Alga, or algae, are simple, plant-like organisms that can be found in various aquatic environments, including oceans, rivers, and lakes. They are primarily photosynthetic, meaning they use sunlight to produce their own food, and they play a crucial role in the ecosystem by providing oxygen and serving as a food source for many aquatic animals. Algae come in various forms, ranging from microscopic phytoplankton to larger seaweeds like kelp. They are classified into different groups based on their color, structure, and habitat, including green algae, red algae, and brown algae. Algae are essential for maintaining the balance of aquatic ecosystems and are also used in various industries, such as food and biofuel production.