Bio chapter 2

movement of substances

what is diffusion

• net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient

• (until dynamic equilibrium)

concentration gradient

the difference in concentration between 2 regions

rate of diffusion across gas to solid

fastest to slowest:

1. gas

2. liquid

3. solid

factors affecting rate of diffusion

• molecular size

• concentration gradient

• kinetic energy of particles

• diffusion distance

• surface area-to-volume ratio (root hair cells and epithelial cells of small intestine have specially adapted long narrow protrusions to increase rate of diffusion of substances)

what is osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential(down a water potential gradient) through a partially permeable membrane

what is water potential

measure of the tendency of water to move from one place to another

a dilute solution has a higher/lower water potential???

a dilute solution has a higher water potential

hypertonic solution

solution which has LOWER water potential than another

hypotonic solution

solution which has HIGHER water potential than another

isotonic solution

solution which has the SAME water potential than another

factors affecting rate of osmosis

• water potential gradient

• distance between regions

• surface area-to-volume ratio

what is turgor pressure

the pressure exerted by the water in the vacuole pressing outwards on the cell wall

what does turgor do

maintains the shape of the soft tissues in plants so that they stay firm and erect

movements of turgor

• open and closing of stomata (guard cells turgidity changes)

• open and closing of flowers

• mimosa

what is active transport

process in which cellular energy is used to move the particles of a substance across a membrane against its concentration gradient to a region of higher concentration

• requires ATP (so only takes place in living cells) by respiration in mitochondria

• requires membrane

how turgidity affects plant vs animal cell in dilute solution

plant cell:

• cell sap has a lower water potential than external solution

• water molecules enter the vacuole via osmosis

• vacuoles expands in volume and pushes the cell membrane and cytoplasm against the cellulose cell wall

• cell becomes TURGID

animal cell:

• cytoplasm has a lower water potential than external solution

• water molecules enter the cytoplasm via osmosis

• cell expands in volume

• plasma membrane is delicate and cell LYSES/BURSTS

how turgidity affects plant vs animal cell in concentrated solution

plant cell:

• cell sap has a higher water potential than external solution

• water molecules leave vacuole via osmosis

• vacuole shrinks in size and plasma membrane and cytoplasm shrinks away from cell wall, becoming PLASMOLYSED

animal cell:

• cytoplasm has a higher water potential than external solution

• water molecules leave the cytoplasm via osmosis

• cell shrinks in volume and becomes CRENATED