Homeostasis (Chapter No.15) - Text Book Exercise - Zoology Paper II (English) - Biology Book Two - Class 2nd Year (XII or 12th) Science Group

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Chapter No.15
HOMEOSTASIS
Zoology Paper II
Text Book Exercise

Multiple Choice Questions

1. Encircle the correct choice:
i) A self-regulating process by which biological systems maintain stability while adjusting to the changing conditions called:
a) Homeostasis ✔
b) Osmoregulation
c) Excretion
d) Biological rhythms

ii) Which does not maintain a stable, homeostatic condition rather it intensifies the change that is happening to the body:
a) Negative feedback
b) Positive feedback ✔
c) Feedback system
d) Excretion

iii) Freshwater organisms also have specialized cells located in their gills and in skin which actively extract Na⁺, Cl^- and Ca⁺⁺ from external medium and excrete (H⁺)or basic (HCO₃^-) for acid base balance in the body fluids are called:
a) Granulocyte
b) Lymphocyte
c) Ionocytes ✔
d) podocyte

iv) Renal cortex produces, an important hormone necessary for the synthesis of RBC’s:
a) Erythropoietin ✔
b) Leukoopoietin
c) Thrombopoietin
d) Renin

v) Glomerulus have specialized cells that are wrapped around blood capillaries that play an active role 1n preventing plasma proteins from entering the urinary ultrafiltrate called:
a) Epithelial cells
b) Podocyte cells ✔
c) Endothelial cells
d) None of them

vi) Tubules secretes ions such as hydrogen, potassium, and NH₃ into the filtrate while reabsorbing the HCO₃^- from the filtrate are called:
a) Distal convoluted tubule
b) Proximal convoluted tubule ✔
c) Collecting duct
d) Loop of Henle

vii) Glomerular Filtration rate (GFR) is in which proportional to the hydrostatic pressure exerted in glomerulus wall:
a) Indirectly proportional
b) Directly proportional ✔
c) Same proportional
d) High proportional

viii) Another Compound that increases the osmotic gradient in inner medulla is the:
a) Urea ✔
b) Water
c) Sulphates
d) Phosphates

ix) The inflammation in Kidneys due to irritation of kidney stones is called:
a) Lithonephritis ✔
b) Edema
c) Sarcoma
d) Encephalitis

x) If the surrounding environment becomes hot or a person do strenuous physical activity the heat produced inside the body and raises body temperature above suitable suitable limit this condition is called:
a) Exothermia
b) Hyperthermia ✔
c) Hypothermia
d) Endothermia

Short Question Answers

2. Write short answers of the following questions:
i) Why the physiological integration of internal body environment is important for living organisms?
Ans: The physiological integration of the internal body environment is important for living organisms because it ensures that various body components such as fluids, tissues, organs, and systems etc. work together efficiently to maintain stability and proper functioning. This coordination allows organisms to respond effectively to environmental changes, regulate vital processes like osmoregulation, excretion, and thermoregulation, and sustain life by maintaining a relatively constant internal environment, This state is known as homeostasis.

ii) Why it is important that positive and negative feedback mechanisms counter act upon each other?
Ans: It is important that positive and negative feedback mechanisms counteract each other to maintain the body's internal stability and homeostasis. Negative feedback helps to restore and keep physiological conditions within normal limits by reversing or reducing changes, ensuring stability. Conversely, positive feedback amplifies certain processes temporarily to achieve specific functions, like blood clotting. The balance and opposition between these two mechanisms prevent excessive or uncontrolled responses, ensuring that bodily functions are properly regulated and that the organism remains healthy and stable.

iii) How the aquatic Osmoregulators overcome the osmoregulatory problems?
Ans: aquatic osmoregulators maintain osmotic balance by actively regulating salt and water through specialized organs, producing appropriate urine concentrations, and utilizing specialized cells to extract or excrete salts as needed.
OR
Ans: Aquatic osmoregulators overcome osmoregulatory problems through specialized adaptations in their organs and physiological processes:
Fresh Water Animals:

• They have an internal hypertonic environment and an external hypotonic environment.
• Water enters their bodies through gills and skin via endosmosis, which can disturb osmotic balance.
• To counteract this, they produce dilute urine in their kidneys to eliminate excess water.
• They actively reabsorb salts (Na⁺, Cl^-) through specialized cells called ionocytes located in the gills and skin, minimizing salt loss.
• These organisms also excrete acids or bases (H⁺ or HCO₃^-) to maintain acid-base balance.

Marine Animals:

• They face the challenge of dehydration due to a hypertonic external environment.
• They drink seawater to replenish lost water.
• Their gills, kidneys, and digestive tract work together to digest marine salts and maintain osmotic balance.
• Excess salts are expelled through specialized salt glands in the gills and rectal glands in the intestine.
• They reabsorb some water and excrete small amounts of urine containing concentrated salts, mainly divalent ions like Mg⁺⁺, SO₄^--, Ca⁺⁺ and Na⁺.

iv) Why animals excrete different types of excretory waste?
Ans: Animals excrete different types of nitrogenous wastes because of variations in their physiology, habitat, and the availability of water. The major types of nitrogenous wastes are ammonia, urea, uric acid, and creatinine. Both wastes and their removal depend upon:

1. The nature of the animal’s food: Herbivores do not excrete as much urea as carnivores because carnivores eat more protein, and therefor excrete more nitrogenous waste.
2. The availability of water: Animals in aquatic environments can excrete ammonia directly because ammonia is highly toxic but easily diluted in water, whereas terrestrial animals need to produce less toxic wastes like urea or uric acid to conserve water.
3. The habitat of the animal: Marine and freshwater animals have adaptations suited to their environments, influencing the type of nitrogenous waste they excrete.
   

Nitrogenous waste is produced as a byproduct of the breakdown of proteins and nucleic acids during metabolism. Different animals have evolved to excrete these wastes in forms that best suit their environmental conditions and physiological needs.

v) What is the use of counter current mechanism in kidney?
Ans: The counter current mechanism is a biological process intend to allow maximum exchange of molecules between two fluids of different concentration which are moving in opposite directions. In the kidney it helps to maximize the reabsorption of water and solutes, maintaining the osmotic gradient in the medulla essential for concentrated urine formation.

vi) What is the role of kidney as an endocrine organ?
Ans: The role of the kidney as an endocrine organ is to secrete vital hormones such as renin and erythropoietin. Renin helps maintain blood pressure, while erythropoietin is involved in the production of red blood cells.

vii) How kidney stones are formed? Ans: Kidney stones are formed when components in the urine, such as calcium, oxalates, uric acid, or phosphate, become too high or when the urine becomes too acidic or basic. These components combine to form crystals, which then progressively grow over months or a year, eventually becoming detectable stones.

viii) What is the impact over the human body if kidneys suddenly or gradually loss the filtering abilities?
Ans: Acute kidney failure is concerned with the suddenly loss of filtering abilities of the kidney. The body can experience a rapid buildup of waste products, fluid imbalance, and electrolyte disturbances, which can lead to symptoms like swelling, fatigue, confusion, and potentially life-threatening complications.
If the loss is gradual (chronic kidney disease), it may initially cause no symptoms, but over time it can lead to fatigue, shortness of breath, swelling in the hands or feet, and blood in the urine. As kidney function declines further, it can result in severe health problems such as high blood pressure, anemia, bone disease, and heart issues, ultimately impairing overall health and potentially leading to organ failure.

ix) What are the problems associated with kidney transplant?
Ans: The problems associated with kidney transplant include:

1. Risk of opportunistic infections due to the use of immunosuppressant drugs like Cyclosporine, which suppress the immune system to prevent rejection but increase susceptibility to infections.
2. Surgical complications like blood clots, bleeding, and leakage or blockage of the tube linking the kidney to the bladder (ureter).
3. Bacterial infections and the potential transmission of infections or cancer from the donated kidney.
4. Serious health risks including death, heart attack, and stroke.

Besides all complications, studies reveal that individuals who undergo kidney transplants generally have better and longer lives compared to those who remain on dialysis.

x) What is hypothermia? How body overcome this condition?
Ans: Hypothermia:
When the body experiences cold environment and body temperature tends to decrease this condition is called hypothermia.
Caution:
To overcome this condition, the body conserves heat through several physiological mechanisms such as:

• Vasoconstriction: Perspiration reduces and blood vessels become narrow to reduce heat loss and carrying blood down to skin.
• The subcutaneous fats become thick and become an insulating layer to conserve heat in the body.
• Sometimes body shivers and this involuntary action of muscles generate heat to warm the body.

These responses help maintain the body's core temperature and prevent further cooling.

Detailed Question Answers

3. Write detailed answers of the following questions::
i) Explain the detailed structure of nephron with labelled diagram?
Ans: STRUCTURE OF NEPHRON:
The structural and functional units of kidney are called nephrons. These nephrons are about one million in each kidney and are microscopic urinary tubules. They mainly perform filtration of blood.

Types Of Nephron
There are two types of nephrons present in the kidneys.

1. The Juxta Medullary Nephrons: have Bowman's capsule longer loop of Henle penetrates Efferent deep inside the medulla.
2. The Cortical Nephrons: with shorter loop of Henle restricts only in cortex region.

Parts Of Nephron:
Juxta medullary nephron consists of two main parts and network of blood vessels. Two main parts of nephrons are:

1. Renal Corpuscle (Malpighian Capsule)
2. Renal Tubule

1. Renal Corpuscle (Malpighian Capsule):

• It consists of a dense cluster of blood capillaries network called glomerulus surrounded by doubled-walled, cup-shaped covering called Bowman's capsule or glomerular capsule and both are collectively called malpighian body.
• Glomerulus is the ball like structure which arises from afferent arterioles.
• Afferent arterioles are blood vessels which enter in the Bowman's capsule and divides and redivides to form thin-walled Glomerulus.
• High volume and pressure of blood facilitates the ultra-filtration in this region.
• Glomerular capillaries have pores of about 70 nm in diameter which prevents the large molecules and blood cells to pass through it.
• Glomerulus have specialized Podocyte cells that are wrapped around blood capillaries. These cells have small slits like opening that play an active role in preventing plasma proteins from entering the urinary ultrafiltrate.
• All the glomerulus capillaries fuse to form efferent arteriole, which exit the malpighian body.

2. Renal Tubules:
It is a tube-like structure which is internally lined by ciliated epithelium and glandular epithelium. It is divide into three region.

a) Proximal Convoluted Tubule (PCT):

• Bowman's capsule further extended and form renal tubule which becomes highly coiled. This coiled region is called proximal convoluted tubule (PCT).
• Most of the essential compounds like glucose, amino acids, electrolytes and water is reabsorbed in this region.

b) Loop Of Henle:

• It is a U-shaped tubules, present in medulla.
• The PCT runs down towards the renal pyramids of medulla to become descending limb, then turns back towards the bowman's corpuscle making an ascending limb of loop of Henle.
• Loop of Henle is the site of reabsorption of water.

c) Distal Convoluted Tubule (DCT):

• Ascending limb of loop of Henlea coiled again and is called distal convoluted tubule (DCT). It is lying in the cortex region.
• Collecting Tubules: Several DCT joins the common duct called collecting duct. Which carry urine to the renal pelvis to exit from the kidney.

Network Of Blood Vessels:
Afferent Arterioles:

• Blood supply to the nephron Renal artery enters in kidney at hilus, which further divides into numerous smaller arterioles called afferent arteriole.
• Afferent arteriole forms the dense network as glornerulus and leaves it as efferent arteriole.
• The diameter of afferent arteriole is larger than efferent arterioles, due to difference in diameter between these arterioles, high pressure in glomerulus than other capillaries elsewhere.

Efferent Arterioles:

• The efferent arterioles extended down and forming a network of capillaries called peritubular capillaries that surround the both PCT and DCT. It provides nutrients and oxygen to the renal, cortex. 
• It moves downward along with loop of Henle give branches which are laterally connected with the capillaries of renal vein or venule in the region of medulla. This complex network capillaries over the loop of Henle called vasa recta.
• After passing through the vasa recta blood flow through peritubular capillaries system and enters in to the renal vein to join venous circulation and leaves the kidney.

ii) Explain the functions of kidney?

Ans: FUNCTIONS OF KIDNEY:
1. Homeostatic Organs Kidneys are very important homeostatic organs. It filters our blood and excretes waste and extra fluid from our body by urine. The process of producing urine occurs in three stages:
a) Glomerular filtration
b) Selective reabsorption, and
c) Tubular secretion

a) Glomerular Filtration:

• Urine is the ultimate kidney product and based upon waste removed from the blood with addition of some other fluids and ions. This process is initiated in the glomerulus when blood is filtered out under hydrostatic pressure leaving the small molecules of waste and other compounds as glornerular filtrate this process is called ultra-filtration.
• Filtrate primarily includes water, electrolytes, some amino acids, bicarbonates and nitrogenous wastes like urea, uric acid and creatinine. Glomerular filtration rate (GFR) is directly proportional to the hydrostatic pressure exerted in its wall. This pressure is increased due to the difference in diameter of both afferent and efferent arterioles.
• Kidney receives 180 liters of blood by circulation in 24 hours and after filtration it produces 2.5 liters urine in normal climatic conditions.
• GFR usually remains constant by autoregulation however it may change depending upon the fluid intake or its variable amount in the body.

b) Selective Reabsorption:

• Selective reabsorption is the process whereby certain molecules after being filtered out of the capillaries along with nitrogenous waste products (i.e., urea) and water in the glomerulus, are reabsorbed from the filtrate as they pass through the nephron and return back to the blood circulation.
• The composition of glomerular filtrate and the urine is different it means that the fluid contents become change while passing through the renal tubules including PCT, loop of henle and DCT in nephron.
• For example, glucose if present in the filtrate but absent in the urine of a healthy person. The amount of urea and uric acid present more in urine than the filtrate. These changes are the outcome of selective reabsorption and the tubular secretion.
• Most of the selective reabsorption of molecules takes place in proximal convoluted tubule (PCT).
• Water (about 67%), Na⁺ and K⁺, variable quantities of C1^- (about 50%), Ca²⁺, Mg²⁺, and HPO₄^2- ions, important nutrients like glucose (100%), amino acids, vitamins and other organic substances are reabsorbed in PCT and given back to the blood circulation.
• Water is absorbed passively while glucose and sodium are absorbed actively. Na⁺ drags the other negatively charged ions due to opposite charge interaction.
• Hormone aldosterone facilitates the sodium and ADH facilitates the water reabsorption.

c) Tubular Secretion:

• In this process certain substances moves in to the filtrate of PCT and DCT from blood plasma. This includes waste that escape during ultra-filtration and remained in the blood. These substances are absorbed actively and include urea, creatinine, hydrogen ions, potassium ions, some hormones and drugs if present.
• Tubular secretion mostly performed by proximal convoluted tubule (PCT) but some of the K⁺ are also secreted from DCT and collecting duct due to reciprocal exchange of Na⁺ with K⁺. It adjust the pH of urine.

d) Counter Current Mechanism:

• The counter current mechanism is biological processes intend to allow maximum exchange of molecules between two fluids of different concentration which are moving in opposite directions. This mechanism involves loop of henle and the environment of medulla.
• In medulla region of the kidney, the ascending limb of loop of henle is permeable to Na⁺, K⁺ and Cl^- ions while impermeable to water. The descending limb of loop of henle is permeable to water. Ascending limb cells have specialized ionic co-transporter protein, each allow one Na⁺ with one K⁺ and two Cl^- hence allow lot of ions to move out from the entire limb. When these ions are actively reabsorbed from the ascending limb and accumulated in medulla, it makes medulla environment hypertonic.
• This movement of ions is also facilitated by a steroid-based hormone called aldosterone secreted from the cortex region of adrenal gland. Movement of water molecules is facilitated by anti-diuretic hormone (ADH) secreted from posterior lobe of pituitary gland.
• Another compound that increases the osmotic gradient in inner medulla is the Urea, it enters in the medulla from the collecting duct and along with other ions, helps the reabsorption of water. This process is called counter current multiplier.
• Now there is another counter current mechanism performed in between nephron loop of Henle and the peritubular capillaries or vasa recta. The loop of Henle is surrounded by peritubular capillaries containing blood. These capillaries are permeable to both water and ions so due to high ionic concentration in the interstitium, water is diffusing out and solutes diffuse inside the capillaries that travel alongside the descending limb, if this blood is carried away it destroy the medullary concentration gradients. Therefore, to counter act this effect the peritubular capillaries alongside of ascending limb releases the extra solutes which diffuse back in to the medulla hence maintaining the concentration gradient inside medulla and making blood more dilute. This process of exchange of gradient in vasa recta or peritubular capillaries is called counter current exchange.Z
• So, the water is secreted then reabsorbed in to the system. Solutes are reabsorbed then secreted in to the medulla. Normally the blood flow is slower in peritubular capillaries or vasa recta to allow time for passive diffusion.

2. Endocrine organ: Kidneys also work as an endocrine organ and secrete some vital hormones like rein and erythropoietin.
| a) Renin: maintains the blood pressure.
b) Erythropoietin is involved in red blood cells production.
3. Form Vitamin D3: Kidney produces an active form of vitamin D3 which helps to absorb calcium and phosphorus in our bones. These important minerals keep bones strong.
4) Balance pH: Kidneys balance the pH of our body by making changes and adjusting amount of bicarbonate HCO^3- from the urine back to the blood and by secretion of H⁺ ions into the urine. Kidney regulates the water balance by producing dilute and concentrated urine according to the external environmental changes.