Transport Accross Cell Membranes

Question 1

What model describes the arrangement of the cell membrane components?

Answer 1

Fluid-mosaic model

The fluid-mosaic model describes the cell membrane’s structure, consisting of a bi-layer of phospholipids with proteins integrated throughout.

Question 2

What does ‘fluid’ refer to in the fluid-mosaic model?

Answer 2

Phospholipids are constantly moving

The term ‘fluid’ indicates the dynamic nature of the phospholipid bilayer.

Question 3

What does ‘mosaic’ refer to in the fluid-mosaic model?

Answer 3

Proteins scattered through the bilayer

‘Mosaic’ refers to the arrangement of proteins embedded in the phospholipid bilayer, akin to tiles in a mosaic.

Question 4

What is a glycoprotein?

Answer 4

Protein with carbohydrate attached

Glycoproteins play key roles in cell recognition and signaling.

Question 5

What is a glycolipid?

Answer 5

Lipid with carbohydrate attached

Glycolipids contribute to the stability and recognition functions of the cell membrane.

Question 6

What is the primary function of the phospholipid bilayer?

Answer 6

Form a barrier to dissolved substances

The hydrophobic center of the bilayer prevents water-soluble substances from passing through.

Question 7

What types of molecules can diffuse through the phospholipid bilayer?

Answer 7

Small, non-polar molecules like CO2

The bilayer allows certain small, non-polar molecules to diffuse freely, while larger or polar molecules require specific transport mechanisms.

Question 8

How do channel proteins and carrier proteins function?

Answer 8

Allow large molecules, polar molecules, and ions to pass through the membrane

These proteins facilitate the transport of substances that cannot easily pass through the lipid bilayer.

Question 9

Can water diffuse through the cell membrane?

Answer 9

Yes, through osmosis due to its small size

Despite being polar, water can pass through the membrane efficiently because of its small molecular size.

Question 10

What role do proteins with carbohydrates attached play in cells?

Answer 10

Act as antigens for cellular recognition

These proteins are crucial for the immune response and help in cell signaling and adhesion.

Question 11

What is the function of cholesterol in the cell membrane?

Answer 11

Restricts movement of molecules and provides stability

Cholesterol fits between phospholipids, reducing membrane fluidity and helping maintain its integrity.

Question 12

What is the role of intrinsic proteins in the cell membrane?

Answer 12

Facilitate active transport or facilitated diffusion

Intrinsic proteins span the membrane and assist in the movement of substances across it.

Question 13

What effect does insulin have on liver cells?

Answer 13

Tells the cell to start absorbing glucose

Insulin binds to receptor proteins, triggering glucose uptake, which is vital for regulating blood sugar levels.

Question 14

What is the importance of cell adhesion in tissues?

Answer 14

Allows cells to connect to one another

Cell adhesion is crucial for forming tissues and maintaining structural integrity in multicellular organisms.

Question 15

True or False: Animal cells maintain their shape through cell walls.

Answer 15

False

Animal cells maintain shape through their cytoskeleton and membrane structure, not through cell walls.

Question 16

What is the role of cytoskeletal filaments in animal cells?

Answer 16

Helps maintain cell shape

Cytoskeletal filaments provide structural support, especially in cells that lack rigid cell walls.

Question 17

What effect do non-polar solvents (e.g., alcohol or acetone) have on cell membranes?

Answer 17

Non-polar solvents disrupt the cell membrane by inserting themselves into the bilayer and forming hydrogen bonds with phospholipids, increasing permeability

Question 18

How does alcohol increase membrane permeability?

Answer 18

Alcohol disrupts the membrane structure by forming hydrogen bonds with phospholipids and breaking bonds in proteins, destabilizing the bilayer.

Question 19

What happens to cell membranes when exposed to high temperatures?

Answer 19

High temperatures increase membrane fluidity, causing the membrane to become more permeable and allowing pigments to leak out.

Question 20

What role does a colorimeter play in studying membrane permeability?

Answer 20

A colorimeter measures the amount of pigment that leaks out of cells by analyzing the absorbance of light in the solution.

Question 21

Why are pigments like betalains used to study membrane permeability?

Answer 21

Betalains are contained in the vacuole of beetroot cells and leak out when the membrane is damaged, allowing for quantifiable analysis of permeability

Question 22

How does a colorimeter determine the concentration of pigments in a solution?

Answer 22

It passes light through the solution and measures how much light is absorbed, using a filter to select the wavelength opposite to the color of the pigment.

Question 23

Why is a calibration curve important when using a colorimeter?

Answer 23

A calibration curve allows the comparison of unknown sample absorbance values to known concentrations to determine the pigment concentration.

Question 24

What is simple diffusion?

Answer 24

Simple diffusion is the passive movement of molecules or ions from an area of high concentration to an area of low concentration until equilibrium is reached

Question 25

What type of molecules can diffuse through a membrane via simple diffusion?

Answer 25

Small, non-polar molecules like oxygen and carbon dioxide.

Question 26

How does the concentration gradient affect simple diffusion?

Answer 26

A greater concentration difference increases the rate of diffusion.

Question 27

How does membrane thickness affect diffusion?

Answer 27

Thinner membranes reduce the distance particles need to travel, increasing diffusion rates.

Question 28

How does surface area affect diffusion?

Answer 28

A larger surface area allows more particles to diffuse at the same time, increasing the rate of diffusion

Question 29

How does temperature affect diffusion?

Answer 29

Higher temperatures increase the kinetic energy of particles, leading to faster diffusion.

Question 30

What is facilitated diffusion?

Answer 30

A passive process where larger or charged particles (e.g., ions, glucose) move down their concentration gradient through carrier or channel proteins in the membrane

Question 31

How do carrier proteins work in facilitated diffusion?

Answer 31

Specific molecules bind to the protein, causing it to change shape and allow the molecule to pass through the membrane

Question 32

How do channel proteins function in facilitated diffusion?

Answer 32

They form pores in the membrane, allowing specific molecules or ions to pass through.

Question 33

What is Fick’s Law?

Answer 33

The rate of diffusion is proportional to the surface area × concentration difference divided by the thickness of the exchange surface.

Question 34

What is the role of carrier proteins in facilitated diffusion?

Answer 34

Carrier proteins bind to large molecules, change shape, and release the molecule on the other side of the membrane.

Question 35

What is the role of channel proteins in facilitated diffusion?

Answer 35

Channel proteins form water-filled, hydrophilic channels that allow specific charged particles or ions to diffuse across the membrane.

Question 36

How does the concentration gradient affect the rate of facilitated diffusion?

Answer 36

A greater concentration difference increases the rate of facilitated diffusion until equilibrium is reached or all proteins are in use.

Question 37

How does the number of channel or carrier proteins affect the rate of facilitated diffusion?

Answer 37

A greater number of proteins increases the rate of diffusion, but once all proteins are in use, the rate cannot increase further, making it a limiting factor.

Question 38

What happens when all channel and carrier proteins are in use during facilitated diffusion?

Answer 38

The rate of diffusion levels off and cannot increase further, even with a higher concentration gradient

Question 39

How do protein channels differ from carrier proteins in facilitated diffusion?

Answer 39

Protein channels act as simple “tunnels” for charged particles, while carrier proteins change shape to transport specific molecules.

Question 40

How is the dilution factor (DF) calculated?

Answer 40

DF = vi (initial volume) divided by vf (final volume)

Question 41

Active transport

Answer 41

The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration requires ATP

Question 42

How does active transport differ from passive transport?

Answer 42

Active transport requires energy (ATP) and moves substances against their concentration gradient, while passive transport does not require energy and moves substances down their concentration gradient.

Question 43

What is the role of carrier proteins in active transport?

Answer 43

Carrier proteins bind to specific molecules and use energy (ATP) to change shape, allowing the molecules to be transported across the membrane against their concentration gradient

Question 44

Give an example of a process that uses active transport

Answer 44

The sodium-potassium pump (Na+/K+ pump) is an example, where sodium ions are pumped out of a cell and potassium ions are pumped into the cell, both against their concentration gradients

Question 45

Why is ATP required for active transport

Answer 45

ATP provides the necessary energy for carrier proteins to change shape and move molecules or ions against their concentration gradients.

Question 46

What is bulk transport (vesicular transport)?

Answer 46

Bulk transport is a type of active transport in which large quantities of materials, such as macromolecules or particles, are transported into or out of the cell in vesicles.

Question 47

What are the two main types of bulk transport?

Answer 47

Endocytosis (taking substances into the cell) and exocytosis (expelling substances from the cell).

Question 48

What is the difference between primary and secondary active transport

Answer 48

Primary active transport directly uses ATP to transport molecules, while secondary active transport uses the energy created by primary active transport (like a sodium gradient) to move other molecules

Question 49

What is the sodium-potassium pump, and why is it important?

Answer 49

The sodium-potassium pump transports sodium ions out of the cell and potassium ions into the cell, crucial for maintaining cellular function, resting membrane potential, and osmotic balance.

Question 50

What is co-transport in active transport

Answer 50

Co-transport involves the simultaneous transport of two different substances across a membrane, one moving down its concentration gradient (providing energy) and the other moving against its gradient