Photosynthesis PDF

PHOTOSYNTHESIS  ENERGY the ability to do work necessary in metabolism Energy flow starts when energy is captured…it is then changed in form, used for work and lost as heat.  How Do Organisms Get Energy? FOOD → consists of organic molecules that store energy in the form of chemical en...

PHOTOSYNTHESIS  ENERGY the ability to do work necessary in metabolism Energy flow starts when energy is captured…it is then changed in form, used for work and lost as heat.  How Do Organisms Get Energy? FOOD → consists of organic molecules that store energy in the form of chemical energy. Different animals have different ways of obtaining food for energy. 1. Autotrophs or Producers - organisms that make their own food - most of them use energy from sunlight to make their own food - they can make food through Photosynthesis - e.g. plants, green algae and some bacteria  - they make food not only for themselves but for other living organisms, as well. - they are considered the starting organisms in all food chains 2. Heterotrophs - cannot make their own food - obtain food by consuming other organisms - they consume autotrophs, other heterotrophs, or both - e.g. animals, fungi and some single-celled organisms  Energy-Giving Molecules 1. Glucose - made during the process of Photosynthesis - plants create glucose with the help of light energy from the sun, water and carbon dioxide - in human body, it is transported by the blood and taken up by the cells for energy source 2. Adenosine Triphosphate (ATP) - stores smaller amount of energy but each molecule releases enough energy to do the work within the cell - used by the cells for other important cellular processes - made during the 1st half of Photosynthesis and is used during the 2nd half where glucose is made - energy is released when it gives up one of its phosphates ATP + water ➔ ADP + inorganic Phosphate + ENERGY The flow of energy through living organisms begins with PHOTOSYNTHESIS in producers. This process stores the energy from the sun in the chemical bonds of glucose molecules. These bonds are released to create ATP in a process called CELLULAR RESPIRATION. These two processes store and release energy in living things. The products of one process are the reactants of the other. The Leaf Plant leaves absorb sunlight to manufacture plant sugars through a process called photosynthesis. In order to get enough light, leaf surfaces are flattened to have a big area. What’s inside the Leaf? Guard Cell Stoma The Chloroplast and Other Photosynthetic Pigments Chloroplasts – cell organelles found in plants and algae Grana (singular: Granum) – where the light reaction occurs Thylakoids – layers of sac-like membranes that make up the Granum - the site of Photosystems I and II -where light-dependent reactions in photosynthesis occurs Photosystems – group of molecules involved in photosynthesis which include chlorophyll Stroma – the space found outside the thylakoids - where Calvin Cycle takes place The Chloroplast PIGMENTS 1. Chlorophyll – chlorophyll a and chlorophyll b are green pigments that absorb all wavelengths of light in the red, blue and violet ranges 2. Carotenoids – are yellow, orange and red pigments that absorb light in blue, green and violet ranges. 3. Phycobilins – pigment found in red algae which give them their reddish color and absorbs light in blue and green ranges  PHOTOSYSTEMS Photosystem – clusters of pigment molecules within the thylakoid - light-harvesting complexes; reaction center Types: 1. Photosystem I - absorbs red light at about 700 nanometer (nm) and its primary reaction center is the special chlorophyll called P 700 2. Photosystem II - absorbs more orange light at 680 nm and its primary reaction center is the special chlorophyll called P 680  PHOTOSYNTHESIS Photosynthesis is the most important life process on Earth. Through this process, more than 99% of the energy used by all living things is provided. Photosynthesis converts light energy from the sun into chemical energy, and release oxygen. Phases: 1. Light-dependent Reaction (Non-cyclic Photophosphorylation) 2. Light-independent Reaction/ Carbon Dioxide Fixation/ C3 Cycle/ Calvin Cycle  Non-cyclic Phosphorylation If PS II antenna complex absorbs solar energy, the high-energy electrons leave the reaction center- where chlorophyll a molecules are found and enter the electron transport system. Here, energy is released as electrons are passed from one carrier to another. The released energy is stored in the form of Hydrogen ion gradient. This gradient is used by enzyme, ATP synthase complex, to drive the synthesis of ATP. ADP + P → ATP + H20  The low-energy electrons move from the electron transport system to PS I where they gain energy when the pigments absorb solar energy. The excited electrons are passed to an electron carrier. The electron carriers send the energized electrons to oxidized nicotinamide dinucleotide phosphate (NADP+), also an electron carrier. Together with the electron, NADP+ picks up hydrogen ion from water to become NADPH. This non-cyclic electron flow is also called Z- pathway or non-cyclic photophosphorylation.  The electrons lost at PS II are replenished by a reaction involving water. Water splits in the presence of light. This is called photolysis. It happens at a system associated with PS II. H20 → H+ + 2e- + O2 The synthesis of ATP through cyclic or non-cyclic photophosphorylation is tied up to the hydrogen ion gradient. This mechanism of ATP production is called chemiosmosis. The products of light-dependent reactions are ATP and NADPH. Non-cyclic photophosphorylation produces ATP and NADPH. The by-product is oxygen gas, which comes from water and is released into the atmosphere.  The Light- Independent Reaction / Dark Reaction/ Carbon Dioxide Fixation/ Calvin Cycle What do plants do with the products of light- dependent reaction – ATP and NADPH? These two substances are high-energy molecules. The energy could be harnessed in making food out of carbon dioxide. How do plants fix carbon dioxide into food? First carbon dioxide enters the leaf through the stomata. It goes into the mesophyll layers and moves to the stroma of the chloroplast. 3 Major Steps: 1. Carbon Fixation Here, carbon dioxide collides with 5- carbon compound called ribulose-1, 5-bisphosphate (RUBP) to yield 6- carbon-containing sugar. The process is catalyzed by RUBP carboxylase. RUBP → 6-carbon compound 2. Reduction Reactions The 6-carbon compound is broken into two molecules of 3-carbon sugar, phosphoglycerate (PGA). This requires two molecules of ATP. 6-carbon compounds → 2 PGA The 2 molecules of PGA are converted into 2 molecules of phosphoglyceraldehyde (PGAL), a 3-carbon compound. PGAL is the first stable product of photosynthesis. It needs 2 molecules of NADPH. 2 PGA → 2 PGAL 3. Regeneration of RuBP RUBP is regenerated from PGAL for the process to continue. A molecule of ATP is needed for the regeneration process. 5 PGAL → 3 RuBP The process occurs in a cyclic manner. Since the first stable product is composed of 3 carbon atoms, it is called C3 Cycle. Melvin Calvin unlocked this process. It is also named as Calvin Cycle. The Calvin Cycle  Three turns of Calvin Cycle are necessary to produce one net gain of PGAL. Five PGAL molecules are needed to regenerate 3 molecules of RUBP. The three turns use up 9 molecules of ATP and 6 molecules of NADPH. PGAL is a substance used by plants to make other organic substances. An example of these organic substances synthesized by plants is glucose. To make one glucose molecule, a 6- carbon sugar, two molecules of PGAL are linked. This means six turns of Calvin cycle.  4 3 1 2