Cellular Process

Question 1

What is diffusion?

Answer 1

passive process in the random mixing of particles in a solution occurring due to the particles kinetic energy.

Question 2

factors influencing diffusion

Answer 2

• steepness of concentration gradient
• temperature
• mass of the diffusing substance
  -surface area
  -diffusion distance

Question 3

simple diffusion

Answer 3

• no energy required
• move due to gradient, e.g. difference in concentrations, pressure, charges etc
• move to equalize gradient, where high moves towards low.
• depends on lipid solubility

Question 4

facilitated diffusion

Answer 4

• solutes too polar or highly charged to move through lipid bilayer by simple diffusion cross the plasma membrane facilitated diffusion.
• this requires a carrier in the membrane but it is not ATP.
• solute goes down a concentration gradient
• occurs through, ion channels and protein transporters (also called carriers)

Question 5

facilitated diffusion through ion channels

Answer 5

integral transmembrane proteins allow the passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer. Chanel is gated, changes in one shape to open pore and changed another way to close it. three types of different gated channels: ligand gated, voltage gated, mechanically gated.

Question 6

facilitated diffusion through protein transmembrane

Answer 6

carrier used to move solute down a concentration gradient. solute binds more often to the carrier on the side of the membrane with a higher concentration of solute. carriers are occupied, transport maximum is reached, process of carrier mediated facilitated diffusion exhibits saturation (the extent to which something is dissolved). usually substances moved by carrier mediated facilitated diffusion include glucose, fructose, galactose and some vitamins.

Question 7

osmosis

Answer 7

• diffusion of water through semi permeable membrane
• permeable to solvent. impermeable to solute.
• water molecules pass through two ways: moving through lipid bilayer through simple diffusion or by moving through aquaporins, integral membrane proteins that function as water channels.
• total solute concentration of a solution is known as osmolarity.
• one osmol is equal to 1 mol of solute particles.

Question 8

tonicity

Answer 8

ability of a solution to change the shape or tone of cells by altering their internal water volume.

Question 9

terminology

Answer 9

Question 10

molecule movement across membranes

Answer 10

Question 11

active transport

Answer 11

• uses energy to move molecules against the concentration gradient.
• transporters known as ‘pumps’
• pumps can be saturated and use two types of energy sources: direct us of ATP in primary active transport or the use of an electrochemical gradient across a membrane to drive the process in secondary active transport.

Question 12

primary active transport

Answer 12

• major primary active transport proteins found in cells: Na+/K+-ATPas, Ca2+- ATPase, H+- ATPase, H+/K+ -ATPase.
  
  • primary active transporter is found in every cell and helps maintain and establish the membrane potential of the cell.

Question 13

secondary active transport

Answer 13

• different from primary active transport as it uses the electrochemical gradient as its energy source rather than pumps.
• transporters that mediate secondary active transport have two binding sites, one for an ion (e.g. Na+) and another for the cotransported molecule (e.g. glucose).
• cotransporters (symporters) move molecules in the same direction.
• counter transporters (antiporters) move molecules in opposite directions.

Question 14

vesicular transport

Answer 14

endocytosis
exocytosis

Question 15

endocytosis

Answer 15

movement of macromolecules into the cell by the pinching of the plasma membrane into membrane bound vesicles.

• packaging of extracellular materials in vesicles at the cell surface.
• involves large amounts of extracellular material.
• requires ATP for energy
• three major types of endocytosis: receptor mediated endocytosis, pinocytosis, phagocytosis.

Question 16

receptor-mediated endocytosis

Answer 16

• highly selective
• vesicle forms after receptor protein in the plasma membrane recognises and binds to a particle in the extracellular fluid.
• example: cells take up cholesterol containing low density lipoproteins (LDLs), antibodies and certain hormones this way.
• involves formation of vesicles at surface of membrane
• clathrin coates vesicle in cytoplasm.

Question 17

pinocytosis

Answer 17

• plasma membrane forms invagination, sinks inward, pinches off and forms a vesicle.
• material dissolves in water to be brought into cell.
• called ‘cell drinking’
• most common form of endocytosis in cells, especially absorptive cells in the intestines and kidneys.
• most proteins and other large molecules are taken up this way.

Question 18

phagocytosis

Answer 18

• used to engulf large, solid, particles such as food, bacteria etc into vesicles.
• known as cell eating
• body cells known as phagocytes carry out phagocytosis.
• this is a vital defence mechanism that helps protect the body from disease.

Question 19

exocytosis

Answer 19

• cytoplasmic vesicle merges with plasma membrane and releases its contents.
• requires ATP as energy and ca2+ ions.
• e.g. golgi body vesicles merge with plasma membrane and release their contents. another example, nerve cells communicate to another cell releasing chemicals at the synaptic terminal.

Question 20

transcytosis

Answer 20

• used to move substance into, across, and out of cell.
• active process
• vesicles undergo endocytosis on one side of the cell, move across, then undergo exocytosis on the opposite side of the cell.
• occurs most often across endothelial cells that line blood vessels and when a women is pregnant, some of her antobodies cross the placenta into the foetal cirulation via transcytosis vesicle merges with the