The protista that is a producer in an aquatic food chain is

Step 1: Analyze the question We need the protist that is a producer in an aquatic food chain. Producers make their own food, usually by photosynthesis, so we are looking for a protist with chlorophyll.

Step 2: Explain the concept Protista is a kingdom of mostly unicellular organisms. They fall into two broad groups:

• Plant-like protists (algae): have chlorophyll and photosynthesize. They form the phytoplankton at the base of aquatic food chains.
• Animal-like protists (protozoans): have no chlorophyll and feed on other organisms (heterotrophs).

Step 3: Examine each option

• A. Trypanosome: a parasitic protozoan that causes sleeping sickness. It lives in blood and is a consumer or parasite, not a producer.
• B. Paramecium: a free-living ciliate that feeds on bacteria and small particles. It is a consumer.
• C. Chlamydomonas: a unicellular green alga with a chloroplast and two flagella. It photosynthesizes and is a producer in ponds, lakes, and other freshwater habitats.
• D. Amoeba: a protozoan that engulfs food by phagocytosis. It is a consumer.

Step 4: Answer Only Chlamydomonas can make its own food, so it is the producer in an aquatic food chain.

Exam tip: Remember "Chlamy = Chlorophyll" (both start with "Chl"). Any protist with chlorophyll, such as Chlamydomonas, Euglena (a mixotroph), Spirogyra, or Volvox, is a producer. Protozoans like Amoeba, Paramecium, and Trypanosoma are consumers or parasites.