“Cell Environment” Notes p. 394 “Cell Environment” Notes

Selectively permeable Some things can pass through the cell membrane & some can’t

Ways of moving through a cell membrane: Passive transport – no energy needed Active transport – needs energy

Diffusion Passive Molecules move from an area of higher concentration to an area of lower concentration

Why diffusion happens Molecules are always moving They bump into each other Causes them to spread out

Osmosis Diffusion of water Passive

Why can’t people drink large amounts of salt water?? Salt water causes water to move out of body cells

Active Transport Move materials through cell membrane, using cellular energy Two types:

1. Transport Proteins “Pick up” outside molecules & bring them inside Uses energy Can move things in or out of cell

2. Engulfing Cell membrane surrounds & engulfs a particle Forms a vacuole with the particle inside Uses energy

Why are cells small? Materials must be able to flow through cytoplasm and reach their destination Keep travel time low! If cell grew too large, it could not function well enough to survive.