1) Describe a technique for measuring photosynthetic rate. 2) Many deciduous tre
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Question
1) Describe a technique for measuring photosynthetic rate.
2) Many deciduous trees have leaves which turn yellow in the fall. What do you suppose is happening in the leaves at the cellular and molecular level?
3) Chloroplasts and mitochondria are both are unusual in that they have double membranes and contain their own set of DNA. Can you think of any explanations for this observation?
4) Some plants (grasses) tend to contain a greater concentration of chlorophyll than others (pines). Can you develop a hypothesis to explain this? Would it be testable?
Explanation / Answer
Few key methods to calculate the rate of photosynthesis. These include:
1) Measuring the uptake of CO2
Using an IRGA - Uptake of CO2 can be measured with the means of an IRGA (Infra-Red Gas Analyser) which can compare the CO2 concentration in gas passing into a chamber surrounding a leaf/plant and the CO2 leaving the chamber.
Using a CO2 monitor - More simply, you could put a plant in a plastic bag and monitor the CO2 concentration in the bag using a CO2 monitor. Naturally, the soil and roots must NOT be in the bag (as they respire). Alternatively, you could place some Bicarbonate Indicator Solution in the bag with the plant and watch the colour change. This would best be done with a reference colour chart to try to make the end-point less subjective. This could give a comparison between several plants. There are difficulties with this method, as I'm sure you can appreciate. The leaf area of the plants should be measured so you can compensate for plant size. Atmospheric air is only 400ppm CO2, so there is not much CO2 to monitor and the plant will soon run out of CO2 to fix.
2)
Measuring photosynthesis via the production of oxygen
Oxygen can be measured by counting bubbles evolved from pondweed, or by using the Audus apparatus to measure the amount of gas evolved over a period of time. To do this, place Cabomba pondweed in an upside down syringe in a water bath connected to a capillary tube (you can also use Elodea, but we find Cabomba more reliable). Put the weed in a solution of NaHCO3 solution. You can then investigate the amount of gas produced at different distances from a lamp.
Answer 2)
The leaves of trees and other plants contain three main pigments: carotene, anthocyanin, and the photosynthetic pigment, chlorophyll, which captures the sun’s energy to make food for plants. As the most abundant pigment, chlorophyll is what gives leaves their green hue in spring and summer.
Another chemical in leaves, auxin, controls a special band of cells at the base of each leaf stem, called the abscission layer. During the growing season, auxin prevents this layer from fully developing and blocking the tiny, internal tubes that connect each leaf to the rest of the tree’s circulatory system.
In fall, however, cooler and shorter days trigger an end to auxin production, allowing the abscission layer to grow and cut off the circulation of water, nutrients and sugar to the leaves. When this happens, chlorophyll disintegrates rapidly, letting carotene shine through as the yellow in maple, aspen and birch leaves. Anthocyanin, meanwhile, provides the oranges and reds of maples, sumacs and oaks. When there’s less sun, anthocyanin isn’t as chemically active and leaves are more orange or yellow than red.
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