Unit 1 Chapter 2A Membranes and Transport Flashcards
With reference of the nature of water molecules and the properties of cellular structures, describe how water molecules enter a plant cell.
- Cell wall is fully permeable to water
- Water can pass through cell wall freely by simple diffusion
- Water is repelled by the hydrophobic core of the phospholipid bilayer of the cell membrane
- Channel proteins in the cell membrane provide a hydrophilic pathway for water to pass through the cell membrane to enter the cell (facilitated diffusion)
Explain how the movement of chloride ions into the mucus facilitates the movement of water molecules.
- The movement of chloride ions causes the concentration of chloride ions in the mucus to be higher than that in the tissue fluid
- Leads to a NET movement of water molecules into the mucus by osmosis
- From a region of higher water potential in the tissue fluid to a region of lower water potential in the mucus
Fluid mosaic model
- Phospholipid + some protein molecules can move laterally within each phospholipid bilayer
- Different type of proteins scatter among the phospholipid molecules in cell membrane (e.g. peripheral proteins, integral proteins…)
- Contains cholesterol
What is the function of cholersterol in membrane fluidity
-> Moderate temperature: bind to fatty acid tail of phospholipid molecules to reduce movement (reduce fluidity)
-> Low temperature: hinder closer packing of fatty acid tails of phospholipid molecules (hinder solidification of membrane; increase fluidity)
What is the function of cholesterol in membrane stability
- rigid ring structure of cholersterol
- confers rigidity
Define passive transport
No energy required: diffusion + facilitated diffusion
Define diffusion
net movement of molecules from a region of higher concentration to region of lower concentration down the concentration gradient across a partially permeable membrane
What are the different kinds of diffusion
- Simple diffusion: small, uncharged, non-polar and hydrophobic molecules
- Facilitated diffusion: polar, charged, hydrophilic molecules (requires carrier proteins / channel proteins)
Functions of carrier proteins
- change shape of specific proteins that binds
- release molecules on the other side of the membrane
Define osmosis
Diffusion / net movement of water molecules down a water potential gradient through a partially permeable membrane
Rate of diffusion formula
Surface area x concentration gradient / thickness of exchange membrane
Arrangement of phospholipids in cell membrne
- Phospholipids are arranged “tail-to-tail” in a bilayer in cell membrane with hydrophilic phosphate heads associate with water in aqueous environment inside a cell and water in aqueous environment outside a cell
- The hydrophobic fatty acid tails orientate away from water in aqueous environment inside and outside a cell, thus forming the hydrophobic core of the phospholipid bilayer in cell membrane
Process of endocytosis
- Cell membrane extends to form foot-like pseudopodia to surround the particles
- Part of the cell membrane then pinches off to form a vesicle to enclose the particles
- Cell membrane folds inward to form a pit to surround the particles
- The pit deepens and part of the cell membrane pinches off to form a pit to enclose the particles
(past paper: spec) Compare and contrast exocytosis and endocytosis (4)
Similarities
- both used to transport large particles
- both involves phosopholipid membrane vescicles
Differences
- exocytosis: export of materials (out of cell)
- endocytosis: import of materials (into the cell)
(past paper: spec) Explain why oxygen molecules can pass directly through the cell membrane. (3)
- oxygen molecule is small
- oxygen molecule is non-polar
- pass between gaps in the cell membrane
(past paper: spec) The enzyme OMP decarboxylas increases the rate of carbon dioxide removal from orotidine monophosphate by 10^17 times. State how OMP decarboxylas increases the rate of this reaction. (2)
- acts as a biological catalyst (1)
- forms an enzyme-substrate complex (1)
(past paper: spec) The enzyme OMP decarboxylase increases the rate of carbon dioxide removal from orotidine monophosphate by 10^17 times. Explain why OMP decarboxylase catlyses this reaction only. (3)
- OMP decarboxylase ==> specific (1)
- active site of the enzyme has particular shape (1)
- binds only with orotidine monophosphate (1)
