Electron density is the measure of the probability of an electron being present at a specific location. In molecules, regions of electron density are usually found around the atom. Through quantum mechanical calculations the electron density can be calculated.

Joule–­Thomson effect deals with the increase or decrease in the temperature of a real gas or a liquid when allowed to expand freely through a valve or other throttling device while kept insulated so that no heat is transferred to or from the fluid, and no external mechanical work is extracted from the fluid. During this process enthalpy of fluid remains constant.

The evidence suggests that land plants evolved from a line of filamentous green algae that invaded land about 410 million years ago during the Silurian period of the Paleozoic era. They are considered to be an ancestral to plants because both they both reproduce chlorophyll a/b, both have cell walls made of cellulose and in conjugation DNA is being shared between one cell to other without actually reproducing.

Bone

It is highly rigid connective tissue that forms the skeleton of vertebrates. They are the type of tissues which comprises of blood vessels and cells. Overall a newborn baby will have around 300 bones and is reduced to 206. The main function of bones are:

1. Serve as a storage of minerals.
2. Provide the structural support.
3. Protect the internal organs of the body.

Cartilage

It is thin, fibrous, flexible connective tissue, which is mainly found in the external ear, larynx, respiratory tract, and the articulating surface of the joints. These cartilages lack blood vessels, therefore the growth and development of these tissues are slower compared to the other tissues. Altogether there are three different types of cartilages and it includes:

1. Hyaline cartilage: It serves as a shock absorber and allows the smooth movement of the bones at joints. They are mainly found in the nose, respiratory tract, and joints
2. Fibrocartilage is found in the knee, and it is tough and inflexible.
3. Elastic cartilage is found in ear, epiglottis, and larynx. It is the most flexible cartilage.

Xylem and phloem are known as complex tissues as they are made up of more than one type of cells. These cells work in a coordinated manner, as a unit, to perform the various functions of the xylem and phloem.

Xylem helps in conducting water and minerals. It also provides mechanical support to plants. It is made up of the following components:

• Tracheids (xylem vessels and xylem tracheids)

• Xylem parenchyma

• Xylem fibres

Tracheids are elongated, thick-walled dead cells with tapering ends. Vessels are long, tubular, and cylindrical structures formed from the vessel members, with each having lignified walls and large central cavities. Both tracheids and vessels lack protoplasm. Xylem fibres consist of thick walls with an almost insignificant lumen. They help in providing mechanical support to the plant. Xylem parenchyma is made up of thin-walled parenchymatous cells that help in the storage of food materials and in the radial conduction of water.

Phloem helps in conducting food materials. It is composed of:

• Sieve tube elements

• Companion cells

• Phloem parenchyma

• Phloem fibres

Sieve tube elements are tube-like elongated structures associated with companion cells. The end walls of sieve tube elements are perforated to form the sieve plate. Sieve tube elements are living cells containing cytoplasm and nucleus. Companion cells are parenchymatous in nature. They help in maintaining the pressure gradient in the sieve tube elements. Phloem parenchyma helps in the storage of food and is made up of long tapering cells, with a dense cytoplasm. Phloem fibres are made up of elongated sclerenchymatous cells with thick cell walls.

Aestivation is the mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl.
There are four main types of aestivation. They are as follows:

1. Valvate aestivation: Sepals or petals in a whorl just touch one another. They do not overlap one another.

It is observed in <i>Calotropis.</i>

2. Twisted aestivation: One margin of the appendage overlaps the margin of the next appendage.

Such type of aestivation is seen in lady’s finger, china rose and cotton.

3. Imbricate aestivation:Margins of sepals or petals overlap one another but not in any particular direction.

It is seen in Gulmohar and <i>Cassia</i>.
4. Vexillary aestivation: It is also known as Papilionaceous type of aestivation.

There are five petals. The largest petal (called standard) overlaps the two
lateral petals (called wings) which further overlap the two smallest anterior petals (called keel).

Pea belongs to Fabaceae family. The flowers of the family Fabaceae have five sepals that are often fused and five clawed petals, upper posterior petal or the vexillum, two lateral free petals or wings, and two anterior petals or the keel.