Final answer:
The key element that would no longer be produced if algae were removed from the ecosphere is Oxygen (A). Algae contribute significantly to oxygen production on Earth, and their elimination would greatly affect the availability of oxygen required by many organisms for respiration.
Step-by-step explanation:
The key element that is no longer produced if algae are removed from the ecosphere is Oxygen (A). Algae, like other photosynthetic organisms, play a crucial role in ecosystems by converting sunlight into chemical energy through the process of photosynthesis. During this process, they produce oxygen and organic compounds that are essential for the survival of many other organisms. If algae are eliminated, the levels of oxygen in the ecosystem would be significantly reduced, leading to detrimental effects on aquatic life and other organisms that depend on oxygen for respiration.
For clarification, algae utilize carbon dioxide, water, and sunlight to carry out photosynthesis, thereby generating oxygen and sugars/carbohydrates, which serve as food for many marine and freshwater species. In addition, algae contribute to the production of a substantial proportion of the Earth's oxygen; it is estimated that phytoplankton, a type of microscopic algae, release over 50% of the oxygen produced on Earth through photosynthesis. Therefore, without algae, there would be a sharp decline in the availability of oxygen necessary for life as we know it.