At the molecular level, salt dissolves in water due to electrical charges and due to the fact that both water and salt compounds are polar, with positive and negative charges on opposite sides in the molecule. The bonds in salt compounds are called ionic because they both have an electrical charge—the chloride ion is negatively charged and the sodium ion is positively charged. Likewise, a water molecule is ionic in nature, but the bond is called covalent, with two hydrogen atoms both situating themselves with their positive charge on one side of the oxygen atom, which has a negative charge. When salt is mixed with water, the salt dissolves because the covalent bonds of water are stronger than the ionic bonds in the salt molecules.

The positively-charged side of the water molecules are attracted to the negatively-charged chloride ions and the negatively-charged side of the water molecules are attracted to the positively-charged sodium ions. Essentially, a tug-of-war ensues with the water molecules winning the match. Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together. After the salt compounds are pulled apart, the sodium and chloride atoms are surrounded by water molecules, as this diagram shows. Once this happens, the salt is dissolved, resulting in a homogeneous solution.

Manures are organic substance that are obtained by the decomposition of dead plants and animal substances.

The formation of slaked lime (calcium hydroxide, Ca(OH)2) when water is added to lime (CaO) is exothermic. CaO(s) + H2O (l) → Ca(OH)2(s) This reaction occurs when water is added to dry portland cement to make concrete, and heat evolution of energy as heat is evident because the mixture becomes warm.

Calcium is a silvery-white metal; it is relatively soft, but much harder than sodium metal.  Calcium is a member of the alkaline-earth metals (Group II on the periodic table); these metals react vigorously with water, although not as violently as the Group I metals such as sodium or potassium:

Ca(s)  +  2H2O(l)  ——>  Ca(OH)2(aq)  +  H2(g)

The prevention of pregnancy in women (by preventing fertilisation) is called contraception. There are four methods of contraception:

1. Barrier method: In barrier method of contraception, the physical devices such as condoms are used by males and females.
2. Chemical method: In chemical methods of preventing pregnancy, the females use two types of pills – oral pills and vaginal pills.
3. Intra-Uterine Contraceptive Devices – The use of intra-uterine contraceptive devices like Copper-T is very effective in preventing pregnancy.  A Copper-T is placed inside the uterus by a doctor to prevent unwanted pregnancies.
4. Surgical method: These methods are available for males as well as for females. Vasectomy is done in males and tubectomy is done in females.

1. Vasectomy - In males, a small portion of the sperm duct (Vasdeferens) is removed by surgical operation and both the cut ends are ligated properly. This prevents the sperms from coming out.
2.  Tubectomy - In females, a small portion of the oviducts is removed by surgical operation and the cut ends are ligated. This prevents the ovum from entering into the oviducts.

The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coil after every half rotation of the coil. Due to this the coil continues to rotate in the same direction.

The water from the soil reaches the leaves by the tissue called Xylem. The root hairs on the root absorb water from the soil and through osmosis the water is transported to leaves through the tissue xylem.

Xylem- Fundamental tissue for transportation of water

In plants, minerals and water are transported through the xylem cells from soil to the leaves. The xylem cells of the stem, roots, and leaves are interconnected forming a conducting channel reaching all plant parts. The root cells obtain ions from the soil which creates a difference in the concentration of ions between the roots and soil. Thus, there is a continuous water movement into the xylem.

Osmosis in plants

Osmosis causes osmotic pressure hence water and minerals are transported from one to another cell. Transpiration leads to a continuous water loss in addition to a suction pressure which is created due to water that is being forced into the xylem cells of the roots.

Transportation from roots

Water is transported to all parts of plants through roots. The transportation takes place in the following manner

• Water through their roots is continuously absorbed by the plants. This water is sent up through the stem to all parts of the plant, including the leaves.
• Only a little amount, of water, is retained in the plant or utilized by it in photosynthesis. The rest of it gets evaporated into the atmosphere as water vapour through the Stomata present in the epidermis of the leaves and other aerial parts of the plant.
• This creates a suction pressure which pulls up water from the xylem of the roots to the stem and then to the leaves.
• Xylem tissues are narrower in its diameter, in the form of capillary tubes (tracheids and fibres), greater will be the force.
• Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.

Thus, it can be said that xylem plays an important role in the transportation of water and minerals once they absorb these and transport them to different plant parts.

The process of taking in oxygen and to use it in the process of break - down of food for cellular needs is called as respiration.

There're three pathways of breakdown of glucose in living organisms. They're as follows:

(i) Aerobic respiration:The process of breaking down of food in the presence of oxygen to form energy is called as aerobic respiration.

The 6 - carbon molecule, glucose is broken down into a 3 - carbon molecule, pyruvate. This all happens in the presence of oxygen. They by - products are Carbon dioxide, Water and Energy.

(ii) Anaerobic respiration: The process of breaking down of food in the absence of oxygen to form energy is called as anaerobic respiration.

During heavy exercise, our body needs more energy to continue our exercise. Here, the more oxygen is needed. But the oxygen taken by nose is insufficient. And there's no time to break down food in the presence of oxygen 'cause of lacking of oxygen.

So, the energy produced in mitochondria in the absence of oxygen produce lactic acid which causes muscle cramps.The pyruvate is again broken down into Lactic acid which's also a three - carbon molecule.

(iii) In mitocondria: The break down of pyruvate using oxygen takes place in mitochondria.

Pyruvate is broken down to give a three - carbon molecules of Carbon dioxide.

The removal of waste material from the body is called excretion.
The unicellular organism remove their wastes directly through the cell membrane by the process of diffusion.
Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration.

Mendel during his study on pea plants stated three laws of inheritance. These were:
1. Law of dominance: A dominant gene will express itself over the recessive gene.
2. Law of segregation: Parental genes are randomly separated to the germ cells such that each germ cell receives only one gene from each pair.
3. Law of independent assortment: Genes for different traits are sorted separately from one another such that the inheritance of one trait is not dependent on the inheritance of the other trait.
Out of these three laws, the law of segregation is the most important law because it has no exceptions and is universally accepted.

Mendel's law of dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. Rather than both alleles contributing to a phenotype, the dominant allele will be expressed exclusively. The Law of Dominance says that when an organism is heterozygous for a trait, only the dominant allele will produce a phenotype. The first cherry is homozygous for the red allele and the second cherry is homozygous for the yellow allele.