Maarg Manthan · Topic 3.5

Homeostasis

Environment & Ecology › Population Ecology and Species Interactions · Topic 3.5

Homeostasis is the ability of an organism, and by extension a population or ecosystem, to maintain a relatively stable internal state in spite of changes in its external environment. The French physiologist Claude Bernard described the constancy of the internal environment in the nineteenth century, and the American physiologist Walter Cannon coined the word homeostasis in 1926. It works through negative feedback, in which a change is detected by a sensor and is opposed by a response that restores the set point, such as sweating when body temperature rises. Organisms deal with environmental change in four ways: regulate, conform, migrate or suspend. Regulators, such as birds and mammals, keep internal conditions constant by thermoregulation and osmoregulation, while conformers, such as most fish and plants, let the body follow the surroundings.

5 min read · UPSC Prelims · Environment & Ecology · Population Ecology and Species Interactions

At a Glance

Term coined Walter Cannon, 1926
Mechanism Negative feedback
Keep steady Regulators
Follow surroundings Conformers
Other responses Migrate, suspend
Exam link UPSC Prelims, Environment & Ecology: Population Ecology and Species Interactions

Where Does It Fit?

This topic follows the account of adaptation. Homeostasis is a physiological adaptation that keeps internal conditions steady, and it also applies to populations and ecosystems. Previous topic: Adaptation in Plants and Animals: Examples. Next topic: Interaction Between Species.

What Is Homeostasis and How Do Organisms Cope With Change?

Concept	Explanation and examples
Homeostasis	Maintenance of a steady internal state, such as body temperature, water and salt balance, blood sugar and pH
Negative feedback	A change triggers a response that opposes it. Example: a rise in body temperature causes sweating, which cools the body
Positive feedback	A change triggers a response that increases the change, as in childbirth contractions
Regulators	Maintain constant internal conditions despite outside change. Examples: mammals and birds (thermoregulation); some fish regulate salt balance
Conformers	Allow internal conditions to change with the surroundings. Examples: most invertebrates, fishes, amphibians and reptiles in temperature; plants
Migration	Move temporarily to a better habitat, like birds flying south, or wildebeest
Suspension	Escape in time: hibernation, aestivation, diapause, spores and seeds

What Are the Physiological Examples and Levels of Homeostasis?

Thermoregulation: endotherms (warm-blooded) produce heat internally and keep body temperature constant; ectotherms (cold-blooded) depend on external heat
Osmoregulation: control of water and salt balance; freshwater fish excrete dilute urine, marine fish drink sea water and excrete salt, and sea birds have salt glands
Excretion: kidneys remove wastes and regulate water
Blood sugar: controlled by insulin and glucagon
Plants: stomata open and close to control water loss; they are mostly conformers
Population homeostasis: density-dependent factors keep numbers near carrying capacity
Ecosystem homeostasis: predator-prey and nutrient feedbacks keep the system stable within limits
Limits: if stress is too strong, homeostasis fails, and the organism or ecosystem may collapse

What Else Should You Remember?

Claude Bernard: described the milieu intérieur, the stable internal environment
Set point: the target value of a variable, like 37 degrees Celsius in humans
Fever: a raised set point during infection
Shivering: generates heat in cold
Vasodilation and vasoconstriction: widening or narrowing of blood vessels to lose or save heat
Camel body temperature: varies widely to save water
Torpor: short daily reduced activity in small birds and bats
Hibernation: long winter sleep with low metabolism
High-altitude response: breathing and haemoglobin adjustments
Gaia hypothesis: James Lovelock’s idea that the Earth regulates itself like an organism
Daisyworld: a model of planetary self-regulation of temperature
Biosphere feedback: carbon dioxide absorbed by oceans and forests resists climate change up to a limit
Tipping points: thresholds beyond which feedbacks reverse
Ice-albedo feedback: melting ice absorbs more heat and increases warming
Eutrophication: a failure of lake homeostasis
Costs of regulation: regulating needs much energy, so small endotherms eat a lot
Tolerance link: homeostasis widens the range of tolerance, as in Range of Tolerance and Maximum Range
Link to adaptation: see Adaptation in Plants and Animals: Examples
Link to ecosystems: see Definition, Functions and Properties of an Ecosystem
Caution: no organism can regulate everything, so every species has limits
Homeostasis in plants: plants show limited regulation of water loss through guard cells but follow outside temperature
Cold-blooded behaviour: lizards bask in the sun and shelter in shade to regulate temperature behaviourally
Metabolic cost: a shrew eats almost continuously because small bodies lose heat fast
Salinity change in estuaries: estuarine animals tolerate wide changes by osmoregulation
Homeostasis in populations: birth and death rates adjust with density to keep numbers steady
Human health: diabetes, fever and dehydration are cases of failed regulation
Exam hint: the term originates in physiology, but questions in ecology apply it to ecosystems too
Feedback loops in climate: sea ice loss and permafrost thaw are positive feedbacks that speed warming
Plant water balance: transpiration cools leaves, an example of regulation by evaporation

Why Does It Matter for the Exam?

Definition: steady internal state
Coined by: Cannon
Groups: regulators and conformers
Current affairs link: climate tipping points
Common errors: saying negative feedback worsens a change or that plants are regulators

As an analytical point, regulation gives independence from the environment but costs energy. Understanding homeostasis helps to see how organisms respond to climate stress and why ecosystems have tipping points.

Why Is This Topic Important?

Idea Steady state
Mechanism Negative feedback
Groups Regulate or conform

What Came Next?

The next topic covers interactions between species. Next topic: Interaction Between Species.

Key People and Terms

Homeostasis Internal steadiness
Negative feedback Opposes change
Endotherm Warm-blooded
Ectotherm Cold-blooded
Osmoregulation Water-salt balance
Torpor Temporary low activity

Exam Corner

Points to Remember

Coined by Walter Cannon, 1926.
Works by negative feedback.
Mammals and birds are regulators of temperature.
Four responses: regulate, conform, migrate, suspend.
Marine fish drink sea water.

Do Not Confuse With

Regulator and conformer Constant versus variable internal state
Negative and positive feedback Opposes versus amplifies
Hibernation and torpor Seasonal versus daily

Memory Hook

Cannon coined, feedback keeps the set point, regulators pay in energy, conformers drift.

Mains Angle

Questions ask for definitions and the four responses. These points help.

Concept Steady state
Responses Four
Ecosystem Feedback

A Question You May Face

An original practice question, not a past paper question.

“What is homeostasis? Explain how organisms cope with environmental stress and relate it to stability of ecosystems.”

How to Answer

Define Homeostasis.
Mechanism Feedback.
Responses Four.
Ecosystem Stability.

GS Relevance

Prelims: definition, feedback, regulators versus conformers, strategies. GS Paper 3: ecology and biology.

Frequently Asked Questions

What is homeostasis?

Homeostasis is the process by which a living organism maintains a stable internal environment, such as body temperature, water balance and chemical composition, despite changes in external conditions. The term was coined by Walter Cannon in 1926, and it works mostly through negative feedback loops.

What is negative feedback?

Negative feedback is a control mechanism in which a change in a variable is detected and a response is triggered that reverses the change and brings the variable back to its set point. For example, when body temperature rises, sweating and widening of skin blood vessels cool the body back to normal.

What is the difference between regulators and conformers?

Regulators are organisms that maintain constant internal conditions, such as body temperature or osmotic concentration, whatever the external conditions, like mammals and birds. Conformers cannot do this, and their internal state changes with the environment, as in most fishes, reptiles, invertebrates and plants.

How do organisms cope with unfavourable conditions other than by regulating?

Besides regulating and conforming, organisms can migrate to another place, as many birds do, or suspend activity in time through hibernation in winter, aestivation in summer, diapause in insects, or by forming spores and seeds. These strategies allow survival through temporary stress.

What is osmoregulation?

Osmoregulation is the control of the water and salt content of the body. Freshwater fish take in water by osmosis and pass out dilute urine, marine bony fish lose water and so drink sea water and excrete excess salt through gills, and sea birds use salt glands. Mammals use the kidneys.

PYQ Practice — Statement Analysis

1 The term homeostasis was coined by Walter Cannon.

True

In 1926.

2 Positive feedback is the main mechanism of homeostasis.

False

Negative feedback is.

3 Mammals are thermal regulators.