Final answer:
The potato (D) is the correct answer as it is a plant capable of photosynthesis, making it a producer and a photoautotroph.
Step-by-step explanation:
The organism that is a producer and performs photosynthesis among the options provided is the potato (D). Potatoes are plants, which are types of the autotrophs, specifically photoautotrophs. This means they use sunlight to convert carbon dioxide and water into glucose and oxygen, a process known as photosynthesis. In contrast, mealworms, fish, and humans are all heterotrophs, which means they cannot produce their own food through photosynthesis and must consume other organisms to obtain energy.