40 Questions
What is the primary function of the hydrophilic regions of proteins in the membrane?
To expose themselves to water
Which of the following is NOT a function of the cell membrane?
Regulating cell growth
What is the average frequency of a phospholipid molecule flip-flopping across the membrane?
Once per month
What is the term for the ability of the cell membrane to allow certain molecules to pass through while keeping others out?
Selective permeability
What is the main component of the cell membrane that helps to maintain its fluidity?
Phospholipids
What is the primary function of the plasma membrane?
To separate the living cell from its surroundings
What is the term for the movement of proteins and lipids within the membrane?
Lateral movement
What is the major role of the cell membrane in maintaining homeostasis?
All of the above
What is the term used to describe the ability of the plasma membrane to allow some substances to cross it more easily than others?
Selective permeability
What is the most abundant lipid in the plasma membrane?
Phospholipid
What is the model that describes the structure of the cell membrane?
Fluid Mosaic Model
What is the term used to describe the structure of phospholipids?
Amphipathic
What is the name of the model that describes the plasma membrane as a fluid structure with a mosaic of proteins embedded in it?
Fluid mosaic model
Who proposed the sandwich model of the plasma membrane?
Hugh Davson and James Danielli
What is the main criticism of the sandwich model of the plasma membrane?
It does not account for the placement of membrane proteins
In a hypotonic solution, what is the concentration of solutes compared to inside the cell?
Lower
What is the function of the integral proteins in the plasma membrane?
To regulate the movement of substances into and out of the cell
What happens to a cell in a hypotonic solution?
It swells and bursts open
What is the direction of water movement in a hypertonic solution?
From inside the cell to the solution
What is the result of a cell in an isotonic solution?
It stays the same
What is the main reason for water movement in osmosis?
Solute concentration difference
What is the term for the bursting of a cell due to excessive water uptake?
Cytolysis
What happens to the cell membrane in a hypertonic solution?
It becomes less permeable
What is the main difference between a hypotonic and a hypertonic solution?
Solute concentration
What is the primary characteristic of passive transport?
It does not use energy from the cell.
What is the net direction of solute movement in diffusion through a membrane?
From an area of high concentration to an area of low concentration.
What is the purpose of proteins in facilitated diffusion?
To carry polar molecules or ions across the membrane.
What is the state of the molecules in a system at equilibrium?
They are evenly spaced, but still moving randomly.
What is the primary difference between simple diffusion and facilitated diffusion?
The use of proteins to facilitate molecule movement.
What is the result of diffusion continuing until all molecules are evenly spaced?
The molecules will continue to move, but will be evenly spaced.
What is the characteristic of molecules that allows them to move from an area of high concentration to an area of low concentration?
Their kinetic energy.
What is the term for the movement of molecules from an area of high concentration to an area of low concentration?
Diffusion.
What is the primary driving force for osmosis?
The concentration gradient of water across a membrane
In a hypotonic solution, what happens to the cell?
The cell will swell due to water gain
What is the term for a solution that has the same concentration of solutes as the cell?
Isotonic solution
What happens to the cell in a hypertonic solution?
The cell will shrink due to water loss
What is the role of solutes in osmosis?
Solutes attract water molecules, causing them to move towards areas of high solute concentration
What is the term for the movement of water across a selectively permeable membrane?
Osmosis
What is the result of a cell in an isotonic solution?
The cell will remain the same size
What is the term for the state of equal water movement in both directions across a membrane?
Dynamic equilibrium
Study Notes
Cell Equilibrium and Osmosis
- In a state of equilibrium, water flows in both directions across the cell membrane, and solute and water concentrations are equal inside and outside the cell.
- Hypotonic solution: has a lower concentration of solutes and a higher concentration of water than inside the cell, resulting in water moving into the cell, causing it to swell and potentially burst (cytolysis).
- Hypertonic solution: has a higher concentration of solutes and a lower concentration of water than inside the cell, resulting in water moving out of the cell, causing it to shrink (plasmolysis).
Cell Membrane Structure and Function
- The plasma membrane is a selective barrier between the cell and its surroundings, controlling the movement of substances in and out of the cell.
- Phospholipids are the most abundant lipid in the plasma membrane, and are amphipathic molecules with hydrophobic and hydrophilic regions.
- The fluid mosaic model describes the plasma membrane as a fluid structure with embedded proteins, allowing for selective permeability.
Functions of Membranes
- Protect the cell
- Control the movement of substances in and out of the cell
- Maintain ion concentrations and homeostasis
- Selectively permeable, allowing some molecules to pass through while keeping others out
Phospholipid Bilayer and Fluidity
- Phospholipids in the plasma membrane can move laterally within the bilayer
- Rarely do molecules flip-flop transversely across the membrane
- The fluidity of the membrane allows for the lateral movement of lipids and proteins
Transport Across Membranes
Passive Transport
- Diffusion: the random movement of particles from an area of high concentration to an area of low concentration
- Osmosis: the diffusion of water across a selectively permeable membrane, moving from high to low water concentration
- Facilitated diffusion: the use of proteins to carry polar molecules or ions across the membrane
Active Transport
- Requires energy from the cell
- Examples include protein pumps, endocytosis, and exocytosis
This quiz covers the concept of equilibrium in cells, and the movement of water in and out of cells in different solutions. It includes isotonic, hypotonic, and hypertonic solutions.
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