Hint: Primary consumers are the one that feeds on the primary producers. They are organisms which consume food from plants directly. These organisms make up the second trophic level of the food chain. Primary consumers are consumed by secondary and tertiary consumers. Primary consumers range from microscopic organisms such as zooplankton to animals as big as elephants. They have specialized teeth to grind and tear hard plant materials.
Complete answer: Herbivores also known as primary consumers take up food directly from the autotrophs. Autotrophs are organisms that make their own food through photosynthesis. There are different types of herbivores based on their feeding mechanism. Algivorous feed on photosynthetic algae. Nectivores consume nectar from the plants, frugivore consumes fruits from the plants and granivores feed on seeds and grains. The examples of primary consumers are ruminants, zooplanktons and herbivorous birds. Ruminants like cows, sheep, giraffes and goats are also called primary herbivorous consumers. They feed on plant material such as grass, roots and branches. The cell walls of plants contain a high amount of cellulose that is difficult to break. The ruminants have an adaptive system that enables them to obtain nutrients through fermentation and digestion. This process takes place in four specialized chambers of their stomach. Zooplanktons are microscopic organisms that live in the ocean. They feed on marine primary producer phytoplankton. Zooplankton is fed by a method called filter feeding. In this method water containing phytoplankton, is passed over specialized filtering structures and the phytoplankton is filtered out and digested. Some species of birds are herbivorous in nature. They nurture fruit, seeds and berries and so call themselves primary users. Herbivorous birds often have morphologically adapted beaks, which allow them to exploit their food source.
Note: There are a large number of primary consumers present on earth. Most of them are smaller in size and have little impact on the ecosystem. Squirrels, mice, and beetles are examples of such primary consumers. Primary consumers help in the transfer of energy thus playing a significant role in the ecosystem. They also help in nutrient recycling.