Stem Case – Photosynthesis – High School (Gizmo)
- Explain the relationship between coral and algae, and how a problem with algae photosynthesis caused coral bleaching in the Great Barrier Reef.
- How did water from the Great Barrier Reef affect ATP, NADPH, and sugars?
- Using the data from the paraquat experiment, explain how you know that paraquat did not cause the coral bleaching.
- Explain why you know that diuron caused the coral to bleach.
The Correct Answer and Explanation is :
- Relationship Between Coral and Algae and Coral Bleaching:
Coral and algae have a mutualistic relationship, where algae (specifically, zooxanthellae) live inside the coral cells. In exchange for a protected environment, algae provide corals with essential nutrients. The algae undergo photosynthesis, converting sunlight, water, and carbon dioxide into sugars and oxygen. The oxygen is used by the coral, while the sugars are transferred to the coral as an energy source. This symbiotic relationship is vital for the coral’s survival and growth. However, when environmental stressors such as increased water temperature, pollution, or changes in light exposure occur, algae may become stressed and stop performing photosynthesis effectively. This causes them to expel the algae from the coral, a process known as coral bleaching. Without the algae, the coral loses its color (since the algae give corals their vibrant hues) and is left vulnerable to disease and starvation, making it less resilient to environmental changes. - Effect of Water from the Great Barrier Reef on ATP, NADPH, and Sugars:
Water from the Great Barrier Reef contains various levels of nutrients and temperature fluctuations, which can affect the functioning of photosynthesis. During normal photosynthesis in algae, sunlight powers the production of ATP and NADPH in the light-dependent reactions. These molecules are then used in the Calvin Cycle to convert carbon dioxide into sugars, which the algae and corals use for energy. When environmental factors like temperature rise, they can disrupt the normal functioning of the photosynthetic machinery. If the algae are unable to photosynthesize efficiently, ATP and NADPH production decreases, which in turn reduces sugar production. As a result, both the coral and the algae struggle to obtain the necessary energy, leading to coral bleaching. - Paraquat Experiment and Coral Bleaching:
Paraquat is an herbicide that inhibits photosynthesis by disrupting the electron transport chain in the light reactions. However, data from the paraquat experiment suggests that paraquat did not cause coral bleaching in the Great Barrier Reef. This is evident from the experiment showing no significant changes in coral color or health after exposure to paraquat. If paraquat had been responsible for coral bleaching, it would have inhibited the photosynthesis process, reducing ATP and NADPH production in the algae, but the experimental results show that the coral remained unaffected by paraquat, ruling it out as a cause of bleaching. - Diuron and Coral Bleaching:
Diuron, a common herbicide used to inhibit photosynthesis, works by blocking the electron transport chain in the photosystem II. This inhibits the ability of algae to carry out photosynthesis and thus prevents the production of essential energy molecules like ATP and NADPH. Experimental data showed that exposure to diuron resulted in a significant decrease in the amount of photosynthesis carried out by algae within the coral, causing them to expel the algae. This disruption of photosynthesis led to coral bleaching, as the coral lost its primary source of nutrition. The clear correlation between diuron exposure and coral bleaching indicates that diuron is a likely cause of the bleaching in the Great Barrier Reef.
By examining the experiments and understanding the role of photosynthesis in coral health, it is evident that diuron is a key contributor to coral bleaching, whereas paraquat did not have the same impact.