Which of the following pairs of organisms are photosynthetic?

Analyze the question: We need the pair in which both organisms can make their own food by photosynthesis (i.e., they contain chlorophyll).

Concept: Photosynthetic organisms contain chlorophyll (or similar pigments) and make food from CO₂ and water using light energy. Heterotrophs (animals, fungi, and many protozoans) cannot.

Check each option:

• A. Amoeba and Paramecium: Both are protozoans that feed heterotrophically (holozoic nutrition). Neither is photosynthetic. ✗
• B. Euglena and Chlamydomonas: Euglena has chloroplasts and photosynthesizes in light (it can also feed heterotrophically in darkness). Chlamydomonas is a unicellular green alga with a cup-shaped chloroplast. Both are photosynthetic. ✓
• C. Volvox and Rhizopus: Volvox is a colonial green alga (photosynthetic), but Rhizopus is a fungus (bread mould) with no chlorophyll. It is a saprophyte. ✗
• D. Nostoc and Plasmodium: Nostoc is a cyanobacterium (photosynthetic), but Plasmodium is a protozoan parasite that causes malaria and is not photosynthetic. ✗

Answer: Only option B has two organisms that are both photosynthetic.

Exam tip: In "pairs" questions, one wrong member makes the entire option wrong. Look for the "odd one out" quickly. Remember these:

• Fungi (Rhizopus, Mucor, yeast, mushroom) are never photosynthetic.
• Parasitic protozoans (Plasmodium, Trypanosoma) are never photosynthetic.
• Algae and cyanobacteria (Chlamydomonas, Volvox, Spirogyra, Nostoc) are photosynthetic.