Question

1. what are tissues made up of?

cells
organ systems
all of the above
organs

Explanation:

In biology (a subfield of Natural Science), tissues are groups of similar cells that work together to perform a specific function. Organ systems are made of organs, and organs are made of tissues, so tissues are made up of cells. The other options (organ systems, all of the above, organs) are incorrect because organ systems are composed of organs, organs are composed of tissues, and tissues are not made of organ systems or organs.

Answer:

A. cells