(a) (i) What is meant by the term autotrophic? (ii) Explain why photosynthesis is an anabolic reaction - Leaving Cert Biology - Question 9 - 2022

Photosynthesis is an anabolic reaction because it involves the synthesis of more complex molecules from simpler ones. During this process, carbon dioxide and water are assembled into glucose (a simple sugar) and oxygen. This requires an input of energy, which is derived from sunlight.

A suitable photosynthetic organism is Elodea (also known as pondweed).

Elodea is suitable for this investigation because it is a water plant that readily absorbs carbon dioxide from the water, allowing for easy observation of bubble formation as an indicator of photosynthesis.

It is important to keep other factors constant because they can influence the rate of photosynthesis. For instance, if the temperature fluctuates, it could affect enzymatic activities and lead to unreliable results. By controlling these variables, we can isolate the effect of light intensity or carbon dioxide concentration on the rate of photosynthesis.

The temperature of the organism was kept constant by using a water bath set to a specific temperature. This maintained a stable environment for the Elodea during the experiment.

The rate of photosynthesis was measured by counting the number of bubbles produced by the Elodea over a set period of time. Each bubble represents the release of oxygen, which is a byproduct of photosynthesis.

The graph at 25 °C is expected to show a gradual increase in the rate of photosynthesis, leveling off as saturation point is reached with increasing light intensity or carbon dioxide concentration.

The graph at 60 °C is expected to show a steep increase initially, but it may decrease significantly after reaching a certain point due to heat stress on the plant, resulting in denaturation of enzymes involved in photosynthesis.