In a terrestrial ecosystem, which are the primary producers?

The correct answer is Option (2) → Herbaceous and woody plants

Producers are the green plants of an ecosystem, which make food by photosynthesis. Which plants act as the main producers depends on the type of ecosystem.

Option (1) Insects and birds — Incorrect. Insects and birds do not make their own food. NCERT lists insects, birds and mammals as common herbivores (primary consumers) in a terrestrial ecosystem.

Option (2) Herbaceous and woody plants — Correct. On land, the major producers are herbaceous and woody plants, that is, herbs, shrubs and trees.

Option (3) Phytoplankton and algae — Incorrect. Phytoplankton and algae are producers of an aquatic ecosystem, such as a pond or the sea, not of a terrestrial one.

NCERT Extract:
Energy Flow – “… The green plant in the ecosystem are called producers. In a terrestrial ecosystem, major producers are herbaceous and woody plants. Likewise, producers in an aquatic ecosystem are various species like phytoplankton, algae and higher plants.”
Energy Flow – “… Obviously the primary consumers will be herbivores. Some common herbivores are insects, birds and mammals in terrestrial ecosystem and molluscs in aquatic ecosystem.”