During what stage of photosynthesis is oxygen gas produced?
a. the Krebs cycle
b. carbon fixation
c. light reactions involving photo-systems I and II
d. cyclic photo-phosphorylation
I think it is c. light reactions involving photo-systems I and II
correct.
You are correct! Oxygen gas is produced during the light reactions involving photo-systems I and II, which is option c.
To better understand why, let's break down the process of photosynthesis and identify the stage where oxygen is produced.
Photosynthesis is a complex process that occurs in plants, algae, and some types of bacteria. It can be divided into two main stages: the light-dependent reactions and the light-independent reactions (or Calvin cycle).
During the light-dependent reactions, light energy is absorbed by chlorophyll in the thylakoid membranes of the chloroplasts. This energy is used to power the synthesis of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are energy-rich molecules.
The light-dependent reactions involve two photo-systems: photo-system I (PSI) and photo-system II (PSII). These two photo-systems work together to capture and transfer light energy. PSII absorbs photons and uses the energy to provide electrons to an electron transport chain, while PSI absorbs additional photons and further increases the energy of the electrons. These high-energy electrons eventually combine with NADP+ and H+ ions to form NADPH, which is crucial for the next stage of photosynthesis.
During the process of electron transportation in PSII, water molecules are split (a process called photolysis) by enzymes in the thylakoid membrane. This splitting of water releases oxygen gas (O2) as a byproduct. The electrons derived from this process replace the electrons lost in PSII, completing the electron transport chain.
So, option c, light reactions involving photo-systems I and II, is the correct stage of photosynthesis when oxygen gas is produced.