2.1.4 Isotopes: Unraveling Photosynthesis

Question 1

isotopes

Answer 1

• often used in biological experiments because they can be detected and followed in biochemical pathways

Question 2

note

Answer 2

• the path of oxygen in photosynthesis was determined using an isotope of oxygen.

Question 3

photosynthesis

Answer 3

• known to use water (H2O) and carbon dioxide (CO2) to form oxygen gas (O2) and glucose (C6H12O6).
• It was originally thought that CO2 (rather than water) was split in this process
• H2O with an oxygen isotope was used to follow the path of the H2O oxygen in photosynthesis.
• To the surprise of many it was found that the H2O split instead of the CO2 because the oxygen from the radiolabeled H2O ended up in the O2 gas.
• The fact that H2O was split instead of CO2 means that there had to be more H2O involved in photosynthesis than was previously thought (because the oxygen isotope is not balanced).
• To balance the equation, six more H2O must be added to the left side of the equation, and 6H2O must be produced as an end product.

Question 4

Which isotope was used in discovering that water is a product of photosynthesis?

Answer 4

• radioactive oxygen

Question 5

Which of the following is both a reactant and a product of photosynthesis?

Answer 5

• water

Question 6

What did researchers originally (and incorrectly) think was the path of the oxygen in water during photosynthesis?

Answer 6

• water to glucose

Question 7

What did researchers identify as the source of oxygen gas in photosynthesis using isotopes?

Answer 7

• water

Question 8

Scientists knew the products of photosynthesis in the early 1900s. What are two of the products?

Answer 8

• oxygen gas and glucose

Question 9

Which of the following is true about the use of radioisotopes in biological experiments?

Answer 9

• They are used to trace biological pathways