Photosynthesis (form 4 biology)


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Photosynthesis (form 4 biology)

  1. 1. In Greek,the word photosynthesis where the word photo (light) and synthesis (composition). A process used by plants and other organisms to convert the light energy captured from the sun into chemical energy that can be used to fuel the organism's activities.
  2. 2.  Occurs in plants,algae, and many species of bacteria, but not in archae (a kind of single celled microorganism). Photosynthetic organisms are called photoautotrophs, since they can create their own food.  In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product.  Photosynthesis is vital for all aerobic life on Earth. In addition to maintain normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth
  3. 3.  Jean Baptiste van Helmont conducted an experiment to find how plant grew.He finally concluded that the plant had grown mainly form the water which was added regularly and not the soil.  Joseph Priestly demonstrated that plants could restore oxygen and were capable of supporting combustion and respiration.Priestly did not know about oxygen but his work showed that plants release oxygen into atmosphere.  Jan Ingenhousz recognised the importance of sunlight and chlorophyll in photosynthesis.  Robert Meyer recognised that plant convert solar energy into chemical energy during photosynthesis  Blackman solved the mystery of photosynthesis.He discovered that photosynthesis involves two principle reactions.
  4. 4. The process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds.
  5. 5. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the Calvin cycle.
  6. 6.  Photosynthetic organisms are photoautotrophs,which means that they are able to synthesize food directly from carbon dioxide and water using energy from light.  However, not all organisms that use light as a source of energy carry out photosynthesis, since photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon.  In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis. Although there are some differences between oxygenic photosynthesis in plants,algae, andcyanobacteria, the overall process is quite similar in these organisms.  However, there are some types of bacteria that carry out anoxygenic photosynthesis, which consumes carbon dioxide but does not release oxygen.  Carbon dioxide is converted into sugars in a process called carbon fixation. Carbon fixation is a redox reaction, so photosynthesis needs to supply both a source of energy to drive this process, and the electrons needed to convert carbon dioxide into a carbohydrate, which is a reduction reaction.  In general outline, photosynthesis is the opposite of cellular respiration, where glucose and other compounds are oxidized to produce carbon dioxide, water, and release chemical energy. However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments.
  7. 7.  Plants take up water from the soil to their roots.  Plants will also absorb carbon dioxide from the atmosphere to be able to carry out photosynthesis.  Sunlight is very vital to plant to be converted in chemical energy.  The end product would be glucose which provide energy for plant and oxygen which benefits human for respiration.
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  10. 10. Leaf Functions   Air space - intercellular gaps within the spongy mesophyll. These gaps are filled with gas that the plant uses (carbon dioxide - CO2 ) and gases that the plant is expelling (oxygen - O2, and water vapor).  Chlorophyll - a molecule in leaves that can use light energy from sunlight to turn water and carbon dioxide gas into sugar and oxygen (this process is called photosynthesis). Chlorophyll is magnesium-based and is green.  Cuticle - the waxy, water-repelling layer on the outer surface of a leaf that helps keep it from dying out (and protect it from invading bacteria, insects, and fungi). The cuticle is secreted by the epidermis (including the guard cells) and is often thinner on the underside of leaves. The cuticle is generally thicker on plants that live in dry environments.  Epidermis - the protective, outler layer of cells on the surface of a leaf. The guard cells (and stoma) are part of the epidermis. The surface of many leaves is coated with a waxy cuticle which is secreted by the epidermis.
  11. 11.  Guard cell - one of a pair of sausage-shaped cells that surround a stoma (a pore in a leaf). Guard cells change shape (as light and humidity change), causing the stoma to open and close.  Palisade mesophyll - a layer of elongated cells located under the upper epidermis. These cells contain most of the leaf's chlorophyll, converting sunlight into usable chemical energy for the plant.  Spongy mesophyll - the layer below the palisade mesophyll; it has irregularly-shaped cells with many air spaces between the cells. These cells contain some chlorophyll. The spongy mesophyll cells communicate with the guard cells (stomata), causing them to open or close, depending on the concentration of gases.  Stoma - (plural stomata) a pore (or opening) in a plant's leaves where water vapor and other gases leave and enter the plant. Stomata are formed by two guard cells that regulate the opening and closing of the pore. Generally, many more stomata are on the bottom of a leaf than on the top.  Vein (vascular bundle) - Veins provide support for the leaf and transport both water and minerals (via xylem) and food energy (via phloem) through the leaf and on to the rest of the plant.
  12. 12. DARKKEY