2.4 Membrane Transport

Question 1

What is the primary function of the plasma membrane in a cell?

Answer 1

The plasma membrane allows for the exchange of nutrients, waste, and communication with the environment and neighboring cells.

Question 2

Why must the plasma membrane be highly selective?

Answer 2

It must take in large food molecules while preventing small, valuable molecules from leaving. It must also recognize foreign harmful substances.

Question 3

What happens when undesirable molecules cross the plasma membrane?

Answer 3

When undesirable molecules cross the plasma membrane, the cell may face negative consequences. These molecules can disrupt cellular functions and lead to harm, regardless of whether their entry or exit is beneficial to the cell. The cell must manage these effects, which can include toxicity, altered metabolism, or impaired signaling. (“TIA” –> toxicity, impaired signaling, altered metabolism)

Question 4

What is passive transport?

Answer 4

Passive transport is the movement of substances across a membrane without the need for chemical energy; it is driven by diffusion.

Question 5

What is diffusion?

Answer 5

Diffusion is the net movement of a substance from a region of higher concentration to a region of lower concentration due to the constant motion of molecules.

Question 6

What factors influence the rate of diffusion?

Answer 6

The rate of diffusion depends on the concentration gradient; a larger gradient results in a faster rate of diffusion.

Question 7

What is dynamic equilibrium in the context of diffusion?

Answer 7

Dynamic equilibrium in diffusion happens when the concentrations of molecules are equal on both sides of a membrane. Even though molecules still move back and forth, the overall concentration stays the same.

Question 8

What is selective permeability?

Answer 8

Selective permeability means that some molecules can diffuse rapidly across a membrane while others cannot without assistance.

Question 9

What two major factors determine the ease of movement across a membrane?

Answer 9

Size and polarity of the molecule or ion.

Question 10

What are the two types of passive transport?

Answer 10

Simple diffusion and facilitated diffusion.

Question 11

What is simple diffusion?

Answer 11

Simple diffusion is the ability of substances to move across a membrane unassisted, meaning that the process does not require energy or help from transport proteins. This primarily involves very small non-polar molecules like O₂ and CO₂ that can pass freely through the lipid bilayer of the membrane.

Question 12

Which types of molecules can readily cross the plasma membrane via simple diffusion?

Answer 12

Very small non-polar molecules (O₂, CO₂), non-polar steroid hormones, non-polar drugs, and small uncharged molecules (water, glycerol).

Question 13

How does the movement rate of small ions compare to that of water during diffusion?

Answer 13

The movement of small ions is about one-billionth the speed of water transport across the membrane.

Question 14

What is facilitated diffusion?

Answer 14

Facilitated diffusion is the process by which the diffusion of polar and charged molecules across a membrane is aided by protein complexes.

Question 15

What drives facilitated diffusion?

Answer 15

The movement of molecules and ions in facilitated diffusion is driven by diffusion based on a concentration gradient across the membrane.

Question 16

What are transport proteins?

Answer 16

Transport proteins are integral membrane proteins that facilitate the transport of substances across the membrane during facilitated diffusion.

Question 17

What are the two types of transport proteins?

Answer 17

The two types of transport proteins are channel proteins and carrier proteins.

Question 18

What is the function of channel proteins?

Answer 18

Channel proteins form hydrophilic pathways in the membrane for water and certain ions to pass through.

Question 19

How do voltage-gated ion channels function?

Answer 19

Voltage-gated ion channels switch between open, closed, and intermediate states in response to changes in voltage across the membrane or by binding signal molecules.

Question 20

How do carrier proteins transport solutes across the membrane?

Answer 20

Carrier proteins bind to specific solutes, change shape, and facilitate the movement of the solute from one side of the membrane to the other.

Question 21

What is a key difference between carrier proteins and channel proteins?

Answer 21

Carrier proteins change shape during transport, while channel proteins provide a continuous passageway.

Question 22

Why is specificity important in transport proteins?

Answer 22

Specificity allows for tight control over what substances enter and exit cells, ensuring the proper functioning of cellular processes.

Question 23

What factors influence the rate of diffusion in facilitated diffusion?

Answer 23

The rate is influenced by the concentration gradient, the efficiency of the transport protein, and the number of transport molecules available.

Question 24

What is osmosis?

Answer 24

Osmosis is the diffusion of water across a membrane, moving from an area of lower solute concentration (high water concentration) to an area of higher solute concentration (low water concentration).

Question 25

What happens to a cell in a hypotonic solution?

Answer 25

In a hypotonic solution, water enters the cell by osmosis, causing the cell to swell, and it may burst if too much water enters.

Question 26

What is a hypertonic solution, and what effect does it have on cells?

Answer 26

A hypertonic solution has a higher concentration of solutes compared to the inside of a cell, leading to water moving out of the cell by osmosis. This can result in the cell shrinking.

Question 26

What occurs in an isotonic solution?

Answer 26

In an isotonic solution, the concentration of water inside and outside the cell is equal, resulting in no net movement of water.

Question 26

What is a hypotonic solution, and what happens to a cell in it?

Answer 26

A hypotonic solution has a lower concentration of solutes compared to the inside of a cell, causing water to enter the cell by osmosis. This can lead to cell swelling and, potentially, bursting.

Question 27

What is active transport?

Answer 27

Active transport is an energy-dependent process that moves substances against their concentration gradient, from a region of lower concentration to a region of higher concentration.

Question 27

What is primary active transport?

Answer 27

Primary active transport moves ions, such as H+, Ca2+, Na+, and K+, across membranes using energy (usually ATP) to establish concentration gradients essential for cellular functions.

Question 27

What is exocytosis?

Answer 27

Exocytosis is the process by which cells export materials, such as secretory proteins, from the cytosol to the exterior by vesicles fusing with the plasma membrane.

Question 27

What is the function of the sodium-potassium pump?

Answer 27

The sodium-potassium pump uses ATP to push 3 sodium ions out of the cell and 2 potassium ions into the cell, which creates a higher concentration of sodium outside the cell. This gradient can then be used by secondary active transporters to move other substances against their concentration gradients.

Question 28

How does secondary active transport work?

Answer 28

Secondary active transport uses the concentration gradient of an ion, established by a primary pump, as its energy source to move another molecule against its concentration gradient.

Question 28

What is an electrochemical gradient?

Answer 28

An electrochemical gradient is the combined effect of voltage (electrical potential difference) and concentration differences of ions across a membrane, creating stored potential energy for transport mechanisms.

Question 28

What is endocytosis?

Answer 28

Endocytosis is the process by which cells import substances from the exterior by engulfing them in vesicles formed from the plasma membrane.

Question 29

What is phagocytosis?

Answer 29

Phagocytosis is a type of endocytosis where cells engulf large particles, such as bacteria or dead cells, often performed by immune cells like macrophages

Question 30

What distinguishes receptor-mediated endocytosis from other forms of endocytosis?

Answer 30

In receptor-mediated endocytosis, specific molecules bind to receptors on the cell surface, triggering the formation of a vesicle to bring the molecules into the cell.

Question 31

What is meant by the term “concentration gradient”?

Answer 31

A concentration gradient refers to the difference in the concentration of a substance across a space or membrane. Substances tend to move from areas of higher concentration to areas of lower concentration.

Question 32

What does it mean that facilitated diffusion is specific?

Answer 32

Facilitated diffusion is specific because it involves carrier proteins or channels that only allow certain molecules to pass through the membrane, ensuring that only specific substances are transported.

Question 33

What happens to a red blood cell placed in a hypotonic solution?

Answer 33

The red blood cell swells and may burst because water moves into the cell by osmosis, as the concentration of solutes in the cytosol of the cell is higher than in the surrounding solution.

Question 34

Why is distilled water considered hypotonic to body cells?

Answer 34

Distilled water has a lower concentration of solutes compared to body cells, causing water to enter the cells by osmosis, which can lead to swelling.

Question 35

Compare the energy requirements of passive transport, primary active transport, and secondary active transport.

Answer 35

Passive transport requires no energy as it relies on concentration gradients, while primary active transport requires energy (usually ATP) to move substances against a gradient. Secondary active transport also requires energy but uses the energy from the concentration gradient established by primary active transport.

Question 37

What is receptor-mediated endocytosis?

Answer 37

Receptor-mediated endocytosis is when cells take in specific molecules by having them bind to receptors on the cell membrane. This binding causes the membrane to form a pit that pinches off to create a vesicle, allowing the cell to absorb important substances like hormones and nutrients.

Question 38

What is active transport?

Answer 38

Active transport is the process of moving substances across a cell membrane against their concentration gradient (from low to high concentration) using energy, usually in the form of ATP. It involves two main types: symport and antiport

Question 39

What is symport?

Answer 39

Symport is a type of active transport where two substances are moved across a cell membrane in the same direction. This process uses energy to transport molecules against their concentration gradient.

Question 40

What is antiport?

Answer 40

Antiport is a type of active transport where one substance moves into the cell while another moves out, allowing for the exchange of molecules. This process requires energy to move substances against their concentration gradient.

Question 41

Give me an example of an antiport

Answer 41

An example is the sodium-potassium pump, which moves sodium ions out of the cell while bringing potassium ions in, maintaining cellular ion balance.

Question 42

Give me an example of a symport

Answer 42

Symport is a type of active transport where two substances are moved across a cell membrane in the same direction. An example is the sodium-glucose symporter, which transports sodium ions and glucose into intestinal cells together.

Question 43

What effects can occur if the transport mechanism malfunctions?

Answer 43

Cell size changes:
Swelling hypotonic solutions or shrinking in hypertonic solutions

Nutrient Absorption Issues: Impaired nutrient uptake, like glucose in the intestines.

Electrolyte Imbalance: Disrupted nerve and muscle function due to faulty ion pumps.

Waste Accumulation: Toxicity from inability to remove waste.
Diseases: Conditions like cystic fibrosis from ion channel malfunctions.