(a) Environmental pollution is an undesirable change in the physical, chemical or biological characteristics of the natural environment, brought about by man's activities. This pollution may affect the soil, rivers, seas or the atmosphere. 

(c) Biodegradable pollutants are sewage and agricultural waste.

Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.
(a)It is through the constant process of evolution taking place in the organisms since the origin of life that such an enormous variety of plants and animals have come to exist on this earth at present.
(b)There is an inbuilt tendency to variation during reproduction due to errors in DNA copying and as a result of sexual reproduction.
(c) Fossils are the remains of impressions of dead plants or animals which died millions of
years ago. They study of fossils helps us to know about the evolution of species. Fossils tell us how new species are developed from the old. Fossils provide evidence of evolution by revealing characteristics of past organisms and the changes that have occurred these organisms to give rise to present organisms. Therefore, fossils have an importance in deciding evolutionary relationship.

A number of resistors are said to be connected in parallel if one end of each is connected to one point and the other end is connected to another point so that the potantial difference across each resistor is the same and is equal to the applied potential difference between the two points. If we connect a voltmeter first across R₁, then across R₂ ad lastly across R₃, it will show same voltage.

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.

Sodium hydroxide (NaOH) is a commonly used base and is hygroscopic, that is, it absorbs moisture from the atmosphere and becomes sticky.  The acidic oxides react with base to give salt and water. The reaction between NaOH and \(CO_2\) can be given as \(2NaOH+CO_2\rightarrow Na_2CO_3+H_2O\)

Orange and lemon are citrus fruits which contain citric acid in their juices.
When these juices are added to pure water the acid will release H+ ions on dissociation and the pH value will decrease from 7 as the acidity increases.

(1) Local people who live around forests: They use forests for grazing their cattle, collecting fruits, firewood, bamboo and thatch.
(2) Industrialists: They collect raw, materials from forests for their industries.
(3) Tourists: They visit forests for recreation.
(4) Forest department of Government: They control the resources of forest.

Defect-Myopia or short-sightedness Correction-Concave lens

(a) not let minerals return to mineral pool
(b) become site of pest breeding.

The small number of tigers are causing a worry for the genetics because if they become extinct then the genes of this species will be lost forever. There will be no scope of again getting this species back to life without their genes.

(ii) The site of fertilisation in human beings is in the fallopian tube of female reproductive system.

CH₃OOH is ethanoic acid.-COOH is the formula of the function a 'group present in ethanoic acid.
Its 5 to 8% solution in water is called vinegar.
Sodium ethanoate and brisk effervescence due to carbon dioxide gas are formed on reaction of ethanoic acid with sodium carbonate.
\(\underset{Ethanol\ acid}{CH_3CH_2OH}\xrightarrow[heat]{Conc. H_2SO_4}\underset{Ethane}{CH_2=CH_2+H_2O}\)

No, depending on the nature of variations different individuals have different kinds of advantages. However, when a drastic 'Change occurs in environment only those organism in the population will survive which have an advantageous variation in that population to survive in changed environment.

When burning of biomass is not involved in production of energy, then there is no chance of pollution. Wind energy, hydel energy, solar energy, etc. are pollution free.

The functional junction between two neurons is called synapse.

Calcium oxide (CaO), commonly known as quicklime 

Breathing is the process by which oxygen is taken in (inhalation) and carbon dioxide is released out (exhalation). Respiration involves the oxidation of the food we eat to release energy. Carbon dioxide produced as a result of this is released out during exhalation.
Aerobic respiration: During aerobic respiration, the oxidation of food takes place in the presence of oxygen. Aerobic respiration can be summarised by the given equation:
\({ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }+{ 6O }_{ 2 }\longrightarrow { 6CO }_{ 2 }+{ 6H }_{ 2 }O+Energy\)
Anaerobic respiration: During anaerobic respiration, food is broken down in the absence of oxygen. It is also known as fermentation and is more common in microorganisms such as yeast.
Sometimes pyruvate gets converted into lactic acid in muscles by the process of anaerobic respiration.
\({ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }\xrightarrow [ ]{ Absenceofoxygen } Alcohol+{ CO }_{ 2 }+{ H }_{ 2 }O+Energy\)

(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) Regions included in central nervous system are the brain and the spinal cord. The brain and the spinal cord. The brain is further divided into three parts - forebrain, midbrain, and hindbrain.
(ii) Three of the functions of the brain are:
Forebrain controls intelligence, learning, memory, thinking, speech, etc.
Midbrain is associated with the sense of sight and hearing.
Hindbrain controls all involuntary actions such as breathing, peristalsis, etc.

(i) The symbols of elements are arranged in increasing order of their atomic number as shown in the below figure

(ii) The symbols of elements are arranged in increasing order of their group numbers as follows:

Reduce means to use a material/commodity in lesser quantity, e.g electricity and water. Reduce means a material that is used once is collected and sent back to a manufacturer so that they can make some other useful material from it. e.g., plastic cups and buckets, glass tumbler, paper, metal objects.
Reuse means using a thing over and over again instead of throwing it away. It does not involve the process of recycling either in small or large scale: e.g., used envelopes, plastic carry bags, bottles of jam.