movement of substances

Question 1

what is diffusion?

Answer 1

• diffusion is the net movement of particles down a concentration gradient
• occurs between solute and solvent particles

Question 2

what affects diffusion

Answer 2

• collision of particles slow down diffusion
• particle size (mass)
• increase in temperature speeds up diffusion
• the steeper the concentration gradient, the faster the rate of diffusion

Question 3

diffusion across a membrane +e.g.s

Answer 3

• the PPM allows some substances to pass through but not others
• smaller particles e.g. oxygen, co2, and glucose can pass through the PPM but larger molecules like starch are unable to

Question 4

what is osmosis?

Answer 4

• net movement of water molecules from a solution of higher water potential to a solution of lower water potential (down a water potential gradient), through a PPM

Question 5

more on osmosis

a dilute salt/sugar solution…
water potential is…
cells are…

Answer 5

• a dilute salt/sugar solution has a higher water potential than a concentrated salt/sugar solution
• water potential is the tendency of water molecules to move from one place to another
• cells are living osmotic systems as they contain dissolved sugars and salts

Question 6

what happens to a cell in a solution of the same water potential?

Answer 6

• there is no net movement of water molecules, and osmosis would not occur. it’s cytoplasm will not change in its size or shape

Question 7

why is turgor important in plants?

Answer 7

• plays an important role in maintaining the shape of soft tissues in plants
• it keeps herbaceous plants firm and upright
• turgor in guard cells cause stoma to open in the day and lack of turgor causes them to close at night

Question 8

what happens if turgidity is affected in plants?

Answer 8

• plasmolysis causes plant tissues to become limp/flaccid -> plant wilts -> plant withers
• water may be added to soil solution to dilute it -> keeps plant firm and upright

Question 9

what is active transport?

Answer 9

active transport is the process in which energy is used by a living organism to ove the particles of a substance against its concentration gradient

Question 10

what are the conditions needed for active transport?

Answer 10

• it only occurs in respiring living cells as it requires energy
• some examples are mineral ions being taken up by root hair cells + glucose and amino acids being taken up by cells in the small intestine

Question 11

how are cells adapted for the absorption of materials? +e.g.s

Answer 11

• increased SA:V ratio = the smaller the cell, the greater its SA:V ratio, the faster the rate of diffusion
• e.g. root hair cells have long extensions and epithelial cells have a folded CSM