Transportation
Transportation in Human Beings: The circulatory system is
responsible for transport of various substances in human
beings. It is composed of the heart, arteries, veins and blood
capillaries. Blood plays the role of the carrier of substances.
1. Heart: Heart is a muscular organ, which is composed of
cardiac muscles.
It is so small that, it can fit inside an adult’s wrist. The
heart is a pumping organ which pumps the blood.
The human heart is composed of four chambers, viz. right
atrium, right ventricle, left ventricle and left atrium.
Systole: Contraction of cardiac muscles is called systole.
Diastole: Relaxation of cardiac muscles is called diastole.
2. Arteries:
These are thick-walled blood vessels which carry
oxygenated blood from the heart to different organs.
Pulmonary arteries are exceptions because they carry
deoxygenated blood from the heart to lungs, where
oxygenation of blood takes place.
3. Veins:
These are thin-walled blood vessels which carry
deoxygenated blood from different organs to the heart,
pulmonary veins are exceptions because they carry
oxygenated blood from lungs to the heart.
Valves are present in veins to prevent back flow of blood.
4. Capillaries: These are the blood vessels which have single-
celled walls.
Blood: Blood is a connective tissue which plays the role of the
carrier for various substances in the body. Blood is composed of
1. Plasma 2. Blood cells 3. Platelets.
Blood plasma: Blood plasma is a pale coloured liquid which is
mostly composed of water. Blood plasma forms the matrix of
blood.
Blood cells: There are two types of blood cells, viz. Red Blood
Cells (RBCs) and White Blood Cells (WBCs).
(a) Red Blood Corpuscles (RBCs): These are of red colour
because of the presence of haemoglobin which is a pigment.
Haemoglobin readily combines with oxygen and carbon
dioxide. The transport of oxygen happens through
haemoglobin. Some part of carbon dioxide is also
transported through haemoglobin.
(b) White Blood Corpuscles (WBCs): These are of pale white
colour. They play important role in the immunity.
Platelets: Platelets are responsible for blood coagulation. Blood
coagulation is a defense mechanism which prevents excess
loss of blood, in case of an injury.
Lymph:
Lymph is similar to blood but RBCs are absent in lymph.
Lymph is formed from the fluid which leaks from blood
capillaries and goes to the intercellular space in the
tissues. This fluid is collected through lymph vessels and
finally return to the blood capillaries.
Lymph also plays an important role in the immune system.
Lymph a yellowish fluids escape from the blood capillaries
into the intercellular spaces contain less proteins than
blood.
Lymph flows from the tissues to the heart assisting in
transportation and destroying germs.
Double circulation: In the human heart, blood passes through
the heart twice in one cardiac cycle. This type of circulation is
called double circulation. One complete heartbeat in which all
the chambers of the heart contract and relax once is called
cardiac cycle. The heart beats about 72 times per minute in a
normal adult. In one cardiac cycle, the heart pumps out 70 mL
blood and thus, about 4900 mL blood in a minute. Double
circulation ensures complete segregation of oxygenated and
deoxygenated blood which is necessary for optimum energy
production in warm-blooded animals.
Transportation in plants: Plants have specialized vascular
tissues for transportation of substances. There are two types of
vascular tissues in plants.
Xylem: Xylem is responsible for transportation of water
and minerals. It is composed of trachids, xylem vessels,
xylem parenchyma and xylem fibre. Tracheids and xylem
vessels are the conducting elements. The xylem makes a
continuous tube in plants which runs from roots to stem
and right up to the veins of leaves.
Carry water and minerals from the leaves to the other part
of the plant.
Phloem: Phloem is responsible for transportation of food.
Phloem is composed of sieve tubes, companion cells,
phloem parenchyma and bast fibers. Sieve tubes are the
conducting elements in phloem.
Carries product of photosynthesis from roots to other part
of the plant.
Transportation in plants
Ascent of sap: The upward movement of water and minerals
from roots to different plant parts is called ascent of sap. Many
factors are at play in ascent of sap and it takes place in many
steps. They are explained as follows :
Root pressure: The walls of cells of root hairs are very thin.
Water from soil enters the root hairs because of osmosis.
Root pressure is responsible for movement of water up to
the base of the stem.
Capillary action: A very fine tube is called capillaiy, water,
or any liquid, rises in the capillary because of physical
forces and this phenomenon is called capillary action.
Water, in stem, rises up to some height because of
capillaiy action.
Adhesion-cohesion of water molecules: Water molecules
make a continuous column in the xylem because of forces
of adhesion and cohesion among the molecules.
Transpiration pull: Loss of water vapour through stomata
and lenticels, in plants, is called transpiration.
Transpiration through stomata creates vacuum which
creates a suction, called transpiration pull. The
transpiration pull sucks the water column from the xylem
tubes and thus, water is able to rise to great heights in
even the tallest plants.
Transport of food: Transport of food in plants happens
because of utilization of energy. Thus, unlike the transport
through xylem, it is a form of active transport. Moreover,
the flow of substances through phloem takes place in both
directions, i.e., it is a two-way traffic in phloem.
Transpiration is the process of loss of water as vapour
from aerial parts of the plant.
Functions
Absorption and upward movement of water and minerals
by creating pull.
Helps in temperature regulation in plant.
Transport of food from leaves (food factory) to different parts of
the plant is called Translocation.
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