a) (i) Name the organelle where photosynthesis occurs - HSC - SSCE Biology - Question 34 - 2004 - Paper 1

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored as glucose. This occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).

In the light-dependent reactions, which take place in the thylakoid membranes of chloroplasts, light energy is absorbed by chlorophyll and is used to split water molecules, releasing oxygen and generating ATP and NADPH.

In the Calvin cycle, which occurs in the stroma, ATP and NADPH produced in the light-dependent reactions are used to convert carbon dioxide into glucose through a series of enzymatic reactions.

1. Collect pond weed and place it in a water-filled beaker.
2. Use a lamp to provide a constant light source at a measured distance from the beaker.
3. Alter the distance of the lamp to vary light intensity while keeping other conditions constant.
4. Measure the rate of gas production (oxygen bubbles) over a fixed time period for each light intensity setting.
5. Repeat the experiment at different temperatures by placing the beaker in water baths set at varying temperatures and observing the changes in gas production.

This investigation helped clarify the relationship between light intensity, temperature, and the rate of photosynthesis. By observing how gas production varied with different conditions, I gained insights into the optimal light and temperature ranges for photosynthesis to occur efficiently. It emphasized the significance of chlorophyll's role in capturing light energy and how environmental factors can influence photosynthetic rates.

New technologies, such as CRISPR gene editing and advanced imaging techniques, have revolutionized biological research. These innovations enable scientists to manipulate genetic material with precision, facilitating studies on gene function and regulation. Furthermore, techniques such as high-throughput sequencing allow for the comprehensive analysis of genomes, transcriptomes, and proteomes, providing deeper insights into biological processes.

Additionally, bioinformatics tools enhance data analysis capabilities, allowing researchers to draw connections between large datasets and biological phenomena. However, ethical considerations and ecological impacts must be weighed alongside these advancements.

The method invented by Tsweet is known as chromatography. Tsweet would have interpreted the results by analyzing the separation of pigments based on their solubility and affinity to the solvent used. Different pigments would travel different distances along the chromatographic medium, allowing for the identification and comparison of pigment composition in plant leaves.

Chlorophyll plays a crucial role in the light reaction of photosynthesis by absorbing sunlight, primarily in the blue and red wavelengths. This absorbed light energy excites electrons in chlorophyll molecules, initiating the process of photophosphorylation. The energized electrons are then transferred through a series of proteins in the thylakoid membrane, contributing to the synthesis of ATP and NADPH, which are essential for the subsequent light-independent reactions.

One significant scientist in this field is Melvin Calvin, who utilized radioactive carbon-14 isotopes in his experiments to trace the path of carbon in photosynthesis. By introducing carbon-14 into plants and analyzing the resultant compounds after photosynthesis, Calvin elucidated the steps of the Calvin cycle, demonstrating how carbon dioxide is fixed into glucose. This research provided foundational knowledge about the mechanisms of photosynthesis and the role of carbon fixation in plant metabolism.