B1.4 - Photosynthesis Flashcards
What are the reactants in photosynthesis?
Water and Carbon dioxide
What is the word equation for photosynthesis?
Carbon dioxide + water -> oxygen + glucose
State the balanced chemical equation for photosynthesis
6CO + 6H O -> 6O + C H O
2 2 2 6 12 6
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 plants
why are leaves and stems green?
since they contain chlorophyll
what is the role of chlorophyll in plants?
to absorb light energy from the sun
What are the two main stages of photosynthesis?
and give a brief description of what happens
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 kind of reaction is photosynthesis, and why?
an endothermic reaction (energy is transferred from surroundings to keep it going - ie. energy from sun)
How is glucose produced during photosynthesis used? (6)
- 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 the presence of 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 that 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 that 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 that 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 that oxygen if given off 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
