Unit 3 AoS 2 – (1) KK1, 2, 4 & 5 (Biochemical Pathway of Photosynthesis) [STUDENT VERSION].pptx
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Unit 3 AoS 2 How are Biochemical Pathways Regulated? KK1, KK2, KK4 & KK5 – Biochemical Pathway of Photosynthesis The general structure of the biochemical pathways in photosynthesis and cellular respiration from initial reactant to...
Unit 3 AoS 2 How are Biochemical Pathways Regulated? KK1, KK2, KK4 & KK5 – Biochemical Pathway of Photosynthesis The general structure of the biochemical pathways in photosynthesis and cellular respiration from initial reactant to final product The general role of enzymes and coenzymes in facilitating steps in photosynthesis and cellular Study Design respiration Key Knowledge Inputs, outputs and locations of the light dependent and light independent stages of photosynthesis in C3 plants (details of biochemical pathway mechanisms are not required). The role of Rubisco in photosynthesis, including adaptations of C3, C4 and CAM plants to maximise the efficiency What is Photosynthesis? It’s the process plants, algae and certain bacteria use to harness energy from sunlight and turn it into chemical energy. The general equation is 6CO2 + 6H2O C6H12O6 + 6O2 So the basic inputs and outputs are: Inputs Outputs Carbon Dioxide(CO2) Oxygen (O2) Water (H2O) Glucose (C6H12O6) **Light energy & Chlorophyll are also needed for the reaction to start** Photosynthesis Basic Reaction Generally, the equation is 6CO2 + 6H2O C6H12O6 + 6O2 However, it can also be written as 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O This second equation shows the presence of 6 extra H2O molecules on both the reactant and product sides. This 2nd equation is slightly more accurate to the actual process, but both are considered correct and balanced equations. Reactants & Products of Photosynthesis Inputs Outputs Carbon Dioxide Oxygen CO2 Released as a gas through the stomata From the air taken in through the stomata Glucose Water H2O Simple sugar formed into sucrose From the soil Stored in the plant for later use. Taken in by transpiration through the root hair cells. Light Required, but NOT an input molecule. Either natural sunlight or artificial light. Chlorophyll The green pigment in plants. Essential to the process Chloroplasts Chloroplasts are double membrane organelles found in plants. They perform a specialized role, Photosynthesis. As such Photosynthesis occurs in the leaves of plants, or any place where chloroplasts are found. Chloroplast Structure Chloroplasts are made with a double membrane: Outer membrane Inner Membrane The 2 key components of the chloroplast are: The Thylakoid A system of membranes within the matrix Thylakoids (fluid filled discs) that stack together to form Grana/Thylakoid Stacks Thylakoid discs contain the chlorophyll pigments used for trapping the light energy. The Stroma The stroma is the liquid that fills the space around the grana. It is full of enzymes and components that help photosynthesis proceed. Chlorophyll Chlorophyll is a green pigment found in the Thylakoids of Chloroplasts. A pigment is a molecule that has a particular color and can absorb light at different wavelengths, depending on the color. Photosynthesis requires Chlorophyll (or another light trapping pigment) to work. Light Trapping pigments: Absorb light energy Include - Chlorophyll (a, b, c, d) & Accessory pigments (Caretonoids, Phychoerythrin) Key Coenzymes in Photosynthesis There are enzymes and coenzymes that play crucial roles in Photosynthesis. Two key coenzymes are: NADP+ NADPH ADP ATP They play a part in both stages of Photosynthesis Stages of Photosynthesis Photosynthesis can be split into two reactions: Light Dependent Light Independent Is the splitting of water Carbon fixing Inputs (Water, NADP+, ADP, Pi) Inputs (Carbon Dioxide, NADPH, ATP) Outputs (Oxygen, NADPH, ATP) Outputs (Glucose, NADP+, ADP, Pi) Directly requires light Doesn't directly require light Occurs on the Thylakoid membranes Occurs in the Stroma In the In the grana 12 NADPH2 stroma Light Dependent Reactions Light Independent Reactions 18 ATP 12 H2O 6 O2 6 CO2 Glucose 6 HO Light Dependent Reaction Location: Thylakoid membranes Reactant molecule: H2O (water) Other important components: Chlorophyll, Light energy, NADP+, ADP, Pi (inorganic Phosphate) Light Dependent Reaction (1) Light energy is absorbed by light absorbing pigments (chlorophyll) within the thylakoid membranes This makes the chlorophyll excited, and it loses an electron Light Dependent Reaction (2) To replace the lost electron, chlorophyll takes electrons from water molecules This separates water into electrons, hydrogen ions (H +) and oxygen gas (O2) Light Dependent Reaction (3) The energised electrons are transferred to the electron transport chain in the thylakoid membrane At the end of the chain, in the stroma NADP+ molecules accept a proton and a pair of electrons to become NADPH Now this energy can be carried on to the light-independent stage Light Dependent Reaction (4) Some of the energy is also used to turn ADP into ATP Light Dependent Reaction – Outputs Oxygen: Leaves the chloroplasts and leaves the leaf cell through the stomata ATP: Energy loaded molecule which will be used as an energy source in the light-independent phase NADPH: Another energy loaded molecule that will be used in the light-independent phase Exam Question 1 A chloroplast is surrounded by a double membrane. a) Name two molecules, as inputs for photosynthesis, that would need to diffuse from the cytosol of the plant cell across the chloroplast membranes and into the chloroplast. b) Under high magnification, the internal structure of a chloroplast is visible. The diagram below shows part of this structure. A higher concentration of oxygen is found in Region R when a plant is photosynthesising compared to when it is not photosynthesising. Account for the differences in oxygen concentrations found in this region. c) Describe the role played by each of the coenzymes NADPH and ATP in photosynthesis. Light Independent Reaction Location: Stroma of the Chloroplasts (the space around the grana) Reactant molecule: Carbon dioxide – taken up through the stomata Other important components: ATP – produced in the light-dependent stage NADPH – produced in the light-dependent stage RuBisCo Light Independent Reaction - Stages It’s also called the “Calvin Cycle” It’s about converting CO2 to Glucose Has 3 key stages: Carbon Fixation Reduction Regeneration of RuBP You do not need to know the specific mechanisms of these stages. However, knowing the basic steps in Carbon Fixation will help later on. An Overview of the Calvin Cycle CO2 molecules enters the cycle and through a series of reactions ends up in 2 3-Carbon molecules. These 3-Carbon molecules then move to the next part of the cycle. When the CO2 is split the oxygen is released. Some of this oxygen then binds with the released H + from the NADPH and makes H2O This is where the “output” water comes from. The NADPH and ATP from the light dependent reaction donate their H +, e- (NADPH) and energy (ATP). This helps additional reactions to occur with the Carbon-based molecules. As the reaction continue, eventually a specific 3C molecule is made and leave the cycle. This goes on to be part of the final Glucose molecule. To make 1 Glucose molecule (C6H12O6) 6 x CO2 molecules are needed Calvin Cycle Video Exam Question 2 Below is a diagram of a chloroplast. a) Name the structure labelled X. (1 mark) b) Complete the following table by referring to the diagram above and your knowledge of photosynthesis. (3 marks) Name of the stage of photosynthesis that occurs at X Two input molecules that are required for reactions at X Two output molecules that Exam Question 3 Which one of the following diagrams correctly represents the inputs and outputs of photosynthesis? A B.. C D.. What is Carbon Fixation? CO2 molecules enter the Calvin Cycle and join a 5C compound called ribulose bisphosphate (or RuBP). An enzyme, RuBP carboxylase (or Rubisco), catalyses the attachment of a CO2 molecule to RuBP CO2 adds 1C to the 5C molecule to make a 6C molecule. But the 6C molecule is unstable, and breaks down into two 3C compounds, GP (glycerate-3-phosphate). The carbon is moved from the inorganic CO2 and “fixed” into an organic compound, hence “Carbon Fixation” Photosynthesis Video Photosynthesis Summary Photosynthesis Stages Activity You will need to form a group with enough people to assign the following jobs to: CO2 Maker Materials 12 x NADPH poles H2O Maker & Collector 6 x C atoms 6 x O2 poles NADPH Mover 24 x H atoms 1 x LDR plate O2 Collector 24 x O atoms 1 x LIR plate Light Dependent Reactor 12 x NADP+ molecules 2 x intermediate 6 x CO2 poles Light Independent Reactor poles 12 x H2O poles Intermediate & Glucose Maker 1 x Glucose The Makers will need to make their molecules, the Reactors will need to move the atoms through their reactions and the collector will need to collect up their molecules as they are made. As a group you should work through the following reaction: 6CO2 + 12H2O 6O2 + C6H12O6 + 6H2O What is Rubisco? An essential enzyme for controlling the first step in the Light Independent Stage of Photosynthesis. It’s responsible for splitting the CO2 and adding the carbon atoms to the 5C molecule. Essentially Rubisco binds CO2, fixing the carbon into the organic 3-PGA, thus initiating the Calvin cycle The Rubisco problem Rubisco should bind with CO as the first step in the Calvin cycle, but sometimes it bind with O 2 2 instead. If it does this then the Calvin cycle can’t happen, which means photosynthesis can properly finish. Instead a different reaction “Photorespiration” happens. Photorespiration This is a wasteful and unwanted process. It interrupts photosynthesis as it has the O2 binding to the Rubisco instead of the CO2. Less photosynthesis means less glucose. This can affect plant growth. More likely to happen when: High O2 concentration & low CO2 concentration High temperatures It can produce Hydrogen Perioxide (H2O2), Ammonia (NH3) waste energy (ATP) and even remake the CO2 it was getting rid of through photosynthesis. Exam Question 4 RuBisCo is an enzyme found in chloroplasts. Its normal function is to catalyse the reaction in which carbon dioxide is a substrate. In certain plants, where the level of carbon dioxide is low in the leaf, RuBisCo uses oxygen as the substrate and releases hydrogen peroxide and ammonia. Explain why it is beneficial for a plant to have a high level of carbon dioxide in its leaves. (2 marks) Rubisco & Substrate Concentration The more of a substrate that is present, the greater chance it has to bind to an enzyme and undergo a reaction. Because rubiscos can bind to both CO2 and O2, plants ‘want’ to Rubisco to be in an environment with: A high CO2 concentration A low O2 concentration This will help make sure CO2 binds to the rubisco and that Photosynthesis happens. This is why plants keep their stomata open, CO 2 comes in and the O2 & water goes out. But if the plant needs to hold on to its water it shuts the stomata. CO2 stops coming in and the O2 & water stop going out. O2 builds up to a higher concentration than the CO2. This allows the O2 to bind to the Rubisco instead of the CO2 Rubisco & High temperatures At normal temperatures, Rubisco’s affinity for CO2 is far greater than that for O2. As temperature increases, the bonds holding Rubisco together ‘loosen. This changes the 3D shape of the enzyme, resulting in a greater affinity towards oxygen. Leading to Rubisco binding oxygen more often. When does Photorespiration happen? Photorespiration is most likely to happen when its: Hot Dry Plants that live in these types of environments need special mechanisms to stop photorespiration from happening. C3, C4 & CAM plants Not all plants do Photosynthesis in the same way. Based on how they restrict photorespiration from happening, plants can be grouped as: C3 C4 CAM Importance of C3, C4 & CAM Plants C3 plants just do basic photosynthesis, and as long as they’re doing this they are the most energy efficient. However, if their climate changes or they in a Hot and/or Dry environment, these plants run the risk of doing Photorespiration instead of Photosynthesis. This is bad Photorespiration is really wasteful and inefficient. C4 and CAM plants have different adaptation to help them maintain Photosynthesis and avoid Photorespiration in these types of C3 C4 CAM environments. C3 Plants A "normal" plant These plants do have any specific mechanisms/adaptations to reduce photo respiration. These plants do both the Light Dependent and Light Independent stages in the same cell. Their first step in the Light Independent is the fixation of carbon dioxide by rubisco, Because this reaction makes a three-carbon compound (3-PGA) they are called “C3” plants. About 85% of the plant species on the planet are C3 plants, including rice, wheat, soybeans and all trees. C3 Plants - Examples About 85% of the plant species on the planet are C3 plants, including rice, wheat, soybeans and all trees. C4 Plants These are plants with a specific adaptation that reduces the chance of photorespiration from happening They do this by having the first part of the Light Independent stage and the rest of the Calvin Cycle happen in different cells. First part of Light Independent – Mesophyll Cell Calvin Cycle – Bundle Sheath Cell (these cells are around the leaf veins) As part of this change in process a new four- carbon compound is made as such they are called “C4” plants C4 Plants - Adaptation In the Mesophyll cell, CO2 from the atmosphere get converted into Malate. This Malate then gets pumped into the Bundle sheath cell. This means the bundle sheath cell always has lots of CO2 (as Malate). Therefore, there’s always a high concentration of CO2 around the Rubisco in the Bundle sheath cell. This means the rest of the photosynthesis reactions are preferred over Photorespiration. This strategy minimises photorespiration in C4 plants. C4 Plants - Examples The C4 pathway is used in about 3%, percent of all vascular plants; some examples are crabgrass, sugarcane and corn. CAM Plants These are plants with a different type of adaptation that reduces the chance of photorespiration from happening They use the crassulacean acid metabolism (CAM) pathway. These plants have all parts of photosynthesis occur in the same cell. However, they split the Light Independent stage into 2 parts with that happen at different times of the day. CAM Plants - Adaptation Night Day Fist part of Light Independent Stomata stay closed to prevent Stage water loss. “Carbon Fixation” Malate is take out of the Stomata are opened to bring in Vacuole. CO2 CO2 is released from the CO2 is then converted through Malate. several reaction to Malate. This creates high CO2 level The Malate is then stored in the around the Rubisco vacuole until it’s needed during This promotes photosynthesis the day. and minimises photorespiration. CAM Plants - Examples Plants that are adapted to dry environments, such as cacti and pineapples, the CAM name comes from the family of plants, the Crassulaceae, in which scientists first discovered the pathway. Exam Question 5 CAM plants thrive in hot and arid environments and have various adaptations to maximise the efficiency of photosynthesis. CAM plants are A. More common globally than C3 plants B. Prone to photorespiration C. Able to undergo carbon fixation at night and the Calvin cycle during the day D. Able to use bundle sheath cells for carbon fixation during the day C3, C4 & CAM plants Video Comparison of C3, C4 & CAM plants Type of Photosynthesis C3 C4 CAM Photorespiration No limiting Yes Yes Limited? Initial CO2 fixation Temporal Separation Spatial separation & rest of Calvin No separation (Occurs at different (Occurs in different cells) Cycle. times) Stomata open Day Day Night Minimises Doesn’t use extra Minimises Advantage Photorespiration & water energy Photorespiration loss Susceptible to Disadvantage Uses extra energy (ATP) Uses extra energy (ATP) Photorespiration Environment best Moderate/cool and Hot & sunny Very hot & dry Exam Question 6 Cyperus papyrus is an endangered plant native around the Nile River. This plant has a long history of use. One of the main uses was in the production of papyrus paper, made from the pith of the plant. This paper was most commonly used in Egypt, where C. papyrus was once abundant. C. papyrus is most suited to grow in temperatures around 30 °C in tropical conditions. Unlike many other plants, it does not require open stomata to stay open for the Calvin cycle to occur. Instead, malic acid produced in the mesophyll cells can be broken down to produce carbon dioxide, which can be taken to bundle sheath cells. Based on this information, it can be assumed that C. papyrus is A. A C3 plant. B. A C4 plant. C. A CAM plant. D. Free of Chloroplasts Modelling C3, C4 and CAM plants Activity Collect a name tag, this will tell you which plant you are and whether you are a C3, C4 or CAM plant. Collect a flowchart and follow the directions on it according to the environmental conditions you come across and the type of plant you are. All instructions are in the flowchart. You are also to start in the Mesophyll Cell Other useful Videos Travel Deep Inside a Leaf [California Academy of Sciences] https://www.youtube.com/watch?v=pwymX2LxnQs Photosynthesis [Bozeman Science] https://www.youtube.com/watch?v=g78utcLQrJ4 Photosynthesis is WAY Crazier than you Think! https://www.youtube.com/watch?v=rvFMBRnR3ms
