Answers to Biology Revision
Answers to Question 1
- Mitosis occurs in all cells but Meiosis occurs in reproductive cells; Mitosis consists of one division involving four stages and Meiosis consists of two successive divisions; in Mitosis genetic variation does not occur but in Meiosis genetic variation occurs; in Mitosis chromosome number remains the same whereas in Meiosis chromosome number is reduced to half.
- Osmosis involves unidirectional flow of solvent molecules and diffusion involves movement on either solute or solvent in both directions; osmosis occurs in liquids only whereas diffusion occurs in all mediums; osmosis is a slow process but diffusion is a rapid process; osmosis takes place across a living or non-living semi-permeable membrane whereas in diffusion no such membrane is needed.
- Hormone is poured into the blood stream and Enzyme on the particular type of food like protein, fat and carbohydrate; the action of hormone is slow whereas the action of enzyme is quick; hormone is produced by ductless glands and enzyme is produced by glands with ducts.
- Myopia-defect of vision in which distant objects are not seen clearly, the lens is too convex and the longitudinal axis of the eye is too long. Hypermetropia- defect of vision in which nearby objects are not seen clearly, the lens is flattened and the eyeball is too short from front to back.
- The nervous system-controls and maintains the body’s internal environment by impulses passing through neurons, sends messages to specific sets of cells like the muscle fibres, glands and other neurons etc, the action is immediate and he effect is brief. The hormonal system-affects bodily activities by releasing chemical messengers called hormones into the blood stream, sends messages to cells in any part of the body, its action is slow and the effects are more lasting and may be permanent.
Answers to Question 2
- Between two divisions, when a cell is resting or not dividing, the phase is called interphase.
- The outward pressure exerted on the cell wall by the fluid contents of the cell under fully turgid condition is called turgor pressure.
- Diffusion Pressure is the pressure with which molecules diffuse into another medium.
- Every cell capable of division passes through a sequence of stages known as cell cycle.
- Chromatid is one of the chromatin thread of chromosome that is joined together by a centromere before separation of anaphase. The two chromatids of a chromosome at metaphase are identical.
- Mendel’s Law of Dominance states that out of a pair of contrasting characters brought together in an offspring, one always dominates over the other. The one that is expressed is dominant and the one that remains masked is recessive.
- Mendelian crosses in which two pairs of contrasting character are taken into consideration at a time are called Dihybrid cross.
- Reflex action is a rapid, automatic response to a stimulus by an organ or system of organs which does not involve the brain for its initiation. Reflex actions are unconditioned, inborn and a natural part of our life.
- Astigmatism is a defect of the cornea or lens of the eye in which rays in one plane are brought to the focus while those in another plane remain out of the focus. It may also be formed when the cornea of the eye is not spherical.
- Endocrine gland is a ductless gland which secretes hormones. The hormones directly diffuse into the blood and are carried to all parts of the body. They are chemical messengers responsible for the harmonious working of the body.
Answers to Question 3
- The root hairs become flaccid when fertilizers are added to the moist soil around it because the concentration of the fluid around it is more which causes plasmolysis in the cells of the root hair.
- Photosynthesis occurs during the day. Due to the synthesis of glucose in the guard cells the stomata opens. When the stomata open the stomatal transpiration also starts taking place. Thus during daytime stomatal transpiration and photosynthesis occurs simultaneously. But at night there is no photosynthesis and the stomata is also closed therefore no transpiration through stomata occurs.
- The genes responsible for colour blindness are found in the X chromosome. This is a recessive trait that does not express phenotypically in heterozygous condition in females. Since the chances are rare therefore females are rarely reported to be colour blind.
- If the twins are produced form the same zygote, they will be identical. But if two zygotes are produced it gives rise to two individuals who may not be identical.
- Adrenalin is a hormone that prepares the body for ‘fright, flight or fight’ and it has extensive effects on the circulation, the muscles and sugar metabolism.
- Very strong sugar solution is hypertonic to the grape juice. The cells of the grapes are losing water to the surrounding resulting in shrinkage of the grapes.
- The two most important reasons for the rapid increase of the population in India are higher birth rate compared to the death rate and advancement in the medical science like better control of infectious diseases which has increased the average life span of human being.
- One can tie shoe laces without seeing because the activity mainly involves touch and coordination of fingers. The activity is learned and memory central in the brain supports it during the action.
- Education can prepare responsible adults who will be able to realize population problem in the country and the role of family planning in a happy and healthy life within individual family and population control of a country.
- Meiosis has two phases-Meiosis I and Meiosis II. In the first meiotic division or in Meiosis-I, the reduction in chromosome numbers take place, thus, two haploid cells are the result of this division.
Answers to Question 4
Answers to Question 5
- Tendon connects muscles to bones whereas ligament connects two bones together or bones to bones.
- Corpus callosum is located in the brain while corpus luteum is located in ovary.
- Ureter is the tube leading from the kidney to the urinary bladder; urethra is the tube draining the urinary bladder.
- Simple reflex is an inborn reflex e.g. blushing. Conditional reflex is that which is learned response to stimuli acquired during the life of an organism e.g. salivation on sight of food.
- Stomatal transpiration takes place through the stomata whereas cuticular transpiration takes place through the cuticle.
Answers to Question 6
- Red cross
- Adrenal Gland.
- Fallopian tube.
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