B1.4 Phototsynthesis Flashcards
(13 cards)
What is the word equation for photosynthesis
Carbon Dioxide + Water ——> Glucose + Oxygen
Where does photosynthesis occur
- It takes place inside the plant’s chloroplasts.
- Light transfers energy from the sun to chlorophyll, where carbon dioxide and water react to make glucose.
Stage 1 - energy transferred from light splits water molecules into oxygen gas and hydrogen ions.
Stage 2 - carbon dioxide gas combines with the hydrogen ions to make glucose.
What happens to the glucose produced
- Some of it is used immediately in respiration. But others are converted into other sugar molecules, such as fructose and sucrose.
- Glucose that is not needed straight away is converted into starch, and stored for when the plant is not photosynthesising.
How can you test for starch
- Testing for starch shows that light, chlorophyll, and carbon dioxide are essential for photosynthesis.
- Place the leaf in boiling water to kill it, and then in boiling ethanol to remove the chlorophyll. After washing the leaf, add a few drops of iodine solution, if starch is present it will turn from, yellow-brown to blue-black.
What do you need to test for presence of starch, sugars, proteins, and fats.
Starch - iodine
Sugars - Benedict’s solution
Proteins - biuret solution
Fats - ethanol
Which factors affect the rate of photosynthesis
Light intensity, carbon dioxide, and temperature are all limiting factors.
What is the effect of the three limiting factors
- The higher the light intensity, the faster the rate of photosynthesis. This continues until photosynthesis is at its maximum rate. In very low light levels, or if there is no light, photosynthesis stops
- Carbon dioxide is one of the reactants, therefore the greater the carbon dioxide concentration, the faster the rate of reaction.
- Photosynthesis is a series of enzyme-controlled reactions. Therefore, the higher the temperature, the faster the reactions occur. However if the temperature is too high, the enzymes will denature and the reactions will stop.
What is the formula of the inverse square law
Relative light intensity = 1 / distance from light source (squared)
How to prove chlorophyll is needed for photosynthesis?
- To prove chlorophyll is needed you should place a destarched variegated plant in sunlight for several hours. You then test one of its leaves for the presence of starch..
How to prove light is needed for photosynthesis>
- Take a destarched plant and cover part of one of its leaves with black card or tin foil. Light cannot reach the covered area of the leaf. Place the plant in sunlight for several hours, and then remove the card and test for the presence of starch.
How to prove carbon dioxide is needed for photosynthesis?
- Take a destarched plant, and place it inside a polythene bag. Before you seal the bag add a pot of soda lime. This absorbs carbon dioxide and water vapour. Place the plant in sunlight for several hours, before testing one of its leaves for the presence of starch.
How to prove oxygen is given off during photosynthesis?
- Place an upturned test tube above an aquatic plant such as the pondweed Elodea. Put the apparatus in the light for maximum photosynthesis when you have collected a full tube of gas, place a glowing splint inside the tube. It will relight because of the oxygen present.
Testing the rate of photosynthesis with light intensity, carbon dioxide concentration and temperature
Light intensity - place a light source at different distances from the Elodea. Count the oxygen bubbles produced per minute at different distances. When you double the distance from a light source, the light intensity falls by a factor of 4 - inverse square law.
Carbon dioxide concentration - add different masses of potassium hydrogen carbonate powder to the water and count the number of bubbles produced per minute. Potassium hydrogen carbonate releases carbon dioxide.
Temperature - place the apparatus in water baths at different temperatures and count the number of bubbles produced per minute.
