Photosynthesis By C Kohn Agricultural Sciences

In a nutshell… O Photosynthesis is the process in which water and carbon dioxide are converted into sugars and oxygen using the energy of the sun. O Light energy is used to split a water molecule in order to obtain the hydrogen needed to power ATP Synthase in the plant cells. O ATP Synthase in the chloroplasts of plant cells produces the ATP needed to make glucose from both CO2 and the hydrogen from water. O Key Points of Photosynthesis: O Light energy is used to split H 2 O into H+ and oxygen O H+ powers the production of ATP by ATP Synthase O ATP is needed to power the creation of glucose from CO 2 and H+ Source: phschool.com

Photosynthesis in a nutshell… ●Sunlight is used to split water into H+ and oxygen. ● H+ powers ATP Synthase. ● ATP powers the production of glucose from H+ and CO 2. ●Sunlight is used to split water into H+ and oxygen. ● H+ powers ATP Synthase. ● ATP powers the production of glucose from H+ and CO 2.

The Plant Cell O We have already discussed several key cellular structures including… O The cell membrane: protects the inside of the cell O The nucleus: where DNA is stored O The ribosomes: protein factories O The mitochondria: ATP factories/cell power plants O Plant cells have two key structures that animal cells do not, including… O Chloroplast: where photosynthesis and glucose (sugar) production occurs. O Cell Wall: the rigid “candy shell” of a plant cell Source: teamcarterlces.com

Photosynthesis O In order to photosynthesize, a cell NEEDS a chloroplast O The only organisms that have chloroplasts in their cells are plants and some kinds of algae O These are the only organisms that can produce their own sugars through photosynthesis. O ALL other living organisms are dependent on photosynthetic organisms for energy. O They can only acquire energy through consuming photosynthetic organisms directly or indirectly Source: scq.ubc.ca Source: teamcarterlces.com

The Chloroplasts O Chloroplasts are organelles found inside the plant cell. O Like the mitochondria, nucleus, and ribosomes, the chloroplasts are a type of cellular organelle. O Chloroplasts are not found in animals cells; only in plants & algae. O Inside each chloroplast organelles are structures called thylakoids that look like little green pancakes. O The thylakoids are the thin green pancakes. O Each “stack” of pancakes is called a grana. O A grana is a “group” of thylakoids O The empty space around the pancakes is called stroma. O If thylakoids are “pancakes”, stroma is the “syrup” O Thylakoids are “hydrogen barrels” – they store the hydrogen protons (H + ) that power ATP Synthase. O Their function is very similar to that of the intermembrane space of the mitochondria. Source: withfriendship.com

Thylakoids vs. Intermembrane Space O The inside of a thylakoid serves the same purpose as the intermembrane space of the mitochondria. O Both store hydrogen (H + ) protons in order to power ATP Synthase.

Thylakoids – green hydrogen pancakes O Thylakoid organelles have a number of important molecules that line their membranes, including... O ATP Synthase: produces ATP when turned by the hydrogen protons (H + ) as they leave the inside of the thylakoid. O Pigments: these are molecules that absorb the energy of light needed to separate H + from water. O Electron Transport System: carries energy from light on electrons (the “wires”) and moves H + into the thylakoid. O NADP+: the “taxi cab” that carries moves hydrogen. O NADP+ is very similar to NAD+ in cellular respiration. Source: 00leesa.blogspot.com

Chlorophyll Pigments O Each thylakoid organelle is lined with light-absorbing pigments. O The primary light-absorbing pigment is called chlorophyll. O Chlorophyll is what absorbs the energy of the light O This energy is needed to remove H + from water molecules O Chlorophyll is also what makes plants green. O Chlorophyll absorbs red and blue wavelengths of light and reflects green wavelengths of light. O “Chlorophyll is what makes plants colorful” Source: bio1100.nicerweb.com

Light Energy O Photosynthesis is powered by the light energy absorbed by pigment molecules in the thylakoid structures. O Light energy is a kind of radiation. O Radiation is any kind of energy that is emitted (moving) O Radiation is energy that travels from one point to another O All kinds of radiation are organized by the amount of energy found in their photons O A photon is simply a “bundle” of energy O Visible light is part of the electromagnetic spectrum O Electromagnetic spectrum: a way to compare all the kinds of radiation that exist from strongest to weakest O X-rays and gamma rays have the most energy from their photons (which is why they can do the most damage to your body and why you need that lead apron for an X-ray). Source: hyperphysics.phy-astr.gsu.edu

Radiation & The Light Bulb O A light bulb is a good example of how radiation can change depending on its strength of its photons. O An incandescent bulb only uses 10% of it’s energy to produce light. O The other 90% is lost as heat. O Most of the energy of the bulb is used to raise the temperature until a strong-enough radiation can be produced to make visible light. O If an incandescent light bulb does not receive enough energy, it will only produce weaker, non-visible kinds of radiation that our eyes cannot detect. O Similarly, a hot stove starts to “glow” as it gets hotter. O The stove is producing radiation that is strong enough to be detected by our eyes. O When it cools, less radiation and weaker radiation are given off.

Light Radiation O The only way in which light radiation is different from any other kind of radiation is that it has a very specific amount of energy in its photons. O Our eyes and structures in plant cells can only detect visible light because they are adapted to this specific range of energy. O Just like we cannot hear a dog whistle because that type sound cannot be detected by our ears, we cannot “see” other forms of electromagnetic radiation that are not visible light. O The range of energy found in light is powerful enough to power photosynthesis but weak enough to not cause damage to cells. O If cells were exposed to any radiation more powerful than light (e.g. ultraviolet rays), they would have problems (e.g. mutations, skin cancer, etc.). Source:

Split Water Molecules O The light energy that is absorbed by the chlorophyll pigments is used to split a water molecule (H 2 O) O H 2 O is split into 2 H + ’s and an oxygen atom O The oxygen atom pairs with another oxygen atom and is released as O 2 O This is where the oxygen released by plants comes from O The only reason plants need sunlight for photosynthesis is to provide the energy needed to split the hydrogen from the oxygen in water. O The H + protons are used to power ATP Synthase O ATP Synthase makes ATP. O ATP powers the production of sugar from CO 2 and the H + from water. Source: phototroph.blogspot.com

Steps in Photosynthesis O Photosynthesis can be broken down into 3 steps: O Photosystem II: light energy is absorbed and used to remove hydrogen from a water molecule so that H + can be used to power ATP production. O This ATP is used to power the combination of CO 2 and H + into glucose. O Photosystem I: ATP Synthase is powered by H + from the thylakoid, making ATP. H + is carried from ATP Synthase by NADP+ so that it can be combined with CO 2 in order to form glucose. O Calvin Cycle: CO 2 is absorbed and combined with H + to produce G3P and then glucose. O This process is powered by ATP from Photosystem II O G3P is a 3-carbon molecule that is a building block for all other plant molecules. Source: bio1100.nicerweb.com

Steps of Photosystem II O Step 1: Light is absorbed by chlorophyll and other pigments. O Primarily red and blue wavelengths are absorbed. Green is reflected O Step 2: Photons from light excite electrons in the pigments. O This energy is used to split a water molecule into hydrogen protons and oxygen. O Step 3: Hydrogen protons (H + ) are stuffed into a thylakoid and power ATP production O H+ protons do this by moving through ATP Synthase to get out of the thylakoid and into the stroma. O ATP Synthase then turns, producing ATP O Oxygen atoms bind to each other and are released from the plant as O 2 Source: hyperphysics.phy-astr.gsu.edu

Steps of Photosystem I O Step 1: Hydrogen leaves the thylakoids through ATP Synthase after powering the production of ATP, making ATP O Step 2: Hydrogen protons are added to a NADP+ (the hydrogen taxi) to form NADPH O Step 3: NADPH moves to the stroma O In the stroma the H + can be added to CO 2 to form glucose during the Calvin Cycle. Source: hyperphysics.phy-astr.gsu.edu

Steps of the Calvin Cycle O Step 1: CO 2 is absorbed into the stroma (empty space) of the chloroplast organelles. O Carbon is separated from the two oxygen molecules. O Oxygen is released as O 2 O Step 2: The lone carbon is combined with a 5-carbon molecule called Rubisco to form an intermediate 6-carbon molecule. O Step 3: The 6-carbon molecule is split to form two G3P molecules O G3P is the precursor to all plant molecules (sugars, amino acids, lipids, etc.) O Step 4: (not shown) One of the G3P’s joins a second G3P to form glucose. O The other G3P reforms the Rubisco enzyme Source: methuen.k12.ma.us

The Calvin Cycle is powered by ATP (not shown) Calvin Cycle 1. CO 2 is absorbed. Carbon is separated from oxygen. O 2 is released. 2. The carbon atom separated from CO 2 is combined with 5-carbon Rubisco. Click for explanations G3P’s on their way to becoming glucose. 3. The 6-carbon molecule is split into two 3-carbon molecules (G3P). One G3P is used to make sugars or other plant molecules. The other is paired with 2 carbon atoms to re-make Rubisco. Rubisco, re-created and ready to bind to the carbon in CO2

Photosynthesis (PSI, PSII, & Calvin) Photosystem II: light energy is used to split water; the H+ is used to power ATP production in ATP Synthase Photosystem I: ATP is made; H+ is picked up by NADP+ to form NADPH. It is taken to the stroma to be added to CO2 to make glucose. Calvin Cycle: CO 2 combines with Rubisco to make 2 G3P’s. and then glucose sugar. H+ atoms are added to the glucose molecule.

Photosynthesis in a nutshell…again Photosystem II: light energy is used to split water; the H+ is used to power ATP production in ATP Synthase Photosystem I: ATP is made; H+ is picked up by NADP+ to form NADPH. It is taken to the stroma to be added to CO2 to make glucose. Calvin Cycle: CO 2 combines with Rubisco to make 2 G3P’s. and then glucose sugar. H+ atoms are added to the glucose molecule.

The Cycle of Respiration & Photosynthesis O When glucose is broken down in respiration, CO 2 and H 2 O are produced. O CO 2 and H 2 O are used to produce glucose and oxygen during photosynthesis. O These two processes are cyclical – the leftover products of one process are the precursors of another. Source: terra.dadeschools.net

Summary O The chloroplast is an organelle found in plant cells; it is where photosynthesis occurs. Chloroplasts have structures inside that include: O Thylakoids – where H + is stored; ATP Synthase is found on the membrane of the thylakoids O The thylakoids have the same function as the intermembrane space of the mitochondria O Grana – a group (or ‘stack’) of thylakoids O Stroma – the empty space around the thylakoids; it is where the manufacturing of the glucose molecule occurs.

Summary O Thylakoid membranes are lined with chlorophyll pigment. O This pigment absorbs sunlight. O The energy from light is needed to separate hydrogen from oxygen in an H 2 O molecule. O Chlorophyll absorbs red and blue light but reflects green light. O Light is a form of radiation (moving energy). O Radiation can be categorized based on the amount of energy found in its photons (bundles of energy). O The electromagnetic spectrum a way to compare all the kinds of radiation that exist from strongest to weakest O Plants use visible light to power photosynthesis because it is strong but not so strong that it would cause cellular damage.

Summary O Photosynthesis can be broken down into 3 steps: O Photosystem II: light energy is absorbed and used to remove hydrogen from a water molecule so that H + can be used to power ATP production. O This ATP is used to power the combination of CO 2 and H + into glucose. O Photosystem I: H + leaves through ATP Synthase (making ATP) and is carried from ATP Synthase by NADP+ so that it can be combined with CO 2 in order to form glucose. O Calvin Cycle: CO 2 is absorbed; its carbon is added to 5-carbon Rubisco and then combined with H + to produce G3P and then glucose. O This process is powered by ATP from Photosystem II O G3P is a 3-carbon molecule that is a building block for all other plant molecules. O The products of photosynthesis (oxygen and glucose) are used in respiration to make ATP. The byproducts of respiration (CO 2 and H 2 O) are used in photosynthesis to produce glucose and oxygen.