LGS A-Level OCR Biology - Unit 2 - Plasma Membranes
The plasma membrane acts as a selective barrier, separating the cell from its environment and controlling the entry and exit of substances. It also helps in cell recognition, enables cell communication through signaling, and facilitates cell-to-cell attachment for tissue formation and stability.
State 4 functions of plasma membranes
Options:
recognition of other cells
separates cell contents from the outside (barrier between cells and its environment)
controls the passage of materials in and out
allow cell communication
phagocytosis
cell to cell attachment
Key Terms
State 4 functions of plasma membranes
Options:
recognition of other cells
separates cell contents from the outside (barrier between cells and its environment)
controls...
State 4 functions of membranes inside cells
Options:
isolates DNA
acts as an intracellular transport system
compartmentalises reactions
can be the site of chemical rea...
Define compartmentalization
The formation of separate membrane-bound areas
Why is compartmentalisation useful in cells?
incompatible reactions occur within the cell
isolates reactions making them more efficient
allows reaction conditions to be maintained ...
Define partially permeable
A membrane that allows some substances to cross but not others
Define cell signalling
A complex system of intercellular communication
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
State 4 functions of plasma membranes | Options: recognition of other cells separates cell contents from the outside (barrier between cells and its environment) controls the passage of materials in and out allow cell communication phagocytosis cell to cell attachment |
State 4 functions of membranes inside cells | Options: isolates DNA acts as an intracellular transport system compartmentalises reactions can be the site of chemical reactions ribosomes attach protection from lysosomes forms vesicles |
Define compartmentalization | The formation of separate membrane-bound areas |
Why is compartmentalisation useful in cells? | incompatible reactions occur within the cell isolates reactions making them more efficient allows reaction conditions to be maintained (e.g chemical gradients) protects cell components |
Define partially permeable | A membrane that allows some substances to cross but not others |
Define cell signalling | A complex system of intercellular communication |
Define phospholipid bilayer | arrangement of phospholipids found in cell membranes the hydrophilic phosphate heads form the inner and outer surface of a membrane , sandwhiching the fatty acid tails to form a hydrophobic core |
Why are membranes referred to as having a ‘fluid-mosaic structure’ ? | the phospholipids are able to move freely relative to each other (fluid) the proteins embedded in the bilayer vary in shape, size, and position (mosaic) |
Define glycoprotein | Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes |
Define glycolipid | Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes |
Define phospholipid | Modified triglycerides, where one fatty acid has been replaced with a phosphate group |
What are channel proteins? | Membrane proteins that provide a hydrophilic channel through a membrane |
What are receptor proteins? | Extrinstic glycopoteins that bind chemical signals, triggering a response by the cell |
What are carrier proteins? | Membrane proteins that play a part in the transport of substances through a membrane |
What is the approximate width of an animal cell plasma membrane? | 7nm |
What are the functions of cholesterol in cell surface membranes? | regulates fluidity and adds stability to membranes - prevents phospholipids from crystallising |
What are the functions of phospholipids in cell surface membranes? | forms basic structure acts as partially permeable barrier allows the passage of lipid soluble molecules prevents water soluble molecules from moving across |
What are the functions of glycoproteins in cell surface membranes? | receptors for chemical signals cell adhesion when chemical binds to the receptor, events inside the cell are set off binding sites for chemical e.g hormones Hydrogen bonds to water to stabilise membrane |
What are the functions of glycolipids in cell surface membranes? | act as antigens that can be recognised by the immune system form hydrogen bond with water molecules to stabilise membrane |
What are the functions of carrier proteins in cell surface membranes? | have an important role in both passive movement of polar molecules and ions down a concentration gradient this involves the shape of the protein changing |
What are the functions of channel proteins in cell surface membranes? | -provide a hydrophillic channel that allows passive movement of polar molecules and ions down a concentration gradient |
What are the functions of extrinsic proteins in cell surface membranes? | -can attach to the cytoskeleton |
Define cell adhesion | The process by which cells make contacts with each other |
Describe 2 ways in which cholesterol regulates membrane fluidity | hydrophillic end of cholesterol interact with phosphate heads hydrophobic end of cholesterol interacts with fatty acid tails pulling the phospholipids together prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together |
What 3 factors affect membrane structure? | Temperature Solvents Cholesterol |
How does an increase in temperature affect cell membranes? | increases membrane fluidity increases membrane permeability carrier and channel proteins are denatured at higher temperatures membrane loses its structure |
Why does an increase in temperature increase membrane permeability? | more temperature means phospholipids move more because they have a higher kinetic energy makes it easier for things to pass through |
How do solvents affect cell membranes? | membrane loses structure | - increases permeability |
Why do solvents increase membrane permeability? | -solvents dissolve phospholipids |
Give an example of a solvent that can dissolve phospholipids | Ethanol, Methanol etc. |
Outline how the effect of temperature on membrane permeability can be investigated | beetroot cells contain betalain when membranes are disrupted the red pigment is released pieces of equal size beetroot are placed in water and heated in waterbaths at different temperatures for the same amount of time the solutions are placed in a colorimeter |
How can a colorimeter show the permeability of membranes? | more permeable means more betalain leaks out | - more betalain means less light is absorbed by the detector |
Outline how the effect of solvents on membrane permeability can be investigated | beetroot cells contain betalain when membranes are disrupted the red pigment is released pieces of equal size beetroot are placed in different concentrations of a solvent for the same amount of time the solutions are placed in a colorimeter |
Suggest 3 improvements of the design of the experiment | cut pieces from same place in beetroot blot surface of beetroot before experiment use same volume of water |