Cell Membrane Design
What are the 2 main parts of a phospholipid?
Hydrophilic head and hydrophobic tail
What is diffusion?
Movement of molecules from high concentration to low concentration.
What is the main difference between active and passive transport?
Active transport requires energy (ATP); passive transport does not.
A cell placed in pure water will most likely:
Swell (hypotonic environment)
What does the cell membrane help maintain by controlling what enters and exits?
homeostasis
Why is the cell membrane called a “fluid mosaic model”?
It’s flexible and made of many moving parts like proteins and lipids.
What is osmosis?
The diffusion of water across a selectively permeable membrane.
What direction does active transport move molecules?
From low concentration to high concentration (against the gradient).
A cell placed in saltwater will most likely:
Answer: Shrink (hypertonic environment)
If temperature increases too much, how does it affect the membrane?
It becomes more fluid or less stable.
What role does cholesterol play in the cell membrane?
It helps stabilize the membrane’s fluidity in different temperatures.
Why does facilitated diffusion need a protein channel?
Some molecules are too large or charged to pass through the lipid bilayer.
Name one example of active transport.
Sodium-potassium pump, endocytosis, or exocytosis.
What happens to water movement in an isotonic solution?
Water moves in and out equally; no net change.
Why can’t large molecules like glucose pass through the bilayer easily?
They’re too big or polar.
Which type of membrane protein spans the entire bilayer and helps transport materials?
Integral (or transmembrane) proteins
Name one example of a molecule that can pass directly through the phospholipid bilayer.
Oxygen, carbon dioxide, or small nonpolar molecules.
What process releases materials from the cell using a vesicle?
Exocytosis
A cell with 10% solute is placed in a 7% solute solution — which way does water move?
Into the cell (hypotonic solution)
A plant cell loses water and the cell membrane pulls away from the cell wall. What type of solution caused this?
Hypertonic solution
Explain why the cell membrane is described as semi-permeable.
It allows some substances to pass freely but blocks others.
True or False: Passive transport requires energy from the cell.
False
What type of active transport involves engulfing large particles or droplets?
Endocytosis (phagocytosis for solids, pinocytosis for liquids)
I have a beaker with 80% salt and 20% water. What will happen when I put a cell in it?
Water will leave the cell causing it to shrink. Hypertonic
Describe how active and passive transport work together to maintain homeostasis.
Passive transport balances normal flow, while active transport moves materials when energy is needed to maintain internal conditions.