TRANSPORT OF SUBSTANCES IN PLANTS

Why do plants need a transport system?

• Every cell needs a supply of water &
nutrients.
– Root cells can easily get water.
– Leaf cells can easily make sugars.
– A transport system (vascular tissue) is needed
to swap these materials.
• Particularly in multicellular plants with high
metabolic rates, large size and low surface area :
volume ratios.
Vascular Tissues
• Xylem tissue
– Water & soluble mineral ions
move up from the roots.
• Phloem tissue
– Sugars travel up or down
to where they are
needed.
Vascular Bundles
• Xylem & Phloem tissues are arranged together
as vascular bundles.
• The structure of these vascular bundles differs in
roots, stems & leaves.
– Roots- Vascular bundles are arranged in the centre of the root.
– Stems-Vascular bundles are arranged towards the outside of the
stem.
– Leaves-Vascular bundles are arranged within the midrib & veins of
the leaf.
VASCULAR BUNDLES IN THE STEM OF MONOCOTS AND DICOTS

MONOCOT STEM DICOT STEM

Numerous vascular bundles and scattered Vascular bundles arranged in a ring
VASCULAR BUNDLES IN THE ROOTS OF MONOCOTS AND DICOTS

DICOT ROOT MONOCOT ROOT

Pith is very small or inconspicuous Pith is large and well developed
Cortex is relatively small Cortex is big
Cambium present Cambium absent
Vessels arranged in V or Y shaped Vessels arranged in a rod or chain
structure

VASCULAR BUNDLES IN THE LEAVES OF MONOCOTS AND DICOTS

MONOCOT LEAF

DICOT LEAF
Xylem

• Carries water from roots to the

rest of the plant (one way flow).
– Elongated cells grow end to end.
– Cell walls become waterproofed
with lignin.
– This kills the cells.
– End walls and contents decay.
– Left with a hollow, thick walled,
strong, waterproof tube.
Features of Xylem
• Narrow tubes allow capillarity to transport water
in an unbroken column.
• Gaps in the lignin (pits) allow water to leak out
into neighbouring xylem or plant tissues.
• Lignin rings/spirals allow xylem to stretch as
branch grows or bends.
• Lack of cell contents or end walls allow water to
flow easily.
• Thick lignin walls prevent tubes from collapsing.
PHOLOEM

• Carries sugars around the plant (two way flow).

• Consists of two types of cell (sieve tube elements & companion cells).
Sieve Tubes
• Cells contain little cytoplasm & no nucleus.
• Cells lined end to end.
• End walls of cells develop into sieve plates.
– Perforated cross walls.
• Transport sugar (sucrose) solution.
Companion Cells
• Lie parallel to sieve tubes.
• Have many mitochondria and large nucleus.
• Have plasmodesmata in walls between these and sieve tubes.
– Gaps to allow substances to flow between them.
MECHANISMS INVOLVED IN TRANSPORT OF SUBSTANCES IN XYLEM
Three processes at work;
1. Transpiration pull
2. Capillary action
3. Root pressure
 TRANSPIRATION PULL
This is a suction force used to draw water in an upward direction from roots to the
leaves. Then water received by the leaves is used for photosynthesis. The excess
water is released to the atmosphere in the form of vapours through stomata. This
will generate a negative pressure in the xylem vessels to pull the water from the soil.

CAPILLARY ACTION
is a physical phenomenon that allows liquid to flow in narrow spaces (xylem)
without the assistance of external forces like gravity. In the context of plant biology,
this process plays a crucial role in the transportation of water from the roots to the
upper parts of the plant through the xylem.
The narrow diameter of the xylem vessels enhances the capillary action. The
smaller the diameter of the tube, the higher the water can rise against gravity. This is
due to the increased interaction between the water molecules and the tube walls,
which creates a stronger adhesive force.

ROOT PRESSURE
The mechanism by which root pressure occurs is osmosis, a process in which water passes
across a semi-permeable membrane from a region of low concentration to one of high
concentration.

It proceeds as follows;

 Through microscopic root hairs, the roots draw water from the earth.
 Solutes (such as minerals) found inside the cells of the roots cause the water within the
roots to be more concentrated than the water in the soil.
 Osmosis allows water from the soil to enter the root cells due to this difference in
concentration.
 Pressure inside the roots increases as more water enters the root cells.
 The plant's vascular system, in primarily the xylem, which functions as a network of small
tubes, is forced to pump water upward by this pressure.
 When the water eventually reaches the remaining portions of the plant, it supplies vital
minerals and aids in functions like photosynthesis.
 In order to ensure the growth and survival of the plant, root pressure essentially aids in
pumping water and minerals up from the roots to the rest of the plant.
 TRANPORTATION IN THE PHLOEM

Translocation- is the movement of nutrients/food substances

throughout the plant. It occurs primarily through the phloem
vessels. Translocation of food substances can be in any direction
(up, down, lateral or radial).
MASS FLOW IN PHLOEM
1. Mass flow is a passive process that occurs from source to
sink along turgor pressure gradient
2. Turgor pressure gradient exist between source and sink
3. The difference drives the movement of solutes from leaves to
other parts of the plant through the phloem
 4. The movement is from the region of high turgor pressure to low
turgor pressure.
Loading the phloem uses the process of ACTIVE TRANSPORT which
uses energy to transport sugars from the mesophyll cells to the
phloem against concentration gradient.

SOURCE – Site of synthesis or green parts of plants e.g leaves

SINK- The site of food storage like fruits, seeds, tubers.

TRANSPIRATION
The process in which plants lose water vapour though
leave stomata.
ENVIRONMENTAL FACTORS THAT AFFECT RATE OF
TRANSPIRATION
FACTOR EFFECT
1. TEMPERATURE High temperature increases
kinetic energy of the water
molecules. Water will then
be lost at higher rate
Low temperature make
water move less hence
lowering the rate of water
loss.
 2. WIND SPEED High wind speed increases
rate of transpiration since
water particles gain kinetic
energy and move into
atmosphere.
Low wind speed lowers the
rate of transpiration since
water particles has low
kinetic energy to move into
atmosphere.
3. LIGHT High light intensity allows
INTENSITY stomata to open to allow
carbon dioxide for
photosynthesis and more
water is lost at high rate.
Low light intensity promote
the closing of the stomata
lowering rate of
transpiration

ADAPTATIONS OF PLANTS TO VARIED

ENVIRONMENTS

ARID ENVIRONMENT
This are dry environments characterized by very low
precipitation. There is high evaporation rate.
Plants that are adapted to live in arid environments
are known as XEROPHYTES.
• Xerophytes are plants adapted to reduce
water loss to enable them to live in very
dry conditions.
– Eg. Cacti, Marram grass.
Xerophytes possess some or all of
these adaptations to prevent
excessive water losS;
 •Stomata sunken in pits creates local humidity/decreases exposure
to air currents;
 •Presence of hairs creates local humidity next to leaf/decreases
exposure to air currents by reducing flow around stomata;
 •Thick waxy cuticle makes more waterproof impermeable to water
 Stomata on inside of rolled leaf creates local humidity/decreases
exposure to air currents because water vapour evaporates into air
space rather than atmosphere e.g. British Marram grass
 •Fewer stomata decreases transpiration as this is where water is
lost;
 • Some plants maintain a low water potential inside the mesophyll
cells.
 Deep root system to access underground water sources e.g
Mesquite tree
 Shallow widespread roots to quickly absorb little rainfall
 Needle like leaves to decrease surface hence reducing
transpiration.
 Leaf shedding by some xerophytes during dry season to reduce
water loss
 Thick trunk e.g baobab to store water
 Spines instead of leaves to prevent water loss
 Succulent leaves to store water e.g aloe vera
 – Increased salt concentration in cells.
 – Reduces evaporation from cell surface

AQUATIC ENVIRONMENTS
This are ecosystems found in water, supporting a vast diversity of
life.
Plants adapted to live in aquatic environments are known as
HYDROPHYTES. Eexamples ; water lillies, water cress,
bulrushes/cattail/reed.

HYDROPHYTES ARE ADAPTED AS FOLLOWS;

 Thin or no waxy cuticle
No need to conserve water so transpiration not a problem.
 Many always-open stomata
Often on upper leaf surfaces - Maximises gas exchange.
 No need for supporting structures
Plant is supported by the water.
 Wide, flat leaves
Capture as much light as possible, and float on water surfaces.
 Small roots
Water can diffuse directly into the stem or leaves.
 Large surface area of underwater stems/roots
Maximises photosynthesis.
 Air sacs in the leaves
Enables leaves/flowers to float.
  Large air spaces in leaf tissue
Provides buoyancy to leaves, allows efficient gas exchange
 Flexible stems and leaves
To prevent damage from water currents
 Floating seeds e.g coconut
 Vegetative reproduction
Some reproduce asexually through fragmentation.
 Reduced xylem tissues
Water transport is minimal, vascular tissues are less developed.

SALINE ENVIRONMENTS
These are ecosystems with high salt concentrations. These include
salt water oceans, saline lakes, salt flats, salt pans.

ADAPTATIONS BY HALOPHYTES
Plants that are adapted to live in salt environments are known as
HALOPHYTES. Halophytes are adapted as follows;
 They have salt glands that excretes excess salt.
 Salt accumulation in vacuoles to reduce toxicity
 Succulence
Thick, fleshy leaves store water to counteract osmotic stress.
 Selective salt uptake
Specialized root membranes filter excess salt while absorbing
water e.g mangroves.

TRANSPORT SYSTEM IN HUMANS

The human transport system is also known as the circulatory system. Circulatory stem is
responsible for transporting oxygen, nutrients, and other substances throughout the body. It also
remove waste.
Components of the circulatory system
HEART: Pumps the blood throughout the body
BLOOD: transport oxygen, nutrients, hormones etc.
BLOOD VESSELS: Arteries, veins, and capillaries that transport blood.
THE HUMAN HEART

THE CARDIAC CYCLE

This refers to the pattern of contraction and relaxation of the heart during one complete
heartbeat. Each cardiac cycle has a diastolic phase (also called diastole) where the heart
chamber is in a state of relaxation and fills with blood that receives from the veins. Systolic
phase (also called systole) where the heart chambers are contracting and pumps the blood
towards the arteries.
Both the atria and ventricles undergo alternating states of systole and diastole. If atria are in
diastole, the ventricles are in systole and vice versa.
 Diastole is when the heart fills with blood
 Systole is when the heart pumps the blood.
Diastole systole
 Heart ventricle muscle relaxes  Heart ventricles muscle contracts
 Ventricles of the heart fill with the  Pushing the blood out of the heart
blood. through aorta and pulmonary artery.
 That is blood returns to the heart from  Blood goes to all of the organs and
organs and tissues of the body. tissues of the body.
  Pressure in the vessels  Blood pressure in vessels increases
decreases(diastolic pressure)

BP = systole/ diastole
Human normal BP = 120/80

DOUBLE CIRCULATION/ DUAL CIRCULATION IN HUMANS

In humans blood passes through the heart twice per circuit. The dual circulatory system is made
up of PULMONARY and SYSTEMIC CIRCUIT.
1. PULMONARY CIRCUIT
i. Deoxygenated blood begins in the right atrium. Before blood can be
pumped around the body, it needs to be pumped to the lungs to get
oxygenated.
ii. The deoxygenated blood is pumped out the right ventricle. The
deoxygenated blood in the right atrium is pumped into the right ventricle.
From here is pumped into the pulmonary circuit through the pulmonary
artery.
iii. The lungs oxygenate the blood. The pulmonary circuit carries the blood to
the lungs where it is oxygenated (via gas exchange).
iv. The oxygenated blood returns to the left atrium. Then the oxygenated
blood is carried back to the heart via the pulmonary vein.

2. SYSTEMIC CIRCUIT
The oxygenated blood is ready to be pumped around the body. The oxygenated blood
returns from the pulmonary circuit, and passes into the left atrium, then into the left
ventricle. The oxygenated blood can now be pumped around the body in the systemic
circuit.
The oxygenated blood is pumped out of the left ventricle. From the left ventricle it is
pumped out into the aorta, and is carried around the body.
The blood gives oxygen to body cells. The blood unloads oxygen and gives it to the
body’s cells. The blood becomes deoxygenated as oxygen is used up.
The deoxygenated blood returns to the right atrium. The vena cava (veins) carry the
blood (now deoxygenated) back to the heart, and the cycle starts again.
ADVANTAGES OF DUAL CIRCULATION
 Efficient separation of oxygenated and deoxygenated blood allows for higher
metabolic rates in humans.
 Oxygenated blood is directly delivered to active tissues, enhancing oxygen
supply.
  Efficient transport of deoxygenated blood back to the lungs ensures proper
oxygenation.

COMPONENTS OF BLOOD

The main components of blood are ;

i. Red blood cells

ii. White blood cells (phagocytes and lymphocytes)
iii. Plasma
iv. Platelets
PLATELETS AND BLOOD CLOTTING

Function of platelets
They help in clotting in wounds or damaged blood vessels walls to prevent excessive loss
of blood & entry of germs. The formation of blood clot involves the following stages;

When the skin cut & blood is flowing out, the platelets are exposed to air, they disintegrate
& release an enzyme called thrombokinase, into the plasma.
Thrombokinase in the presence of calcium ions found in the blood can now change the
plasma protein prothrombin to an active enzyme thrombin.
Thrombin reacts with the soluble plasma protein fibrinogen and changes it to insoluble
fibrin which forms a network of fibers around the injured part.
The blood cells become trapped in the fibers, dry up, die and harden to form a scab under
which the wound can heal & prevent entry of foreign particles.

WHITE BLOOD CELLS AND IMMUNITY

PHAGOCYTES;

They are irregular in shape & can change their form.

They have a lobed nucleus.
 The cells move by the flowing action of the their cytoplasm and can sometimes pass
through the capillary walls.
They are made in the bone marrow.

Function of phagocytes.
They accumulate on the site of injury / infection in order to attack the invading bacteria.
They destroy bacteria & dead tissue cells by flowing around, engulfing and digesting
them, and this action is known as phagocytosis. This helps to prevent the spread of
harmful bacteria & accelerate the healing process.

LYMPHOCYTES
 They are smaller than phagocytes.

 Have a round nucleus which occupies most of the cell

 They are made in the spleen & the lymph nodes

Lymphocytes work together with phagocytes to destroy pathogens.

Function of lymphocytes;

The lymphocytes has a large nucleus that produce chemical substances called antibodies which
attack foreign substances called antigens in the body. The antibodies can adhere to the surfaces of
the microorganism, making them;

i) Clump/group together (agglutination)

ii) cause them to disintegrate (lysis). The remains of the microorganisms are then
ingested by the phagocytes.
 iii) Weaken microorganisms.

NATURAL IMMUNITY
The immunity is acquired from exposure to the disease organism through infection with the actual
diseases.

Happens after infection.

Steps of natural immunity

 One is infected by a germ

 Recognition: Detecting a potentially harmful foreign antigen.
 Immune system (lymphocytes) produces antibodies to fight the pathogens.
 The body remembers (due to memory cells ) the antibodies to fight the germ again if the
body is exposed to it in the future.

ARTIFICIAL IMMUNITY
The person must be artificially and intentionally exposed to foreign antigens/parhogens
(actively), or given someone else’s antibodies (passively), in order to generate a protective
immune response.
Artificially acquired active immunity is protection produced by intentional exposure of a
person to antigens in a vaccine, so as to produce an active and lasting immune response.
The antigens in the vaccine stimulate the immune system to produce antibodies and
memory cells which are specifically directed against the antigens in the vaccine. After the
immunization, if the living infectious agents with the same antigens that were in the vaccine
get into the person’s body, the correct antibodies are already present and they bind to the
infectious agents. The memory cells generate a rapid immune response from the rest of the
immune system, and the infectious agents are quickly attacked and destroyed, often before
symptoms of the disease can develop.

Vaccination produces active immunity, the body produces its own antibodies
against a particular antigen.
Immunity may also be passive whereby the individual is given ready made
antibodies. Passive immunity can happen naturally when maternal antibodies are
transferred to the fetus through placenta and also in the breast milk. Passive
immunity provides immediate protection but the body does not develop memory
therefore the patient is at risk of being infected by the same pathogen later.

SUMMARY
 ACTIVE (involves PASSIVE(ivolves use of
production of antibodies antibodies produced by
by patients lymphocytes) another animal)
NATURAL IMMUNITY  Inherited Antibodies received via
 acquired placenta.
ARTIFICIAL IMMUNITY Vaccination From injection of serum
containing antibodies.

BLOOD VESSELS
a) Arteries
 Have a smaller lumen as compared to veins
 Have thick walls made of many fibrous elastic tissue
 Arteries divide into arterioles (smaller vessels) which have less elastic tissue but more muscle
fibres than the larger arteries.
 Largest artery is called the aorta

Muscle layer

Lining of lumen

lumen

All Arteries serve to carry oxygenated blood from the heart to different body parts, (except the pulmonary
artery)

b) Veins

 Largest vein is called the vena cava

 Have a wider lumen
 Have thinner walls with fewer fibrous & less elastic tissues.
 Have valves
 Veins divide into venules (smaller vessels)

Wider
 valve

All veins carry deoxygenated blood from various body tissues to the heart, (except the pulmonary vein)

c) Capillaries
 These are tiny vessels which are one cell thick (have diameter of about 0.001mm)
 They are semi-permeable to allow tissue fluids and gases to escape through them.
 Blood flows very slowly in the capillaries.

Cell

Capillaries supply all living cells with oxygen and food nutrients, and pick up substances from the cells i.e.
allows for the exchange of substances between the blood stream and body cells.

Arteries Arterioles Capillaries Venules Veins

Transfer of materials at capillaries

The blood pressure in the capillaries forces part of the plasma fluids out through the capillary walls. This
fluid is known as tissue fluids. The tissue fluid is similar to plasma but has fewer proteins and it supplies
the cells with dissolved food substances & O2.

When the tissue fluid returns back to capillary it contains waste products e.g. CO 2 from respiration. The
deoxygenated blood then leaves the capillaries through the venules which recombine to form veins.
BLOOD RELATED DISEASES VS BLOOD VESSELS STRUCTURE

DISEASE EXPLANATION
i. STROKE  Arteries of brain are blocked reducing
 Caused by blocked arteries, bursting and blood flow
leaking of blood vessel in the brain.  Blood vessels such as arteries may break
NB blocked arteris may be caused by or leak leading to reduced blood flow to
fatty deposits that build up in the blood brain cells
vessels

ii. CARDIAC ARREST  Coronary arteries become clogged with
 Caused by narrowing of the arteries that cholesterol and other deposits reducing
supply the heart muscles with oxygen. blood flow to the heart. This reduces
oxygen supply by blood to the heart
muscles. Then low respiration hence low
energy level for the heart muscles.
iii. CORONARY HEART DISEASES  Cholesterol may build up in the arteries
and turns into plaque, which narrows
 Caused by damage to the coronary coronary arteries.
arteries that supply blood to the heart  Long-term inflammation, high blood
become damaged or diseased. pressure, or diabetes can damage the
inner walls of coronary arteries.
iv. HYPERTENSION/ HIGH BLOOD  The force in the blood pushing against the
PRESSURE wall of the blood is high for too long. This
 High blood pressure damages blood may damage the arteries.
vessels by causing them to weaken and
stretch. Arteries may also harden due to
high blood pressure.
PREVENTION OF BLOOD RELATED DISEASES

 Regular exercise
 Have balanced diet and reduce excess fats
 Manage stress
 Maintain healthy weight

PREVALENCE OF CARDIAC DISEASES IN BOTSWANA

The prevalence of hypertension, stroke/heart attack is comparatively high in Botswana. This can be
attributed to many factors such as obesity, lack of exercise(inactivity), smoking, poor diet with high
sodium intake.
 THE LYMPHATIC SYSTEM
The lymphatic system is a network of organs, vessels, and tissues that play a crucial role in
maintaining fluid balance and protecting against infections. Key components of the
lymphatic system include;
1. Lymph nodes: These swell in response to infections and contain immune
system cells. cleanse lymph as it filters through them. They clear out damaged
cells and cancer cells. Lymph nodes also store lymphocytes and other immune
system cells that attack and destroy harmful substances like bacteria
2. Lymphatic vessels: These collect and circulate excess fluid (lymph) in the
body.
3. Lymphoid organs: Such as the bone marrow, thymus, spleen, tonsils.
4. Lymphatic tissue: Which is part of the immune system.

FUNCTIONS OF THE LYMPHATIC SYSTEM

 Fluid balance: help return excess tissue fluid (lymph) back into bloodstream,
maintaining proper fluid levels in the body.
 Immune defense: the lymphatic system plays a key role in the immune response,
filtering harmful substances and producing white blood cells (lymphocytes) that
fight infection.
 Absorption of fats: It absorbs fats and fat-soluble vitamins from the digestive
system and transports them to the blood stream.
 Waste removal: it helps remove cellular waste, toxins, and abnormal cells from
tissues.
 Transport of lymph: lymph vessels carry lymph ( a clear fluid containing immune
cells and waste ) throughout the body, allowing for immune surveillance and waste
removal.