Covering the plants to block light may result in eradication. In reservoirs and lake systems the water level may be lowered in winter with the aim of controlling the population. The success is related to the degree of desiccation, air temperature (at best freezing conditions after drainage), and the presence of snow. As the plant spreads through fragmentation, mechanical controls should only be undertaken during mass developments and when the risk of spread to other water systems is minimal. Using mechanical controls during an ongoing invasion may promote the spread due to fragmentation.
The first event in photosynthesis - the primary photoevent-is always the absorption of a photon by a pigment. The most abundant(and effective) pigments are chlorophylls a and b. However, asyou will see in part B, chlorophylls can only absorb a portion of thevisible spectrum. To use light which is not absorbed by chlorophyllsplants employ accessory pigments, primarily carotenoids andxanthophylls. In this exercise you will examine the pigmentsextracted from several different plant tissues.
If Kayser-Fleischer rings are present on ophthalmologic examination and ceruloplasmin levels are below 200 mg/litre in a patient with neurologic signs or symptoms, the diagnosis of Wilson disease is established.
If a patient is asymptomatic, exhibits isolated liver disease, or lacks corneal rings, the coexistence of a hepatic copper concentration above 250 µg/g (dry weight) and a low serum ceruloplasmin level also is sufficient to make the diagnosis.
Even when transplantation is unavailable for patients, it remains imperative to make the diagnosis of Wilson disease for the purpose of aggressive medical therapy and family screening.
Your mission will be to design an experiment to study some aspectof photosynthesis, using the techniques which you learned in thefirst part of the lab. Remember, we are more concerned with yourexperimental design than with your results.
To demonstrate CO uptake we will use ourold friend This time we will use an indicator, phenolred, to demonstrate a change in pH resulting from photosyntheticCO uptake. Phenol red(phenol-sulfonphthalein) turns yellow at pH 7. We will place in a dilute solution of phenol redacidified with carbonic acid, and watch it raise the pH of thesolution.
In Step Three, regeneration of the acceptor molecule occurs. For every six molecules of triose phosphate formed, five are used to form three molecules of RuBP. In this conversion, energy from ATP is also required. From the other molecule of triose phosphate other compounds are synthesized. These include carbohydrates (sugars and starch, and sucrose for translocation in the phloem), lipids, and amino acids. In these conversions energy from ATP is also required. How the products of photosynthesis sustain the whole of the plant is summarised in .
Plants take up CO2 from their environment and incorporate it intocarbohydrate during the dark reactions of photosynthesis. This can bedemonstrated with aquatic plants by measuring the rise in pH as aplant photosynthesizes. Recall from the previous lab that CO2dissolves in water to form carbonic acid:
A culture of Chlorella, a unicellular alga, was used in these experiments, in place of mesophyll cells. This was because they have similar photosynthesis and they allow easy sampling. Samples of the photosynthesising cells, taken at frequent intervals after a pulse of 14CO2 had been given were harvested and analysed. The intermediates that became progressively labelled with the carbon-14 were isolated by chromatography and then identified.
Fascinating ‘detective work’ by biochemists has shown us how photosynthesis works, step by step. Not surprisingly, photosynthesis consists of a complex set of many reactions taking place in chloroplasts in the light. However, these reactions divide naturally into two stages.
The rate of photosynthesis can be measured in an aquatic plant, using a microburette – also called a photosynthometer (). The experiment requires a freshly cut shoot of aquatic green pondweed which, when inverted, produces a vigorous stream of gas bubbles from the base. The bubbles tell us the pondweed is actively photosynthesising. The pondweed is placed in a very dilute solution of sodium hydrogencarbonate, which supplies the carbon dioxide (as hydrogencarbonate ions) required by the plant for photosynthesis. The quantity of gas evolved in a given time is measured by drawing the gas bubble that collects into the capillary tube and measuring its length. This length is then converted to a volume.
The chlorophyll that has been extracted from leaves and dissolved in an organic solvent still absorbs light. However, chlorophyll in solution cannot use light energy to make sugar. This is because, in the extraction process, chlorophyll has been separated from the membrane systems and enzymes that surround it in chloroplasts. These are also essential for carrying out the biochemical steps of photosynthesis, as we shall now discover.