Characteristics of blood
Region
Higher pressure deoxygenated blood
Lower pressure oxygenated blood
Higher pressure oxygenated blood
Lower pressure deoxygenated blood
(f)(i) To which organ Z does the blood flow to after leaving the heart?
(ii) What would take place when blood reaches organ Z?
(a) (i) R
(ii) P and R
(iii) Q
(b) G has to withstand greater pressure as it has to transport blood furthest compared
to F which only transports blood to the nearby lungs.
(c) (i) Septum
(ii) It prevents mixing of oxygenated and deoxygenated blood. It ensures that blood
reaching all organs are fully oxygenated so that organs function at maximum efficiency.
49
(d) There will be backflow of blood. Heart muscles will enlarge to compensate for
greater pressure needed to force the blood out. Heart disease will develop (heart
enlargement)
(e)
Characteristics of blood
Region
Higher pressure deoxygenated blood
B
Lower pressure oxygenated blood
D
Higher pressure oxygenated blood
C
Lower pressure deoxygenated blood
A
(f)(i) Lungs
(ii) Carbon dioxide diffuses out from the bloodstream into the lungs. Oxygen diffuses
into the bloodstream from the lungs.
50
4. The photomicrograph below shows the cross-sections of two blood vessels lying
side by side.
The compositions of the blood in these two blood vessels are compared as shown in
the table below
Composition of blood
Vessel X
Vessel Y
Oxygen
Lower
Higher
Carbon dioxide
Higher
Lower
(a) With reference to the photomicrograph only, decide which vessel, X or Y, is an
artery. Give a reason for your answer.
(b) Explain how the structure of vessel X is related to its function
(c) With reference to the information given in the table, suggest an organ which X and
Y are associated with. Name X and Y.
(a) X; it has narrow lumen or thick muscular walls.
(b) It has narrow lumen to maintain high pressure blood flow and thick muscular walls
to withstand high pressure.
(c) Lungs: X is pulmonary artery as it is the only artery which has low oxygen content;
Y is pulmonary vein as it is the only vein with high oxygen content.
51
5. The diagram below shows a heart in which the coronary arteries are partially
blocked. It is treated by a coronary bypass operation. This involves grafting sections of
vein from the patient’s leg to the heart.
(a) Name the blood vessel leading into chamber X
(b) Name the organ which receives blood from vessel Y.
(c) The circulation of blood around the body is reduced as a result of the partial
blockage of the coronary arteries. Explain why this happens.
(d) Suggest two reasons why a coronary bypass operation is preferable to a heart
transplant operation.
(e) Suggest an advantage and a disadvantage of using veins instead of arteries in the
grafting surgery.
(a) Pulmonary vein
(b) Lungs
(c) The heart muscles receive less oxygen and nutrients due to blockage. There is not
enough energy to pump blood at high pressure, resulting in poor circulation of blood at
low pressure.
(d) Less risky; difficult to find matching donor;
tissue rejection may occur for heart transplant
(any two)
(e) Advantage: Lumen of veins are wide. This reduces the chances of a relapse as the
lumen is wide enough to reduce the risk of another blockage.
Disadvantage: The wide lumen that reduces pressure means heart muscles receive
blood at lower pressure. The person cannot physically exert himself.
52
During Coronary Artery Bypass Grafting, a healthy artery or vein from the body is
connected, or grafted, to the blocked coronary artery. The grafted artery or vein
bypasses (that is, goes around) the blocked portion of the coronary artery. This creates
a new path for oxygen-rich blood to flow to the heart muscle.
53
6.(a)(i) What is the function of the heart in the human circulatory system?
(ii) State two features of the heart which enables it to perform its function.
(b)(i) List all the components found in blood.
(ii) Which component is responsible for transporting hormones and food substances
around the body?
(c) (i) By taking the left atrium as the starting point, place the sequence of the blood
flow correctly using the following items given below.
Pulmonary vein
Renal artery
Right ventricle
Pulmonary artery
Lungs
Right atrium
Renal vein
Left ventricle
(ii) Name the organ in the body in which the blood would arrive at the end of this
sequence.
(d) State one chemical substance which passes in a higher amount
(i) from capillaries to muscle cells before an exercise
(ii) from muscle cells to capillaries after an exercise
(a) (i) To pump blood so that it can flow in the vessels
(ii) It contains valves to prevent the back flow of blood and it has muscular wall to
exert pressure on blood.
(b) (i) Plasma, white blood cells, red blood cells and platelets
(ii) Plasma
(c)(i) Left atrium  Left ventricle  Renal artery  Renal vein Right atrium  Right
ventricle  Pulmonary artery  Lungs  Pulmonary vein
(ii) Heart
(d) (i) Oxygen
(ii) Carbon dioxide
54
7. The diagram below shows the blood flow containing blood cells in a capillary.
(a)(i) Name the blood cell X.
(ii) What is the main function of X?
(b) White blood cells are made up of lymphocytes and phagocytes. What is their
function?
(c) Name two other components in the blood which are not identified in the diagram.
(d) The capillary wall is one-cell thick. What is the advantage of having a one-cell thick
wall?
(a) (i) Red blood cells (ii) To transport oxygen
(b) To kill bacteria (c) Plasma and platelets
(d) It allows easier diffusion of substances so that the exchange of substances
between the blood and the body cells is more efficient.
55
8. Fill in the blanks in the following table. The first one is done for you.
Blood
vessel
Structure
Function
Arteries
Thick muscular wall
Narrow lumen
Transport blood away from the heart
Transport oxygenated blood only (except
in the case of the pulmonary artery)
Arterioles
Tiny branches of arteries
that lead to capillaries
Transport blood from arteries to capillaries
arteries to capillaries
Arterioles are the main regulators of blood
flow and pressure
Capillaries Capillaries are tiny
(extremely narrow) blood
vessels
Walls are only one cell
thick
Exchange of oxygen, carbon dioxide ,
water, salts, etc between the blood and the
surrounding body tissues.
Venules
Minute branches of veins
that drain blood from
capillaries and into veins
Drain blood from capillaries into veins, for
return to the heart
Veins
Thin muscular wall
Wide lumen
Presence of valves
Transport blood towards the heart
Transport deoxygenated blood only
(except in the case of the pulmonary vein)
56