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Chapter: Transportation

Transportation in plants:

  1. Plants make their food through the process of photosynthesis using CO2 and water in the presence of sunlight. Apart from these sources plants also require some raw materials for building up their body.
  2. Soil is the richest source of these raw materials. The raw materials include nitrogen, phosphorus and other minerals.
  3. Plants absorb these raw materials through roots. Since, root is the part of plant body which is in contact with the soil.
  4. If the distance between soil-containing organs and chlorophyll containing organs is small the raw materials can easily diffuse through all parts of the plant body. But in case if the distance is large plants need a special transport system for this purpose.
  5. Plant transport system will move energy store from leaves and raw material from roots.
  6. There are two transport systems in plants one is the xylem which conducts water and minerals from the soil and the other is phloem which transports products of photosynthesis to other parts of the plant.

a. Xylem:

cells of this tissue are mostly dead and have thick walls. They are mainly of the following types:

  1. Tracheids: These are long narrow cells with walls that are not permeable to water. Tracheids die when they undergo and then their cytoplasm disintegrates. Disintegration of cytoplasm results in hollow cells which are connected with each other through which water can pass.
  2. Xylem vessels: These are tubular structures and are much wider than tracheids. They are arranged on top of one another like a pipeline. The death of the cells results in the disintegration of cell walls at both the ends because of which stacked vessels become continuous tubes. The water and minerals flow freely in vertical direction through these tubes
  3. Xylem parenchyma: Food is stored by xylem parenchyma
  4. Xylem fibers: Mainly support the plant.

b. Phloem:

Phloem is made up of four types of elements: sieve tubes, companion cells, phloem fibers and phloem parenchyma. Sieve tubes are tubular cells with perforated walls. Unlike xylem, materials can move in both the direction in Phloem. Phloem transports food from leaves to other parts of the plant. Phloem cells are living cells, the only exception is the phloem fibers.

Water Uptake

Root hair cells

Root hairs are the hair like structures on the epidermis of a plant root. They are invisible to the naked eye since they are lateral extensions of a single cell and are rarely branched. Root hairs are found in the region of maturation of the root. The main function of root hairs is to collect water, minerals and nutrients from the soil and take this solution to the plants through roots. Root hairs are directly involved in the synthesis of nodules in legume plants. Root hairs cells secrete acids which helps in solubilizing minerals into ionic form , making ions easier to take up.

Uptake of water through roots:

The roots of the plant are adapted to absorb both minerals and water from the soil. The water enters the plant through the root hair cells. Roots have enormous surface area and therefore they penetrate between the particles of soil.

  1. Transpiration: water is lost from the leaves and lowers the water potential in the leaf tissues.
  2. Water moves from xylem to the entire leaf tissues downward water potential gradient.
  3. Due to the tension caused by water loss from the leaves water moves up the stem in the xylem.
  4. Water uptake occurs by osmosis from the soil solution into the root cells.


It is defined as the evaporation of water at the surface of the mesophyll followed by loss of water vapour from plant leaves through stomata.

Evaporation from leaves:

Water evaporates from the parts of a plant that are exposed to the atmosphere. For example, the entire shoot system of a terrestrial plant and upper leaf surface of a floating aquatic plant. Large amount of water loss takes place through the stomata which are the minute openings on the leaf surface. Usually more number of stomata are present lower surface of the leaf than the upper surface. The lower surface of leaf is less exposed to the warming effects of suns radiation, which would speed up the evaporation rate. The stomata allow the uptake of CO2 for photosynthesis. When the stomata are open water evaporated from the spongy mesophyll cell can diffuse out of the leaf down the water potential gradient. Water cannot diffuse into the leaf through stomata since the air spaces inside the leaf are completely saturated. Instead water must be absorbed from the soil solution and drawn up through the plant. Since water is lost through the stomatal opening in the leaf, transpiration is affected by the leaf structure and by conditions in the atmosphere.

Factors affecting rate of transpiration:

  1. Wind: Humid air is moved away from the leaf surface and increases rate of transpiration.
  2. Temperature: the water holding capacity of the air is increased due to high temperature and thereby rate of transpiration is increased.
  3. Low humidity: low humidity increases the water potential gradient between the leaf and atmosphere and increases transpiration
  4. High light intensity: it causes stomata to open for the purpose of transpiration but the opening of stomata allows transpiration to occur.


Wilting refers to the loss of rigidity in the non-woody part of the plant. This occurs due to excess loss of water from the plants. Turgor pressure in non-lignified plant cells falls to zero with excess loss of water, this results in wilting. If the water loss exceeds water uptake then the cells become flaccid and the tissue becomes limp thereby the plant is no longer supported. Wilting affects the growth of the plant and its transpiration. Plant dies due to permanent wilting


It is defined as the movement of food material like sucrose and amino acids from leaves to other parts of the plant. The translocation process takes place with the help of adjacent companion cells through the sieve tubes both in upward and downward direction. The translocation process in phloem requires energy. Material like sucrose is transferred into phloem tissue using energy from ATP. As a result osmotic pressure of the tissue increases causing water to move into it. Osmotic pressure moves material with less pressure into phloem. This allows phloem to move material according to the plant needs.

Transport in humans

Circulatory system

Blood flows throughout the body in a system of tube like blood vessels arranged in such a way that they all eventually lead back to heart. The blood flows away from the heart in vessels called arteries and it flows back to heart through vessels called veins. Capillaries join the arteries and veins. The main artery in humans and most of the animals is the aorta and the main vein is called the vena cava.

Double circulation

  1. The heart is a muscular organ which has the size of our closed fist. Since both oxygen and carbon dioxide have to be transported by blood, our heart has four chambers which prevent the mixing of oxygen rich blood with the blood containing carbon dioxide.
  2. The carbon dioxide rich blood has to be transported to lungs and the oxygenated blood from lungs has to be brought back to the heart.
  3. The oxygen rich blood is then pumped to the rest of the body.
  4. Oxygen rich blood from the lungs comes to the left atrium. The left atrium relaxes while collecting the blood and then contracts while the blood is transferred to left ventricle as it expands. When the left ventricle contracts the blood is pumped out of the body.
  5. De- oxygenated blood from the body comes to the upper chamber on the right side, i.e. Right atrium as it expands.
  6. As the right atrium contracts, the corresponding lower chamber, the right ventricle dilates, this transfers blood to right ventricle, which in turn pumps it to lungs for oxygenation.

Oxygen enters the blood in the lungs:

  1. The separation of right and left side of the heart prevents the mixing of oxygenated blood with the deoxygenated blood. The separation of the heart into four chambers also allows the efficient supply of oxygen to the body.
  2. This kind of a separation of heart is useful in most of the animals and birds which need high amounts of energy to maintain their body temperature.
  3. Animals like amphibians and reptiles have a three chambered heart where there is a slight mixing of oxygenated blood with the deoxygenated blood.
  4. Fishes on the other hand have a two chambered heart, the blood is pumped to gills and is oxygenated there and then passes to the remaining body.  As a result in fishes, blood goes only once through the heart during one cycle of passage through the body.
  5. In case of vertebrates the blood goes twice to the heart during each cycle and this is called double circulation.

The tubes- blood vessels

  1. Arteries and vessels carry blood away from the heart to various organs in the body and arteries have thick, elastic walls since the blood they collect from the heart is under high pressure.
  2. Veins on the other hand collect the blood from different organs and bring it back to heart. Veins do not have thick walls because the blood they collect from the organs is not under pressure.
  3. Veins have valves to ensure that the blood flow is only in one direction.
  4. The arteries divide into smaller vessels once they reach the organ in order to bring the blood in contact with all the individual cells.
  5. The smallest vessels are called capillaries; their walls are about one cell thick. Exchange of material between blood and surrounding cells takes place across this thin wall.
  6. Capillaries join to form veins which convey blood from organs to heart.

The working of heart

Heart beats about 70 times per minutes in a healthy person during normal levels of activity. The heart muscles are called the cardiac muscles, they are different from other muscles as they do not get tired and this is because each contraction of the heart is followed by a relaxation. Even when the heart is beating fast during exercise, the period of relaxation allows the muscle to recover so that it is not tired. The pattern of contraction and relaxation is always kept going by electrical impulses sent from a region of the heart called the pacemaker. It is a specialized tissue in the wall of the right atrium. The signals from the pacemaker make sure that the atria contract just before the ventricles, so the blood flows from atria to ventricles and they also see to that the heartbeat is fast enough to meet the demands of the tissue for oxygen and nutrients, and for the removal of wastes. Valves that are present in the veins prevent the backward flow of blood.

Effect of physical activity on pulse rate

The contraction of ventricles forces blood at high pressure into the arteries. This pressure needs to carry blood to the working tissue, but it must not be so high that it damages the blood vessels. The blood pressure can be raised by

  1. Making the ventricles contract more powerfully
  2. Narrowing the diameter of arteries.

Stress or excitement also raises the blood pressure. A diet with more of saturated fat can cause high blood pressure by clogging up arteries.

The high pressure generated when the ventricles contract forces blood out into the arteries. As a result the elastic walls of arteries expand and then relax creating a pulse in the arteries. Pulse can be felt wherever an artery is pressed against solid surface, such as bone. The pulse should always be felt with index finger and not the thumb finger since the thumb finger has the pulse of its own. There is no pulse in the vein since the blood in the veins has no pressure and the walls of veins are not elastic. During physical exercise the person often has lower pulse rate than the other people and this because while exercising the muscles work hard. They need more oxygen and glucose to release energy by respiration, so they need increased circulation of blood to supply the oxygen and glucose and this achieved in two ways.

  1. The heart pumps more blood each minute it pumps more quickly and more deeply.
  2. Sphincters control the distribution of blood i.e. rings of muscles open to increase the blood flow to the muscles and close to decrease the blood flow to less important areas like the gut.

Coronary heart disease

It is a type of heart disease which occurs due to the block in one of the coronary arteries. The block in the coronary arteries interrupts the blood supply to the heart as a result the heart muscles are deprived of glucose and oxygen and thereby poisonous wastes such as lactic acid can build up. Due to the lactic acid built up, part of the heart muscle stops contracting resulting in heart attack. Heart attack can be fatal since other tissues in the body no longer receive oxygen and glucose. A healthy coronary artery may be narrowed by atheroma so that blood flow through it is restricted. The risk of developing CHD is increased by Poor diet which results in high levels of cholesterol and saturated fatty acids in the blood, by smoking, lack of exercises and stress. CHD can also occur if there is a family history of heart disease.

Preventive measures:

We can prevent CHD by maintaining a healthy life style- avoid smoking, regular exercise. We need to keep a check on diet. The food we take must have less fat content. We can also prevent heart disease by taking half an aspirin a day.  Aspirin seems to help stop small clots forming which could block the artery. Drinking small quantity of alcohol, preferably red wine is also known to prevent clot formation in arteries.

Blood vessels to and from lungs, liver, heart, kidney

1. Liver:

Hepatic artery carries oxygenated blood to the liver and hepatic vein returns the blood with a regulated optimum concentration of food substances from the liver to circulation. Hepatic portal vein carries blood containing variable amounts of the absorbed products of digestion from the digestive system to the liver.

2. Lungs:

Pulmonary artery carries unlike other arteries carries the deoxygenated blood containing a high carbon dioxide to the liver. Pulmonary vein unlike other veins carries the oxygenated blood with high oxygen concentration and low carbon dioxide concentration to the circulation

3. Heart:

Aorta- the main artery supplies the oxygenated blood at high pressure to the organs and tissues of the body. Vena cava -the main vein returns the deoxygenated blood at low pressure from organs and tissues to the heart.

4. Kidney

Renal artery carries oxygenated blood with a high concentration of urea to the kidneys and renal vein returns the blood with reduced urea concentration to the circulation.

Arteries, Veins and Capillaries


They carry blood away from the heart to the tissues. Blood flowing through arteries is under high pressure with high oxygen concentration and low carbon dioxide concentration (pulmonary artery is an exception). The elastic walls of the artery expand and relax as blood is forced out of the heart. Thick walls of the artery allow withstanding high pressure of blood.


Veins carry blood from the tissue to heart. Blood flowing through veins is at low pressure with low oxygen concentration (pulmonary vein is an exception) valves present in the veins prevent the backflow of blood. Large diameter and thin walls of veins reduce resistance to the flow of blood.


They link arteries and veins. They are about one cell thick and they are highly branched so that they cover an enormous surface area, giving more space for the diffusion to occur.

Composition of blood

A medium that flows in the system and carries materials around the body is the blood. The average adult human has about 5 dm3 of blood which contains a number of blood cells suspended in a watery liquid called the plasma. The blood cell suspended in plasma are red blood cells (erythrocytes), white blood cells (lymphocytes), white blood cells(lymphocytes), platelets.

Functions of the blood cells:

  1. Red blood cells transport oxygen from lungs to all respiring tissues. They prepare carbon dioxide for the transport from all respiring tissues to lungs.
  2. White blood cells (phagocytes) remove microorganisms that invade the body and might cause infection. The phagocyte engulfs the microorganism.
  3. Lymphocytes produce antibodies that help in the defense against disease
  4. Platelets are the cells involved in blood clot formation