B1.4 Phototsynthesis

Question 1

What is the word equation for photosynthesis

Answer 1

Carbon Dioxide + Water ——> Glucose + Oxygen

Question 2

Where does photosynthesis occur

Answer 2

• 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. Glucose stores energy within its chemical bonds.

Question 3

What happens to the glucose produced

Answer 3

• 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.

Question 4

How can you test for starch

Answer 4

• 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.

Question 5

What do you need to test for presence of starch, sugars, proteins, and fats.

Answer 5

Starch - iodine
Sugars - Benedict’s solution
Proteins - biuret solution
Fats - ethanol

Question 6

Which factors affect the rate of photosynthesis

Answer 6

Light intensity, carbon dioxide, and temperature are all limiting factors.

Question 7

What is the effect of the three limiting factors

Answer 7

• The higher the light intensity, the faster the rate of photosynthesis.
• 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.

Question 8

What is the formula of the inverse square law

Answer 8

Relative light intensity = 1 / distance from light source (squared)