A.P. Biology Chapter 10- Photosynthesis Scale: 0 - No understanding of the concept and chemical process of photosynthesis. 1- With help, a partial understanding of the reactants and products of the photosynthesis process. 2 - A general understanding of the r eactants and products of the photosynthesis process and the function of the process in living things. 3 - An understanding of two stages of photosynthesis and can predict the effects of changes to the process on biological systems. 4- A complete understanding of two stages of photosynthesis, effects on biological systems, the ability to apply these concepts to new, unique situations such as analyzing data and making predictions using my knowledge Letter Percent Marzano Scale Score A 89.5-100 3.0 4 B 79.5 89.4 2.5 2.99 C 69.5 79.4 2.0 2.49 D 59.5 69.4 1.0 1.99 F 0 59.4 0 -.99 Learning Progress I am a at the start of the unit. Comments: I am a at the end of the unit. Comments: ********************************************************************************** Overall, photosynthesis is the conversion of the Sun s energy to stored chemical energy. (glucose) The overall reaction for photosynthesis: 6 CO 2 + 6 H 2 0 + light C 6 H 12 O 6 + 6O 2 Two different types of organisms here on the earth. 1) Autotrophs- Feed themselves. Auto=self troph = feeding Use CO2, inorganics from the environment to make food Also known as producers. Most plants and algae- Use CO2, H2O and minerals chemosynthesis and photosynthesis 2) Heterotrophs- Live on compounds from other organisms Hetero = different troph = feeding Consumers Decomposers
10.1- Light energy to chemical energy Photosynthesis takes place in the chloroplasts ( anywhere that the plant is green - green from chlorophyll ). In leaves, the chloroplasts are found in the middle layer of the leaf called the mesophyll. The CO2 and O2 enter and leave from the stomata (pores) *ANIMATION
CHLOROPLAST STRUCTURE: The fluid inside of the double membrane chloroplast is called stroma There are disks inside of the chloroplasts called thylakoids, and can be in stacks called grana. The chlorophyll can be located specifically inside of the thylakoid membranes. Comparison of photosynthesis with cellular respiration: Similarities : series of redox reactions involve create ATP energy have an ETC and a cycle of reactions E- carriers Include same chemicals (CO2, H2O, ATP, O2) Differences : Photosynth. reverses the direction of the electron flow. Because of the reverse direction, energy is required. (ANABOLIC vs. CR is CATABOLIC) Energy in photosynthesis begins with the sun s energy ; CR is a chemical compound Photo.=2 stages; CR = 3 stages NADPH vs. NADH/FADH2 **NOTE: Oxygen from the reaction comes from the water splitting, NOT the carbon dioxide (as originally thought). Splitting of water is the electron source from the hydrogen atoms.
Overview of photosynthesis: 2 STAGES 1) Light reactions : Takes place in the thylakoids Converts solar energy to chemical energy. Transfer of electrons and hydrogen from water to NAD P + (reduced to NAD P H). Process gives off oxygen. This reaction will make some ATP by chemiosmosis, but process is called photophosphorylation. 2) Calvin Cycle ( named after Melvin Calvin AKA Light INdependent or DARK Reactions ). Takes place in the stroma. LIGHT is NOT necessary for process to take place Incorporates CO 2 into organic molecules located in the chloroplasts (called carbon fixation). Calvin cycle then reduces these molecules to carbohydrates by the addition of electrons given off from the water in the light reactions. Requires ATP (from the light reactions) STAGE #1: Light Reactions * Animation Light is electromagnetic energy and travels in waves. Distance between the light waves is called wavelength. The most important part of this wavelength (to us as humans) is the visible light spectrum (380nm 750nm). Light is both wave and packets. These packets of light are called photons. The shorter the wavelength the greater the amount of energy!!!
Pigments absorb visible light. Different pigments absorb different wavelengths of light. Green light is NOT ABSORBED by green plants. * THEREFORE, reflected! (We can measure the amount of absorbed light by a device called a photospectrometer, or spec 20, and the results are the absorption spectrum). Chlorophyll a - absorbs violet/blue and red. The pigment will have a blue/green color. Accessory pigments- Chlorophyll b - very similar to chlorophyll a, but has a yellow/green Caratenoids - Absorbs violet and blue/green light. Has a yellow/orange color *Reflected. Provide photoprotection - absorb and dissipate excessive light energy that can damage the plant. Engelmann s experiment *ANIMATION
What happens to the light when it reaches the chlorophyll? Where did the absorbed wavelength go? Electrons in a chlorophyll molecule are excited to a higher energy level. When the electrons are in their normal orbit they are in the ground state, but when the electrons are in their higher energy level, they are in the excited state. The excited electrons cannot stay in this state for long (unstable). The energy exits as both heat and photons. Photosystems : Reaction centers surrounded by a number of light harvesting complexes. (2 TYPES) o Each photosystem contains pigment molecules bound to a protein o Photons from the light are passed from pigment molecule to pigment molecule until it reaches the reaction center. o Reaction centers: A protein housing that holds two chlorophyll a molecules and a primary electron acceptor. These chlorophyll a molecules will be boosted to a higher energy level where they will then donate their electrons.
Two different photosystems: Photosystem 2 (also called P680 for the red wavelength that it absorbs best, or PS II) Photosystem 1 (also called P700 for the deep red wavelength. that it absorbs best, or PS I) ****NOTE: Photosystem 2 comes BEFORE photosystem 1 in its location in the thylakoid membrane because it was discovered AFTER PS I was discovered. TWO possible pathways for the electron flow: Non-cyclic pathway- Predominant route; Straight flow down the ETC 1) Photons (light) hit pigment molecules in the light harvesting complexes. These photons are then passed along until they reach one of the two P680 chlorophyll a molecules in PS II. These photons kick the electrons of the chlorophyll a into a higher energy level. 2) This excited electron is captured by the primary electron acceptor 3) During this, w ater is split into two electrons, 2 hydrogen ions, and oxygen. These electrons are going to be passed to the two chlorophyll a molecules that just donated their electrons to the primary electron acceptor. 4) Electrons go from the primary electron acceptor of PS II to the start of the PS I by a system similar to the ETC (chain is made of proteins- Pq, Cytochrome, Pe) 5) ETC provides energy for the synthesis of ATP molecules 6) The same process that happens in PS II then begins in PS I, except the electrons are donated by the ETC. 7) The primary electron acceptor will donate its electrons to another ETC 8) Two electrons are then used to reduce NADP + to NADPH.
***Summing up the non-cyclic pathway= produces ATP AND NADPH *** Cyclic electron flow Uses photosystem I, but NOT PS II. Does NOT produce NADPH Does NOT produce oxygen DOES produce ATP * The Calvin cycle uses more ATP than NADPH so we need more ATP. AFTER ETC, chemiosmosis occurs (like in CR) CHEMIOSMOSIS in Chloroplasts: still in the membrane of the thylakoids, after the ETC increase concentration of H+ in the intermembrane space by e- helping to pull across membrane H+ then flow down the concentration gradient, through ATP synthase, into the stroma. This generates ATP for the Calvin Cycle (Stage #2)
STAGE # 2: Calvin Cycle (AKA Light Independent Reaction OR DARK Reactions) Similar to the Citric Acid cycle (C.R.) because starting material is regenerated (hence cycle!) Calvin cycle is ANABOLIC- building, not breaking down! *HINT- C YCLES INVOLVE C O2 Steps of the cycle: Carbon enters cycle in the form of CO 2 and leaves in the form of sugar Uses ATP to build molecules and NADPH to donate electrons Calvin cycle does NOT produce glucose, it produces a 3 carbon sugar G3P (glyceraldehyde-3-phosphate) Cycle must turn 3 times for 1 G3P 3 parts of the cycle: 1) Carbon fixation - Each CO 2 goes in ONE AT A TIME and attaches to a 5 carbon sugar (RuBP). *From the back end of the previous turn in the cycle! The enzyme that causes this attachment is called RUBISCO and is likely the most abundant protein on the earth. 2) Reduction- Addition of phosphate from ATP and electrons from NADPH 3) Regeneration of RuBP- ATP must be added to change five-3 carbon molecules to three- 5 carbon molecules.
* TED Ed ANIMATION * OVERALL PRODUCTS : Overall, for 1 G3P we must use 9 ATP and 6 NADPH (2 G3P = 1 Glucose ; 6 turns = 1 glucose) ******************************************************************************************* Alternative methods in hot climates Dehydration is a problem. Plants close stomata in order to conserve water, but with this oxygen and carbon dioxide increase. Photorespiration : uses oxygen to make carbon dioxide for Calvin cycle, but uses more ingredients than it produces, so it is actually not useful and can be considered a waste. Possibly evolutionary baggage from a time when oxygen levels were low. Can take up to 50% of carbon fixed in Calvin cycle. Two types of plants with adaptations to hot climate s : *ANIMATION C4 and CAM plants, reduce photorespiration and increase usefulness in the Calvin cycle. C3 - Majority of plants that are around us- much photorespiration 1. C4 - Some crop plants and grasses (corn, sugarcane, etc ) Uses an alternate method of carbon fixation. Unique leaf structure. PEP carboxylase used in the preliminary has no affinity for oxygen and high affinity to carbon dioxide (better than if trying to use rubisco to fix carbon) 2. CAM - Water storing plants (cactus, pineapple). Stomata open during the night and close during the day.
**Both C4 and CAM use a preliminary step that incorporates carbon dioxide into organic acids. These acids will then donate their carbon.
Overview of Photosynthesis: Know and UNDERSTAND!