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LIFE PROCESS

INTRODUCTION TO CHAPTER

Life processes are the maintenance functions carried out by living organisms to prevent break down and damage. They require energy which comes from the outside the body of the organism. The seven life processes are movement, reproduction, sensitivity, nutrition, excretion, respiration and growth.

Life science is any branch of natural science, like biology, medicine, zoology, botany, anthropology, or ecology, that deal with living organisms, their structure and their life process.

WHAT ARE LIFE PROCESSBiology is the science that deals with living things. Sometimes it is necessary to make a difference between organisms that are alive, and other things that are not alive. This might not be as easy as it seems, but in general:

1. Living things react to stimuli.

2 .Living things interact with their environment, which includes members of the same and other species.

3 .Living things have a metabolism: they take in food which they convert to the energy they need.

4.Living things reproduce: they give birth to others of the same species. This is not true of all individual organisms. In eusocial organisms, some castes cannot reproduce. But, since the sterile workers are all the produce of a single queen, they are one collective.

Many things that appear to be one organism are in fact several living together. An example is lichen. Lichen is a symbiosis between a blue-green alga and a fungus. Organisms that live together may not reproduce together, but their life processes are bound up together. They help each other to live.

1.NUTRITIONNutrition provides the cells of an organism with food, in a form they can use. Organisms need food to be able to keep their bodies working properly. They also need food to be able to do certain things. Malnutrition can happen when a person doesn't eat the right amount of nutrients. They can get better by changing their diet so it has the right amount of nutrients.

Different organisms have different food requirements, and they eat different things in order to meet those requirements. Animals that do not eat meat, for example, will have to get certain nutrients like protein from other foods.

1.1 AUTOTROPHIC NUTRITION :-The term autotroph has been derived from two Greek wards-auto means self and troph means nutrition. In this mode of nutrition, the organisms prepare their own food from simple raw materials like water, carbon dioxide and mineral salts in the presence of sunlight. Chlorophylls present in the chloroplast or green plants are the site of food production. Accordingly all green plants are the examples of this category. The process by which they synthesize food is known as photosynthesis. Some nongreen becteria like sulphur bacteria can use energy which they derive from some chemical reactions occurring in them. With this energy they manufacture their food. This process is called chemosynthesis. Thus the autotrophs include both the photosynthetic and chemosynthetic organisms.

1.2 HETEROTROPHIC NUTRITION

The word heterotrophy has been derived from two Greek words-hetero means different and troph refers to nutrition of food. The organisms which derive their food from others are known as heterotrophic organisms. They depend for their food on other organisms, hence they are called consumers. All animals, human beings and non-green plans like fungi come under this category. They consume complex organic food prepared by autotrophs or producers and break it into simple from to derive nourishment. Thus the difference between heterotrophy and autotrophs is basically in the mode of production of food. Due to lack of chlorophyll, heterotrophs cannot synthesize their food while autotrophs can perform photosynthesis.

Heterotrophs may be parasitic, saprophytic and holozoic.

1.2.1 parasitic :-

The term has been derived from two Greek works: Para means feeding and sites means grains. Parasitic organisms are those which live on or inside other living organisms to derive their food. Such a mode of nutrition is known as parasitic nutrition. A parasite derives its food (nutrition) from the host in different ways the mode of feeding depends upon its habit, habitat, and modifications. An ectoparasite, which lives on the outer surface of the host, may have certain devices to obtain blood from the host. A mosquito gets a blood meal by inserting its mouth parts into the skin, but a leech has rasping jaws which lacerate the skin of cattle and man. The blood which oozes out is sucked by the leech. A hook-work living in the intestine of man sucks the digested food of the host through its mouth. But a tapeworm which lives in the intestine of man does not even have a mouth of its own. Neither does it have an alimentary canal. A tape-worm thus obtains nutrition through its body surface. An intracellular parasite such as Plasmadium lives on the protoplasm of the cell it has invaded, viruses, fungi and some non-green plants have parasitic mode of nutrition.

1.2.2 Saprophytic :-

The word saprophyte has been derived from the Greek words sapro meaning rotten and phyto meaning plants. Saprophytic organisms derive their food from decomposing dead organisms. The complex organic compounds become simpler in dead organisms when the decomposition sets in. they feed on substances which were once part of living organisms such as stored food, wood, leather and rotten plant products. The common examples of saprophtyes are fungi (moulds, mushrooms, yeasts) and many bacteria. Saprophytes secrete enzymes which are released on he substrate (i.e., the place on which they grow). These enzymes digest and break down the complex food material like starch into simpler ones. The soluble end product like sugar is then absorbed back by the saprophyte. This is called extracellular digestion. The saprophytic mode of nutrition can best be shown by the common bread mould, Rhizopus mucor (pin mould), Neurospora (pink bread mould), Morchella (sponge fungus) and Agaricus (mushrrom) also represent similar mode3 of nutrition

1.2.3 Holozoic

The word holozoic has been derived from Greek words: holos means whole and zoon means animal. Holozoic nutrition involves ingestion of complex organic substances. The food of most animals contains large organic substances. In this mode, small or large particles of food are consumed through an opening called mouth (Ingestion). Then these are hydrolyzed into simpler and soluble forms (digestion). Simplified products are absorbed into the body and the undigested product is removed from the body (Egestion).

2. NUTRITION IN HUMAN BEINGS

The nutrition in human beings (or man) takes place through human digestive system. The human digestive system consists of the alimentary canal and its associated glands. The various organs of the human digestive system in sequence are: Mouth, Oesophagus (or Food pipe), Stomach, Small intestine and Large intestine.

The glands which are associated with the human digestive system and form a part of the human digestive system are: Salivary glands, Liver and Pancreas. The human alimentary canal which runs from mouth to anus is about 9 meters long tube. The ducts of various glands open into the alimentary canal and pour the secretions of the digestive juices into the alimentary canal. We will now describe the various steps of nutrition in human beings (or man).

The human beings have a special organ for the ingestion of food. It is called mouth. So, in human beings, food is ingested through the mouth. The food is put into the mouth with the help of hands.

2.1 INGESTION :-

In human beings, the digestion of food begins in the mouth itself. In fact, the digestion of food starts as soon as we put food in our mouth. This happens as follows: The mouth cavity (or buccal cavity) contains teeth, tongue, and salivary glands. The teeth cut the food into small pieces, chew and grind it. So, the teeth help in physical digestion. The salivary glands in our mouth produce saliva.

2.2 DIGESTION :-

Our tongue helps in mixing this saliva with food. Saliva is a watery liquid so it wets the food in our mouth. The wetted food can be swallowed more easily. Many times we have observed that when we see or eat a food which we really like, our mouth 'waters'. This watering of mouth is due to the production of saliva by the salivary glands in the mouth.The salivary glands help in chemical digestion by secreting enzymes. The human saliva contains an enzyme called salivary amylase which digests the starch present in food into sugar. Thus, the digestion of starch (carbohydrate) begins in the mouth itself. Since the food remains in the mouth only for a short time, so the digestion of food remains incomplete in mouth.

The slightly digested food in the mouth is swallowed by the tongue and goes down the food pipe called oesophagus. The oesophagus carries food to the stomach. This happens as follows: The walls of food pipe have muscles which can contract and expand alternately. When the slightly digested food enters the food pipe, the walls of food pipe start contraction and expansion movements.The contraction and expansion movement of the walls of food pipe is called peristaltic movement. This peristaltic movement of food pipe (or oesophagus) pushes the slightly digested food into the stomach (In fact, the peristaltic movement moves the food in all the digestive organs throughout the alimentary canal).The stomach is a J-shaped organ present on the left side of the abdomen. The food is further digested in the stomach.The food is churned in the stomach for about three hours. During this time, the food breaks down into still smaller pieces and forms a semi-solid paste. The stomach wall contains three tubular glands in its walls. The glands present in the walls of the stomach secrete gastric juice.

The gastric juice contains three substances: hydrochloric acid, the enzyme pepsin and mucus. Due to the presence of hydrochloric acid, the gastric juice is acidic in nature. In the acidic medium, the enzyme pepsin begins the digestion of proteins present in food to form smaller molecules.

Thus, the protein digestion begins in the stomach. Please note that the protein digesting enzyme pepsin is active only in the presence of an acid. So, the function of hydrochloric acid in the stomach is to make the medium of gastric juice acidic so that the enzyme pepsin can digest the proteins properly.Another function of hydrochloric acid is that it kills any bacteria which may enter the stomach with food. The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid.If mucus is not secreted, hydrochloric acid will cause the erosion of inner lining of stomach leading to the formation of ulcers in the stomach. The partially digested food then goes from the stomach into the small intestine. The exit of food from stomach is regulated by a 'sphincter muscle' which releases it in small amounts into the small intestine.From the stomach, the partially digested food enters the small intestine. The small intestine is the largest part of the alimentary canal. It is about 6.5 metres long in an adult man. Though the small intestine is very long, it is called small intestine because it is very narrow.The small intestine is arranged in the form of a coil in our belly. Please note that the length of the small intestine differs in various animals depending on the type of food they eat. For example, cellulose is a carbohydrate food which is digested with difficulty. So, the herbivorous animals like cow which eat grass need a longer 'small intestine' to allow the cellulose present in grass to be digested completely. On the other hand, meat is a food which is easier to digest. So, the carnivorous animals like tigers which eat meat have a shorter 'small intestine'.

The small intestine in human beings is the site of complete digestion of food (like carbohydrates, proteins and fats). This happens as follows:

(a) The small intestine receives the secretions of two glands: liver and pancreas. Liver secretes bile. Bile is a greenish yellow liquid made in the liver which is normally stored in the gall bladder. Bile is alkaline, and contains salts which help to emulsify or break the fats (or lipids) present in the food. Thus, bile performs two functions:(i) makes the acidic food coming from the stomach alkaline so that

pancreatic enzymes can act on it, and (ii) bile salts break the fats present in the food into small globules making it easy for the enzymes to act and digest them.

(b) The walls of small intestine contain glands which secrete intestinal juice. The intestinal juice contains a number of enzymes which complete the digestion of complex carbohydrates into glucose, proteins into amino acids and fats into fatty acids and glycerol. Glucose, amino acids, fatty acids and glycerol are small, water soluble molecules. In this way, the process of digestion converts the large and insoluble food molecules into small, water soluble molecules. The chemical digestion of food is brought about by biological catalysts called enzymes.

2.3 ABSORPTION :-After digestion, the molecules of food become so small that they can pass through the walls of the small intestine (which contain blood capillaries) and go into our blood. This is called absorption. The small intestine is the main region for the absorption of digested food. In fact, the small intestine is especially adapted for absorbing the digested food.The inner surface of small intestine has millions of tiny, finger like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area. And the large surface area of small intestine helps in the rapid absorption of digested food. The digested food which is absorbed through the walls of the small intestine goes into our blood.

2.4 ASSIMILATION :-The blood carries digested and dissolved food to all the parts of the body where it becomes assimilated as part of the cells. This assimilated food is used by the body cells for obtaining energy as well as for growth and repair of the body.The energy is released by the oxidation of assimilated food in the cells during respiration. The digested food which is not used by our body immediately is stored in the liver in the form of a carbohydrate called 'glycogen'. This stored glycogen can be used as a source of energy by the body as and when required.

2.4 EGESTION :-A part of the food which we eat cannot be digested by our body. This undigested food cannot be absorbed in the small intestine. So, the undigested food passes from the small intestine into a wider tube called large intestine. (It is called large intestine because it is a quite wide tube).The walls of large intestine absorb most of the water from the undigested food (with the help of villi). Due to this, the undigested part of food becomes almost solid. The last part of the large intestine called 'rectum' stores this undigested food for some time. And when we go to the toilet, then this undigested food is passed out (or egested) from our body through anus as faeces or 'stool'. The act of expelling the faeces is called egestion or defecation. The exit of faeces is controlled by the anal sphincter.

2. RESPIRATION

The respiratory system (or ventilatory system) is a biological system consisting of specific organs and structures used for the process of respiration in an organism. The respiratory system is involved in the intake and exchange of oxygen and carbon dioxide between an organism and the environment.

In air-breathing vertebrates like human beings, respiration takes place in the respiratory organs called lungs. The passage of air into the lungs to supply the body with oxygen is known as inhalation, and the passage of air out of the lungs to expel carbon dioxide is known as exhalation; this process is collectively called breathing or ventilation. In humans and other mammals, the anatomical features of the respiratory system include trachea, bronchi, bronchioles, lungs, and diaphragm. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveoli air sacs in the lungs.[1]

In fish and many invertebrates, respiration takes place through the gills. Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.[2]

The Diaphragm's Role in Breathing:-

Inhalation and exhalation are the processes by which the body brings in oxygen and expels carbon dioxide. The breathing process is aided by a large dome-shaped muscle under the lungs called the diaphragm.

When you breathe in, the diaphragm contracts downward, creating a vacuum that causes a rush of fresh air into the lungs.

The opposite occurs with exhalation, where the diaphragm relaxes upwards, pushing on the lungs, allowing them to deflate.

The respiratory system has built-in methods to prevent harmful substances in the air from entering the lungs.

Respiratory SystemSmall hairs in your nose, called cilia, help filter out large particles. Cilia are also found along your air passages and move in a sweeping motion to keep the air passages clean. But if harmful substances, such as cigarette smoke, are inhaled, the cilia stop functioning properly, causing health problems like bronchitis.

Mucus produced by cells in the trachea and bronchial tubes keeps air passages moist and aids in stopping dust, bacteria and viruses, allergy-causing substances, and other substances from entering the lungs.

Impurities that do reach the deeper parts of the lungs can be moved up via mucous and coughed out or swallowed.

The process of breakdown of glucose molecules involves two major stages - glycolysis (anaerobic respiration) and aerobic respiration ( Kreb’s cycle and ETS Pathway).Glycolysis

Cellular respiration begins at this stage in the cytoplasm of the cells, and yields 2 carbon-based molecules called pyruvate, and 2 molecules of ATP. Oxygen plays no part during this stage, so it is called anaerobic respiration.Glycolysis is the metabolic pathway that converts one Glucose molecule into 2 molecules of Pyruvate.Glycolysis occurs when the cell needs energy and it takes place in the cytoplasm.Glycolysis, the linear pathway, occurs in (cytosol of all eukaryotes) animals, Plants and in the microbial cells. Glycolysis yields two molecules of ATP, two molecules of pyruvic acid and two electron carrying molecules of NADH.Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. In the absence of oxygen, glycolysis allows cells to make small amounts of ATP which is known as fermentation process.

Aerobic Respiration This process takes place in specialized structures within the cell called mitochondria, and uses the products of glycolysis. The energy released is stored in the form of ATP molecules. Usually, a total of 38 ATP molecules are produced.Breakdown of glucose: C6H12O6 + 6O2 ------> 6CO2 + 6H2O + Energy.

BREAK DOWN OF GLUCOSE :-

3. TRANSPORTATION

The circulatory system also called the cardiovascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from cells in the body to nourish it and help to fight diseases, stabilize body temperature and pH, and to maintain homeostasis.

The circulatory system is often seen to be composed of both the cardiovascular system, which distributes blood, and the lymphatic system, which circulates lymph.[1]These are two separate systems. The passage of lymph for example takes a lot longer than that of blood.[2] Blood is a fluid consisting of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from the interstitial fluid (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning 'heart'-'vessel') system comprises the blood, heart, and blood vessels.[3] The lymph, lymph nodes, and lymph vessels form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph.

While humans, as well as other vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The lymphatic system, on the other hand, is an open system providing an accessory route for excess interstitial fluid to get returned to the blood.[4] The more primitive, diploblastic animal phyla lack circulatory systems.

3.1 Human beings

HUMAN CARDIOVASCULAR SYSTEM :-

Depiction of the heart and circulatory system

Cross section of a human arteryThe essential components of the human cardiovascular system are the heart, blood, and blood vessels.[5] It includes: the pulmonary circulation, a "loop" through the lungs where blood is oxygenated; and the systemic circulation, a "loop" through the rest of the body to provide oxygenated blood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight.[6] Blood consists of plasma, red blood cells, white blood cells, and platelets. Also, the digestive system works with the circulatory system to provide the nutrients the system needs to keep the heart pumping.[7]

CLOSED CADIOVASCULAR SYSTEM :-

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is not closed.

TWO TYPES OF CIRCULATION :-

Pulmonary circulation :

Circulation showing pulmonary and systemic circuits.

The pulmonary circulatory system is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein.

Oxygen deprived blood from the superior and inferior vena cava, enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, whereby CO2 is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the left atrium.[7]

Systemic circulation :

Systemic circulation is the circulation of the blood to all parts of the body except the lungs. Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart. Systemic circulation is, distance-wise, much longer than pulmonary circulation, transporting blood to every part of the body.[7]

3.2 plants

Plants have two systems for the transportation of substances - using two different types of transport tissue. Xylem transports water and solutes from the roots to the leaves, while phloem transports food from the leaves to the rest of the plant. Transpiration is the process by which water evaporates from the leaves, which results in more water being drawn up from the roots. Plants have adaptations to reduce excessive water loss.

XYLEM AND PHLOEM :-

Plants have two transport systems to move food, water and minerals through their roots, stems and leaves. These systems use continuous tubes called xylem and phloem, and together they are known as vascular bundles.

Plant root

Plant root

XYLEM :-

Xylem vessels are involved in the movement of water through a plant - from its roots to its leaves via the stem.

During this process:

Water is absorbed from the soil through root hair cells.

Water moves by osmosis [osmosis: The net movement of water molecules across a partially-permeable membrane from a region of low solute concentration to a region of high solute concentration.] from root cell to root cell until it reaches the xylem.

It is transported through the xylem vessels up the stem to the leaves.

It evaporates [evaporate: The process in which a liquid turns into a gas.] from the leaves (transpiration).

The xylem tubes are made from dead xylem cells which have the cell walls removed at the end of the cells, forming tubes through which the water and dissolved mineral ions can flow. The rest of the xylem cell has a thick, reinforced cell wall which provides strength.

PHLOEM :-

Phloem vessels are involved in translocation. Dissolved sugars, produced during photosynthesis [photosynthesis: A chemical process used by plants and algae to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis.] , and other soluble food molecules are moved from the leaves to growing tissues (eg the tips of the roots and shoots) and storage tissues (eg in the roots).

In contrast to xylem, phloem consists of columns of living cells. The cell walls of these cells do not completely break down, but instead form small holes at the ends of the cell. The ends of the cell are referred to as sieve plates. The connection of phloem cells effectively forms a tube which allows dissolved sugars to be transported.

3. EXCRETION3.1 humans

Excretion is the removal of toxic materials, the waste products of metabolism and substance in excess of requirements from organisms. Metabolism is chemical reactions taking place inside cells, including respiration.

The body excretes three main waste materials. These are Carbon Dioxide, Urea and Water. Excretion is a very important feature to us because without it toxic substances will build up in our bodies and kill us. It also helps in maintaining the composition of body fluids.

The Excretory System of humans is made up of 4 structures: Two kidneys, two ureters, a bladder, and the urethra. The kidneys act as a filter to filter the waste products from the blood, the ureters are tubes that transport the main waste products (urine) from the kidneys to the bladder, where it is stored until it is excreted out of the body through the urethra.

Formation of urea :-

•When you eat a food high in protein, it is digested in the small intestine into amino acids.

•The villi on the walls of the small intestine absorb the amino acids into the hepatic portal vein.

Hepatic portal vein is a special vein that transports digested material from the small intestine to the liver.

•The liver plays a big role in maintaining the level of protein in our body. It absorbs all amino acids from the hepatic portal vein. If the body needs proteins, they will pass through the liver into the blood stream to be used by the body cells to make protein.

If the body does not need proteins. The liver will absorb excess amino acids and break them down into carbohydrates and nitrogen. The formula of amino acids is CHON; here we remove the nitrogen from the molecule, to get a carbohydrate. This is called deamination. Nitrogen is made into urea which is a nitrogenous waste product.

•The products are then released to the blood stream.

Kidneys Structure:-A kidney consists of two main structures:

•Cortex (outer layer)•MedullaBetween the cortex and the Medulla, there is a structure called the nephron. The nephron is the where filtration of toxic materials from the blood takes place. We have many of them in each kidney.

In the centre of the kidney there is a cavity called the pelvis which leads to the ureter.

Structure of Nephrone:-

The nephrone starts with a cup shaped structure called Bowman’s capsule. Inside the Bowman’s capsule there is a very dense network of blood capillaries entering as capillaries from the renal artery and exiting as capillaries from the renal vein. This dense network of capillaries is called Glomerulus. The rest of the nephrone is a long coiled tube where materials filtered from the blood flow in. At some point the coiled tube becomes straight and is bent in a U shape tube, this part is called loop of Henle and it is surrounded by a network of capillaries from the renal vein, it is where reabsorption takes place. All nephrones end at a large tube called the Collecting duct where content of the nephrones are transported to the pelvis, to be secreted in the ureter.

3.2 plantsExcretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys and skin.[1] This is in contrast with secretion, where the substance may have specific tasks after leaving the cell. Excretion is an essential process in all forms of life. In mammals urine is carried out through the urethra and that is part of the excretory system.

In single-celled organisms, waste products are discharged directly through the surface of the cell.

Chemical structure of uric acid.Plants produce carbon dioxide and water as respiratory waste products. In green plants, the carbon dioxide released during respiration gets utilized during photosynthesis. Oxygen can be thought of as a waste product generated during photosynthesis, and exits through stomata, root cell walls, and other routes. Plants can get rid of excess water by transpiration and guttation. It has been shown that the leaf acts as an 'excretophore' and, in addition to being a green plant's primary organ of photosynthesis, is also used as the plant's method of excreting toxic wastes. Other waste materials that are exuded by some plants — resin, saps, latex, etc. are forced from the interior of the plant by hydrostatic pressures inside the plant and by absorptive forces of plant cells. These latter processes do not need added energy, they act passively. However, during the pre-abscission phase, the metabolic levels of a leaf are high.[2][3] Plants also excrete some waste substances into the soil around them.[4]

In animals, the main excretory products are carbon dioxide, ammonia (in ammoniotelics), urea (in ureotelics), uric acid (in uricotelics), guanine (in Arachnida) and creatine.

Aquatic animals usually excrete ammonia directly into the external environment, as this compound has high solubility and there is ample water available for dilution. In terrestrial animals ammonia-like compounds are converted into other nitrogenous materials as there is less water in the environment and ammonia itself is toxic.

White cast of uric acid defecated with the dark feces from a lizard. Insects, birds and some other reptiles also undergo a similar mechanism.Birds excrete their nitrogenous wastes as uric acid in the form of a paste. This is metabolically more expensive, but allows more efficient water retention and it can be stored more easily in the egg. Many avian species, especially seabirds, can also excrete salt via specialized nasal salt glands, the saline solution leaving through nostrils in the beak.

In insects, a system involving Malpighian tubules is utilized to excrete metabolic waste. Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal matter.

The excreted material may be called dejecta or ejecta.[5] In pathology the word ejecta is more commonly used.[6]

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HARPREET SINGHCLASS : 10 TH