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1.4.7Inquiry Process

Functions of Life — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 8 of 160

📚 IB Biology HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5The Functions

Any organism, however small, must carry out all of these functions to count as alive.

Metabolism
  • Metabolism All the chemical reactions inside a cell, from releasing energy to building molecules, catalysed by enzymes, supplied by nutrition.
Growth
  • Growth An irreversible increase in size or cell number, achieved through taking in materials and synthesising new structures.
Response
  • Response Detecting changes in the surroundings and reacting to them, for example moving towards light or away from toxins.
Homeostasis
  • Homeostasis Keeping internal conditions such as water content and temperature within narrow limits despite external change.
Excretion
  • Excretion Removing waste products of metabolism, such as carbon dioxide and nitrogenous wastes, from the organism.
Reproduction
  • Reproduction Producing offspring, sexually or asexually, so that genes pass on to the next generation.

Part 2 of 5A Unicellular Example

A Unicellular Example
Paramecium feeding
  • Paramecium feeding This ciliate sweeps food particles into a gullet and digests them inside food vacuoles, which is its nutrition.
Paramecium homeostasis
  • Paramecium homeostasis A contractile vacuole pumps out excess water that enters by osmosis, keeping the cell from bursting.
Paramecium response
  • Paramecium response Cilia reverse their beat when the cell meets an obstacle or harmful chemical, so it backs away and turns.
Paramecium reproduction
  • Paramecium reproduction The cell usually divides by binary fission, though it can also exchange genetic material in conjugation.

Part 3 of 5Testing for Life

1
Observe the specimen for movement or growth over time to look for response and growth.
2
Measure gas exchange, such as oxygen uptake or carbon dioxide release, to show metabolism by respiration.
3
Look for evidence of waste release, for example a change in the pH or colour of the surrounding medium.
4
Note any division or offspring to confirm reproduction.
5
Conclude that a specimen is alive only if the evidence covers the full set of functions.
FunctionPlant exampleAnimal example
NutritionPhotosynthesisDigestion
ResponseShoots grow towards lightReflex withdrawal
ExcretionOxygen, water vapour lostUrea in urine

Part 4 of 5Worked Example

Question Explain how a single-celled alga such as Euglena carries out all the functions of life despite being only one cell.

  1. Nutrition and metabolismchloroplasts carry out photosynthesis and enzymes catalyse the reactions that build and release energy.
  2. Responsean eyespot detects light and the flagellum moves the cell towards it.
  3. Homeostasis and excretiona contractile vacuole removes excess water and dissolved waste, and gas exchange removes carbon dioxide.
  4. Growth and reproductionthe cell increases in size and then divides by mitosis into two cells.

Answer One cell can perform every function of life because it contains all the organelles and enzymes needed, so no tissues or organs are required.

Part 5 of 5Exam Checklist & Tips

1.4.7 – Key Points for the Exam

  • Metabolism The sum of all chemical reactions in an organism.
  • Homeostasis Maintenance of a stable internal environment.
  • Excretion Removal of metabolic waste products.
  • Response A reaction to a stimulus from the environment.
  • Nutrition Obtaining energy and materials needed for life.

Common Mistakes

  • Mixing up excretion with egestion; egestion removes undigested food, not metabolic waste.
  • Defining growth as any size increase; it must be permanent, unlike a swelling after drinking.
  • Saying a mule is not alive because it cannot reproduce;
    • the full set is required of the species, not each individual.
  • Treating response as only movement; plants respond by growth.

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