C1 SL: Photosynthesis, Chromatography, Limiting factors

Glycolysis is HL only

Photosynthesis

The biological process by which producers, such as plants and algae, convert light energy from the sun into chemical energy stored in glucose molecules. This process uses water and carbon dioxide as inputs, with oxygen released as a byproduct. It primarily occurs in the chloroplasts of plant cells, where the pigment chlorophyll captures light energy to drive the reactions.

Light-dependent reactions

The initial stages of photosynthesis that occur in the thylakoid membranes of chloroplasts. These reactions utilise light energy to convert ADP into ATP, and reduce NADP into NADPH. They also generate oxygen through the process of photolysis.

Light-independent reactions

Also known as Calvin Cycle, it’s the second stage of photosynthesis. These reactions occur in the stroma of chloroplasts and involve the fixation of carbon dioxide and the production of carbohydrates using the ATP and NADPH generated in the light-dependent reactions.

Photolysis

The first stage of photosynthesis, which is the light-dependant reaction that includes the splitting of water molecules using light energy of photons, releasing electrons, protons, and oxygen (as a waste product). Occurs in the thylakoid membranes (thylakoids) of the chloroplasts.

Carbon fixation

It is a part of light-independent reactions of photosynthesis that occurs in the stroma of a chloroplast. It’s the conversion of inorganic carbon into organic carbon through the addition of hydrogen to carbon absorbed from the air using ATP generated in light-dependent reactions.

Chromatography

A technique used to separate mixtures of substances, such as pigments, based on the movement of the different substances on a piece of paper by capillary action.

Process of chromatography

The stationary phase is typically chromatography paper, while the mobile phase is a solvent like acetone or ethanol. A sample of each pigment is applied near the bottom of the stationary phase, and as the solvent moves up by capillary action, the pigments travel at different rates, creating separate spots. Pigments with higher solubility in the solvent travel faster, while those with a stronger affinity for the stationary phase move slower. The resulting pattern of separated pigments, known as the chromatogram, can be analyzed to identify different pigments based on their unique retention factor (Rf) values.

Retention factor (R_f)

Constant in chromatography which is the ratio of the distance moved by a pigment to the distance moved by the solvent.

Action spectrum

A graph that shows the effectiveness of different wavelengths of light in driving of photosynthesis (or another biological process).

Absorption spectrum

A graph that shows the wavelengths of light absorbed by each pigment.

Factors that affect the rate of photosynthesis

Carbon dioxide concentration, light intensity and temperature.

How can hydrogen carbonate indicator solution measure the rate of photosynthesis?

This indicator will change colour as the concentration of carbon dioxide changes. If the plant is not photosynthesising and is only respiring, the carbon dioxide concentration will increase and the indicator will turn more orange/yellow. If the plant is photosynthesising, carbon dioxide is being absorbed and the indicator will become more purple.

Two main methods of measuring the impact of carbon dioxide.

1. Using enclosed greenhouses where the concentration of CO₂ can be carefully monitored and controlled. Total biomass produced could be measured or the yield of the fruits/vegetables grown. The limitations are that, as it’s done in controlled conditions, there are natural factors that are not taken into account.

2. FACE. CO2 is released around a circular area through pipes. Sensors within the area monitor CO2 levels. This allows for a more natural way of measuring the impact of CO2. However, this method is usually very expensive to carry out.