An example of homeostasis in living organisms is

Step 1: Analyze the question Homeostasis is the maintenance of a constant internal environment (e.g., body temperature, water level, blood sugar) despite changes in the external environment. We need the option that describes this.

Step 2: Concept Homeostasis involves regulating internal conditions such as:

• Temperature regulation (sweating, panting)
• Osmoregulation (water balance)
• Blood sugar control
• Excretion of wastes

Step 3: Evaluate each option

• A. Cooling effect from evaporation of water from the body surface: This is sweating, which removes heat and keeps body temperature stable. This is a classic example of thermoregulation, a form of homeostasis. ✔
• B. Root hairs growing towards light: Roots generally don't grow toward light, and a growth response to a directional stimulus is a tropism, not homeostasis. ✘
• C. Chameleon changing colour to match foliage: This is camouflage/adaptation, a response to the external surroundings and not regulation of the internal environment. ✘
• D. Release of phosphorus into the phloem in phosphorus-deficient soil: This is a nutrient transport or mineral process. It is not a regulatory mechanism that maintains a stable internal condition. ✘

Step 4: Answer The correct option is A.

Exam tip: When you see "homeostasis", look for words linked to keeping things constant: temperature control, water balance, sugar level, or excretion. Responses to light, touch, or gravity point to tropisms or other responses, not homeostasis.