B1.4

Question 1

recall the products and reactants of photosynthesis

Answer 1

reactants:

• carbon dioxide
• water

products:

• glucose
• oxygen

Question 2

recall where photosynthesis takes place including how the plants get the reactants they need

Answer 2

• Plant leaves are the main photosynthetic organ
• the carbon dioxide needed enters through the stomata
• water enters through the roots and is transported to leaves in the xylem
• photosynthesis takes place in the chloroplasts which contain a green pigment called chlorophyll needed to absorb light energy

Question 3

recall the word and symbol equation for photosynthesis

Answer 3

• Carbon dioxide + water + energy from light → glucose+ oxygen
• 6CO₂ + 6H₂O + (sunlight energy) → C₆H₁₂O₆ + 6O₂

Question 4

describe the process of photosynthesis

Answer 4

• Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

Question 5

is photosynthesis an exothermic or endothermic reaction

explain your answer

Answer 5

• endothermic
• because it takes in light energy from the surrounding environment

Question 6

describe the starch experiment to investigate photosynthesis

Answer 6

1. drop leaf in boiling water to kill and preserve it.
2. leave the leaf for 10 minutes in hot ethanol in a boiling tube to remove chlorophyll.
3. dip leaf in boiling water to soften it.
4. The leaf is spread out in a Petri dish and covered with iodine solution.
5. The areas that had the chlorophyll stain blue-black.
6. The areas that had no chlorophyll remain pale.

Question 7

what are the

1. dependent
2. independent
3. controlled variables of the starch experiment

Answer 7

• Independent variable – the presence or absence of chlorophyll.
• Dependent variable – whether starch is present or not.
• Control variables – methods and equipment used.

Question 8

what are the risks of the starch experiment

Answer 8

• Care must be taken when using boiling water because it can burn
• Care must be taken when using boiling ethanol by turning off Bunsen burners as the ethanol is highly flammable.
• Iodine solution is an irritant so eye protection must be worn.

Question 9

describe the pondweed experiment to investigate photosythes

Answer 9

1. Set up a boiling tube containing 45 cm³ of sodium hydrogencarbonate solution (1%)
2. Allow the tube to stand for a few minutes and shake to disperse any air bubbles that might form.
3. Cut 8cm of a piece of the pondweed, Cabomba.
4. Use forceps to place the pondweed in the boiling tube carefully.
5. Position the boiling tube so that the pondweed is 10 cm away from the light source
6. . Allow the boiling tube to stand for five minutes.
7. Count the number of bubbles emerging from the cut end of the stems in one minute.
8. Repeat the count five times and record your results.
9. Calculate the average number of bubbles produced per minute.
10. Repeat the experiment at different distances away from the light source.

Question 10

explain the results of the pondweed experiment

Answer 10

• the light intensity is proportional to distance
• it will decrease as the distance away from the bulb increases
• so light intensity for the investigation can be varied by changing the distance from the lamp to the plant

Question 11

what are the

1. dependent
2. independent
3. controlled variables of the pondweed experiment

Answer 11

• Independent variable – distance from the light source/light intensity.
• Dependent variable – the number of bubbles produced per minute.
• Control variables – concentration of sodium hydrogen carbonate solution, temperature, using the same piece of Cabomba pondweed each time.

Question 12

describe the risks of the pondweed experiment

Answer 12

• Care must be taken when using water near electrical equipment. Ensure that your hands are dry when handling the lamp.

Question 13

explain the effect of temperature on the rate of photosynthesis

Answer 13

if the temperature is too low:

• enzymes will work slower
• the rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates.
• meaning the rate of reaction is decreased

if the temperature is too high:

• enzymes will denature
• rate of reaction decreases dramatically
• this can start at 45 °° C

Question 14

explain the effect of light on the rate of photosynthesis

Answer 14

• as light level is increased the rate of photosynthesis raises steadily linear but only up to a certain point
• after that point another factor is limiting the rate photosynthesis
• this could be cor2 concentration or temperature
• even if the light intensity is increased it will no longer have any effect

extra

• if light intensities are increased to extreme levels this actually slows down the rate of reaction but these conditions do not occur naturally in nature

Question 15

explain the effect of carbon dioxide concentration on the rate of photosynthesis

Answer 15

• carbon dioxide is one of the raw reactants needed for photosynthesis
• If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.
• only up to a point after that another factor , light intensity or temperature becomes the limiting factor for photosynthesis