Class 7 Science Transportation in Animals and Plants Chapter Notes

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Transportation in Animals and Plants

TRANSPORT OF MATERIALS
All organisms have a way of transporting substances from one part of the body to another. Complex animals
and plants have well developed transport system. It is responsible for the following:
* Supply of nutrients and oxygen to every cell of the body.
* Transport of substances formed in one part of the body to those parts where they are needed, like harmones and certain enzymes in animals and food in plants.
*Removal of harmful substances produced during metabolism like carbondioxide ammonia and urea etc., from the place of formation of the region of excretion.
Mode of Transport
Animals and plants have different modes of transport of substances The substances transported are also different.
* Transport in animals is by circulatory system.
*Transport in plants is by vascular system.

CIRCULATORY SYSTEM
Circulatory system is the life support system that provides our body cells with food and oxygen. It takes away waste products from the body cells.
Circulatory system is a system of vessels which connects all the cells, tissue and organ of the body together.

Parts of Circulatory System
There are three main parts of the circulatory system - heart, blood vessels and blood.
Heart: The human heart is a conical muscular organ, about the size of a man’s first. It is the main pumping organ and lies in the rib cage, between the two lungs. The human heart has four chambers. The upper two chambers are larger and are called the right and left ventricles.

Auricles have comparatively thinner walls. The auricles receive blood from different parts of the body through the veins, which pour the blood into the ventricles. The opening of the auricle to the ventricle is guarded by a value which controls the flow of blood.
The ventricles have thick muscular walls which pump the blood to various parts of the body through the arteries (Fig. 1).

The right auricle and the right ventricle receive carbon dioxide rich blood through the pre-vena and post-vena cava and pour it into the right ventricle. The left and right side of heart are separated by a muscular wall called septum. The left auricle and left ventricle receive the oxygen rich blood from the lungs through the pulmonary veins. There is a complete separation of the pure and impure blood in the heart. This is ensured by the number of valves present in the heart, that allow unidirectional flow of blood. Thus, the passage of blood in the heart can be summarized as follows:

When the right and left ventricles are full of blood, the heart is in an expanded condition, called the diastole. Then the ventricles contract, the left ventricle sends oxygen rich blood to different parts of body through the aorta, while the right ventricle sends the carbondioxide rich blood to the lungs through the pulmonary arteries for purification. This state of contraction is called systole.
The alternate systole and diastole produce a lubb: dub sound – the heart beat. A normal human heartbeats 72-80 times per minute, while a new born baby’s heartbeat can be upto 140 beats per minute. The human heart pumps about 5 litres of blood per minute.

Thus, impure blood from the body first enters the right side of the heart and then goes to the lungs for purification. Form lungs the blood again enters the heart from the left side, from where it is pumped to various parts of the body. This type of circulation of blood is called double type of circulation. The force or pressure, with which the blood is forced out of the heart can be left in the artery near the wrist. This is called the pulse. Doctors use a stethoscope (Fig, 2) to record the pulse / heart beat. The pulse rate increases during fever and exercise.

The pressure in the arteries during systole and diastole is called the blood pressure. The normal blood pressure of an adult is 120/80. Exercise consumption of fats and anxiety are the two major and most common factors responsible for increase in blood pressure.

Blood Vessel
There are three types of blood vessel. (a) arteries; (b) veins; (c) capillaries

Arteries: Each heart beat pumps blood into blood vessels called the arteries carry oxygen rich blood away from the heart to the various organs of the body. They lie deep in the muscles and can be noticed only at the 

places where we feel the pulse, like the throbbing at the hollow spot on the wrist. Arteries further divide arteries are called aortae.

Veins: They bring carbondioxide – rich blood from the various organs of the body to the heart. Veins are located just below the skin. The main veins are called pre-cavals and post cavals. The pressure with which
the blood rushes through the veins can be measured with the help of an instrument called sphygmomanometer.

Capillaries: Capillaries are the thinnest and finest blood vessels. The arteries branch into smaller arteries and finally into capillaries. The capillaries unite to form the vein. The thin walls help in performing their functions effectively.

Importance of Cappillaries

Capillaries have very thin walls which help
a) In picking up CO2 and other wastes from every cell and passing them into the alveoli and kidneys respectively.
b) Picking up oxygen and digested food from the alveoli in lungs and small intestine and passing them to each and every body cell for cellular respiration.

Blood Blood is the main transporting tissue in our body. It carries food air waste products hormones etc. Our body contains 3 to 5 litres of blood.

Blood consists of plasma (the fluid part) and blood cell (of three types, which float in the plasma).

Plasma: A yellowish coloured fluid medium and contains water (about 85 – 90%) inorganic and organic substances. Orgnaic substances are mainly proteins. Plasma also carries dissolved excretory products, hormones, enzymes, digested food and even CO2. Blood also contains three types of blood cells:
a) RBC or red blood corpuscles or erythrocytes
b) WBC or white blood corpuscles or leucocytes

RBC. RBC’s are non nucleated disc-shaped cells. The red colour of RBC is due to the presence of the protein haemoglobin. There are about 5- 5.5 million RBC’s in one ml of oxygen blood and are responsible to different parts of the body. Oxygen combines with haemoglobin to form oxyhemoglobin.

When oxygen rich blood reaches the tissue and cells of the body, oxygen is released for use in cellular respiration. Hence the haemoglobin free to carry more oxygen.
Anaemia is a very common disorder in which the amount of haemoglobin gets lowered. This leads to decrease in the oxygen carrying capacity of blood.

WBC: The number of WBCs in blood is less than the number of RBCs. They are comparatively bigger in size than RBCs and are meant for protecting the body against harmful bacteria and diseases. They show Amoeba like movements and are capable of ingesting foreign material. WBCs are the first ones to reach an infected or injured part of the body by passing through the walls the blood vessels.

Platelets: These help in blood clotting at the area of injury and block blood flow. Hence they prevent blood loss. These are smaller in size than RBCs. Haemophilia or bleeder’s disease is a genetic platelet disorder. In a person suffering from haemophilia, there is no clotting of blood. Even a small wound or cut can prove fatal for such people as they can bleed to death.

Functions of Blood

1. It is a medium for exchange of oxygen and carbondioxide in the alveoli of lungs and body cells.
2. Blood capillaries present in the villi of small intestine help in the absorption of food.
3. Harmones secreted by different endocrine glands in the body are also circulated throughout the body via blood.
4. Plalelets present in the blood help in blood clotting and thus prevent excessive blood loss.
5. Blood circulates in the body and perform the function of collecting and transporting waste materials to the excretory organs for excretion
6. Blood circulation also maintains a constant internal body temperature.
7. WBCs present in blood protect us from germ and infections.

TRANSPORT OF SUBSTANCES IN PLANTS
Different flowering plants herb, shrub and trees draw water from soil through their roots. Many of the outer cells at the root extend to form root hairs.

Root Hairs

The root hairs absorb water along with dissolved minerals and transport it to the leaves through xylem part of vascular system (Fig.3). Leaves are known as the “Food factories”. Food is prepared here by the process of photosynthesis. The raw materials required are water from soil, carbondioxide from atmosphere, chlorophyll present in leaves, sunlight from the sun.

Food that is prepared in the leaves is in the form of glucose. It is converted into a soluble sugar and transported through phloem to storage organs like seed, fruits, stem and root. Thus xylem and phloem are present as vascular system in plants throughout their body, that is from roots to leaves covering the stem and the branches.

Note: A group of cells, mostly of similar type performing specialised function. Group of tissues make an organ. Xylem and phloem are examples of plant tissues.

Conduction of Water and Minerals through Xylem
The process by which water and minerals salts are transported from xylem of root and carried upward to the stem, branches and leaves is called Ascent of sap. There are two important forces responsible for the uptake of water and minerals in plants — one arising from the roots and the other by the leaves from the top. The mode of transport in different kinds of plants – herbs, shrubs and trees is almost the same. [Fig. 4]

The two kinds of forces are:

1. Root pressure 2. Transpiration pull
Root Pressure: The roots of a plant are in direct contact with water in the soil. The branching nature of root hairs provide a large surface area for absorption of water and mineral salts. Root cells contain large vacuoles filled with a fluid, the cell sap. The cell sap has a higher concentration of salt than the soil water such a feature enable the root hair cells to draw water from soil, through a process known as osmosis. The continuous absorption of water by root hairs build up sufficient force to push the water upwards through the xylem
vessels.
Xylem are complex tissues composed of more than one type of cells they consist mainly of dead elements tracheids, vessels, xylem fibres and a living element xylem parenchyma.

Transpiration Pull: The loss of water from the aerial parts of plants in the form of water vapours is known as transpiration. Water evaporates through stomata, the tiny pores present on leaf surfaces.
When water is lost from the leaves either due to transpiration or consumed in the process of photosynthesis, the water column becomes greatly stretched and creates a pull. The continuity of water column does not break due to the forces operating between the water molecules and also between the water molecules and the wall of the xylem vessels. The transpiration pull is sufficient to raise water in leaves of the tallest trees.

Thus due to combined effect of push force due to root pressure and pull force due to transpiration by leaf cells, water moves upwards along the xylem vessel (Fig,. 5).

OSMOSIS

This is a physiological process taking place when two solutions having different concentrations are separated by a semipermeable membrane. A semipermeable membranes is one that allows only water molecules to pass through. The movement of water molecules takes place across the membrane from a dilute solution to a concentrated solution. This process enables cell to cell movement of water in the root cells after it is absorbed from the soil by the root hairs. Thus water finally reaches the xylem of root.

Conduction of prepared food through Phloem
Food prepared by the green leaves by the process of photosynthesis needs to be sent to storage organs and other parts of the plant body. The process by which it takes place is known as Translocation of prepared food. Special type of vascular tissue, the phloem is responsible for carrying the prepared food to all parts of the plant. Phloem is a complex tissue consisting of living elements - sieve tubs companion cells, phloem parenchyma and a dead element, phloem fibres. These are continuous vessels from leaves to other part of
the plant.

EXCRETION
Many harmful and unnecessary substances or by - products are produced in the body of living organisms due to continuous synthesis (nutrition) and breakdown (respiration) of materials. The unwanted by products or waste materials include carbondioxide, water vapour, nitrogenous wastes like urea, uric acid etc. If they are allowed to accumulate in our body beyond a certain concentration, they poison the cells and slow down the metabolic process. Thus, these waste products must be thrown out of the body as such or changed into
harmless material before being removed form the body. Hence, the process of removal of metabolic waste materials from the body is called excretion.

Excretion in Unicellular Organisms

A large part of ammonia remains unused in our body. It is either excreted as such, or after conversion to urea or uric acid. In unicellular organisms like Amoeba, Paramoecium, Hydra and Sponges, there are no special organs for excretions. The waste products are thrown out into the surrounding water through the general body surface by diffusion directly from the cells in which they are produced.

Excretion in Animals

In higher or multicellular organisms direct diffusion process for waste removal is too slow. Larger animals have a well developed excretory system. For example.
 • Earthworms and leechs have developed specialised organs nephridia (tubular structure)
 • Insects have Malpighian tubules
 • Vertebrates have kidneys.

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