Cell membrane
How do phospholipids move in the membrane?
They move side‑to‑side in the bilayer.
Why can oxygen diffuse easily across the membrane?
Oxygen diffuses easily because it is small and nonpolar.
Why does active transport require ATP?
It needs ATP to move molecules against the gradient.
Why must cells maintain stable internal conditions?
They must stay stable to function properly.
What is the key difference between active and passive transport?
Active uses energy and passive does not.
What do carbohydrate chains on the membrane do?
They help cells recognize each other.
What determines the direction water moves during osmosis?
Water moves toward the higher solute concentration.
Why would a cell use endocytosis?
It uses endocytosis to bring in large particles.
How does the membrane help with homeostasis?
It controls what enters and leaves.
How does solute concentration affect water movement?
Water moves toward higher solute levels.
What is the purpose of protein channels?
They allow specific molecules to pass through.
Why do some molecules need channel proteins?
They need channels because they are too large or charged.
Why would a cell use exocytosis?
It uses exocytosis to release materials.
Why is pH balance important for cells?
Enzymes only work at certain pH levels.
Why are membrane proteins important?
They help transport and communication.
What does cholesterol do in the membrane?
Cholesterol helps stabilize the membrane.
What makes diffusion happen faster?
A larger concentration difference speeds it up.
What does the sodium‑potassium pump do?
It moves sodium out and potassium in.
How do cells maintain water balance?
They regulate water movement through osmosis.
Why does a cell shrink in a hypertonic solution?
Water leaves the cell.
Why is the cell membrane flexible?
It is flexible because phospholipids can move sideways.
Why do plant cells not burst in hypotonic solutions?
Their cell wall prevents bursting.
Why does the cell use vesicles for large materials?
Large materials cannot pass through the membrane.
How do cells respond to temperature changes?
They adjust enzyme activity to stay stable.
How do feedback systems help cells survive?
They adjust internal conditions when they change.