2024 Photosynthesis PDF

Recap of Metabolism  In metabolism, we oxidized carbons from sugars to extract energy These electrons from sugars are ultimately (after multiple serial electron transfers) accepted by O2 to make H2O But the life first has to make the reduced carbon (e.g. sugars) to use as a source of ene...

Recap of Metabolism  In metabolism, we oxidized carbons from sugars to extract energy These electrons from sugars are ultimately (after multiple serial electron transfers) accepted by O2 to make H2O But the life first has to make the reduced carbon (e.g. sugars) to use as a source of energy through oxidation. This is done through photosynthesis, where organisms use solar energy to reduce carbons from CO2 and convert it into a reduced form (sugars). The electrons for these reduction reactions come from H2O, which gets oxidized to O2.  Photosynthesis Sunshine plays a bigger role in our lives than you may think. All the food we eat and the fossil fuels we burn are products of photosynthesis. Plants turn solar energy into food which is nice of them because animals can’t eat sunshine. When animals eat plants and other animals, that original solar energy is passed along the food chain. Photosynthesis is the process that converts solar energy into chemical energy that is used by biological systems (that means us). Photosynthesis has 3 major events: 1. Sunlight is converted into chemical energy 2. Water (H2O) is split into oxygen (O2) 3. Carbon dioxide (CO2) is fixed into sugars (C6H12O6) The photosynthesis reaction: 6 CO2 + 12 H2O + sunlight 🡪 C6H12O6 + 6 H2O + 6 O2 6 Carbon 12 Water 1 Sugar 6 Water 6 Oxygen dioxide molecules (glucose) molecules molecules molecules molecule Photosynthesis is carried out by: certain bacteria plants These organisms are known as photoautotrophs or producers meaning they make their own food and energy from the sun. most algae cyanobacteria phytoplankton Consumers such as herbivores and carnivores depend on the products of photosynthesis that producers make to live.  Glucose (C6H12O6) is a Glucose sugar During photosynthesis, plants produce glucose molecules when they convert light energy into Plants produce sugars as a source of food. chemical energy. The chemical However, they produce way more than they energy is stored in the bonds of need to survive. This is a great benefit for all glucose. the species that depend on glucose for energy. All biological energy comes from glucose. Plants also use the glucose they produce for energy. When animals digest plants, they are breaking down the glucose bonds to release stored energy to power their bodies.  Plant Chef Glucose in Plants Why do plants make glucose? “My masterpiece!” What is it plants do with glucose? Glucose Glucose molecules can be broken apart for energy to power reactions. Plants can also make glucose into carbohydrate chains called polysaccharides. Can we digest cellulose ???? poly = many saccharide = carbohydrate Glucose is a monosaccharide. Glucose Glucose is a simple sugar because it is one of the smallest units of carbohydrates. mono = one saccharide There are 2 polysaccharide chains in plants: Cellulose Starch Cellulose is the structural Starch is a long term energy store that component of cell walls. the plant can use later. O O O O O O O O  Each atom’s movement can be traced through the photosynthesis reaction. Each letter stands for the A water 6 element the atom is made 1 8 molecule of One A carbon of, so dioxide the letter C means H CThe sunlight Othe molecule has 2 providesglucose (sugar) molecule has 1 12.01 an atom of carbon. hydrogen and 1.008 16.00 1 energy has 6 carbon, 12 for the reaction. carbon and 2 oxygen atoms. Hydrogen hydrogen and 6 Oxygen oxygen atoms. Carbon oxygen atoms. 6 CO2 + 12 H2O + sunlight 🡪 C6H12O6 + 6 H2O + 6 O2 Before After 6 carbon atoms 6 carbon atoms If 6 carbon dioxide If 12 water molecules are 12 oxygen atoms 12 hydrogen atoms molecules are used used there are 24 hydrogen 6 oxygen atoms there are 6 carbon atoms (12 x 2 = 24) and 12 24 hydrogen atoms 12 hydrogen atoms atoms and 12 oxygen oxygen atoms total. 12 oxygen atoms 6 oxygen atoms atoms total (6 x 2 = 12). 12 oxygen atoms 6 oxygen atoms 6 oxygen atoms If you count every atom before and 24 oxygen atoms 24 oxygen atoms after the reaction they are balanced. 24 hydrogen atoms 24 hydrogen atoms  Through evolution, plant cells, certain bacteria and some algae have acquired chloroplasts to help carry out the photosynthetic reaction. Chloroplasts are a plastid or plant cell organelle. Chloroplasts are full of round flattened discs called thylakoids. A stack of thylakoids is called a granum. Both pictures are of chloroplasts in plant cells at different magnifications. Chloroplast Stroma is the Chloroplasts are where photosynthesis occurs. space inside chloroplasts  Where did chloroplasts come from? A very long time ago, plant cells were once ancient eukaryotic cells that had enveloped a cyanobacteria. Eventually, the cyanobacteria became a part of the cell and dependent upon it for life which in turn gave the cell the ability to photosynthesize. This is called the endosymbiotic theory. (endo = inside) Mitochondria are also believed to have been engulfed by ancient eukaryotic cells through endosymbiosis. There are many reasons why scientists believe this theory. Plant DNA One is that chloroplasts have their own Bacterial DNA Chloroplast DNA DNA that is different from plant DNA but similar to bacterial DNA.  Cyanobacteria Cyan comes from the Greek word cyanin which means aqua colored. Not all bacteria that undergo photosynthesis are cyanobacteria but all cyanobacteria are photosynthetic bacteria e.g. purple bacteria are not cyanobacteria but were the first bacteria discovered that can photosynthesize. Cyanobacteria undergo photosynthesis in lakes, ponds, and oceans. Cyanobacteria lack chloroplasts - why do you think that is? Photosynthesis in plants happens in the chloroplasts. Chloroplasts are full of thylakoids stacked in granum. The thylakoid membranes are lined by pigments such as chlorophyll and carotenoids. Chlorophyll is a green pigment and is the most abundant. Chlorophyll absorbs all wavelength colors except green, which is reflected off giving These pigments harvest plants their green appearance. light energy packets or photons when they absorb sunlight. The Photosynthesis Reaction is divided into two parts: Light Reactions Dark Reactions Light reactions or Dark reactions or “light independent “light dependent reactions” reactions” do not need light energy to capture light energy to power power their reactions and can occur day photosynthesis. or night. Light reactions occur during the day time. Discovered by three scientists, the dark reactions are also called the Calvin-Bensen-Bassham cycle or just They take place in the thylakoids. Calvin Cycle. Pigments in the thylakoid membranes form protein complexes called Photosystem I and Photosystem II. C B B These photosystems harvest photons to Dark reactions occur in the stroma of charge up energy carrying molecules that chloroplasts (the space that surrounds will power the dark reactions. thylakoids) and fix carbon dioxide into glucose. Energy Carrying Molecules: ATP & NADP+ adenosine triphosphate Both are energy carrier molecules used in photosynthesis and cellular respiration. “ATP” NADP+ can hold excited electrons (e-) A P P P charged from the light energy harvested R three phosphate by chlorophyll to become NADPH. adenosine = groups Eventually, NADPH passes the electron adenine + ribose it’s holding to power the dark reactions and reverts back to NADP+. ATP is called the “cellular currency” because it is used to power all the nicotinamide adenine dinucleotide phosphate reactions that take place in the cells of all living things. When ATP’s third phosphate is N “NADP+” broken off it releases energy that the cell can use. P P A R R ATP is made when a third phosphate group is added to P ADP (diphosphate, di = two). NADP is a very complex molecule, this is a simplification. Light Reactions The energy absorbed by the chlorophyll during the light reactions is used to power photosystem II (P680) that breaks the bonds of water absorbed through the plant’s roots. Photosystem II T PSII H Y Freed oxygen atoms bind with each other to form the gas O2. O _ O _ L H HO A O2 is a byproduct 2of photosynthesis not used by K the plant so it is released through the stomata of O plants. I Stomata (Greek for mouth) are little pores in O2 D leaves that open and close to let oxygen out and carbon dioxide in. Light Reactions When water molecules break apart, the remaining two hydrogen atoms have a positive charge and are called protons. These protons are kept inside the thylakoid by the thylakoid membrane. T H Y L H+ H+ H+ H+ H+ A H+ H+ H+ K O When there are more protons inside the I ATP thylakoid than in the stroma outside, protons D maker want to leave the crowded thylakoid. When the protons (H+) cross the membrane to leave, a protein uses their passage to power ATP production. The protein ATP synthase attaches a phosphate group to ADP (D = di or two) making it ATP (T = tri or three). Light Reactions The light energy absorbed by chlorophyll also powers photosystem I (P700) that charges up the energy carrier molecule NADP+ into NADPH. NADP+ NADPH T PSI PSII NADPH then carries its energy over to H Y power the dark reactions or Calvin Cycle. L A K O I D  NADPH Light Reactions NADP+ Summary T PSI PSII Photons are absorbed by the pigments to H power photosystem I and photosystem II. Y O_ L H _ H Photosystem II (P680) splits water A molecules into two protons (H+) and oxygen K atoms are expelled as O2 gas through the O stomata. I ATP maker Protons cross the thylakoid membrane and D power protein complex ATP synthase to make ATP. NADP+ is powered up by photosystem I (P700) to make NADPH to be used in the dark reactions. Light dependent reactions finish with charged NADPH, ATP, and released O2. Dark Reactions Also called the Calvin Cycle, the dark reactions start and end with the same products hence “cycle”. All the dark reactions take place in the stroma of the chloroplast. The Calvin Cycle starts with RuBP molecules and carbon dioxide molecules. An enzyme called Rubisco combines them into an unstable intermediate. RuBP (ribulose 1,5- biphosphate) Rubisco CO2 Since the intermediate of This is the reason plants take in combined RuBP and CO2 is carbon dioxide, to start the Calvin unstable it quickly splits in Cycle and begin the conversion of half and forms 2 molecules RuBP into RuBP glucose. is the starting molecule and ending molecule of of 3-PGA which are stable. the Calvin Cycle. It will be remade at the end of the 3-phosphoglycerate cycle so that the cycle can begin again.  Dark Reactions The ATP and NADPH from the light reactions provide the energy to convert the two molecules of 3-PGA into their final form. The left overs are reused in the light reactions to remake ATP and NADPH. 2 G3P (Glyceraldehyde -3- phosphate) are joined to make a glucose molecule. + 🡪  Dark Reactions Not all G3P is made into glucose. The Calvin Cycle occurs in every stroma in every chloroplast in every plant cell every second of every day. The spent ATP from the reaction Most of the G3P made during the Calvin Cycle are leaves ADP and a phosphate group. made into RuBP, the starting molecule, with energy These are reused in the light from ATP molecules. reactions to make more ATP. Now the Calvin Cycle can begin again. This is how this works as a cycle:  Chloroplast Dark Reactions Summary The Calvin Cycle converts the carbon from carbon dioxide into glucose in the stroma. This is called carbon fixation because carbon is fixed into another form. Photosynthesis is carried out in two steps. First, in two light dependent photosystems. Second, in a light independent carbon fixation cycle called the Calvin Cycle. Through this process, the plant is able to convert sunlight, water, and CO2 into glucose (or sugar) and ATP. As a byproduct of this process, O2 is released.  Summary Plants are the producers of the biosphere creating the oxygen and glucose needed for most organisms. Chloroplasts are the site of photosynthesis in plants. Chloroplasts contain thylakoids where the light reactions take place. Light reactions convert sunlight into ATP and NADPH. The dark reactions or Calvin Cycle uses ATP and NADPH to convert CO2 into sugar. The light reactions and the dark reactions cooperate to convert light energy into chemical energy housed in glucose. Plants and animals use glucose to power metabolic processes. Read about C3 and C4 Plants https://www.youtube.com/watch?v=Lhd7WbWV8aw When plants absorb carbon dioxide from the air, they are removing carbon from the atmosphere and fixing carbon into forms usable by other organisms. The burning of fossil fuels for energy, releases carbon dioxide gas into the atmosphere increasing the amount of carbon in the atmosphere. Human’s excessive dependence on fossil fuels has led to an increase in the level of CO2, a green house gas that traps heat in the atmosphere and heats up the earth. The rate at which human’s are burning fossil fuels is too high for plants and oceans to take carbon out of the atmosphere. Deforestation is a contributing factor to the excessive amounts of CO2 in the atmosphere and is also due to human influence. With the destruction of entire forests every day, we reduce the number of plants available to reduce carbon in the atmosphere.