B4.2.5—Mixotrophic nutrition
Mixotrophic nutrition combines autotrophic production with heterotrophic feeding, allowing organisms to use light and organic food sources flexibly in communities.
- Syllabus
- First assessment 2025
- Objective
- B4.2.5
- Level
- HL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1A
Typical marks1
Common command terms
- Outline
- Identify
Scoring notes
- Common mistake
- Calling mixotrophs only autotrophs because they photosynthesise.
Recent exam appearances
November 2025Paper1A ["HL"] · TZ335[ 1 ]B4.2.5—Mixotrophic nutrition
Practice this objective
Coverage 2025–2025 · Updated 15 Jul 2026
Mixotrophs Switch Between Nutritional Modes
A mixotroph combines autotrophic and heterotrophic nutrition. Some mixotrophs require both modes, while facultative mixotrophs can shift their balance with conditions.
Euglena is a freshwater protist with photosynthetic chloroplasts that can also obtain organic carbon heterotrophically. Many oceanic plankton combine photosynthesis with uptake or ingestion of organic material.
Obligate mixotrophy requires contributions from both modes to meet nutritional needs; facultative mixotrophy permits a switch when light, inorganic nutrients or prey availability changes.
A facultative planktonic mixotroph may rely more on photosynthesis in bright, nutrient-rich surface water and increase heterotrophic feeding when light becomes limiting.
Mixotrophic does not mean every mode is used equally or simultaneously. State the carbon and energy source under the particular condition.
Mixotrophic nutrition
Assessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, multiple choice, commonly using Outline / Identify.
Command terms
Outline / Identify
What earns marks
Build the answer around this relationship: Mixotrophs combine autotrophic and heterotrophic nutrition.
Watch for
Calling mixotrophs only autotrophs because they photosynthesise.
Representative question
Question 1
Outline the reason that some species of protists are classified as mixotrophs.
Niches, Nutrition, And Competition
A niche is the role of a species in a community, including habitat, abiotic tolerances, nutrition, activity, reproduction, and interactions. The evidence should match the question: nutrition mode, oxygen tolerance, feeding adaptation, predator-prey interaction, plant light strategy, fundamental versus realized niche, or competitive exclusion.
- Definition answers should include role plus habitat/resources/interactions, not only place.
- Nutrition modes explain how organisms obtain carbon, energy, or organic matter.
- Adaptation examples should be linked to feeding, defence, light harvesting, or competition.
- Fundamental versus realized niche and competitive exclusion are tested together because interactions narrow where species actually live.
Concept essentials
- Mixotrophs combine autotrophic and heterotrophic nutrition.
- Euglena can photosynthesise and feed on bacteria.
- Some mixotrophs act as both producers and consumers.
- Mixotrophy can provide nutritional flexibility in changing conditions.