Question

what is the primary structure of the cell - membrane?
a. a carbohydrate chain
b. a double layer of dna
c. a single layer of protein
d. a phospholipid bilayer

which transport process requires energy to move molecules against their concentration gradient?
a. facilitated diffusion
b. osmosis
c. simple diffusion
d. active transport

how does the structure of the phospholipid bilayer contribute to its function?
a. the hydrophilic heads face outwards, creating a barrier to all substances.
b. the hydrophobic tails face outwards, repelling water.
c. the hydrophilic heads face inwards, allowing easy passage of water - soluble substances.
d. the hydrophobic tails face inwards, creating a barrier to most water - soluble substances.

what is selective permeability?
a. the ability of the cell to divide and reproduce.
b. the ability of the cell to produce energy.
c. the ability of the cell membrane to regulate what enters and exits the cell.
d. the ability of the cell membrane to store nutrients.

Explanation:

1. The cell - membrane's primary structure is a phospholipid bilayer. Phospholipids have hydrophilic heads and hydrophobic tails that arrange in a bilayer to form the basic structure of the membrane.
2. Active transport requires energy (usually ATP) to move molecules against their concentration gradient, while facilitated diffusion, osmosis, and simple diffusion move molecules along the concentration gradient without the need for additional energy input.
3. In the phospholipid bilayer, the hydrophilic heads face outward (towards the aqueous environment inside and outside the cell), and the hydrophobic tails face inward, creating a barrier to most water - soluble substances.
4. Selective permeability is the ability of the cell membrane to regulate what enters and exits the cell, allowing some substances to pass through while restricting others.

Answer:

1. d. A phospholipid bilayer
2. d. Active transport
3. d. The hydrophobic tails face inward, creating a barrier to most water - soluble substances.
4. c. The ability of the cell membrane to regulate what enters and exits the cell