What are the reactants in photosynthesis?
Carbon dioxide and water
What is the word equation for photosynthesis?
Carbon dioxide + water -> glucose + oxygen
State the balanced chemical equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
What happens during photosynthesis?
Carbon dioxide is absorbed from the air, and water is absorbed from the soil. Energy from the sun is converted to light energy.
those three substances react together to make glucose
waste products (ie. oxygen) is released into the atmosphere
Where does photosynthesis occur?
In the chloroplasts of plant cells
Why are leaves and stems green?
Because they contain chlorophyll
What is the role of chlorophyll?
To absorb light energy from the sun
What are the two stages of photosynthesis?
Stage 1 - Light Dependent
- when energy transferred from light splits water molecules into hydrogen ions and oxygen gas
Stage 2 - Light Independent
- when carbon dioxide gas combines with hydrogen ions to make glucose
What type of reaction is photosynthesis and why?
Endothermic because it requires energy from the surroundings (light energy)
Give uses of glucose produced in photosynthesis
respiration
converted into sugar molecules and stored in fruit
starch (food stores used at night - when no sunlight)
cellulose (cell walls)
nitrogen = proteins (for growth and repair)
fats and oils (food store + growth)
HINT - don’t need all uses, only correct idea (not in spec)
Describe how to test a leaf for starch
place leaf in beaker of boiling water to kill it + break down the cell walls = iodine absorbed
place a leaf into a boiling tube of boiling ethanol for 1 minute (to remove chlorophyll in order to see colour change better) using forceps (ensure water bath used to heat ethanol, as flammable)
then wash it under water to remove the ethanol and to soften it
place the leaf on a white tile, spread it out, and add a few drops of iodine solution (mixture of iodine and potassium iodide) on it
if the leaf turns from yellow/brown to black/blue, it contains ethanol
How do you prove chlorophyll is needed for photosynthesis?
place a destarched (placing the plant in the dark for a minimum of 24 hours) variegated leaf (ie. has white and green parts) into sunlight for a few hours
then test for starch by adding a few drops of iodine
if plant becomes black-blue = starch is present (chlorophyll present there)
if leaf stays orange = no starch present (no chlorophyll present there)
How do you prove light is needed for photosynthesis?
get a destarched leaf and cover half ish with a piece of black card
place the leaf in sunlight for a few hours
take the black card off and test for starch
How do you prove carbon dioxide is needed for photosynthesis?
Place a destarched plant in a sealed plastic bag with a pot of soda lime (which absorbs carbon dioxide)
place the plant in sunlight for a few hours
test the leaves for starch
How do you prove oxygen is produced during photosynthesis?
place an upside test tube on a beaker of a sea plant
as the test tube fills up with air/bubbles, put a glowing splint in the test tube
it will relight if oxygen is present
State three factors affecting the rate of photosynthesis
Light intensity, carbon dioxide concentration, temperature
Describe the effect of light intensity on photosynthesis
Increasing light intensity increases the rate until another factor becomes limiting
Describe the effect of carbon dioxide concentration on photosynthesis
Increasing carbon dioxide concentration increases the rate until another factor becomes limiting
Describe the effect of temperature on photosynthesis
Rate increases with temperature until enzymes denature at high temperatures
Describe one way to measure the rate of photosynthesis
Count oxygen bubbles produced per minute or measure volume of oxygen produced
How do you investigate the effect of light intensity on photosynthesis?
Change the distance of a light source from pondweed
What is the equation for relative light intensity?
Relative light intensity = 1 ÷ distance²
How do you investigate the effect of carbon dioxide concentration?
Add potassium hydrogen carbonate to water to release carbon dioxide
How do you investigate the effect of temperature on photosynthesis?
Place the apparatus in water baths at different temperatures
