Topic 2 - Cell Membranes And Transport Flashcards
(39 cards)
What is the cell membrane?
Controls the movement of substances into and out of cells its structure is described by the fluid mosaic which highlights its dynamic nature and diverse components.
What is the phospholipid bilayer as a feature of the cell membrane?
- composed of phosphate lipids arranged in two layers
- Hydrophilic heads face outwards interacting with water inside and outside the cell.
- hydrophobic point inward avoiding water and creating a hydrophobic core.
- Allows molecules to pass through and prevent passage of water, soil molecules and ions
What is fluidity in terms of the cell membrane?
- The phosphate lipids can move laterally making the membrane flexible and self-sealing.
- this property enables processes like endocytosis and exocytosis.
What are proteins as a component of the cell membrane?
- embedded in the phospholipid bilayer and play key roles
- Intrinsic proteins span the membrane and include channel proteins and carry proteins which aid in the transport of substances
- Extrinsic proteins are located on the membrane surface providing mechanical support or acting as receptors
- Facilitate active transport and facilitated diffusion act as receptors for hormones and other signalling molecules
What is cholesterol in terms of the cell membrane?
- found within the bilayer
- increases stability and reduces membrane fluid at high temperatures
- Prevent leakage of water and dissolved ions due to its hydrophobic nature.
What are glycolipids?
- lipids with attached carbohydrate chains.
- Act as cell surface receptors for specific molecules
- Help in cell recognition and adhesion forming tissues.
What are glycoproteins?
- proteins with attached carbohydrate chains
- Act as receptors
- Enable self recognition and communication
Why is the cell membrane selectively permeable?
- Only specific molecules can pass through depending on size, charge and solubility.
- Small non-polar molecules pass easily.
- Large polar molecules require proteins for transport.
Why is the cell membrane dynamic and flexible?
The fluid nature allows the membrane to adapt to changes in cell shape and to repair minor damages.
Why is the cell membrane self sealing?
The bile layer can reseal itself after small disruptions essential for vesicle formation and fusion.
What is the role of carrier proteins?
Transport specific molecules via active transport or facilitated diffusion.
What are channel proteins?
Provide pathways for ions and polar molecules.
What is meant by the fluid mosaic model?
The membrane is described as a fluid mosaic structure because:
- Fluid: the phospholipids can move naturally giving the membrane flexibility.
- Mosaic: proteins are various shapes and sizes are embedded throughout the phosphate lipid bilayer.
What is diffusion?
A type of passive transport that involves the movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached.
What is facilitated diffusion?
The passive movement of polar charged or water soluble molecules across the cell membrane with the help of specific transport proteins.
What is simple diffusion?
The passive movement of small nonpolar lipid soluble molecules directly through the phospholipid bilayer.
What are four factors affecting diffusion?
- steepness of concentration gradient
- Surface area to volume ratio
- Thickness of membrane
- Temperature
How does a higher temperature increase diffusion rate?
Higher temperature increases molecular kinetic energy enhancing diffusion rates.
What is osmosis?
Passive transport that involves the movement of water molecules across a partially permeable membrane. It occurs from an area of high water potential to an area of low water potential until equilibrium is reached.
What is meant by water potential?
Water potential is the measure of the tendency of water molecules to move and is measured in kilopascals.
What is meant by a partially permeable membrane?
A membrane that allows the passage of water molecules but restricts the movement of larger molecules like solutes.
How does osmosis in animal cells occur?
- if the surrounding solution has higher water potential water enters the cells which may cause it to burst.
- If a surrounding solution has lower water potential water leaves the cell causing it to shrink.
How does osmosis work in plant cells?
- When water enters the cell in a hypotonic solution the cell becomes turgid due to the pressure exerted by the cell wall.
- In a hypertonic solution leaves the cell causing the cell membrane to pull away from the cell wall.
What are three factors affecting osmosis?
- Water potential gradient steepness.
- Thickness of membrane.
- Surface area to volume ratio.
