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:

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

Snake

Earth worm Frog

hydra

Amoeba sp..

Multicellular Unicellular

1

LivingLiving


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

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.


O2

2

Co2


LEARNING OBJECTIVE: 1.2 Synthesising the concept of circulatory system.


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)

What is a circulatory system? 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.

The circulatory system also transports the waste products of cell metabolism to the lungs and kidneys where they can be expelled from


CIRCULATORYSYSTEM OF HUMAN

CIRCULATORYSYSTEM OF HUMAN

BLOODBLOOD HEARTHEART THE BLOODVESSELS

THE BLOODVESSELS

PLASMAPLASMA BLOOD CELLSBLOOD CELLS Perform various functions

Perform various functions

RED BLOOD CELLSRED BLOOD CELLS PLATELETSPLATELETSWHITE BLOOD CELLS

WHITE BLOOD CELLS

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http://www.naturalhealthschool.com/glossary.html#metabolism


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

DIAGRAM 1: Blood and haemolymph as medium of transport in humans and animals as well as their distinctive functions.


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has 3 general functions

throughthrough

protects the body

from

regulatestransports

important in the

Medium of transport

Humans and Animals Invertebrates

A blood-like nutritive fluid which fills the

entire body

ProtectionRegulationTransportation

HaemolymphBlood

in in

is called is called

is

Transportation of water, inorganic salts, and organic

compounds

Lungs cellsLungs cellsNutrients, hormones and antibodies throughout the body

O2

CO2

1pH of body fluids2body temperature3water content of the

cells

excessive blood loss

diseases / infections

Body Immune System

Blood Clotting


The composition of human blood

DIAGRAM 2: Composition of human blood

DIAGRAM 3: Major functions of constituents in the plasma

Photograph Structure Functions 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.


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comprises

comprises

55% Plasma 45% Cellular Components

Human Blood

Erythrocytes Leucocytes Platelets

ERYTHROCYTES


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.


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)

DIAGRAM 4


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Characteristic arteries capillaries veins

WallThick, muscular,

elastic

One-cell thick, no muscle or elastic

tissue

Thin, less muscular, less elastic

Lumen Small Very small Large

Valve No valve No valveHave valves which maintain the one- way flow of blood

Blood pressure high Very low Low

Direction of blood flow

From heart to the organs

(away from the heart)

From arteries to veins

From all parts of the body to the heart

(blood returns to the blood)

Blood contentOxygenated blood

except the pulmonary artery

Oxygenated bloodAt 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 heart to the tissue

Allow rapid gaseous exchange between the blood and the

body cells by diffusion

Allow blood from the tissues to return to

the heart

The Human HeartThe structure and function of the human heart1The 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)


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DIAGRAM 5: The flow of blood in the heart

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.

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

Blood goes to the left lung

5

Blood comes from the head and arms

2

3

4

3

4

6Blood flows to the

body

1

Bicuspid valve

Key: Oxygenated blood; Deoxygenated t blood.


Explain how blood is propelled through the human circulatory systemThe 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

Key: SA – Sinoatrial; AV – Atrioventricular; p.m- pacemaker


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Heart

Made up of

Cardiac muscle

Characterized as

means

Interconnected tissues

Interconnected tissues MyogenicMyogenic

allows

Electrical impulses to

spread rapidly through the

heart

Need no stimulation by nerve impulses when contracts neither relaxes

Pacemaker

Pacemaker

Initiated & coordinated by the

causing

Wall of the right atrium

Located in the

generates

Electrical

impulses

Parasympathetic Nerves

Sympathetic Nerves

Hormones(Adrenaline)

Controlled by

radiated from

SA node(Primary p.m)

causing

AV node

Impulses transmitted to

Bundle of His fibres

bundle branches

Purkinje fibres

contractionof the heartApex of

the heart

The spread of impulses over the walls of atria →

contraction of atria

DIAGRAM 6: The position of

the SA node, AV node andPurkinje

Fibres


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 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.


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 veins3. 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 mmHg6. 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


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weaker cardiac muscle contractionlower the heartbeat rateSmooth muscles of the arteries relax and the arteries dilate. This reduces the resistance of blood flow in the blood vessels (Vasodilation).

Action of effectors

Blood pressure decreases

Normal blood pressure

Blood pressure increases (for example, during physical exercise)

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


Compare and contrast the circulatory systems in the following: humans, fish and amphibians.

2 types of circulatory systems:1. Open circulatory system2. 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

Stronger cardiac muscle contractionIncrease the heartbeat rateSmooth muscles of the arteries contract thus increases the resistance of blood flow in the blood vessels (Vasoconstriction)

Action of effectors

Blood pressure increases

Normal blood pressure

Blood pressure decreases (for example, when

in a state of shock)

Baroreceptors in arch of aorta and carotid arteries are less stimulated

decreased rate of nerve

impulses sent to

cardiovascular centre in medulla oblongata in the

brain

Sends nerve impulses to the

effectors


2. The closed circulatory system comprises single and double circulatory system.


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.

Single circulatory systemConsists of 1 atrium & 1 ventricleBlood 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.

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The open circulatory system

Circulatory System In Fish



Double circulatory systemFrogs 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.

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Circulatory System In Amphibians

(b) Frog


Double circulatory system

• 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.


Double circulatory systemThe 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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Circulatory System In Humans


• 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.

Conceptualise the circulatory system in humans

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.

LEARNING OBJECTIVE: 1.3 Understanding the mechanism of blood clotting.


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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


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When a blood vessel in the body is damaged, the connective tissue in the vessel wall is exposed to blood plasma

1 Platelets stick rapidly to the collagen fibres in the connective tissue and release chemicals called clotting factors that make the surrounding platelets sticky

2

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.

3

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.

4

The clumped platelets, the damaged cells and clotting factors in the plasma form activators

5These 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)

6

(Continue to the next page)

(from previous page)


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(b) Thrombophilia

(a) Haemophilia


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Thrombin catalyses the conversion of the soluble protein (fibrinogen) in blood plasma into the insoluble fibrin.

7Fibrin will aggregate to form a mesh of long threads over the wound, trapping red blood cells thus sealing the wound.

8

The resulting blood clot hardens when exposed to air to form a scab.

9


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.

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.


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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. 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.


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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. 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.


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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. 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.


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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. 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.


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LEARNING OBJECTIVE: 1.4 Synthesising the Concept of Lymphatic System.


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.

The blind-ended capillaries originate in connective tissues of nearly all parts of body.


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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 duct2. Thoracic duct.

Structure of Lymphatic vessel A – Afferent vessel; B – nodule; C –ValveD – 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 valves2. skeletal muscles contraction3. breathing movement4. Intestinal movement5. smooth muscle contraction of lymphatic vessels

The lymphatic system includes other body organs such as thymus and spleen.


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A

D

C

B

E

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 system1. 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.


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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.

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

SIMILARITIESContents: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.


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DIFFERENCESBLOODContents:1. Erythrocytes present.2. Plasma proteins

present. 3. Contains white blood

cells.

Functions:1. Transports mainly

water-soluble substances.

INTERSTITIAL FLUIDContents: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.

LYMPHContents: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.


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A prolonged oedema will cause the skin to swell and stretch. The skin will become taut and shinny.

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

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.


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lymph capillary

network of capillaries

body cells

lymphatic vessel

Venule

Interstitial space

Interstitial fluid

lymph

arteriole


Comparison between the blood circulatory system and the lymphatic system.

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, leucocytes, platelets, dissolved substances, waste products and protein plasma.

Composition of medium

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.


31


LEARNING OBJECTIVE: 1.5 Understanding the role of the circulatory system in body’s defense mechanism


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


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SpecificNon SpecificComprises of

First line of defence

Second line of defence

Classified into Classified into

Third line of defence

Consist ofConsist of

Skin

Mucous membrane

Phagocytic white blood cells

Immune SystemTears n Saliva;HCl (gastric juice)

Production of antibody by the lymphocytes

by way of


Describe phagocytosis.

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 antibodies remain in the body. The infected person gets well. Further


33

A B

DC E

PseudopodiumBacteria-containing vacuole

Enzyme-containing lysosome

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)


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.


34

IMMUNITY

Comprises of

ACTIVE IMMUNITY PASSIVE IMMUNITY

Comprises of Comprises of

Natural Active Immunity

ArtificialAcquired Active Immunity

Natural Passive Immunity

ArtificialAcquired Passive Immunity

Examples

Examples Examples ExamplesTuberculosis, Smallpox and

MeaslesRubella,

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


35


LEARNING OBJECTIVE: 1.6 Appreciating a Healthy Cardiovascular System


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 diseasesHeart Failure The inability of the heart to pump

blood at an adequate rateHeart Attack Sudden interruption or insufficient

blood to the heartStroke 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 muscleHigh Blood Pressure High pressure in the arteries

Risk factors contributing to cardiovascular diseases:


36

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

Heart attacks, strokes, and arteriosclerosis

stressDiet high in LDL (bad cholesterol)

makes

As a result

thusincreases the risk of

As a consequence

caused by

Obesity and Overweight

over intake of carbohydrates n fats

Lacks of vitamin Bs and folic acid in diet

caused by


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.

LEARNING OBJECTIVE: 1.7 The Transport of Substances In Plants

Learning outcome:A student is able to:Biology Form Five Notes © Copyright Maryam Shah 2007

37

coronary heart diseases, stroke & peripheral vascular diseases

Improper dietamount of amino acid Homocysteine found in the blood

The oxidation of good cholesterol to LDL

caused by

increases

promotes

closely related to

Diabetes mellitus

related toLow in High-density Lipoprotein (HDL) and high triglycerides levels

High Blood cholesterol

Tobacco smoke

Physically inactive


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.


38


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.


39

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.

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.

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.


40

The root

Dicotyledonous Stem

Phloem

Xylem

Vascular tissue

Phloem

Xylem

Monocotyledonous Stem

Dicotyledonous Root

Phloem

Xylem

Pith

Phloem

Xylem

Monocotyledonous Root

Cambium

Pith

Vascular bundle


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.


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The leaf

Xylem

PhloemVascular 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 vessels2. tracheids3. 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.


42

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 tubes2. companion cells3. 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.


43

Sclerenchyma cells

Parenchyma cells

Sieve tubesCompanion 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 cytoplasmCytoplasm 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.


44


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.(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.


45


(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.

3. Outside the stomata, the air in the atmosphere is less saturated.


46


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


47

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 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.

In this way, water continues to move inwards from cell to cell until eventually it reaches the cortex.


48

The movement of water through root pressure

The movement of water through capillary action


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.


49

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.

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.


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Temperature

Air movement

Relative humidity


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.

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.


51

thick inner wall

stomatal pore opens

stomatal pore closes

chloroplast

guard cell pair attached at both

ends


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


Transport mechanism in plants

Water & mineral Food

xylem phloem

Vascular tissues

involves

Vessels and tracheids

Translocation

Transpirational pull

Root pressure

Capillary action

transported byTranspiration

Sieve tubes

consists of

Involves in

Air movement

Temperature

Light intensity

affectedby

Relative humidity

make up

of substances

important for

Cooling effects effects

absorption of water and mineral ions

and mineral salt

maintaining constant osmotic pressure in plants

driven by

results in in driven by

driven by

water movement

The opening and closing of stomataregulated by

52

chapter transport biology spm

Education