Section 2 - Cell Membranes Flashcards
What do electron micrographs show about cell membranes? (2)
1) The cell-surface membrane consists of a double layer of phospholipid molecules tightly packed together.
2) Bigger protein molecules are embedded in the phospholipid molecules. Some proteins go all the way through the membrane and some only go halfway.
What is another term for cell-surface membranes?
Plasma membranes
What are the 4 different ways substances pass through membranes?
1) Diffusion
2) Osmosis
3) Facilitated Diffusion
4) Active transport
Describe how substances pass through membranes by diffusion (3)
1) The particles of liquids and gases are constantly moving about. This movement causes the particles to spread from an area of higher concentration to an area of lower concentration.
2) Particles will diffuse through the cell membrane as long as they are small enough to pass through the very small gaps between the phospholipid molecules. Water, oxygen and carbon dioxide molecules can do this.
3) The cell doesn’t need to provide any energy for this process.
Describe how substances pass through membranes by osmosis
Osmosis is the diffusion of water molecules across a partially permeable membrane from a region of higher concentration of water molecules to a region of lower concentration of water molecules. The cell doesn’t need to provide energy.
What is another term for concentration of water molecules?
Water potential
Why must glucose and many other water-soluble molecules be helped across the membrane by carrier proteins?
They are too big to diffuse across the membrane by themselves
Each substance has its own _________ carrier protein
specific
Describe how a glucose molecule can diffuse through a cell membrane (2)
1) A molecule of glucose fits onto the outside end of a glucose carrier protein.
2) This causes the protein to change shape, allowing the glucose molecule to diffuse through it into the cytoplasm of the cell. The cell doesn’t need to provide any energy.
Why do mineral ions need help to cross the membrane?
They have electrical charges on them
What allows mineral ions to diffuse through the membrane?
Specific channel proteins
Describe how substances pass through membranes by active transport
The substance fits into a specific carrier protein, then molecules of ATP provide the energy to change the shape of the protein. As it changes shape, the protein actively transports the substance through the membrane.
When a cell needs to move substances across the membrane from a region of lower concentration to a region of higher concentration, what must it provide?
Energy
What are the carrier proteins that move substances from a region of lower concentration to a region of higher concentration sometimes called?
Pumps
