movement of substances

Question 1

what are the 2 types of transport

Answer 1

passive transport- movement of a substance from a region of higher concentration to a region of lower concentration across a cell membrane, with no input of energy from the cell ( diffusion, osmosis)

active trasport- movement of substances from a region of lower concentration to a region of higher concentration and needs energy from cell respiration

Question 2

what is a concentration gradient how is it related to diffusion

Answer 2

the concentration gradient is the difference in concentration between 2 regions

• the particles posses kinetic energy thus move about constantly and randomly

Question 3

how is a concentration gradient related to diffusion

Answer 3

• the movement of fluid molecules is random
• particles will diffuse down their concentration gradient
• diffusion stops when particles dispersed evenly( with no concentration gradient), and a state of equillibrium is reached
• the steeper the concentration gradient, the faster the diffusion

Question 4

what is the definition of diffusion

Answer 4

diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration

• diffusion can occur with or without a membrane

Question 5

describe diffusion across a membrane

Answer 5

the cell surface membrane allows some substances to pass through but not others, small molecules are able to pass through but not large molecules

Question 6

why is diffusion important

Answer 6

• gaseous exchange during respiration and photoynthesis
• excreting wste products
• absroption of digested food into blood through walls of small intestine

Question 7

describe the diffusion of gases plants

Answer 7

during photosynthesis- carbon dioxide diffuses into the leaf

during transpiration- water vapour diffuses out of the leaf

Question 8

what determines the rate of diffusion

Answer 8

• steepness of concentration gradient: the greater the difference between the 2 sides (of a membrane), the higher the rate of diffsion
• temperature: higher temperature result in molecules with higher kinetic energy, molecules move about faster, thus, higher rate of diffusion
• surface area to volume ratio: as surface area to volume ratio increases, the rate of diffusion increases
• type of molecule or ion: larger mass/size of molecules need more energy to move, thus lower rate of diffusion
• thickness of barrier: the thicker the cell walls in plant cells, the slower diffusion occurs. cell membrane in plants and animals are about the same thickness and permeability
• state of matter: diffusion is slow in solids, faster in liquids and fastest in gases

Question 9

state the 3 different types of membrane

Answer 9

• a fully permeable membrane: allows all molecules lage or small to pass through it
• a partially permeable membrane only allows small molecules to pass through it but not larger ones
• an impermeable membrane does not allow any molecules to pass through it

Question 10

what is the definition od osmosis

Answer 10

osmosis is the net movement of water molecules from a rejoin of higher water potential to a rejoin of lower water portential through a partially permeable membrane

Question 11

what happens to animal cells in a solution of high water potential

Answer 11

cytoplasm has lower water potential than surrounding solution, water molecules enters by osmosis, thus causing the cell to expand and burst

Question 12

what happens to animal cells in a solution with low water potential

Answer 12

cytoplasm has higher water potential than otside soultion, water molecules leaves by osmosis, thus, cell shrinks in size and becomes crenated

Question 13

what happens to a plant cell in a solution with highe water potential

Answer 13

1. cell sap has lower water potential than surrounding solution 2. water molecules enter by osmosis 3. cell expands and becomes turgid 4. cell wall prevents cell from bursting

Question 14

what happes to a cell in a solution with low water potential

Answer 14

1. cell sap has higher water potential than surrounding solution 2. water molecules leaves by osmosis 3. cytoplasm shrinks away from cell wall and becomes plasmolysed

Question 15

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

Answer 15

a cell that is immersed in a solution with the same water potential as its cytoplasm will not change in its size ot shape

Question 16

why is turgor important in plants

Answer 16

• plasmolysis causes tissues to become limp or flaccid
• when a tissue or plant becomes flaccid, turgidity is lost and the plant wilts
• water may be added to the soil to dilute the soil solution to keep the plant firm and upright
• turgor plays an important role in maintaining the shape or soft tissues in plants

Question 17

why is turgor important in plants

Answer 17

• changes in turgot also cause the movements of certain plant cell, for example, guard cells regulate stomatal pore sizes during transpiration and gaeseous exchange at the leaves
• turgor provides mechanical support to herbaceous (non woody) plants to keep them firm and upright
• it keeps leaves flat to increase surface area for maximum light absorption and gaeseous exchange during photosynthesis

Question 18

wht does surface area to volume ratio mean to a cell

Answer 18

the greater the surface area to volume ratio, the higher the rate fo diffusion

Question 18

wht does surface area to volume ratio mean to a cell

Answer 18

the greater the surface area to volume ratio, the higher the rate fo diffusion

Question 19

how are cells adapted for the absorption of materials

Answer 19

• they increase their surface area to volume ratio by:
• > having long protrution (root hair cell)
• > having a folded cell membrane (epithelial cells)

Question 20

what is active transport

Answer 20

active transport is the process in which energy is used to move a substance across a membrane against a concentration gradient