Most organisms need complex substances such as carbohydrates and sugars. Those that cannot make them take them in in the form of oils, fats, sugars, proteins. These they obtain from their diet.
Plants can only take nutrients in solution. So they are limited to taking in simple inorganic substances like phosphorous, calcium and zinc. Yet, plants make living protoplasm, which is a mix of complex substances. These they make from the basic components of carbon dioxide and water. These are converted into sugars, which in turn can be converted into the complex materials the plant needs to metabolize, from oils, scent chemicals and pollen grains. The obvious question is where does the energy to do this come from? The answer is light!
Plants do an amazing thing in that they have the ability to use molecules of water and carbon dioxide and, using energy from sunlight, create food in form of sugars.
Plants are only organisms to have photosynthetic leaves.They use the molecules in the formula:
6CO2 plus 6H20 in presence of sunlight and chlorophyll gives C6 H12O6 (glucose)
Water is obtained from the soil or water (if aquatic of hydroponically grown) via their root hairs (not inter cellular spaces) and Co2 from air.
Photosynthesis takes place in the chloroplasts of cells. These are organelles present in large numbers in the palisade cells. They contain pigment chlorophyll in green plants. Chlorophyll may also be present in other cells.
The process is carried out in not one but two phases – the light and dark reaction.
In the light Dependant phase electrons in chlorophyll are struck by light and the energy excites them so they go to a higher energy state. This energy is converted in a series of reactions to ATP (adenose triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). Water is split in the process, releasing oxygen as a by produce of that reaction (H2O) split into H2 and O.
Remember water is H2O. Release the molecular bond and energy is released. ATP is the universal molecule in life and without it, rest of process does not arise.
In the dark process carbon dioxide from the atmosphere (or water for aquatics) is captured and modified by the addition of the hydrogen (obtained from splitting of water) to form carbohydrates. The incorporation of carbon dioxide into organic compounds is known as carbon fixation.
The energy for this comes from the first phase of the photosynthetic process. Living systems cannot directly use light energy but can, through a series of complicated reactions, convert it into C-C bond energy that can be stored in compounds (here as glucose) and released by glycolosis and other metabolic processes.
Chlorophyll works as it absorbs light in range of spectrum of normal day light. White light is made up of different color lights each color has a specific wavelength. Chlorophyll absorbs all apart from green light (so looks green as green light reflected). Other plants live in areas where normal light does not penetrate and only certain colors of the spectrum reach them e.g. seaweed, some aquatic plants. These carry other pigments such as carotene (red) which absorb other wave lengths apart from red.
Hence different colors (browns, reds of seaweeds and other algae).
So, this amazing process occurs in two phases, the first (light Dependant) requires the energy of light to make energy carrying molecules used in the second process. The light independent (dark) process occurs when the products of the light dependent process are used to form C-C bonds of carbohydrates. Dark reactions can usually occur in the dark but they will only take place if products from the light dependent process are available.
Each phase takes place in different parts (grana and stroma of chloroplast).
Plants are carbon sinks and absorb more carbon in carbon dioxide from air than give off. Some CO2 given off by respiration but overall, more absorbed than given off. So plants remove atmospheric Carbon. However, burning fossil fuels in which this carbon stored releases it to the air affects carbon cycle.
Plants and man are directly dependent on each other as plants produce most of oxygen we use for respiration. We and other animals produce CO2 for plants. Plant do produce CO2 but this is quickly used in photosynthesis.
So, plants continue to amaze and are vital for our survival, Next time you look at a leaf, think of the chemistry!
