NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State

NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State Solutions to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State Notes and select need one. NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State Question Answers Download PDF. NIOS Study Material of Class 12 Biology Notes Paper 314.

NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State

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Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Biology Chapter 18 Homeostasis: The Steady State Solutions, NIOS Senior Secondary Course Biology Solutions for All Chapter, You can practice these here.

Homeostasis: The Steady State

Chapter: 18




1. Define homeostasis.

Ans: The homeostasis is defined “as the regulation of a steady internal condition of body”.

2. List any three chemicals whose concentration in our body has to be maintained at particular levels.

Ans: (i) Sugar.

(ii) Salt. and 

(iii) Water.

3. To obtain enough oxygen for respiration at high altitudes, what does the body do?

Ans. Body adds more red blood corpuscles to the blood.


1. How do the following temperatures affect the enzymes?

(i) 45°C and above __________.

Ans: Denatured.

(ii) 0°C and below __________.

Ans: Inactive.

2. (i) At what temperature range do enzymes act best?

Ans: 35-40°C. 

(ii) What technical term do you use for this temperature?

Ans: Optimum temperature.


1. Classify the following animals as endotherm or ectotherms:

Camel, Bat, Earthworm, Cockroach, Fish, Wall lizard, Polar bear, Sparrow.

(a) Endotherms __________.

Ans: Endotherms = Camel, Bat, Polar bear. Sparrow.

(b) Ectotherm __________.

Ans: Ectotherms = Earthworm, Cockroach, Fish. Wall lizard.

2. Explain the following terms and give one or more synonymous terms for each:

(a) Poikilotherms ___________.

Ans: Poikilotherms (cold blooded): The animals whose body temperature changes along with that of surroundings.

(b) Homoiotherms __________.

Ans: Homoiotherms (warm blooded): The animals whose body temperature remains steady and does not change with that of surroundings.

3. Mention one way each by which each of the following fight severe cold:

(i) Crocodiles.

Ans: Crocodile: Basks in the sun on land.

 (ii) Honey-bee.

Ans: Honey-bees: They crowd together for collective warmth i.e. they huddle.

(iii) Common frog. 

Ans: Common frog: It hibernates in winter.

(iv) Wall lizard.

Ans: Wall lizard: It hides at safe places.


1. Rearrange the following in their correct sequence in a homeostasis:

Effector, Set point, Integrating centre, Sensor.

Ans: Set point, Sensor, Integrating centre, Effectors.

2. State in one word or sentence:

(i) The normal body core temperature of humans __________.

Ans: 37°C.

(ii) The function of feathers in bird and the hairs of rabbit __________.

Ans:  Trap air to prevent heat Loss.

(ii) Effect of shivering __________.

Ans: Warm up in cold weather.


1. Name the two kinds of feedback mechanisms.

Ans. (i) Negative feedback. and 

(ii) positive feedback.

2. Which kind of feedback mechanism normally operates in homeostasis?

Ans: Negative feedback mechanism.


1. List the three conditions necessary for the body cells to function properly.

Ans: The three conditions are:

(i) Proper temperature.

(ii) A suitable pH.

(iii) The presence of proper concentration of chemicals in cells of body.

2. When do we pass out more concentrated urine during hot summers or cold winters?

Ans: The urine passed out is more concentrated in hot summers. In hot weather. we lose more water in perspiration.

3. How does our body deal with any extra sugar absorbed into the blood after meals?

Ans: The excess of sugar in body is converted into glycogen by the liver.

4. What is our normal RBC count per cubic millimetre? Will it go up or go down if a plain dweller shifts to a mountain or hill?

Ans: About 5 million RBCs per cubic mm. of blood. The RBCs count would go up when a plain dweller shifts to a mountain or hill.

5. In which temperature range do the enzymes in our body act best?

Ans: Between 35-40°C.

6. Name the two terms often used synonymously for ectotherms.

Ans: (i) Poikilotherms. and 

(ii) Cold blooded.

7. Name any two animals, which tolerate the intense heat of the deserts by promoting heat loss.

Ans: (i) Camels. and 

(ii) Desert rats.

8. Which kind of feedback mechanism, the positive or the negative, normally operates in bringing about water-salt balance in our body?

Ans: Negative feedback mechanism.

9. How is the enzymatic activity affected upon cooling?

Ans: The enzymes become less efficient when the temperature is lower than optimum. At zero temperature, the enzymes are inactive.

10. How do honeybees fight cold during intense winter?

Ans: The honeybees huddle together in the hive to fight cold during intense winter. So they conserve heat collectively.

11. Differentiate between the two terms homeotherms and poikilotherms.

Ans: Differences between homeotherms and poikilotherms:

1. They keep their body temperature constant.They acquire body tem-perature from their sur- roundings.
2. e.g. Birds and Mam- mals.e.g. Frogs and fishes.

12. Give any two examples of preventing loss of body heat by postural behaviour in humans.

Ans: (i) During sleeping we hold our arms and legs closely folded near our body in curved posture.

(ii) While standing on, we hold our arms cross folded tightly over our chest.

13. List the components of homeostasis in their proper sequence.

Ans: Various components of homeostasis in proper sequence are:

Norm (a set point) → A sensor → An integrating centre → Effectors.

14. Differentiate between positive and negative feedback mechanism.

Ans: Difference between positive and negative feedback mechanisms:

Positive Feedback mechanismNegative Feedback mechanism
1. It is of rare occurrence in living systems.It operates mostly.
2. e.g. coagulation of blood.e.g. thermoregulation.
3. It includes several steps.Any deviation from the set point is reversed to normal condition.

15. Explain the role of the following in thermoregulation in humans:

(i) Sweat glands.

Ans: Sweat Glands: When there is less/reduced supply of blood to sweat glands of our skin, then the sweat production is decreased or becomes nil. There is no evaporation of water from body. So there is no heat loss at all.

(ii) Skeletal muscles.

Ans: Skeletal Muscles: During heavy physical work, there is over production of heat in our body.

(iii) Blood vessels in the skin.

Ans: Blood vessels in skin: There is vaso-constriction and blood supply to skin is decreased. So there is less loss of heat at all by radiation.

16. What is meant by feedback mechanism? What are its two types? Which one of these is applicable to thermoregulation and why?

Ans: Feedback Mechanism: It refers to “the use of part of the output of a system to control its performance”. It is of two types:

(a) Negative feedback. and 

(b) positive feed-back.

To reduce output negative feedback is used. To increase output positive feedback is used.

Thermoregulation is operated by negative feedback mechanism.

Various homeostatic regulations work through negative feedback. This means “reversing change to a norm”. Positive feedback are rare that produces changes in the same direction as first one occurs.

17. Why is thermoregulation required in our body?

Ans: Thermoregulation: Maintenance of a dynamic constancy of the internal environment or steady state is called homeostasis.

The thermal energy is produced during exergonic reactions of metabolism. Fish, amphibians, reptiles and plants loose most of their thermal energy to their environment. These ectotherms depend on their environment for temperature regulation.

The mammals, birds and some fishes (e.g. sword fish) retain thermal energy for use. They have insulating devices like hairs, feathers and fat etc. for retardation of heat loss to the environment. They are called endothermic or homeo-thermous. When the temperature is cold the superficial blood vessel contract to divert the warm blood to deeper vessels. When external tem-perature is warm, superficial blood vessel dilate.

18. Differentiate between endotherms and ectotherms. Which one of these do you think can survive better if there is a sudden change in environmental temperature?

Ans: Distinguish between Endotherms and Ectotherms:

1. They have internal heat regulating mechanisms.Their body temperature rises or falls with that of their surroundings.
2. Examples of endo- therms are birds and mammals.Example are insects, fishes and frogs as well as lizards, etc.

19. Differentiate between physiological and behavioural responses for thermoregulation in humans.

Ans: Difference between Physiological and Behavioural Responses for thermo- regulation in humans:

Physiological ResponseBehavioural Response
1. All adjustments are not under control of our will.It includes conscious as well as all subconscious actions of body and are under our will.
2. Example: Increase/ decrease in cell meta- bolism of our body, sweating, etc.Example: During cold we move to some warmer place.

20. Explain the role of hypothalamus during heat regulation in humans.

Ans: Role of Hypothalamus during heat Regulation in humans: In thermoregulation (heat regulation) in human beings, sense receptor located in the skin and the hypothalamus act as a sensor. The hypothalamus and certain adjoining parts of the brain serve as integrating centre. The skin, blood vessels located in our skin and our skeletal muscles act as effectors.

21. Explain the relationship between sensor and integrating centre during any one kind of homeostasis.

Ans: The hypothalamus and parts of brain (adjoining it) work as integrating centre. The skin and hypothalamus act as sensors.

Fig. 18.4. Negative feedback loop.

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