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Plants - Photosynthesis

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Moving water from roots to leaves is a problem that terrestrial plants have had to overcome. But there is an advantage for the plant that grows its leaves on stems and high branches. Light can reach the leaves more easily, which is important for photosynthesis. Photosynthesis is an energy storing process that is important to animals as well as plants. Free energy from sunlight is captured and stored as sugars and starches in plant tissues. The way the leaves are arranged on stems ensures that the plant takes maximum advantage of the available light. The key to photosynthesis is the chloroplast. There are large numbers of chloroplasts found in the middle tissue of the leaf. In low light they are distributed fairly evenly, but bright light causes them to move to a less exposed position. The most noticeable characteristic of chloroplasts is their green colour. The colour comes from a pigment called chlorophyll which is concentrated in the grana. We can show that without the chlorophyll photosynthesis does not take place. First, we boil the leaf to fix it, then we put it into alcohol. Boiling the leaf in alcohol removes the chlorophyll. A few drops of iodine soon reveal a blue-black colour which indicates where starch is present in the leaf. We can see that starch is only produced in the parts of the leaf that were green, that is, where chlorophyll was present. Chemical analysis of chloroplasts shows that chlorophyll and a series of other compounds are organised in the thylakoid membranes in a systematic way. When light strikes the thylakoid membranes, chlorophyll and other associated pigments are oxidised, which causes the release of electrons. The electron flow initiated by this input of light energy is coupled with the formation of Adenosine Triphosphate, or ATP. The reaction is known as the light reaction of photosynthesis. Because electrons are being lost from the chlorophyll, they have to be replaced. The plant does this by splitting water molecules and using electrons from hydrogen, leaving oxygen as a waste product. When water plants like Elodea are photosynthesising it is easy to see the bubbles of waste oxygen being released. ATP molecules are energy storing molecules, they provide the energy that enables the plant to combine carbon dioxide with other compounds to make sugars. This activity occurs in the stroma of the chloroplast and does not require light. It is therefore known as the dark reaction of photosynthesis.

Video Details

Duration: 3 minutes and 4 seconds
Country: United Kingdom
Language: English
Views: 43
Posted by: ang_ruiz on Oct 10, 2014

Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the Sun, into chemical energy that can be later released to fuel the organisms' activities.

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