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Coral reefs are among the most diverse and productive ecosystems on Earth, providing habitat, food, and economic resources for millions of species and humans alike. A key aspect of their success lies in the complex and intricate symbiotic relationships they harbor. At the heart of these relationships is the symbiosis between coral polyps and zooxanthellae, a type of photosynthetic algae. This mutualistic relationship is vital for the health and growth of coral reefs.

Zooxanthellae live within the tissues of coral polyps, where they perform photosynthesis, converting sunlight into energy. This process not only provides energy to the zooxanthellae but also supplies the coral with essential nutrients, such as glucose, glycerol, and amino acids. In return, the coral provides the zooxanthellae with a protected environment and the compounds necessary for photosynthesis, including carbon dioxide and nitrogenous waste.

The symbiotic relationship between coral and zooxanthellae is highly sensitive to environmental changes. Factors such as water temperature, light availability, and water quality can impact the efficiency of photosynthesis and the health of coral reefs. When water temperatures rise beyond optimal levels, corals may expel their zooxanthellae in a stress response known as coral bleaching. This event leaves the coral vulnerable, as it loses its primary source of energy and becomes more susceptible to disease and death.

In addition to zooxanthellae, coral reefs host a diverse array of symbiotic relationships involving various marine organisms. For example, many reef fish engage in cleaning symbiosis, where cleaner fish remove parasites from larger fish. This interaction benefits both parties, as the cleaner fish gain nourishment from consuming the parasites, while the larger fish enjoy improved health and reduced parasite loads.

Furthermore, coral reefs are home to mutualistic relationships between crustaceans and corals. Some shrimp and crab species live among the coral branches, providing defense against predators such as starfish. In return, these crustaceans receive shelter and a steady food supply.

Understanding the myriad symbiotic interactions within coral reefs is crucial for their conservation and management. As climate change and human activities continue to threaten coral reefs globally, protecting these vital ecosystems requires a comprehensive approach that considers the complex interdependencies that sustain them.

Questions: 1. What is the primary role of zooxanthellae in coral reefs? A) To provide coral polyps with protection B) To perform photosynthesis and supply nutrients C) To act as predators of coral polyps D) To remove parasites from coral reefs 2. The word "harbor" in the first paragraph is closest in meaning to: A) Destroy B) Shelter C) Attack D) Isolate 3. Which of the following is NOT provided to zooxanthellae by coral polyps? A) Carbon dioxide B) Sunlight C) A protected environment D) Nitrogenous waste 4. What happens when corals experience bleaching? A) They expel zooxanthellae and become more vulnerable B) They grow faster due to increased nutrients C) They develop new symbiotic relationships D) They become less susceptible to disease 5. What can be inferred about cleaning symbiosis in coral reefs? A) It primarily benefits the larger fish B) It leads to an increase in parasite populations C) It involves crustaceans and coral branches D) It is a mutually beneficial relationship 6. Why are crustaceans important to coral reefs, according to the passage? A) They perform photosynthesis B) They defend corals against predators C) They remove harmful algae D) They provide coral polyps with nutrients 7. The phrase "cleaning symbiosis" in the fourth paragraph refers to: A) The removal of parasites from larger fish B) The process of photosynthesis C) The expulsion of zooxanthellae D) The protection offered by coral branches 8. Where would the following sentence best fit in the passage? "This loss of zooxanthellae can lead to the coral turning white, hence the term 'bleaching.'" A) After the first sentence of the third paragraph B) After the second sentence of the third paragraph C) After the last sentence of the third paragraph D) After the first sentence of the fourth paragraph 9. Which of the following best summarizes the passage? A) Coral reefs are threatened by predators and require human intervention to survive. B) Symbiotic relationships are essential for the health and sustainability of coral reefs. C) Zooxanthellae are the only organisms contributing to coral reef conservation. D) Coral bleaching is the primary threat to marine ecosystems. 10. According to the passage, what is one impact of rising water temperatures on coral reefs? A) Increased diversity of symbiotic relationships B) Expulsion of zooxanthellae from coral polyps C) Enhanced photosynthesis and coral growth D) Improved health of reef fish populations Answer Key: 1. (B) 2. (B) 3. (B) 4. (A) 5. (D) 6. (B) 7. (A) 8. (B) 9. (B) 10. (B) ---