The main food sources of the birds( the plentiful recourses within the environment occupied by the species)
Simple....
as you've learned... cells create tissue..tissue creates organs...organs create organ systems..and organ systems create organisms. They all work together to create something...
An example:
muscle cell-->>muscle tissue-->>heart-->>circulatory system-->>the circulatory system makes up a part of the body.
Thus, your answer.
Answer: B
Explanation: Hope this helps :)
D. Certain genes are turned on and others are turned off; this action produces adult cells that are specialized
The difference between active and passive cellular transport is that active transport requires energy for the ions and molecules to move across the cell membrane whereas passive cellular transport does not an energy input.
