Carbon dioxide is more soluble in water than oxygen and hence is mostly transported in the dissolved form in our blood. Carbon dioxide (CO2) is more soluble in water than oxygen. That is why, as compared to oxygen a much larger volume of it is transported in dissolved form in our blood from tissues to the lungs.

Copper turns green because of chemical reactions with the elements. Just as iron that is left unprotected in open air will corrode and form a flaky orange-red outer layer, copper that is exposed to the elements undergoes a series of chemical reactions that give the shiny metal a pale green outer layer called a patina. Copper metal when exposed to air turns green in colour due to corrosion. When copper vessel is exposed to air in rainy season, the metal reacts with gases and moisture and atmospheric gases to form a mixture of copper carbonate and copper hydroxide. This gives a green colour to the surface of copper metal.

DNA is a group of molecules that is responsible for carrying and transmitting the hereditary materials or the genetic instructions from parents to offsprings.

DNA was first recognized and identified by the Swiss biologist, Johannes Friedrich Miescher in 1869 during his research on white blood cells.

The double helix structure of a DNA molecule was later discovered through the experimental data by James Watson and Francis Crick. Finally, it was proved that DNA is responsible for storing the genetic information of a human being.

1000 milliamperes makes 1 ampere
So, 20000 milliamperes makes 20 ampere

Exchange of gases takes place between the alveoli of lungs and the surrounding blood capillaries.  The two main gases exchanged are oxygen and carbon-dioxide. Oxygen is absorbed by the blood capillaries from the lungs alveoli by diffusion while carbon dioxide is absorbed by the lungs alveoli from blood capillaries by diffusion. Transport of oxygen and carbon dioxide occurs with the help of respiratory pigment called hemoglobin. Haemoglobin, the iron-containing respiratory pigment is a red coloured pigment of blood, which has a very high affinity for oxygen. Haemoglobin though is purple coloured but oxyhemoglobin is of bright red colour. Oxygen is transported from lungs to the body cells in the form of oxyhemoglobin. Carbon dioxide is transported from the body cell to the lungs in the forms of carboxyhemoglobin, carbonic acid, bicarbonates of sodium and potassium.

Neutralization is a chemical reaction in which acid and base combine to form salt and water. Acids donate H⁺ and bases donate OH^-  in water which combine to form water molecules.

Example
HCl + NaOH---NaCl + H₂O
and HNO₃ + KOH---KNO₃+ H₂O

Variations arise in organism by:
The phenomenon is the passing of genes and heredity.

Variation occurs when one gene in the organism is mutated.If it allows the organism to survive longer than the others in the population without the mutation, it gives the mutated organism a higher chance to pass on its genes. When these genes are passed on, their kids may have the mutation but they will carry the mutated gene. As long as this helps the organism survive it will continue to be passed on to the next generation. After many generations, the mutated trait becomes common which means they have evolved.

Example- For example, a population of long beaks inhabit a particular area. Now, the food can be consumed properly with short beaks. If due to some variations, there may be a possibility that there are some birds with short beaks in that population. So, in the new area, they will survive better and reproduce more which will lead to the evolution of more and new species.

II. Variations is useful for the survival of species because:

1. Variation acts as a source of raw material for evolution of species.

2. Variation leads to genetic diversity, which is a key for the evolution of species. Animals are able to adapt themselves to the changing environment by inheriting some of the beneficial variations. Organisms are better suited to face the struggle for existence due to the presence of variations.

3. Variations give the species an individuality of their own. In the absence of variation, there would be no science of heredity as all individuals of a race, would be identical to one another in all aspects.

All the variants, however, do not have equal chances of survival. Depending on the environmental conditions, the nature favours only those variants that are able to adjust to the changing environment. The theory of natural selection favours the survival of the fittest. 

Salts are ionic in nature due to the presence of ions. They are brittle, hard and crystalline solids. Salt is white, odorless and it has a salty taste. All potassium (K), ammonium (NH4+) and sodium (Na) salts are soluble in water (H2O). Common salt is obtained from sea-water by the process of evaporation. Sea water is trapped in large, shallow pools and allowed to stand there. The sun's heat evaporates the water slowly and common salt is left behind. Used as a preservative in pickles and in curing meat and fish. Used in the manufacture of soap. Used to melt the ice in winter in cold countries. Used for making chemical likes washing Soda, baking soda etc.

The potential energy of the of water in the reservoir gets converted into the kinetic energy of the flowing water. The flowing water rotates the turbine shaft connected to the generator which produces electricity. and Thus kinetic energy of water transforms into the mechanical energy of turbine which further gets converted into the electric energy.

The disadvantages of building large dams are:

• Damming of rivers and regulating their flow result in excessive sedimentation at the bottom of the reservoir. This may hamper aquatic life and their migration to other water bodies.
• Building of dams result in the submergence of land and vegetation. This results in the decomposition of vegetation.
• Construction of large dams results in the displacement of villagers and communities. The villagers have to give up their lands and their means of livelihood.
• Large forest areas are also submerged because of the building of dams. This threatens our biodiversity.
• Dams which were initially built to control floods are now causing floods because of sedimentation. In case of excessive rainfall, the release of water from dams often floods the area, causing damage to lives and property.

Nitrification is a step in the nitrogen cycle.
When plants and animals die, their proteins are decomposed by ceratin microorganisms to ammonia. This process is called ammonification. Certain soil bacteria oxidise the ammonia into nitrites and then into nitrates. This process is called nitrification and is carried out by nitrifying bacteria like Nitrosomonas and Nitrobacter.

The mode of nutrition in Amoeba is holozoic and various steps involved in the process of nutrition are:

Ingestion: Amoeba ingests food with the help of its finger-like extensions, called pseudopodia, when a food particle approaches Amoeba it forms pseudopodia around it and forms a food vacuole inside the Amoeba
Digestion: Various enzymes from the cytoplasm enter into the food vacuole and break them down into simple soluble molecules
Absorption: The simple soluble food is absorbed by cytoplasm of Amoeba from food vacuoles through the process of diffusion
Assimilation: Amoeba cell obtains energy from the absorbed food through respiration and this energy is utilized by Amoeba for its growth and repair of the body
Egestion: When a considerable amount of undigested food gets collected inside Amoeba, its cell membrane ruptures and throws out the undigested food