The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1.
Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. Inheritance 3. Speciation Animal Physiology 1. The remaining function of the light-dependent reaction is to generate the other energy-carrier molecule, NADPH. As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll.
Now that the solar energy is stored in energy carriers, it can be used to make a sugar molecule. The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll a to the electron transport chain, which pumps hydrogen ions into the thylakoid interior the lumen.
This action builds up a high concentration of hydrogen ions. The ions flow through ATP synthase via chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis.
Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy and reducing power carrier for the light-independent reactions. Unless otherwise noted, images on this page are licensed under CC-BY 4. Text adapted from: OpenStax , Concepts of Biology. OpenStax CNX. Skip to content Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle.
Figure 1 Light energy is absorbed by a chlorophyll molecule and is passed along a pathway to other chlorophyll molecules. The energy culminates in a molecule of chlorophyll found in the reaction center. A molecule of water splits to release an electron, which is needed to replace the one donated. Oxygen and hydrogen ions are also formed from the splitting of water. Figure 3 Energy from light is used by the chloroplast electron transport chain to pump protons across the thylakoid membrane into the lumen of the thylakoid.
The sun emits an enormous amount of electromagnetic radiation solar energy. Scientists can determine the amount of energy of a wave by measuring its wavelength, the distance between two consecutive, similar points in a series of waves, such as from crest to crest or trough to trough Figure 5.
Visible light constitutes only one of many types of electromagnetic radiation emitted from the sun. The electromagnetic spectrum is the range of all possible wavelengths of radiation Figure 5. Each wavelength corresponds to a different amount of energy carried. Each type of electromagnetic radiation has a characteristic range of wavelengths.
The longer the wavelength or the more stretched out it appears , the less energy is carried. Short, tight waves carry the most energy. This may seem illogical, but think of it in terms of a piece of moving rope. It takes little effort by a person to move a rope in long, wide waves. To make a rope move in short, tight waves, a person would need to apply significantly more energy. The sun emits a broad range of electromagnetic radiation, including X-rays and ultraviolet UV rays.
The higher-energy waves are dangerous to living things; for example, X-rays and UV rays can be harmful to humans. Light energy enters the process of photosynthesis when pigments absorb the light. In plants, pigment molecules absorb only visible light for photosynthesis. The visible light seen by humans as white light actually exists in a rainbow of colors.
Certain objects, such as a prism or a drop of water, disperse white light to reveal these colors to the human eye. The visible light portion of the electromagnetic spectrum is perceived by the human eye as a rainbow of colors, with violet and blue having shorter wavelengths and, therefore, higher energy.
At the other end of the spectrum toward red, the wavelengths are longer and have lower energy. Different kinds of pigments exist, and each absorbs only certain wavelengths colors of visible light.
Pigments reflect the color of the wavelengths that they cannot absorb. All photosynthetic organisms contain a pigment called chlorophyll a , which humans see as the common green color associated with plants. Chlorophyll a absorbs wavelengths from either end of the visible spectrum blue and red , but not from green.
Because green is reflected, chlorophyll appears green. Other pigment types include chlorophyll b which absorbs blue and red-orange light and the carotenoids.
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