1.4 membrane structure
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what are the different ways of transport particle move across membranes
• simple diffusion • facilitated diffusion • osmosis • active transport
the membrane is ‘semipermeable’ what does semipermeable mean
to allow some, but not all molecules through. - controls what goes in and out of the cell
what is passive transport
a form of transport which does not require energy as the molecules move from a high to low concentration->down the concentration gradient
examples of passive transport
• diffusion • factiliated diffusion • osmosis
what is active transport
transport through the membrane which does require require energy as the molecule move from a low to high concentration–> moves against the concentratioon gradient
examples of active transport
• ion pumps - phagocytosis
what is a concentration gradient
where the concentration is different across an area -i.e high and low concentration
what is the difference between passive and active transport
• passive doesn’t require energy and goes from high to low concentration • active does require energy and goes from low to high concentration
Diffusion is a form of what type of transport
passive transport
what is diffusion
passive movement of particles • down the concentration gradient • higher to lower concentration • requires no energy
how does diffusion occur
occurs as the consequence of random motion of particles
why can’t all substances diffuse
• the mebrane is semi-permeable so many substances can’t diffuse due to size or polarity
steep gradient
large difference in concentration between the two areas
what affects the speed of diffusion
• the steepness of the concentration gradient - steeper concentration gradient= faster diffusion • size of the molecules • temperature
examples of substances that move via diffusion
mostly gases - oxygen carbon dioxide -glucose
facilitated diffusion
passive transport of molecules or ions across a cell membrane • done through transmembrane integral proteins which transport the molecules
polar molecules
• cannot freely diffuse due to the hydrophobic nature of the fatty acid tails of the phospholipids • are transported by proteins in the form of transmembrane
examples of factilated diffusion
- glucose sodium ions - chloride ions - amino acids - nucleosides
ion channels
facilitated diffusion that involves channel proteins - opens a channel to allow smaller molecules instead of binding to molecules
examples of molecules that ion channels allow through
• sodium • potassium • calcium • chlorine
why do some molecules use factilated diffusion
the lipid bilayer is impermeable to them e.g. the glucose molecule is to large to pass through unassisted
what is osmosis
the movement of water molecules from an area of higher water concentration to an area of lower concentration through a semi-permeable membrane. osmosis is a form of passive transport does not require energy
through osmosis, will water move to the hypertonic or hypotonic area and through what type of transport
the hypertonic area ( the low water area) through osmosis
what is osmolarity
the measure of a solutes concentration