ICSE Class 7 Biology Chapter 02 Organisation in Living Things

Organisation in Living Things

Different Units - Working in Coordination

Syllabus

1. Characteristics of living things (revision).

2. Cells - tissues - organs - organ systems - organism.

3. Plant tissues: location and function: - Meristematic tissue - Permanent - simple (parenchyma, collenchyma, sclerenchyma) and complex (xylem, phloem)

4. Animal tissues - location and function: - Epithelial tissue - Connective tissue - tendons, ligaments, bone, cartilage and blood. - Muscular tissue - voluntary and involuntary muscles. - Nervous tissue.

5. Organs in animals and plants.

6. Organ systems and their functions with reference to the human body.

7. Organism - population - community - ecosystem - biosphere - Study of permanent slides of animal and plant tissues - drawing of the same (E)

Teacher's Note

Living organisms display hierarchical organization, from cells to ecosystems, demonstrating how complex life systems emerge from simpler components working together.

You have studied in the previous chapter about cell - the structural and functional unit of life. All living organisms, plants and animals are made up of tiny microscopic cells.

The cell, whether that of a unicellular organism or a multicellular organism, consists of protoplasm - the living substance. Cells organise to form tissues. Tissues organise to form organs and organs form organ systems. The organ systems are present in both, plants and animals of higher groups. You have also learnt that there are various organelles present inside the cell. These organelles are arranged in a highly organised manner to perform specific functions. Thus, we can say that the cell is an organised structure.

Definition of Organisation

The term "organisation" means the manner in which small units of any structure or system are arranged into larger ones and the larger ones into still larger ones in hierarchy, where the units of each level coordinate with one another towards a particular goal.

Organisation can be seen not just within the cell or an organism, but in the whole living world. From the cells that form an organism to all organisms and their surroundings, the living world is organised step by step. Each step in the organisation of a living being or the living world is called the level of organisation. Each higher level of organisation is more complex than the lower one.

Different Levels of Organisation

Three categories of the grades or levels of organisation are recognised in the living world.

1. Individual or organism level of organisation,

2. Levels of organisation lower to the organisms, and

3. Levels of organisation higher to the organisms.

Teacher's Note

Understanding organizational levels helps explain why a scratch to your skin might hurt but doesn't affect your entire body's function - each level operates somewhat independently while contributing to the whole.

1. Individual or Organism Level of Organisation

An individual organism, may it be unicellular or multicellular, or a plant or an animal, is a separate biological unit. This is the organism level, and is considered to be a biological unit as regards all physiological activities, like growth, respiration, nutrition, excretion, reproduction, responsiveness, etc.

2. Levels of Organisation Lower to the Organism

i. Organ System Level

In higher organisms (e.g. humans), various organs in the organ system level work in a coordinated manner to constitute one individual. For example, the systems like the digestive, respiratory, excretory and nervous systems in animals and, root system, shoot system, etc. in plants, show "organ system level" of organisation. In an organ system, the various organs function in a coordinated manner. For example, the organs like the mouth, oesophagus, stomach, intestine, etc., of the digestive system (Fig. 2.2) work in coordination.

ii. Organ Level

The level of organisation lower to the organ system is the organ level of organisation. Intestine, stomach, heart, kidney, root, stem, leaf, flower, etc., represents the organ level of organisation (Fig. 2.3).

iii. Tissue Level

Organs in turn are made up of various types of tissues. For example, our intestine is made up of different tissues like muscle cells, gland cells, nerve cells, etc. A tissue is defined as a group of cells which are similar in structure and perform a specific function.

iv. Cell Level

The tissues, in turn are made up of cells. You already know that all life-activities take place inside the cell. In unicellular organisms, like bacteria and yeast, these activities take place within a single cell. In multicellular organisms, all the cells of the body carry out life-activities. That means, life begins with the formation of a cell.

Different tissues group together and function in coordination to form an organ.

3. Levels of Organisation Higher to the Organisms

i. Population Level

An organism cannot live in isolation. For its survival and continuity of its race, it has to live in association with other individuals of its own species. All the organisms of the same species living in a particular locality constitute the population which is the higher level next to the organisms. The individuals of the same species in a population resemble one another in appearance with only minor differences. The individuals of a species in a population can interbreed among themselves.

ii. Community Level

The population of different species found in a particular place constitute the community. For instance, in a garden, one can find population of various types of flowering plants, different kinds of insects, birds and rodents. Populations of all these different species found in the garden constitute a biotic community. ("Biotic" refers to the organisms. It is different from human communities).

iii. Ecosystem Level

The biotic communities in an area interact with the physical or non-living environment and the two or more communities together constitute the next level of organisation called ecosystem. A forest, a mountain, a garden, a paddy field, a pond, etc., are the examples of ecosystem. An aquarium is an example of artificial ecosystem.

Biome

A group of ecosystems constitute a biome. It is a natural grouping of various ecosystems on the basis of climatic conditions. Thus, a biome can be defined as, "a group of ecosystems taken together in a geographically localised area having the same type of climatic conditions". A biome is actually a very big ecosystem having the same type of climatic conditions. So, biomes can also be termed as major or big-sized ecosystems. Some common examples of biomes are: temperate forests, deserts (like Thar Desert in India, Sahara desert in Africa), evergreen forests, alpine forests, sea, big lakes (like Dal Lake in Kashmir), etc.

iv. Biosphere Level

The total world of life is called the biosphere. It is the entire inhabited part of the earth, its water and the atmosphere including the living and non-living components. It is about 13 kilometres extending from the life present in water to the air up above. Thus, biosphere consists of two major components - biotic that includes all plants, animals and micro-organisms; and abiotic that includes physical environment, soil and atmosphere (gases, temperature, humidity, pressure, etc.). Biosphere is the combination of all the ecosystems of the earth's environment. The biosphere surrounding the earth can be divided into three parts:

1. Hydrosphere. It is represented by all the water on the earth that is, the part of oceans, seas, rivers, streams and ponds. Life exists even upto 5 kilometres below the sea level.

2. Lithosphere. It represents the solid substratum of the earth's crust such as rocks, soil and nutrients.

3. Atmosphere. It is the gaseous cover that envelopes the hydrosphere and the lithosphere on the earth. Organisms exist upto 7-8 kilometres in the air above the sea level.

Principles of Biological Organisation

1. Smaller units in the lower level of organisation group together to form the unit of higher level. For example, cells group to form tissues, organs, organ-systems and finally, the entire organism.

2. Higher up the level of organisation, the system becomes more complex in its structure and function.

3. The unit of the level of organisation is independent in its mode of existence and activity. For example, an individual is a unit in the biosphere organisation of the earth. It has an independent existence.

4. Every step of the level of organisation has its own specialised structure and function. For example, stomach is an organ of digestive system. Its structure and function is different from the intestine which is also an organ of digestive system.

5. Every step of the organisation combines the lower levels and thus makes the system more and more complex.

6. Any damage or harm done at the higher level may not affect the lower levels of organisation but any damage done at lower level will affect the higher levels of organisation.

Tissues

All multicellular organisms (animals and plants) start their life as a single cell (the fertilised egg or zygote). The fertilised egg divides repeatedly to produce thousands, millions or billions of cells (trillions in human body). Some of these cells form skin, some form muscles, some others form bones, and still others form blood. A group of cells, which are similar in structure, and perform the same particular function, form a tissue. For example, the surface cells of the skin form one tissue, the cells constituting muscles are contractile and constitute the muscle tissue, or the green cells of a leaf form one tissue and the wood forming cells of the stem constitute another tissue.

Kinds of Tissues

The plant and animal body consists of a variety of tissues, each of which performs a specific function.

Plant Tissues

Plant tissues are basically of two kinds:

1. Meristematic tissues are made up of actively dividing cells. Their only function is to produce more cells leading to the growth of the plant body.

Meristematic tissues are found at all growing points in a plant, like the tips of roots, stems and branches, where growth in length occurs. The growth in the thickness of stem is also due to meristematic tissues.

The main characteristics of meristematic tissues, are as follows:

(i) The cells are small.

(ii) The cell-walls are thin.

(iii) The nuclei are large and conspicuous.

(iv) The cells are almost without vacuoles.

(v) The cells actively divide to add new cells.

2. Permanent (Non-dividing) tissues: The permanent tissues form the bulk of the plant body. These tissues do not divide. They become specialised and remain same throughout their life.

According to the function, the permanent tissues are of three types:

(i) Protective tissue,

(ii) Supportive tissue,

(iii) Conducting tissue.

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