(a) Increase in the population of grasshopper.
(b) Migration or death of snakes due to food scarcity.
(c) The ecological balance is distributed.
(d) Decrease in the production of grass.

Tyndall effect

As our eye cannot focus the objects placed closer than 25 cm on the retina. we are unable to see the objects clearly.

The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons.

No this is because when there is a change in any species, there is change only in a part or a few members of the species population.

(a) No, she should not take the medicine.
(b) Of course she should visit a doctor to get information.
(c) She is having 50% chances of having a male child as 50% sperms carry Y chromosome and 50% X chromosome.

The functional junction between two neurons is called synapse.

The substance which has less resistivity is a better conductor.
(i) Iron is a better conductor than mercury.
(ii) Silver is the best conductor as it has the least resistivity.

(i) Mercury
ii) Sodium
(iii) Silver
(iv) Lead

A catalyst changes the rate of reaction without taking part in the reaction itself.

A solution of ammonia in water results in the formation of ammonium hydroxide (NH₄OH).  Ammonium hydroxide is basic in nature and turns red litmus blue.

(i) Scale for measuring [H⁺] concentration in a solution is called pH scale.
(ii) pH of Neutral solution is 7
pH of Acidic solution is 0 to below 7
pH of Basic solution is 7 to 14

(a) A food chain involves interaction between the living organisms of an ecosystem.
(b) A food chain is always straight.
(c) A food chain has a unidirectional flow of energy from sun to producers and then to consumers.
(d) A food chain has three or four or five trophic levels.
(e) According to law of thermodynamics, 80 - 90% of energy is lost as heat. 

(a) Mendel choose garden pea for his experiment because pea plants was self fertilising and have short life cycle.
(b) Mendel performed experiments on a garden pea (Pisumsativum) with different visible contrasting characters. He selected seven contrasting pairs of characters such as tall / short plants, purple / white flower colour etc.
(c) Mendel performed his experiment on tall and dwarf plant and interpreted his results to show that the traits may be dominant or recessive. Parent plants: True breeding tall pea plant was crossed with true breeding dwarf pea plant. Production of F₁ plants: All F₁ plants were found to be tall. Results of self-pollination ofF₁ plants or F₂plants: Mendel found that on self-pollination of F₁ plants, the progenies obtained in F₂ generations were not all tall plants. Instead, one- fourth of F₂plants were found to be dwarf.
Mendel's explanation for the reappearance of the short trait: From this experiment, Mendel concluded that the F₁ tall plants were not true breeding. They were carrying
both the traits. They appeared tall, because the tall trait was dominant over the dwarf trait.

Soaps are sodium or potassium salts of fatty acids having -COONa group. Detergents are sodium or potassium salts of sulphonic acids have -S02Na and -so4Na group.
Cleansing action of soap.
Soap molecules consists of a large hydrocarbon tail which is hydrophobic (water-hating or water repelling) with a negatively charged head which is hydrophilic (water-loving) as show in figure.

When a soap is dissolved in water, the molecules associate together as clusters called micelles in which water molecules, being polar in nature. surround the ions and the hydrocarbon part of the molecule attracts grease, oil and dirt.
The tails stick inwards and the heads outwards. In cleansing, the hydrocarbon tail attaches itself to oily dirt. When water is agitated (shaken vigorously), the oily dirt tends
. to lift off from the dirty surface and dissociate into fragments.
This gives opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by soap molecules.
The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirtis removed
Hard water has Ca²⁺ and Mg²⁺ ions. When it reacts with soap, it forms insoluble compound and the soap goes waste.

The mechanism of urine formation includes three steps namely,
(i) Glomerular ultra-filtration
(ii) Tubular reabsorption
(iii) Tubular secretion
(i)Glomerular Ultrafiltration:
Ultrafiltration of blood takes place inthe Malphighian body which acts as a biological filter. A Malphighian body comprises of Bowman's capsule and glomeruli.
The blood from the kidney flows through the capillaries of glomerulus where the blood pressure, is comparatively high and so brings about effective filtration. The hydrostatic pressure of the blood is always greater than the opposing pressures existing in the plasma protein and renal capillaries. Thus, the available net filtering force is chiefly responsible for glomerular filtration. The fluid in the capsule which is obtained by this process is termed glomerular filtrate. In man it is about 125ml/min. In 24 hours, the total volume of glomerular filtrate is 170 to 180 litres.
(ii) Tubular Reabsorption: Reabsorption takes place in the 'uriniferous tubules. Reabsorption of useful substances is a differential or selective process. The glomerular filtrate contains many useful substances such as glucose, amino acids, mineral salts and vitamins dissolved in large amount of water. Substances such as glucose, sodium and calcium, are actively reabsorbed in large quantities. Substances like urea and uric acid etc are reabsorbed in small quantities by a simple diffusion process or passive reabsorption. Substances like creatinine are not reabsorbed. They are completely eliminated.
Proximal convoluted tubule is responsible for the reabsorption of water, glucose, sodium phosphate and bicarbonates. On entering the distal convoluted tubule, the urine becomes nearly isotonic to the surrounding tissue fluid due to the active transport of sodium and passive transport of water. As urine (isotonic) passes into the collecting tubule it becomes once again hypertonic by the osmotic reabsorption of water under the influence of the hormone ADH. Thus the urine formed contains 96% of water, 2% urea and 2% of the metabolic products.
(iii) Tubular Secretion: This is the final step in the formation of urine during which the walls of tubule actively remove additional waste substances which are harmful to the body from the blood that have escaped filtration.

At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.
Onh's law does not hold good under all conditions as it is not a fundamental law of nature like Newton's laws. It is obeyed by metallic conductors only when physical condition like temperature etc., are kept unchanged. It is not obeyed by a lamp filament.

Various plant hormones and their effects are as follows:
(i) Auxin : Promotes cell elongation and thus promotes growth of a plant part.
(ii) Gibberellins : Promotes growth.
(iii) Cytokinin :  Promotes cell division and thus promotes growth.
(iv) Abscissic acid : Inhibits growth and is responsible for shedding or older parts.

(a)

Organismns using anaerobic mode of respiration are anaerobes. e.g. yeast, bacteria, etc.

(i) X - Carbon, Y - Diamond, Z - Graphite
(ii) Non-metal
(iii) Tin.

If magnification is 1, the image size is same as that of object size.
Since, magnification is positive, the image is erect and virtual.

Menstruation occurs when the egg is not fertilised. Every month, uterus prepares itself to receive a fertilised egg. To nourish the embryo, its lining becomes thick and spongy. In case, egg is not fertilised, this lining breaks and discharges out of the body through the vagina in the form of blood. This is referred to as menstruation.

The transport of soluble products of photosynthesis is known as translocation. Translocation in plants occurs by means of the vascular tissue known as phloem. Translocation is necessary because without it, the food prepared by the leaves cannot reach other parts of the plant.
(i)In plants, the synthesis of sugars takes place in the leaves by the process of photosynthesis.
(ii)Hormones are synthesised away from their targrt site.

(a) The solar cells are costly and hence the energy available from them expensive.
(b) 15 km/h is the minimum wind velocity required to obtain useful energy with a windmill.
(c) Nuclear fission is the process in which a radioactive atom splits up into smaller nuclei when struck with low energy neutrons.

(i) Maxwell's right hand thumb rule:
It's a convenient way of finding the direction of magnetic field associated with a current carrying conductor. It states that, if you hold the current carrying straight wire in the grip of your right hand in such a way that the stretched thumb points in the direction of current, then the direction of the curl of the fingers will give the direction of the magnetic field. This rule is also called Maxwell's corkscrew rule.
(ii) Fleming's left hand rule:
The direction of force which acts on a current carrying conductor placed in a magnetic field is given by Fleming's left hand rule.
It states that, if the forefinger, thumb and middle finger of left hand are stretched mutually perpendicular to each other, such that the forefinger points along the direction of external magnetic field, middle finger indicates the direction of current, then the thumb points towards the direction of force acting on the conductor.
(iii) Fleming's right hand rule gives the direction of induced current in a coil due to it's rotation in a magnetic field. If the forefinger points in the directions of magnetic field, thumb in the direction of motion of the conductor, then the central finger points in the direction of current induced in the conductor.

(1) People participation in the management of forests can help in increasingly forest produces as well as in their conservation.
(2) in 1972, the West Bengal Forest Department formulated a novel scheme to revive the degraded Sal forests by involving the local people.
(3) A far-sighted forest officer A.K. Banerjee involved the villages of the area around the forest in the protection of 1272 hectares of badly degraded Sal forest.
(4) In return for help in protecting the forest, the villagers were given employment in both silviculture and harvesting operations of the forest, 25% of the final harvest produce, and were allowed to collect firewood and fodder from the forest area on nominal payment.
(5) With the active and willing participation of local people living around the forest, the degraded Sal forest of Arabari became thick and green within ten years.

(a) Element 'A' is non-metal because it belongs to Group VII therefore it has 7 electrons in its outermost shell. It needs one electron to acquire nearest inert gas configuration and form a monovalent -ve ion.
(b) Atom of element C has a larger size than that of element A because C belongs to the 3rd period therefore it has three shells whereas A belongs to the 2nd period thus it has two shells.
(c) Element B has a valency of 1 because it belongs to Group I and has one valence electron. To complete its outermost shell or to acquire nearest noble gas configuration it loses one electron and forms a monovalent +ve ion.