Karyokinesis is the division of the nucleus that occurs in four stages. They are prophase, metaphase, anaphase and Telophase. During prophase, the chromatin condenses to form chromosomes. centrioles develop into asters and move towards the opposite poles. Mitosis is the process in which the nucleus of a eukaryotic cell divides. During this process, sister chromatids separate from each other and move to opposite poles of the cell. This happens in four phases, called prophase, metaphase, anaphase, and telophase.

The main objectives of herbaria making are :

• To preserve plant specimens for reference.
• To identify plants on the basis of herbarium specimens.
• To study the vegetation different localities at of various times intervals.

The main step to prepare herbarium sheet are:

• Collection and pressing of specimens. Fresh materials are pressed in plant press in herbarium press.
• Drying of specimens. ...
• Mounting of specimens on herbarium sheets. ...
• Labeling of specimens. ...
• Storage and filling of herbarium sheets. ...
• Protection of herbarium sheets.

Prion, an abnormal form of a normally harmless protein found in the brain that is responsible for a variety of fatal neurodegenerative diseases of animals, including humans, called transmissible spongiform encephalopathies.

Proin contains the active ingredient phenylpropanolamine, an adrenergic agent that works by tightening the bladder sphincter muscle, which helps to control urine leakage.

A heterocyst is a differentiated cyanobacterial cell that carries out nitrogen fixation. The heterocysts function as the sites for nitrogen fixation under aerobic conditions. They are formed in response to a lack of fixed nitrogen (NH₄ or NO₃).

A taxonomic key is a device for quickly and easily identifying to which species an unknown plant belongs. The key consists of a series of choices, based on observed features of the plant specimen.

Enterokinase, also called Enteropeptidase, proteolytic enzyme (q.v.), secreted from the duodenal mucosa, that changes the inactive pancreatic secretion trypsinogen into trypsin, one of the enzymes that digest proteins. Enteropeptidase (also called enterokinase) is an enzyme produced by cells of the duodenum and is involved in digestion in humans and other animals. Enteropeptidase converts trypsinogen (a zymogen) into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes.

Digestive enzymes helps in digesting complex food materials into simpler molecules for absorption by the body. During digestion of food, different parts of the alimentary canal produces different digestive enzymes that helps in digestion of different components of food. For example, saliva produces salivary amylase that digests the starch. Stomach contain gastric glands that produces pepsin that helps in protein digestion. Apart from that other enzymes such as trypsin, chymotrypsin also helps in protein digestion.

Protozoans are microscopic unicellular eukaryotic organisms with heterotrophic mode of nutrition. Their nutrition may be holozoic, saprobic, or parasitic. These are divided into four major groups.

(1) Amoeboid protozoans or sarcodines : They are unicellular, jelly-like protozoa found in fresh or sea water and in moist soil. Their body lacks a periplast. Therefore, they may be naked or covered by a calcareous shell. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia for locomotion. These pseudopodia or false feet help in movement and capturing prey. They include free living forms such as Amoeba or parasitic forms such as Entamoeba.

(2) Flagellated protozoans or zooflagellates: They are free living, non-photosynthetic flagellates without a cell wall. They possess flagella for locomotion and capturing prey. They include parasitic forms such as Trypanosoma, which causes sleeping sickness in human beings and free living forms such as Noctiluca.

(3) Ciliated protozoans or ciliates: They are aquatic individuals that form a large group of protozoa. Their characteristic features are the presence of numerous cilia on the entire body surface and the presence of two types of nuclei. All the cilia beat in the same direction to move the water laden food inside a cavity called gullet. They include organisms such as Paramaecium, Vorticella etc.

(4) Sporozoans : They include disease causing endoparasites and other pathogens. They are uninucleate and their body is covered by a pellicle. They do not possess cilia or flagella. They include the malaria causing parasite Plasmodium.

A counter-current mechanism system is a mechanism that expends energy to create a concentration gradient. ... For example, it can refer to the process that is underlying the process of urine concentration, that is, the production of hyperosmotic urine by the mammalian kidney.  The counter-current mechanism takes place in Juxtamedullary nephron. The function of the counter-current multiplier is to produce the hyperosmotic Medullary Interstitium. The ADH promotes water reabsorption through the walls of the distal convoluted tubule and collecting duct. Mammals have the ability to produce concentrated urine. The Henle's loop and vasa recta plays significant role in concentrating urine. The flow of filtrate in two limb of Henle's loop and blood flow in two limbs of vasa recta are in opposite direction hence form counter current.

The sac-like structures in a cell surrounded by membrane are called lysosomes.

They keep the cells clean by digesting and breaking the outside materials like bacteria, food entering the cell or worn-out cell organelles into small pieces.

They can digest these organic materials due to the presence of strong digestive enzymes that can brreak down organic compounds. Therefore, lysosome is also known as a suicide sac.

Many scientists believe that lysosomes are not present in plant cells and their function of lysosomes in plants is performed by vacuole.

Pulvinus is a group of cells present at the base of a leaf or a leaflet, which when loose water brings about the changes in the position of the leaves. It is also responsible for the folding of the leaves when flowers are touched or injured.

Mushroom shaped gland is present in 6thand 7thabdominalsegments of male cockroach. It acts as an accessory reproductive gland.
Mushroom gland has two types of tubules:
a) Utriculi majores/peripheral tubules: Form the inner layer of spermatophore.
b) Utriculi breviores: Nourishes the sperms.

Titin is the largest protein in the body, with a molecular weight of 3 million Dalton and composed of 27,000 amino acids. Titin is a giant structural sarcomeric protein with a molecular weight of more than 3800 kD. The largest human protein, it forms the third filament system in striated muscle along with actin and myosin. Titin is the largest protein in the body, with a molecular weight of 3 million Dalton and composed of 27,000 amino acids. Paradoxically, this huge structure was elusive until the last decade but, since it was described in muscle tissue, its importance has rapidly emerged.

There are five levels: cells, tissue, organs, organ systems, and organisms. All living things are made up of cells. Cells are the simplest level of organization. Many cells working together form tissue.