1. Introduction

Membranes are selectively permeable. This means that membranes allow the cell to “select” what can pass through the membrane. This, in turn, allows the cell to determine what can enter or leave the cell, and what can’t.

In what follows, we’ll look at a few ways that things make their way across the cell membrane.

2. Diffusion

Diffusion is the tendency of molecules to spread out from where they’re more concentrated to where they’re less concentrated.

01_diffusion
Diffusion: the molecules (represented in red) are initially highly concentrated in one area. Through diffusion, they spread out until they’re evenly distributed.

 

  • Put a drop of ink into a cup of water. Over time, you’ll see the ink slowly spread out until it’s uniformly distributed throughout the cup. That’s diffusion.

    Blausen_0315_Diffusion
    Diffusion (by Blausen via Wikipedia)
  • A fragrance (or bad odor) released in one part of a room spreads throughout the entire room. That’s diffusion.
22_concentration-gradient-from-cuny-brooklyn
From CUNY, Brooklyn

A key idea related to diffusion is the idea of a concentration gradient. A gradient is a slope. In the same way that a ball will roll down a slope, molecules in a fluid will move down a concentration gradient, spreading out from higher concentration to lower concentration. So when you think of diffusion, just imagine that the diffusing molecules are flowing down a slope, moving from where they’re more concentrated (on the left side of this diagram) to less concentrated (on the right side). The -ΔG indicates that this process is spontaneous . You don’t have to add any outside energy to this system to make diffusion happen (and we’ll learn more about spontaneity in an upcoming module).

image004
Animation from leavingbio.net. Permission pending.

Both simple diffusion and facilitated diffusion are forms of passive transport. In passive transport:

  • The cell doesn’t have to expend any energy to make these processes happen.
  • The energy is in the kinetic energy of the molecules themselves.

You can see diffusion down a concentration gradient in the animation on the right: the molecules, represented by cubes, are flowing down their concentration gradient as they diffuse from where they’re in higher concentration (below the membrane) to where they’re in lower concentration (above the membrane)

In cells, diffusion can be of two types: simple diffusion or facilitated diffusion.

Simple Diffusion Facilitated diffusion
03_simple diffusion 04_facilitated diffusion
Simple diffusion is when a molecule diffuses right through the phospholipid bilayer. Non-polar molecules (such as steroid hormones) can do this. So can gases like carbon dioxide and oxygen. Facilitated diffusion is diffusion through a protein channel. Ions and polar molecules pass through membranes in this way. These channels are specific. For example, a channel that lets a sodium ion through won’t let a potassium ion through.
(image source: premedHQ.com, permission pending)

 

3. Active Transport

05_active transport
active transport, via premedHQ.com

Cells, at times, need to move substances from lower concentration to higher concentration. Unlike diffusion, which occurs spontaneously, this requires the cell to expend energy as it pumps materials up a concentration gradient.

This type of energy-requiring movement of materials from lower to higher concentration is called active transport.

In diagrams like this one, look for two clues that tell you that it’s about active transport. First of all, follow the arrow. If the molecules are moving from where there are very few of them to where there’s a lot of them, it’s active transport. Also, if you see “ATP” going into a pump or protein channel, you know that the cell is expending its energy (in the form of ATP) to do the work of pumping molecules up a concentration gradient.

4. Endocytosis

In endocytosis, the membrane pinches in. This creates a pocket that surrounds material outside the membrane. Like active transport, this requires cell energy.

There are three types of endocytosis:

Pinocytosis Phagocytosis Receptor Mediated Endocytosis
07_pinocytosis 08_phagocytosis 09_receptor mediated endocytosis
In pinocytosis, the membrane pinches in (1). The pinching in continues (2) until a vesicle forms (3), surrounding some of the extracellular fluid and whatever was inside it.Think of pinocytosis as the cell taking a small “sip” of the material outside the membrane. During phagocytosis, the cell uses its membrane to surround a particle (or even another cell). The membrane pinches in (1)  to form a vesicle which enters the cytoplasm (2).Phagocytosis is used by white blood cells in the immune response to swallow invaders. Single celled organisms like amoebas use phagocytosis to eat. In receptor mediated endocytosis, a piece of the membrane pinches in response to some molecule that binds with a receptor embedded in the membrane.
Images from www.boundless.com. Used under Creative Commons 4.0 license

5. Exocytosis

10_exocytosis
Exocytosis, by Juancoronado1974 via wikimedia commons

Exocytosis is the opposite of endocytosis. A vesicle filled with a molecule that the cell needs to release (1) fuses with the cell membrane (2). As the membrane of the vesicle fuses with the membrane of the cell, the vesicle’s contents are released into the fluid outside the cell.

06_plasma-cells-secreting-antibodies
Exocytosis in action: B cells secreting antibodies as part of the immune response

Exocytosis is how cells, such as B cells (a type of white blood cell), export the proteins they’ve manufactured. For more detail about the cellular machinery involved, take a look at my tutorial on the endomembrane system.

6. Membrane Transport Flashcards

[qdeck random = “true;” style=”width: 528px; border: 2px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Membrane Transport Flashcards (M8)”]

[h] Flashcards: Cell Membrane Transport

[i] If you haven’t used a set of flashcards on sciencemusicvideos before, here’s what you need to know.

  • Click ‘Check Answer’ to see the answer to each card.
  • If you know it, click ‘Got it.”
  • If you don’t know it as well as you’d like, click ‘Need more practice,’ and that card will go to the bottom of the deck so you can practice it again.
  • ‘Shuffle’ lets you shuffle the deck.

[!] Card 1+++++++++++++++++++++++++++++++++++[/!]

[q]The boundary that surrounds the cytoplasm of the cell is the ______ ______________

[textentry]

[a]The boundary that surrounds the cytoplasm of the cell is the cell membrane. 

[!] Card 2+++++++++++++++++++++++++++++++++++[/!]

[q]Membranes allow certain molecules to pass through but not others. In other words, membranes are ________-_______________.

[textentry]

[a] Membranes allow certain molecules to pass through but not others. In other words, membranes are selectively-permeable. (note that semi-permeable means just about the same thing).

[!] Card 3+++++++++++++++++++++[/!]

[q]_____________ is the movement of molecules from where they’re more concentrated to where they’re less concentrated.

[textentry]

[a]Diffusion is the movement of molecules from where they’re more concentrated to where they’re less concentrated.

[!] Card 4+++++++++++++++++++++[/!]

[q]One way to talk about diffusion is to say the molecules in a fluid will move down a _____________ ____________.

[textentry]

[a]One way to talk about diffusion is to say the molecules in a fluid will move down a concentration gradient.

[!] Card 5+++++++++++++++++++++[/!]

[q]When substances diffuse directly through a membrane’s phospholipid bilayer, the process is called _____________ ____________.

[textentry]

[a]When substances diffuse directly through a membrane’s phospholipid bilayer, the process is called simple diffusion.

[!] Card 6+++++++++++++++++++++[/!]

[q]When substances diffuse into a cell by passing through a protein channel, the process is called _____________ ____________.

[textentry]

[a]When substances diffuse into a cell by passing through a protein channel, the process is called facilitated diffusion.

[!] Card 7+++++++++++++++++++++[/!]

[q]When cells expend energy to move a substance from lower concentration to higher concentration, this process is known as _____________ ____________.

[textentry]

[a]When cells expend energy to move a substance from lower concentration to higher concentration, this process is known as active transport.

[!] Card 8+++++++++++++++++++++[/!]

[q]A vesicle filled with some substance fuses with the membrane, releasing that substance outside the cell. This process is called ____________.

[textentry]

[a]A vesicle filled with some substance fuses with the membrane, releasing that substance outside the cell. This process is called exocytosis.

[!] Card 9+++++++++++++++++++++[/!]

[q]The cell membrane pinches in, taking in something outside of the cell and enclosing it within a vesicle. This process is called ____________.

[textentry]

[a]The cell membrane pinches in, taking in something outside of the cell and enclosing it within a vesicle. This process is called endocytosis.

[!] Card 10+++++++++++++++++++++[/!]

[q]The kind of endocytosis in which a small portion of the membrane pinches in, allowing the cell to “take a sip” of the fluid outside of the cell, is called _________

[textentry]

[a]The kind of endocytosis in which a small portion of the membrane pinches in, allowing the cell to “take a sip” of the fluid outside of the cell, is called pinocytosis.

[!] Card 11+++++++++++++++++++++[/!]

[q]The kind of endocytosis in which a large portion of the membrane surrounds a food particle (or even another cell), and then brings that particle into the cell is called _________

[textentry]

[a]The kind of endocytosis in which a large portion of the membrane surrounds a food particle (or even another cell), and then brings that particle into the cell is called phagocytosis.

[!] Card 12+++++++++++++++++++++[/!]

[q]The kind of endocytosis in which the membrane only pinches in when a molecule outside the cell binds with a receptor molecule in the membrane is called ____________.

[textentry]

[a]The kind of endocytosis in which the membrane only pinches in when a molecule outside the cell binds with a receptor molecule in the membrane is called receptor-mediated endocytosis.

[!] Card 13+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is [textentry]

[a]The best name for the process shown in this diagram is diffusion. 

[!] Card 14+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is [textentry]

[a]The best name for the process shown in this diagram is simple diffusion.

[!] Card 15+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is [textentry]

[a]The best name for the process shown in this diagram is facilitated diffusion.

[!] Card 16+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is [textentry]

[a]The best name for the process shown in this diagram is active transport.

[!] Card 17+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is [textentry]

[a]The best name for the process shown in this diagram is exocytosis.

[!] Card 18+++++++++++++++++++++[/!]

[q]The best name for the process shown at “A,” “B,” and “C” in this diagram is [textentry]

[a]The best name for the process shown in this diagram is endocytosis.

[!] Card 19+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is [textentry]

[a]The specific type of endocytosis shown in this diagram is pinocytosis.

[!] Card 20+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is [textentry]

[a]The specific type of endocytosis shown in this diagram is phagocytosis

[!] Card 21+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is [textentry]

[a]The specific type of endocytosis shown in this diagram is receptor-mediated endocytosis

[x]

If you want more practice, please press the restart button below. Otherwise, follow the links below.
[restart]
[/qdeck]

7. Quiz: Cell Membrane Transport

[qwiz random = “true;” style = “border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Membrane Transport Quiz (M8)”]

[h] Quiz: Cell Membrane Transport
[i]This activity tests you on your understanding of membranes and transport. Here’s how the quiz works:

  • Each question is multiple choice, but the entire quiz is like a series of flashcards.
  • If you get the question right, it comes off the deck.
  • If you get the question wrong, it goes to the bottom of the deck, so you can try it again.

[!] Question 1++++++++++++++[/!]

[q labels = “top”]

 

 

 

[l]lower concentration

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]higher concentration

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[!] Question 2++++++++++++++[/!]

[q labels = “top”]

[l]ink molecules in high concentration

[fx] No.  Please try again.

[f*] Excellent!

[l]ink molecules spread out

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[!] Question 3++++++++++++++[/!]

[q labels = “top”]

[l]simple diffusion

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]active transport

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]facilitated diffusion

[fx] No.  Please try again.

[f*] Great!

[!] Question 4++++++++++++++[/!]

[q labels = “top”]

[l]active transport

[fx] No.  Please try again.

[f*] Great!

[l]simple diffusion

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]facilitated diffusion

[fx] No.  Please try again.

[f*] Excellent!

[!] Question 5++++++++++++++[/!]

[q labels = “top”]

____________________________ _________________________

[l]exocytosis

[fx] No.  Please try again.

[f*] Good!

[l]endocytosis

[fx] No.  Please try again.

[f*] Great!

[!] Question 6++++++++++++++[/!]

[q labels = “top”]

[l]pinocytosis

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]phagocytosis

[fx] No.  Please try again.

[f*] Great!

[l]receptor-mediated endocytosis

[fx] No.  Please try again.

[f*] Good!

[!] Question 7++++++++++++++[/!]

[q labels = “top”]

[l]molecules released from the cell

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]vesicle

[fx] No.  Please try again.

[f*] Great!

[l]molecules inside vesicle

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[!] Question 1++++++++++++++[/!]

[q] When a cube of sugar is placed in a beaker of water, sugar molecules spread through the beaker by

[c]endocytosis

[c*]diffusion

[c]facilitated diffusion

[c]active transport

[f]No. Endocytosis involves a membrane pinching in to bring outside material inside the cell. The spreading out of these sugar molecules is a an example of substances moving from higher concentration to lower concentration. What’s that kind of movement called?

[f]Excellent. This is an example of diffusion.

[f]No. Facilitated diffusion involves molecules moving across a membrane through a protein channel. Drop the “facilitated” part, and you’ll have the answer.

[f]No. Active transport involves cells using energy to pump materials from lower to higher concentration. The spreading out of these sugar molecules is a an example of substances moving from higher concentration to lower concentration. What’s that kind of movement called?

[!] Question 2++++++++++++++[/!]

[q] Diffusion is a term for the movement of molecules from

[c] an area of low concentration to an area of high concentration.

[c] outside of the cell to inside the cell

[c*] an area of high concentration to an area of low concentration.

[c] a nucleus to the mitochondria.

[f]No. Look at this diagram, and see if you can come up with the right explanation.

01_diffusion
This is diffusion. Notice how the molecules are “bunched up” on the left and spread out on the right. Which description fits this image?

[f]Not necessarily. Diffusion might move materials into a cell, but it can also move materials out of a cell. Look at this image and see if you can figure out the right answer.

01_diffusion
This is diffusion. Notice how the molecules are “bunched up” on the left and spread out on the right. Which description fits this image?

[f]Exactly. Diffusion is the movement of a substance from high to low concentration.

[f]No. Diffusion is not about movement from any one specific place to another. It’s much more general. Look at this image and see if you can figure out the right answer.

01_diffusion
This is diffusion. Notice how the molecules are “bunched up” on the left and spread out on the right. Which description fits this image?

[!] Question 3++++++++++++++[/!]

[q] Diffusion is about the random movement of

[c] cells

[c] organisms

[c] cell membranes

[c*] molecules

[f]No. Diffusion is about random movement on a very small level. Next time, choose a level much smaller than cells.

[f]No. Diffusion is about random movement on a very small level. Next time, choose a level much smaller than organisms.

[f]No. Diffusion is about random movement on a very small level. Next time, choose a level much smaller than even a cell membrane.

[f]Yes. Diffusion is about the random movement of molecules.

[!] Question 4++++++++++++++[/!]

[q] For diffusion to occur, there must be:

[c] a membrane

[c*] a gradient

[c] water

[c] ATP

[f]No. Diffusion does not require a membrane. It can occur in a cup of water, or a room. In terms of the molecules that are diffusing, what does diffusion require?

[f]Yes. Diffusion requires a gradient–a difference in concentration levels.

[f]No. Diffusion can occur in water, and water can diffuse, but water is not required for diffusion. In terms of the molecules that are diffusing, what does diffusion require?

[f]No. ATP is the cell’s immediate energy source, and cell energy is not required for diffusion. In terms of this question, what does diffusion require.

[!] Question 5++++++++++++++[/!]

[q] Cell membrane channels are made of

[c] phospholipids.

[c] carbohydrates.

[c] DNA.

[c] RNA.

[c*] proteins.

[f]No. Phospholipids make up the bilayer, which is the key structural part of the membrane. The channels are made of something else.

[f]No. Carbohydrates are positioned on the outer surface of the membrane, providing for cell-recognition. The channels are made of something else.

[f]No. DNA is not part of the membrane. What could these channels be made of?

[f]No. RNA is not part of the membrane. What could these channels be made of?

[f]Excellent! Membrane channels are made of protein

[!] Question 6++++++++++++++[/!]

[q] The cell membrane lets only some things in and out. The best way to describe that is to say that the membrane is

[c*] semi-permeable

[c] impenetrable.

[c] permeable

[c] impermeable

[f] That’s right. Membranes let materials pass in and out of the cell, but they do so in a very selective way. This makes the membrane semi-permeable. Note that “selectively permeable” means just about the same thing.

[f] No. ‘Impenetrable’ means that nothing can pass through. If membranes were impenetrable, they wouldn’t be able to let food and needed substances into the cell, and to let wastes out. Next time, select a choice that reflects the membrane’s ability to select what substances will enter the cell, and what substances will leave.

[f] No. Membranes are permeable to some substances, but not to everything. If membranes were freely permeable, they wouldn’t be able to keep needed substances in the cell, let unwanted wastes out, and and keep unwanted substances from entering. Next time, select a choice that reflects the membrane’s ability to select what substances will enter the cell, and what substances will leave.

[f] No. ‘impermeable’ means that nothing can pass through. If membranes were impermeable, they wouldn’t be able to let food and needed substances into the cell, and to let wastes out. Next time, select a choice that reflects the membrane’s ability to select what substances will enter the cell, and what substances will leave.

[!] Question 7++++++++++++++[/!]

[q]When molecules diffuse, they flow

[c]up their concentration gradient

[c*]down their concentration gradient

[f]No. Flowing up a concentration gradient is what happens in active transport.

[f]Yes. During diffusion, molecules flow down their concentration gradient.

[!] Question 8++++++++++++++[/!]

[q] True or false: In active transport, a cell uses the kinetic energy in molecules and lets them flow down their concentration gradient.

[c] TRUE

[c*] FALSE

[f]No. In active transport, a cell is “fighting” diffusion, which is driven by molecules’ kinetic energy.  What that means is that cells need to use their own energy to move a substance up a concentration gradient.

[f]Correct. This statement is false because in active transport, the cell has to use its own energy.

[!] Question 9++++++++++++++[/!]

[q] If you were a molecule, then facilitated diffusion would be most like

[c] Being carried across a stream.

[c] Walking across a room.

[c*] Coasting across a bridge on your bike.

[c] Riding a ski lift.

[f]No. In facilitated diffusion, the cell lets a molecule pass through its membrane by providing a channel. From a molecule’s perspective, being carried across a stream seems more like active transport, since the carrier has to expend energy. Which choice involves a passageway that’s facilitating your crossing?

[f]No. In facilitated diffusion, the cell lets a molecule pass through its membrane by providing a channel. From a molecule’s perspective, walking across a room seems like diffusion (moving) but not facilitated diffusion (moving across a barrier). Which choice involves a passageway that’s facilitating your crossing?

[f]Yes! This question has been driving students crazy for at least 20 years, so you should be happy that you got it right. In facilitated diffusion, the cell lets a molecule pass through its membrane by providing a channel. If you coast across a bridge on your bike, you’re using your  kinetic energy to cross a barrier, using a passageway (the bridge) that facilitates your crossing.

[f]No. In facilitated diffusion, the cell lets a molecule pass through its membrane by providing a channel. From a molecule’s perspective, riding a ski lift seems more like active transport, since the carrier (the ski lift) has to expend energy. Which choice involves a passageway that’s facilitating your crossing?

[!] Question 10++++++++++++++[/!]

[q] Molecules which diffuse through a cell membrane by facilitated diffusion:

[c] Require an expenditure of cell energy

[c] Move from an area of low concentration to an area of high concentration

[c] are able to flow directly through the cell’s phospholipid bilayer.

[c*] Require the aid of transport proteins

[f]No. Like all forms of diffusion, facilitated diffusion involves the kinetic energy in the diffusing molecules. No extra energy expenditure by the cell is involved.

[f]No. Like all forms of diffusion, facilitated diffusion involves movement of materials from higher to lower concentration.

[f]No. To facilitate means to assist. The point of facilitated diffusion is that it involves molecules that can’t diffuse through the phospholipid bilayer, and need some kind of assistance to make their way through.

[f]Fabulous! Molecules that pass through the membrane by facilitated diffusion are doing so with the assistance of a protein channel or transport protein that facilitates their passage.

[!] Question 11++++++++++++++[/!]

[q] A molecule that can diffuse freely through a phospholipid bilayer is probably

[c] polar

[c] Positively charged

[c*] non-polar

[c] a large protein

[f]No. Polar molecules can’t pass through the hydrophobic, non-polar part of the phospholipid bilayer. Just remember that oil (non-polar) and water (polar) don’t mix.

[f]No. Charged molecules can’t pass through the hydrophobic, non-polar part of the phospholipid bilayer.

[f]Yes. Non-polar molecules (fats, oils, steroid hormones) can freely pass through a phospholipid bilayer.

[f]No. Large proteins can’t pass directly through a phospholipid bilayer. If they entered a cell at all, it would have to be through a transport protein.

[!] Question 12++++++++++++++[/!]

[q] Which of the following best describes what occurs during facilitated diffusion?

[c] In facilitated diffusion, substances diffuse through the phospholid bilayer as they enter or leave the cell. No cell energy is required.

[c] In facilitated diffusion, the cell uses its own energy to pump substances from lower concentration to higher concentration.

[c*] In facilitated diffusion, molecules diffuse into the cell through protein channels. No cell energy is required.

[c] In facilitated diffusion, the cell uses its own energy to pump materials through the phospholipid bilayer.

[f] No. In facilitated diffusion, the cell provides  protein channels  or carrier proteins to allow substances to diffuse  into or out of the cell. No energy is required on the cell’s part.

[f] No. In facilitated diffusion, the cell provides  protein channels or uses carrier proteins to allow substances to diffuse  into or out of the cell. No energy is required on the cell’s part. Instead, the energy is provided by the kinetic energy of the diffusing molecules.

[f] Excellent! Facilitated diffusion is still a form of diffusion, but rather than simply diffusing through the lipid bilayer, the passage of molecules is facilitated (made easier) through protein channels or carrier proteins that let specific molecules pass through the membrane.

[f] No. In facilitated diffusion, the cell provides  protein channels or carrier proteins to allow substances to diffuse  into or out of the cell. No energy is required on the cell’s part. Instead, the energy is provided by the kinetic energy of the diffusing molecules.

[!] Question 13++++++++++++++[/!]

[q]When a substance created inside the cell is exported outside the cell, it leaves the cell through

[c]endocytosis

[c*]exocytosis

[c]phagocytosis

[f]No. Endocytosis means “into the cell.” What the term for “leaving the cell?”

[f]Yes. When a substance created inside the cell is exported outside the cell, it leaves the cell through exocytosis.

[f]No. Phagocytosis involves cells engulfing foreign objects and bringing them into the cell. Here, you’re looking for a term that means “leaving the cell.”

[!] Question 14++++++++++++++[/!]

[q] Passive transport is defined as the movement of any substance across a membrane without the use of

[c*] cell energy

[c] membrane channels

[c] diffusion

[f]Correct. Passive transport is defined as the movement of any substance across a membrane without the use of cell energy.

[f]No. Passive transport includes diffusion through membrane channels. Consider the fact that “passive transport” is the opposite of “active transport,” and you’ll have your answer.

[f]No. The term passive transport has a lot in common with the term diffusion. Consider the fact that “passive transport” is the opposite of “active transport,” and you’ll have your answer.

[!] Question 15++++++++++++++[/!]

[q] Which of the following terms describes the process by which the cell membrane moves substances from lower concentration to higher concentration.

[c] facilitated diffusion

[c] osmosis

[c] diffusion

[c*] active transport.

[f] No. In facilitated diffusion, molecules are still diffusing from higher to lower concentration. However, rather than simply diffusing through the lipid bilayer, they pass through a protein channel. Next time, choose a process that reflects the need for cells to actively pump materials from lower to higher concentration.

[f] No. Osmosis is the diffusion of water. Like all diffusion processes, water moves from where it is more concentrated to where it is less concentrated.

[f] No. Diffusion is the movement of substances from higher concentration to lower concentration.

[f] Correct! Active transport involves cells having to pump materials from lower to higher concentration, against the direction of diffusion.

[!]Question 16 REVISED+++++++++++[/!]

[q]In nerve cells, the amount of positively charged potassium ions inside the cell is much higher than the amount outside the cell. In order for the cell to take up more potassium, which process is required?

[c*]active transport

[c]passive transport

[c]facilitated diffusion

[c]simple diffusion

[f]Yes. The cell is going to have to expend its own energy to move the potassium from lower concentration, outside the cell, to higher concentration inside the cell.

[f]No. Passive transport is essentially the same as diffusion. It results in equal concentration of substances across membranes. What process works against diffusion?

[f]No. Facilitated diffusion results in equal concentration of substances across membranes. What process works against diffusion?

[f]No. Simple diffusion is essentially the same as diffusion. It results in equal concentration of substances across membranes. What process works against diffusion?

[!]Question 17 added+++++++++++[/!]

[q]In the diagram below, number 3 is

[c*]active transport

[c]facilitated diffusion

[c]simple diffusion

[f]Yes. In number 3, the cell is moving molecules from lower to higher concentration, a process known as active transport.

[f]No. Facilitated diffusion allows materials to diffuse down their concentration gradients, but provides a protein channel for the materials to pass through. Is number 3 going up or down its concentration gradient.

[f]No. Simple diffusion is movement of materials directly through the phospholipid bilayer.

[!]Question 17 added+++++++++++[/!]

[q]In the diagram below, number 1 is

[c]active transport

[c]facilitated diffusion

[c*]simple diffusion

[f]No. In active transport, the cell moves molecules from lower to higher concentration. In number 1,  the movement is from higher to lower.

[f]No. In facilitated diffusion, materials are allowed to diffuse down their concentration gradients, but a protein channel is provided for the materials to pass through. There’s no channel in number 1.

[f]Yes. Number 1 is simple diffusion through the phospholipid bilayer. In number 3, the materials are not going though the phospholipid bilayer, but through a carrier protein.

[!] Question 17, REVISED+++++++++++++[/!]

[q] As part of the immune response, a white blood cell swallows an invading bacteria. Another name for that process is

[c] exocytosis.

[c] passive transport.

[c*] phagocytosis.

[c] facilitated diffusion

[f]No. Exocytosis moves things out of the cell.

[f]No. Passive transport includes processes that don’t require any cell energy, like simple and facilitated diffusion. Swallowing an entire cell requires a lot of energy.

[f]Yes. Phagocytosis is the name for the process in which cells swallow particles or other cells.

[f]No. Facilitated diffusion involves molecules diffusing through protein channels. What’s above is a form of endocytosis.

[!] Question 18++++++++++++++[/!]

[q]As shown in this diagram, the type of endocytosis in which molecules bind with receptors on the membrane, causing the membrane to pinch in and create a coated vesicle is called.

[c]phagocytosis

[c]pinocytosis

[c*]receptor mediated-endocytosis

[f]No. Phagocytosis involves significant extension of the membrane. These extensions, called pseudopods, engulf large particles or entire cells.

[f]No. Pinocytosis doesn’t involve the binding of receptors.

[f]Yes. What’s shown here is receptor-mediated endocytosis.

[!] Question 19++++++++++++++[/!]

[q]The type of endocytosis in which the membrane pinches in and takes a small “sip” of whatever is outside the membrane is called

[c]phagocytosis

[c*]pinocytosis

[c]receptor mediated-endocytosis

[f]No. Phagocytosis involves significant extension of the membrane. These extensions, called pseudopods, engulf large particles or entire cells.

[f]Yes. What’s shown here is pinocytosis, a small pinching in of the cell membrane that enables the cell to “take a sip” of the surrounding extracellular fluid.

[f]No. Receptor mediated endocytosis does involve pinching of the membrane, but the process is initiated by the binding of certain substances to receptors, which you don’t see here.

[!] Question 20++++++++++++++[/!]

[q]In this type of endocytosis there are significant extension of the membrane. These extensions, called pseudopods, engulf large particles or entire cells.

[c*]phagocytosis

[c]pinocytosis

[c]receptor mediated-endocytosis

[f]Yes. What’s shown here is phagocytosis.

[f]No. Pinocytosis is a small pinching in of the cell membrane that enables the cell to “take a sip” of the surrounding extracellular fluid.What shown here is on a much larger scale.

[f]No. Receptor mediated endocytosis does involve pinching of the membrane, but the process is initiated by the binding of certain substances to receptors, which you don’t see here. Also, the process shown here involves membrane changes on a much larger scale.

[/!]

[!] Card 3+++++++++++++++++++++[/!]

[q]_____________ is the movement of molecules from where they’re more concentrated to where they’re less concentrated.

[hangman]

[c]diffusion

[f]Fantastic! Diffusion is the movement of molecules from where they’re more concentrated to where they’re less concentrated.

[!] Card 4+++++++++++++++++++++[/!]

[q]One way to talk about diffusion is to say the molecules in a fluid will move down a _____________ ____________.

[hangman]

[c]concentration gradient

[f]Genius! One way to talk about diffusion is to say the molecules in a fluid will move down a concentration gradient.

[!] Card 5+++++++++++++++++++++[/!]

[q]When substances diffuse directly through a membrane’s phospholipid bilayer, the process is called _____________ ____________.

[hangman]

[c]simple diffusion

[f]Correct! When substances diffuse directly through a membrane’s phospholipid bilayer, the process is called simple diffusion.

[!] Card 6+++++++++++++++++++++[/!]

[q]When substances diffuse into a cell by passing through a protein channel, the process is called _____________ ____________.

[hangman]

[c]facilitated diffusion

[f]Yes! When substances diffuse directly through a membrane’s phospholipid bilayer, the process is called facilitated diffusion.

[!] Card 7+++++++++++++++++++++[/!]

[q]When cells expend energy to move a substance from lower concentration to higher concentration, this process is known as _____________ ____________.

[hangman]

[c]active transport

[f]Perfect! When cells expend energy to move a substance from lower concentration to higher concentration, this process is known as active transport.

[!] Card 8+++++++++++++++++++++[/!]

[q]A vesicle filled with some substance fuses with the membrane, releasing that substance outside the cell. This process is called ____________.

[hangman]

[c]exocytosis

[f]Nice! A vesicle filled with some substance fuses with the membrane, releasing that substance outside the cell. This process is called exocytosis.

[!] Card 9+++++++++++++++++++++[/!]

[q]The cell membrane pinches in, taking in something outside of the cell and enclosing it within a vesicle. This process is called ____________.

[hangman]

[c]endocytosis

[f]Great! The cell membrane pinches in, taking in something outside of the cell and enclosing it within a vesicle. This process is called endocytosis.

[!] Card 10+++++++++++++++++++++[/!]

[q]The kind of endocytosis in which a small portion of the membrane pinches in, allowing the cell to “take a sip” of the fluid outside of the cell, is called _________

[hangman]

[c]pinocytosis

[f]Good job! The kind of endocytosis in which a small portion of the membrane pinches in, allowing the cell to “take a sip” of the fluid outside of the cell, is called pinocytosis.

[!] Card 11+++++++++++++++++++++[/!]

[q]The kind of endocytosis in which a large portion of the membrane surrounds a food particle (or even another cell), and then brings that particle into the cell is called _________

[hangman]

[c]phagocytosis

[f]Awesome! The kind of endocytosis in which a large portion of the membrane surrounds a food particle (or even another cell), and then brings that particle into the cell is called phagocytosis.

 

[!] Card 13+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is

[hangman]

[c]diffusion

[f]Genius! The best name for the process shown in this diagram is diffusion

[!] Card 14+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is

[hangman]

[c]simple diffusion

[f]Correct! The best name for the process shown in this diagram is simple diffusion.

[!] Card 1+++++++++++++++++++++++++++++++++++[/!]

[!] Card 15+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is

[hangman]

[c]facilitated diffusion

[f]Yes! The best name for the process shown in this diagram is facilitated diffusion.

[!] Card 16+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is

[hangman]

[c]active transport

[f]Perfect! The best name for the process shown in this diagram is active transport.

[!] Card 17+++++++++++++++++++++[/!]

[q]The best name for the process shown in this diagram is

[hangman]

[c]exocytosis

[f]Nice! The best name for the process shown in this diagram is exocytosis.

[!] Card 18+++++++++++++++++++++[/!]

[q]The best name for the process shown at “A,” “B,” and “C” in this diagram is

[hangman]

[c]endocytosis

[f]Great! The best name for the process shown in this diagram is endocytosis.

[!] Card 19+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is

[hangman]

[c]pinocytosis

[f]Good job! The specific type of endocytosis shown in this diagram is pinocytosis.

[!] Card 20+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is

[hangman]

[c]phagocytosis

[f]Awesome! The specific type of endocytosis shown in this diagram is phagocytosis

[!] Card 21+++++++++++++++++++++[/!]

[q]The specific type of endocytosis shown in this diagram is

[hangman]

[c]receptor-mediated endocytosis

[f]Fantastic! The specific type of endocytosis shown in this diagram is receptor-mediated endocytosis

[x]

[restart]

[/qwiz]

8. Next