Which of the following in not a Primary Producer?

Primary producers are also referred to as autotrophs. They are organisms that use sunlight and some materials that are gotten from nonliving sources to obtain their energy. They have the ability to manufacture their foods by themselves. These living organisms are usually green plants.

Hence, phytoplankton, grasses, algae, and trees are primary producers, but fungus is not a primary producer. Instead, the fungus is recognized as a decomposer. We can also find some organisms that are primary producers in running water, such as protists, higher plants, algae, and some bacteria.

This chain goes as thus: the consumers depend on the autotrophs for their feeding, and in the end, decomposers eat up the dead plants and animals. Fungi is a typical decomposer and not a producer. The food chain starts with the producer, and it ends with the decomposers, to which fungi belong. Fungi are reckoned to be the main decomposers of nature.

The fungus is not a primary producer because even though it looks like a plant, it will not have the ability to create its own food. Plants are known to have the ability to create their own food through the process of photosynthesis. Fungi will be getting the food that they need through absorption from different food products.

They will be getting their food from different products. Due to this, fungi can be considered as secondary consumers instead of primary consumers. The main reason why fungus cannot be considered as a producer is because of the definition of “producers” alone which is that they have the ability to make their own food.

Fungi and other organisms that attain their biomass from oxidizing organic materials are called decomposers and not primary producers. A fungus is any group of eukaryotic organisms that include yeast and molds, such as mushrooms.

These organisms are grouped within their separate kingdom, which is different from plants and animals' respective kingdoms. Before initiating molecular methods for phylogenetic examination, taxonomists considered fungi to be members of the plant kingdom because of definite similarities in general morphology and growth habitat. Like plants, fungi often grow in soil. Mushrooms sometimes look like certain types of plants, such as mosses.

The correct answer is – Fungus.
In biology, primary producers are also known as autotrophs. They are groups of organisms that able to produce organic compounds using basic carbon substances. Examples of organic compounds produced include proteins, carbohydrates, and fats.

Primary producers are also able to convert one form of energy to another form of energy. They form an integral part of the food chain. Examples are algae, plants, phytoplankton, grasses, and trees. They use energy from sunlight with inorganic compounds like carbon to form organic compounds through the process of photosynthesis.

Autotrophs are further divided into chemoautotroph and photoautotroph.
Heterotrophs are the opposite of autotrophs. Heterotrophs cannot produce their own food. They are not producers. They depend on primary producers. Examples are fungi, animals, protists, and bacteria. They are classified as primary, secondary, and tertiary consumers.