Flashcards in Transport across membranes Deck (56)
Define the term ''simple diffusion''.
Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down the concentration gradient.
Define the term ''facilitated diffusion''.
The diffusion of particles through carrier or channel proteins in the plasma membrane
* Define the term “osmosis”.
The diffusion of water across a partially permeable membrane down a water potential gradient. A passive process (does not require energy).
* Define the term “passive transport”.
The movements of substances across cell membranes without the requirement of energy.
* Define the term “active transport”.
The movement of particles across the plasma membrane against a concentration gradient. Requires energy and carrier proteins.
* Define the term“endocytosis”.
The process by which a cell surrounds substances with a section of its plasma membrane and takes them into the cell. An active process requiring ATP.
* Define the term “exocytosis”.
The bulk transport of materials out of cells. Vesicles containing the material fuse with the cell surface membrane and the contents are released to the outside of the cell.
* Define the term “pinocytosis”.
The endocytosis of liquid materials.
* Define the term “phagocytosis”.
The process by which white blood cells called phagocytes recognise non-self cells and engulf them and digest them within a vesicle called a phagolysosome.
Explain the difference between a channel protein and a carrier protein and link this to their functions.
Channel proteins are only involved in passive transportion. They provide a hydrophilic channel for polar molecules and ions.
Carrier proteins are involved in both active and passive transportation. It often involves the shape of the carrier protein itself changing.
State 3 particular examples of channel proteins and 3 carrier proteins and for each describe the role that they perform.
- GLUT1 is found in almost all animal cells and specifically helps to transport glucose across the plasma membrane
Explain the importance of the structure of ATP in active transport.
1)Small - it can move easily acroos and within cells.
2)Water soluable - energy requiring processes happen in aqueous environments .
3)Contains bonds between phosphate with immediate energy; large enough to be useful for cellular reactions but not so large that energy is wasted as heat.
4)Releases in small quantities - small quantities are suitable to most cellular needs so that energy is not wasted as heat
5) Easily regenerated - can be recharged with energy.
List the factors affecting the rate of diffusion of a molecule.
- Temperature: the higher the temp the higher the rate of diffusion as the particles have more kinetic energy.
- Concentration difference: the greater the difference the faster the rate of diffusion because the overall movement from the higher concentration to lower concentration will be larger. There is a steeper concentration gradient.
- Surface area: a big surface area means a higher rate of diffusion.
- Thickness of membrane: thinner membrane means faster rate.
How can substances move across a membrane by simple diffusion.
Diffusion happens because gas or liquid particles have kinetic energy. The movement is random and an uneven distribution of particles will eventually become an equal distribution. It is a passive process and it will continue until there is a concentration equilibrium between the two areas.
State which types of molecule can move across a membrane by simple diffusion.
Non-polar molecules like oxygen freely diffuse through, down a concentration gradient.
The hydrophobic interior of the membrane repels ions so they can't pass through easily.
Polar molecules like water can diffuse through membranes but only at a very slow rate. Small ones pass through more easily.
Explain, in a paragraph and with a diagram, how substances can move across a membrane by facilitated diffusion (include protein specificity).
Membranes contain channel proteins through which polar molecules and ions can pass. Membranes with protein channels are selectively permeable as protein channels are specific to one molecule of ion. It can also involve carrier proteins which change shape when a specific molecules binds to it. It doesn't require energy and is down the concentration gradient.
Same factors affecting it as simple diffusion but also the number of channel proteins.
Explain, in a paragraph and with a diagram, how substances can move across a membrane by active transport.
Active transport is the movement of molecules or ions into or out of a cell from a region of low concentration to a region of high concentration against the conc gradient.
Requires energy and carrier proteins, metabolic energy is supplied by ATP.
A molecules attaches to a carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.
Explain, in a paragraph and with a diagram, how substances can move into a cell by endocytosis (using phagocytosis as an example).
Some molecules are way too large (proteins, lipids, some carbs and some white blood cells i.e. phagocytes) to be taken into a cell by carrier proteins. Instead a cell can surround a substance with a section of its plasma membrane, the membrane pinches off to form to a vesicle inside the cell containing the ingested substance.
This uses ATP for energy.
Explain, in a paragraph and with a diagram, how substances can move out of a cell by exocytosis (using secretion as an example).
Some substances produced by the cell like hormones or digestive enzymes or lipids need to be released from the cell. Vesicles containing these substances pinch off from the sacks of the golgi apparatus and move toward the plasma membrane. The vesicles fuse with the plasma membrane and release their contents outside the cell. It uses ATP.
Identify which transport mechanisms require an input of energy from ATP.
Active transport, endocytosis and exocytosis.
Explain why it is easier for an oxygen molecule to diffuse across a membrane than a water molecule.
Because an oxgen molecules is non-polar so it doesn't get repelled by the hydrophobic interior of the membrane.
Explain why steroid hormones can easily cross a membrane by simple diffusion.
They are lipid derived hormones so they can pass through every cell in our body.
Explain why ions are only able to cross a membrane through a protein channel.
Because they are repelled by the hydrophobic interior of the membrane. So they need to be transported in a protein channel.
Describe how to carry out an investigation to investigate how the rate of diffusion is affected by surface area.
1) Cut different sizes of agar jelly with phenolphthalein indicator in it.
2) Put into a beaker of NaOH and time and long it takes for the the agar to turn pink.
Describe and explain the results you would expect to see in an investigation into how the rate of diffusion is affected by surface area.
The higher the surface area to volume ratio, the faster the rate of diffusion.
Describe how to carry out an experiment to investigate how the rate of diffusion is affected by temperature.
1) Prepare agar jelly and cut into equal sized cubes
2) Prepare several different boiling tubes containing the same concentration of HCL and put them in separate water baths of different temperatures
3) When the HCL has reached desired temp put the agr jelly in and time how long it takes the cube to go colourless.
Describe and explain the results you would expect to see in an investigation into how the rate of diffusion is affected by temperature.
The higher the temp, the faster the rate of diffusion.
Define the term “solvent”.
A liquid in which substances (or solutes) are dissolved forming a solution.
Define the term “solute”
A substance dissolved in a solvent to form a component of a solution.