Question

which is an important difference between light - dependent (l - d) and light - independent (l - ind) reactions in photosynthesis? the l - d reactions need co₂ and light energy, and the l - ind reactions needs water and o₂. the l - d reactions require light energy and water, and the l - ind reactions require atp, nadph, and co₂. the l - d reactions can only occur during daylight, and the l - ind reactions can only occur during the night. the l - d reactions need water and co₂, and the l - ind reactions need co₂ and light.

Explanation:

• Light - dependent reactions (L - D): Use light energy and water. Light energy is absorbed by chlorophyll, and water is split (photolysis) to release oxygen. The process generates ATP (through photophosphorylation) and NADPH.
• Light - independent reactions (L - IND): Also known as the Calvin cycle. Do not require light directly. Use ATP, NADPH (from L - D reactions) and \(CO_2\) to produce glucose (carbon fixation, reduction, and regeneration of RuBP steps).

Now let's analyze each option:

• Option 1: L - D reactions do not need \(CO_2\), and L - IND reactions do not need \(O_2\). So this option is incorrect.
• Option 2: L - D reactions require light energy (to excite electrons in photosystems) and water (for photolysis). L - IND reactions (Calvin cycle) require ATP (for energy), NADPH (for reducing power) and \(CO_2\) (for carbon fixation). This option is correct.
• Option 3: L - IND reactions can occur during the day as well (they do not depend on light, but they depend on the products of L - D reactions which are made during the day). So this option is incorrect.
• Option 4: L - D reactions do not need \(CO_2\), and L - IND reactions do not need light. So this option is incorrect.

Answer:

The L - D reactions require light energy and water, and the L - IND reactions require ATP, NADPH, and \(CO_2\) (the second option).