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Questions and Answers
Which type of molecules readily diffuse through the cell membrane's lipid bilayer without the aid of transport proteins?
Which type of molecules readily diffuse through the cell membrane's lipid bilayer without the aid of transport proteins?
- Small, nonpolar molecules like oxygen (correct)
- Proteins and amino acids
- Large, polar molecules like glucose
- Charged ions such as sodium and potassium
Why do large, polar molecules need transport proteins to cross the cell membrane?
Why do large, polar molecules need transport proteins to cross the cell membrane?
- They are actively pumped out of the cell by the membrane.
- They are too large to fit through the pores in the membrane.
- They are repelled by the charged phosphate heads of the lipid bilayer.
- They cannot pass through the hydrophobic lipid bilayer. (correct)
Ions cross cell membranes through...
Ions cross cell membranes through...
- Simple diffusion directly across the lipid bilayer.
- Active transport pumps using energy to move against the gradient.
- Both B and C (correct)
- Facilitated diffusion via ion channels or transport proteins.
Which of the following transport mechanisms requires the cell to expend energy?
Which of the following transport mechanisms requires the cell to expend energy?
How does osmosis facilitate the movement of water across a cell membrane?
How does osmosis facilitate the movement of water across a cell membrane?
The sodium-potassium pump functions by:
The sodium-potassium pump functions by:
What is the key difference between exocytosis and endocytosis?
What is the key difference between exocytosis and endocytosis?
The membrane potential is primarily caused by:
The membrane potential is primarily caused by:
During depolarization, what typically happens to the membrane potential?
During depolarization, what typically happens to the membrane potential?
What ionic movement primarily drives the process of repolarization following an action potential?
What ionic movement primarily drives the process of repolarization following an action potential?
Flashcards
Substances diffusing freely
Substances diffusing freely
Small, nonpolar molecules like oxygen and carbon dioxide, and fat-soluble molecules, can pass directly through the cell membrane without help. Some small polar molecules like water and urea can also diffuse to a limited extent.
Substances double lipid layer blocks
Substances double lipid layer blocks
Large molecules such as glucose, proteins, charged ions, and polar molecules have difficulty passing because they cannot cross the hydrophobic lipid layer without transport proteins.
What are ion channels?
What are ion channels?
Proteins in the cell membrane that form specific channels for ions; they can be open all the time or regulated by signals.
Membrane Transport Protein
Membrane Transport Protein
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Passive transport
Passive transport
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What is osmosis?
What is osmosis?
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Active transport
Active transport
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Exocytosis vs Endocytosis
Exocytosis vs Endocytosis
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Membrane potential
Membrane potential
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Depolarization & Repolarization
Depolarization & Repolarization
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Study Notes
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Small nonpolar molecules (oxygen, carbon dioxide) and fat-soluble molecules can freely diffuse through the double lipid layer of the cell membrane.
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Some small polar substances such as water and urea can diffuse to a limited extent.
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Large molecules like glucose and proteins, charged ions and polar molecules, are hindered by the double lipid layer, as they cannot cross the hydrophobic lipid layer without transport proteins.
Ion Channels
- Ion channels are proteins in the cell membrane.
- They form specific channels for ions.
- They can either be open all the time or be regulated by signals.
Membrane Transport Protein
- Membrane transport proteins assist substances across the membrane.
- These include ion channels, carrier proteins, and pumps.
- Pumps transport molecules actively or passively.
Passive Membrane Transport
- Passive membrane transport is the transport of substances without energy use.
- It includes simple diffusion, facilitated diffusion, and osmosis.
- Simple diffusion occurs when substances move directly across the membrane.
- Facilitated diffusion occurs when substances are transported through specific transport proteins.
- Osmosis is diffusion where water moves through a semipermeable membrane to even out concentration differences.
Water Transport
- Water is transported through the cell membrane by osmosis.
Active Transport
- Active transport happens when the concentration of a particular substance needs to be higher inside the cell than outside.
- For example, the Na+/K+ pump pumps sodium out and potassium into the cell.
Exocytosis and Endocytosis
- Exocytosis is the mechanism for uptake into the cell.
- Endocytosis is the mechanism for secretion out of the cell.
Membrane Potential
- Membrane potential is the voltage difference between the inside and outside of the cell membrane.
- It is created by unequal ion distribution.
Depolarization and Repolarization
- Depolarization occurs when the membrane potential becomes more positive, often as Na+ flows into the cell.
- Repolarization occurs when the membrane potential returns to resting levels as K+ flows out therefore maintaining the balance of electrolytes.
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