Read the following paragraph and answer the questions.
Lakes are freshwater ecosystems that may be natural or more frequently, artificially created by the construction of dams and tanks. Damming rivers alters a flowing water ecosystem to a still water ecosystem. This is usually developed for irrigation, or for water storage for urban or industrial use and hydroelectric power generation. There are several types of lakes - oligotrophic, dystrophic, eutrophic, endemic, volcanic, meromictic and artificial. Their biodiversity includes algae, which derives energy from the sun. This is transferred to microscopic animals which feed on the algae. Herbivorous fish, which in turn are preyed upon by larger carnivorous fish. Some specialised fish, such as catfish, feed on the detritus on the muddy bed of the lake; they are called bottom feeders or bottom dwellers. Fisherfolk depend heavily on this freshwater ecosystem, and farmers use it for water for their fields.
Sunlight penetrates the water surface of shallow parts of a lake ecosystem used by the aquatic plants. From the aquatic plants, energy is transferred to herbivorous animals and carnivores that live in water. These animals excrete waste products, which settle at the bottom of the lake and are broken down by small animals such as molluscs and worms that live in the mud in the lake bed. This acts as the nutrient material used by aquatic plants for their growth. During this process plants use carbon from CO2 for their growth and release oxygen. This oxygen is then used by aquatic animals, which filter water through their respiratory system.