Amoebas are single-celled organism that need to obtain food in order to
1. release oxygen into the air
2. protect themselves from other living things
3. get the energy they need to carry out life functions
4. remove harmful chemicals from the environment

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation: