Photosynthesis
- plants, algae (protists), bacteria act as producers / autotrophs
- make their own complex organic food from simple inorganic substances
- carbon skeletons of intermediates derived from breakdown of glucose
produced in photosynthesis used to form other organic molecules like
lipids protein
- light energy captured by chlorophyll is converted to chemical energy stored in
food produced
light energy
carbon dioxide + water carbohydrates + oxygen@cell
(glucose) + (by product)
simple inorganic chlorophyll complex organic
6 CO2 + 6 H2O C6H12O6 + 6O2
significance of photosynthesis
- Providing basic food source in ecosystems
- (most) food chains: start w/ plants/algae (food source for other orgs)
- Maintaining energy flow in ecosystems
- ultimate source of energy: sun
- light en from sun <captured> converted to chem en stored in body
- chem en <transferred> along food chains + <lost> as heat from respiration
- allow continuous input of energy to ecosystems
- Maintaining O2 and CO2 balance
- Respiration: consume O2, release CO2
- Photosynthesis: release O2 > replace O2 consumed
- > maintain O2 balance in atmosphere
- Photosynthesis: consume CO2
- > balance increase of CO2 in atmosphere
requirements (factors) of photosynthesis
- Light + CO2 + Chlorophyll
- water is also necessary for photosynthesis
- but there is no simple experiment to show that water is a necessary factor
- a plant will die if all water is removed
- determined by detecting reactants used/ (by) products produced
Practical 20.1: detection of O2 release
, Procedures
(qualitative)
1) Set up the apparatus as shown
wear safety goggles + gloves
cut the stem of (water plant) underwater
> prevent formation of air bubbles that block stem
2) Dilute sodium hydrogencarbonate solution provides CO2 to the (water plant)
for carrying out photosynthesis
3) Allow time for (water plant) to equilibrate > rate of photosynthesis is steady
4) Expose the setup to bright light for at least 24 hours to collect enough gas released
from the (water plant)
5) Remove the test tube carefully and stopper the mouth of the test tube under water
6) Put a glowing splint over the mouth of the test tube to test for oxygen
(quantitative)
- no of bubbles released per minute
- assumption: size of bubbles is the same throughout the experiment
- volume of gas released per unit time
- By directing gas bubbles to syringe with rubber tubing
OR replace test tube with measuring cylinder
- time taken to reach same volume of gas
Result
- Hydrilla gives out gas bubbles
- When using a glowing splint to test the gas collected, the splint relights
Conclusion
- The gas released from the Hydrilla is oxygen
Testing for oxygen produced by photosynthesis
- Sodium hydrogencarbonate powder provides carbon dioxide for the plant to carry
out photosynthesis
Steps
1. Fill a transparent plastic bottle with water. Add two spatulas of sodium
hydrogencarbonate powder to the water and mix well.
2. Put some green water plants (hydrilla) into the bottle
- plants, algae (protists), bacteria act as producers / autotrophs
- make their own complex organic food from simple inorganic substances
- carbon skeletons of intermediates derived from breakdown of glucose
produced in photosynthesis used to form other organic molecules like
lipids protein
- light energy captured by chlorophyll is converted to chemical energy stored in
food produced
light energy
carbon dioxide + water carbohydrates + oxygen@cell
(glucose) + (by product)
simple inorganic chlorophyll complex organic
6 CO2 + 6 H2O C6H12O6 + 6O2
significance of photosynthesis
- Providing basic food source in ecosystems
- (most) food chains: start w/ plants/algae (food source for other orgs)
- Maintaining energy flow in ecosystems
- ultimate source of energy: sun
- light en from sun <captured> converted to chem en stored in body
- chem en <transferred> along food chains + <lost> as heat from respiration
- allow continuous input of energy to ecosystems
- Maintaining O2 and CO2 balance
- Respiration: consume O2, release CO2
- Photosynthesis: release O2 > replace O2 consumed
- > maintain O2 balance in atmosphere
- Photosynthesis: consume CO2
- > balance increase of CO2 in atmosphere
requirements (factors) of photosynthesis
- Light + CO2 + Chlorophyll
- water is also necessary for photosynthesis
- but there is no simple experiment to show that water is a necessary factor
- a plant will die if all water is removed
- determined by detecting reactants used/ (by) products produced
Practical 20.1: detection of O2 release
, Procedures
(qualitative)
1) Set up the apparatus as shown
wear safety goggles + gloves
cut the stem of (water plant) underwater
> prevent formation of air bubbles that block stem
2) Dilute sodium hydrogencarbonate solution provides CO2 to the (water plant)
for carrying out photosynthesis
3) Allow time for (water plant) to equilibrate > rate of photosynthesis is steady
4) Expose the setup to bright light for at least 24 hours to collect enough gas released
from the (water plant)
5) Remove the test tube carefully and stopper the mouth of the test tube under water
6) Put a glowing splint over the mouth of the test tube to test for oxygen
(quantitative)
- no of bubbles released per minute
- assumption: size of bubbles is the same throughout the experiment
- volume of gas released per unit time
- By directing gas bubbles to syringe with rubber tubing
OR replace test tube with measuring cylinder
- time taken to reach same volume of gas
Result
- Hydrilla gives out gas bubbles
- When using a glowing splint to test the gas collected, the splint relights
Conclusion
- The gas released from the Hydrilla is oxygen
Testing for oxygen produced by photosynthesis
- Sodium hydrogencarbonate powder provides carbon dioxide for the plant to carry
out photosynthesis
Steps
1. Fill a transparent plastic bottle with water. Add two spatulas of sodium
hydrogencarbonate powder to the water and mix well.
2. Put some green water plants (hydrilla) into the bottle
