Bacteriophages are the viruses which infect bacteria. These viruses that parasitizes the bacteria. Bacteriophages were discovered independently by Frederick William Twort in 1915 and Félix d’Hérelle in 1917.
Phylum Annelida (L., annelus = little ring or F., anneler = to arrange in rings) is a group of bilaterally symmetrical, coelomate, and segmented animals known commonly as segmented worms. Members of this phylum exhibit a body divided into repeated segments called metameres, which give them structural and functional division. Annelids are triploblastic and possess a true coelom, which is divided by septa, and a closed circulatory system. They have a complete digestive system, a well-developed nervous system with a ventral nerve cord, and excretory structures called nephridia. Respiration occurs through the body surface, gills, or parapodia.
Phylum Aschelminthes (Gr., askes = cavity ; helmins = worm) is a group of bilaterally symmetrical, unsegmented, and pseudocoelomate animals. They are typically characterized by a cylindrical or thread-like body covered with a tough, flexible cuticle. The phylum includes organisms that are predominantly aquatic or parasitic in nature, such as nematodes (roundworms).
Phylum Platyhelminthes (Gr., platys = flat ; helmins = worms) refers to a group of invertebrate animals commonly known as flatworms. They are characterized by their soft, unsegmented, dorsoventrally flattened bodies. Members of this phylum are bilaterally symmetrical, triploblastic (having three embryonic germ layers), and acoelomate, meaning they lack a true body cavity. Platyhelminthes exhibit cephalization (a distinct head region) and possess a simple organ system level of organization.
Phylum Ctenophora (Gr., kestos=comb; phoros=bearing) is a group of marine invertebrates commonly known as comb jellies. These organisms are characterized by their gelatinous bodies, biradial symmetry, and the presence of eight rows of ciliary plates (combs) that they use for locomotion. Unlike jellyfish, which belong to Phylum Cnidaria, ctenophores lack stinging cells (cnidocytes) and instead capture prey using sticky cells called colloblasts.
Viruses are intracellular obligate parasites, non-cellular (acellular) sub-microscopic organisms. The word “virus” means venom or poisonous fluid. They lack cell organelles and make use of the protein synthetic machinery of the host cell.
Coral colonies grow continuously in size by budding of polyps and often form extensive masses, known as coral reefs.
Aurelia aurita is easily recognised by its soft bell or umbrella-shaped body with four red or purple horseshoe-shaped gonads on its upper surface and four long and narrow oral lobes hanging downward from the lower surface.
Phylum Coelenterata (Gr., koilos = hollow ; enteron = intestine), also known as Phylum Cnidaria, is a group of aquatic, mostly marine animals characterized by a simple body structure with a single opening serving as both mouth and anus. Members of this phylum have a diploblastic body (two tissue layers: ectoderm and endoderm) and radial symmetry. They possess specialized stinging cells called cnidocytes containing nematocysts, used for defense and capturing prey. Coelenterates exhibit two main body forms: the sessile polyp (e.g., Hydra) and the free-floating medusa (e.g., jellyfish). This phylum includes organisms like corals, sea anemones, and hydroids, playing important roles in marine ecosystems, such as reef-building.
The main difference between apoptosis and necrosis is the way in which cell death occurs. Apoptosis is a programmed and controlled process of cell death that plays a vital role in normal development, tissue maintenance, and removing damaged cells. It does not cause inflammation as the cell contents are contained and recycled. Necrosis, on the other hand, is an uncontrolled and unplanned cell death caused by injury, infection, or toxins, often leading to inflammation as the cell contents are released into the surrounding tissue.