2.9.2Additional lessons
Methods of Nutrition — IB Biology SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 46 of 142
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.
Part 1 of 6Autotrophs and Heterotrophs
Autotroph
- Autotroph An organism that makes its own organic compounds from simple inorganic substances such as carbon dioxide.
Photoautotroph
- Photoautotroph Uses light energy for photosynthesis; plants, algae and cyanobacteria are examples.
Chemoautotroph
- Chemoautotroph Some bacteria obtain energy from inorganic chemical reactions, not light, to make organic compounds.
Heterotroph
- Heterotroph An organism that obtains organic molecules by feeding on other organisms or their remains.
Mixotroph
- Mixotroph An organism that can use both autotrophic and heterotrophic nutrition, such as Euglena.
Part 2 of 6Types of Heterotroph
Types of Heterotroph
Consumer
- Consumer Ingests other living organisms, digests them inside the body and absorbs the products.
Detritivore
- Detritivore Ingests dead organic matter such as leaf litter and digests it internally;
- earthworms and woodlice are examples.
Saprotroph
- Saprotroph Secretes digestive enzymes onto dead matter and absorbs the products;
- many fungi and bacteria do this.
Digestion
- Digestion Detritivores digest internally, whereas saprotrophs digest externally before absorption.
| Type | Food source | Digestion |
|---|---|---|
| Consumer | Living organisms | Internal |
| Detritivore | Dead organic matter | Internal |
| Saprotroph | Dead organic matter | External then absorption |
Part 3 of 6Comparing Methods
1
A producer captures energy from light or chemicals and builds organic molecules.
2
A consumer eats producers or other consumers and obtains its energy from their organic compounds.
3
Detritivores break dead material into smaller pieces, increasing its surface area for decomposers.
4
Saprotrophs release nutrients such as nitrogen and phosphorus back into the ecosystem for producers to reuse.
Part 4 of 6Nutrition in Ecosystems
Nutrition in Ecosystems
Energy flow
- Energy flow Heterotrophs depend directly or indirectly on the energy that autotrophs capture from light or chemicals.
Recycling
- Recycling Detritivores and saprotrophs release nutrients from dead matter so that they can be reused by producers.
Classification
- Classification Some organisms change feeding method with conditions, so the categories describe how an organism feeds at the time.
Part 5 of 6Examples
Examples
Plant
- Plant A sunflower makes sugars by photosynthesis and is an autotroph.
Earthworm
- Earthworm An earthworm swallows soil and dead leaves, digests them inside its gut and is a detritivore.
Mushroom
- Mushroom A fungus secretes enzymes onto dead wood, absorbs the products and is a saprotroph.
Part 6 of 6Exam Checklist & Tips
2.9.2 – Key Points for the Exam
- Autotroph An organism that produces its own organic compounds from inorganic substances.
- Heterotroph An organism that obtains organic compounds from other organisms.
- Detritivore A heterotroph that ingests dead organic matter and digests it internally.
- Saprotroph A heterotroph that digests dead matter externally by secreted enzymes.
Common Mistakes
- Treating detritivores and saprotrophs as identical; one digests inside the body and the other outside.
- Saying that plants do not respire; they respire all the time as well as photosynthesise.
- Writing that fungi photosynthesise; fungi are heterotrophs.
- Calling all autotrophs plants, when algae and bacteria can also be autotrophs.
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