Excretion - animals - class-X

There are majorly the types of excretory product - Ammonia, Urea, and Uric acid. 

Insects are uricotelic i.e, they excrete uric acid. 

In Uricotelic organisms, the end product of nitrogen metabolism is uric acid.  include terrestrial arthropods (including insects), lizards, snakes, and birds. 

Nitrogenous waste substances such as ammonia, urea or uric acid are produced during protein metabolism according to the species. A small amount of nitrogenous waste substances are also produced during the metabolism of nucleic acids. Ammonia is the most toxic, followed by urea and then uric acid.

Nitrogenous waste that is produced in the body needs to be excreted from the body as they are toxic to an organism. The waste is excreted in 3 forms, namely ammonia, uric acid, and urea. Ammonia is more water-soluble and most toxic. It requires less energy for excretion. Animals excreting nitrogenous waste in the form of ammonia are called as ammonotelic. Aquatic animals like protozoans, crustaceans, poriferans, fishes where water is not a constraint are ammonotelic. Urea requires comparatively more energy and is less toxic in nature. Animals excreting nitrogenous waste in the form of urea are called as ureotelic. Examples include cartilaginous fish, amphibians, mammals including humans. Uric acid is least soluble in water and is least toxic. However, it requires a large amount of energy. Examples include reptiles, birds.

The major excretory products are carbon dioxide, excess water, and nitrogenous compounds like ammonia, urea, uric acid, etc. Carbon dioxide and water are produced in the process of tissue respiration. Nitrogenous compounds are formed from the breakdown of proteins and amino acids.
So, the correct option is "B" (Mineral salt).

Ammonia was the first and simplest excretory substance in the animal body and is excreted as it is toxic. It requires large amounts of water for its excretion and so it is seen in most aquatic vertebrates and invertebrates.

A) Perspiration (sweating) is the loss of water and salts through the surface of the skin. This water evaporates. Urine is mostly water and is also composed of salts and is excreted by the animal into the environment. While breathing, minute molecules of water or water vapour are given out into the environment along with carbon dioxide.

Organisms can store their wastes in different glands and organs such as the kidneys, sweat glands, lungs etc. All the nitrogenous and solid wastes are stored by different organisms for a certain period in certain body organs such as the kidneys and the intestines, after which they are eliminated from the body. So, the correct option is 'True'.

Earthworms excrete ammonia when sufficient water is available, because a large volume of water is needed by the animal to dissolve ammonia and eliminate it from, the body. Whereas in drier environment the animal eliminates urea as it requires only considerable amount of water for the excretion of urea because urea is very soluble in water.

The end products of aerobic metabolism of carbohydrates are carbon dioxide and water. Carbon dioxide remains dissolved in the blood and is carried by the veins to the lungs for oxygenation. If carbon dioxide is not removed from the metabolizing tissues, it will be toxic for that tissue and stop metabolism.

Urea is both osmoregulator as well as nitrogenous waste. Urea is produced in the liver and excreted through urine. The urea helps in osmoregulation by participating in counter current system, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule.  

The excretory product of spider is guanine. It is formed as a result of nucleotide metabolism. It does not require water for elimination because it is less soluble than uric acid and helps to conserve more water.

The characteristic shared by urea, uric acid and ammonia are they are nitrogenous wastes. In comparison to Ammonia and Urea, uric acid is the least toxic and the least soluble in water. It can be stored in cells and body tissues without any toxic effects and hence needs less water for excretion when compared to Ammonia and urea.

For terrestrial vertebrates, nitrogenous wastes are removed from body fluids by the action of the kidneys, the same organ involved in maintaining water balance. Ammonia the direct waste produced as a byproduct of protein metabolism.  Produced by all animals.  Because of its toxicity, many animals convert ammonia into a less toxic form.  Any conversion of ammonia into other forms comes at a price, for animals must expend cellular energy (ATP) to convert ammonia to either form of nitrogenous waste listed below.

Chemicals that the body makes when there is not enough insulin in the blood and it must break down fat instead of the sugar glucose for energy. The ketone bodies -- acetone,  acetoacetate, and beta-hydroxybutyrate -- are toxic acidic chemicals. They build up in the blood and then spill over into the urine. The body can also rid itself of acetone through the lungs. This gives the breath a fruity odor.

Urea synthesis is a five-step cyclic process, with five distinctive enzymes. One turn of the cycle consumes 2 molecules of ammonia and  1 molecule of carbon dioxide and creates 1 molecule of urea ((NH2)2CO. Hence  16  molecules of ammonia are required to form 8 molecules of urea.

Ammonia is more water soluble and more toxic than Urea or uric acid. Ammonia is extremely toxic and its accumulation in the body can be lethal. So the liver converts toxic ammonia into less toxic urea through the urea cycle.

Ketone bodies are byproducts in the metabolism of fat. During starvation or fasting conditions the liver synthesizes glucose through a process called gluconeogenesis. Gluconeogenesis is a metabolic pathway that results in the generation of glucose from fat. During gluconeogenesis, the ketone bodies are formed as byproducts where the product is glucose. The Kerone bodies consist of acetoacetic acid, acetone and beta-hydroxybutyric acid.

• Birds, reptiles, and fishes produce uric acid waste and they are called Uricothelic organisms.
  
• They tend to excrete uric acid as its waste which is in the form of a white paste or powder.
• Producing uric acid over urea is advantageous because it is less toxic and reduces water loss and the subsequent need for water.  in these organisms.
• The correct answer is OPTION A.

When muscles work continuously enough, oxygen is not reached to muscles to burn glucose aerobically in such conditions glucose is converted into lactic acid i.e anaerobic glycolysis. The lactic acid produced in muscles is moved to the liver and converted to glucose. In ureotelic organisms, lactic acid is converted into Glucose through the Cori cycle. This metabolic cycle was discovered by Carl Ferdinand Cori and  Gerty Cori, hence named Cori cycle.