The cell membrane is also known as the plasma membrane. It is the outermost covering of animal cells. It is a semi-permeable membrane composed of lipids and proteins. The main functions of the cell membrane include:

1. Protecting the integrity of the interior cell.

2. Providing support and maintaining the shape of the cell.

3. Helps in regulating cell growth through the balance of endocytosis and exocytosis.

4. The cell membrane also plays an important role in cell signalling and communication.

5. It acts as a selectively permeable membrane by allowing the entry of only selected substances into the cell.

Prokaryotic cell envelope possess chemically complex cell envelope. The cell envelope comprises of three layers: the outermost glycocalyx, the cell wall and the plasma membrane. All the three layers together act as a single protective unit.
Bacteria is classified into two groups based on the response to the gram staining method −
Gram positive:- Cells that take up the gram stain and are stained dark blue or purple.
Gram negative:- Cells that do not take up the gram stain and are stained pink or light red.
If glycocalyx is present as a loose sheath it is called slime layer. At times glycocalyx is present as thick and tough layer then it is called capsule.
The cell wall determines the shape of the cell and also provides structural support to the cell. The plasma membrane is semi-permeable in nature.
A special membranous structure called mesosome is formed by the extensions of plasma membrane into the cell.
Bacteria may be motile or non-motile based on the presence of thin filamentous extensions called flagella. Flagella helps in motility. Bacterial flagella are composed of three parts −
1.Filament
2.Hook
3.Basal Body
Pili are elongated structures made up of pilin proteins. Fimbriae are small bristle like fibres which mostly help in attachment of the bacteria to different surfaces.

Prokaryotic cells have different characteristic features. The characteristics of the prokaryotic cells are mentioned below.

1. They lack a nuclear membrane.

2. Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent.

3. The genetic material is present on a single chromosome.

4. The histone proteins, the important constituents of eukaryotic chromosomes, are lacking in them.

5. The cell wall is made up of carbohydrates and amino acids.

6. The plasma membrane acts as the mitochondrial membrane carrying respiratory enzymes.

7. They divide asexually by binary fission. The sexual mode of reproduction involves conjugation.

CELL THEORY

• Schleiden and Schwann together formulated the cell theory.
• Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells.
• Cell theory states that
• All living organisms are composed of cells and products of cells.
• All cells arise from pre-existing cells.

Each alveolus is made up of highly-permeable and thin layers of squamous epithelial cells. Similarly, the blood capillaries have layers of squamous epithelial cells. Oxygen-rich air enters the body through the nose and reaches the alveoli. The deoxygenated (carbon dioxide-rich) blood from the body is brought to the heart by the veins. The heart pumps it to the lungs for oxygenation. The exchange of O₂ and CO₂ takes place between the blood capillaries surrounding the alveoli and the gases present in the alveoli.

Thus, the alveoli are the sites for gaseous exchange. The exchange of gases takes place by simple diffusion because of pressure or concentration differences. The barrier between the alveoli and the capillaries is thin and the diffusion of gases takes place from higher partial pressure to lower partial pressure. The venous blood that reaches the alveoli has lower partial pressure of O₂ and higher partial pressure of CO₂ as compared to alveolar air. Hence, oxygen diffuses into blood. Simultaneously, carbon dioxide diffuses out of blood and into the alveoli.

Each alveolus is made up of highly-permeable and thin layers of squamous epithelial cells. Similarly, the blood capillaries have layers of squamous epithelial cells. Oxygen-rich air enters the body through the nose and reaches the alveoli. The deoxygenated (carbon dioxide-rich) blood from the body is brought to the heart by the veins. The heart pumps it to the lungs for oxygenation. The exchange of O2 and CO2 takes place between the blood capillaries surrounding the alveoli and the gases present in the alveoli.

Thus, the alveoli are the sites for gaseous exchange. The exchange of gases takes place by simple diffusion because of pressure or concentration differences. The barrier between the alveoli and the capillaries is thin and the diffusion of gases takes place from higher partial pressure to lower partial pressure. The venous blood that reaches the alveoli has lower partial pressure of O2 and higher partial pressure of CO2 as compared to alveolar air. Hence, oxygen diffuses into blood. Simultaneously, carbon dioxide diffuses out of blood and into the alveoli.

Abscisic acid acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone. Abscisic acid is called stress hormones as it induces various responses in plants against stress conditions.

It increases the tolerance of plants toward various stresses. It induces the closure of the stomata during water stress. It promotes seed dormancy and ensures seed germination during favourable conditions. It helps seeds withstand desiccation. It also helps in inducing dormancy in plants at the end of the growing season and promotes abscission of leaves, fruits, and flowers.

Carolus Linnaeus, who gave an organism classification, named as 'father of taxonomy'.

Anatomy of Earthworm

Externally, a thin non-cellular cuticle covers the body wall of the earthworm. Underneath this cuticle, a layer of the epidermis, followed by two muscle layers and coelomic epithelium (inner layer) is sheathed. The epithelium consists of a single layer of glandular columnar epithelium.

**** papilla: A skin tag that projects up from the junction between the skin and the inside lining of the ****. **** papillae tend to occur with **** fissures and may be detected on a digital examination of the **** or with a scope. Removal is only necessary if the **** papillae are causing symptoms. **** papillae are acquired structures that arise from the base of the rectal columns of Morgagni at the dentate line. Hypertrophied **** papillae are essentially skin tags that pro- ject up from the dentate line or from the junction between the skin and the epithelial lining of the ****. 

Connective tissue is a major supporting tissue in the body that provides structural framework and support to different tissues. Blood is regarded as a connective tissue because as the blood is circulated throughout the body due to pumping action of heart, it carries different materials and gases from one part of the body to another. Hence, it connects different tissues and organs of the body and thus, called as a connective tissue.

Nervous or the nerve tissue is the main tissue of our nervous system. It monitors and regulates the functions of the body. Nervous tissue consists of two cells: nerve cells or <a href="https://byjus.com/biology/neurons/">neurons</a> and glial cells, which helps transmit nerve impulses and also provides nutrients to neurons. Brain, Spinal Cord, and nerves are composed of nervous tissue, they are specialized for being stimulated to transmit stimulus from one to another part of the body rapidly.

Structure Of Nervous Tissue

• It is made of nerve cells or neurons, all of which consists of an axon. Axons are long stem-like projections emerging out of the cell, responsible for communicating with other cells called the Target cells, thereby passing impulses
• The main part is the cell body which contains the nucleus, cytoplasm and cell organelles. Extensions of the cell membrane are referred to as processes.
• Dendrite is a highly branched processes, responsible for receiving information from other neurons and synapses (specialized point of contact). Information of other neurons is provided by dendrites to connect with its cell body.
• Information in a neuron is unidirectional as it passes through neurons from dendrites, across the cell body down the axon.

Muscular tissue is a specialized tissue in animals which applies forces to different parts of the body by contraction. It is made up of thin and elongated cells called muscle fibers. It controls the movement of an organism.

The cytoplasm in the muscle fibers is called sarcoplasm. It contains a network of membrane called the sarcoplasmic reticulum. The membrane surrounding the muscle fibers is called sarcolemma.

Properties of Muscular Tissue

1. Contractibility– It is the ability of muscle cells to shorten forcefully.

2. Extensibility– A muscle has the ability to be stretched.

3. Elasticity– The muscles have the ability to recoil back to its original length after being stretched.

4. Excitability– The muscle tissue responds to a stimulus delivered from a motor neuron or hormone.

Types of Muscular Tissue

The muscular tissue is of three types:

• Skeletal Muscle Tissue

• Smooth Muscle Tissue

• Cardiac Muscle Tissue

• Glandular epithelium is a type of epithelial tissue which covers the glands (both exocrine and endocrine) of our body. Their main function is secretion. Both endocrine and exocrine glands produce their secretions through the glandular epithelium via special cells called goblet cells. 
• Glandular epithelium in the reproductive tract is called endocervical glandular epithelium and helps in sexual functions by secreting lubricating fluid during sexual excitation.
•  The glandular epithelium also lines the intestine where it helps in the absorption of nutrients. Thus it aids in digestion. Thus glandular epithelium is a multifunctional tissue that combines with other tissues to perform vital functions of the body.

1. ICBN:  International Code of Nomenclature of Bacteria

2. ICZN: International Code of Zoological Nomenclature.

G0 (quiescent phase) also known as the inactive stage of the cell cycle, is the stage when the cell remains metabolically active, but do not proliferate unless called on to do so. Such cells are used for replacing the cells lost during injury.

Kinetochore is a structure on chromatids at which the spindle fibres attach during cell division to pull the sister chromatids apart. Their proteins help to hold the sister chromatids together and also play a role in chromosome editing.

Kinetochore is observed in eukaryotes as an assembly on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis.

Crossing over is the swapping of genetic material that occurs in the germ line. During the formation of egg and sperm cells, also known as meiosis, paired chromosomes from each parent align so that similar DNA sequences from the paired chromosomes cross over one another. Crossing over occurs between prophase I and metaphase I and is the process where two homologous non-sister chromatids pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.

Mitosis is the process of cell division wherein the chromosomes replicate and gets equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division. Mitosis produces 2 diploid cells. The old name for meiosis was reduction/ division. Meiosis I reduces the ploidy level from 2n to n (reduction) while Meiosis II divides the remaining set of chromosomes in a mitosis-like process (division).

Karyokinesis is defined as the division of the nucleus during the M phase of the cell cycle. ... The daughter chromosome is separated into two daughter nuclei. Cytokinesis, on the other hand, is defined as the division of the cytoplasm during the M phase of the cell cycle. Karyokinesis is followed by the cytokinesis in the mitotic division. In plant cells, the cytoplasm of the parent cell is divided by the formation of a cell plate in the middle of the parent cell. In animal cells, a cleavage furrow is formed by the plasma membrane, separating the two daughter cells.

The length of the muscle cell is 1-40 micrometers.
Nerve cells possess a cell body and one to many thin, fiber-like axons.
Some nerve cells possess axons as long as 1 meter.