12. (a) (i) In what main part of a plant does most photosynthesis take place? (ii) In what cell structure does photosynthesis take place? (b) (i) What is the main source of energy for photosynthesis? (ii) Suggest two reasons why life on earth might not continue without photosynthesis - Leaving Cert Biology - Question 12 - 2008

Photosynthesis occurs in the chloroplasts, specifically within the stroma and thylakoid membranes.

The main source of energy for photosynthesis is light, primarily from the sun.

1. A lack of oxygen production would occur, making it impossible for aerobic organisms to survive.
2. The food chain would collapse as plants serve as primary producers, leading to a loss of energy sources for herbivores and, subsequently, for carnivores.

1. The three products are hydrogen ions (H⁺), electrons, and oxygen (O₂).
2. H⁺ ions are used to help synthesize ATP and NADPH. Electrons are transferred to chlorophyll to facilitate further reactions in the light-dependent reactions, and oxygen is released as a byproduct.

In my experiment, I used a water plant such as Elodea. I measured the rate of photosynthesis by counting the number of oxygen bubbles released under different light conditions. I set up a light source at varying distances to assess its effect while controlling factors like carbon dioxide by using sodium bicarbonate in the water. I ensured to use a thermometer to monitor water temperature. The setup included a beaker with water, the plant, and a ruler to measure distances. I recorded the number of bubbles per minute as my result, repeated the measurements for accuracy, and calculated the average.