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#heterotrophs

3 public questions tagged with this topic.

General Biology of Protists

Protists show all modes of nutrition EXCEPT

Protists exhibit remarkable nutritional diversity including photoautotrophy via chloroplasts, heterotrophy through phagocytosis, osmotrophy absorbing dissolved organics, and mixotrophy combining photosynthesis and ingestion in genera like Euglena and Dinobryon. Chemoautotrophy, however, involving oxidation of inorganic substrates such as ammonia, hydrogen sulfide, ferrous iron to generate energy for carbon fixation, is restricted to prokaryotic Bacteria and Archaea including nitrifiers and sulfur oxidizers. No free-living protist employs inorganic chemical lithotrophy for autotrophic growth, marking absence of chemoautotrophic protists and metabolic boundary between eukaryotic protists and chemolithotrophic bacteria.

Ref: OpenStax Biology 2e Chapter 23 Protist nutrition modes chemoautotrophy absent; Raven Biology chemoautotrophs prokaryotes nitrifiers

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Ecosystem Ecology & PRODUCTIVITY

Which of these is not an autotroph?

Fungi obtain organic carbon by secreting extracellular enzymes and absorbing the resulting soluble compounds. They lack photosynthetic pigments and do not fix inorganic carbon as their principal carbon source, unlike cyanobacteria, algae, and photosynthetic members of the phytoplankton. Ecosystem production is measured over a stated area and interval because it is a flux, not simply material present at one moment. Producers convert inorganic carbon into organic compounds, respiration returns some carbon to the environment, and heterotrophs redistribute and mineralize the remainder. Aquatic and terrestrial systems differ greatly in producer size, longevity, nutrient delivery, and turnover, so standing biomass alone is a poor proxy for annual production. A mechanistic interpretation therefore follows carbon sources, transformations, and losses. In this context, the keyed term, Fungi, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17

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ECOSYSTEM TYPES

Which zone contains only heterotrophs in lakes?

The profundal zone is the deep, open-water region of a lake below effective light penetration. Because irradiance there falls beneath the compensation level, photosynthesis cannot balance the respiration of producers; rooted plants and sustained phytoplankton production are therefore absent. Its food web is dominated by heterotrophic organisms that obtain organic carbon made elsewhere. Bacteria and fungi decompose sinking detritus, while invertebrates and fishes consume particles, microbes, or other animals. In a stratified eutrophic lake, this respiration can deplete oxygen in the profundal water because atmospheric mixing is restricted. Calling the region “only heterotrophic” is a textbook simplification: chemoautotrophic microorganisms can occur under suitable chemical conditions, and organisms may move between zones. Nevertheless, heterotrophy overwhelmingly characterizes this light-limited habitat. Littoral water is shallow enough for rooted vegetation and attached algae, while the limnetic or pelagic surface region supports phytoplankton. The decisive mechanism is the shortage of photosynthetically active radiation, which removes local photosynthetic production and makes the profundal community dependent on imported organic matter.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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