S.N. Agnatha Gnathostomata 1. Mouth is circular without jaws. Mouth is provided with jaws. 2. Paired appendages are lacking. Paired appendages are present, may be fins or limbs. 3. Notochord is persistent. Notochord is usually replaced by a vertebral column. 4. Vertebral column is not developed or is represented by imperfect neural arches over the notochord. Vertebral column is fully developed. 5. There are 8-10 pairs of cranial nerves. There are 10-12 pairs of cranial nerves. 6. Only a single median nostril and olfactory sac are present. Paired nostrils and olfactory sacs are p ..read more

Kidney is the most important excretory organ of frog. Frog mainly excretes urea, ammonia and water. In tadpole, kidney is pronephric but in adult kidney is mesonephric. Tadpole is ammonotelic while adult is ureotelic. Kidney is a paired organ. It lies in the abdominal cavity inside the sub-vertebral lymph sinus. They are dark reddish colored. Dorsal and ventral surfaces are flat. A long light yellow colored adrenal gland lies in its dorsal surface. It functions as an endocrine gland. Gonads lie towards the anterior end of adrenal gland. Numerous thin finger shaped structures encircle these st ..read more

The blood vessels which carry oxygenated blood away from the heart and supply blood to various body parts collectively constitute the arterial system. The major blood vessels arising from the left ventricle is called a systemic aorta. This aorta branches off to form many smaller arteries, which in turn branch off many times into arterioles. The aorta runs upwards and sharply curves or arches downwards. The upward running portion of aorta is called the ascending aorta,  and the downward curving aorta is called a descending aorta. 1. Ascending aorta: It gives off: Coronary arteries: Ther ..read more

What is nitrogen fixation? The phenomenon of conversion of free nitrogen into nitrogenous salts to make it available for absorption by plants is called nitrogen fixation. On the basis of agents through which the nitrogen is fixed, the fixation of nitrogen is divided into two types: Physical nitrogen fixation Biological nitrogen fixation                           Source: https://www.sciencefacts.net/nitrogen-fixation.html Physical nitrogen fixation: Out of total nitrogen fixed by natural agencies, approximately 10% of this o ..read more

A tissue, consisting of sheets or bundle of cells (muscle fibers) which is capable of contracting and producing movement or tension in the body is called muscular tissue. These tissues are usually mesodermal in origin and consist of thin and elongated cells called muscle fibers. Each fiber contains fine longitudinal fibrils called myofibrils. The cytoplasm inside a muscle fiber is called sarcoplasm. Sarcoplasm contains a network of membranes called sarcoplasmic reticulum. Each muscle fiber is externally covered by a membrane called sarcolemma. The muscle fiber exhibit the property of: Irrita ..read more

What is coal? Coal is a solid, black, readily combustible fossil fuel found as thick layers in deep mines under the surface of the earth. It is usually one inch to several feet thick between shale, sandstone and other sedimentary rocks. It is formed from the highly compressed remains of plants. It contains a large amount of carbon-based material (approximately 50% of its weight). It takes a significant amount of time (few million years) for the formation of coal. The formation of coal begins in areas of swampy wetlands where groundwater is near or slightly above the topsoil. Because of t ..read more

What are fossils? The term fossil comes from the Latin word fossilis, which literally means ‘dug up’. Fossils are the remnants, impressions, or traces of animals, plants or any other living organisms that existed in the past geologic age, millions of years ago and have been preserved in Earth’s crust. Fossils not only refer to the bones, shell, teeth or any hard structures of plants or animals which have been preserved in the rocks, but also to any impressions or traces left by ancient plants and animals. Fossils tell us about the history of life on Earth and provide more reliable evidence in ..read more

A variety of mushrooms are found naturally growing on rotten logs of wood, dead barks of trees, fallow lands, forest beds, animal excreta etc. They differ in several characteristics and may be edible or poisonous. Mushroom poisoning caused by the ingestion of toxic mushrooms is called mycetism. About 30 wild species of mushrooms are known to be consistently fatal due to high levels of toxicity. Eating wild mushrooms is bad because they contain high levels of heavy metals, other chemicals and toxins which can trigger fatal health problems. Many people are not aware of the toxic and hallucinoge ..read more

Food adulteration is the intentional addition of non-permitted foreign matter in food which increases the volume and weight of food. This helps increase volume of trade by showing lower prices leading to more economic gains. Sometimes, food adulteration may be incidental as well. The health of consumers is compromised if they consume adulterated food. It may endanger and affect their physiological functions due to either addition of a deleterious substance or the removal of vital components. Food adulteration may occur either by: Deliberate or intentional addition, substitution or subtractio ..read more

The sensation of taste is called gustation or gustatory response. Various chemoreceptors present in the tongue help in getting the sense of taste. The sense of taste (gustation) and smell (olfaction) are clearly interrelated. That’s why, a person whose nasal passages are blocked by a cold cannot get the proper taste of food effectively. Despite some similarities, taste and smell are separate and distinct senses. Location and Structure of Taste receptors: The surface of our tongue is covered with many small protuberances or outgrowths called papillae, which give a tongue its bumpy appearance ..read more