Morphallaxis is the regeneration of a whole body from a small body part. When a Hydra is cut into two halves, each half generates the rest of the body resulting in two complete, functional, and independent Hydra. During morphallaxis, neighboring tissues of the small body part reorganize themselves to develop the rest of the body part. Two types of morphogenetic gradients are found in Hydra. They are the head activation gradient that directs one head formation and the head inhibition gradient that directs a foot formation.
Morphallaxis was discovered in hydra by Genevan naturalist Abraham Trembley. This type of regeneration is found mostly in invertebrates. A blastema is formed on the wounded site during epimorphosis. However, a blastema is absent in the morphallaxis process.
The stomach is the widest region of the alimentary canal. It is a hollow organ present between the esophagus and the small intestine. The stomach is divided into four parts. They are (i) the Cardiac part, (ii) the Fundus part, (iii) the Body, and (iv) the Pyloric part. The cardiac part of the cardia is the region of the stomach, which is present near the heart. The cardiac sphincter or the gastroesophageal sphincter lies in the opening between the esophagus and stomach is present in the cardiac part.
The cardiac glands are found in the cardiac part of the stomach. The cardiac glands secrete mucus, which coats the stomach and protects it from self-digestion from the acids and enzymes. The number of cardiac glands is fewer as compared to the other gastric glands. There are two kinds of cardiac glands: (i) simple tubular with short ducts and (ii) compound racemose resembling the Brunner’s glands present in the duodenum.
Stomata (or stomates) are a tiny pores found in the epidermis of leaves, stems, and other soft aerial part of plants. The size ranges from around 10-14 µm in length and 3-12 µm in breadth. In mesophytic plants, stomata present both on the upper or adaxial surface as well as the lower or abaxial surface of the leaves. In monocots, the number of stomata present on the upper surface is similar to the number in the lower surface of the leaf. On the other hand, in dicots, the number of stomata present on the upper surface is lower than the number of stomata on the lower surface.
Lotus as well as in other aquatic plants, the leaves are float on the surface of the water. In this conditions, stomata are present only on their upper surface of the leaves and helps in exchange of gases between the plant and the atmosphere. In contrast, in completely submerged plants the stomata are absent and gaseous exchange takes plce through the epidermal cells.
Digested lipids are absorbed from the lacteals as triglycerides or neutral fats. In the stomach, gastric lipase digests the fats into monoglycerides and fatty acids. In the small intestine, intestinal and pancreatic lipase digests the fats first into diglycerides and then into monoglycerides, releasing a fatty acid at each step. Therefore, the lipase converts fats into monoglycerides and fatty acids.
Free fatty acids, monoglycerides, and lysolecithin pass the membrane of microvilli to enter the intestinal epithelial cells. In the epithelial cells, these molecules are used to synthesize triglycerides and phospholipids. Then triglycerides, phospholipids, cholesterol are mixed with protein to form small fat molecules called chylomicrons. Thereafter, these chylomicrons are released from the intestinal cells into the lacteals (the lymphatic capillaries) of the intestinal villi.
The brain is covered by three membrane or meninges. The innermost membrane is called piamater. It is thin and very delicate and supplies with blood vessels. The piamater is present very close to the brain. Next to the piamater is the arachnoid membrane, which is a spider webby-like structure. The outermost membrane is called the duramater and is presently close to the inside of the skull.
The space present between piamater and the arachnoid membrane is called the subarachnoid space. The subarachnoid space is filled with cerebrospinal fluid, which serves as a cushion for the central nervous system and protects it from shock. The fluid also provides a medium for the exchange of respiratory gases, food materials, waste, etc between the brain and the body.
Bryophytes are photosynthetic land plants. They are non-vascular as they are devoid of vascular tissue. The life cycle of bryophyte is consists of alternating generations between haploid (n) gametophytes stage and diploid (2n) sporophyte stage. During the gametophytic stage, haploid male gametes are formed in a specialized structure called antheridium and haploid female gametes are formed in a specialized structure called archegonium.
The male gametes or sperms are biflagellated. They need water to reach the archegonium to fertilize with eggs. The two haploid gametes fuse to form a diploid zygote (2n) is formed. The zygote grows inside the archegonia and later developed into a diploid sporophyte. The mature sporophytes remain attached to the female gametophyte and produced haploid spores inside the sporangium through meiosis. Under favorable conditions, spores are dispersed and grown to new gametophytes. The sporophytes are not photosynthetic and directly depend on the female gametophytes for their nutrition. Therefore, they are parasitic in nature.
The vagus nerve is the tenth cranial nerve (X). It is also known as the “vagrant” or “wandering” nerves. The nerve fibers travel through the neck to the thoracic cavity and through the oesophageal opening in the diaphragm to the abdominal cavity in humans. They provide nerve connections to the heart, lungs, esophagus, pancreas, liver, stomach, small intestine, and upper part of the large intestine.
The pharyngeal and laryngeal branches of the vagus nerves transmit motor impulses to the pharynx, soft palate, and larynx. The cardiac branches of the vagus nerves regulate to slow the rate of heartbeat. The bronchial branch of the vagus nerves constricts the bronchi. The esophageal branches of the vagus nerves control involuntary muscles in the esophagus, stomach, pancreas, gallbladder, and small intestine, stimulating gastrointestinal secretions and peristalsis movement. It also provides taste sensation to the root of the tongue.
The cataract is a cloudy area in the eye lens that leads to blurry vision or a decrease in vision. The Age-Related Nuclear Cataract (ARNC) is a cataract that developed in the lens during aging. Cataracts can form in different places on the lens. In the posterior subcapsular cataract, a cloudy area developed in the back of the lens. In a nuclear cataract, a cloudy area developed in the middle of the lens. In the cortical cataract, a cloudy area developed on the edges of the lens.
The development of a cloudy area in the lens is caused due to aggregation of lens proteins called α-crystallin. These crystallin proteins are present in the lens fiber in a soluble form. With the advancement of age, these soluble crystallin proteins denatured and unfolded over time and forms aggregates. Slowly high molecular weight protein aggregates increase in the human lens. This aggregation of proteins makes the lens transparent to opaque.
Holozoic nutrition is a type of heterotrophic nutrition in which the cell ingests liquid or solid food particles. This kind of nutrition is found in unicellular organisms such as amoeba as well as in multicellular animals such as humans. In the holozoic type of nutrition, liquid or solid food particle is taken by the cell and then further broken down into small fragments. The animals get energy as well as organic building blocks by ingesting and then digesting the food particles.
Several stages of holozoic nutrition are (i) Ingestion (intake of food through the mouth or phagocytosis), (ii) Digestion (physical breakdown of large food particles into small particles, and enzymatic breakdown of complex molecules into simple molecules), (iii) Absorption (transport of the digested products into the body or cytoplasm). (iv) Assimilation (utilization of the absorbed molecules in different metabolic processes) and (v) Egestion (removal of undigested material).
Zingiber officinale or ginger is an underground modified stem called a rhizome. Ginger is widely used as a spice and in Ayurveda and traditional medicine. The rhizome is a perennial underground stem. Continuously it produces aerial shoots and new leaves during the favorable season. The stem is differentiated into nodes and internodes. The rhizome in ginger is branched in a cymose fashion. The ginger rhizomes are fleshy and juicy with a mild taste. Upon mature, the rhizomes become fibrous and nearly dry.
Corm, tuber and bulb are also modified stems. A corm is usually short, thick and unbranced underground stem (Colocasia), tuber is an oval or spherical underground stem and does not bear adventatious roots (potato) and bulb is an pyriform-spherical underground stem with several fleshy scales enclosing the terminal bud (onion).