Topic 2: 2.1 Flashcards
Diffusion
Net movement of particles from an area of high concentration to low concentration, down a concentration gradient
- passive process -> no additional energy needed
Effect of surface area to volume ratio
Larger organisms have a smaller surface area to volume ratio than small organisms
-> this means that gas exchange happens at a slower rate so large organisms have mass transport systems to keep up with the demand
Gas exchange surfaces feautres
Gas exchange surfaces have features which increase the rate of diffusion
Examples:
- large surface area to volume ratio
- short diffusion distance
- steep concentration gradient
. Alveolar epithelium: gas exchange surface in mammals -> oxygen diffuses out of the alveoli into the blood and carbon dioxide diffuses into the alveoli from the blood
Lung adaptations
. Lots of alveoli -> large surface area
. The alveoli and capillary endothelium are each one cell thick and their cells are flattened forming capillary and alveoli walls -> short diffusion pathway
. Good blood supply from capillaries and good ventilation with air -> steep concentration gradient
Ficks law
Relates rate of diffusion to the concentration gradient, surface area and thickness of exchange surface
It states that:
. Surface area is directly proportional to the rate of diffusion
. Concentration gradient is directly proportional to the rate of diffusion
. Thickness of surface is inversely proportional to the rate of diffusion
Membrane functions
Plasma membrane:
. Separates cell contents from surroundings
. Controls what comes in and out of cells
Membrane within cells:
. Separates contents of organelle from cytoplasm
. Controls passage of certain particles into and out of organelles
. Site of certain chemical reactions
Membrane structure and properties: cholesterol
Type of lipid found in between phospholipids forming bonds with them
-> this makes the membrane more fluid at high temperatures and more rigid at low temperatures
Membrane structure and properties: internal proteins
Embedded in plasma membrane for transport of particles
. Examples:
- channel proteins
- carrier proteins
Membrane structure and properties: phospholipids
Form a continuos bilayer in membrane -> a single phospholipid is made up of a phosphate hydrophilic head and two hydrophobic fatty acid tails
. Formation of bilayer:
- the head is hydrophilic (attracts water) so the phosphate head flip outwards towards the tissue fluid or cytoplasm as both contain water
- the tail is made up of two fatty acids making it hydrophobic (repel water) so the fatty acid tails flip inwards
Membrane structure and properties: external proteins
Receptors that carry out cell signalling on the surface of the membrane -> they bind to messengers (eg hormones) to create a change in that cell
. Examples:
-> glycoprotein -> made up of carbohydrates and protein
-> glycolipid -> made up of carbohydrate and fatty acid
Fluid mosaic model
Shows that proteins are randomly distributed in cell membranes making them fluid
-> fluid: as phospholipids are free to move in the plane of the membrane
-> mosaic: proteins are embedded in various shapes, sizes and positions
Ósmosis
Movement of water molecules from an area of low concentration of solutes (high water concentration)to and area of high concentration of solutes (low water concentration) though a partially permeable membrane
. Free water molecules. Those that are not used as solvent
Permeability of membranes
Membranes are partially permeable which means that they allow the transport of certain particles -> all membranes will be completely permeable to small uncharged particles which pass in between the phospholipids
-> charged particles: they’re water-soluble substances so they’re repelled by the phospholipid tail and so can’t go through membrane
-> large particles: they don’t fit the gaps between phospholipids and so can’t go through membrane
Effect of temperature un membrane permeability
. At high temperatures the phospholipids can move around more because they have more energy and so aren’t as closely packed together and increases permeability
-> at extremely high temperatures the proteins in the membrane denature and water expands in the cell causing pressure on the membrane which deforms the cell membrane structure and so it looses control over what enters
. At low temperatures the phospholipids can’t move around because they don’t have much energy and so they are closely packed together and this decreases permeability
Facilitated diffusion
Diffusion of particles in cell membrane down a concentration gradient through carrier and channel proteins
-> passive process
Carrier proteins
Move large molecules down their concentration gradient
-> each carrier protein is specific to one particle only
1. A large molecule attaches to a carrier protein in the membrane
2. The particles kinetic energy cause the protein shape releasing the molecule on the other side of the membrane
Channel proteins
Form pores/ channels in in the phospholipid in the membrane for charged particles to diffuse through down their concentration gradient preventing them from being repelled by the fatty acid tails
-> each channel protein is specific to one particles only
Active transport
Movement of particles against a concentration gradient through carrier proteins using ATP
. ATP: produced by respiration -> its hydrolysed in the cel to release energy
-> used as an immediate source of energy in the cell
Endocytosis
Bulk transport of large molecules into the cell using energy from ATP
1. Cell membranes surrounds the molecule
2. Membrane pinches off to form a vesicle inside the cell containing the molecule
Exocytosis
Bulk transport of large molecules out of the cell using energy ATP
1. Vesicle containing the molecule pinch off from the sacs of the Golgi apparatus and moves towards the cell membrane
2. Vesicles fuses with the cell membrane and it:
- releases the molecule out of the cell
- inserts the molecule into the cell membrane
What evidence led to the fluid mosaic model
- Microscope images show proteins in the bilayer
- Phospholipids form a bilayer
- Lipid-soluble molecules move faster across membranes
- Coloured/tagged/labelled proteins can be seen to move within a membrane
