Chapter 7 Photosynthesis: Using Light to Make Food

thylakoids

-A system of interconnected membranous sacs called thylakoids segregates the stroma from another compartment, the thylakoid space -Thylakoids are concentrated in stacks called grana -Thylakoids: round disks; site of light energy harnessing; where sun's energy is stacked -inside thylakoid a process is going on as well as the outside (compartmentalize cells in order for them to do better work and be more efficient)

1. light reaction

-Actually, photosynthesis occurs in two metabolic stages -One stage involves the light reactions -In the light reactions, light energy is converted in the thylakoid membranes to chemical energy and O2 -Water is split to provide the O2 as well as electrons -H+ ions reduce NADP+ to NADPH, which is an electron carrier similar to NADH -NADPH is temporarily stored and then shuttled into the Calvin cycle where it is used to make sugar -Finally, the light reactions generate ATP -light reaction: where sun's energy is captured; where water is split; hydrogens cannot survive on own because no oxidation #; takes place to reduce NADP (carrier molecule whose job is to carry hydrogen; that hydrogen is used in other reaction) NADP is reduced into NADPH -light reactions will also generate some ATP for the plant -light reactions produce both NADPH and ATP

Stroma

-An envelope of two membranes encloses the stroma, the dense fluid within the chloroplast -chloroplasts is a double membrane structure -stroma: dense fluid; site for sugar production thylakoids: round disks; site of light energy harnessing; where sun's energy is stacked inside thylakoid a process is going on as well as the outside (compartmentalize cells in order for them to do better work and be more efficient)

Autotrophs / (2 types)

-Autotrophs are living things that are able to make their own food without using organic molecules derived from any other living thing -Autotrophs that use the energy of light to produce organic molecules are called photoautotrophs (photosynthetic organisms such as bacteria, etc.) -Most plants, algae and other protists, and some prokaryotes are photoautotrophs (cyanobacteria) -autotrophs can make their own food 2 very specific types: 1. Chemosynthetic: takes chemicals and produces food from the chemicals Ex.) go deep down in ocean; they have bacteria that live around sulfur vents in order to take the sulfur being released (chemicals) in order to make food for themselves 2. Photosynthetic: takes sun's light and produces sugar & oxygen; have chloroplast

Chloroplasts contain several different pigments and all absorb light of different wavelengths:

-Chlorophyll a absorbs blue violet and red light and reflects green -Chlorophyll b absorbs blue and orange and reflects yellow-green -The carotenoids (excessary pigments; not that successful at producing sugar; why trees that are not evergreens in winter lose chlorophyll; their leaves are not adapted) absorb mainly blue-green light and reflect yellow and orange -chloroplasts contain pigments called chlorophyll and carotenoids (green) -plants have internal clock; in order to keep warm has to lose chlorophyll -left with red, yellow, orange (as tree loses chlorophyll, leaves behind carotenoids) -oak tree has waxy leaves to be adapted to winter and ones that do not have wavy leaf coating do not adapt in winter

Chlorophyll

-Chlorophyll, an important light absorbing pigment in chloroplasts, is responsible for the green color of plants (absorbs every light wave, except green and yellow) (plants essential role bc without it sun's light cannot be absorbed) -Chlorophyll plays a central role in converting solar energy to chemical energy

Mesophyll

-Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf -mesophyll: interior place in tissue; area where photosynthetic activity takes place; job is strictly for photosynthesis; cannot operate unless it has all necessary elements (water absorbed into roots) vascular tissue in plant: transfer fluid from roots to leaves

electrons

-In photosynthesis, electrons gain energy by being boosted up an energy hill -Light energy captured by chlorophyll molecules provides the boost for the electrons -As a result, light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules -in photosynthesis, electrons gain energy by being boosted uphill (energy hill) -light energy is captured and electrons become excited and begin to be passed down chain while releasing energy along the way -energy created along light reaction is going to be used to make the chemical energy we call sugar -light reaction: where sun's energy is captured; where water is split; hydrogens cannot survive on own because no oxidation #; takes place to reduce NADP (carrier molecule whose job is to carry hydrogen; that hydrogen is used in other reaction) -NADP is reduced into NADPH -light reactions will also generate some ATP for the plant -light reactions produce both NADPH and ATP

electrons in photosynthesis

-In photosynthesis, electrons gain energy by being boosted up an energy hill -Light energy captured by chlorophyll molecules provides the boost for the electrons -As a result, light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules -in photosynthesis, electrons gain energy by being boosted uphill (energy hill) -light energy is captured and electrons become excited and begin to be passed down chain while releasing energy along the way -energy created along light reaction is going to be used to make the chemical energy we call sugar light reaction: where sun's energy is captured; where water is split; hydrogens cannot survive on own because no oxidation #; takes place to reduce NADP (carrier molecule whose job is to carry hydrogen; that hydrogen is used in other reaction) NADP is reduced into NADPH light reactions will also generate some ATP for the plant light reactions produce both NADPH and ATP

photon

-Light behaves as discrete packets of energy called photons -A photon is a fixed quantity of light energy, and the shorter the wavelength, the greater the energy -light reaction's job is to capture energy -light energy is radiant; pure energy comes to earth in a photon; travels in waves; as this energy is striking a point, these waves will energize these single points; light energy is like a sound wave; however, much more energetic than sound wave

redox process

-Photosynthesis, like respiration, is a redox (oxidation-reduction) process -Water molecules are split apart by oxidation, which means that they lose electrons along with hydrogen ions (H+) -Then CO2 is reduced to sugar as electrons and hydrogen ions are added to it -Photosynthesis is a redox reaction like respiration (both breaking down/building up water molecules) -reduced means to gain -oxides means to lose -cellular respiration harnesses chemical energy through redox reactions -basically everything done in photosynthesis is reversed in respiration

redox process

-Photosynthesis, like respiration, is a redox (oxidation-reduction) process -Water molecules are split apart by oxidation, which means that they lose electrons along with hydrogen ions (H+) -Then CO2 is reduced to sugar as electrons and hydrogen ions are added to it -photosynthesis is a redox reaction like respiration (both breaking down/building up water molecules) -reduced means to gain -oxides means to lose -Recall that cellular respiration uses redox reactions to harvest the chemical energy stored in a glucose molecule -This is accomplished by oxidizing the sugar and reducing O2 to H2O -The electrons lose potential as they travel down an energy hill, the electron transport system -In contrast, the food-producing redox reactions of photosynthesis reverse the flow and involve an uphill climb -cellular respiration harnesses chemical energy through redox reactions -basically everything done in photosynthesis is reversed in respiration

pigment

-Pigments, molecules that absorb light, are built into the thylakoid membrane -Plant pigments absorb some wavelengths of light and transmit others -We see the color of the wavelengths that are transmitted; for example, chlorophyll transmits green -pigment: absorbs and reflects -white = reflected -black = absorbed -use wavelengths to excite the electrons -water enters plant and water molecule splits apart into hydrogens and oxygens -hydrogen has 1 electron (that one electron is stolen; what is responsible for powering the reaction)

Photosynthesis

-Plants use water and atmospheric carbon dioxide to produce a simple sugar and liberate oxygen -Earth's plants produce 160 billion metric tons of sugar each year through photosynthesis, a process that converts solar energy to chemical energy -this sugar is either stored in plant, cell wall -Sugar is food for humans and for animals that we consume -plants harness chemical energy in order for us to use as a fuel source -sugar is food for humans and animals that we consume -photosynthesis happens when carbon dioxide and water are taken into plant; light present; carbon dioxide and water then make sugar and oxygen

Plant Power

-Scientists have suggested that plants can be used in "energy plantations" to create a fuel source to replace fossil fuels (plants called "energy plantations" because they make chemical energy "fuel source for every organism on earth") -by taking chemical resource we can actually convert it into a fuel source -plants and algae can give us alternative fuel (renewable resource)

Stomata

-Stomata are tiny pores in the leaf that allow carbon dioxide to enter and oxygen to exit (gas exchange; carbon dioxide coming in and oxygen going out; water leaves plant through stomata) -Veins in the leaf deliver water absorbed by roots -Stomata: openings that resembles lips (open and close); water goes in and out of openings in stomata; has guard cell (job is to open and close it; too much gas escaping, closes it; too little gas, opens it) trichomes (tiny hairs): allow guard cells to know when to open and close openings in stomata

ATP and NADPH power sugar synthesis in the Calvin cycle

-The Calvin cycle makes sugar within a chloroplast -To produce sugar, the necessary ingredients are atmospheric CO2, ATP, and NADPH, which were generated in the light reactions -Using these three ingredients, an energy-rich, three-carbon sugar called glyceraldehyde-3-phosphate (G3P) is produced -A plant cell may then use G3P to make glucose and other organic molecules -as long as ATP and NADPH present, calvin cycle continues on and on -once atp made in thylakoid they are kicked out and head to stroma -CO2 important compound in photosynthesis -C6H12O6 = CO2 very instrumental in helping build up this sugar; reason why necessary gas exchange happens through stoma -ATP and NADPH happens in light reaction -NADPH: NADP is a molecule that carries the hydrogen that hydrogen molecule in light reaction is carried to calvin cycle to help build up sugar molecule

Chloroplast

-The ability to photosynthesize is directly related to the structure of chloroplasts (organelle where photosynthesis takes place) -Chloroplasts are organelles consisting of photosynthetic pigments, enzymes, and other molecules grouped together in membranes -Job of chloroplast is to manufacture sugar plant needs and sugar plant will pass down; chloroplast contains chlorophyll (chlorophyll is a pigment that absorbs and reflects light waves; job of chlorophyll is to absorb red, blue, purple and reflect blue and yellow; traps sun's energy) Ex.) most plants are this; some bacteria -Chloroplasts are the major sites of photosynthesis in green plants

2. Calvin Cycle

-The second stage is the Calvin cycle, which occurs in the stroma of the chloroplast -It is a cyclic series of reactions that builds sugar molecules from CO2 and the products of the light reactions -During the Calvin cycle, CO2 is incorporated into organic compounds, a process called carbon fixation -NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle -ATP from the light reactions provides chemical energy for the Calvin cycle -The Calvin cycle is often called the dark (or light-independent) reactions Calvin Cycle: -second stage in photosynthesis, in which sugar is made -takes place in the stroma and takes NADPH and carbon dioxide to make sugar -often called light independent reaction because it does not direct sunlight -only light reactions need direct sunlight, not Calvin Cycle

steps of calvin cycle

-The starting material for the Calvin cycle is a five-carbon sugar named ribulose bisphosphate (RuBP) -The next step is a carbon (CO2) fixation step aided by an enzyme called rubisco -This is repeated over and over, one carbon at a time starting material/molecule is ribulose biphosphate (RuBP) -this combines with carbon dioxide (very 1st step called carbon fixation; begins process of calvin cycle) -this process is repeated over and over again -as long as G3P and carbon dioxide is present, this process will repeatedly happen (carbon fixation) -if you stop light reaction, you will stop production of sugar -calvin cycle process is indirectly dependent on light reaction process 1.process of carbon fixation (RuBP waiting and combines with CO2; once this happens cycle begins) 2. reduction (gaining electrons; building up molecules; added phosphates and hydrogens) 3. release one molecule of G3P and other goes back into the cycle 4. regeneration of RuBP and carbon fixation then happens again

light spectrum

-photosynthesis uses visible light spectrum -radio waves = least energetic -gamma waves = most energetic -UV radiation falls in between -purple most energetic (wavelength closest) and red -least energetic (wavelength farthest) -a wavelength is measured from peak to peak -as each peaks strikes area is how we measure wavelength -plants would want to absorb all blue and purple since it is very energetic

Photosynthesis Formula

6CO2 (carbon dioxide) + 6H2O (water) --> (light energy) --> C6H12O6 (glucose) + O2 (oxygen gas)

products of light reactions

NADPH, ATP, and O2 are the products of the light reactions -at the end of the light reaction, you end up with NADPH, ATP, and oxygen released from the tree all begins with trapping light energy, splitting water, and stealing electron