Conventional Sources of Energy:

The sources of energy which have been in use since a long time are called conventional sources of energy. Coal, petroleum, natural gas, hydel energy, wind energy and nuclear energy are considered to be the conventional sources of energy. Additionally, firewood is also a conventional source of energy but its usage is now limited to kitchens in rural parts of India.

Fossil Fuels:

Coal: Coal was formed millions of years ago. The plants got buried under swamps and due to high pressure and high temperature inside the earth; they were converted into coal. Coal is the highest used energy source in India. During the days of steam engine, coal was used in steam engines. Moreover, coal was also used as kitchen fuel; before LPG became popular. Now-a-days, coal is mainly being used in the industries.

Petroleum: Petroleum was also formed millions of years ago. The animals got buried under the ocean surface and were converted into petroleum; in due course of time. Petroleum is the third major source of energy being used today. Petroleum products are used as automobile fuel and also in the industries. Natural gas mainly comes from oil wells and is also a major source of energy.

Non-renewable Sources of Energy: It takes millions of years for the formation of fossil fuels. Since they cannot be replenished in the foreseeable future, they are known as non-renewable sources of energy.

Renewable Sources of Energy: Those sources of energy which can be replenished quickly are called renewable sources of energy. Hydel energy, wind energy and solar energy are examples of renewable sources of energy.

Hydel Energy: Hydel energy is produced by utilizing the kinetic energy of flowing water. Huge dams are built over a source of water. Water is collected behind the dam and released. When water falls on urbine; the turbine moves; because of kinetic energy of water. Thus, electricity is generated by the turbine. Electricity; thus generated is called hydel energy or hydroelectricity. Water in the reservoir is replenished with rainwater and so availability of water is not a problem for hydroelectricity.

Thermal Power Plant: In a thermal power plant, coal or petroleum is used for converting water into steam. The steam is used to run the turbine; to generate electricity.

The ending of the play 'Mother's Day' is justified as by the end the insensitive family realises the importance of the selfless mother. It is a great day for Mrs. Pearson who doesn't get the love and affection, that she deserves, from her family. In this sense, it is her day; a turning point in her life.

According to regional continuity model:​​

1) homo sapiens were distributed in different parts of the world.

2) the rate of evolution was different in different regions.

3) this created difference in physical appearance

According to replacement model:

1) all the forms of older man was replaced by modern man.

2) originated in Africa.

3) changes in physical appearance due to adaptation.

The following statement means that the grandmother accepted her separation from the life of the grandsons without any objection.

The phrase means that the separation was duly accepted without any ill will or unfulfilled demand.

She even did not laid her opinion upon them rather came out without any ill will.

Their relationship changed when they moved to the city. The author was admitted to good English school and she went to the school by bus. Now grandmother couldn’t walk with author to the school like she used to be in the village and not she could not help the author with her lessons. In village grandmother used to teach lessons. In city both got different rooms to stay and now author has less time to spend with her grandmother. In this story city life actually changed their relationship.

Carbon is a component of all organic compounds of protoplasm like carbohydrates, lipids, proteins, nucleic acids, enzymes, hormones, etc. It constitutes 49% of dry weight of organisms and is next only to water in abundance. Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. A considerable amount of carbon returns to the atmosphere as CO_2​ through respiratory activities of producers and consumers. Decomposers also contribute substantially to CO₂​ pool by their processing of waste materials and dead organic matter of land or oceans. Burning of wood, forest fire and combustion of organic matter, fossil fuels, volcanic activities are additional sources for releasing CO₂​ in the atmosphere.

The main features of the life of man in Neolithic Age are as below :
1. Discovery of the Better Tools : In this period, the man had invented more beautiful, smooth and polished tools. These tools were more useful as compared to the earlier ones.
2. Beginning of the Cultivation : In this period man had become food producer instead of food gatherer. That man developed his farming during this period. The work made him to lead a settled life ultimately.

3. Domestication  of Animals : Man started domestication of those animals that were useful to him. He started the use of animals of farming and for riding. He also started getting milk and often meat from them.

4. Invention of the Wheel : It was a great achievement of this age. The invention made the carriage and transport easier. It also helped in the making of the spinning wheel.

In February 2019, scientists reported evidence that Neanderthals walked upright much like modern humans. More laterally curved radius with a radial tuberosity placed more medially, a longer radial neck, a more ovoid radial head, and a well-developed interosseous crest. There, the Neanderthal ancestor evolved into Homo neanderthalensis some 400,000 to 500,000 years ago. The human ancestor remained in Africa, evolving into our own species—Homo sapiens. The two groups may not have cross paths again until modern humans exited Africa some 50,000 years ago.

"Homo erectus spanned a large [temporal] and geographic range," said Adam Van Arsdale, an anthropologist at Wellesley College in Massachusetts, explaining the significance of H. erectus. "It is also important because it's the first fossil ancestral to modern humans that, in many ways, shares a lot of its ecology."

In particular, H. erectus had a similar range of body sizes to modern humans, and it is the first human ancestor to have similar limb and torso proportions to those seen in modern humans. This suggests it had adapted to walking on two feet in a more open, grassland environment, rather than swinging from tree branch to branch.  

Homo habilis is regarded as the first human and the first species of the genus Homo. Homo habilis means “handy human.” Members of this species were apparently able to use tools, build shelters, and fashion protective clothing. 

Homo habilis is an archaic species of Stone Age human which lived between roughly 2.3 and 1.5 million years ago (mya), during the Early Pleistocene. The species was first discovered by anthropologists Mary and Louis Leakey at Olduvai Gorge, Tanzania in 1955, associated with the Oldowan stone tool industry.

H. habilis is considered to be intermediate between Australopithecus afarensis and H. erectus. It has been suggested reclassifying the species as Australopithecus habilis, as one of the main arguments for its classification into Homo was the now outdated idea that it was the earliest human ancestor to use stone tools. H. habilis likely used tools for butchering meat which it scavenged from more fearsome carnivores.

In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce.

Darwin's theory of evolution is known as 'The Theory of Natural Selection'. It can be described as follows:
(i) Within any population there is natural variation. Some individuals have more favourable variations than others.
(ii) Even though all species produce a large number of offspring's, populations remain fairly constant naturally.
(iii) This is due to the struggle between members of the same species and different species for food, space and mate.
(iv) The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favourable variations survive and reproduce. This is called natural selection.
(v) The individuals having favourable variations pass on these variations to their progeny from generation to generation.
(vi) These variations when accumulated over a long period of time, lead to the origin of a new species.

Drainage pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land. A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material. That is, the subsurface geology has a similar resistance to weathering so there is no apparent control over the direction the tributaries take.

 In animals, metamerism is defined as a mesodermal event resulting in serial repetition of unit subdivisions of ectoderm and mesoderm products. Endoderm is not involved in metamerism. Segmentation is not the same concept as metamerism. Segmentation can be confined only to ectodermally derived tissue, e.g., in the Cestoda tapeworms. Metamerism is far more important biologically since it results in metameres, also called somites, that play a critical role in advanced locomotion.

The Ganga is the most important river of India both from the point of view of its basin and cultural significance. It rises in the Gangotri glacier near Gaumukh which is 3,900 m high from sea level in the Uttarkashi district of Uttarakhand. It is known as the Bhagirathi in this region

The author's Grandmother is a lady who is very spiritual and is a lady not accustomed to the Modern Techniques, styles and way of life. She has a kind heart and is very kind to animals. She is very much accustomed to the Village Way of Life. She is the frequent visitor of the temple. Her view and perspective of music is that it is the monopoly of harlots.

For any given isotope, the sum of the numbers of protons and neutrons in the nucleus is called the mass number. This is because each proton and each neutron weigh one atomic mass unit (amu). By adding together the number of protons and neutrons and multiplying by 1 amu, you can calculate the mass of the atom. The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.