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CET - Cell Membranes
OCR A level Biology F211
| Question | Answer |
|---|---|
| What is the function of the plasma membrane? | 1.PARTIALLY PERMEABLE – they let some molecules through but not others. Substances can move across the membrane by diffusion, osmosis or active transport. 2.Allow recognition by other cells e.g. cells of the immune system. 3.Allow cell communication. |
| What is the function of membranes within cells? | 1.Divide cell into different compartments - different functions more efficient. 2.Some are folded, surface area making chemical reactions more efficient. 3.Form vesicles - transport. 4.Control substances entering and leaving organelle (PP). |
| How thick is the fluid mosaic? | 7nm. |
| What is the fluid mosaic made of? | Mostly phospholipids. |
| What other molecules are found in the bilayer? | Cholesterol, protein, glycoprotein and glycolipids. |
| What is the function of phospholipids in the bilayer? | Form a barrier to dissolved substances - hydrophobic tails point inwards so water soluble substances can't pass through. |
| What is the function of cholesterol in the bilayer? | Gives membrane stability, fit in between phospholipids and bind to hydrophobic tails, so they pack more closely - more rigid membrane. |
| What is the function of proteins in the bilayer? | Control what enters and laves cell. Some form channels allowing small/charged particles through. Carrier proteins transport molecules/ions by active transport + facilitated diffusion. Also act as receptors in cell signalling. |
| What is a receptor in cell signalling? | When a molecule binds to the protein a chemical reaction is triggered inside the cell. |
| What is the function of glycolipids and glycoproteins in cell membranes? | Act as receptors for messenger molecules. Drugs, hormones and antibodies can bind to them. Receptors for cell signalling. Are antigens. Stabilise membrane by forming H-bonds with surrounding water. |
| How do temperatures below 0 affect the membrane? | Phospholipids have less energy, move less, are packed tightly, membrane is rigid. Chennel proteins and carrier proteins denature, increasing permeability. Ice crystals may pierce the membrane - hightly permeable when thaws. |
| How do temperatures between 0 and 45 affect the membrane? | Phospholipids can move and aren't so tightly packed - membrane partially permeable. Phospholipids move more at higher temperatures, increasing permeability. |
| How do temperatures above 45 affect the membrane? | Begins to break down, becomes more permeable. Water incide cell expands, pressure on membrane. Channel and carrier proteins denature, cannot control what enters or leaves cell, increasing permeability. |
| Why do cells need to communicate? | To control bodily processes and respond to environmental changes. |
| How do cells communicate using messenger molecules? | Cell releases molecule, which travels to another cell. Messenger molecule detected by cell by binding to receptor on cell membrane. |
| What is the role of cell membrane receptors in cell signalling? | Proteins are receptors for messenger molecules. Specific shapes - complementary mess molecules bind. Different cells have different types of receptors - bind to different mess molecules. Cell that responds to particular mess molecule icalled target cell. |
| How do drugs act on cell membrane rceptors? | Bind to receptor in cell membrane. Either trigger a response in the cell or block receptor and prevent it from working. |
| Define diffusion? | Net movement of particles down the concentration gradient from an area of higher concentration to an area of lower concentration. |
| What factors affect diffusion rate? | Higher conc grad means faster diffusion rate. Thinner exchange surface gives faster diffusion rate. Large SA gives faster diffusion rate. |
| Define osmosis? | Net movement of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential. |
| What is water potential? | The potential of water molecules to diffuse out of or into a solution. |
| How does the water potential of the surrounding solution affect cells? | When surrounding water pot is higher, water moves in, animal cell to bust, plant cell becomes turgid (vacuole swells). Water potentials are the same nothing happens. Solution water potential lower, animal cell shrinks, plant becomes plasmolysed. |
| What is facilitated diffusion? | When particles are too large or charged to diffuse directly through phospholipid bilayer so diffuse through carrier or channel proteins in cell membrane. |
| Is facilitated diffusion passive or active? | Passive. |
| What is the difference between a carrier protein and a channel protein? | In a carrier protein, the molecule attaching causes it to change shape so the molecule can pass through. Channel proteins are just pores, which facilitate diffusion of particular particles. |
| What is active transport? | Uses energy to move molecules and ions across plasma membrane, against a concentration gradient. Involves carrier protein. |
| How is active transport similar and different to facilitated diffusion? | Similar: molecule attaches to carrier protein, which changes shape, and it is released on the other side. Different: ATP is required. |
| How do cells take in substances by endocytosis? | Large molecule surrounded by cell with section of membrane, which pinches off to form a vesicle around molecule. |
| How do cells secrete substances by exocytosis? | Vesicles carry substances from Golgi to plasma membrane. Vesicles fuse with membrane and release contents. Some are inserted straight into the plasma membrane (eg membrane proteins). |
Created by:
emm142
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