Biology 1 Quarter 2 Week 2A Energy Transformation (Light Reactions) PDF

# WEEKLY LEARNING ACTIVITY SHEETS ## Biology 1 Quarter 2 Week 2A ### ENERGY TRANSFORMATION (LIGHT REACTIONS) #### Learning Competency: Describe the patterns of electron flow through light reaction events. (STEM_BIO11/12-IIa-j-4) #### Specific Objectives: 1. Determine the essential molecules involv...

# WEEKLY LEARNING ACTIVITY SHEETS ## Biology 1 Quarter 2 Week 2A ### ENERGY TRANSFORMATION (LIGHT REACTIONS) #### Learning Competency: Describe the patterns of electron flow through light reaction events. (STEM_BIO11/12-IIa-j-4) #### Specific Objectives: 1. Determine the essential molecules involved in the light reactions; 2. Describe the events and processes happening during light reactions; and 3. Distinguish the importance of sunlight to photosynthesis. #### Key Concepts ##### Why is photosynthesis important? Photosynthesis is a vital process in which life here on Earth largely depends. As autotrophs, plants can make their food with raw materials from water, carbon dioxide, and sunlight. On the other hand, humans and other living organisms depend on plants to survive since they cannot make their food. If photosynthesis is stopped, there would soon be little food or other organic matter on Earth. Then, most organisms would disappear, and in time Earth's atmosphere would have no amount of oxygen in the air. The only organisms that could probably exist under such conditions would be the chemosynthetic bacteria, which uses certain inorganic compounds' chemical energy and are not dependent on light energy conversion. Thus, it is deemed essential to understanding a vital process for the sustenance of life, photosynthesis. ##### Stages of Photosynthesis Photosynthesis happens in a two-way process. These include the light reaction stage and the dark reaction stage or the Calvin Cycle. Stage one: Light reactions ##### Light reactions Light reactions use sunlight to start with the electron transfer. Light reduces Nicotinamide Adenine Dinucleotide Phosphate (NADP+) to Nicotinamide Adenine Dinucleotide Phosphate Hydrogen (NADPH) and splits water producing oxygen as a byproduct. This results to form Adenosine Triphosphate (ATP) through phosphorylation. This process takes place in the thylakoids inside the chloroplast. ##### Products of the Light Reactions The product of light reactions is Hydrogen and ATP. These are then transferred to the second stage of photosynthesis, the Calvin Cycle. The mitochondria of plant cells can use some of the oxygen produced by this process for aerobic respiration. However, most oxygen diffuses out of plant cells and out of the leaves through the stomata. Increasing the concentration of oxygen in the Earth's atmosphere is the overall effect of photosynthesis. ##### Stage Two: Calvin Cycle or Dark Reactions Calvin Cycle is the second stage in the light reaction. This is sometimes referred to as 'dark reactions' because it does not need light energy for its processes to happen. This stage requires energy supplied by the Adenosine Triphosphate (ATP) made during the light reactions. Then, ATP is broken down to release energy used to combine hydrogen (from the light reactions) with carbon dioxide to produce Glucose (C6H12O6) which is a sugar. Specific enzymes control the reactions of carbon fixation. This stage takes place in the stroma inside the chloroplast. After the energy transfer, the energy carrier molecule returns Adenosine Diphosphate (ADP), inorganic phosphate, and NADP+ to the light reactions. ##### Light Reactions Events  The process starts when light energy or photons is absorbed by a pigment molecule of the light-harvesting complex of Photosystem II and is passed on to other pigment molecules nearby until the energy makes it to the reaction center. In the reaction center, it is absorbed by the P680 pair of chlorophyll a. 1. In this pair of chlorophyll, the electron is raised to an excited state and is transferred to the primary electron acceptor. Then P680 loses its electron and becomes positively charged (P680+). 2. The positively charged molecule, P680+ attracts electrons from a water molecule, resulting in the splitting up of water H20 into two electrons, the two hydrogen ions (H+), and an oxygen atom with the supply of light energy. The oxygen atom immediately combines with another oxygen atom to form an oxygen molecule (O2), then released outside the leaf through the stomata. 3. Inside the stroma, the excited electrons are then passed on from the primary electron acceptor to the electron carrier molecules through the electron transport chain until they reach Photosystem I. The electron carrier molecules involved are plastoquinone (Pq), a cytochrome complex, and plastocyanin (Pc). 4. At every transfer of electrons, these release small amounts of energy. Then, this energy is used to pump hydrogen ions across the membrane. The splitting up of water molecules makes an uneven distribution of hydrogen ions in the stroma and the lumen. Through the aid of a membrane protein called ATP synthase, the H+ ions try to equalize their distribution by transferring from the lumen to the stroma. This process is called chemiosmosis. The transfer of hydrogen ions through the ATP synthase channel causes the production of ATP from ADP. ATP contains high-energy phosphate bonds. 5. Meanwhile, when a photon is absorbed and energy is passed on from one pigment molecule to another, the energy reaches the reaction center complex of Photosystem I. The energy excites the electron present in the pair of P700 chlorophyll located here. The excited electron is then moved to a primary electron acceptor, making the P700 positively charged and seeking electrons to fill up the missing ones. The electrons from Photosystem II fill this up passed on through the electron transport chain. 6. As the photo-excited electron from the primary electron acceptor of Photosystem I enters another electron transfer chain, it passes the electron to an iron-containing protein called ferredoxin (Fd). 7. Lastly, an enzyme, the NADP+ reductase, then transfers the electron to NADP+ and stabilizes it by adding a proton (H+) to form NADPH. NADPH is then released to the stroma and becomes part of the Calvin Cycle. ### Cyclic Electron Flow  Aside from the usual electron flow route described in the events of the light reactions, photo-excited electrons may take a short-circuited path which utilizes Photosystem I but not Photosystem II. The ferredoxin goes back to the cycle and passes the electron to the cytochrome complex and the plastocyanin (Pc). until it reaches P700 chlorophyll instead of transferring the electron to NADP+ reductase. Because of this, no NADPH is produced, but ATP is still synthesized. # WEEKLY LEARNING ACTIVITY SHEETS ## Biology 1, Quarter 2, Week 2B ENERGY ### TRANSFORMATION (CALVIN CYCLE) #### Learning Competency: Describe the significant events of the Calvin cycle. (STEM_BIO11/12-IIa-j-5) #### Specific Objectives 1. Determine the phases of the Calvin Cycle; 2. Identify the important molecules needed in the Calvin Cycle; and 3. Describe the molecules produced in the Calvin Cycle. #### Key Concepts ##### Calvin Cycle You, like all living organisms here on Earth, are a carbon-based life form. This only means that the complex molecules of your amazing body are built on carbon backbones. You might already know that you're carbon-based, but have you ever asked where all of that carbon comes from? Apparently, the atoms of carbon in your body were once part of carbon dioxide molecules in the air. Carbon atoms end up inside you, and in other life forms, thanks to the second stage of photosynthesis, known as the Calvin cycle. The Calvin cycle or "dark reactions" is a process that autotrophs, like plants and algae, use to make carbon dioxide from the air into Glucose (C6H1206) which is a sugar, the food they need to grow. This is the process where the second stage of photosynthesis happens to form Glucose (C6H12O6) from CO2 using chemical energy stored in the ATP and NADPH, the products of light reactions. This happens in the stroma of the chloroplast.  Calvin Cycle is very significant to every living thing on Earth since we depend on it. Here's how: plants depend in the Calvin Cycle for energy and food. Other organisms like herbivores, also depend on it indirectly because they are fed on plants. Even animals that eat other organisms, such as carnivores, depend on the Calvin Cycle. Without it, we wouldn't have the food, energy, and nutrients we need to survive. ##### Reactions of the Calvin Cycle There are three main stages in a Calvin Cycle: Carbon fixation, Reduction, and Regeneration of the starting molecule. ##### Phase 1: Carbon Fixation  Carbon fixation is a process of merging CO2, an inorganic carbon molecule into an organic material. In this phase, the CO2 molecule is attached to a five-carbon sugar molecule, ribulose biphosphate (RuBP) with the help an enzyme named rubisco or RuBP carboxylase, believed to be the most abundant protein in the chloroplast and probably on Earth. The resulting product of carbon fixation is a six-carbon sugar, which is extremely unstable and immediately splits in half. The split forms two molecules of 3- phosphoglycerate (3-Carbon). ##### Phase 2: Reduction  In reduction phase, a phosphate group (from ATP) is then attached to each 3-phosphoglycerate by an enzyme, forming 1,3-phosphoglycerate. To produce Glyceraldyde-3-phosphate G3P, NADPH swoops in and reduces 1,3- biphosphogycerate. The produced six G3Ps by the Calvin Cycle, five are recycled to give three molecules of RuBP. Of the six G3P's produced, only one G3P leaves the cycle to be packaged for use by the cell. It needs two molecules of G3P to make one molecule of glucose. The products formed during the Calvin cycle, ADP and NADP+, will then be brought back to the thylakoid membrane and then will enter the light reactions. Inside the thylakoid, they will be 'recharged' with energy and become ATP and NADPH. ##### Phase 3: Regeneration of RuBP Five molecules of Glyceraldyde-3-phosphate G3P shall undergo complex enzymatic reactions to produce three molecules of Ribulose Biphosphate (RuBP). The cell needs another three molecules of ATP, but also provides another set of Ribulose Biphosphate (RuBP) to continue the cycle. G3P after its release from the cycle The two Glyceraldyde-3-phosphate G3Ps can combine to form six-carbon sugar. They could either be glucose or fructose (C6H12O6). Eventually, glucose and fructose can be combined to form sucrose. Starch is formed when glucose is connected in chains. In lipid and protein synthesis G3Ps can also be used. ❖ Making of a carbohydrate: In making one molecule of G3P, the chloroplast needs the following: 1. 3 molecules of CO2 2. 9 molecules of ATP 3. 6 molecules of NADPH ❖ Important points to know in the Calvin Cycle  The sugar produced in the Calvin Cycle is not the six-carbon Glucose that we are familiar with. The product in the Calvin Cycle is a three-carbon sugar known as G3P or Glyceraldehyde-3-Phosphate. The glucose is formed later on. There is a need for the Calvin Cycle to 'spin' three times to make one molecule of Glyceraldehyde-3-Phosphate (G3P) from three molecules of CO2.