12th Class

Human Evolution

During the course of evolution different animal species evolved special organs for a successful life like wings in insects, birds and bats for flying, claws for holding, burrowing and climbing in rats and squirrels and fins or paddles in aquatic life for swimming. Similarly, most significant event in human evolution has been evolution of brain which enabled him to become most superior member of animal kingdom. The large and more complex brain evolved greater ability of thinking, logical power and capacity of taking decisions depending on the situation. Present human species is named as Homo sapiens sapiens (Sapient = wise). T. H. Huxley (1863) in his book ‘Man's Place in Nature’ made first attempt to explain scientific grounds of upbringing of man. Charles Darwin (1871) in his book ‘The Descent of Man’ gave his ideas about ancestry of man. (i) Systematic position of man in animal kingdom Phylum more...

Catgeory: 12th Class

Evidence of Organic Evolution

The following are the evidences in favour of Organic Evolution : (i) Evidences from Classification : All the known living animals and plants have been classified into various species, genera, families, order, classes, phyla and kingdoms. The classification of a particular animal is attempted only after its extensive study. It is seen that every living being is related with other living being. The relations may be very close or may be quite apart. On their relationship, they are put under various orders, classes, phyla etc. On the superficial examination one can hardly believe that they are interrelated. But after their careful study they can be arranged in definite order, Protozoa (acellular) being at the base while Chordata at the top. No doubt, there is some sort of gap between chordates and non-chordates today but who known that this gap may be filled some day by some further discoveries. Moreover, the more...

Catgeory: 12th Class

Types And Significance Of Chemical Bonds

A chemical bond is an attractive force that links two atoms to form a molecule. Chemical bonds act like a powerful 'glue' that holds atoms close together. Three kinds of chemical bonds are: ionic bonds, covalent bonds and hydrogen bonds. (1) Ionic Bonds (i) When an atom loses or gains a valence electron, ions are formed. (ii) Positively and negatively charged ions are attracted to one another. (iii) When this force of attraction holds ions having opposite charges together, it is called ionic bond. (2) Covalent Bonds (i) When a covalent bond forms, neither of the combining atoms loses or gains electrons. (ii) Instead, the atoms form a molecule by sharing one, two or three pairs of their valence electrons. (iii) The greater the number of electron pairs shared between two atoms, the stronger the covalent bond. (iv) Covalent bonds are the most common chemical bonds in living organisms. (v) more...

Catgeory: 12th Class

Thermoregulation

As far as temperature regulation is concerned, animals can be divided into two groups: poikilothermous and homeothermous. Poikilothermic means 'having a variable temperature'. Poikilothermic animals are described as 'cold-blooded', their body temperature changing with fluctuation in the environmental temperature. Homeothermic means 'having the same temperature'. Homeothermic animals (mammals, birds and a few fishes like tuna fish and sword fish) are popularly described as 'warm-blooded'; their body temperature is independent of environmental temperature. In cold conditions their blood is at a temperature higher than that of their surroundings. More useful terms are ectothermic and endothermic. Ectothermic animals, as the word implies, gain heat from the environment, i.e., from outside the body. Endothermic animals generate heat from within the body and keep it there.

Catgeory: 12th Class

Reproduction

(1) Reproduction is one of the most important life functions. (2) Reproduction is the only way that living things can perpetuate themselves. (3) There are a number of different ways that various kinds of organisms reproduce and compensate for the loss of life due to death. (4) some reproductive processes known as sexual reproduction involve two organisms and their sex cells. (5) Asexual reproduction occurs when organisms make identical copies of themselves. Differences between Asexual and Sexual Reproduction

Asexual Reproduction

Sexual Reproduction

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Catgeory: 12th Class

Matter and Energy

Technically speaking, matter and energy are interchange able as expressed by Albert Einstein's famous equation \[E=m{{c}^{2}}\]: energy equals mass times the square of the speed of light \[({{c}^{2}}).\] For the chemical reactions that occur within living organisms, however, we can treat matter and energy as quite distinct from one another. Matter is the physical material of the universe; energy is the capacity to do work. Close and Open system : A system is a portion of the universe that is selected within a definite boundary. The part other than the system is called surrounding. As system is said to be closed if it can exchange energy but not matter, and in this energy can be gained or lost (through stainless walls) but not matter. A system said to be open if it can exchange matter and energy with surroundings. All living systems are open systems because they are continuously exchanging matter more...

Catgeory: 12th Class

Life Span

The average longevity of an organisms from birth to death is called life span. It is different in different living organisms. The life span of some common plants and animals has been listed in Table. Life Span

Organism

Average life span

May-fly

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Catgeory: 12th Class

Levels of Biological Organization

(1) Levels of Organization common in both living and non-living (i) Atomic level : The lowest level of organization in both living and non-living is the atom. All living organisms are basically made up of four chemical elements carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) with only about 1% other elements. The non-living matter may possess other elements (such as silica, calcium, iron, etc.) in variable composition. (ii) Molecular level : Atoms combine to form molecules, which undergo chemical reactions to form organelles. Atoms \[\to \] Molecules \[\to \] Inorganic compounds \[\to \] Simple organic compounds \[\to \] Complex organic compound \[\to \] Protoplasm \[\to \] Cell. (2) Levels of Organization found only in living organisms (i) Cellular level : All multicellular organisms are made up of cells. The cell is considered as basic unit of life and constitutes the smallest level of organisation of the living organisms. (ii) Tissue level : more...

Catgeory: 12th Class

Laws of Thermodynamics

The laws of thermodynamics describe the basic properties of energy. All interactions among pieces of matter are governed by the two laws of thermodynamics. The laws of thermodynamics deal with ?isolated systems? which are any parts of the universe that cannot exchange either matter or energy with any other parts. First Law of Thermodynamics : The first law of thermodynamics states that energy can neither be created nor destroyed; but energy can change from one form to another. In other words, within an isolated system the total quantity of energy remains constant. The first law is therefore often called the law of conservation of energy. Second law of Thermodynamics : The second law of thermodynamics states that the amount of useful energy always decreases when energy is converted from one form to another. In other words, every transfer or transformation of energy makes the universe disordered; no physical process or more...

Catgeory: 12th Class

Kinetic and Potential Energy

Kinetic energy is the energy of movement and this include not only movement of large objects but also movements such as electrical energy (movement of electrons) and heat (movement of atoms and molecules). Potential energy is stored energy that can be released as kinetic energy under right conditions. The food which you eat has chemical potential energy, some of which is converted into kinetic energy.

Catgeory: 12th Class

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