Chapter Transport Biology SPM

CHAPTER 1: TRANSPORT
LEARNING OBJECTIVE: 1.1 The importance of having a transport system in
some multicellular organisms.
Learning outcome :
A student is able to :
 Identify the problem that could be faced by multicellular organisms in
obtaining their cellular requirements and getting rid of their waste
product.
 Suggest how the problem is overcome in multicellular organisms.
Previous knowledge : Unicellular and multicellular organisms.
CONTENT:
Introduction:
Multicellular Unicellular
Earth worm Frog
Snake
hydra
 All living organisms constantly need to exchange food, waste materials and gases
with their surroundings in order to survive and grow.
 Thus Transport System is needed in order to distribute the food and oxygen
throughout the body and to remove the waste materials such as carbon dioxide.
Biology Form Five Notes © Copyright Maryam Shah 2007
Amoeba sp..
1
LLiivviinngg oorrggaanniissmmss

The substance that are required by
living things
The substance that are needed to be
eliminated from living organisms
 Oxygen
 Nutrients
 Water
 Mineral salt
 Vitamins
 Carbon dioxide
 Nitrogenous waste
How the unicellular obtained their
cellular requirements and eliminated
their waste products
How the multicellular obtained their
cellular requirements and eliminated
their waste products
 Through a process of diffusion
 Example : Transportation of
oxygen and carbon dioxide in
amoeba sp. is through simple
diffusion
 They need a system
 Example :
 Blood circulatory system to
transport nutrient
 Respiratory system to obtain
oxygen and to eliminate carbon
dioxide
O2
The problems that could be faced by multicellular organisms in obtaining their cellular
requirements and getting rid of their waste product:
 The oxygen and nutrients needed by the cells could not be supplied by simple diffusion
through body surface area.
 Neither can waste products be removed quickly enough.
 This is due to the fact that as organisms become larger, the total surface area to
volume ratio becomes smaller. In other words, the cells in multicellular organisms are
situated far away from the external environment.
 These problems are overcome by having a circulatory system to transport substances
throughout the body.
2
Co2

LEARNING OBJECTIVE: 1.2 Synthesising the concept of circulatory system.
Learning outcome :
 State what a circulatory system is
 State the three components of circulatory system in humans and animals
 State the medium of transport in humans and animals
 State the composition of human blood
 Explain the function of blood and haemolymph in transport
Previous knowledge : Circulatory system (lower form)
CIRCULATORY
CIRCULATORY
SYSTEM OF HUMAN
SYSTEM OF HUMAN
BBLLOOOODD HHEEAARRTT THE BLOOD
WHITE BLOOD
CELLS
 What is a circulatory system?
THE BLOOD
VESSELS
Perform various
functions
 Circulatory system is the system of structures consisting of the heart,
blood vessels and the blood which is circulated throughout the body.
 It is also called as vascular system.
 The circulatory system is responsible for the transport of nutrients
and oxygen to cells and the removal of waste products from the
body as well as protection of the body from infections.
 The circulatory system transports oxygen from the lungs and nutrients
from the digestive tract to every cell in the body, allowing for the
continuation of cell metabolism.
VESSELS
PPLLAASSMMAA BBLLOOOODD CCEELLLLSS Perform various
functions
RREEDD BBLLOOOODD CCEELLLLSS WHITE BLOOD PPLLAATTEELLEETTSS
CELLS
3

 The circulatory system also transports the waste products of cell
metabolism to the lungs and kidneys where they can be expelled from
the body. Without this important function toxic substances would
quickly build up in the body.
 The components of circulatory system in humans and animals are:
 Blood
 Blood vessels
 Heart
 The medium of transport in humans and animals
in in
is called is called
Blood Haemolymph
protects the
body from
transports regulates
O2
CO2
DIAGRAM 1: Blood and haemolymph as medium of transport in humans
and animals as well as their distinctive functions.
4
has 3 general functions
through through
important in
the
Medium of transport
Humans and Animals Invertebrates
A blood-like
nutritive fluid
which fills the
entire body
Transportation Regulation Protection
is
Transportation
of water,
inorganic
salts, and
organic
compounds
Lungs cells
Lungs cells
Nutrients, hormones
and antibodies
throughout the body
1pH of body fluids
2body temperature
3water content of the
cells
excessive blood
loss
diseases /
infections
Body Immune
System
Blood Clotting

 The composition of human blood
Human Blood
comprises
55% Plasma 45% Cellular Components
DIAGRAM 2: Composition of human blood
DIAGRAM 3: Major functions of constituents in the plasma
Photograph Structure Functions
5
comprises
Erythrocytes Leucocytes Platelets
ERYTHROCYTES

 Erythrocytes are tiny
biconcave disks, thin in
the middle and thicker
around the periphery.
 Does not have a nucleus.
 7.5 μm in diameter.
 Each of which contain
250 million molecules of
haemoglobin (O2-carrying
protein pigment)
 Provides a large ratio of
TSA/V for gaseous
exchange.
 Haemoglobin is the
material that gives blood its
red colour.
 The haem group that found
in the haemoglobin contains
an iron atom that is the site
for O2 binding.
Blood Cells Structure Functions
White blood cells
(Leucocytes)
 Leucocytes are colourless
and contain nucleus and
mitochondria.
 Irregular in shape and
larger than red blood
cells.
 They are made by the
stem cells in the bone
marrow.
 They are classified as
either granular or
agranular
 Fight infections in various
ways.
 Most activities take place in
the interstitial fluid outside
the blood vessels.
 They can squeeze through
the pores in the blood
capillaries and fight the
pathogens present in the
interstitial fluid.
Platelets
 Platelets are fragments of
large cells from the bone
marrow
 No nucleus and are about
2-3 μm in diameter.
 Important in blood clotting
mechanism
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LEUCOCYTES
Granulocytes Agranulocytes
Neutrophils
Engulf and
digest bacteria
and dead cells
Eosinophils
Release
enzymes to
combat
inflammation in
allergic reaction
Basophils
Involved in
combating
inflammotary
and allergic
reactions
Lymphocytes
Produce the
immune response
against foreign
substances
Monocytes
Engulf and
digest bacteria
and dead cells

LEARNING OBJECTIVE: 1.2 Synthesising the concept of circulatory system.
Learning outcome :
 Describe the structure of human blood vessels
 Explain how blood is propelled through the human circulatory system
 Explain briefly how blood pressure is regulated
 Compare and contrast the circulatory systems in the following: humans,
fish and amphibians.
 Conceptualise the circulatory system in humans
Previous knowledge : blood as a component of circulatory system in previous
lesson.
CONTENT:
 The structure of human blood vessels (Refer to Diagram 4)
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DIAGRAM 4
Characteristic arteries capillaries veins
Wall Thick, muscular,
elastic
One-cell thick, no
muscle or elastic
tissue
Thin, less muscular,
less elastic
Lumen Small Very small Large
Valve No valve No valve
Have valves which
maintain the one-way
flow of blood
Blood pressure high Very low Low
Direction of blood
From heart to the
flow
organs
(away from the heart)
From arteries to
veins
From all parts of the
body to the heart
(blood returns to the
blood)
Blood content
Oxygenated blood
except the pulmonary
artery
Oxygenated blood
At the arteriole ends
and deoxygenated
blood at the venule
ends
Deoxygenated blood
except the pulmonary
veins
Function To transport blood
quickly at high
pressure from the
Allow rapid gaseous
exchange between
the blood and the
Allow blood from the
tissues to return to
the heart
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heart to the tissue body cells by
diffusion
The Human Heart
The structure and function of the human heart
1The heart is a cone-shaped, muscular organ
about the size of a clenched fist.
2The heart pumps the blood which
(a) carries vital materials required by the
body.
(b) removes waste product that the body
does not need
3The human heart has 4 muscular chambers:
(a) The two upper chambers are the atria
and the two lower chambers are the
ventricles.
(b) The atria receive blood returning to
the heart while the ventricles pump
blood out of the heart.
4The heart contracts and relaxes in a
rhythmic cycle.
(a) When it contracts, it pumps blood.
(b) When it relaxes, its chambers are filled
with blood.
5The atria have relatively thin walls and
function as collection chambers.
(a) Right atrium receives deoxygenated
blood from the vena cava
(b) Left atrium receives oxygenated
blood from the pulmonary veins.
6 As the atria contract, blood is pumped into
the ventricles. The ventricles have
thicker walls and stronger contractions
than the atria.
7 The muscular wall of the left ventricle is
thicker than the wall of the right ventricle.
This is because the left ventricles needs to
pump blood to all parts of the body while
the right ventricle pumps blood to the
lungs only.
8 The heart has valves that allow blood to
flow in one direction only.
(a) Tricuspid valve and Bicuspid valve.
(b) These two valves prevent the blood
from flowing back into the atria.
(c) The Semi-lunar valves which are
located at the exits, where the
pulmonary artery and aorta leave the
heart.
(d) These valves prevent blood from
flowing back into the ventricles when
the ventricles relax. (Refer Diagram 5
for detail)
9

Blood flows to the
DIAGRAM 5: The flow of blood in the heart
2
1 Oxygenated blood from the lungs enters the
left atrium through the pulmonary veins.
2 Deoxygenated blood from the rest of the
body enters the right atrium via the vena
cava.
3 As blood fills the atria, the atria contract and
push the blood through the bicuspid and
tricuspid valves into the two ventricles.
Blood goes to the
4 When the ventricles contract, the semi-lunar
valves are forced open and blood is
pushed into the pulmonary arteries and the
aorta.
5 Deoxygenated blood is pumped through the
pulmonary arteries to the lungs.
6 Oxygenated blood is pump through the
aorta to the rest of the body.
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Blood goes to the right lung
Blood comes from
left lung
5
Blood comes from
right lung
1
left lung
5
Blood comes from the head and arms
3
4
3
4
6
body
1
Bicuspid valve
Key: Oxygenated blood; Deoxygenated
t blood.

 Explain how blood is propelled through the human circulatory system
The circulation of blood in humans is a result of the following action:
(a) The pumping of the heart
(b) Contracting of the skeletal muscles around veins
 The pumping of heart
Initiated &
coordinated by
the
Located in the
Interconnecte
d tissues Myogenic Myogenic
Key: SA – Sinoatrial; AV – Atrioventricular;
p.m- pacemaker
Pacemake
r
Pacemake
r
11
Hear
t
Made up of
Cardiac
muscle
Characterized as
means
Interconnecte
d tissues
allows
Electrical
impulses to
spread rapidly
through the
heart
Need no
stimulation by
nerve impulses
when contracts
neither relaxes
causing
Wall of the
right atrium
generates
Electrica
l
impulses
Controlled by
contractio
n
of the
heaArptex of
the heart
Parasympathetic
Nerves
Sympathetic
Nerves
Hormones
(Adrenaline)
radiated
from
Purkinje
fibres
SA node
(Primary p.m)
causing
Bundle of
His fibres
AV
node
Impulses
transmitted to
bundle
branches
The spread of impulses
over the walls of atria →
contraction of atria
DIAGRAM 6: The
position of the SA
node, AV node
andPurkinje Fibres

The contraction pushes the blood out to the lung and
body. The sound of the heart contracting and the
valves opening and closing produces a characteristic
“lub-dub” sound. The lub sound is associated with the
closure of the atrioventricular valves while dub
indicates the closing of the semilunar valves.
 Contraction of skeletal muscles around veins
 Blood is sent through the circulatory system with the help of the
contractions of the skeletal muscles around the veins.
 When skeletal muscles contract, the veins constrict and blood is pushed
along through the veins. The veins have one-way valves that allow blood
to flow in the direction towards the heart
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Semilunar
valves
Atrioventricular
valves

 The regulatory mechanism of blood pressure
1. Blood pressure is defined as the pressure which is exerted by the blood
when it flows along a vessel.
2. It is greater in arteries than in veins
3. Flows from high pressure areas to low pressure areas.
4. SYSTOLE STAGE –contraction of the ventricles where blood pressure
is the highest.
5. Normal Human blood pressure: 120/80 mmHg
6. 120 – is the systolic pressure.
7. 80 – is the diastolic pressure ( the lowest pressure during the relaxation
phase (DIASTOLE STAGE)
8. Regulated by negative feedback mechanism.
9. Baroreceptors are pressure receptors located at the ARC OF THE
AORTA and CAROTID ARTERIES. (Refer Diagram 7 for detail)
10.These receptors sent nerve impulses continuously to the cardiovascular
centre in the medulla oblongata to help regulate the blood pressure.
DIAGRAM 7: Baroreceptors in the arch of the aorta and carotid arteries
Action of effectors
Blood pressure
increases (for
example, during
physical
exercise)
Normal blood
pressure
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weaker cardiac muscle contraction
lower the heartbeat rate
Smooth muscles of the arteries relax and the
arteries dilate. This reduces the resistance of
blood flow in the blood vessels (Vasodilation).
Blood pressure
decreases
Baroreceptors in
arch of aorta and
carotid arteries
are stimulated
increased
rate of
nerve
impulses
sent to
cardiovascular
centre in medulla
oblongata in the
brain
Sends nerve
impulses to the
effectors

Baroreceptors in
arch of aorta and
carotid arteries
are less
stimulated
decreased
rate of
nerve
impulses
sent to
Action of effectors
cardiovascular
centre in medulla
oblongata in the
Stronger cardiac muscle contraction
Increase the heartbeat rate
Smooth muscles of the arteries contract thus
increases the resistance of blood flow in the
blood vessels (Vasoconstriction)
Blood pressure
decreases (for
example, when
in a state of
shock)
Normal blood
pressure
Blood pressure
increases
brain
Sends nerve
impulses to the
effectors
 Compare and contrast the circulatory systems in the following:
humans, fish and amphibians.
2 types of circulatory systems:
1. Open circulatory system
2. Closed circulatory system
1. The open circulatory system consist of:
 one or more heart
 a network of vessels
 and a large open space within the body (haemocoel).
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DIAGRAM 8: The negative feedback regulation of blood pressure

One or more hearts pump the
haemolymph through the
vessels and into the haemocoel.
The haemocoel contains the soft
internal organs and is filled with
haemolymph.
Here, a chemical exchange between
the haemolymph and the body
cells takes place.
The haemolymph flows from the
hearts into the haemocoel when
the hearts contract.
When the heart relax, the
haemolymph is drawn through
pores called ostia back into the
hearts.
The ostia are equipped with valves
that close when the hearts
contract.
2. The closed circulatory system comprises single and double circulatory
system.
Single circulatory system
Consists of 1 atrium & 1 ventricle
Blood flows from ventricle to the gill
capillaries (gaseous exchange
occurs)
Gill capillaries converge into a vessel
that carries the oxygenated blood to
the body capillaries or systemic
capillaries (o2 diffuses into the
tissues while co2 diffuses out of the
tissues and into the capillaries)
The deoxygenated blood then returns to
the atrium of the heart through the
veins.
Single circulatory means having only
one circuit of blood flow that is
the blood goes to the gill
capillaries and then to the
systemic capillaries.
15
The open circulatory system
Circulatory System In Fish

Double circulatory system
Frogs and other amphibians have three-chambered
heart (two atria & one
ventricle)
Deoxygenated blood from the body is
delivered into the right atrium;
while oxygenated blood from the
lungs is delivered into the left
atrium.
Blood from both atria then enters a
single ventricle. Although there is
some mixing of oxygenated and
deoxygenated blood inside the
ventricle, most of the oxygenated
blood remains in the left portion of
the ventricle while deoxygenated
blood tends to remain in the right
portion of the ventricle.
16
Circulatory System In Amphibians
(b) Frog

The ventricles then pumps blood through
the pulmocutaneous circulation
and the systemic circulation.
The pulmocutaneous circulation leads to
the gas exchange tissues, which are
the lungs and skin. Here, gaseous
exchange occurs.
The oxygenated blood returns to the
left atrium of the heart and most of
it is then pumped into the
systemic circulation.
The systemic circulation carries
oxygenated blood to body tissues &
returns the deoxygenated blood to
the right atrium through the veins
Since the blood flows in two separate
circuits; pulmocutaneous
circulation and systemic circulation,
the system is identified as double
circulatory system.
(b) Frog
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• Humans have four-chambered heart:
two atria and two completely
separated ventricles.
• Deoxygenated blood and oxygenated
blood do not mix.
• The four chambers ensure an efficient
and rapid delivery of highly oxygenated
blood to the organs of the body.
• In the pulmonary circulation,
deoxygenated blood in the right ventricle
is pumped into the pulmonary arteries.
• These arteries carry the blood to the
lungs where it passes through the blood
capillaries.
• This allows the removal of co2 and the
intake of o2 from the air into the alveoli.
Circulatory System In Humans

 Conceptualise the circulatory system in humans
18
 The circulatory system in humans comprises two separate circulations
that are the pulmonary circulation and the systemic circulation.
 The pulmonary circulation carries blood from the heart to the lungs
and back to the heart while the systemic circulation carries blood from
the heart to all parts of the body and back to the heart.
 These two separate circulations make up the double circulatory
system.
 It means in a complete circulation, the blood flows through the heart
twice.
 The Double Circulation is to ensure that oxygenated blood is
constantly delivered to the cells.
• In the systemic circulation, blood is
carried from the heart to the other part of
the body except the lungs.
• The oxygenated blood from the lungs
returns to the left atrium and flows into
the left ventricle.
• The oxygenated blood is then pumped
into the systemic capillaries via the aorta.
• Since there are two separate circuits; the
systemic and the pulmonary circulations,
humans are known to have a double
circulatory system.
• In a complete circulation, the blood flows
through the heart twice.
• This is to ensure that oxygenated blood
is constantly delivered to the cells.

LEARNING OBJECTIVE: 1.3 Understanding the mechanism of blood
clotting.
Learning outcome :
 Explain the necessity for blood clotting at the side of damaged blood
vessels.
 Explain the mechanism of blood clotting.
 Predict the consequences of impaired blood clotting mechanism in an
individual.
Previous knowledge : The general function of blood in previous lesson.
CONTENT:
 Blood clotting is necessary to:
(a) prevent serious blood loss when a person is injured
(b) maintain blood pressure.
(c) maintain the circulation of blood in a closed circulatory system.
(d) prevent the entry of microorganisms and foreign substances into
the body through the damaged blood vessels.
 Blood clotting mechanism
2
1 Platelets stick rapidly
5
6
19
When a blood vessel in
the body is damaged,
the connective tissue in
the vessel wall is
exposed to blood
plasma
to the collagen fibres
in the connective tissue
and release chemicals
called clotting factors
that make the
surrounding platelets
sticky
3
The aggregation of
platelets forms a plug
called a platelet plug.
A platelet plug can stop
blood loss completely if
the damage to the
vessel is small.
4
When the damage in the
vessel is severe, the plug
is reinforced by a clot of
fibrin which is formed
through a series of steps.
The clumped platelets,
the damaged cells and
clotting factors in the
plasma form activators
These activators
(thromboplastins), together
with calcium ions and
vitamin K, convert the
prothrombin (an inactive
plasma protein) to thrombin
(active plasma protein which
acts as an enzyme)

7
8
9
 Consequences of impaired blood clotting mechanism in an individual.
Blood clotting mechanism would be impaired if there are defects in the:
(a) blood vessels
(b) blood clotting factors or in
(c) platelets.
There are 2 types of blood disorders identified as the consequences of
impaired blood clotting mechanism:
(a) Haemophilia
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Thrombin catalyses
the conversion of the
soluble protein
(fibrinogen) in
blood plasma into
the insoluble fibrin.
Fibrin will aggregate to
form a mesh of long
threads over the wound,
trapping red blood cells
thus sealing the wound.
The resulting blood clot
hardens when exposed
to air to form a scab.
(Continue to the next page)
(from previous page)

(b) Thrombophilia
(a) Haemophilia
 Haemophilia is a hereditary illness.
 It is caused by a lack of clotting factors.
 It impairs the body’s ability to control bleeding.
 When a blood vessel is injured, a scab will not form.
 The vessel will continue to bleed excessively for a very long
period of time.
 The bleeding can be external, due to skin by a scrape, a cut or
an abrasion.
 It can be internal, into muscles, joints or as hollow organs.
21

 It might therefore be visible as skin bruises or invisible like
bleeding in the brain.
 For haemophiliacs, the bleeding even from minor cuts can
cause excessive bleeding and death.
 Today, haemophilia can be controlled quite successfully.
 Regular injections of clotting factors like Factor VIII can
prevent excessive bleeding.
(b) Thrombophilia
 Thrombophilia is the reverse when compared to haemophilia.
 It is caused by a defect in the blood vessel walls.
 The present of a blood clot attaching to the vessel walls will
decelerate the blood flow.
Defect in the vessel wall: the present of a blood clot
 Impaired blood clotting factors and mutation of prothrombin
also can cause thrombophilia.
 People with thrombophilia have an increased tendency to
dangerous blood clots in the arteries or veins.
 A clot formation inside an unbroken blood vessel is known as
thrombosis.
 The blood clot is called thrombus.
 Sometimes, a thrombus may dislodge and move along the blood
circulatory system.
 The blood clot which moves in a bloodstream is called an
embolus.
 The embolus moves along until it gets stuck to a narrow artery.
 When this happens, the blood flow in the blood vessel is
obstructed.
 The consequences due to embolism depend on the size of
embolus and which artery it is obstructing.
 If a clot is lodged in a coronary artery, the cardiac tissue will
no longer receive oxygenated blood.
22

 The cardiac tissue may die and leads to a heart attack.
 If a clot blocks the blood flow to the brain, it may cause stroke.
LEARNING OBJECTIVE: 1.4 Synthesising the Concept of Lymphatic System.
Learning outcome :
 Describe the formation of interstitial fluid.
 State the composition of interstitial fluid.
 State the importance of interstitial fluid.
 Describe the fate of interstitial fluid.
Previous knowledge : The content of blood plasma in previous lesson.
CONTENT:
 How is interstitial fluid formed?
 When blood flows through the capillaries a pressure is exerted on the
capillaries.
 The pressure is called hydrostatic pressure.
23

 The pressure is generated by the pumping action of the heart.
 At the same time, osmotic pressure is created between the capillaries
and surrounding tissues.
 This is due to the inability of large solute to penetrate the capillary
walls.
 However, the hydrostatic pressure is more than the osmotic pressure.
 So, the fluid from the blood is pushed out by filtration.
 The net pressure inside the artery is more than the outside.
 Hence the water is forced out of the capillaries by filtration and fills
the spaces between the cells.
 The water which contains dissolved substances forms interstitial fluid.
 What are the compositions of interstitial fluid?
 Interstitial fluid is a clear fluid which originates from blood.
 Therefore it contains most of the substances found in the blood such as
water, dissolved nutrients, hormones, waste products, gasses and small
proteins except erythrocytes, plasma protein and platelets.
 Leucocytes are present in the interstitial fluid since they can squeeze
through the pores in between the capillary cells.
 What is the importance of interstitial fluid?
 Fills the space found in between the cells.
 Acts as the medium of diffusion of nutrients (from the blood to the
cells) and waste products (from the cells into the blood)
 Provides optimal environment for the cells.
 Nutrients uptake and waste products elimination are examples of
cellular activities.
 A constant and stable environment is needed for cellular
activities.
 This environment of individual cell is the interstitial fluid.
 For example, the pH of interstitial fluid is kept between pH 7.35
to pH 7.45 for optimal cellular activities.
 The optimal temperature that is kept constant is 370C.
 Neurotransmission between neuron and target cells happen across
the interstitial fluid.
 Intercellular communication becomes easier with the presence
of interstitial fluid, hormones and neurotransmitters.
 They fill up the gaps between cells.
 For instance, leucocytes release hormone into the interstitial fluid.
 These hormones diffuse to the nearby target cells, through
interstitial fluid.
24

 The more specialised synaptic signalling occurs through
neurotransmitters.
 Neurotransmitters are released into the interstitial fluid by
neuron.
 The neurotransmitters are transmitted to the target cells through
interstitial fluid.
 Provides moist medium for the cells.
 A cell needs moist environment for effective exchange of
substances.
 The interstitial fluid bathes the cells.
 The cells environment therefore becomes moist thus allows the
exchange of materials to occur effectively.
 What is the fate of interstitial fluid?
 About 90% of the fluid that leaves the blood at the arterial end of the
capillary re-enters at the venous end.
 This is due to the net pressure inside the capillary is less than the
interstitial space and also as the blood flows towards the venous
end, it becomes more concentrated with solutes.
 This build-up of solutes induces osmosis.
 Hence, the interstitial fluid is drawn back into the blood vessel again.
 The interstitial fluid must be returned to the circulatory system to
maintain the normal blood volume.
25

 However, not as much fluid is absorbed back into the blood capillary
as is filtered out.
 About 10% of the fluid that still remains in the interstitial space is
equivalent to about 4 litres of fluid lost from the blood capillaries each
day.
 The fluid loss is returned to the blood through the lymphatic
system.
 If the interstitial fluid is not passed into the lymphatic system, the area
will swell up. This condition is called oedema.
LEARNING OBJECTIVE: 1.4 Synthesising the Concept of Lymphatic System.
Learning outcome :
 Describe the structure of lymphatic system.
 Explain how the lymphatic system compliments the circulatory system.
 Compare the content of blood, interstitial fluid and lymph.
 Predict what will happen if interstitial fluid fails to return to the
circulatory system.
 Conceptualise the relationship between the lymphatic system and
circulatory system
Previous knowledge : The importance of interstitial fluid in previous lesson.
CONTENT:
 The structure of lymphatic system.
 The lymphatic system is also a circulatory system.
 It has vessels that branches out through the body except for the brain.
 They begin with blind-ended capillaries.
26

 The blind-ended capillaries originate in connective tissues of nearly
all parts of body.
 The capillaries converge into small lymph vessels which eventually
converge into larger vessels.
 Within the lymphatic vessels there are one-way valves that ensure the
continuous flow of the lymph away from the tissues. These valves also
prevent the backflow of lymph.
 Located at intervals along the lymphatic vessels are lymph nodes.
These nodes produce and store lymphocytes; hence they help to
defend the body against infection.
 The lymphatic vessels drain into two larger ducts:
1. Right lymphatic duct
2. Thoracic duct.
27

Structure of Lymphatic vessel A – Afferent vessel; B – nodule; C –Valve
D – Capsule; E – Efferent vessel
 The right lymphatic duct receives lymph from the right arm, shoulder
area and the right side of the head and neck.
 The thoracic duct receives lymph from the left of the head, neck and
chest, the left upper limb and the entire body below the ribs.
 These ducts drain to the large veins in the neck: the right and left
subclavian veins. Hence, lymph drains back into the blood.
 Lymphatic system does not have a pump.
 The lymph is propelled along its vessels by:
1. one-way valves
2. skeletal muscles contraction
3. breathing movement
4. Intestinal movement
5. smooth muscle contraction of lymphatic vessels
 The lymphatic system includes other body organs such as thymus and
spleen.
28
E C
D
A
B
Lymph
nodes

 Thymus is a soft, bilobed organ which is located behind the sternum.
It is surrounded by a connective tissue capsule. The connective tissue
extends inside the thymus thus dividing it into lobules. The lobules
contain lymphocytes which eventually will mature into T-lymphocytes
(or T-cells) in thymus.
 The spleen lies in the upper abdominal cavity. It is the largest
lymphatic organ. The spleen contains blood instead of lymph. The
white pulp of spleen contains lymphocytes while the red pulp contains
red blood cells, macrophages and lymphocytes.
 Explain how the lymphatic system compliments the circulatory
system
1. By maintaining the blood volume and pressure
 Plasma is forced out into the interstitial spaces when the blood
flows through the capillaries.
 85% of the fluid that leaves the blood at the arterial end of the
capillary re-enters at the venous end.
 The other 15% diffused into the lymphatic vessels to form
lymph.
 The lymphatic system restores excess interstitial fluid into the
circulatory system.
 This process maintains the normal blood volume and hence the
pressure.
2. As means of transportation of fatty acids and plasma proteins
 Blood capillaries are not permeable to plasma protein.
 On the other hand, lymphatic vessels are permeable to big
molecules such as plasma proteins and fatty acids.
 They are porous.
 So the lymphatic capillaries collect any plasma protein in the
interstitial space.
 These proteins might have leaked into the interstitial space.
 In the small intestine, the fatty acids are not absorbed into the
capillaries.
 Instead they are absorbed into the lymphatic vessels called
lacteals.
 Lacteals transport fatty acids and drain them into the
circulatory system.
3. Centre of production of blood cells
 Monocytes, macrophages and lymphocytes are cells found in
the blood.
 They defend the body against pathogens.
 These blood cells are produced by spleen and lymph nodes.
 These cells mature and are released into the circulatory system.
29

4. Centre of destruction of blood cells
 The spleen filters worn out red blood cells and deformed
platelets.
 Macrophages found in the spleen destroy these blood cells by
phagocytosis.
 Compare the content of blood, interstitial fluid and lymph.
BLOOD INTERSTITIAL
FLUID
LYMPH
SIMILARITIES
Contents:
1. Water is the main component.
2. All of them contain glucose,amino acids,minerals,
vitamins,hormones,enzymes and respiratory gases.
Functions:
1. All of them make up the internal environment of the body.
2. All of them function in transport of substances.
3. All of them function in the body’s defense system.
DIFFERENCES
30

BLOOD
Contents:
1. Erythrocytes present.
2. Plasma proteins
present.
3. Contains white blood
cells.
Functions:
1. Transports mainly
water-soluble
substances.
INTERSTITIAL FLUID
Contents:
1. Erythrocytes absent.
2. Plasma proteins
absent.
3. Has the least white
blood cells.
Functions:
1. Functions in
providing nutrients to
body cells and
removing their waste
products.
LYMPH
Contents:
1. Erythrocytes absent.
2. Plasma proteins
absent.
3. Has the most white
blood cells.
Functions:
1. Transports mainly
lipid-soluble
substances.
Comparison on the content of blood, interstitial fluid and lymph
 Predict what will happen if interstitial fluid fails to return to the
circulatory system.
 If the excess fluid is not returned to the bloodstream, body tissues will
become swollen because too much fluid is retained.
 An excessive accumulation of interstitial fluid in the spaces between
the cells will result in a condition known as oedema. It is not a disease
but a clinical condition.
 It occurs when the body’s normal balance of fluid intake and output is
disturbed.
 Oedema may be caused by a blocked lymphatic vessel.
 A prolonged oedema will cause the skin to swell and stretch. The skin
will become taut and shinny.
31

 The prolonged and excessive swelling will cause the connective
tissues under the skin to be damaged.
 This will lead to skin hardening.
 Conceptualise the relationship between the lymphatic system and
circulatory system
Interstitial space
Venule
arteriole
 As the blood flows through the circulatory system, fluid from the
plasma diffuses into the interstitial spaces in the arterial end.
 The interstitial fluid is reabsorbed into the bloodstream at the
venous end.
 The interstitial fluid that has not been reabsorbed into the
bloodstream diffuses into the lymph capillaries.
 The lymph collected throughout the body drains into the blood
circulation via the thoracic ducts and the right lymphatic duct
that join the veins in the neck.
Comparison between the blood circulatory system and the lymphatic system.
32
lymph capillary
network of capillaries
body cells
lymphatic vessel
Interstitial fluid
lymph

Circulatory System Similarities Lymphatic System
 Both are circulatory systems
 The medium is contained in vessels
Circulatory System Differences Lymphatic System
 Closed continuous
circuit throughout the
body.
 Comprises heart,
arteries, veins and
capillaries.
Structure  Open circuit from the
tissues into lymphatic
vessels.
 Comprises right
lymphatic duct and
thoracic duct, lymph
nodes, lymphatic
vessels and capillaries
thymus and spleen
Blood Medium Lymph
Erythrocytes,
Composition of
leucocytes, platelets,
medium
dissolved substances,
waste products and
protein plasma.
Leucocytes, dissolved
substances, waste
products and protein
plasma.
Collects and distributes
oxygen, nutrients, waste
products, and hormones
to the tissues of entire
body.
Role of medium Collects and removes
waste products left
behind in the tissues.
By the kidneys. Filtration By lymph nodes.
Blood is visible and
damaged blood vessels
caused obvious signs
Vessel damage Lymph is invisible and
damaged lymphatic
system is difficult to
detect
Blood is propelled
throughout the body by
the pumping of the heart
and the muscular
movement.
Propulsion Lymph is not pumped. It
passively flows from the
tissues into the lymph
capillaries aided by
muscular movement,
breathing mechanism
and blood circulation.
33

LEARNING OBJECTIVE: 1.5 Understanding the role of the circulatory
system in body’s defense mechanism
Learning outcome :
 State another function of the circulatory system.
 Identify the three lines of defence mechanism.
 Describe phagocytosis.
 State the meaning of antigen and antibody.
 State the meaning of immunity and immunisation.
 Relate antigen and antibody to immunity.
 Name and give examples of various types of immunity.
 State the effects of human immunodeficiency virus (HIV) on the body’s
defence mechanism.
 Describe the transmission of HIV.
 Suggest ways to prevent the spread of acquired immune deficiency
syndrome (AIDS).
Previous knowledge : The general functions of blood circulatory system in
previous lesson.
CONTENT:
 State another function of the circulatory system.
Besides transport, the circulatory system of our body is also important to
protect our body from infectous diseases caused by harmful
microorganisms called pathogens.
 Identify the three lines of defence mechanism.
Defence Mechanism
Comprises of
Classified into Classified into
Tears n Saliva; Immune System
HCl (gastric juice)
34
Non Specific Specific
First line
of defence
Second line
of defence
Third line of
defence
Consist of
Consist of
Skin
Mucous
membrane
Phagocytic
white
blood cells
by way of
Production of
antibody by the
lymphocytes

 Describe phagocytosis.
Pseudopodium
Bacteria-containing
vacuole
Enzyme-containing
lysosome
 State the meaning of antigen and antibody.
Antigen is a protein molecule or soluble polysaccharides that can be
found in the walls or membranes of a pathogen while antibody is a
globulin protein molecule produced by lymphocytes in response to the
entry of pathogens or antigens.
 State the meaning of immunity and immunisation.
Immunity is body’s ability to fight diseases caused by infection of
pathogens.
Immunisation is the process of obtaining immunity through either
vaccination or injection of antiserum.
 Relate antigen and antibody to immunity.
I mmunity is the body’s ability to fight diseases caused by infection of
pathogens or any foreign substance when introduced into the body. The
foreign substance which is also known as antigen will induce the
production of antibodies by the lymphocytes. Antigen is destroyed and
35
A B
C D E
A - Neutrophyl moves towards the bacteria once it senses the
chemical secretions released by the microbe. (Chemotaxis)
B - Neutrophyl attaches itself against the bacteria. (Adherence)
C - Neutrophyl projects its pseudopodium to trap the bacteria into
a vacuole. (Ingestion)
D - The enzyme-containing lysosome fuses with the bacteria-containing
vacuole.
E - The bacteria cell is digested by the enzyme and the product of
the digestion is absorbed into the entire cell of neutrophyl.
(Digestion)

antibodies remain in the body. The infected person gets well. Further
entry of the same type of antigen is quickly destroyed by antibodies
caused by the presence of memory cells. The person does not get ill
again. He is said to be immuned to the disease. This is known as the
immune response.
 Name and give examples of various types of immunity.
 State the effects of human immunodeficiency virus (HIV) on the
body’s defence mechanism.
During HIV infection, the virus attacks the lymphocytes known as T-Cells
which are responsible in protecting the body from infection of
pathogens. The reduction of the number of T-cells cause the improper
function of the immune system to fight against HIV as well as other
secondary infections (caused by bacteria and other viruses).
 Describe the transmission of HIV.
HIV can be transmitted through seminal fluid, blood, breast milk and
vaginal discharge. Transmission may occur during blood transfusion from
donor to recipient; or during sexual contact with an HIV carrier or AIDS
patient; or through sharing of needles especially among drug addicts; or
from an HIV positive mother to the baby either during the foetal stage or
during breast feeding.
36
IMMUNITY
Comprises of
ACTIVE IMMUNITY PASSIVE IMMUNITY
Comprises of Comprises of
Natural Active
Immunity
Artificial
Acquired
Active
Immunity
Natural
Passive
Immunity
Artificial
Acquired
Passive
Immunity
Examples
Examples Examples Examples
Tuberculosis,
Smallpox and
Measles
Rubella,
Hepatitis B,
Poliomyelitis
Antibody
found in
colostrum
during breast
feeding
Antiserum for
tetanus and
diphtheria

 Suggest ways to prevent the spread of acquired immune deficiency
syndrome (AIDS).
Avoiding drug use and never share needles for drugs, steroids,
medications, tattooing or body piercing.
Counselling to the HIV positive patients, so that they do not spread the
virus to others
Practising safe sex using condoms as a barrier to prevent contact with
infectious semen
Educating the school children and public about the risk factors of AIDS
through awareness campaigns
Strict screening of blood before transfusion
37

LEARNING OBJECTIVE: 1.6 Appreciating a Healthy Cardiovascular System
Learning outcome :
 Select and practise suitable ways to maintain a healthy cardiovascular
system
Previous knowledge : The functions of cardiovascular system in previous
lesson.
CONTENT:
 Cardiovascular diseases and its descriptions:
Type of cardiovascular diseases Definition of diseases
Heart Failure The inability of the heart to pump
blood at an adequate rate
Heart Attack Sudden interruption or insufficient
blood to the heart
Stroke A sudden loss of brain function caused
by a blockage or a rupture of a blood
vessel to the brain
Cardiomyopathy Disease or disorder of the heart muscle
High Blood Pressure High pressure in the arteries
 Risk factors contributing to cardiovascular diseases:
38
High Blood
Pressure
The heart works
harder than normal
The heart expands
and contracts at a
faster rate
Heart & arteries
become more
prone to injuries
Diet high in LDL stress
(bad cholesterol)
Heart attacks, strokes, and
arteriosclerosis
makes
As a result
thus
increases the risk of
As a consequence
caused by

High Blood
cholesterol
Physically
inactive
 Ways to maintain a healthy cardiovascular system:
1. Avoid smoking - The nicotine content in a cigarette smoke will cause
the contraction of artery and increase the blood pressure. As a result the
heart has to pump harder in order to ensure the blood flows.
2. Avoid misused of drugs - Drugs like cocaine can cause irregular beat
of the heart and therefore might lead to heart attack and stroke.
3. Maintain suitable body weight - Maintaining body weight according
to Body Mass Index (BMI) is advisable to reduce the risk of having
high blood pressure and cardiovascular diseases.
4. Take healthy food (balanced diet) - Low in salt and sugar content, low
in saturated fat and cholesterol.
5. Eat more fruits and vegetables - Antioxidant – containing food,
vitamins A, C and E may destroy the free radicals that damage the
artery wall
6. Stay fit - Optimum exercise for 30 minutes every 3 times a week may
help you to hinder stress and reduce body weight.
39
Obesity and
Overweight
coronary heart
diseases, stroke
& peripheral
vascular
diseases
over intake of
carbohydrates n fats
Improper diet
Lacks of vitamin Bs
and folic acid in diet
amount of amino acid
Homocysteine
found in the blood
The oxidation of
good cholesterol to
LDL
caused by
caused by
increases
promotes
closely related to
Diabetes
mellitus
Low in High-density related to
Lipoprotein (HDL) and high
triglycerides levels
Tobacco
smoke

LEARNING OBJECTIVE: 1.7 The Transport of Substances In Plants
Learning outcome:
A student is able to:
 State the necessity for transport of substances in plants.
 Identify the vascular tissue in stem, root and leaf.
 State the role of vascular tissue in the transport of substances.
 Describe the structure of vascular tissue.
 Relate the structure of xylem to transport.
 Relate the structure of phloem to transport.
 Predict the effect of removing a ring of phloem tissue from a plant.
Previous knowledge : The concept of transport of substances in the human
circulatory system had been studied in previous lesson.
CONTENT:
 State the necessity for transport of substances in plants.
Water and mineral salts absorbed by the roots have to be transported to
all parts of the plant. Water is an important component of cells. It acts as
solvent and is often a reactant in cell metabolism. Mineral ions are
required for chlorophyll synthesis, healthy plant growth and
development. Organic food materials synthesised by the leaves during
photosynthesis need to be sent to growing regions, storage organs and
other parts of plants.
 Identify the vascular tissue in stem, root and leaf.
 The vascular tissues transport substances in plants.
 There are two types of vascular tissues: xylem and phloem.
 Xylem transports water and dissolved mineral salts absorbed by the
roots up the stems and to the leaves. In woody plants, the xylem
tissue also provides mechanical support to the plant.
 Phloem transports organic substances from the leaves down to the
storage organs and from the storage organs such as the roots up to the
growing regions such as the buds.
 Vascular tissues are found in the roots, stems and leaves of a plant.
40

The various arrangement of vascular tissue in root, stem and leaf
 Describe the structure of vascular tissue.
 The stem has an epidermal layer that helps maintain the shape of the
stem.
a. In young plants, the epidermal cells secrete a waterproof cuticle.
b. In older plants, the epidermis may be absent, and is replaced by
bark.
 Inside the epidermis is the cortex layer. The cortex layer is made up of
collenchyma cells which provide support and flexibility to the stem.
 The inner parts of the stems consist of vascular bundles and the pith
which is the central region of a stem.
a. The pith is used for food storage in young plants.
b. The pith may be absent in older plants, making them hollow.
 In dicotyledonous plants, the vascular tissues of the stem are
grouped together to form vascular bundles.
a. The vascular bundles are arranged in a ring around the pith.
41
The Stem

b. In each vascular bundle, xylem is found towards the inside of the
stem with the phloem on the outside. A tissue called the cambium
lies between the xylem and the phloem.
 In monocotyledonous plants, the vascular bundles are scattered
throughout the stem.
Dicotyledonous Stem
Vascular
bundle
Note that: The vascular bundle encircles the
pith. The phloem is found on the outer side
while xylem on the inner side of the bundle.
Vascular
tissue
Note that: The vascular bundles are
scattered throughout the stem
Note that: The vascular bundle is in a star
shape whereby the phloems fill the area
between the xylems
Note that: The vascular bundles form a ring
around the pith, with the xylem tissue
alternating with the phloem tissue.
42
The root
Phloem
Xylem
Phloem
Xylem
Monocotyledonous Stem
Dicotyledonous Root
Phloem
Xylem
Pith
Phloem
Xylem
Monocotyledonous Root
Cambium
Pith

 The outmost layer is the epidermis. The epidermis of the roots does not
have waxy cuticles.
 The epidermis absorbs water and dissolved mineral ions from the soil.
 Specialised epidermal cells grow outwards to form root hairs.
 Root hairs increase the surface area for water absorption.
 The region between the epidermis and the vascular cylinder is the
cortex. The cortex is made up of parenchyma cells which store starch
grains.
 Located immediately after the cortex is a single layer of cells called the
endodermis.
 Next to the endodermis is the pericycle. The pericycle consists of
sclerenchyma tissue which provides mechanical support for the roots.
 In the roots, the vascular tissue is located in the vascular cylinder
consists of vascular tissue and the pericycle.
 The vascular tissues of roots are continuous with the vascular tissues of
stems.
 In a dicotyledonous plant, the xylem radiates from the centre of the
vascular cylinder, usually forming the shape of a star while the phloem
fills the area between the xylem.
 In a monocotyledonous plant,
a. the vascular cylinder has a central core called the pith.
b. the pith contains parenchyma cells.
c. the vascular tissues form a ring around the pith, with the xylem
tissue alternating with the phloem tissue.
43
The leaf
Xylem
Phloem
Vascular
bundle

 The leaf consists of a broad portion called the lamina (leaf blade).
 The leaf blade is connected to the stem by a stalk called the petiole.
 Inside the petiole are the vascular tissues of xylem and phloem that are
continuous with those in the stem, root and lamina.
 The leaf blade contains leaf veins. Vascular tissues are found in the
leaf veins.
 Xylem forms the upper part of a vascular bundle in the leaf while
phloem forms the lower part of the vascular bundle.
a. The xylem transports water and mineral salts to the leaves.
b. The phloem transports sucrose and other products of
photosynthesis from the leaves.
 Relate the structure of xylem to transport.
 Xylem contains four types of cells:
1. xylem vessels
2. tracheids
3. fibres (a type of sclerenchyma)
4. parenchyma
 The parenchyma stores food substances while the fibres provide
support to the xylem.
 Xylem vessels and tracheids are water-conducting cells.
 They are elongated cells arranged end to end.
 During growth, the walls of the xylem vessels and tracheids are
thickened with lignin deposits making them strong and impermeable
so that they do not collapse under the tension created by the upward
pull of water during transpiration (transpirational pull).
 The lignin also prevents the entry of food substances. Hence, the
cytoplasm of these cells disintegrates leaving a cavity in the centre of
the cells. As a result, mature xylem vessels and tracheids are hollow
and dead.
 The walls of the xylem vessels and tracheids are perforated by a
series of holes called pits. The pits allow water and mineral salts to
pass sideways between the cells.
44
Sclerenchyma
cells
Parenchyma
cells
Tracheids Xylem vessel

 Tracheids are longer and have a smaller diameter compared to xylem
vessels. They are pointed at the ends. The end walls breakdown in
the pits and this allows water to pass from cell to cell.
 The end walls of the xylem vessels are open so that the cells join end
to end to form a long continuous hollow tube.
 This arrangement allows water to flow upwards continuously from
one cell to the next.
 Relate the structure of phloem to transport.
 Phloem tissue is composed of four types of cells:
1. sieve tubes
2. companion cells
3. fibres (a type of sclerenchyma)
4. parenchyma
 Organic substances such as sucrose and amino acids are transported
along the sieve tubes of the phloem.
(a) The sieve tube is a cylindrical column comprising long cells
arranged end to end.
(b) The sieve tube is a living cell.
(c) When mature, it has no nucleus and its cytoplasm is pushed to the
sides of the cell.
(d) The end walls of each cell are perforated by pores to form sieve
plates which allow substances to pass from one cell to another.
(e) Each sieve tube cell is kept alive and its function is supported by one
or more companion cells.
 A companion cell is a normal cell with a nucleus and a large number
of mitochondria, indicating that it has active metabolism. It provides
the sieve tube cell with proteins, ATP and other nutrients.
 The parenchyma stores food substances while the fibres provide
support to the phloem.
 Below are the differences in structure and function between phloem
and xylem.
45
Sclerenchyma
cells
Parenchyma
cells
Sieve tubes
Companion cells

Xylem Aspect Phloem
Composed of tracheids and vessel
elements
Composed of sieve tubes and
companion cells
Cell walls are thick Cell walls are thin
Impermeable cell walls Permeable cell walls
Dead at functional maturity Living at functional maturity
No cytoplasm Cytoplasm is in a form of strand
that lines the cell
Cell walls are lignified Cell walls are made of cellulose
Transports water and mineral ions
to all parts of plants
FUNCTION
Transports sucrose and other
organic compounds
Flows upwards
(Root → Stem → Leaves)
Flows both up and down
(source → sink)
 Predict the effect of removing a ring of phloem tissue from a plant.
 The tissue just above the ring swells whereas that below the ring
withers.
 The removal of phloem tissue interrupts the downward movement
of the organic substances synthesised in the leaves.
 The accumulation of organic substances causes the swelling above
the ring.
 The leaves above the ring do not wilt because the xylem has not been
removed. Hence the flow of water in the xylem vessels is not
disrupted.
46

LEARNING OBJECTIVE: 1.8 The Transport of Organic Substances and
Water In Plants
Learning outcome:
A student is able to:
 state what translocation is.
 explain the importance of translocation in plants.
 describe the process of transpiration.
 explain the importance of transpiration.
 describe the pathway of water from the soil to the leaves.
 state external conditions affecting transpiration.
 design experiments to study factors affecting the rate of transpiration.
 explain the role of root pressure in the movement of water in plants.
 explain the role of cohesion and adhesion of water in the movement of
water in plants.
 conceptualise the transport mechanism in plants
Previous knowledge : The concept of transport of water and organic substances
had been studied in previous lesson.
CONTENT:
 State what translocation is.
Translocation is the movement of sugar, other organic and inorganic
solutes from one place to another within the plant through phloem.
Concentration gradient drives this process. The locations where the
solutes are produced are the sources. The locations where these solutes
are needed are the sinks. The sources have high concentration of solutes
while the sinks have low concentration of solutes.
 Explain the importance of translocation in plants.
47

(a) The survival of a plant depends on the transport of organic
substances from the leaves to the storage organs such as the roots,
fruits or to the growth regions such as buds.
(b) Translocation enables sucrose the product of photosynthesis, to be
stored or converted into other sugars when it reaches its destination.
 Explain the importance of transpiration.
 Transpiration is the loss of water vapour through evaporation in
plants.
 This loss of water is replaced by the absorption of water from soil by
the plant roots.
(a) only 1% of this water is used by plant cells for photosynthesis
and to remain turgid.
(b) The remaining 99% evaporates from the leaves and is lost to the
atmosphere through transpiration.
 About 90% of transpiration takes place through the stomata of the
leaves. Transpiration also occurs through the lenticels of woody stems.
Stomatal pore Lenticels
 Transpiration is important in:
(a) helping in the absorption and transport of water and mineral ions
from the roots to the different parts of the plants.
(b) producing a cooling effect in plants.
(c) helping to supply water to all plant cells for metabolic processes.
(d) helping to prevent plants from wilting by maintaining cell
turgidity.
 The continuous stream of flowing water from the roots to leaves is
called the transpiration stream.
 describe the process of transpiration.
1. The surfaces of the mesophyll cells are covered by a thin layer of
water.
2. Heat from the sun causes the water on the external surfaces of the
mesophyll cells to evaporate, thus saturating the air spaces in the
mesophyll with water vapour.
48

3. Outside the stomata, the air in the atmosphere is less saturated.
4. This means that the concentration of water vapour in the atmosphere is
lower than the concentration of water vapour in the air spaces of the
leaf.
5. Hence, the water vapour in the air spaces of the leaf evaporates and
diffuses into the atmosphere through the stomata.
6. The movement of air carries water vapour away from the stomata.
7. The loss of water from a mesophyll cell makes the cell hypertonic
to an adjacent cell.
8. Water from the adjacent cell diffuses into the mesophyll cell by
osmosis.
9. In the same way, water continues to diffuse from the neighbouring
cells into the adjacent cells by osmosis.
10.Eventually water is drawn from the xylem vessels in the veins.
11.A pulling force is then created to pull water up the xylem vessels
as a result of the evaporation of water vapour from the mesophyll
cells.
12.This pull is called the transpirational pull.
 describe the pathway of water from the soil to the leaves.
 explain the role of root pressure in the movement of water in plants.
 explain the role of cohesion and adhesion of water in the movement
of water in plants.
The pathway of water from the soil to the leaves is assisted by:
(a) root pressure.
(b) capillary action.
(c) transpirational pull
49

The movement of water through transpirational pull
 During transpiration, water evaporated from the spongy mesophyll
cells.
 Transpiration in the leaves forces the movement of water from the soil
up the stem.
 The water vapour fills the air spaces between the spongy mesophyll
cells.
 Water vapour diffuses to the atmosphere through the stomata.
 The lost of water from a mesophyll cell makes the cell hypertonic as
compared to an adjacent cell/ increase the cell osmotic pressure.
 As a result, the water molecule diffuses from the adjacent cells by
osmosis.
 In the same way, water continues to diffuse into adjacent cells from
neighbouring cells.
 Eventually, water is drawn from the xylem vessels in the veins.
 A pulling force is thus created to draw water up the xylem vessels
due to the evaporation of water from the mesophyll cells.
 This pull is called the transpirational pull.
The movement of water through capillary action
 The cohesive and adhesive properties of water which is due to
hydrogen bonding holds the water molecules together and enables a
continuous column of water along the stem and upwards to the
leaves.
 The long narrow xylem vessels of stem provide capillary action that
drives water from the roots to the tree top.
 The water molecules adhere to one another by cohesive forces. The
cohesion of water prevents the water column from breaking apart as it
is pulled upwards.
 The water molecules adhere to the walls of the xylem vessels by
adhesive forces. The adhesion of water molecules to the walls of
xylem vessels and tracheids prevents gravity from pulling the water
down the column.
 The cytoplasm of root hair cells is hypertonic to the surrounding soil
water.
 The water from the soil thus moves into the cell sap of the adjacent
cells in the cortex by osmosis.
50
The movement of water through root pressure

 In this way, water continues to move inwards from cell to cell until
eventually it reaches the cortex.
 Water flows through the cytoplasm, vacuoles and cell walls of the
parenchyma cells in the cortex until it reaches the endodermis.
 Once it reaches the endodermal cells, the water moves through the
cytoplasm and vacuoles instead of the cell walls due to the presence of
special features called Casparian strips which line the sides of the
endodermal cells.
 The Casparian strip is impermeable to water thus blocking the water
flow. The water somehow continues to move inwards through the
cytoplasm and vacuoles until it gradually reaches the xylem vessels.
 The gradient of water concentration which exists across the cortex
creates a pushing force that results in the inflow of water into the
xylem.
 At the same time, ions from the soil are actively pumped into the
xylem and this causes osmotic pressure to increase.
 These phenomena produces root pressure that helps to push water and
mineral ions into the xylem from the roots upwards to the stem.
 State external conditions affecting transpiration.
The external conditions that affect the rate of transpiration are:
(a) Light intensity
(b) Temperature
(c) Air movement
(d) Relative humidity
 An increase in light intensity increases the rate of transpiration.
 Light stimulates the opening of the stomata.
 As a result, the stomata open wider. Hence, more water vapour
evaporates through the stomata.
51
Light intensity

 An increase in temperature increases the rate of transpiration.
 As the temperature increases the rate of evaporation of water from the
surfaces of the mesophyll cells also increases.
 As the water vapour that diffuses through the stomata accumulates near
the leaf surface, a faster air movement helps to remove the water
vapour.
 Air movement increases the concentration gradient between the water
vapour in the leaf and that outside the leaf. This increases the
transpiration rate.
 When the air is still, the transpiration rate decreases or stops altogether.
52
Temperature
Air movement

 High humidity surrounding the leaves reduces the evaporation of water
from the stomata.
 This causes transpiration to slow down.
 A rise in temperature lowers the relative humidity of the surrounding
air, and this increases the rate of transpiration.
Effect of the relative humidity on the rate of transpiration
 Explain the regulation of transpiration by the stomata
 Stomata are found abundantly on the lower epidermis of a
dicotyledonous leaf.
 Each stoma is surrounded by two guard cells which regulate gaseous
exchange by opening and closing the stoma.
 To allow the plant to photosynthesise and at the same time, prevent the
excessive loss of water, the stomata open in response to high light
intensity and a decrease in the levels of carbon dioxide in the air
spaces of the leaf.
 Stomata open during the day and close at night.
53
Relative humidity

stomatal pore
opens
stomatal pore
closes
thick inner wall
chloroplast
The opening of a stoma The closing of a stoma
 The mechanism of the opening of a stoma.
1. During the day, light stimulates photosynthesis in the guard
cells.
2. They start synthesising glucose and generate the energy required
for active transport.
3. The guard cells accumulate potassium ions (K+) from adjacent
cells through active transport.
4. They become hypertonic and water enters the cells by osmosis.
5. As a result, they swell up and become turgid.
6. Since the inner cell walls of the guard cells are thicker than the
outer walls, the guard cells bend outward and the stoma opens.
This is because the thinner outer wall stretches more than the
thicker inner wall.
 The mechanism of the closing of a stoma.
1. At night, when photosynthesis does not take place, potassium ions
exit the guard cells and water also leaves the cells by osmosis.
2. The guard cells become flaccid and the stoma closes.
 conceptualise the transport mechanism in plants
54
guard cell pair
attached at both
ends

Cooling effects
maintaining constant osmotic
pressure in plants
Capillary action
affected
by
Light intensity
water
movement
Transport mechanism in
plants
of substances
Water & mineral Food
xylem phloem
consists of
Vascular tissues
involves
Vessels and
tracheids
Translocation
Transpirational
pull
Root pressure
transported by
Transpiration
Sieve tubes
Involves in
Air
movement
Temperature
Relative humidity
make up
important for
effects
absorption of water and
mineral ions
and mineral salt
driven by
results in
in driven by
driven by
The opening and
regulated by closing of stomata
55

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