Plamsa Membrane Flashcards
what is passive movement? Active movement?
no energy. energy
what substances are permeable?
small uncharged particles such as oxygen and carbon dioxide, lipid-soluble and non-polar molecules such as alcohol and steroids
what are permeable or semipermeable molecules?
small polar molecules such as water and urea
what substances are non-permeable and how do they enter?
small ions such as potassium ions, sodium ions and chloride ions and large, polar, water-soluble molecules such as amino acids and glucose. via a protein channel
what are the different transport processes? (5)
diffusion, facilitated diffusion, osmosis, active transport, bulk transport
what is the definition of diffusion?
the net movement of substances from a region of high concentration to a region of low concentration (concentration gradient)
how does diffusion work, does it require energy and when does it stop?
molecules diffuse down the concentration gradient, no energy, it stops when the concentration is even on both sides of the membrane
what is facilitated diffusion? when is this necessary? is energy needed? How does this work?
sometimes a carrier molecule is needed to move molecules down a protein channel. substances that cannot diffuse through the bilayer. no energy is needed. Carrier molecules, envelope and release the transported molecule. It is highly selective, carrier for glucose only binds with glucose.
what is the definition of osmosis?
The net movement of water across the SPM from an area of high concentration of water (low solute) to low concentration of water (high solute)
what is osmosis and when does it occur?
the diffusion of water. it occurs when there is a difference in the concentrations of water on two sides of a membrane
How does a plant cell become turgid?
water molecules move by osmosis into the vacuole. The vacuole swells and pushes the plasma membrane against the cell wall, making it turgid. this keeps the cell firm, helping it to maintain shape and form.
what is plasmolysis?
when plant cells shrink as water is drawn out
can a plant cell burst if too much water is taken in?
no because of the cell wall
what is crenation?
when an animal cell shrinks
what is the definition of active transport?
the net movement of dissolves substances into or out of the cells against the concentration gradient.
when is active transport needed? does it need energy? what does it involve?
sometimes a cell needs a substance that is found in low concentrations outside the cell but high inside the cell. this requires energy (ATP) and carrier proteins
what is bulk transport endocytosis?
The process where substances are brought into a cell by a folding of the plasma membrane and the creation of a vesicle
what is phagocytosis?
endocytosis of solids
what is pinocytosis?
endocytosis of liquids
what is exocytosis?
The process whereby a vesicle fuses with the plasma membrane to allow the release of its contents from the cell.
What controls the movement of substances between the extracellular and intracellular fluid?
the plasma membrane
How is the plasma membrane made up? What does it do? What does its composition depend on?
it consists of two layers of phospholipid molecules with other molecules including proteins, carbohydrates and cholesterol scattered throughout. keeps the interior of the cell separate from the exterior. composition depends on the needs of the cell
Most membranes are asymmetrical. What does this mean?
The layers have different properties to each other eg. the pattern of proteins and carbohydrates.
What other functions does the plasma membrane preform?
functions such as cell recognition and commutation with other cells.
What are phospholipid bilayers like and why are they called bilayers?
they have a hydrophobic (water repelling) tail and a hydrophilic (water attracting) head. It is called a bilayer because it has two layers of phospholipids, the heads on the outer sides and the tails meeting in the middle.
What does the phospholipid nature of the plasma membrane mean for the cell?
the plasma membrane is impermeable to water soluble particles, ions and polar molecules. The movement of these particles is controlled by protein channels which allows the exchange of molecules to be regulated. This is important for cellular respiration, digestion and elimination of wastes - to keep it alive.
Plasma membranes are fluid structures. what does this mean? What does the level of fluidity depend on?
that individual phospholipids and some proteins are free to move between the layers but they rarely go from one side to the other. depends on the percentage of unsaturated fatty acids in the phospholipid molecules. The higher the % the more fluid.
What is a phospholipid?
A molecule consists of long chain of fatty acids (hydrophobic) and a phosphate (hydrophilic). This is the major component of plasma membranes.
What is cholesterol and what does it do?
a fatty molecule that is between the phospholipids. cholesterol gives stability to the membrane without altering fluidity and reduces permeability of the membrane to small water soluble molecules.
where are proteins located in the membrane? What are the two different types? What do these two different types do?
They can move around but may be limited to certain areas. Proteins that are a permanent part of the membrane are called integral proteins. temporary ones are called peripheral proteins. When integral proteins span both layers they are called transmembrane proteins. Peripheral proteins bind to integral proteins or penetrate into the surface of the plasma membrane.
Where are carbohydrates in the membrane? what does this form? What do they do?
they are usually linked to protruding proteins (forming glycoproteins) or to lipids (glycolipids) on the outer surface of the membrane. They play the role of recognition and adhesion between cells and in the recognition of antibodies, hormones and viruses by cells.
