# DBT JRF 2022 — Question 150

Exam: DBT JRF 2022 · Section: B · Topic: Marine Biotechnology › Coral Symbiosis & Zooxanthellae · Difficulty: Medium

## Question

Choose the correct option to fill up the blanks: _____________ nourish the host coral as well as help it deposit its skeleton. They perform _____________ and pass on some of the _____________ they make to the coral.

## Options

- **A.** hermatypic corals, scavenging, organic matter
- **B.** scleractinian, respiration, calcium
- **C.** ahermatypic corals, synthesis, calcium
- **D.** Zooxanthellae, photosynthesis, organic matter

## Answer

Option D

## Explanation

Zooxanthellae: symbiotic relationship with coral: Zooxanthellae are symbiotic dinoflagellate algae (Symbiodinium spp.) that live within the endodermal cells of reef-building (hermatypic/scleractinian) corals: Relationship: • Zooxanthellae perform PHOTOSYNTHESIS within coral tissues. • They transfer 90–95% of their photosynthetically fixed carbon (sugars, glycerol, amino acids) to the coral host as ORGANIC MATTER. • This organic matter provides the majority of the coral's energy (up to 95% of energy needs). • This energy powers: - Coral metabolism - Calcium carbonate skeleton deposition ( $\text{Ca}^{2+} + 2\text{HCO}_3^- \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} + \text{CO}_2$ ) Corol bleaching: • Thermal stress causes corals to expel zooxanthellae → loss of colour and energy source → coral bleaching and eventual death. Corals provide CO₂ and nitrogenous wastes to the zooxanthellae (mutualistic symbiosis). Answer: Zooxanthellae perform photosynthesis and pass organic matter (photosynthates) to the coral, nourishing it and fuelling calcium carbonate skeleton deposition.

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