In the case of amoeba-like unicellular organisms, all functions are performed by organelles of that single cell. However, most of the organisms are multicellular. How are the various processes brought in their body? Groups of cells come together, so as to perform the various functions of the body.
Are you familiar with the sequence- lettersg words g sentences g lessons g text book? Similarly, organization of the body of organisms follows a definite hierarchy. You have already studied cells and cell organelles in that hierarchy.
‘A group of cells having the same origin, same structure and same function is called ‘tissue’. Millions of cells are present in the body of multicellular organisms. These cells are divided into different groups and each group performs a definite function. For example, we can perform movements due to contraction-relaxation of muscles. Conducting tissues in plants transport water and food to all its parts. All functions of the body occur with full efficiency due to the specific organization of cells and their division of work.
Plants being sedentary, most of their tissues are of the type that give support. There are dead cells in some tissues and these do not need much attention. Growth of the plants occurs in specific parts of their body where the tissues contain dividing cells. As animals have to move from place to place in search of food, shelter and partners, their energy needs are greater. Most of the tissues of animals are made up of living cells. Uniform growth occurs throughout the body of an animal and they do not have different dividing and non-dividing tissue. This means that plants and animals have different types of tissue to performing the necessary functions.
In the body of animal different organs come together to perform a specific function. Organs like the lungs and trachea, with the help of the contraction and relaxation of some muscles bring about the function of respiration. Different tissues perform different functions in the organs. Accordingly, tissues are classified into different types.
There are four main types of animal tissues, namely epithelial tissue, connective tissue, muscular tissue and nervous tissue.
Protective coverings in the animal body are called epithelial tissues. Cells in this tissue are closely packed and form continuous layers. Any material that enters the body first encounters epithelial tissue. Cells of epithelial tissue are separated from the cells of other underlying tissues by a fibrous membrane. The skin, mucous layer of the mouth cavity, inner surface of blood vessels, walls of the alveoli, etc. are made up of epithelial tissues.
Connective tissue :
Tissues which join different parts of the body are called connective tissues. Cells in this type of tissue are loosely arranged with a ground substance in the free spaces in between. The ground substance may be solid, liquid like water or jelly-like.
Bend your arm at elbow. Observe the muscles in the front and the back of the arm. Straighten the arm and observe the same muscles again. Do the same with your leg folding it at the knee joint. Did you experience the contraction and relaxation of muscles at every movement? Which type of muscle is the diaphragm of the respiratory system? Try this Try this Can you recall? Use your brain power ! Muscle fibres and muscular tissues are formed from special type of contractile proteins due to which this contraction and relaxation is possible. Muscular tissues are made up of the long cells of muscle fibres. Muscular movement occurs due to contraction and relaxation of the contractile proteins in these cells.
Often you must have identified the singer by merely listening to the song or identified what is being cooked in the kitchen by the mere smell! What helps us do this?
Nervous tissue enables us to respond to stimulii like touch, sound, odour, colour, etc.
Cells of the nervous tissue are specially made to become excited and to conduct that excitation form one part of body to other. The cell body which contains the cytoplasm and the nucleus is the main part of each nerve cell. Numerous, small, branched fibres called dendrites arise from the cell body. One of the fibres, however, is extremely long. It is called as the axon. The length of a nerve cell may even be up to one meter. Many nerve cells are bound together with the help of connective tissue to form a nerve. Nervous tissue is present in the brain, spinal cord and the network of nerves spread all through the body. In most animals, action in response to a stimules occurs due to the integrated functioning of nervous tissue and muscular tissue.
As shown in the figure 17.3, place an onion on each gas jar in such a way that its base (roots) will remain dipped in water. Measure and record the length of the roots of both onions on the first, second and third day. On the fourth day, cut off 1 cm of the roots of the onion in flask B.
As meristematic tissue is present in specific parts of a plant, growth occurs in those parts only. Cells of meristematic tissue contain thick cytoplasm, a conspicuous nucleus and a thin cell wall and are compactly packed together. Vacuoles are usually absent in these cells. These cells are highly active. To bring about plant growth is the main function of meristematic tissue. According to the location, meristematic tissue is of three types as given below.
After their growth is complete, new cells formed by division of meristematic tissue lose their ability to divide and start to perform a specific function at specific place. Thus, they permanently acquire a specific structure, shape and location and perform a specific function. This is called as differentiation and permanent tissues are formed from these differentiated cells. There are two types of permanent tissues-simple permanent and complex permanent tissue.
Simple permanent tissues
These are made up of only one type of cells. According to function, they are of the following different types.
Take a fresh and fleshy leaf of Rhoeo, lily or any other plant. Pull and press it, tearing it obliquely in such a way that its transparent epidermis will be visible at the cut margins. Take the transparent epidermis with the forceps and keep it in dilute safranin solution. for 1 minute. Spread it on a slide, cover with a cover-slip and observe it under a compound microscope.
The entire outer surface of a plant is made up of only one layer of cells. That layer is called ‘epidermis’. Cells of the epidermis are flat and as there are no intercellular spaces between them, a single continuous layer is formed. The epidermis of the stem and leaves is covered by a waxy layer of ‘cuticle’ due to which water in the underlying parts is retained.
Some cells in the body of living organisms are ‘totipotent’, that is if provided a proper environment, a new organism can grow from these cells. It was realized that with the help of this property of the cells and their genetically controlled biochemical processes, varieties of high yielding crops and new species of animals and various vaccines could be produced. This led to the rise of a new branch in biology, ‘biotechnology’.
With the help of this technique it has become possible to produce plants and animals bearing some new characterstics in addition to their natural ones. The techniques of bringing about improvements in living organisms by artificial genetic changes and by hybridization for the welfare of human beings, are together called ‘Biotechnology’. It includes the techiques of genetic engineering and tissue culture. Its uses are in the production of cash crops, improvement in varieties of cash crops, increase in abilities of plants to withstand environmental stresses, vaccine production, early diagnosis of congenital diseases, organ transplant, cancer research, production of artificial skin, cartilage, etc. in laboratories.
You must have seen flowers of same variety but of 2 or 3 different colours borne by same plant. How is this possible? Let us learn about a modern technique related to farming and gardening
‘Ex vivo growth of cells or tissues in an aseptic and nutrient-rich medium’ is called tissue culture. Nowadays, a complete organism can be developed from a single cell or from tissue with help of the tissue culture technique. A liquid, solid or gel-like medium prepared from agar, which supplies nutrients and energy necessary for tissue culture is used in this technique
Changes in agricultural management due to biotechnology
- Genetically Modified Crops (GM crops) are being produced by introducing changes in DNA of natural crops. Normally, such varieties are not found in nature. Thus, new varieties are produced artificially. Different useful characters are introduced in such varieties.
- Ability to withstand environmental stress- Some naturally occurring varieties cannot withstand envioromental stresses like frequently changing temperature, wet and dry famines, changing climate, etc. However, GM crops can grow in any of such adverse conditions.
- As GM crops are resistant to insect pests, pathogens, chemical weedicides, etc, the use of harmful chemicals like pesticides can be avoided.
- Due to use of seeds of GM crops, there is improvement in nutritive value and decrease in loss of crops
In this way, as seeds of a better quality of crops are being produced, farmers all over the world are cultivating the GM crops on large scale. The area under its cultivation is increasing day by day. High Yielding Varieties of GM crops like banana, maize, rice, potato, soybean, tomato, cotton, apple, brinjal, papaya, beet, rose, tobacco, wheat, etc. are available. Pest-resistant genes have been introduced in some of these GM crops. For example, Maize : MON 810, MON 863. Potato : Amflora Rice : Golden Rice Soybean : Vistive Gold Tomato : Vaishali Cotton : BT cotton
Application of biotechnology in floriculture, nurseries and forestry
Nurseries are necessary for various purposes like growing gardens on a large scale, afforestation, reforestation, etc. Seedlings have to be supplied in large numbers for all these purposes. It is profitable in such cases to produce plantlets with the help of tissue culture techniques.
- Tissue culture can be used to grow those plants on a large scale, which bear flowers, fruits of excellent quality.
- Fully grown plants can be produced in shorter durations.
- Plants can be grown on a large scale even if means of pollination or germinating seeds are not available. For example, orchids or pitcher plant do not germinate but these plants can easily be produced by means of tissue culture.
- In a bioreactor, cells can be grown in a more nutritive medium and protected from pathogens. Bioreactors are useful for producing plantlets on a very large scale.
- Large numbers of seedlings/plantlets can be produced in a short time using minimum resources and materials.
- Usually, plants produced by tissue culture and genetic modification techniques are disease-free. Plantlets produced by tissue culture of the meristem are virus-free.
- Embryos formed by conventional hybridization technique between two or more varieties may not grow fully for some reasons. However, embryos produced by tissue culture technique always complete their growth.
- Rare and endangered plants can be grown by tissue culture technique and can thus be protected from extinction. Similarly, various parts and seeds of such plants can be preserved by tissue culture and those varieties can be protected. These are the uses of tissue culture and biotecnology in the case of plants. Next year, we will study the use of this technique in the medical field and for conservation of animals.
If sufficient land is available, the emerging field of ‘agri-tourism’ would be a good business. Plantlets of flowering, medicinal, ornamental, vegetable plants and fruit trees can be produced on a large scale by the tissue culture technique. And, by growing some of the plants fully a selfsufficient agritourism centre can be developed.
l Mango, chikoo (sapota), guava, coconut, custard apple and some other regional fruit trees. l Shade giving local or exotic attractive plants. l Ornamental and flowering plants. l Butterfly garden. l Medicinal plant garden. l Organic vegetables and fruits. People visit places with such attractions in large numbers. Selling plantlets / seedlings, fruits, vegetables at such place can be quite profitable.
Agro-complementary occupations :
- Animal husbandry
Visit a modern cowshed nearby and record the following points – The number of cattle, their variety, total milk production, cleanliness in cattle-shed, arrangements for health care of cattle. In India, animal husbandry is practised for milk production and for using the catttle as help in farming operations. Ex. Cows and buffaloes are raised for milk and bulls and male buffaloes for pulling the heavy loads. Local Indian varieties of cows like sahiwal, sindhi, gir, lal kandhari, devni, khillari, dangi, etc. and exotic varieties like jersey, brown Swiss, Holstein, etc. are kept for their milk. Proper care of cattle is necessary for a clean and high yield of milk.
- A balanced diet i.e. which includes all constitents of food should be given to cattle. It must include fibre-rich coarse food, fodder, and sufficient water.
- The cattle-shed should be clean and dry with proper ventilation and a roof.
- Cattle should be regularly vaccinated
- Poultry farming
Rearing of egg and meat yielding chickens is called poultry farming. The objectives behind development of new hybrid varieties from a cross between Indian varieties like Aseel and exotic varieties like Leghorn are as follows : to produce good quality chickens in large numbers, to develop the ability to withstand high temperature, to use by-products of agriculture as poultry feed, etc. Rhode Island Red, New Hampshire, Plymouth Rock, Black Rock are varieties of chicken reared for eggs as well as meat.
Silkworms (moths) are reared for production of silk. Bombyx mori is the most commonly used variety for this purpose. The life cycle of the silk moth consists of four stages, namely egg, larva, pupa and adult. Thousands of eggs deposited by female moths are incubated artificially to shorten the incubation period. Larvae hatching out of eggs are released on mulberry plants. Larvae are nourished by feeding on mulberry leaves. After feeding for 3 – 4 days, larvae move to branches of mulberry plant. The silk thread is formed from the secretion of their salivary glands. Larvae spin this thread around themselves to form a cocoon. The cocoon may be spherical in shape. Ten days before the pupa turns into an adult, all the cocoons are transferred into boiling water. due to the boiling water, the pupa dies in the cocoon and silk fibres become loose. These fibres are unwound, processed and reeled. Various kinds of fabric is woven from silk threads.