structure and function (gas exchange in flowering plants)

how can photosynthesis and respiration occur at the same time UNOFFICIAL

think where they occur

about gases used/produced

photosynthesis happens in chloroplasts

respiration happens in mitochondria

use each others gases

	respiration	photosynthesis
O2
reason
CO2
reason

	respiration	photosynthesis
O2	O2 diffuses from high concentration (OUTSIDE) to low conc. (INSIDE)	O2 diffuses from area of high conc. (INSIDE) to low conc. (OUTSIDE)
reason	respiring cells use up oxygen so conc. of O2 inside leaf is always low	photosynthesising cells produce O2 as a waste product. so conc. is always high inside leaf.
CO2	CO2 diffuses from high conc. (INSIDE) to low conc. (OUTSIDE)	CO2 diffuses from area of high conc. (OUTSIDE) to area of low conc. (INSIDE)
reason	respiring cells release waste CO2 so conc. inside leaf is always high	photosynthesising cells use up CO2 so conc. inside is always low.

pathway of a CO2 molecule for photosynthesis

1. diffuses from high (outside) to low (inside) through open stomata

2. diffuses into air spaces in spongy mesophyll

3. diffuses through cell membrane/wall of mesophyll cells

4. dissolves in cytoplasm, diffuses into chloroplast to be used in photosynthesis

adaptations of a leaf for gas exchange (at least 4)

close _____ between

thin ___ _____

close contact between cells/air spaces - efficient gas exchange

thin cell walls - gas can easily diffuse in

spongy layer - allows gas movement, increases surface are for diffusion

• stomata allow diffusion of CO2/O2 inside/outside leaf

• large SA - more space for diffusion of gases

when stomata are open, guard cells are _______
when stomata are closed, guard cells are _______

when stomata are open, guard cells are TURGID
when stomata are closed, guard cells are FLACCID

what do stomata control (2)

• control rate of transpiration/water vapour loss

  • allow CO2/O2 to diffuse in/out of leaf

when do stomata close (2)

• low light intensity - photosynthesis can’t happen without light, so no gas exchange is needed - stomata close to prevent water loss

• low water availability - if too much water escapes by not being replaced by the transpiration water from soil, plant will die (so prioritizes keeping plant alive, over photosynthesis which needs gas exchange/stomata open)

when are stomata open

• light available

• water available

plants only photosynthesise in ________, cells respire ________

plants only photosynthesise in light, cells respire constantly

	rate of photosynthesis vs respiration	net movement of gases
Day
Night
Cloudy

	rate of photosynthesis vs respiration	net movement of gases
Day	photosynthesis rate generally higher than respiration	net movement/ diffusion of CO2 into leaf. net diffusion of O2 out
Night	no photosynthesis (no light), only respiration	net O2 in, net CO2 out
Cloudy	rate of p/s and respiration are equal	no net movement of gases in/out

	tube contents (+ cotton wool)	colour change	reason
A
B
C
D

	tube contents (+ cotton wool)	colour change	reason
A	no leaf	stays orange	no leaf = no photosynthesis or respiration
B	leaf + light	orange → purple	more photosynthesis than respiration in light. photosynthesis uses up CO2 → less CO2 → purple
C	leaf + aluminium foil (no light)	orange → yellow	no photosynthesis (no light) but cells still respire. respiration releases CO2 → more CO2 → yellow
D	leaf + gauze (partial light)	stays orange	rate of p/s = rate of respiration. no net movement of CO2 (release of CO2 = intake of CO2)

light needed for CO2 gas exchange CORMM`S

C - change tube contents (A - no leaf, B - leaf with light, C- leaf with aluminium foil, D - leaf with gauze)

O - same species, age, health of leaf

R - repeat x3

M - observe colour change of hydrogen carbonate indicator

M - after 3 hours

S - same temperature, same volume of indicator, same starting CO2 concentration, same number/size of leaves