It is the
process of movement of water and other molecules to the concerned parts of the
organism.
Transportation in Human Beings
Human circulatory system: Blood, Heart & Blood
vessels.
Blood
Blood is a
fluid connective tissue.
It consists of a fluid medium called plasma in
which blood cells (RBC, WBC & platelets) are suspended.
Plasma transports food, O2, CO2 and
nitrogenous wastes.
Oxygen is mainly transported by Haemoglobin.
Normal level of haemoglobin in human beings:
- In men: 14 to 17 g/ 100
ml.
- In women: 12 to 15 g/ 100
ml.
- In children: 11 to 16 g/ 100 ml.
The normal level of haemoglobin in animals like buffalo or cow is 10.4 to
16.4 g/ 100 ml. Haemoglobin content in calves is
higher than male and female animals.
Adult men do more work than women and children. So they need more oxygen to
get energy. That’s why adult men have more haemoglobin.
Haemoglobin level in human is comparatively more than that of animals like
cattle because human body needs more oxygen to do various biological works.
Our pump – the
heart
A schematic sectional view of the human heart
Heart pumps the blood all over the body.
It is a muscular organ that is as big as our fist.
It has 4 chambers: 2 upper right and left atria
and 2 lower right and left ventricles.
Right chambers carry CO2-rich (deoxygenated)
blood. Left chambers carry O2-rich (oxygenated) blood.
Deoxygenated blood reaches the lungs to remove CO2.
Oxygenated blood from the lungs is brought back to the heart and then pumped to
the rest of the body.
Pumping process of heart:
- Oxygenated blood from the lungs →
left atrium relaxes → blood enters left atrium → left atrium contracts &
left ventricle relaxes → blood enters left ventricle → left ventricle contracts
→ blood is pumped out to the body.
- Deoxygenated
blood from the body → right atrium relaxes → blood enters right atrium → right
atrium contracts & right ventricle dilates → blood transfers to right
ventricle → right ventricle contracts → blood is pumped into the lungs for
oxygenation.
Since ventricles have to pump blood into various organs,
they have thicker muscular walls than that of atria.
Heart has valves to prevent the backflow of blood
when the atria or ventricles contract.
Schematic
representation of transport and exchange of oxygen and CO2
Oxygen enters the blood in the lungs
The separation of right side and left side of the heart prevents
mixing of oxygenated and deoxygenated blood. This allows a highly efficient supply
of oxygen to the body. It is useful in animals that need high energy (birds
& mammals) to maintain body temperature.
Animals like amphibians & many reptiles do not
use energy to maintain temperature. They depend on the temperature in the environment.
Such animals have 3-chambered heart, and tolerate some mixing of the
oxygenated and deoxygenated blood.
Fishes have only 2-chambered heart. Here, circulation
occurs as follows:
Deoxygenated blood
enters the heart → pumped to gills → blood is oxygenated in gills → blood to rest
of the body.
Thus, blood goes
only once through the heart during one cycle of passage through the body.
In other vertebrates, blood goes through the heart twice
during each cycle. This is called double circulation.
Blood pressure (BP)
- It is the force
that blood exerts against the wall of a vessel. This is much greater in
arteries than in veins.
- Systolic pressure: Blood pressure in
the artery during ventricular systole (contraction). It is about 120
mm Hg.
- Diastolic pressure:
Blood pressure in
the artery during ventricular diastole (relaxation). It is about 80 mm Hg.
- Sphygmomanometer: An instrument to
measure BP.
- High BP (hypertension) is caused by
the constriction of arterioles, which increases resistance to blood flow. It
leads to the rupture of an artery and internal bleeding.
The tubes –
blood vessels
It includes arteries, veins and capillaries.
Arteries: They carry blood from heart to various body parts. Since
the blood emerges from the heart under high pressure, the arteries have thick,
elastic walls.
On reaching an
organ or tissue, the artery divides into small branches (arterioles) to
bring the blood in contact with all the cells.
Veins: They collect the blood from different organs and bring
it back to the heart. They have no thick walls because the blood is no
longer under pressure. Instead, they have valves to flow the blood only in one
direction.
Capillaries: The smallest vessels having walls which are one-cell
thick. Through this wall, exchange of material between blood and
surrounding cells takes place.
The capillaries
join together to form veins that convey the blood away from the organ or
tissue.
Maintenance by platelets
Leakage or loss of blood due to injury leads to reduction in pressure and
efficiency of circulatory system.
To avoid this, the platelet cells plug these leaks
to clot the blood at the points of injury.
Lymph (Tissue
fluid):
Through the pores in the capillary walls, some amount of
plasma, proteins and blood cells escape into intercellular spaces in the
tissues to form lymph.
It is similar to blood plasma but colourless and contains
less protein.
From intercellular spaces, lymph drains into lymphatic
capillaries, which join to large lymph vessels that finally open into larger veins.
Lymph carries digested fat from intestine and drains
excess fluid from extracellular space back into the blood.
Soil is the nearest and richest source of raw materials (water & minerals).
If the distance between roots & leaves are small,
energy and raw materials can easily diffuse to all parts. But if the distance is
large, a transportation system is essential.
Plants do not move and have enormous dead cells. So, they need only low energy and slow transport systems.
Plant transport systems include 2 independently organised conducting tubes:
- Xylem: It moves water & minerals
from the soil.
- Phloem: It transports products of
photosynthesis (energy stores) from leaves to other parts.
Transport of
water
In xylem tissue,
vessels &
tracheids of the roots, stems and leaves are interconnected to form water-conducting channels reaching all parts.
At the roots, cells actively take up ions from soil. This
creates a difference in the concentration of ions between root and soil. So, water
moves into the root from the soil. Thus there is steady movement of water into
root xylem, creating a column of water pushing upwards.
But this pressure is not enough to move water over the heights. So, plants use another strategy called
transpiration.
Transpiration is the loss of water vapour from the aerial parts (mainly
stomata of leaves) of the plant. It can be proved by the following activity.
- Take two small same
sized pots with same amount of soil. One should have a plant in it. In other
pot, place a stick of the same height as the plant.
- Cover the soil
in both pots with a plastic sheet so that moisture cannot escape by
evaporation.
- Cover both sets with
plastic sheets and place in bright sunlight for half an hour.
- In pot with plant, water
droplets are found in plastic sheet. It is due to condensation of water vapour
released by transpiration. In other pot, water droplets are not formed.
The water which is lost through the stomata is replaced by water from the xylem vessels in the leaf.
Transpiration creates a suction which pulls water from
the xylem cells of roots.
Thus, transpiration helps in the absorption and upward
movement of water & minerals from roots to the leaves. It also helps in temperature
regulation.
Generally, stomata are closed at night. So, plants depend
on the root pressure for water transport at night.
During the day when stomata
are open, the transpiration pull is the major driving force in the water
transport.Transport of
food & other substances
Transport of soluble products of photosynthesis (food) from leaves to other parts is called
translocation.
It occurs in a vascular tissue called phloem.
Phloem also transports amino acids & other
substances.
These substances are delivered to the storage organs of roots,
fruits and seeds and to growing organs.
Translocation takes place in the sieve tubes with
the help of adjacent companion cells both in upward and downward
directions.
Xylem transport occurs mainly by simple physical forces.
But for the translocation in phloem, energy is utilised.
Material like sucrose is transferred into phloem using energy
from ATP. This increases the osmotic pressure of the tissue causing water to
move into it. This pressure moves the material in the phloem to tissues. E.g.,
in the spring, sugar stored in root or stem is transported to the buds which
need energy to grow.
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