CBSE Class 7 Science Advanced Biology Transportation in Plants and Animals Notes Set 01

Transportation in Plants and Animals

Need for a Transport System

Every living thing has to move food, gases, hormones and waste substances from one part of its body to another. Plants and animals do this in different ways. In the higher animals the job is done by the circulatory system, whose main parts are the heart, the blood and the blood vessels. In plants it is done by two special tissues: xylem, which moves water, and phloem, which moves food.

A semi-permeable membrane is a thin layer that lets only some molecules pass through it and stops others. The plasma membrane of a cell is an example.

Transportation in Plants

Absorption by Roots

A plant takes in water and minerals through its roots. The outer layer of the root (epidermis) has tiny tube-like outgrowths called root hairs. They spread out into the soil and greatly increase the surface of the root that is in contact with soil water, so absorption becomes faster. The membrane of a root hair is semi-permeable, so it lets water and some minerals pass.

Fig. 5.1(b) A root with root hairs

Fig. 5.2 Uptake of minerals by root hair

Plants absorb from the soil mainly by two processes, diffusion and osmosis.

Diffusion and Osmosis

Diffusion is the spreading of particles of a gas, a liquid or a solid from the place where they are crowded (high concentration) to the place where they are fewer (low concentration). When water molecules spread in this way across a semi-permeable membrane, the process is called osmosis.

Fig. 5.3 Diffusion and osmosis

Difference between Diffusion and Osmosis

Absorption of Water

The soil around a root has plenty of water, while the cytoplasm of a root hair cell has less. Water therefore passes from the soil, through the semi-permeable membrane of the root hair, into the cell. This movement of water is osmosis.

Fig. 5.4 Absorption of water through osmosis

After water enters, the root hair cell holds more water than its neighbours. So water moves on into the next cell, and in this manner it travels from cell to cell towards the inner part of the root.

Absorption of Minerals

The soil has mineral salts such as those of calcium (Ca), magnesium (Mg), nitrogen (N) and phosphorus (P). They are dissolved in soil water as ions, and the roots take them up in two ways.
1. Diffusion: ions enter the root hair cell by diffusion only when the soil has a higher concentration of them than the cell has.
2. Active transport: the root hair cell can also pull ions in from a place where they are less concentrated (the soil) to a place where they are more concentrated (inside the cell). This needs energy from the cell.

Fig. 5.5 Uptake of minerals by root hair through active transport

Difference between Diffusion and Active Transport of Minerals

Conduction in Plants

Conduction means carrying a substance from one part of the plant to another. Leaves are the main place where photosynthesis takes place. In photosynthesis the plant uses water and carbon dioxide to make carbohydrates, with sunlight trapped by the green pigment chlorophyll. The water has to travel from the roots up to the leaves, and the food made in the leaves has to be sent to all other parts for growth. Two conducting tissues do these jobs: xylem carries water and phloem carries food.

Fig. 5.6 Conduction of water and food in plants

Xylem

Xylem runs from the top of the plant to the bottom. It lifts water and dissolved minerals from the roots to the aerial (above-ground) parts. The movement is in a single direction, upwards. Xylem is made of four kinds of elements: tracheids, vessels, xylem parenchyma and xylem fibres. Of these, the vessels, tracheids and fibres are dead cells.

Phloem

Phloem carries the food made in the leaves to the other parts of the plant, and the movement can be in both directions (bidirectional). Its elements are sieve tube elements, phloem fibres, phloem parenchyma and companion cells.

Differences between Xylem and Phloem

Fig. 5.8 Xylem and phloem vessels

Translocation of Food

The carbohydrates made during photosynthesis are carried through the phloem, and the flow can be in both directions. Sieve tubes are long tubes whose cells are stacked one above another, and food moves through them from the leaves to the rest of the plant.

Fig. 5.9 Leaf anatomy illustrating transportation

Transpiration

The loss of water as water vapour from the leaves through the stomata is called transpiration. It is the force that pulls water upwards through the xylem. Stomata are tiny pores on the surface of leaves, and each pore is guarded by two kidney-shaped guard cells that open and close it.

Fig. 5.10(a) Illustration of opening and closing of stoma

Importance of Transpiration

1. It gets rid of the extra water in the plant.
2. It helps to keep the water and salt levels in the plant in balance.
3. It cools the plant.
4. It helps the roots to absorb water.

Transportation in Animals

Animals have an organised system for moving gases, nutrients and other chemical substances around the body. The type of system depends on the kind of animal.
1. Very small (microscopic) organisms depend on simple diffusion and osmosis, which can carry substances only over short distances.
2. In insects a colourless body fluid called haemolymph carries the materials.
3. Higher animals have a separate circulatory system, and the heart is the organ that pumps the blood.
4. Fish have a two-chambered heart and amphibians have a three-chambered heart. Reptiles also have a three-chambered heart, except crocodiles, which have a four-chambered heart.
5. Birds and mammals have a four-chambered heart.

Fig. 5.11 Transport system in two-, three- and four-chambered heart

Types of Circulatory System

Circulatory systems are of two kinds, depending on whether blood vessels are absent or present.

Human Circulatory System

The human circulatory system moves oxygen, digested food, water and minerals to every cell. It also collects carbon dioxide and other waste substances from the cells so that they can be removed from the body. It is made of the heart, the blood and the blood vessels.

Blood

Blood is a red fluid that flows through the blood vessels and carries materials around the body. It is a connective tissue. It has two main parts, plasma and blood cells.

Components of Blood

Plasma: the straw-coloured liquid part of blood. About 92 per cent of it is water, and the other 8 per cent is dissolved substances such as proteins. Plasma is the fluid in which the blood cells float and are carried.

Blood cells: three kinds of cells are suspended in the plasma: red blood cells (RBCs or erythrocytes), white blood cells (WBCs or leucocytes) and platelets (thrombocytes).

RBCs: a mature RBC is a biconcave disc with no nucleus. RBCs are the most numerous cells in blood. They contain the red pigment haemoglobin, which joins with oxygen in the lungs to form oxyhaemoglobin and carries it to all parts of the body. Haemoglobin also picks up carbon dioxide from the body parts and brings it to the lungs.

Fig. 5.12 Formation of oxyhaemoglobin

WBCs: these cells are colourless, fewer than RBCs, irregular in shape and have a nucleus. Their job is to protect the body from harmful foreign substances. They are of two kinds: granulocytes, which have granules in their cytoplasm (for example eosinophils, basophils and neutrophils), and agranulocytes, which do not (for example lymphocytes and monocytes).

Platelets: these are colourless cells that help the blood to clot. When the body is hurt, blood flows out of the wound. Platelets gather at the injury and the blood there dries into a clot, which stops too much blood from being lost.

Fig. 5.13 Formation of blood clot

Fig. 5.14 Components of blood

Fig. 5.15 Composition of blood and percentage

Blood Vessels

Blood vessels are tubes that carry blood from the heart to every part of the body and back. They are of three types: arteries, veins and capillaries.

Fig. 5.16 Illustration of artery and vein

Fig. 5.17 Types of blood vessels

Differences between Arteries, Veins and Capillaries

Fig. 5.18 Blood vessels

Blood Groups

White blood cells make antibodies, which are special proteins that fight foreign substances. Antigens are the proteins that make the body produce antibodies, and each antigen causes the formation of its own specific antibody. Depending on which antigens are on the surface of the RBCs and which antibodies are in the plasma, human blood is divided into groups.

Rh blood grouping: this is another way of grouping blood. A person whose RBCs carry the Rh (Rhesus) factor, a protein, is Rh positive, and a person whose RBCs do not carry it is Rh negative. If an Rh negative person is given Rh positive blood, the body makes antibodies against the Rh factor, which can cause serious medical problems.

Blood transfusion: this is the medical procedure of giving the blood of a healthy donor to a person who needs blood. The giver is the donor and the receiver is the recipient. The two bloods must be compatible. The table below shows which transfusions are possible.

Heart

The heart is a muscular organ that pumps blood to all parts of the body. It has four chambers. The two upper chambers are the right atrium and the left atrium (singular: atrium), and the two lower chambers are the left and right ventricles. The aorta is the main artery and it carries oxygenated blood. The pulmonary artery is the only artery that carries deoxygenated blood, and it takes it from the heart to the lungs. The superior vena cava and the inferior vena cava are two large veins that bring deoxygenated blood to the heart, the first from the upper part of the body and the second from the lower part. The pulmonary vein is the only vein that carries oxygenated blood, and it brings it from the lungs to the heart. An adult heart is about the size of a fist.

Fig. 5.19 Structure of human heart

Flow of Blood

Blood flows without a break through the body, in two circuits. In pulmonary circulation, blood travels from the heart to the lungs and returns from the lungs to the heart. In systemic circulation, blood travels from the heart to the body organs and returns from the body organs to the heart. (An auricle is a small pouch-like extension that comes out of each atrium.)

The path of the blood is as follows.
1. The right atrium receives deoxygenated blood from the whole body through the superior and inferior vena cava.
2. The blood passes from the right atrium to the right ventricle.
3. The right ventricle sends it to the lungs through the pulmonary artery.
4. In the lungs gases are exchanged and the blood becomes oxygenated.
5. The pulmonary vein brings this oxygenated blood to the left atrium.
6. The blood passes from the left atrium to the left ventricle.
7. The left ventricle pumps it into the aorta, the largest artery, which branches to supply every part of the body.
8. In the capillaries, nutrients and oxygen pass to the cells and the blood collects carbon dioxide.

Thus the blood passes through the heart two times in one complete round of the body. This is called double circulation.

Fig. 5.20 Double circulation in human heart and single circulation in fish heart

Sequence of blood flow: from the body, deoxygenated blood goes to the right atrium, then the right ventricle, then the pulmonary artery, then the lungs. Oxygenated blood leaves the lungs by the pulmonary vein to the left atrium, then the left ventricle, and then to the body.

Fig. 5.21 Schematic diagram of blood circulation (blue line indicates deoxygenated blood and red line indicates oxygenated blood)

Pulse

Your pulse is the number of times your heart beats in one minute, so pulse rate and heart rate are the same thing. It can be felt at places such as the wrist, the neck and the ankle. It differs from person to person, is lower at rest and rises during exercise. A doctor uses a stethoscope to listen to the heartbeat. In a resting adult the normal rate is 60 to 100 beats per minute (bpm). A lower resting rate shows that the heart works more efficiently. Only well-trained adult athletes have a normal resting pulse of 40 to 60 beats per minute.

Disorders Related to the Circulatory System

1. Hypertension: a condition of high blood pressure.
2. Heart attack: when the heart muscle does not get enough blood, it is damaged and cannot work properly.
3. Heart failure: the heart cannot pump as much blood as the body parts need.

Key Points to Remember

1. In higher animals the transport system is the circulatory system made of the heart, blood and blood vessels.
2. In plants, xylem carries water and minerals and phloem carries food.
3. Water and minerals enter the plant through the roots, by osmosis, diffusion and active transport.
4. Conduction is the movement of a substance from one part of a plant to another.
5. Food made by photosynthesis moves through the phloem in both directions.
6. Transpiration is the loss of water vapour through stomata and it pulls water up the xylem.
7. The human circulatory system carries oxygen, nutrients, water and minerals to the cells and removes carbon dioxide and wastes.
8. Blood flows in two circuits, pulmonary and systemic, and passes twice through the heart in one round (double circulation).
9. Pulse is the number of heartbeats per minute.
10. Hypertension, heart attack and heart failure are heart disorders.