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Biology Definitions (Jamnabai Narsee School, Mumbai)

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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) In the struggle for existence the individuals showing variations in the right directions survive and the variations are transmitted to the offspring; others with unfavourable variations perish. This was called by Charles Darwin the survival of the fittest . Organs similar in structure and origin but different in function are called homologous organs. Organs similar in function but different in structure and origin are termed analogous organs. The changes in the properties of population of organisms or groups of such populations over the course of generations are considered as biological or organic evolution. Convergent evolution is a form of analogy in which unrelated species independently develop similarities because they live in similar environments, do similar things, or are subject to similar architectural demands. Stimulus is a detectable change in the internal or external environment which influences or causes a temporary increase of physiological activity or response in the whole organism or in any of its parts. Plant hormones also known as phytohormones are chemical messengers that are produced in one part of the plant and have a physiological effect on a target tissue that may be distant from the site of production. These influences plant growth and responses. Growth is an irreversible change in the structure and/or development of a cell, tissue or organism. Apical dominance is a phenomenon of the suppression of growth of lateral buds by apical buds of a plant. The development and production of fruits without fertilization or seed formation is called parthenocarpy. The structural cause of the leaf fall is the formation of a layer of cork across the base of the petiole and the development of a well-defined separation layer called abscission layer. Senescence is the ageing process in plants. Bolting is the premature production of a flowering stem on agricultural or horticultural crops before the crop is harvested, in a natural attempt to produce seeds and hence reproduce. In the initial stages of their growth, young leaves remain rolled or folded and later due to more rapid growth on the upper surface, the leaves open, become flat and straight. The opening of the leaves is called epinasty. (2) Seed dormancy is the time period after maturation during which a seed will not germinate even when provided with all the conditions necessary for germination (i.e. water, oxygen, suitable temperature) The biological phenomenon of growth or body movements of an organism in respose to an environment stimulus is known as tropism. The response of the organism or its part is said to be positive if the growth is towards the stimulus. The response of the organism or its part is said to be negative if the growth is away from the stimulus. The root is Positively geotropic It grows towards the soil Positively hydrotropic It grows towards the water Negatively phototropic It grows away from sunlight The stem is Negatively geotropic It grows away from the soil Negatively hydrotropic It grows away from water Positively phototropic It grows towards sunlight Chemotropism is the phenomenon of growth or movement of a plant part towards the source of nutrients or chemicals. Hydrotropism is the movement of plant parts in response to water or moisture. Thigmotropism is the directional response of a plant organ to touch or physical contact with a solid object. Geotropism or gravitropism means growing towards the earth or force of gravitation. Phototropism means the movement in response to the stimulus of light. Auxins are powerful growth stimulants and are effective even at low temperatures which promotes growth in plants by cell-elongation. Ethylene is a gaseous unsaturated hydrocarbon hormone at ordinary temperature and are commonly used for ripening of fruits and inducing flowering in mango. (3) Abscisic acid (ABA) is a growth retarding hormone and inhibits plant growth and seed germination. Cytokinins are plant hormones which have specific effects on cell division and stimulate cell division. Gibberellins are plant hormones mainly distributed in the meristematic regions of the plant, widely used in horticulture and food industry and enhances longitudinal growth of internodes in dwarf plants. Phototaxis is a light-induced movement of organisms consisting of a single or just a few cells(motile organisms), usually towards the light. Photoperiodism is the process of stimulation of a plant to flower by exposure to length of light period. The light stimulus is perceived by the leaves. Absorption by roots Define the following: 1) Imbibition is the phenomenon by which the living or dead plant cells absorb water by surface attraction. 2) Diffusion is the free movement of the molecules of a substance (solid, liquid, gases) from their region of higher concentration to their region of lower concentration when the two are in direct contact. 3) Osmosis is the movement of water molecules from their region of higher concentration to their region of lower concentration across a semi permeable membrane. 4) Endosmosis is the inward diffusion of water molecules from their region of higher concentration to their region of lower concentration across a semi permeable membrane thereby making the cell turgid when placed in a hypotonic solution. 5) Exosmosis is the outward diffusion of water molecules from their region of higher concentration to their region of lower concentration across a semi permeable membrane thereby making the cell flaccid when placed in a hypertonic solution. 6) Tonicity is the relative concentration of the solutions that determine the direction and the extent of diffusion. 7) Hypertonic solution is the solution which has a higher solute concentration as compared to the cell sap resulting in exosmosis thereby making the cell flaccid. 8) Hypotonic solution is the solution which has a lower solute concentration as compared to the cell sap resulting in endosmosis thereby making the cell turgid. (4) 9) Isotonic solution is the solution whose relative concentration of water molecules and the solute is the same as that of the cell sap resulting in no net movement of water molecules across the cell membrane. 10) Active transport is the passage of substances (salts / ions) from their region of lower concentration to their region of higher concentration across a living cell membrane using energy in the form of ATP. 11) Turgidity is the phenomenon in which the cell is fully distended and cannot accommodate any more water when placed in a hypotonic solution. 12) Plasmolysis / Flaccidity is the phenomenon in which there is shrinkage of the cell contents and the cell membrane moves away from the cell wall when the cell is placed in a hypertonic solution. 13) Turgid cell is the state of a cell in which the cell is fully distended and cannot accommodate any more water when placed in a hypotonic solution. 14) Flaccid cell is the state of a cell in which there is shrinkage of the cell contents and the cell membrane moves away from the cell wall when the cell is placed in a hypertonic solution. 15) Turgor pressure is the outward pressure exerted by the cell contents on to the cell wall in a fully turgid cell. 16) Wall pressure is the inward pressure exerted by the cell wall on to the cell contents in a fully turgid cell. 17) Deplasmolysis is the phenomenon of the recovery of plasmolysis which occurs when a plasmolysed cell is placed in a hypotonic solution thereby resulting in the swelling of the protoplasm due to endosmosis. 18) Root pressure is the pressure developed in the cortical cells of the root due to alternate turgidity and flaccidity of the cells due to cell to cell osmosis resulting in the ascent of sap. 19) Osmotic pressure is the minimum pressure that must be exerted to prevent the passage of the pure solvent into the solution when the two are separated by a semi permeable membrane. Photosynthesis 1. Photosynthesis: Photosynthesis is the process in which living plant cells, containing chlorophyll, produce glucose from carbon dioxide and water by using sunlight. Oxygen is given out as a by product. 2. Photolysis: Photolysis is the splitting of the water molecules into hydrogen ions and hydroxyl ions in the presence of sunlight and grana. 3. Phosphorylation: Phosphorylation is the process in which electrons are used in converting ADP (Adenosine Di Phosphate) into energy rich compound ATP (Adenosine Tri Phosphate) by adding one phosphate group Pi (inorganic phosphate). (5) 4. Photophosphorylation: Photophosphorylation is the process of converting ADP (Adenosine Di Phosphate) into energy rich compound ATP (Adenosine Tri Phosphate) by adding one phosphate group Pi (inorganic phosphate) using electrons that comes from light (photons). 5. Polymerisation: Polymerisation is the process of transforming several molecules of glucose to one molecule of starch. 6. Carbon Cycle: Carbon cycle is a series of chemical reactions in which carbon dioxide of the air is used by living organisms (plants for photosynthesis) and finally returned into the air (plant and animal respiration, fossilization and combustion.). 7. Destarched Plant: A destarched plant is one whose leaves are free from pre- existing starch. It is done by placing the plant in dark room for 24 48 hours. The Reproductive system 1) Reproduction is the formation of new individuals by sexual or asexual means, which can repeat the process in their own turn. 2) Spermatogenesis is the process of production of sperms by the seminiferous tubules of the testes. 3) Oogenesis is the process by which the ova producing cells give rise to the mature ovum. 4) Ovulation is the process of release of a mature ovum by the rupturing of the graafian follicle which takes place on the 13th or the 14th day of the menstrual cycle. The remnant of the follicle then becomes corpus luteum. 5) Semen is the mixture of sperms and secretions from Seminal vesicle , Prostate gland and Bulbo urethral gland. 6) Puberty is the period during which immature reproductive system of boys and girls mature and becomes capable of reproducing. 7) Menarche is the onset of menstruation in a young female at about the age of 13 years. 8) Menopause is the permanent stoppage of menstruation in female occurring at about the age of 45yrs. 9) Menstrual phase is the phase of menstrual cycle which lasts for 3 -5 days during which bleeding is caused due to the shedding of the uterine lining rupturing the blood vessels. 10) Follicular phase is the phase of menstrual cycle which lasts from 5th 12th day during which the follicle grows, secretion of the oestrogen increases resulting in the thickening of the wall of the uterus. 11) Ovulatory phase is the phase which occurs on the 13th or 14th day of the menstrual cycle during which the graafian follicle ruptures and the mature egg is released. 12) Luteal phase is the phase of menstrual cycle which lasts from 15th 28th day during which (6) the ruptured graafian follicle turns into a hormone producing tissue called Corpus luteum. 13) Fertilisation is the fusion of the nucleus of the male gamete (sperm) with the nucleus of the female gamete (ovum) to form a zygote. 14) Implantation is the fixing of the blastocyst to the wall of the uterus. 15) Gestation is the full term of the development of the embryo in the uterus. It lasts for about 280 days. 16) Parturition is the act of expelling the full term foetus from the mother s uterus at the end of gestation due to the contraction of the uterine muscle. 17) Fraternal twins are the dizygotic twins which are produced when two eggs are released from ovaries at a time and both may get fertilised to produce two individuals. 18) Identical twins are the monozygotic twins in which a single fertilised egg may get split and separated into two parts during its early stages of cell division. Each of these two split parts then behave as an independent egg and produces one complete individual each. Endocrine System Define the following: 1) Hormones are the chemical secretions secreted by the Endocrine gland, poured directly into the blood and act on the target organs or cells away from the source. 2) Endocrine glands are the ductless glands which secrete hormones that are poured directly into the blood and act on the target organs or cells away from the source. 3) Islets of Langerhans are the special group of hormone secreting cells present on the pancreas. 4) Insulin shock is the condition in which a person becomes unconscious due to overdose of insulin leading to hypoglycaemia. 5) Tropic hormones are the hormones secreted by the anterior lobe of pituitary which stimulates other endocrine glands to secrete their hormones. Nervous System 1. Reflex Action: Reflex Action is an automatic, quick and involuntary action in the body brought about by a stimulus. 2. Reflex Arc: Reflex Arc is the shortest route taken by an impulse from a receptor to an effector. 3. Conditioned Reflex: A conditioned reflex is an involuntary, spontaneous automatic response brought about due to a previously learned experience. (7) 4. Natural reflex: A natural reflex is an involuntary, spontaneous automatic response brought about right from birth and which does not require previous learning or experience. 5. Stimulus: Stimulus is an agent or a sudden change of the external or internal environment that results in a change in an organism or any of its body parts. 6. Response: Response is the change in an organism resulting due to stimulus. 7. Impulse: Impulse is a wave of irritability that sweeps over the nerve cell. 8. Receptors: Receptors are the specialised epithelial cells which, on receiving the stimulus, set up waves of impulses towards the central nervous system. 9. Effectors: Effectors are muscles or glands which, on receiving the impulse from the brain or spinal cord, contract or secrete substances. 10. Synapse: Synapse is the point of contact between the terminal branches of the axon of a neuron with the dendrites of the next neuron separated by a fine gap. 11. Nerve: Nerve is a bundle of nerve fibres (axons) of separate neurons, enclosed in a tubular sheet. 12. Ganglia: Ganglia are the aggregates of the nerve cells (cell bodies) from which the nerve fibres may arise or enter into. Sense Organs 1. Accommodation of the eye: Accommodation of the eye is the process of focusing the eye lens at different distances (far or nearby) to see objects clearly by changing the curvature of the elastic lens. 2. Stereoscopic Vision: To perceive depth or relative distance of objects in both eyes, and their images by a kind of overlapping in the brain giving the brain a three dimensional effect. 3. Adaptation of the eye: Adaptation of the eye is the ability of the pupil of the eye to adjust to different intensity of light by regulating its size. 4. After Image: If one looks at a bright coloured object and then looks at a dark surface, an image of the object in the same colour will persist. This is known as persistence image or after image. It lasts for one tenth of a second. 5. Conjunctivitis: When the conjunctiva of the eye turns red due to viral infection, it is called conjunctivitis. --------------------------------------------x---------------------------------x-------------------------------- (8) (9)

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