4.1 Cell Transport Mechanisms Flashcards
why are transport systems needed in cells
-cells require a supply of chemicals like glucose or oxygen for cellular respiration
-respiration is what supplies us with energy for the other reactions of life, and produces waste product carbon dioxide
-waste products need to be removed
what is the role of the cell surface membrane
acts as a gatekeeper for the cell and controls the transport of materials into and out of the membrane
also control transport within the cells, e.g ER and golgi apparatus are membrane bound organelles that control the movement of substances within the cell
what are the roles of the following structures within the cell
-glycoproteins
-peripheral proteins
-membrane bilayer
-integral proteins
- Gly. often act as antigens, important for cell recognition or hormone receptors
- Per. may be enzymes, involved in regulating transport
- Bil. fluid bilayer of phospholipids, the polar heads face the inside and outside of the cell, with a hydrophobic lipid core
- Int. main transport system of the membranes, forming permanent
what is the difference between active and passive transport
Passive transport takes place as a result of concentration or pressure gradients and involves no energy whilst active transport requires (ATP) adenosine trio phosphate
name and define the three modes of passive transport
Diffusion- movement of particles in a liquid or gas from an area of relatively high concentration to an area of relatively low concentration
Facilitated diffusion- Diffusion that takes place through carrier proteins or the protein lined pores in the cell membrane
Osmosis- the movement of solvent molecules down a concentration gradient through a partially permeable membrane
name and define the three modes of active transport
Endocytosis- the movement of large molecules into cells through vesicle formation
Exocytosis- The movement of large molecules out of cells through vesicle formation
Active transport- the direct movement of substances across a cell membrane using ATP produced in cellular respiration
name the factors that affect how a molecule would be transported across a membrane
- the size of the molecule
- its solubility in lipids and water
- the presence of absence of charge
give examples of small molecules, a large molecule and a charged particle
Small - oxygen and carbon dioxide (pass freely)
Large - steroid hormones
Charged - sodium ions
Define diffusion and state WHY it happens
The movement of molecules from an area of high concentration to an area of low concentration
This is due to the random movement that occurs because of the energy they have, which is dependent on the temperature
which molecules can and can’t move across a membrane by simple diffusion
Can - oxygen and carbon dioxide because they’re small
Can’t - anything larger than carbon dioxide, and ions
Which molecules move by facilitated diffusion
anything with a strong positive or negative charge or large molecules
How does facilitated diffusion work by gated channels
Large or charged molecules e.g. amino acids move across the cell membrane down a concentration gradient
using the specific proteins in the membrane (that form pores) that only allow specific substances to move through passively by changing shape
what is a gated channel
Channels that only open only when specific molecules are present or when there’s an electrical charge across the membrane e.g. passing of nerve impulses
describe the form of facilitated diffusion that occurs with carrier proteins found floating around the surface of the membrane
the carrier proteins are found on the outside of the cell when there is a higher conc. pf the molecule on the outside (and visa versa)
the carrier proteins are specific to each molecule or group of molecules
the proteins pick up the molecule, change shape, transport it through the membrane an release it
it does not require energy
define osmosis
the net movement of molecules from a region of high concentration to a region of low concentration through a partially permeable membrane
what is considered when finding the osmotic concentration
the osmotic concentrations concerns only the solutes that have an osmotic effect. Many large, insoluble molecules found in the cytoplasm, (starch and lipids) don’t affect the movement of water
describe how to model osmosis in cells
using an artificial membrane that is permeable to some molecules but not others e.g water and sucrose
define an isotonic solution
osmotic concentration of the solutes in the solution is the same as the those in the cells
define a hypotonic solution
the osmotic concentration of the solutes in the solution us lower than that in the cytoplasm of the cells
define a hypertonic solution
The external solution has a high solute concentration and low water concentration in comparison to the cells
why does osmosis in animals need to be kept to a minimum
because animal cells are fragile, they shrivel and burst easily and cytoplasm looses is structure
how is hydrostatic pressure induced
when cytoplasm swells and presses against cell walls
what is pressure potential
the inward pressure of cell wall on the cytoplasm
when is the cell in turgor
when the osmotic force of water moving into the plant is equal to the pressure potential
incipient plasmolysis
when a cell is put in a slightly hypertonic solution, the membrane begins to pull away from the cell wall and the protoplasm shrinks.
what is water potential
- a measure of the potential of water to move OUT of a solution by osmosis
- the maximum value is given as 0, and it would be the value of pure water, so anything else is negative
if the turgor pressure is equal to the osmotic potential, what is happening?
water moves into cell by osmosis, cell swells, cell wall stops further swelling, hydrostatic pressure induced, turgor pressure induced (inwards pressure), turgor pressure rises until its equal to osmotic force pulling water into cell
what is osmotic potential
the potential of water to move out of a solution across a partially permeable membrane from a hypotonic to hypertonic solution
define osmosis
the net movement of water from an area of higher osmotic potential to an area of lower osmotic potential through a partially permeable membrane
define osmosis (water potential)
the net movement of water molecules from an area of higher water potential to an area of lower water potential
equation for water potential
turgor pressure + osmotic potential
turgor pressure- usually +ive
osmotic potential - always -ive
what is active transport
is the movement of substances across a membrane with a carrier protein against the concentration gradient using energy in the form of ATP supplied by the cell
describe the use of ATP
the enzyme ATPase catalyses hydrolysis of ATP which breaks a bond and forms two more, releasing the energy used by the cell
describe the process of endocytosis
large molecule of a certain shape will be transported by a protein in the cell membrane that changes shape to transport the molecule onto the other side of the cell. The change in shape requires energy from ATP hydrolysis. The carrier protein then reverts back to original shape to allow for transportation of more molecules
what are the points of evidence for active transport
- it only takes place in living things
- rate of active transport depends on temp. and oxygen conc. which affect respiration rate and ATP production rate
- cells that are known to carry out a lot of active transport have a lot of mitochondria to respire and produce ATP
- poisons that prevent ATPase working also prevent active transport
