Cell Membrane Basics
What is the main function of the cell membrane?
What is to control what enters and exits the cell.
What is the movement of molecules from high concentration to low concentration called?
What is Diffusion?
What is osmosis?
Answer: The diffusion of water across a semi-permeable membrane.
What tool would you use to observe cells in a membrane investigation?
Answer: A microscope.
Why is the cell membrane sometimes called the “gatekeeper”?
Answer: Because it controls what enters and exits the cell.
What does “semi-permeable” mean?
Allows some substances to pass through, but not others.
What process uses proteins to help move larger molecules across the membrane?
Answer: Facilitated diffusion.
In a hypertonic solution, does water move into or out of the cell?
Answer: Out of the cell.
How could you use dialysis tubing to model a cell membrane?
Answer: Fill it with a solution and place it in another solution to observe what passes through.
Why do doctors give saline IVs instead of pure water?
Answer: Saline is isotonic; pure water would cause cells to swell and burst.
Which two main molecules make up most of the cell membrane’s structure?
What are Phospholipids and proteins?
How is active transport different from diffusion?
Answer: Active transport requires energy (ATP) and can move molecules against the concentration gradient.
Compare what happens to plant cells in hypotonic vs. hypertonic solutions.
Answer: Hypotonic → swell (turgid); Hypertonic → shrink (plasmolysis).
In an experiment with iodine and starch, how can you tell if diffusion has occurred?
Answer: The starch solution turns blue-black if iodine diffuses in.
How do nutrients from digested food enter the bloodstream through cell membranes?
Answer: By diffusion or active transport across intestinal cell membranes.
Explain how the structure of phospholipids makes the cell membrane semi-permeable.
What are their hydrophilic heads and hydrophobic tails form a bilayer that selectively allows certain molecules through.
Give an example of a substance that moves in or out of a cell by diffusion.
Answer: Oxygen (in) or carbon dioxide (out).
A potato slice in salt water shrinks. Explain why.
Answer: Water moves out of the potato cells by osmosis because the salt solution is hypertonic.
How can you use an egg soaked in vinegar (to remove the shell) as a model to investigate osmosis across a semi-permeable membrane?
The egg’s membrane acts like a cell membrane. Placing the egg in different solutions (water, corn syrup, salt water) shows how water moves in or out by osmosis, changing the egg’s size and mass.
Predict what might happen if a person is severely dehydrated on the cellular level.
Answer: Cells lose water, shrink, and may not function properly.
Predict what might happen to a cell if its membrane lost selective permeability.
Harmful substances could enter or essential substances could leak out, disrupting cell function or causing death.
A cell needs to bring in more glucose than is naturally available by diffusion. Propose how it might accomplish this.
Answer: Use active transport with carrier proteins and energy from ATP.
Predict what would happen to red blood cells if placed in pure water.
Answer: Water would enter by osmosis, causing them to swell and possibly burst (lyse).
Design a simple investigation to test how temperature affects diffusion rate through a semi-permeable membrane.
Answer: Place dialysis tubing in warm and cold solutions with dye; measure color spread over time.
A freshwater fish is accidentally placed in saltwater. Explain what happens to its cells and why.
Answer: Water leaves the fish’s cells (hypertonic environment), causing them to shrink and leading to dehydration or death.