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Cell Membrane
Cell and Molecular Biology
| Question | Answer |
|---|---|
| State FOUR functions of membranes in cells. | 1) Control of entry and exit of materials 2) Isolate organelles and enzymes for metabolic reactions 3) Provide an internal transport system 4) Provide surfaces on which processes can occur |
| What is the role of extrinsic (peripheral) proteins in a membrane? | They give mechanical support to the membrane. They may also have enzymes used in cell signalling. |
| What is the role of intrinsic (integral) proteins in a membrane? | These are embedded throughout the membrane. Two types: Channel proteins - form open water-filled tubes to allow water-soluble ions to diffuse. Carrier proteins - change shape to move specific molecules such as glucose and amino acids across the membrane |
| Why is the arrangement of cell-surface membrane described as a fluid-mosaic model? | Fluid - due to the ability of the phospholipids and protein molecules to move relative to each other. The membrane is flexible. Mosaic - due to the varying shape, size and pattern of the proteins in the bilayer. |
| List the roles of phospholipids in cell surface membranes. | 1) Allow lipid soluble substances to enter and leave the cell 2) Prevent entry and exit of water-soluble substances 3) Give membrane fluidity |
| List the roles of cholesterol in cell surface membranes. | 1) Reduce lateral movement of phospholipids 2) Regulate membrane fluidity depending on temperature 3) Prevent passage of dissolved polar molecules and ions across the membrane |
| List the roles of glycolipids in cell surface membranes. | 1) Act as recognition sites 2) Help maintain stability of the membrane 3) Help cells attach to one another and form tissues. |
| List the roles of glycoproteins in cell surface membranes. | 1) Act as recognition sites for hormones and neurotransmitters 2) Help cells attach to one another and form tissues 3) Allow cells to recognize one another e.g. lymphocytes can recognize an organism's own cells. |
| List the roles of proteins in cell surface membranes. | 1) Provide structural support 2) Act as carrier proteins transporting glucose and amino acids 3) Function as enzymes 4) Form channel proteins for sodium, potassium etc 5) Act as energy transducers 6) Cell recognition etc |
| Name of transport processes which require energy. | Active transport |
| Name of transport processes which do not require energy. | Passive transport |
| What is diffusion? | The net movement of molecules or ions from a region where they are more highly concentrated to one where there concentration is lower until equilibrium is established. |
| What is dynamic equilibrium. | The even distribution of particles which are continuously in motion/changing position. |
| What is facilitated diffusion? | It is the passive movement of particles down/along a concentration gradient however it only occurs at specific points on the cell membrane where special proteins (channel and carrier proteins) are located. |
| These are water-filled channels across a membrane which allow water soluble ions to pass through. They are specific to particular ions. | Channel proteins |
| There proteins undergo conformational changes in shape to allow molecules entry and exit. | Carrier proteins |
| What is osmosis? | The passage of water from a region where there is a higher water potential to a region of lower water potential through a partially (selectively) permeable membrane until equilibrium is established. Osmosis is the diffusion of water. |
| What is a solute? | The substance which dissolves eg. glucose. |
| What is a solvent? | The substance in which a solute dissolves . eg. water |
| What is a solution? | solute + solvent |
| What is a hypotonic solution? | A solution with more water than solute ie. a higher water potential |
| What is a hypertonic solution? | A solution with less water than solute ie. a lower water potential |
| What is an isotonic solution? | A solution with equal concentration of solute and water. |
| T or F. There is always a net movement of water from a hypotonic solution to a hypertonic solution. | True |
| What is active transport? | The movement of molecules or ions into or out of cell from a region of lower concentration to a region of higher concentration using energy and carrier molecules. |
| Describe 5 key features of active transport. | 1) Metabolic energy (ATP) is needed 2) Materials are moved AGAINST concentration gradient from low to high conc. 3) Carrier proteins involved which act as pumps. 4) Carrier proteins change shape. 5) Process selective to specific substances. |
| Name two processes which: - occur along a concentration gradient - do not require ATP to supply energy - never use carrier molecules | Diffusion and osmosis |
| Name one process which: - occurs along a concentration gradient - does not require ATP to supply energy - uses carrier molecules | Facilitated diffusion |
| Name one process which: - occurs against a concentration gradient - requires ATP to supply energy - uses carrier molecules | Active transport |
| What is endocytosis? | The bulk movement of material into a cell. Process requires ATP. E.g. Engulfing of bacteria and other pathogens by white blood cells. |
| What is exocytosis? | The bulk movement of material out of a cell. Process requires ATP. Egg. release of hormones from adrenal glands. |
| Name the two forms of endocytosis. | 1) Phagocytosis 2) Pinocytosis |
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CAPE Biology Unit 1
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