2.10.2Inquiry Process
Methods of Nutrition — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 97 of 160
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.
Section 1 of 5Autotrophs and Heterotrophs
The first split in classifying nutrition is whether the organism makes its own food or eats other organisms.
Autotroph
- Autotroph An organism that makes its own organic molecules from simple inorganic substances such as carbon dioxide and water.
Photoautotroph
- Photoautotroph An autotroph that uses light energy for synthesis, including plants, algae and cyanobacteria.
Chemoautotroph
- Chemoautotroph An autotroph that uses energy from oxidising inorganic chemicals, for example sulfur-oxidising bacteria at deep-sea vents.
Heterotroph
- Heterotroph An organism that must take in ready-made organic molecules, obtained by feeding on other organisms or their remains.
| Type | Carbon source | Energy source | Example |
|---|---|---|---|
| Photoautotroph | CO₂ | Light | Oak tree |
| Chemoautotroph | CO₂ | Inorganic chemical reactions | Nitrifying bacteria |
| Heterotroph | Organic compounds | Organic compounds | Lion |
Section 2 of 5Kinds of Heterotroph
Kinds of Heterotroph
Consumers
- Consumers Animals that ingest other living or recently killed organisms and digest them inside the body, such as herbivores and carnivores.
Detritivores
- Detritivores Animals that ingest dead organic matter such as leaf litter or dung and digest it internally, for example earthworms and woodlice.
Saprotrophs
- Saprotrophs Fungi and bacteria that secrete digestive enzymes onto dead material and absorb the soluble products, known as external digestion.
Why it matters
- Why it matters Detritivores and saprotrophs recycle nutrients from dead material back to producers, keeping ecosystems running.
Section 3 of 5Mixotrophs
Some organisms refuse to fit into only one category.
Definition
- Definition A mixotroph uses both autotrophic and heterotrophic nutrition, depending on conditions or at the same time.
Euglena
- Euglena This single-celled organism photosynthesises in light with chloroplasts but can absorb organic nutrients when light is poor.
Carnivorous plants
- Carnivorous plants Plants like the Venus flytrap photosynthesise but also digest trapped insects to obtain nitrogen in poor soils.
Advantage
- Advantage Flexible nutrition lets a species survive in habitats where either light or food is unreliable.
Section 4 of 5Choosing the Right Term
1
Ask first whether the organism makes organic molecules from CO₂; if it does, it is an autotroph.
2
If it needs organic food, it is a heterotroph, so ask next whether it eats living organisms or dead matter.
3
If it ingests living prey and digests it internally, it is a consumer.
4
If it ingests dead matter and digests internally, it is a detritivore.
5
If it releases enzymes outside and absorbs the products, it is a saprotroph.
Section 5 of 5Exam Checklist & Tips
2.10.2 – Key Points for the Exam
- Autotroph An organism that synthesises organic molecules from inorganic substances.
- Heterotroph An organism that obtains organic molecules by consuming other organisms or their remains.
- Detritivore A heterotroph that ingests dead organic matter and digests it internally.
- Saprotroph A heterotroph that digests dead matter externally by secreted enzymes and absorbs the products.
- Mixotroph An organism able to use both autotrophic and heterotrophic nutrition.
Common Mistakes
- Calling fungi detritivores; they are saprotrophs because digestion is external.
- Assuming all autotrophs use light; chemoautotrophs use chemical energy.
- Saying plants are heterotrophs because they take up minerals; minerals are not organic food.
- Thinking decomposers is a precise term; give the exact method of nutrition instead.
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