Hint: Deer occupies the second trophic level in the food chain. They are the primary consumer which feed directly on the producer. They eat only grass and leaves. They consume carbohydrates which is produced by plants through photosynthesis.
To answer this question, we must know about the food habits of the animals.
On the basis of the food habit, animal are classified as
-Herbivores- These are the animals which only eat plant and plant products. For example- deer, cow, buffalo etc. These animals occupy the second trophic level. These organisms occupy the second highest level of energy after the producers. These animals are physically and physiologically adapted for eating plant based products.
-Carnivore- The carnivores are the animals which feed on the other animal for food. They primarily feed on the herbivores. They are called the secondary consumers. They occupy the third trophic level in the food chain. They obtain food either by hunting or killing other animals. Some carnivores act as scavengers. They occupy the top level in the food chain and are known as apex predators.
-Omnivore- the animals which feed on both plants and animals are called omnivores. For example- Bear
Deer eat only plant products and so are called herbivores.
Note: The herbivores have specialised teeth for chewing, grinding and grasping grass. They have certain microbes present in their gut which help them to digest the plant matter. The cellulose is difficult to digest. The flora mainly comprise of cellulose digesting organisms.