Membrane Movement

The cell membrane's job is...

• to block all things from moving into the cell

• to control what enters & leaves the cell

• to help a cell stand upright

• to join one cell with another

Answer explanation

The cell membrane is semipermeable, which means some things can pass through, while others cannot. The membrane is made of mostly phospholipids and proteins. The phospholipids are both hydrophilic (water loving) and hydrophobic (water fearing). Some of the proteins act as tunnels that allow large or charged particle to pass in or out of the cell.

The two MAIN components of a cell membrane are

• phospholipids

• nucleic acids

• proteins

• carbohydrates

Answer explanation

The lipid tails on a phospholipid are hydrophilic.

• true

• false

Answer explanation

Lipids are hydrophobic. They are nonpolar, so they do not mix well with water.

The phosphates on a phospholipid are hydrophilic.

• true

• false

Answer explanation

Phosphates are hydrophilic. They have polarity (slightly charged sides), so they mix well with water.

Facilitated diffusion _____________.

• requires ATP (energy)

• moves against the concentration gradient

• requires NO energy

• moves with the concentration gradient

Answer explanation

Facilitated diffusion moves large or charged particles across the cell membrane from an area of high concentration to an area of low concentration. This requires NO energy, because the particles are moving WITH the concentration gradient.

Osmosis is the diffusion of water across a semipermeable membrane.

• true

• false

What does active transport require?

• The process requires the cell to use energy

• The cell needs to be supported by a cell wall.

• The process requires a transport protein.

• The process requires an isotonic solution

Answer explanation

Active transport moves large or charged particles through a transport protein. The molecules move AGAINST the concentration gradient (from low to high). Just like rolling a ball uphill, this requires energy.

A substance dissolved in water is known as a solute.

• true

• false

Answer explanation

The substance the dissolves the solute is called the

• solvent, like the water in salt water

• solute, like the salt in salt water

Answer explanation

You have a nice cool glass of lemonade. Which substance is the solvent?

• sugar

• water

• lemon juice

• ice

Answer explanation

In lemonade, water dissolves everything else, so it is the solvent.