Ch 2 · Adaptive Features · IGCSE Biology 0610
Topic 2 of 3 in Variation and Selection — IGCSE Biology 0610 — 38 lessons.
Introduction
A polar bear would not last a week in the Sahara, and a camel would fare no better on Arctic ice. Each species carries features that suit it to where it lives. Questions usually show an unfamiliar organism and ask you to describe its adaptive features; the skill tested is linking a feature to how it helps the organism survive or reproduce.
Key ideas — What an adaptive feature is
Cambridge defines an adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment. Three words in that definition carry marks.
🧑🏫 Teacher's explanation
Think of an adaptive feature as a 'survival toolkit' that is hardcoded into your DNA. Imagine a professional athlete; having high lung capacity is an inherited trait that helps them perform better and potentially pass those genes to their children. This is different from a tan you get from the sun, which is an acquired trait and won't be passed on.
📖 Definitions
🔍 Worked example — Easy
A desert fox has large ears with many blood vessels near the surface of the skin. Identify the type of adaptive feature and explain how it aids survival.
🔍 Worked example — Standard
A species of nocturnal rodent stays underground during the day and only emerges at night. Classify this feature and explain its advantage.
🔍 Worked example — Exam-style
Compare the adaptive features of a xerophyte (e.g., a cactus) and a hydrophyte (e.g., a water lily) regarding their leaves.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) Define the term 'adaptive feature'. [2] (b) Explain how the thick, scaly skin acts as an adaptive feature for this lizard. [2] [4 marks]
Key ideas — Interpreting images and information
Examiners award marks for the pairing feature + benefit. "It has large ears" earns nothing on its own; the benefit must follow: "...which have a large surface area for losing heat by radiation, so the animal does not overheat".
🧑🏫 Teacher's explanation
Think of an organism like a piece of specialized equipment. A mountain climber doesn't just have 'clothes'; they have 'waterproof, insulated layers' to prevent hypothermia. In biology, an adaptive feature isn't just a physical trait; it is a tool that solves a specific problem posed by the environment. If the environment changes, the tool might become useless.
📖 Definitions
🔍 Worked example — Easy
A student writes: 'A polar bear has thick fur.' Explain why this answer would receive zero marks in a Cambridge IGCSE exam and provide a complete answer.
🔍 Worked example — Standard
Describe two adaptive features of a camel that help it survive in a desert environment.
🔍 Worked example — Exam-style
A plant is found growing in a marshy, waterlogged area. It has very large, thin leaves and air-filled tissues (aerenchyma) in its stems. Interpret these features to explain how they help the plant survive.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) Identify the environmental challenge faced by this rodent during the day. [1] (b) Explain how being nocturnal acts as an adaptive feature for this rodent. [2] [3 marks]
Key ideas — Hydrophytes and xerophytes
🧑🏫 Teacher's explanation
Think of plants as being caught in a tug-of-war between needing to breathe (gas exchange) and needing to stay hydrated (preventing water loss). Every plant has a 'budget' for water. Hydrophytes live in a world of infinite supply but face a shortage of oxygen; they don't need to worry about losing water, so they invest their energy into floating and breathing underwater. Xerophytes live in a world of extreme scarcity; they must be masters of conservation, spending their energy on 'sealing' themselves off to prevent evaporation.
📖 Definitions
🔍 Worked example — Easy
A student observes a leaf from a desert plant. The leaf has a very thick, waxy cuticle. Explain how this feature helps the plant survive.
🔍 Worked example — Standard
Compare the position of stomata in a floating water lily (hydrophyte) versus a typical land plant.
🔍 Worked example — Exam-style
A xerophyte has leaves that roll up into cylinders. Explain how this adaptation reduces the rate of transpiration.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the main function of these spines. [1] (b) Explain how this modification helps the plant survive in a desert environment. [2] [3 marks]
Worked example
Question. The fennec fox lives in the Sahara desert. It has very large ears, pale sandy-coloured fur and thick fur on the soles of its feet, and it hunts at night. Describe how each of these features is adaptive. [4]
🔍 Worked example — Easy
A desert plant (xerophyte) has leaves that are reduced to sharp spines. Describe how this is an adaptive feature. [2]
🔍 Worked example — Standard
A species of fish lives in a very deep, dark part of the ocean. It has large, highly sensitive eyes. Explain how this feature is adaptive. [2]
🔍 Worked example — Exam-style
A desert fox has large ears. Explain how this feature is an adaptive feature for survival in a hot environment. [2]
⚠️ Common errors
Common mistakes
Practice
Answers