The semi-permeable or selectively permeable cell membrane is the cell's gatekeeper. In most cases, it helps to determine the passage of ions and molecules into and out of the cell. The other determining factor is the extracellular/intracellular concentration gradient. What follows is a discussion of the transport mechanisms involved in the passage of substances into and out of a cell. 00:25: Someone's baking cookies. You're not in the kitchen, you can't see them, but you can smell the cookies baking. That delicious cook odor has diffused to your nose. Diffused, means it moved from an area of high concentration, which was the kitchen oven, to an area of lower concentration, your nose in another part of the house. Diffusion relies on the kinetic energy of molecules and the concentration gradient. Diffusion plays an important role in the transport of molecules into and out of the cell. Let's take a look at a cellular example. Ions and small molecules, like oxygen, move throughout the cell membrane via diffusion. Let's assume the blue circles are oxygen molecules, they are outside of the cell membrane. The oxygen will diffuse, or move, through this cell membrane from high concentration to low concentration, until equilibrium is reached. The cell expends no energy, so this is a method of passive transport. 01:27: A special type of diffusion is osmosis. Osmosis is the diffusion of water across a semi-permeable membrane until equilibrium is reached. Water moves across the membrane from high to low in this example. Let's take a look at a real example. Here's a raw shell-less egg paste in corn syrup. The concentration of water inside the egg or the cell is higher than outside in the corn syrup. We would expect, according to our previous explanation that the water would diffuse out of the egg and into the cup. The egg is not alive, there's no energy expended, here's what happens. Correct, the water moved out of the egg and it shrivels up. Larger molecules, like glucose, also move with the concentration gradient from high to low concentration. Again, no cell energy is expended, but due to the size of the molecules they need a special gateway or channel through the membrane. Because these protein channels are used, this method of transport is called facilitated transport. In this image, some green dots represent glucose. Living cells always require glucose because it's the cell's source of energy. It is always moving from high to low concentration, into the cell. But because it is a larger molecule, it moves through this channel. Some ions are actively moved into and out of the cell. This requires cell energy, ATP, and is referred to as active transport. 03:06: A classic example of the sodium potassium pump. The process of moving sodium and potassium ions across the cell membrane is an active transport process involving the hydrolysis of ATP to provide the necessary energy. It involves the enzyme referred to as the sodium potassium ATPase. The process is responsible for maintaining the large excess of sodium outside the cell and the large excess of potassium ions on the inside of the cell. It accomplishes the transport of three sodium to the outside of the cell and the transport of two potassium ions to the inside. The pump requires both the use of cell energy and protein channels to accomplish this. The sodium potassium pump is an important contributor to action potential produced by nerve cells. Substances must move into and out of cells and they use a variety of transport mechanisms.

Question

The semi-permeable or selectively permeable cell membrane is the cell's gatekeeper. In most cases, it helps to determine the passage of ions and molecules into and out of the cell. The other determining factor is the extracellular/intracellular concentration gradient. What follows is a discussion of the transport mechanisms involved in the passage of substances into and out of a cell. 00:25: Someone's baking cookies. You're not in the kitchen, you can't see them, but you can smell the cookies baking. That delicious cook odor has diffused to your nose. Diffused, means it moved from an area of high concentration, which was the kitchen oven, to an area of lower concentration, your nose in another part of the house. Diffusion relies on the kinetic energy of molecules and the concentration gradient. Diffusion plays an important role in the transport of molecules into and out of the cell. Let's take a look at a cellular example. Ions and small molecules, like oxygen, move throughout the cell membrane via diffusion. Let's assume the blue circles are oxygen molecules, they are outside of the cell membrane. The oxygen will diffuse, or move, through this cell membrane from high concentration to low concentration, until equilibrium is reached. The cell expends no energy, so this is a method of passive transport. 01:27: A special type of diffusion is osmosis. Osmosis is the diffusion of water across a semi-permeable membrane until equilibrium is reached. Water moves across the membrane from high to low in this example. Let's take a look at a real example. Here's a raw shell-less egg paste in corn syrup. The concentration of water inside the egg or the cell is higher than outside in the corn syrup. We would expect, according to our previous explanation that the water would diffuse out of the egg and into the cup. The egg is not alive, there's no energy expended, here's what happens. Correct, the water moved out of the egg and it shrivels up. Larger molecules, like glucose, also move with the concentration gradient from high to low concentration. Again, no cell energy is expended, but due to the size of the molecules they need a special gateway or channel through the membrane. Because these protein channels are used, this method of transport is called facilitated transport. In this image, some green dots represent glucose. Living cells always require glucose because it's the cell's source of energy. It is always moving from high to low concentration, into the cell. But because it is a larger molecule, it moves through this channel. Some ions are actively moved into and out of the cell. This requires cell energy, ATP, and is referred to as active transport. 03:06: A classic example of the sodium potassium pump. The process of moving sodium and potassium ions across the cell membrane is an active transport process involving the hydrolysis of ATP to provide the necessary energy. It involves the enzyme referred to as the sodium potassium ATPase. The process is responsible for maintaining the large excess of sodium outside the cell and the large excess of potassium ions on the inside of the cell. It accomplishes the transport of three sodium to the outside of the cell and the transport of two potassium ions to the inside. The pump requires both the use of cell energy and protein channels to accomplish this. The sodium potassium pump is an important contributor to action potential produced by nerve cells. Substances must move into and out of cells and they use a variety of transport mechanisms.

Close
Question 1
All BUT one is a method of passive transport in cells.
Responses
A OsmosisOsmosis
B Sodium/Potassium pumpSodium/Potassium pump
C Facilitated transportFacilitated transport
Question 2
During _____________, molecules like glucose, use a protein channel to enter or leave the cell.
Responses
A active transportactive transport
B facilitated transportfacilitated transport
C ionic pump mechanismsionic pump mechanisms
Question 3
The diffusion of water through a semipermeable membrane is an example of _________ and __________.
Responses
A osmosis; passive transportosmosis; passive transport
B osmosis; active transportosmosis; active transport
C hydrolysis; passive transporthydrolysis; passive transport

Please answer all 3 questions correctly!!!

Answer 1

Question 1: The correct answer is B, Sodium/Potassium pump. The sodium/potassium pump is an example of active transport, not passive transport.

Question 2: The correct answer is B, facilitated transport. During facilitated transport, molecules like glucose use protein channels to enter or leave the cell.

Question 3: The correct answer is A, osmosis; passive transport. The diffusion of water through a semipermeable membrane is an example of osmosis, which is a type of passive transport.

Answer 2

Question 1: All BUT one is a method of passive transport in cells.

B. Sodium/Potassium pump

Question 2: During _____________, molecules like glucose, use a protein channel to enter or leave the cell.
B. facilitated transport

Question 3: The diffusion of water through a semipermeable membrane is an example of _________ and __________.
A. osmosis; passive transport

Answer 3

Question 1: All BUT one is a method of passive transport in cells.

Correct answer: B. Sodium/Potassium pump

Explanation: Passive transport refers to the movement of molecules or ions across a cell membrane without the use of energy. Osmosis, facilitated transport, and diffusion are all examples of passive transport because they rely on the concentration gradient and do not require energy expenditure. However, the sodium/potassium pump is an example of active transport, as it requires ATP (cell energy) to transport sodium and potassium ions against their concentration gradient.

Question 2: During _____________, molecules like glucose, use a protein channel to enter or leave the cell.
Correct answer: B. facilitated transport

Explanation: Facilitated transport is a type of passive transport where molecules such as glucose move across the cell membrane with the help of protein channels. These protein channels act as gateways for the larger molecules, allowing them to move from an area of high concentration to an area of low concentration without the need for energy expenditure.

Question 3: The diffusion of water through a semipermeable membrane is an example of _________ and __________.
Correct answer: A. osmosis; passive transport

Explanation: The diffusion of water through a semipermeable membrane is known as osmosis. Osmosis is a passive transport process where water molecules move from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution) until equilibrium is reached. Osmosis does not require energy expenditure, making it a form of passive transport.