PhotosynthesisBy 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 powerATP Synthase in the plant cells.

O ATP Synthase in the chloroplastsof 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 H2O into H+ and oxygen

O H+ powers the production of ATP by ATP SynthaseO ATP is needed to power the creation of glucose from CO2 and H+

Source: phschool.com

H+

H+

CO2 Photosynthesis in a

nutshell…

H2

O

●Sunlight is used to split water into H+ and oxygen. ● H+ powers ATP Synthase. ● ATP powers the production of glucose from H+ and CO2.

Glucose

O

The Plant CellO 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

PhotosynthesisO In order to photosynthesize, a cell

NEEDS a chloroplastO The only organisms that have chloroplasts in

their cells are plants and some kinds of algaeO 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 ChloroplastsO 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 thylakoidsO 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 moleculesthat 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 PigmentsO 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 lightO 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 EnergyO 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 photonsO A photon is simply a “bundle” of energy

O Visible light is part of the electromagnetic spectrumO Electromagnetic spectrum: a way to compare all the kinds of

radiation that exist from strongest to weakestO 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 BulbO 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 RadiationO 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: http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html

Split Water MoleculesO The light energy that is absorbed by the

chlorophyll pigments is used to split a water molecule (H2O)

O H2O is split into 2 H+’s and an oxygen atomO The oxygen atom pairs with another

oxygen atom and is released as O2 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

CO2 and the H+ from water.

Source: phototroph.blogspot.com

Steps in PhotosynthesisO 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+ canbe used to power ATP production.O This ATP is used to power the combination of

CO2 and H+ into glucose.

O Photosystem I: ATP Synthase is poweredby H+ from the thylakoid, making ATP. H+ is carried from ATP Synthase by NADP+ so that it can be combined with CO2 in order to form glucose.

O Calvin Cycle: CO2 is absorbed and combined with H+ to produce G3P and then glucose.O This process is powered by ATP from

Photosystem IIO G3P is a 3-carbon molecule that is a

building block for all other plant molecules.

Source: bio1100.nicerweb.com

Steps of Photosystem IIO 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 otherand are released from the plant as O2 Source: hyperphysics.phy-astr.gsu.edu

Steps of Photosystem IO 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 CO2 to form glucose duringthe Calvin Cycle.

Source: hyperphysics.phy-astr.gsu.edu

Steps of the Calvin CycleO Step 1: CO2 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 O2

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 moleculesO 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 enzymeSource: methuen.k12.ma.us

12

3

The Calvin Cycle is powered by ATP (not

shown)Calvin Cycle

1. CO2 is absorbed. Carbon is separated from oxygen. O2 is

released.

2. The carbon atom separated from CO2 is

combined with 5-carbon Rubisco.

Click for explanationsG3P’s o

n their w

ay

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 th

e

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: CO2 combines with Rubisco to make 2 G3P’s. and then glucose sugar. H+ atoms are added to the glucose molecule.

H+

H+

CO2

Photosynthesis in a nutshell…again

H2

O

Glucose

O

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: CO2 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, CO2 and H2O are produced.

O CO2 and H2O 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 thylakoidsO The thylakoids have the same function as the

intermembrane space of the mitochondriaO Grana – a group (or ‘stack’) of thylakoidsO Stroma – the empty space around the

thylakoids; it is where the manufacturing of the glucose molecule occurs.

SummaryO 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 H2O 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 weakestO Plants use visible light to power photosynthesis because it

is strong but not so strong that it would cause cellular damage.

SummaryO 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 CO2 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 CO2 in order to form glucose.

O Calvin Cycle: CO2 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 IIO 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 (CO2 and H2O) are used in photosynthesis to produce glucose and oxygen.