Cell Membrane Structure and Function
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Questions and Answers

What characteristic of the cell membrane helps maintain homeostasis within the cell?

  • It allows any molecule to pass through.
  • It reacts with all types of molecules.
  • It is impermeable to all molecules.
  • It is selectively permeable. (correct)

What is the primary reason small non-polar molecules can easily pass through the cell membrane?

  • They can dissolve in the hydrophobic interior. (correct)
  • They require energy to cross the membrane.
  • They are attracted to polar molecules.
  • They are repelled by the water outside the membrane.

What is the term used to describe the movement of molecules from an area of high concentration to an area of low concentration?

  • Diffusion (correct)
  • Facilitated transport
  • Osmosis
  • Active transport

Which components are found in the phospholipid bilayer of the cell membrane?

<p>Hydrophilic heads and hydrophobic tails (A)</p> Signup and view all the answers

How does temperature affect the rate of diffusion across a membrane?

<p>Higher temperatures increase the rate of diffusion. (A)</p> Signup and view all the answers

Why are polar molecules unable to pass through the hydrophobic interior of the cell membrane?

<p>They are not soluble in fats. (C)</p> Signup and view all the answers

What is the term used to describe the flexible structure of the plasma membrane, which allows components to float and move laterally?

<p>Fluid mosaic model (A)</p> Signup and view all the answers

What determines whether a molecule can pass through the lipid bilayer of the cell membrane?

<p>Size and charge (A)</p> Signup and view all the answers

What occurs in a hypotonic solution?

<p>Solute concentration inside the cell is higher than outside. (A), Water enters the cell potentially causing lysis. (B)</p> Signup and view all the answers

How does facilitated diffusion differ from simple diffusion?

<p>Facilitated diffusion does not require energy and needs transport proteins. (B), Facilitated diffusion only occurs with polar molecules. (D)</p> Signup and view all the answers

Which process requires cellular energy (ATP) to occur?

<p>Active transport of sodium ions using the Na+-K+ pump. (C)</p> Signup and view all the answers

Which statement accurately describes a hypertonic solution?

<p>Cell loses water, potentially leading to plasmolysis. (A)</p> Signup and view all the answers

What describes active transport most accurately?

<p>Utilizes cellular energy to transport substances against their concentration gradient. (B)</p> Signup and view all the answers

In which process do vesicles fuse with the cell membrane to release their contents?

<p>Exocytosis. (D)</p> Signup and view all the answers

What is the main mechanism for the passage of small, non-polar molecules through the cell membrane?

<p>Simple diffusion directly across the lipid bilayer. (A)</p> Signup and view all the answers

What is the result of active transport in neurons?

<p>Establishes a sodium concentration gradient necessary for electrical signaling. (C)</p> Signup and view all the answers

Flashcards

What is the cell membrane?

The cell membrane is a thin, flexible barrier that surrounds every cell, regulating what enters and leaves the cell.

What is the cell membrane made of?

The cell membrane is composed of a phospholipid bilayer, a double layer of phospholipid molecules with hydrophilic heads (water-loving) and hydrophobic tails (water-fearing).

What are the types of proteins in the cell membrane?

Integral proteins span the entire membrane, while peripheral proteins are attached to one side.

Why is the cell membrane called a 'fluid mosaic'?

The cell membrane is called a "fluid mosaic" because its components move freely within the membrane, like a mosaic made of different pieces.

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What is diffusion?

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, across a membrane, without requiring energy.

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What is a semi-permeable membrane?

A semi-permeable membrane allows only certain molecules to pass through, like a filter with specific sized holes.

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What is osmosis?

Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.

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What determines if a molecule can cross the cell membrane?

The size and charge of a molecule determine whether it can pass through the cell membrane. Small, non-polar molecules pass easily, while large, polar molecules require help from proteins.

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Osmosis

Movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.

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Hypotonic Solution

A solution where the concentration of solutes outside the cell is lower than inside the cell. Water moves into the cell.

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Hypertonic Solution

A solution where the concentration of solutes outside the cell is higher than inside the cell. Water moves out of the cell.

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Isotonic Solution

A solution where the concentration of solutes outside the cell is equal to that inside the cell. There is no net water movement.

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Passive Transport

The movement of a substance across a cell membrane without the use of the cell's energy. It moves from high concentration to low concentration.

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Simple Diffusion

The passage of small, non-polar molecules directly across the cell membrane.

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Facilitated Diffusion

The movement of materials across a cell membrane with the help of a transport protein. It also moves from high concentration to low concentration.

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Active Transport

The movement of material across a cell membrane using cellular energy (ATP). It moves from an area of lower concentration to an area of higher concentration.

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Study Notes

Cell Membrane Structure and Function

  • The cell membrane regulates what enters and leaves the cell
  • It provides some protection and support
  • Also known as a phospholipid bilayer
  • Contains phospholipids with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails
  • Also has integral (spanning the entire bilayer) and peripheral proteins
  • Cells exist in an aqueous environment (mostly water)
  • The plasma membrane is often described as a "fluid mosaic" due to its flexible, dynamic structure with many components
  • Molecules move laterally (side-to-side) within the membrane

Diffusion

  • Movement of molecules across a membrane from an area of high concentration to an area of low concentration
  • Does not require energy input
  • Rate affected by temperature, molecule size, and concentration gradient

Selectively Permeable Membrane

  • Allows only certain molecules to pass through
  • Critical for cell homeostasis and maintaining internal environment

Factors Affecting Membrane Permeability

  • Size: Small molecules pass more easily
  • Charge: Nonpolar molecules pass more readily; polar molecules (and ions) do not pass easily through the hydrophobic interior.

Osmosis

  • Movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration
  • Hypotonic solution: Solute concentration outside the cell is lower than inside, water moves into the cell (cell may burst - lysis)
  • Isotonic solution: Solute concentration outside the cell is equal to inside, no net water movement
  • Hypertonic solution: Solute concentration outside the cell is higher than inside, water moves out of the cell (cell may shrivel - plasmolysis)

Passive Transport

  • Movement of substances across a membrane without energy expenditure
  • Simple diffusion: Small nonpolar molecules (e.g., oxygen, carbon dioxide) pass directly through the membrane
  • Facilitated diffusion: Movement of molecules through a transport protein (e.g., channel or carrier proteins). Does not require energy input, but uses proteins to facilitate movement from high to low concentration.

Active Transport

  • Movement of substances across a membrane using energy expenditure (ATP)
  • Moves substances against their concentration gradient (from low to high concentration)
  • Example: Sodium-potassium pump (Na+-K+ pump) in neurons

Bulk Transport

  • Exocytosis: Movement of materials out of the cell (e.g., release of neurotransmitters)
  • Endocytosis: Movement of materials into the cell. Includes phagocytosis ("cellular eating", e.g., immune cells ingesting bacteria) and pinocytosis ("cellular drinking").

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Movement Through the Membrane 3 PDF Biology Notes

Description

This quiz explores the structure and function of cell membranes, including their composition and the principles of diffusion. Topics covered include selectively permeable membranes and the fluid mosaic model. Test your understanding of how cell membranes regulate the movement of molecules.

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