Solved Exercise, Bio-12, Ch-15


(i) ________ is the ability of an organism to regulate its fluid contents. (osmoregulation)

(ii) The detoxification of ammonia to _________ requires the precursor of ornithine. (urea)

(iii) In kidney, nephron is closely associated with network of _________. (capillaries)

(iv) In insects, salt and water reabsorption takes places in the_________. (rectum)

(v) The antidiuretic hormone acts on _________ to promote reabsorption of water in vertebrate nephron. (collecting ducts)

(vi) The nephrons arranged along the border of cortex and medulla, with tubular system looping deep in the inner medulla, are called _________. (juxtamedullary nephrons)

(vii) The non-surgical procedure of removing kidney stone is termed as_________. (lithotripsy)

(viii) _________ is the homeostatic thermostat in human. (hypothalamus)


(i) The protection of internal environment from the harms of fluctuation in external environment is termed:   

(a)   Osmoregulation

(b)   Thermoregulation

(c)   Excretion

(d)   Homeostasis

EXPLANATION: Homeostasis refers to the body’s ability to maintain a stable internal environment despite changes in the external surroundings. It involves various physiological processes that regulate factors like temperature, blood sugar, and pH to keep the internal conditions within a narrow, optimal range for the proper functioning of cells and organs. Essentially, it is the body’s way of protecting itself from the potential negative effects of external environmental fluctuations.

(ii) The category of plants that has adaptation of small and thick leaves to limit water loss is called:          

(a)   Hydrophytes

(b)   Xerophytes

(c)   Mesophytes

(d)   Hygrophytes

EXPLANATION: Xerophytes are a category of plants that have adapted to environments with limited water availability. These plants feature small and thick leaves, which help reduce water loss through evaporation. The adaptation of these characteristics allows xerophytes to thrive in arid or dry conditions by efficiently conserving water and maintaining their hydration levels.

(iii) The environment where the animals produce large volumes of urine.

(a)   Hypotonic aquatic

(b)   Isotonic aquatic

(c)   Hypertonic aquatic

(d)   Terrestrial

EXPLANATION: In a hypotonic aquatic environment, animals produce large volumes of urine. This is because the surrounding water has a lower concentration of dissolved substances compared to the internal fluids of the animals. To prevent an excessive influx of water into their bodies, these animals excrete a significant amount of diluted urine. This adaptation helps them maintain the balance of salts and water within their bodies, ensuring proper osmoregulation in an environment where there is a tendency for water to move into their cells.

(iv) Which of the following is called excretophore i.e., contributing mainly in the elimination of wastes in plants?

(a)   Stem

(b)   Roots

(c)   Leaves

(d)   Flowers

EXPLANATION: ‘Excretophores’ typically refers to structures or cells involved in excretion or waste elimination. In autumn, the plants shed their old yellow leaves. In this way, they get rid of their accumulated wastes. That’s why, leaves are said to be ‘excretophores’.

(v) The excretory product that requires minimum water for its removal is: 

(a)   Urea

(b)   Uric acid

(c)   Ammonia

(d)   Creatinine

EXPLANATION: Uric acid is an excretory product that requires minimal water for its removal. Unlike other nitrogenous waste products like ammonia or urea, uric acid is relatively insoluble in water. This characteristic makes it suitable for organisms, such as birds and reptiles, that inhabit environments with limited water availability.

(vi) The group of animals whose excretory system is structurally associated with digestive tract:      

(a)   Vertebrates

(b)   Earthworm

(c)   Planarian

(d)   Insects

EXPLANATION: In insects, the excretory system is structurally associated with the digestive tract. The excretory system in insects consists of tube-like structures called Malpighian tubules, which are connected to the digestive tract. These tubules play a crucial role in filtering waste products and excess ions from the hemolymph (insect blood). The filtered waste then moves into the digestive tract, ultimately getting expelled from the insect’s body.

(vii) The excretory structures that deliver urine from kidney to urinary bladder.

(a)   Urethra

(b)   Pelvis

(c)   Ureter

(d)   Collecting tubule

EXPLANATION: Ureters are slender tubes that carry urine from the kidneys to the urinary bladder. Through uereters, urine flows from the renal pelvis, a part of the kidney, to the bladder for storage.

(viii) The metabolic wastes that ingested into the body and must be removed. 

(a)   Pesticides

(b)   Drugs

(c)   Food additives

(d)   All of these

EXPLANATION: All of the substances mentioned in the options can be considered wastes that the body may need to eliminate, even though they are not metabolic by-products in the strict sense. This is because they are not produced as a result of metabolism in our body, rather they are ingested along with food, and must be expelled out as wastes for their harmful effects.

(ix) Which of the following is not endotherm?

(a)   Bird

(b)   Amphibian

(c)   Flying insect

(d)   Mammal

EXPLANATION: Amphibians are ectothermic organisms, meaning they rely on external sources of heat to regulate their body temperature. Unlike endothermic animals, such as mammals and birds, which generate heat internally through metabolic processes.

(x) Name the type of adaptations from the following that is responsible for shivering thermogenesis.

(a)   Structural

(b)   Physiological

(c)   Behavioral

(d)   None of these

EXPLANATION: Shivering thermogenesis is a physiological adaptation in animals where involuntary muscle contractions, or shivering, generate heat to raise body temperature and maintain metabolic functions in cold environments.



The animals whose body fluids are kept isotonic to the external environment even for marine saltwater environment. These animals thus do not require actively to adjust their internal osmotic state, so are known as ‘osmoconformers’.

Examples: Marine invertebrates like jellyfish, sea anemones, and some marine worms.


The animals whose body fluid concentrations differ noticeably the outside environment actively regulate to discharge excess water in hypotonic and excrete salts in hypertonic conditions therefore, are called as ‘osmoregulators’.

Examples: Mammals including humans, freshwater fish like trout, birds, such as penguins, Crustaceans like crabs and lobsters.

ANHYDROBIOSIS:Terrestrial animals can tolerate dehydration and it differs in various animals. This characteristic is known as anhydrobiosis.”

Example: Tardigrades, tiny water bears, can survive extreme conditions by losing almost all body water and entering a suspended animation state called anhydrobiosis. In this state, they can endure harsh environments and revive when water is available again.

Filtration occurs only at the glomeruli of the nephron because the glomerular capillaries have a unique structure with pores that allow small molecules like water, ions, and waste products to pass through. The fraction of the blood pressure reaching here provides the filtration pressure. This selective permeability is crucial for the initial step of urine formation, ensuring that essential substances are retained while waste products are filtered out in the renal corpuscle.

Stony materials are found in the kidney and these cause urinary obstruction and are generally complicated by infections. These stones have specified chemical nature. These are formed in metabolic disease:

Hypercalcemia i.e. high level of circulating calcium in blood because of other diseases.

Hyperoxaluria i.e. higher blood level of oxalates is other contributing factor in the formation of calcium oxalate stones.

Oxalates are present in green vegetables and tomatoes therefore may be the source of hyperoxaluria.

The incidence of calcium oxalate type stones is 70% of all the kidney stones. The incidence of other types of stones of calcium phosphate and of uric acid is 15% and 10% respectively.

These salts are precipitated out during urine formation and accumulate later to form stone.


“Various factors of pathological and chemical nature may progressively destroy the nephron, particularly its glomerular part. The condition is termed as renal failure.”

This results in increase in the plasma level of urea and other nitrogenous wastes. The rise in urea causes complications of increase in blood pressure and anemia etc.

High Temperature Adaptation:

Most plants have adapted to survive in heat stress as the plants of temperate regions face the stress of 40°C and above temperature. The cells of these plants synthesize large quantities of special proteins called heat-shock proteins. These proteins embrace enzymes and other proteins thus help to prevent denaturation.

Low Temperature Adaptation:

The plants native to cold region such as oaks, maples, roses and other plants have adapted to bring changes in solutes composition of the cells, which causes cytosol to super cool without ice formation, although ice crystals may form in the cell walls. This avoids the formation of ice crystals within protoplasm that perforates membranes and organelles hence killing the cells.


Nature of Excretory Products in Relation to Habitats:


Ammonia is very toxic and dissolves quickly in body fluids. Thus, it must be kept in low concentration in the body. To maintain its low concentration below that of body requires large volume of water also to eliminate it in urine as it is produced. This is possible in an hypotonic environment. Therefore, ammonia kept as the excretory product of the animals inhabiting hypotonic (e.g. fresh water) environment. About 500 ml water is needed to excrete 1g of ammonia nitrogen.


In restricted supply of water, ammonia cannot be kept as excretory product, the other alternative is to change it into less toxic substance such as urea. Urea requires only 50 ml of water for its 1g of nitrogen removal. Here excretory nitrogen is metabolically converted into urea by ‘urea cycle’ in the animals inhabiting environment with restricted supply of water e.g. terrestrial mammals.


Animals inhabiting environment with acute shortage of water supply require an excretory product which can be excreted with minimum amount of water. Only 1ml water is required to eliminate 1g of nitrogen in the form of uric acid. Therefore, the reptiles and birds that inhabit arid environment, excrete uric acid as excretory product.

Animals excreting ammonia, urea and uric acid are called as ammonotelic, ureotelic and uricotelic respectively. Ureotely and uricotely are evolutionary adaptations of nitrogenous waste in their habitats.


Earthworm is an ideal example of another type of tubular excretory system called as metanephridium. Each segment of earthworm has a pair of metanephridia. This system has an internal ciliated opening the nephrostome immersed in coelomic fluid and enveloped by a network of capillaries. Nephrostome collects coelomic fluid. As fluid moves along the tubule, epithelium reabsorbs salt from the lumen and sends to blood vessels surrounding the nephridium. The left over appears as urine containing nitrogenous waste.


(1) Center of Metabolism: Liver is the central station of metabolism and consequently the body’s central metabolic clearing house. Due to this characteristic, liver functions are pivotal to homeostasis and involve interaction with most of body’s organs systems.

(2) Supporter of Kidney: Liver supports the excretory role of the kidney by detoxifying many chemical poisons and produce ammonia, urea and uric acids from the nitrogen of amino acids.

(3) Skin as Excretory Organ: Removal of salts with water by the sweat glands and of sebum by sebaceous glands seems to be excretory in nature. The removal of water and salts from sweat glands is for the purpose of thermoregulation and of sebum on the skin is for protection against microorganism. Therefore, in context of definition of excretion, skin may not be considered as an excretory organ.

(4) Urea & Urea Cycle: Among the various nitrogenous wastes described earlier, urea is the principal excretory product and liver form it from the waste nitrogen. The metabolic pathways involved in the production of urea are termed as urea cycle. Two ammonia and one carbon dioxide molecules are shunted into the cycle to generate one molecule of urea. One ammonia molecule combines with carbon dioxide and already available precursor from previous cycle ornithine to form citrulline, subsequently another ammonia combines to form arginine. The arginine is split by arginase to form urea and the precursor ornithine for next cycle.

Nitrogenous wastes: NH3 , urea, uric acidSupports kidney in waste disposal
Plasma proteins: like a) prothrombin, fibrinogen b) albumin etc.a) Blood clotting b) maintain osmotic balance of blood
BileEmulsifies fats in small intestine
Lipids, cholesterol, lipoproteinsRegulate blood chemistry, store energy and help to maintain cell membranes
Storage: IronOxygenation of tissues as constituent of haemoglobin
GlycogenEnergy reserves
Conversion: Excess glucose in blood to glycogen, lactic, acid to glycogen and stored glycogen to glucoseEnergy storage and use
Recyclings: Contents of old red blood cells (e.g., iron and other constitution of haemoglobin)Oxygenation of tissue
Detoxification: Many harmful chemicals (e.g., food additives, pesticides, drugs etc.)Assist kidney in toxin disposal  

Consult textbook at page 12 —15.

Consult textbook at page 12 —15.

Consult textbook at page 18 —19.

Consult textbook at page 15 —16.

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