Photosynthesis Photosynthetic Organisms 3 — Questions and Answers
Question 1: Which photosynthetic organisms are responsible for producing roughly half of Earth's oxygen?
- Tropical rainforests
- Marine phytoplankton (Correct answer)
- Freshwater algae
- Temperate grasslands
Correct answer: Marine phytoplankton
Marine phytoplankton, including diatoms, dinoflagellates, and cyanobacteria, generate approximately 50% of Earth's oxygen through photosynthesis.
Question 2: Green sulfur bacteria differ from cyanobacteria because they use ______ instead of water as an electron donor.
- Carbon dioxide
- Hydrogen sulfide (Correct answer)
- Nitrogen gas
- Methane
Correct answer: Hydrogen sulfide
Green sulfur bacteria perform anoxygenic photosynthesis using H2S as the electron donor, releasing sulfur instead of oxygen.
Question 3: What is the term for unicellular photosynthetic organisms that drift in aquatic environments?
- Zooplankton
- Nekton
- Phytoplankton (Correct answer)
- Benthos
Correct answer: Phytoplankton
Phytoplankton are microscopic photosynthetic organisms that float near the water surface where sunlight is available.
Question 4: Dinoflagellates are notable photosynthetic protists that can cause:
- Coral bleaching and red tides (Correct answer)
- Acid rain
- Nitrogen fixation
- Soil acidification
Correct answer: Coral bleaching and red tides
Dinoflagellate blooms cause red tides, producing toxins harmful to marine life, and some species cause coral bleaching when they abandon coral hosts.
Question 5: Which photosynthetic symbiont lives inside coral reef organisms and provides them with nutrients?
- Diatoms
- Zooxanthellae (Symbiodinium) (Correct answer)
- Cyanobacteria
- Green algae
Correct answer: Zooxanthellae (Symbiodinium)
Zooxanthellae are dinoflagellate algae that live within coral tissues, providing photosynthate in exchange for nutrients and CO2.
Question 6: Kelp forests are composed of which type of photosynthetic organism?
- Red algae
- Green algae
- Brown algae (phaeophytes) (Correct answer)
- Cyanobacteria
Correct answer: Brown algae (phaeophytes)
Kelp is a large brown alga (class Phaeophyceae) that forms underwater forests, providing critical habitat in cold coastal waters.
Question 7: Which characteristic distinguishes C4 plants from C3 plants in terms of leaf anatomy?
- Larger stomata
- Kranz anatomy with bundle sheath cells (Correct answer)
- Absence of chloroplasts in guard cells
- Thicker cuticle layers
Correct answer: Kranz anatomy with bundle sheath cells
C4 plants have Kranz anatomy, where CO2 is first fixed in mesophyll cells then concentrated in bundle sheath cells for the Calvin cycle.
Photosynthesis Photosynthetic Organisms 3
Which photosynthetic organisms are responsible for producing roughly half of Earth's oxygen?