A. Suppose
an experiement is performed in which plants receive contaminated water
or carbon dioxide.
Carbon dioxide Water
plant A
normal
radioactive
plant B
radioactive
normal
Each plant undergoes all parts of photosynthesis,
and you examine the oxygen and glucose given off during the process.
1. Which plant(s) will produce radioactive
glucose? Both plant A and B
2. Which plant(s) will produce radioactive
oxygen gas? Only plant A
Given that the light dependent reaction uses water
and sun energy to produce ATP, NADPH (H+ and e- from water transferred
to NADP+), and oxygen gas; while the light independent reaction uses carbon
dioxide, ATP, and NADPH to produce glucose then:
plant A receives radioactive H and O from water
plant B receives radioactive O and C from
carbon dioxide
Therefore, in plant A radioactive O from water contaminates the oxygen gas given off at the end of the light dependent phase, and because H+ from water (but not O) are transferred into the Calvin Benson cycle by NADP+, then the radioactive H are incorporated into that plantís glucose. On the other hand, plant B will receive non-contaminated water and give off radioactive free oxygen, but receives contaminated C and O from radioactive carbon dioxide which is incorporated into the glucose.
B. You monitor photosynthetic oxygen production from a leaf under white light. What happens to the amount of oxygen produced (i.e. what happnes to photosynthesis)--does it increase, decrease, remain the same--when you:
3. use
a red filter (no red light reaches the plant) decrease
oxygen production (photosynthesis)
Since chlorophyll a (the main pigment in plants)
absorbs the light energy in the red spectrum, then depriving the plant
of that energy source will decrease photosynthesis
4. use
a blue filter decrease oxygen production
more than in #3
Since chlorophyll a absorbs most of the light
energy used for photosynthesis in the blue spectrum, then depriving the
plant of that energy source will decrease photosynthesis (O2 produced).
5. use
a green filter remain (approximately)
the same
Since chlorophyll a does not absorb energy in
the green spectrum, depriving the plant of that energy source will NOT
affect photosynthesis.
C. Suppose
you use a molecule that binds up all the plantís available RuBP.
6. Will the amount of glucose produced
by the plant increase/decrease/remain the same? Why?
Since the plant depends on RuBP to capture carbon
dioxide from the air (remember that the C and O from carbon dioxide are
the source for the C and O in glucose) during the Calvin Benson cycle,
the plant will cease its production of glucose because it will have no
C or O to put in the molecule. Therefore, the amount of glucose will
decrease. The plant would die because it would have no glucose to
break down for energy (during respiration).