Topic 2: Transport Across Cell Membranes Flashcards
(32 cards)
Define simple diffusion
Net movement of particles down a concentration gradient from a high concentration to a low concentration.
Define facilitated diffusion
Transport of large polar molecules and ions into and out of a cell, involving the use of carrier and channel proteins.
Define osmosis
The net movement of water molecules from a region with high water potential to an area with low water potential across a partially permeable membrane.
Define active transport
Movement of molecules against a concentration gradient from a region of low concentration to a region of high concentration. Using energy from the hydrolysis of ATP
Is diffusion a passive or active process? Give a reason
Passive - doesn’t require energy
Is Active transport a passive or active process? Give a reason
Active - uses ATP
Describe how phospholipids are arranged in a plasma membrane.
Hydrophilic phosphate head faces outwards whilst the hydrophobic fatty acid tails faces inward, making the centre non-polar.
How does the bilayer formed by phospholipids affect entry and exist of substances into and out of the cell?
Hydrophobic tail facing inwards makes the centre non-polar, so it only allows small, non-polar, lipid-soluble substances to pass through.
Explain why the structure of a plasma membrane is described as a fluid mosaic.
Fluid: Phospholipids are constantly moving laterally
Mosaic: Proteins and phospholipids are different size molecules which are scattered across the structure like mosaic tiles.
What components does the phospholipid contain?
-Glycoproteins
-Glycolipids
-Channel proteins
-Carrier proteins
-Cholesterol
What are the intrinsic proteins and what do they allow?
-Channel and carrier proteins
- Allow large, polar molecules and ions to pass through the membrane
What are the extrinsic proteins and what do they allow?
-Glycoproteins and Glycolipids
-Acts as receptors and antigens for cell signalling
What is the role of cholesterol in the membrane and how does it achieve this?
Regulates the fluidity, increasing the stability of the membrane by binding to the fatty acid tails, causing them to pack together, reducing the lateral movement of the bilayer.
What are the factors that affect diffusion?
-Concentration gradient
-Diffusion distance
-Surface area
-Temperature
How does concentration gradient affect diffusion?
The greater the concentration difference the faster the diffusion rate
How does the diffusion distance affect diffusion?
The thinner the membrane the faster the rate of diffusion as there’s a shorter distance the particles have to travel.
How does the surface area affect diffusion?
The larger the surface area the faster the rate as increasing the surface area means more particles can be exchanged in the same amount of time.
How does temperature affect diffusion?
At higher temperatures, particles will have more kinetic energy so they will move faster, increasing the rate of diffusion.
Describe the role of carrier proteins.
-Move large molecules across the membrane.
-Large molecules attach causing the protein to change shape and release the molecule on the other side of the membrane.
What does channel proteins do?
Form pores for charged particles to diffuse through.
Describe the transport process to up taking glucose in the small intestine.
- Na+ ions are actively transported out of epithelial cell into the blood by the Na+/K+ pump
2.Creates a concentration gradient
3.Na+ diffuses from the lumen of the ileum into the epithelial down the concentration gradient via co-transport with glucose. - Glucose then leaves, going down the concentration gradient through a channel protein by facilitated diffusion.
What is a hypotonic solution and what will happen to the cell?
Solution that as a higher water potential than the inside of the cell, so water will move into the cell by osmosis.
What effect does a hypotonic cell have on an animal cell?
Swell up and burst (lysed) as the cell membrane isn’t strong enough to withstand the pressure of the increased volume of water inside the cell.
What effect does a hypotonic solution have on a plant cell?
Vacuole fills up with water and pushes the cell membrane onto cell wall, which can withstand the pressure so the cell becomes turgid (normal state).
