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BIOLOGY STD:10 CHAPTERS: CELL, HUMAN EVOLUTION AND CHEMICAL CORDINATION IN PLANTS Cell is the fundamental, structural and functional unit of an organism. Organelles are the specialized membrane bound living structures in a cell, concerned with specific functions. The living part of a cell which consist of cytoplasm, nucleus and other living bodies are collectively called protoplasm or protoplast. Semi-permeable is a membrane that allows only certain substances particularly solvent molecules to pass through while preventing others. Freely permeable allows all substances in solution to enter and leave the cell without hindrance. Evolution is a slow and continuous process whereby complex forms of life have emerged from simpler forms through millions of years. Vestigial structures are evolutionary remains that have ceased to be of any use to the possessor but still persist generation after generation in a reduced form. Origin of new species by gradual modification is called speciation. Industrial melanism, the darkness of the skin, feathers, or fur acquired by a population of animals living in an industrial region where the environment is soot-darkened. The melanisation of a population increases the probability that its members will survive and reproduce and it takes place over the course of many generations as the result of natural selection of the lighter, more conspicuous animals by predators. Variation is any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation). Natural selection (a theory first proposed by Charles Darwin) is a process by which organisms best suited to their environment become the ones to survive and leave descendants. (1)
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