Biology STAAR Practice Test 2025 – Comprehensive All-in-One Guide to Mastering the State of Texas Readiness Exam!

Active transport is a process used by cells to move substances across their membrane against the concentration gradient, meaning from an area of lower concentration to an area of higher concentration. This movement is essential for maintaining essential concentrations of ions and nutrients inside the cell. Unlike passive transport, which occurs naturally and does not require energy, active transport requires cellular energy, typically in the form of ATP (adenosine triphosphate).

The involvement of energy is critical because it allows cells to accumulate substances even when they are already present in higher concentrations inside the cell. This can be important for various cellular functions, including nutrient uptake and ion regulation. Thus, the process of active transport is heavily reliant on energy provided by the cell.

Other options, such as oxygen or glucose, do not directly pertain to the fundamental requirement of energy for active transport. While water is vital for various biological processes and can be involved in transport mechanisms, it does not represent a requirement for the functioning of active transport specifically.