Plants are the only photosynthetic organisms to have leaves (and not all plants have leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells.
The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf, and the products of photosynthesis, sugar and oxygen, leave the leaf.
Background Information:
Photosynthesis is essential to life on this planet. Living species wouldn't be here without it! Recent measurements have shown a dramatic increase in concentrations of CO2, which is Carbon Dioxide in our atmosphere. Our lifestyles are largely responsible for this increase in CO2 emissions. As scientists and special interest groups debate the existence of global warming, polar ice caps are melting and the Canadian permafrost is melting. Trees can reduce the introduction of CO2 into the atmosphere by cooling our cities and cleaning the air. There are at least two ways trees can reduce atmospheric levels of CO2. First, trees can shade potential heat sinks like buildings, pavement, and vehicles. Reducing the number of heat sinks in the city will reduce our dependence upon air conditioning, which means reducing fossil fuel consumption used for the production of electricity. Second, trees (and all plants) sequester CO2 from the atmosphere during the process of photosynthesis and release oxygen.
Scientific Knowledge:
Sunlight plays a much larger role in our sustenance than we may expect: all the food we eat and all the fossil fuel we use is a product of photosynthesis, which is the process that converts energy in sunlight to chemical forms of energy that can be used by biological systems. Photosynthesis is carried out by many different organisms, ranging from plants to bacteria (Figure 1). The best-known form of photosynthesis is the one carried out by higher plants and algae, as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans. All these organisms convert CO2 (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Electrons for this reduction reaction ultimately come from water, which is then converted to oxygen and protons. Energy for this process is provided by light, which is absorbed by pigments (primarily chlorophylls and carotenoids). Chlorophylls absorb blue and red light and carotenoids absorb blue-green light (Figure 2), but photosynthetic pigments in plants do not effectively absorb green and yellow light; therefore, light of these colours is either reflected by leaves or passes through the leaves. This is why plants are green.
Figure 2. Absorption spectrum of isolated chlorophyll and carotenoid species. The colour associated with the various wavelengths is indicated above the graph.
Other photosynthetic organisms, such as cyanobacteria (formerly known as blue-green algae) and red algae, have additional pigments called phycobilins that are red or blue and that absorb the colours of visible light that are not effectively absorbed by chlorophyll and carotenoids. Yet other organisms, such as the purple and green bacteria (which, by the way, look fairly brown under many growth conditions), contain bacteriochlorophyll that absorbs in the infrared, in addition to in the blue part of the spectrum. These bacteria do not evolve oxygen, but perform photosynthesis under anaerobic (oxygen-less) conditions. These bacteria efficiently use infrared light for photosynthesis. Infrared is light with wavelengths above 700 nm that cannot be seen by the human eye; some bacterial species can use infrared light with wavelengths of up to 1000 nm. However, most pigments are not very effective in absorbing ultraviolet light (<400 nm), which also cannot be seen by the human eye. Light with wavelengths below 330 nm becomes increasingly damaging to cells, but virtually all light at these short wavelengths is filtered out by the atmosphere (most prominently the ozone layer) before reaching the earth. Even though most plants are capable of producing compounds that absorb ultraviolet light, an increased exposure to light around 300 nm has detrimental effects on plant productivity.
Fair Test:
We did the experiment twice. We say many changes. On the first experiment, we did the bubbles weren’t increasing at all, there were a few bubbles, but not that much. The longer we moved the light,
