Topic 4: TRANSPORTATION OF MATERIALS IN LIVING THINGS
TOPIC 4: TRANSPORTATION
OF MATERIALS IN LIVING THINGS
The
Concept of Transportation of Materials in Living Things
The
Concept of Transportation of Materials in Living Things
Explain
the concept of transportation of materials in living things
Unicellular organisms (for example amoeba),
nutrients (for example oxygen and food) and waste products (for example carbon
dioxide) can simply diffuse into or out of the cells from the surroundings. But
in multi cellular organisms (for example humans and trees), many cells are very
far away from the body surface, hence a transport system is required for the exchange
of materials.
Organisms require transport systems so as to carry
out various life processes. These life processes include nutrition,
respiration, excretion, growth and development, movement,reproduction and
coordination. For these life processes to take place, transport of materials is
inevitable. Materials are transported either from environment into the
organisms or from one part of an organism to another, and can also be
transported from an organism into the environment.
For example, during nutrition organisms take in
food substances that they need to produce energy, grow and carry out other life
processes. These food substances must be taken in from the environment. The
same case applies to reproduction which requires the movement of gametes(sex cells)
from the sex organs to the area where fertilization occurs. Therefore,
transport is very important for the survival and existence of living things.
The
Importance of Materials in Living Things
Outline
the importance of materials in living things
Transport of materials is very important for the
survival and development of living organisms. If transportation never existed,
then no life on earth could be possible. The following is an outline of the
importance of transport of materials in living things:
(i)
It
facilitates the removal of waste materials from the organism’s body, the excess
of which could harm an organism.
(ii)
It
ensures that essential materials like oxygen, nutrients, water, hormones and
mineral salts are supplied to the cells and tissues as required.
(iii) It enables essential substances to move from one
part of the body to another. For example, food manufactured by photosynthesis
in plant leaves is transported from leaves to other organs of the plant for use
or storage.
Diffusion,
Osmosis and Mass- flow
The
Meaning of Osmosis, Diffusion and Mass- Flow
Explain the meaning of osmosis, diffusion and mass-
flow
Life processes in organisms take place at the cell
level. Therefore, it is necessary for substances to move in and out of the
cells. There are two ways through which substances can move across the
membrane. Materials in living organisms move by diffusion, osmosis and mass
flow.
Diffusion
This is the movement of materials from a region of
higher concentration to a region of lower concentration until equilibrium of
two sides is maintained. Diffusion can also be defined as the movement of ions
or molecules from the region of higher concentration to the region of lower
concentration, without involving any permeable membrane. A difference in
concentration of a substance between two regions is known as concentration
gradient.
Materials are transported in the body system of
living things from the area where they are abundant to areas where they are
less abundant, and this process or mechanism of transportation in these animals
is termed as diffusion. Diffusion occurs in exchange of gases like oxygen or
carbon dioxide during respiration in animals and plants. Also, diffusion takes
place during distribution of nutrients and digested foods in living organisms.
Osmosis
This is the movement of water molecules from a
region of higher concentration to a region of lower concentration through a
semi-permeable membrane. A partially-permeable membrane is a membrane that
allows small particles such as water molecules to pass through it, but not
larger particles such as sugar molecules and ions from salts. Examples of
semi-permeable membranes are cell membranes and a pig’s bladder. These
membranes allow transportation of water through them. In spite of the fact that
they allow transportation of water through them, they do not permit the passage
of sugar or salt molecules because they are solutes. Osmosis occurs when water
moves down its concentration gradient across the semi-permeable membrane.
Therefore,
for osmosis to take place there must be:
(i) two solutions with different concentrations; and
(ii) a partially permeable membrane to separate them.
(iii)
A
dilute solution has a high water concentration, while a concentrated solution
has a low water concentration. For example, when salt is dissolved in water:
(iv) A little dissolved salt produces a dilute solution
with a high water concentration
(v)
A lot
of dissolved salt produces a concentrated solution with a low water
concentration.
Diagram
of osmosis
Mass flow
Diffusion and osmosis occurs very slowly and cover
short distances. In animals and plants, materials are usually transported a
long distance and in large quantities. For example, food nutrients from the
small intestine have to be moved to cells in the extremities such as toes and
fingers, where the nutrient materials have to be transported a long distance.
Therefore, an efficient and fast mechanism is required to facilitate this
movement. That is when mass flow comes in.
Mass flow is the movement of materials in large
quantities and across a long distance in the body of an organism due to
differences in pressure between the two regions. Materials in higher plants and
animals are moved by the process of mass flow. For example, the manufactured
food in plant leaves has to be moved to all plant parts, for use or storage, by
mass flow.
Experiments
to Demonstrate the Process of Diffusion, Osmosis and Mass Flow
Carryout experiments to demonstrate the process of
diffusion, osmosis and mass flow
Demonstration of the process of
diffusion
Take a bottle of perfume and move to one corner of
the classroom. Open a bottle and observe what happens. The result is, after a
few seconds, the whole classroom is filled with a smell of the perfume. This
means that the molecules of the perfume moves from the region of higher
concentration (the bottle) to a region of lower concentration (air). That is
why the smell is felt by a person standing several meters away from the source
of the perfume.
Some important processes that involve diffusion
are:
(i)
Gaseous
exchange in the lungs of animals and in the leaves of plants
(ii)
Absorption
of digested food in the ileum the process of diffusion
(iii)
Removal
of west materials from cells
(iv) Absorption of nutrients and oxygen into cells
Demonstration of the process of
osmosis
Procedure
Peel a potato and cut it as shown in the diagram
below. Then fill the depression with brine(concentrated solution of sodium
chloride). Leave the set up until the next day and observe what happens to the
level of brine in the potato.
Result
In the following day, you will find that the level
of brine will have risen as shown. This means that water has moved from the
potato to the brine solution causing the brine level to rise up. The water has
moved from a region of high water concentration (the potato) through the cell
membranes of the potato cells (partially permeable membrane) to the region of
low water concentration (the brine).
The
Differences between Diffusion, Osmosis and Mass Flow
Outline the differences between diffusion, osmosis
and mass flow
Differences between diffusion and
osmosis
|
Diffusion |
Osmosis |
|
It is the movement of all types of substances
from the area of their higher concentration to the area of their lower
concentration |
It is the movement of only solvent or water from
the area of their higher concentration to the area of their lower
concentration through a partially permeable membrane |
|
Diffusion can operate in any medium |
Osmosis operates only in a liquid medium |
|
Diffusion is applicable to all types
ofsubsstances (soilds, liquids and gases) |
It is applicable only to solvent part of a
solution |
|
It does not require any semi-permeablemembrane |
A semi-permeable membrane is a must foroperation
of osmosis |
|
It is purely dependent upon the free energy ofthe
diffusing substance |
Osmosis is dependent upon the degree of reduction
of free energy of one solvent over that of another |
|
It helps in equalizing the concentration of
thediffusing substance througout the availablespace |
It does not equalize the concentration of solvent
on the two sides of the system |
|
Turgor pressure or hydrostatic pressure does not
normally operate in diffusion |
Osmosis is opposed by turgor or hydrostatic
pressure of system |
|
It is not influenced by solute potential |
Osmosis is dependent upon the solute potential |
|
Diffusion of a substance is mostly dependent of
the presence of other substances |
It is dependent upon the number of particles of
other substances dissolved in a liquid |
|
Factors like water potential, solute potential
and pressure potential do not affect diffusion |
Factors like water potential, solute potential
and pressure potential affect osmosis in a living system |
The
Roles of Diffusion, Osmosis and Mass Flow in Movement of Materials in Living
Organisms
Explain
the roles of diffusion, osmosis and mass flow in movement of materials in
living organisms
Materials are transported in the body system of
living things from the area where they are abundant to areas where they are
less abundant, and this process or mechanism of transportation in these animals
is termed as diffusion. Diffusion occurs in exchange of gases like oxygen or
carbon dioxide during respiration in animals and plants. Also, diffusion takes
place during distribution of nutrients and digested foods in living organisms.
(i)
Through
the process of osmosis, nutrients get transported to cells and waste materials
get moved out of them.
(ii)
The
pressure within and outside each cell is maintained by osmosis as this process
ensures a balance of fluid volume on both sides of the cell wall. If fluid
volume within a cell is more than the fluid volume outside it, such pressure
could lead the cell to become turgid and explode. On the contrary, if fluid
volume outside the cell is more than the fluid volume within, such pressure
could lead the cell to cave in. Both cases would be detrimental to normal and
healthy cellular function.
(iii)
It is
via osmosis only that roots of plants are able to absorb moisture from the soil
and transport it upwards, towards the leaves to carry out photosynthesis.
Plants wouldn't exist without osmosis; and without plants, no other life could
exist as they are a vital link of the entire food chain of the planet.
(iv)
Without
osmosis, it would be impossible for our bodies to separate and expel toxic
wastes and keep the bloodstream free from impurities. The process of blood
purification is carried out by the kidneys which isolate the impurities in the
form of urine.
(v)
Therefore,
the role of osmosis is twofold: it helps maintain a stable internal environment
in a living organism by keeping the pressure of intercellular and intracellular
fluids balanced. It also allows the absorption of nutrients and expulsion of
waste from various bodily organs on the cellular level. These are two of the
most essential functions that a living organism cannot do without.
Transport of Materials in Mammals, the Structure of the Mammalian Heart
The
External and Internal Structures of the Mammalian Heart
Describe the external and internal structures of
the mammalian heart
TRANSPORT OF MATERIALS IN MAMMALS
Mammals are the complex multicellular organisms
whose bodies are made up of numerous cells and tissues. In this case, diffusion
alone is not enough to insure efficient carrying out of life process. Therefore
mammals have an elaborate transport system that is made up of the heart ,blood
and blood vessel.
The
structure of the mammalian heart
The heart is a muscular organ about the size of a
closed fist that functions as the body’s circulatory pump. It takes in
deoxygenated blood through the veins and delivers it to the lungs for
oxygenation before pumping it into the various arteries. The heart is located
in the thoracic cavity between the two lungs.
The external structure of the mammalian heart is as
shown in the labelled diagram below:
The mammalian heart is broader at the top and
narrower at the bottom. It is enclosed by a double layer of tough and elastic
membranes called pericardium. These membranes prevent the heart from
ever-expanding when beating very fast. Also the pericardium secrets a fluid
which enables the membranes to move smoothly against each other.
The walls of the ventricles are thicker than those
of the auricles because the ventricles pump blood a greater distance than the
auricles. Auricles pump blood to the ventricles while the ventricles pump blood
to the other parts of the body.
The left ventricle is thicker than the right
ventricle because the right ventricle pumps blood to thelungs while the left
ventricle pumps blood to the rest of the body parts.The heart consists of four
chambers, right and left atria and right and left ventricles. Thefunctions of
each part and the associated structures are as follows:
(i)
The
right atrium links to the right ventricle by the tricuspid valve. This valve
prevents back flow of the blood into the atrium above, when the ventricle
contracts.
(ii)
The
left atrium links to the left ventricle by the bicuspid valve. This valve also
prevents back flow of the blood into the atrium above, when the ventricle
contracts.
(iii)
Semi-lunar
(pocket) valves are found in the blood vessels leaving the heart (pulmonary
artery and aorta). They only allow exit of blood from the heart through these
vessels following ventricular contractions.
(iv)
Ventricles
have thicker muscular walls than atria. When each atrium contracts, it only
needsto propel the blood a short distance into each ventricle while ventricles
pump blood to distantbody parts.
(v) The left ventricle has even thicker muscular walls
than the right ventricle. The left ventricle needs a more powerful contraction
to propel blood to the systemic circulation (all of the body apart from the
lungs). The right ventricle propels blood to the nearby lungs. So, the
contraction does not need to be so powerful.
INTERNAL STRUCTURE OF THE MAMMALIAN HEART
The heart has several valves. And these valves have
flaps that ensure that blood flows in one direction only.
These valves include the following:
(i)
The
tricuspid valve; found between the right auricle and right ventricle
(ii)
The
bicuspid valve: found between left auricle and left ventricle
(iii)
Semi-lunar
valves which are located at the bases of the pulmonary artery and aorta to
prevent blood from flowing back into the ventricles.
These valves will close if the blood flows back.
The valves are held in place by tendons which prevent the flaps from turning
inside out.The right and left sides of the heart are separated by septum which
is a thick muscular wall which prevents mixing of oxygenated and deoxygenated
blood.
The
Functions of the External and Internal Parts of the Mammalian Heart
Explain the functions of the external and internal
parts of the mammalian heart
Functions of parts of the mammalian
heart
|
Part of the heart |
Function |
|
Aorta |
The largest artery in the body; it conducts
freshly oxygenated blood from the heart to the tissues. |
|
Superior vena cava |
Large vein that brings deoxygenated blood from
the upper parts of the body to the right atrium |
|
Inferior vena cava |
Large vein that brings deoxygenated blood from
lower regions of the body to right atrium |
|
Pulmonary artery |
Carries deoxygenated blood from the right
ventricle to the lungs |
|
Pulmonary vein |
Blood vessel that carries oxygenated blood from
the lungs to the left atrium |
|
Right atrium |
This chamber of the heart receives deoxygenated
blood from the body (from the superior and inferior vena cava). |
|
Left atrium |
This chamber of the heart receives oxygenated blood
from the lungs |
|
Tricuspid valve |
Located on the right side of the heart between
the right atrium (RA)and right ventricle (RV) |
|
Bicuspid valve |
Located on the left side of the heart between the
left atrium (LA) and the left ventricle (LV) |
|
Right ventricle |
The chamber of the heart that pumps deoxygenated
blood to the lungs |
|
Left ventricle |
Receives blood from the left atrium and pumps it
into the aorta for transport to the body cells |
|
Septum |
Divides the right and left chambers of the heart |
The
Adaptations of the Parts of the Mammalian Heart to their Functions
Explain the adaptations of the parts of the
mammalian heart to their functions
The heart is adapted to carry out its functions by
having the following features:
(i)
The
cardiac muscle is adapted to be highly resistant to fatigue.
(ii)
The
heart has a large number of mitochondria enabling continuous supply of energy
to the heart and numerous myoglobins (oxygen storing pigment).
(iii)
The
presence of the cardiac muscles enables the heart to beat rhythmically.
(iv)
The
pericardium which surrounds and protects the heart from physical damage.
(v)
Pericardial
fluid which prevents friction when the heart beats.
(vi)
The
outer layer of the pericardium attaches to the breastbone and other structures
in the chestcavity and thus helps to hold the heart in place.
(vii) Bicuspid and tricuspid valves between atria and
ventricles which prevent the backflow ofblood.
(viii)Septum
which prevents the mixing of deoxygenated blood in the right and oxygenated
blood in the left chambers of the heart.
(ix)
Its
own blood supply for supplying nutrients and removing waste.
(x)
The
left ventricle has thick muscular wall to pump blood at a higher pressure to
the distant body tissues,
(xi)
The
heart is supplied with the nerves which control the rate of heartbeat depending
on the body requirements.
Blood vessels
Blood vessels are intricate networks of hollow
tubes that transport blood throughout the entirebody. This is an essential
function as blood delivers valuable nutrients to and removes wastesfrom our
cells. Blood vessels are constructed of layers of connective tissue and muscle.
Theinner blood vessel layer is formed of endothelium. In capillaries and
sinusoids, endotheliumcomprises the majority of the vessel. There are three
types of blood vessels namely arteries,veins and capillaries. Each of these
vessels has a different structure and function.
The
Structure of Arteries, Veins and Capillaries
Describe the structure of arteries, veins and
capillaries
Basic structure
(i) Capillaries consist of anendothelium whichis only
one cell thick.
(ii) Walls of arteries and veins consist of 3 layers.
(iii) The inner layer consists of a thin layer of
endothelial cells.
(iv) The middle layer is made up of smooth muscle with
some elastic fibres. This layer controls the diameter of the vessel and hence
the amount of blood and its rate of flow.
(v) The outer layer is composed of connective tissue;
this holds the blood vessels in place in the body.
Detailed structure
Arteries
(i) The walls of arteries are much thicker as it
carries blood away from the heart at high pressure.
(ii) Major arteries close to the heart also have thick
layers of smooth muscle in their walls to withstand the increases in pressure
as the heart pumps.
(iii) The walls also have a large proportion of elastic
fibres in both the inner and middle layers – this allows for the arteries to
stretch according to the increases in volume of blood. As the heart relaxes the
artery walls return to their original position, hence pushing the blood along –
maintaining a constant flow in one direction.
(iv)
Arteries
are near the surface of the skin; the changes in the arteries diameter can be
felt as a pulse.
Veins
(i) The walls of veins are thinner than the walls of
arteries, as the blood they receive from the capillaries is at a much lower
pressure.
(ii) The walls have fewer elastic fibres and the lumen
is wider (to allow for easier blood flow).
(iii)
Veins
have two mechanisms for keeping the blood flow constant and in one direction.
Firstly, many veins are close to muscles, hence when the muscles contract they
compress the walls of the vein – pumping blood forwards. Veins also have valves
which are spaced along regular intervals in veins. They work much like one-way
swinging doors – as the blood is forced through the valve opens. However, once
the pressure drops and the blood flow decreases, the valve shuts – preventing
back flow of blood.
Capillaries
(i) They are extremely, tiny microscopic vessels that
bring blood into close contact with the tissues, for the exchange of chemical
substances between cells and the bloodstream.
(ii) The one cell thick endothelial layer is a continuation
of the lumen arteries and veins.
(iii) Diffusion is a relatively slow process and hence
the structure of capillaries is suited to slowing down the flow of blood.
(iv) In order to maximize the exchange of substances
between the blood and cells, capillaries have thin walls (for more efficient
diffusion) a small lumen (that forces blood cells to pass through in single
file, slowing down the rate of flow and maximizing their exposed surface area).
(v) They form an expansive blood flow network, such
that no cells are far from blood supply
How different blood vessels are adapted for their
function
|
Blood
vessel |
Function |
Adaptation |
|
Artery |
Carries blood away from heart at high pressure |
Thick, elastic, muscular walls to withstand
pressure and to exert force (pulse) |
|
Vein |
Returns low-pressure blood to heart |
Large diameter to offer least flow resistance.
Valves to prevent back flow. |
|
Capillary |
Allows exchange of materials between blood and
tissues |
Thin, permeable walls |
Cross section of vein
Differences between arteries, veins and
capillaries
|
Arteries |
Veins |
Capillaries |
|
All arteries carry blood away from the heart |
All veins carry blood towards the heart |
Capillaries carry blood from arteries to the veins |
|
With the exception of the pulmonary artery, all
arteries carry oxygenated blood |
With the exception of the pulmonary vein, all
veins carry deoxygenated blood |
Blood slowly loses its oxygen |
|
They carry blood which is usually rich
in digested food materials |
Except for the hepatic portal vein, they carry
blood which usually has little digested
food materials |
Blood slowly loses its food |
|
Have relatively narrower lumens (see diagrams
above) |
Have relatively wide lumens (see diagrams above) |
Have relatively narrow lumens (see diagrams
above) |
|
Have relatively a thick layer of muscles and elastic fibres |
Have relatively a thin layer
of muscles and elastic fibres |
They do not have muscles
and elastic fibres |
|
They have thick
outer walls |
They have thin outer walls |
Walls are only one cell thick |
|
They carry blood at high
pressure |
They carry blood at low pressure |
Pressure gradually falls as blood flows from arteries to veins |
|
Do not have valves (except for the semi-lunar
valves of the pulmonary artery and the aorta) |
Have valves throughout the main veins of the body
to prevent the back flow of blood. |
Have no valves |
|
Have bright red blood (because it is rich in
oxygen) |
Brown-red blood |
Brown-red blood |
|
Located deep in the to body surface |
Located near to body surface |
Capillaries are found inside all tissues |
|
Walls are not
permeable |
Walls are not permeable |
Walls are permeable |
|
Blood flows in pulses |
Nopulse |
Pulse gradually disappears |
The
Blood
The
Major Components of the Blood
List the major components of the blood
Blood is the red fluid that circulates in our blood
vessels. The average human body contains about 4 to 5 litres of blood. Blood is
classified as a connective tissue and consists of two main components:
(i)
Plasma
which is a clear extracellular fluid.
(ii) The solid component, which are made up of the blood
cells and platelets
The solid component is made up of blood cells
except for the platelets, which are tiny fragmentsof bone marrow cells.
The solid component consists of blood cells
(corpuscles) which include:
(i)
Erythrocytes,
also known as red blood cells (RBCs)
(ii)
Leukocytes,
also known as white blood cells (WBCs)
(iii) Platelets, also known as thrombocytes
Red blood cells, most white blood cells, and
platelets are produced in the bone marrow, the soft fatty tissue inside bone
cavities. The white blood cells (lymphocytes) are also produced in the lymph
nodes and spleen, and in the thymus gland.
Within the bone marrow, all blood cells originate
from a single type of unspecialized cell calleda stem cell. When a stem cell
divides, it first becomes an immature red blood cell, white bloodcell, or
platelet-producing cell. The immature cell then divides, matures further, and
ultimatelybecomes a mature red blood cell, white blood cell, or platelet.
Blood cells
By volume, the plasma constitutes about 55% of
whole blood, and red blood cells, platelets and white blood cells about 45%.
The
Function of Major Blood Components
Explain the function of major blood components
Red blood cells
Red blood cells (RBCs) have two main functions:
(i)
To
pick up oxygen from the lungs and deliver it to tissues elsewhere.
(ii)
To
pick up carbon dioxide from other tissues and unload it in the lungs.
Erythrocytes transport oxygen in the blood through
the red pigment called haemoglobin.Haemoglobin contains iron and proteins
joined to greatly increase the oxygen carrying capacity of erythrocytes. The
high surface area to volume ratio of erythrocytes allows oxygen to be easily
transferred into the cells in the lungs and out of the cells in the capillaries
of the systemic tissues.Erythrocytes are produced inside red bone marrow from
stem cells at the astonishing rate of about 2 million cells every second.
White
blood cells
Although the white blood cells accounts for only
about 1% of the blood, they play a very important role in the body. Their main
function is to protect the body against disease pathogens.There are two of
white blood cells, each of which plays a specific role in protection of the
body against illness and disease.
(i)
Phagocytes:
Engulf and digest invading bacteria and viruses (pathogens). It is the body’s
main defence against germs (microbes).
(ii) Lymphocytes: produce antibodies which neutralize
antigens from bacteria or viruses. They kill microbes or make them clump
together, to be removed in the lymph glands.
White blood cells are produced in the yellow marrow
of the bone, spleen, thymus and lymphatic system.
Platelets
Platelets are small fragments of bone marrow cells
and are therefore not really classified as cells themselves. Platelets have the
following functions:
(i)
Secrete
vasoconstrictors which constrict blood vessels, causing vascular spasms in
broken blood vessels.
(ii)
Form
temporary platelet plugs to stop bleeding.
(iii)
Secrete
procoagulants (clotting factors) to promote blood clotting.
(iv)
Dissolve
blood clots when they are no longer needed.
(v)
Digest
and destroy bacteria.
(vi)
Secrete
chemicals that attract neutrophils and monocytes to sites of inflammation.
(vii) Secrete growth factors to maintain the linings of
blood vessels.
In general, the blood platelets functions in
healing of the wounds when the skin gets broken. This is achieved by clumping
together of the platelets to form a network of mesh, hence bleeding is stopped.
Plasma
Plasma is the non-cellular or liquid portion of the
blood. Plasma is a mixture of water, proteins, and dissolved substances. Around
90% of plasma is made of water, although the exact percentage varies depending
upon the hydration levels of the individual. Blood plasma has the following
functions:
(i)
Plasma
serves as a transport medium for delivering nutrients to the cells of the
various organs of the body.
(ii)
It
transports waste products derived from cellular metabolism to the kidneys,
liver, and lungs for excretion.
(iii)
It
fights infections since it contains antibodies.
(iv)
It is
also a transport system for blood cells, and it plays a critical role in
maintaining normal blood pressure.
(v)
Plasma
helps to distribute heat throughout the body and to maintain homeostasis, or
biological stability, including acid-base balance in the blood and body
(vi) It carries and transports some hormones.
The
Effects of HIV on White Blood Cells
Explain the effects of HIV on white blood cells
The HIVs in the blood of a HIV-positive person
attack the white blood cells (lymphocytes). The viruses reproduce and increase
in number within the lymphocytes. Then the lymphocytes burst and release more
viruses in the bloodstream. The released viruses attack more, new white
cells.The attack continues in that cycle until many white cells are destroyed.
Because there are only a few white cells left to fight against pathogens, the
body immunity gets low. Once the immunity is lowered, the body is often
attacked by diseases and a person suffers from AIDS.
Blood
Groups and Blood Transfusion
The
Concepts of Blood Group and Blood Transfusion
Explain the concepts of blood group and blood
transfusion
Human blood can be grouped into four blood groups namely
groups A, B, AB and O. They were discovered in 1900 and 1901 at the University
of Vienna by Karl Landsteiner in the process of trying to learn why blood
transfusions sometimes cause death and at other times save a patient.This
classification is based on the type of antigens in the red blood cells and
antibodies in the plasma.
Red blood cells have proteins (antigens) on their
surface: A, B or A and B. Plasma hasantibodies which can cause agglutination:
anti-A and anti-B.
Serum is blood plasma without fibrinogen. It can be
stored without clotting, and is used in transfusions.
|
Blood
group |
Antigen |
Antibodies |
Agglutinates |
|
A |
A |
Anti-B |
Anti-A serum |
|
B |
B |
Anti-A |
Anti-B serum |
|
AB |
A and B |
None |
Anti-A and anti-B serums |
|
O |
None |
Anti-A and anti-B |
Neither serum |
Consider the table above. People with type A blood
will have the A antigen on the surface of their red cells (as shown in the
table). As a result, anti-A antibodies will not be produced by them because
they would cause the destruction of their own blood. However, if B type blood
is injected into their systems, anti-B antibodies in their plasma will
recognize it as alien and burst or agglutinate the introduced red cells in
order to cleanse the blood of alien protein.
Individuals with type O blood do not produce any
antigens. Therefore, their blood normally willnot be rejected when it is given
to others with different blood types. As a result, type O peopleare universal
donors for transfusions, but they can receive only type O blood themselves.
Thosewho have type AB blood do not make any antibodies. Their blood does not
discriminate againstany other blood type. Consequently, they are universal
receivers for transfusions, but their bloodwill be agglutinated when given to
people with every other type because they produce both kindsof antigens.
Blood grouping
It is easy and inexpensive to determine an
individual's blood type from a few drops of blood.This is how blood
typing/grouping it is done: A serum containing anti-A antibodies is mixed with
some of the blood. Another serum with anti-B antibodies is mixed with the
remaining sample. Whether or not agglutination occurs in either sample
indicates the blood type. For instance, if an individual's blood sample is
agglutinated by the anti-A antibody, but not the anti-B antibody, it means that
the A antigen is present but not the B antigen. Therefore, the blood type is A.
Rhesus
factor
Some people have another antigen called Rhesus
antigen on their red blood cells while others do not have it. Those having this
antigen are referred to as Rhesus positive (Rh+) and those without are it are
Rhesus negative (Rh-). Rh antigen occurs in red blood cells and Rh antibody
occurs in blood plasma.
If Rh antibody mixes with Rh antigen during blood
transfusion, agglutination will occur. Rh+ can stimulate the Rh- to produce
antibodies to act against Rh+ antigens. However, the Rh- cannot stimulate the
Rh+ blood to produce antibodies against Rh-. Therefore, an Rh+ person can
receive blood from the Rh- donor. The donated blood below is group AB rhesus
positive (AB+).
The
Relationship between Blood Groups and Blood Transfusion
Outline the relationship between blood groups and
blood transfusion
Blood transfusion
Blood transfusion is the transfer of blood from one
person (donor) to another person (recipient)through blood vessels. Transfusion
is done to replace lost blood due to illness, accidents or bleeding. The donor
is the person who gives blood while the recipient is the person who receives
blood.
When performing blood transfusions it is important
to avoid combining corresponding antigens and antibodies because they cause
agglutination of red blood cells which may lead to death of the recipient.
Agglutination is the clumping of red blood cells. Blood transfusion is only
possible if blood groups are compatible. Blood group compatibilities are as
shown in the table below.
|
Recipient |
Donor |
|||
|
A |
B |
AB |
O |
|
|
A |
√ |
× |
× |
√ |
|
B |
× |
√ |
× |
√ |
|
AB |
√ |
√ |
√ |
√ |
|
O |
× |
× |
× |
√ |
Note: a tick (√) means compatible and a cross (×)
means incompatible.
Individuals with blood group AB can receive blood
from individuals of all blood groups and are known as universal recipients.
Individuals with blood group O can donate blood to individuals of all blood
groups and are known as universal donors.
The
Advantages and Disadvantages for Blood Transfusion
Explain the advantages and disadvantages for blood
transfusion
Advantages of blood transfusions
Blood transfusion does so much for patients in
need. The gift of life is donated, tested, processed and sent to hospitals’
transfusion service departments where more important work is done to ensure it
is compatible with the recipient.
Blood transfusion has a number of advantages. These
are some of the benefits the donated bloodcan provide for patients in need:
(i)
Increase
low haemoglobin levels: low haemoglobin can cause damage to body organs and
tissues due to low oxygen levels. Donated blood, with sufficient haemoglobin,
can correct the problem of low haemoglobin level of the recipient.
(ii)
Help
stop bleeding: bleeding may not be controlled if platelets and/or clotting
factors are low. Receiving blood with high clotting factors can solve the
problem.
(iii)
Keeps
the heart pumping: low blood volume can lead to low pressure and the heart may
not be able maintain the circulation of blood.
(iv)
Help
with serious blood infections when other methods fail. For example, blood
transfusion may serve as a treatment method for people with sickle cell anaemia
or blood cancer(leukaemia).
(v)
Provide
red cells and platelets when the bone marrow is compromised as with blood
cancers, bone marrow transplants, chemotherapy, etc.
(vi)
Provide
red cells and platelets for patients with blood disorders such as sickle cell.
(vii) Save someone’s life: people who have had a big loss
of blood due to a number of reasons can have their lives saved once they
receive donated blood.
(viii)Because
blood transfusion involves screening of the donor’s blood, if the donor has any
health problem it can be detected and hence treated before getting worse.
Disadvantages of blood transfusions
Although blood transfusions can be life-saving,
they are not without risks. The following are disadvantages of blood
transfusions:
Medical reactions:
(i)
Allergic
reaction: This is the most common reaction. It happens during the
transfusionwhen the body reacts to plasma proteins or other substances in the
donated blood.
(ii)
Fever
reaction: The person gets a sudden fever during or within 24 hours of
thetransfusion. Headache, nausea, chills, or a general feeling of discomfort
may come withthe fever.
(iii)
Haemolytic
reactions: In very rare cases, the patient's blood destroys the donor red
bloodcells. This is called haemolysis. This can be severe and may result in
bleeding and inkidney failure.
Diseases: If
proper screening of the donated blood is not observed, it can cause
transmission of diseases from the donor to the recipient. Examples of such
transmissible diseases are HIV virus, hepatitis, and other infections.
Patients who are given too much blood can develop
high blood pressure, a concern for people who have heart disease.
Precautions
to be Taken During Blood Transfusion
Outline precautions to be taken during blood
transfusion
Blood transfusion precautions
Certain precautions and guidelines must be adhered
to in blood transfusion to ensure the safety of the procedure. The precautions
may include the following:
(i)
Donated
blood must carefully and thoroughly be screened for any infectious diseases
before being transfused to the recipient. The blood should be screened for
diseases like hepatitis B, HIV virus, and all sexually transmitted diseases
(STDs).
(ii)
The
donated blood must be matched with the recipient's blood type, as incompatible
blood types can cause a serious adverse reaction (transfusion reaction). Blood
is introduced slowly by gravity flow directly into the veins (intravenous
infusion) so that medical personnel can observe the patient for signs of
adverse reactions.
(iii)
During
blood transfusion, vital signs such as body temperature, heart rate, and blood
pressure are carefully monitored.
(iv)
Some
patients may get a sudden fever during or within 24 hours of the transfusion,
which may be relieved with pain-relieving drugs such as panadol, diclofenac or
paracetamol.This fever is a common reaction to the white blood cells present in
donated blood.
Blood
Circulation
Blood
Circulation in Humans
Describe blood circulation in humans
Blood circulation is the flow of blood from the
heart to all body parts and back to the heart.Blood circulation or circulatory
system, also called cardiovascular system, is one of three mainsystems in human
body which consist of organs and tissues.
The cardiovascular systems of humans are closed, so
the blood never leaves the network of bloodvessels. But oxygen and nutrients
diffuse across blood vessel layers and enter interstitial fluid,which carries
it to the target cells and carbon dioxide and wastes in the opposite direction.
The human blood circulation consists of two
circulations namely the pulmonary circulation andsystemic circulation.
Pulmonary circulation
Pulmonary circulation is the movement of blood from
the heart, to the lungs, and back to theheart again. This is just one phase of
the overall circulatory system. In this type of circulation,the blood flows
from the right ventricle to the lungs and from the lungs to the left auricle.
In thepulmonary circulation, the blood circulates to and from the lungs, to
release the carbon dioxideand pick up new oxygen.
In the pulmonary circulation, blood from all body
parts (except the lungs) enters the right auriclethrough vena cava. From the
right auricle the blood descends into the right ventricle through thetricuspid
valve. When the ventricle contracts, the blood is pushed into the pulmonary
artery thatbranches into two main parts: one going to the left lung, and
another to the right lung. The fresh,oxygenated blood returns to the left
auricle of the heart through the pulmonary vein.
Systemic circulation
Systemic circulation is the flow of blood between
the heart and the body parts. In this particularcirculation, the blood flows
from the left ventricle to different parts of the body and from22different
parts of the body to the right auricle. The systemic circulation supplies
nourishment toall of the tissues located throughout your body, with the
exception of the heart and lungs becausethey have their own systems. Systemic
circulation is a major part of the overall circulatorysystem. In this
circulation, the blood circulates into the body’s systems, bringing oxygen to
all itsorgans, structures and tissues and collecting carbon dioxide waste.
The systemic cycle begins when the oxygenated blood
coming from the lungs enters the leftauricle. As the chamber fills, it presses
open the bicuspid valve and the blood flows down intothe left ventricle. When
the ventricles contract during a heartbeat, the blood on the left side isforced
into the aorta. This largest artery of the body is an inch wide. The blood
leaving the aortabrings oxygen to all the body’s cells through the network of
ever smaller arteries and capillaries.The used blood from the body returns to
the heart through the network of veins. All of the bloodfrom the body is
eventually collected into the two largest veins: the superior vena cava,
whichreceives blood from the upper body, and the inferior vena cava, which
receives blood from thelower body region. Both venae cavae empty the blood into
the right auricle of the heart.
The process by which blood passes through the heart
twice before it returns to the other parts ofthe body is called double
circulation.
The
Importance of Blood Circulation in Humans
Explain the importance of blood circulation in
humans
Importance of blood circulation
Blood circulation is essential for a healthy body.
Blood circulation is important because itfacilitates the following processes to
take place in the body:
(i)
Every
cell in the body needs to received oxygen and nutrients. Blood rich in oxygen
is sent tothe body organs, tissues and cells to nourish them through blood
circulation.
(ii)
It
enables transportation of waste products from body tissues to excretory organs
so as to beremoved from the body.
(iii)
Protects
the body against diseases and infections through the white blood cells.
(iv)
Facilitates
blood clotting to prevent loss of blood.
(v)
Maintains
body temperature by distributing body heat evenly from the liver and spleen to
allbody parts.
Disorders
and Diseases of the Human Blood Circulatory System
Mention disorders and diseases of the human blood
circulatory system
Additional notes on diseases and
disorders of the circulatory system:
Hypertension
High blood pressure (hypertension) is defined as
high pressure (tension) in the arteries, which arethe vessels that carry blood
from the heart to the rest of the body.
Blood pressure readings are given as two numbers.
The systolic blood pressure (the top number)equals the pressure in the arteries
as the heart contracts. The diastolic pressure (the bottomnumber) is the
pressure in the arteries as the heart relaxes. Normal blood pressure is
below120/80; blood pressure between 120/80 and 139/89 is called
"pre-hypertension," and a bloodpressure of 140/90 or above is
considered high blood pressure.
Complications of high blood pressure include heart
disease, kidney (renal) disease, hardening ofthe arteries (atherosclerosis or
arteriosclerosis), eye damage, and stroke (brain damage).
The
Causes, Symptoms and Effects and Control/Measures of the Disorders and Diseases
of the Human Blood Circulatory System
Outline the causes, symptoms and effects and
control/measures of the disorders and diseases of the human blood circulatory
system
Causes and effects of diseases and
disorders of the human vascular system
|
Disease / Disorder |
Description |
Causes |
Effects / Symptoms |
|
|
1 |
Anaemia |
A reduction in the quantity of(oxygen carrying)
haemoglobin in the blood and/or below normal quantity of red blood cells. |
§ Haemorrhagic anaemia - due to loss of blood § Iron-deficiency anaemia - due to insufficient
iron, often due tdietary deficiency. § Haemolytic anaemia result from the increased destruction
of red blood cells e.g.due to toxic chemicals, autoimmunity, the action of
parasites, abnormal forms of haemoglobin or abnormal red blood cells. § Anaemia can also be caused by the impaired
production of red blood cells, as in leukaemia(when red blood cell production
in the bone marrow is suppressed). |
§ Excessive tiredness § Breathless nesson exertion § Pallor (i.e.looking pale, esp. on face and palms) § Low resistance to infection |
|
2 |
Angina |
Pain afterphysical effort |
Narrowed coronary arteries being unable to supply
increased blood flow required for increased physical exertion. (The arteries
may have been narrowed by the accumulation of atheromatousplaque - see
atherosclerosis, below.) |
Typical symptoms include short-term discomfort
such as an ache, pain or tightness across the front of the chest when or
immediately following exertion or other situations in which heart rate is
increased e.g. due to panic or an argument.Other less common effects &
symptoms are also possible e.g. similar pain when or soon after eating. |
|
Aneurysm |
Balloon-like bulge or swelling in the wall of a
nartery |
In general, causes can be genetic or due to
disease, e.g.1. a degenerative disease a syphilitic infection -causing damage
to the muscular coat of the blood vessel2.a congenital deficiency in the
muscular wall |
Aneurysms can cause the wall of the blood vessel
to weaken. When an aneurysm gets bigger the risk of rupture increases. That
can lead to severe haemorrhage(bleeding) and other complications - some of
which may be life threatening. |
|
|
3 |
Arteriosclerosis |
Hardening of the arteries.(Arteriolosclerosis is
the hardening of arterioles.)Artery walls thicken, stiffen and lose
elasticity, a progressive condition that typically worsens overtime unless
action is taken to address it.Note: Healthy
arteries are flexible and elastic. |
High blood pressure (also known as hypertension)
is widely cited as a cause of, or at least a contributory factor to, the
development of arteriosclerosis.To reduce risk, keep blood pressure within a
healthy range. See also how to reduce risk of atherosclerosis (below). |
Arteriosclerosis (in combination with
atherosclerosis or otherwise) can reduce the flow of blood, hence the supply
of oxygen, nutrients etc.,to tissues in the affected area.Arteriosclerosis
can affect any artery in the body but is of greatest concern when occurs in
the heart (coronary arteries) or the brain. |
|
4 |
Atherosclerosis (Atheroma)- a commontype
ofarteriosclerosis (see above) |
•Multiple fatty plaques(consisting of
e.g.cholesterol and triglyceride)accumulate on the inner walls of arteries.To
reduce risk:1. Eat sensibly (see balanced diet)2.Don't smoke3. Take
appropriate regular exercise4. Maintain a healthy body weight5. Do not
consume excessive alcohol |
A chronic disease that can remain asymptomatic
for decades. However, blood flow is restricted and eventually
obstructed.Various complications of advanced atherosclerosis are possible.
One of the most significant risks is of an infarction due to soft plaque
suddenly rupturing, causing the formation of a thrombus(blood clot) that can
slow or stop blood flow leading to death of the tissues fed by the
artery.Thrombosis of a coronary artery can cause a heart attack(Myocardial
infarction).The same process in an artery to the brain is commonly called
stroke.6. Coronary thrombosisA thrombus is a blood clot.Thrombosis is a
condition in which blood changes from a liquid into aCoronary thrombosis can
occur due to the accumulation of fatty deposits (plaques)inside the arteries,
i.e.atherosclerosis. The hardening of arteries (arteriosclerosis)can also
contribute to reducedCan lead to a |
|
|
6. |
Coronary thrombosis |
A thrombus is a blood clot.Thrombosis is a
condition in which blood changes from a liquid into a solid state, producing
a 'clot'(thrombus). Coronary thrombosis is the condition in which the
thrombus is formed in one of the 3 major coronary arteries that supply the
heart. |
Coronary thrombosis can occur due to the
accumulation of fatty deposits (plaques)inside the arteries,
i.e.atherosclerosis. The hardening of arteries (arteriosclerosis)can also
contribute to reduced blood flow leading to coronary thrombosis. |
§ sudden sharp pain behind the sternum (breastbone) § sudden sharp pain on the left hand side of the
chest, that might spread down the left arm § pain radiating towards the jaw, ear, hands
stomach, right arm § constricting sensation in the throat are a
difficulty breathing § sudden, severe dizziness and/or fainting,
experienced with pain. |
|
7. |
Haemophilia |
Blood clots onlyvery slowly. |
Deficiency of either of two blood coagulation
factors:o Factor VIII(antihaemophilic factor), oro Factor IX(Christmas
factor)· Hereditary -symptoms in males; may be 'carried' by females who can
pass itto their sons without being affected themselves. |
The person might experience prolonged bleeding
after any injury that causes an open wound. In severe cases of haemophilia
there may be spontaneous bleeding into muscles and joints.Treatment: Bleeding
incases of haemophilia has been treated by transfusions of plasma containing
the missing factor, or with concentrated preparations of Factor VIII or
Factor IX obtained by freezing fresh plasma. |
|
8 |
Haematoma |
A collection or accumulation of blood outside the
blood vessels, which may clot forming as welling. |
§ An intra cerebral haematoma may be due to a head
injury. § A perineal haematoma may occur due to bleeding
from a vaginal tear or episiotomy (cut) during child birth. |
§ An intracranial haematoma might compress the
brain and increase pressure within the skull § A sub dural haematoma can be life threatening |
|
9.Haemorrhoids |
Haemorrhoids(also called'piles')
areswellingscontainingenlarged andswollen bloodvessels in oraround therectum
and anus. |
§ excessive body weight § prolonged constipation e.g. due to insufficient
dietary fibre. § prolonged diarrhoea § lifting heavy objects frequently § pregnancy – which can place increased pressure on
pelvic blood vessels, though haemorrhoids often disappear after the birth § age (above 50 years) § family history of haemorrhoids (genetic
predisposition) |
§ Bleeding (bright red blood) after passing a stool § A pile moving down, outside of the anus(prolapse) § a mucus discharge after passing a stool § itchiness around the anus § soreness and inflammation around the anus § sensation of bowels still beingfull and in need
of emptying |
The
Lymphatics System
The
Concept of Lymphatics
Explain the concept of lymphatics
The lymphatic system is a network of tissues and
organs that primarily consists of lymph vessels, lymph nodes and lymph. The
tonsils, adenoids, spleen and thymus are all part of the lymphatic system.
There are 600 to 700 lymph nodes in the human body
that filter the lymph before it returns to thecirculatory system.
The spleen, which is the largest lymphatic organ,
is located on the left side of the body just above the kidney.
The thymus, which stores immature lymphocytes and
prepares them to become active T cells, is located in the chest just above the
heart.
Tonsils are large clusters of lymphatic cells found
in the pharynx.
The
Components of the Human Lymphatic System
Describe the components of the human lymphatic
system
The Human Lymphatic System
Functions of the lymphatic system
The lymphatic system performs the following
functions:
(i)
Removes
excess fluid and waste products from the interstitial spaces between the cells
and returns it into the bloodstream.
(ii)
It
also functions in transporting white blood cells to and from the lymph nodes
into the bones, and antigen-presenting cells (APCs), such as dendritic cells,
to the lymph nodes where an immune response is stimulated.
(iii)
Special
lymph vessels (lacteals) absorb fat and fat-soluble vitamins from the small
intestine and deliver these nutrients to the cells of the body where they are
used by the cells.
(iv)
Protects
the body against germs. Lymph glands produce lymphocytes which produce
antibodies that fight against microbes. They also contain phagocytes, which eat
dead white cells and microbes in the lymph.
The
Common Disorders and Diseases of the Lymphatic System
Mention the common disorders and diseases of the
lymphatic system
There are several diseases and disorders that
affect the lymphatic system. The two common disorders of the lymphatic system
are lymphoedema and lymphatic filariasis (elephantiasis).
Lymphoedema
Lymphoedema is a chronic swelling of the limbs
caused by the accumulation of lymph fluid that occurs if the lymphatic system
is damaged or not functioning properly. While the limbs are typically involved,
the face, neck and abdomen may also be affected.
The lymphatic system consists of a series of lymph
nodes (glands) connected by a network of vessels, similar to blood vessels.
Fluid surrounding body tissues usually drains into near by lymph vessels so it
can be transported back into the blood. However, if the lymph vessels are
blocked, the fluid can't be reabsorbed and will build up in the tissue.
Symptoms
Swelling of the limbs (arms or legs) is the common
symptom of this disorder.
Effects
Unlike oedema, lymphoedema is a long-term condition
that can cause discomfort, pain and a loss of mobility.
Elephantiasis
Lymphatic filariasis, commonly known as elephantiasis,
is a parasitic infection that causes extreme swelling in the arms and legs. It
is a painful and profoundly disfiguring disease. While the infection is usually
acquired in childhood, its visible manifestations occur later in life, causing
temporary or permanent disability.
The disease is caused by the filarial worm, which
is transmitted form human to human via thefemale mosquito when it takes a blood
meal. The parasite grows into an adult worm that lives inthe lymphatic system
of humans.
Symptoms
Elephantiasis is typically characterized by a
thickening of the skin and subcutaneous tissue that gives rise to the grossly
enlarged and swollen limbs that earn the condition its name. In addition to the
characteristic swelling, people with this disorder sometimes have bouts of
fever and headache.
Cause
The disease is caused by thread-like nematode
worms, known as filariae. The larvae(microfilariae) of the parasite are taken
up by the mosquito when it feeds. When the larvae reachthe third stage of
development, they are introduced to a new host, who then develops theinfection.
Effects
(i)
Filarial
infection can cause lymphoedema of the limbs, genital disease (hydrocele,
chylocele,and swelling of the scrotum and penis). It also causes recurrent
acute attacks, which are extremely painf ul and are accompanied by fever.
(ii)
The
infected people may have lymphatic and kidney damages.
(iii)
Sometimes
the swollen limbs become infected.
(iv)
The
infected person is disabled and cannot work to earn his/her living.
Causes,
Symptoms, Effects and Prevention of Disorders and Diseases of the Human
Lymphatic System
Explain causes, symptoms, effects and prevention of
disorders and diseases of the human lymphatic system
Prevention and control
Effective treatment and preventive efforts would
include:
(i)
spraying
insecticides to kill mosquitoes;
(ii)
giving
antibiotics to prevent or control infection;
(iii)
giving
medications to kill micro filariae circulating in the blood;
(iv)
applying
pressure bandages to reduce swelling; and
(v)
surgically
removing infected tissue.
Transport
of Material in Plants in Plants, the Vascular System
The
Concept of Vascular System
Explain the concept of vascular system
TRANSPORTATION IN PLANTS
Materials to be transported across the plant body
are water, minerals and food. Apart from these nutrients, substances like the
hormones also have to be transported. The transport of materials takes place
through a specialized tissue called the vascular tissue. The tissue is made up
of xylem and phloem tissues. Xylem tissue transports water and mineral salts from
the soil to all parts of the plant. Phloem tissue transports manufactured food
from the sites of photosynthesis to all parts of the plant.
In between the xylem and phloem is the vascular
cambium. The cells of cambium tissue divide to form a new xylem and phloem. As
these cells divide and multiply, the plant increases its girth.The xylem grows
inward from the vascular cambium while the phloem grows outward from the
vascular cambium.
The arrangement of the vascular bundles in the
stem, root and leaf of dicot and mocot plants differs in a number of ways. The
diagrams below show the manner they are arranged in there spective organs.
The vascular tissue in the root is arranged in the
inner portion of the root, which is called the vascular cylinder. A layer of
cells known as the endodermis separates the vascular tissue from the ground
tissue in the outer portion of the root. The endodermis is exclusive to roots,
and serves as a checkpoint for materials entering the root’s vascular system. A
waxy substance called suber in is present on the walls of the endodermal cells.
This waxy region, known as the Casparian strip, forces water and solutes to
cross the plasma membranes of endodermal cells instead of slipping between the
cells. This ensures that only materials required by the root pass through the
endodermis, while toxic substances and pathogens are generally excluded. The
outermost cell layer of the root’s vascular tissue is the pericycle, an area
that can give rise to lateral roots. In dicot roots, the xylem and phloem are
arranged alternately in an X shape, whereas in monocot roots, the vascular
tissue is arranged in a ring around the pith.In
In monocot stems, the vascular bundles are
scattered throughout the stem as indicated in the figure below.
In dicot stems, the vascular bundles are arranged
in a ring around the pith.
The arrangement of vascular bundles in the leaves
of dicots and monocots differs. The diagrams below show the differences in
arrangement of the bundles. Can you notice the differences? The xylem and
phloem vessels are enclosed in a bundle sheath.
Components
of Vascular System
Describe components of vascular system
The vascular (transport) system in plants is made
of vascular bundles. The vascular bundles are made of xylem and phloem which
are separated by a wall called vascular cambium, often simply shortened as
cambium (see diagrams discussed in the previous section).
Xylem
It is the vascular tissue that transports water
across the plant body. Xylem is made up of four different types of cells. They
are tracheids, vessels, xylem fibres and xylem parenchyma. Of these only
tracheids and vessels are involved in the transport of water and minerals.
Tracheids
Tracheids are elongated dead cells that have
sloping end walls. The cavity is empty as the cellsare dead. The walls are
thickened with a material called lignin to prevent them from collapsingas water
is transported up the plant. These thickenings are in different patterns. The
cells arearranged end to end.
Vessels
Vessels are also dead cells that have variously
patterned thickened walls. These thickenings are due to lignin. The vessels are
arranged end to end. The end walls of the vessels are either partially or fully
dissolved. This results in the formation of long tubes that carry water.The
xylem vessels and tracheids together form long tubes that have a narrow
diameter. Thus they function as capillaries (narrow tubes) to transport water.
Phloem
It is the vascular tissue that transports organic
substances like sucrose across the plant body. It is made up of four types of
cells namely sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Except for phloem fibres, all the other three types of cells are living. Sieve
tubes and companion cells are mainly involved in the transport of the
materials.
Sieve
tubes
They are tubes formed by cells that are joined end
to end. The end walls of these cells have perforations. The mature sieve tube
cells are enucleated. The cytoplasm of the sieve tube cells is continuous
through the perforations of the end walls. This helps in the transport of
materials.
Companion
cells
They are smaller cells associated with the sieve
tubes. They have dense cytoplasm and elongatednucleus. They are in contact with
the sieve tube cell through pores in the wall.
The
Function of Vascular System in Plants
Explain the function of vascular system in plants
The vascular system is mainly responsible for
transportation of materials within a plant body.The xylem and phloem tissues
are specialized to perform different functions in a plant body.
Functions ofphloem
The xylem functions in transport (translocation) of
manufactured food from the leaves to the cells of the plant, storage organs,
fruits, etc.
Functions ofxylem
§ Provides support for woody plants.
§ Transports water and solutes from roots to all
plant parts.
Absorption
and Movement of Water and Mineral Salts in Plants
The
Functions of Root Hairs in Absorption and Movement of Water and Mineral Salts
in Plants
Explain
the functions of root hairs in absorption and movement of water and mineral
salts in plants
Water and mineral uptake by roots
Plants absorb water from the soil through the root
and transport it to the stem, leaves and flowers. Roots have root hairs that
are unicellular, thin-walled outgrowths of the epiblema (skin of the root).
The root hairs are in close contact with the thin
film of water surrounding the soil particles.There are mineral salts such as
nitrates, chlorides, sulphates, phosphates, etc., dissolved in thiswater.
Water is absorbed by osmosis, while the minerals
are absorbed as ions by active transport(transport against the law of
diffusion, by spending cellular energy). The cell membrane has transport
proteins that allow the ions to cross the membrane. The ions then move upward
through the xylem, to the leaves and other aerial parts of the plant.
The cell wall of each root hair is permeable to
water and minerals, but its cell membrane and the membrane around the vacuole
are semi permeable membranes. The root hair cells take up mineral ions by active
transport.
This creates a concentration difference of these
ions between the root and the soil. Now, the soil solution has higher water
content than the cell sap of the root hair. Hence, water from the soil diffuses
into the root hair. The root hair cells now become turgid, while the adjacent
cells of the cortex have lower water content.
This results in the diffusion of water from the
root hairs into the cortical cells (see figure below).After passing through the
cortical cells by osmosis, the water reaches the endodermis (tissue separating
the cortex from the vascular tissues). The endodermis forces water into the
xylem tubes through passage cells.
The pressure with which water is pushed into the
xylem tubes of the root is called root pressure.The water moving upwards forms
a column, which is maintained up to a certain height due to root pressure.
The
Movement of Water and Dissolved Mineral Salts in Plants
Outline the movement of water and dissolved mineral
salts in plants
Upward movement of water within the
plant
There are several processes that enable the water
to move up a plant. These processes include root pressure, transpiration pull,
cohesion, adhesion and capillarity.
Root
pressure
As long as the soil is damp, there will be water
taken in by the root hairs. As more water is taken in, the water that is
already in the xylem vessel will be pushed up the plant. This is called root
push or root pressure and it helps to push water up to the leaves.
Root pressure is capable, under ideal atmospheric conditions,
of pushing water one or two feet above the ground. Since root pressure is not
strong enough to move water up very high, another process called transpiration
pull is needed to enable the water to continue moving up the plant.
Experiments
to Demonstrate Transpiration pull, Root Pressure and Capillarity
Conduct experiments to demonstrate transpiration
pull, root pressure and capillarity
Transpiration pull
Transpiration is the loss of water through the
leaves and other parts of the plant. Most transpiration occurs through
openings, called stomata, on the underside of the leaves. As transpiration
occurs, water is lost. This water is replaced by water in the xylem vessels.
This causes an upward pull (transpiration pull or transpiration stream) on the
water in the vessels.Thus, water is pulled up through the plant, and more
enters by the roots to replace it.
Cohesion
Cohesion is the force of attraction between similar
molecules. Transpiration pull is possiblebecause water molecules cling to each
other by cohesion. When water molecules cling to eachother as they move up the
stem and into the leaves, they pull up more water molecules up theplant. This
process, however, is facilitated by transpiration pull since the water
molecules lostthrough transpiration is being replaced by more water molecules
absorbed by the roots.
Adhesion
Adhesion
Adhesion is the force of attraction between
different molecules. As water molecules are stuck together by cohesion, the
entire column of water in the xylem adheres to the sides of the xylem.It is
said that the water in under tension as the column moves up the xylem. At the
same time, the xylem tube narrows because of the tension.
Cohesion and adhesion forces maintain a continuous
column of water in the xylem vessels from the roots to the leaves of plants.
Capillarity
Capillarity is the tendency of water to rise
through narrow tubes. The lumen of xylem tracheids and vessels is very narrow
and this enables water to rise through it by capillarity. Capillarity is
assisted by adhesion and cohesion forces.
The
Concept of Transpiration
Explain the concept of transpiration
Transpiration is the evaporation of water from
plants. It occurs chiefly through the leaves while their stomata are open for
the passage of carbon dioxide and oxygen during photosynthesis.
Transpiration also occurs through the cuticle and
lenticels. Lenticels are pores in the stems of woody plants that allow gaseous
exchange between the atmosphere and the internal tissues.
The
Significance of Transpiration in Plants
Outline the significance of transpiration in plants
Transpiration is of immense importance in plant
life as it is of great benefit to the plant. The following are the reasons why
transpiration is important in plants.
Cooling of the plant
The leaves absorb the radiant energy. Some of the
light energy is utilized in photosynthesis. The rest is converted into heat
energy resulting in an increase in leaf temperature. However, rapid loss of
water in the form of water vapour from the aerial parts of the plant through
transpiration brings down their temperature. Transpiration thus provides a
significant cooling effect which keeps the plant from being overheated.
Mineral transport
Mineral salts remain dissolved in the soil water
and are absorbed by the roots. Minerals that are absorbed and accumulated in
the xylem duct of the root move up and are distributed in the plant by the
transpiration stream.
Water movement
The absorbed water is transported from roots to
leaves through the xylem vessels. This is greatly influenced by transpiration
pull. Water loss due to transpiration results in the development of low water
potential in the leaf tissues. Thus, water moves from the xylem vessels to the
leaf cells.
Development of mechanical tissues
Greater amount of transpiration helps in the
development of mechanical tissues in plants. The plants become healthier and
more compact, the cell walls become thick and cutinized and the plants are able
to resist the attack of fungi and bacteria.
Maintenance of turgidity
Transpiration maintains an optimum degree of
turgidity in cells. Under favourable conditions ,plants absorb excess amount of
water, which is given off by transpiration to maintain the optimum turgidity
for better growth.
Increase of taste of fruits
The solutes inside the cell become more
concentrated when transpiration is rapid. Consequently, the concentration of
sugar solution in the cells of fruits increases and fruits taste sweeter.
Wilting
When the rate of evaporation is higher than that of
absorption of water from the soil, as it occurs during drought conditions, the
plant wilts. Wilting is beneficial when a plant cannot obtain enough water to
replace that lost by the plant through transpiration because it causes the
closure of the stomata (singular: stoma). Thus, the rate of evaporation is
greatly reduced.
Transpiration
as a necessary evil
Transpiration
is a necessary evil because of the following facts:-
(i)
A
large amount of absorbed water is lost during transpiration which is harmful to
plants.
(ii)
Unnecessary
wastage of energy takes place during the process of water absorption which
islost due to transpiration.
(iii)
When
the rate of transpiration is high in plants growing in soil deficient in water,
an internal water deficit develops in plants which may affect metabolic
process.
(iv)
Many
xerophytes undergo structural modifications and adaptations to check
transpiration.
(v)
Considering
both the beneficial and harmful effects of transpiration, it may be concluded
that itis definitely advantageous in spite of its harmful consequences.
Factors
Affecting the Rate of Transpiration in Plants
Outline factors affecting the rate of transpiration
in plants
The rate of transpiration can be affected by both
plant features and environmental factors.
Plant factors
These plant parameters help plants control rates of
transpiration by serving as forms of resistance to water movement out of the
plant. They include the following:-
Root
system
Plants with extensive root systems absorb a great
amount of water and therefore much water ismoved up the plant. Thus, plants
with extensive root systems have higher rates of transpirationthan those with
few roots.
Size
of leaves
A plant with broad leaves tend to lose more water
than that with small leaves. This is because the broad leaves have large
surface areas over which transpiration takes place.
Leaf
structure
The structure of a leaf has a great influence on
the rate of transpiration. The following areanatomical structures of a leaf
that affect the rate of transpiration:-
Number
of stomata
Stomata are pores in the leaf that allow gaseous
exchange to take place, and water vapour to leave the plant. Special cells
called guard cells control each pore’s opening or closing. Some plants have
many stomata while others have a few stomata. The more the stomata, the higher
the rate of transpiration and vice versa.
Position
of stomata
Plants with few stomata on the upper surface of the
leaf experiences a little transpiration compared to those with many stomata on
the lower leaf surface. This is because the upper surface is highly stricken by
direct sunlight hence increasing the rate of transpiration.
Epidermal
hairs
Epidermal hair on the leaf traps a thin layer of
still air close to the leaf surface. For the water lostfrom the leaf to get
into the atmosphere, it has to cross this resistant layer of air. The layer
thuschecks excessive loss of water from the leaf. Likewise, the water vapour
from the leaf is alsotrapped by the epidermal hairs. This prevents further loss
of water vapour from the leaves andhence slows down the rate of transpiration.
Size
of stomatal air spaces
Large air spaces between the cells of the spongy
mesophyll and stomata, called substomatal airspaces, increase the rate of
transpiration. Small substomatal air spaces reduce the rate of transpiration.
Cuticle
The cuticle is the waxy layer present on all
above-ground tissue of a plant and serves as a barrier to water movement out of
a leaf. Because the cuticle is made of wax, it is very hydrophobic or
‘water-repelling’. Therefore, water does not move through it very easily. The
thicker the cuticle layer on a leaf surface, the slower the transpiration rate.
Cuticle thickness varies widely among plant species. In general, plants from
hot, dry climates have thicker cuticles than plants from cool, moist climates.
In addition, leaves that develop under direct sunlight will have much thicker
cuticles than leaves that develop under shade conditions.
Environmental factors
Some environmental conditions create the driving
force for movement of water out of the plant.Others alter the plant’s ability
to control water loss.
Light
Plants transpire more rapidly in the light than in
the dark. This is largely because light stimulates the opening of the stomata
(mechanism). Light also speeds up transpiration by warming the leaf.
Photosynthesis occurs in the presence of light. A
higher light intensity increases the rate of photosynthesis in the guard cells.
As the guard cells absorb water from the soil for photosynthesis, they become
turgid and hence the stomata are opened, and hence a higher rate of
transpiration.
Temperature
Plants transpire more rapidly at higher
temperatures because water evaporates more rapidly as the temperature rises. At
30°C, a leaf may transpire three times as fast as it does at 20°C.
Relative
humidity
Relative humidity is the amount of water vapour in
the air compared to the amount of water vapour that air could hold at a given
temperature. When the air is less moist, the relative humidity is low, and thus
the rate of transpiration is greater. When relative humidity is high, the
atmosphere contains more moisture, reducing the rate of transpiration.
Therefore, transpiration increases with the decrease in relative humidity.
The rate of diffusion of any substance increases as
the difference in concentration of thesubstances in the two regions increases.
When the surrounding air is less humidity, diffusion ofwater out of the leaf
goes on more rapidly.
Wind
The wind removes water vapour and thus increases
the rate of transpiration. High winds lead to stomatal closure to stop the
rapid water loss and hence bring a drop in rate of transpiration.Moderate winds
may reduce transpiration by lowering the temperature of the leaf.
When there is no breeze, the air surrounding a leaf
becomes increasingly humid thus reducing the rate of transpiration. When a
breeze is present, the humid air is carried away and replaced by drier air,
thus increasing the rate of transpiration.
Soil
water
The source of water for transpiration out of the
plant comes from the soil. Plants with adequate soil moisture will normally
transpire at high rates because the soil provides the water to move through the
plant. Plants cannot continue to transpire without wilting if the soil is very
dry because the water in the xylem that moves out through the leaves is not
being replaced by the soil water. Thus, the rate of transpiration will increase
when there is adequate amount of water in the soil and will decrease when the
soil contains little moisture.
Atmospheric
pressure
Transpiration is high at low atmospheric pressure
and it is low at high atmospheric pressure.Plants that grow naturally at higher
altitudes, where the atmospheric pressure is low, have modified leaves to reduce
the rate of transpiration.