Homeostasis and Cell Membrane Structure

Which statement best describes selective permeability of the cell membrane?

• It allows all substances to cross freely

• It blocks all molecules from crossing

• It lets some molecules pass but not others

• It only allows water to pass always

Answer explanation

Selective permeability means the cell membrane allows some molecules to pass while blocking others, ensuring that essential substances can enter and harmful ones are kept out.

The plasma membrane is primarily composed of a bilayer of which molecules?

• Triglycerides in a double sheet

• Amino acids forming a lattice

• Nucleic acids forming two strands

• Phospholipids arranged tail to tail

Answer explanation

The plasma membrane is primarily composed of phospholipids, which are arranged in a bilayer with their hydrophobic tails facing inward, creating a barrier that separates the cell from its environment.

What role does the cell membrane play in homeostasis?

• It produces proteins for the cell

• It controls DNA replication cycles

• It regulates transport into and out of cells

• It creates energy for the organism

Answer explanation

The cell membrane regulates transport into and out of cells, maintaining homeostasis by controlling the movement of substances, ensuring the internal environment remains stable despite external changes.

Tags

NGSS.HS-LS1-3

In a phospholipid, which part is hydrophilic and faces outward toward water?

• The cholesterol rings facing outward

• The fatty acid tails facing inward

• The phosphate head facing outward

• The protein channel lining outward

Answer explanation

In a phospholipid, the phosphate head is hydrophilic and faces outward toward water, while the fatty acid tails are hydrophobic and face inward. This arrangement forms a bilayer, essential for cell membrane structure.

Which molecules move most easily through the lipid bilayer without help?

• Charged ions like sodium and chloride

• Large polar sugars like glucose

• Small nonpolar gases like oxygen

• Big proteins with hydrophilic regions

Answer explanation

Small nonpolar gases like oxygen can easily pass through the lipid bilayer due to their size and nonpolar nature, allowing them to diffuse without assistance, unlike charged ions or large polar molecules.

Membrane proteins that form pores to move polar molecules across are called what?

• Nuclear pores for transport

• Ribosome gates for passage

• Carrier lipids for diffusion

• Protein channels in membranes

Answer explanation

Membrane proteins that form pores to facilitate the movement of polar molecules are known as protein channels in membranes. They allow selective passage, distinguishing them from other options like nuclear pores or carrier lipids.

Which statement accurately compares integral and peripheral proteins?

• Both are cholesterol molecules in bilayer

• Both float on surface without embedding

• Integral sit on surface; peripheral span bilayer

• Integral go through the bilayer; peripheral attach surface

Answer explanation

Integral proteins span the entire lipid bilayer, allowing them to interact with both the interior and exterior of the cell. In contrast, peripheral proteins are attached to the surface of the membrane, not embedded within it.

Carbohydrate chains attached to membrane proteins and lipids mainly function in what?

• Energy production by respiration

• Cell identification and communication

• Chromosome replication control

• Protein synthesis and folding

Answer explanation

Carbohydrate chains on membrane proteins and lipids primarily serve as recognition sites for cell identification and communication, allowing cells to interact and respond to their environment.

Which combination best describes the interior core of the phospholipid bilayer?

• Aqueous and water-rich core region

• Ionic and highly charged core region

• Nonpolar and hydrophobic core region

• Polar and hydrophilic core region

Answer explanation

The interior core of the phospholipid bilayer is nonpolar and hydrophobic, which prevents water and polar molecules from passing through, maintaining the bilayer's integrity and function.

Which set correctly pairs membrane component with its function?

• Aid in cell recognition signaling

• Protein channels

• Create hydrophobic interior core

• Glycoproteins

• Facilitate passage of polar molecules

• Cholesterol

• Helps maintain membrane fluidity

• Phospholipid tails