CH5 transport across membranes Flashcards
What is diffusion
The net movement of particles from a region of higher concentration to an area of lower concentration
Why are cells often microscopic
- particles are constantly colliding which slows them down
- over shorter distances there are fewer collisions so is faster
What leads to increased diffusion rate
- increased temperature
- greater concentration difference
What particles are able to diffuse across the phospholipid bilayer
Non-polar molecules
Why are polar molecules unable to diffuse across phospholipid bilayer
Hydrophobic interior repels substances with a charge
What increases rate of diffusion across membranes
- increased surface area
- thinner membrane
What is facilitated diffusion
Diffusion across a membrane through protein channels (usually specific to one molecule or ion) or carrier proteins
What is active transport
Movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration requiring energy and carrier proteins
What is the process of active transport
- molecule or ion to be transported binds to receptors in channel of carrier protein
- on inside of cell ATP binds to carrier protein and is hydrolysed to adp and phosphate
- binding of phosphate molecule causes protein to change shape and open up to inside of cell
- phosphate released and recombines with ADP to form ATP
- carrier protein returns to original shape
Why is bulk transport used
To move large molecules such as enzymes and hormones into and out of cells
What are the two types of endocytosis
- phagocytosis with solids
- pinocytosis with liquids
What is the process of endocytosis
- cell-surface membrane invaginates when it comes into contact with material to be transported
- membrane enfolds material until eventually membrane fuses forming a vesicle
- vesicle pinches off and moves into cytoplasm
What is the process of exocytosis
Vesicles move towards and fuse with cell surface membrane, contents are then released outside of the cell
What is osmosis
The net movement of water from a solution of higher water potential to a solution of lower water potential across a partially permeable membrane
What is water potential
The pressure exerted by water molecules as they collide with a membrane or container
What is the water potential of water
0
What occurs if water moves into a solution
An increase in hydrostatic pressure
What happens when an animal cell is placed in water
- water moves in, cell bursts, cytolysis
- water moves out, cell shrivels, crenation
What happens when a plant cell is placed in water
- water moves in, increased turgor, cell is turgid
- water moves out, cell surface membrane pulls away from cell wall, cell is plasmolysed
