Chapter 13 Homeostasis Solved Exercise | MCQs Short Long Questions with Answers

Chapter 13 – Homeostasis, Osmoregulation & Thermoregulation

Solved Exercise

SECTION 1: MULTIPLE CHOICE QUESTIONS

1. Which term covers the rest of the three? (a) Osmoregulation (b) Excretion (c) Thermoregulation (d) Homeostasis

Answer: (d) Homeostasis Explanation: Homeostasis is the broader term that includes osmoregulation, excretion and thermoregulation.

2. Marine fishes compensate for water loss by: (a) Producing dilute urine (b) Drinking seawater (c) Absorbing salt (d) Reducing thirst

Answer: (b) Drinking seawater

3. How do freshwater fish primarily gain water? (a) Drinking (b) Active transport (c) Osmosis (d) Diffusion

Answer: (c) Osmosis

4. What is the primary heat source for endotherms? (a) Sunlight (b) Internal metabolism (c) Warm rocks (d) Convection

Answer: (b) Internal metabolism

5. What is the control center for human thermoregulation? (a) Pituitary gland (b) Hypothalamus (c) Adrenal gland (d) Medulla oblongata

Answer: (b) Hypothalamus

6. Which waste product requires the most water for excretion? (a) Ammonia (b) Urea (c) Uric acid (d) Creatinine

Answer: (a) Ammonia

7. Which nitrogenous waste is the least toxic and water-insoluble? (a) Urea (b) Ammonia (c) Uric acid (d) Nitrate

Answer: (c) Uric acid

8. In which part of the body does the conversion of ammonia to urea take place? (a) Liver (b) Muscles (c) Brain (d) Small intestine

Answer: (a) Liver

SECTION 2: SHORT QUESTIONS

1. Define osmoregulators and osmoconformers.

Osmoregulators: Animals that actively maintain a constant internal concentration of water and salts irrespective of the external environment (e.g., humans, freshwater fishes, most terrestrial vertebrates).

Osmoconformers: Animals whose internal body fluid concentration changes according to the surrounding medium and remains almost isotonic to it (e.g., most marine invertebrates, sharks and hagfish).

2. Define thermoregulation and explain its needs.

Thermoregulation is the homeostatic process by which living organisms maintain their internal body temperature within a narrow and tolerable range despite continuous changes in the external environment.

Needs / Importance:

Enzymes function efficiently only within a specific temperature range.
It maintains optimum metabolic rate.
It protects the selective permeability of cell membranes.
It ensures proper functioning of all organs and systems.

3. What are the two types of animals on the basis of the ability to thermoregulate?

Homeotherms – Animals that maintain a constant body temperature (warm-blooded animals).
Poikilotherms – Animals whose body temperature fluctuates with the external environment (cold-blooded animals).

4. Differentiate between the following:

A. Osmoregulators vs Osmoconformers

Feature	Osmoregulators	Osmoconformers
Internal concentration	Remains nearly constant	Changes with the environment
Energy expenditure	High	Very low
Habitat	Freshwater, terrestrial & some marine	Mostly marine
Examples	Humans, birds, freshwater fishes	Sharks, rays, most marine invertebrates

B. Ectotherms vs Endotherms

Feature	Ectotherms	Endotherms
Source of body heat	External environment	Internal metabolism
Body temperature	Variable	Nearly constant
Metabolic rate	Low	High
Food requirement	Less	More
Examples	Fishes, amphibians, reptiles	Birds and mammals

C. Vasodilation vs Vasoconstriction

Feature	Vasodilation	Vasoconstriction
Meaning	Widening of blood vessels	Narrowing of blood vessels
Heat loss	Increases	Decreases
Occurs when	Body temperature rises	Body temperature falls

D. Ureotelic vs Uricotelic

Feature	Ureotelic	Uricotelic
Nitrogenous waste	Urea	Uric acid
Toxicity	Moderate	Least toxic
Water requirement	Moderate	Very low
Examples	Mammals, adult amphibians, sharks	Birds, reptiles, insects

SECTION 3: LONG QUESTIONS

1. Describe three elements which operate homeostatic mechanisms.

Every homeostatic mechanism operates through three essential components:

1. Receptors (Sensors) These are specialized structures that detect changes (stimuli) in the internal or external environment and send signals to the control centre. Example: Thermoreceptors in the skin and hypothalamus.

2. Control Centre It receives information from receptors, compares it with the set point, and decides the appropriate response. Example: Hypothalamus acts as the body’s thermostat.

3. Effectors These are organs or tissues that carry out the response to restore the normal condition. Example: Sweat glands, blood vessels, skeletal muscles.

2. Relate the homeostatic mechanisms with the negative and positive feedback systems.

Homeostasis is maintained primarily through feedback mechanisms:

Negative Feedback It is the most common mechanism. It detects a change and produces a response that reverses or reduces that change, bringing the body back to the set point. Examples: Regulation of body temperature, blood glucose level, blood pressure and water balance.

Positive Feedback It is rare. It intensifies the original change until a specific process is completed. Examples: Childbirth (oxytocin) and blood clotting.

3. Explain the different methods of osmoregulation found in freshwater, marine water and terrestrial habitats.

Freshwater Habitat Body fluids are hypertonic to the surrounding water. Water continuously enters the body by osmosis. Freshwater animals produce large quantities of dilute urine and actively absorb salts through gills or skin.

Marine Habitat Body fluids are hypotonic. Water is continuously lost. Marine bony fishes drink seawater, excrete excess salts through gills, and produce small amounts of concentrated urine.

Terrestrial Habitat The main problem is water loss through evaporation. Terrestrial animals possess waterproof body coverings, produce concentrated urine (urea or uric acid), and show behavioural adaptations to conserve water.

4. Explain the nature of nitrogenous wastes in relation to habitat.

The type of nitrogenous waste excreted depends upon the availability of water in the habitat:

Ammonia – Highly toxic and highly soluble. Requires large amount of water. Excreted by aquatic animals (ammonotelic animals) such as most bony fishes and tadpoles.
Urea – Moderately toxic and requires less water. Excreted by ureotelic animals (mammals, adult amphibians and sharks).
Uric Acid – Least toxic and almost insoluble in water. Requires minimum water. Excreted by uricotelic animals (birds, reptiles and insects) living in dry environments.

5. Classify animals on the basis of the source of body’s heat.

Animals are classified into two groups on the basis of the source of body heat:

1. Ectotherms These animals obtain most of their body heat from external sources such as sunlight and warm rocks. Their body temperature changes with the environment. Examples: Fishes, amphibians, reptiles and most invertebrates.

2. Endotherms These animals generate most of their body heat through internal metabolic activities. They maintain a relatively constant body temperature. Examples: Birds and mammals.

6. Classify the animals on the bases of the ability to thermoregulate.

1. Homeotherms Animals that maintain a constant internal body temperature irrespective of external temperature changes (warm-blooded animals). Most endotherms are homeotherms.

2. Poikilotherms Animals whose body temperature fluctuates with the surrounding temperature (cold-blooded animals). Most ectotherms are poikilotherms.

7. Describe the regulatory strategies in man for thermoregulation.

Human body temperature is regulated by the hypothalamus (the body’s thermostat) through the following strategies:

When body temperature rises (above 37°C):