Big Idea 2Big Idea 2

Ch. 10 – PhotosynthesisCh. 10 – Photosynthesis

Essential Knowledge 2.A.2Essential Knowledge 2.A.2

All energy for life comes from All energy for life comes from the sunthe sun, either directly or , either directly or indirectly.indirectly.

Autotrophs Autotrophs are organisms that are organisms that make their own food- most get make their own food- most get their energy from the sun (some, their energy from the sun (some, called chemoautotrophs, use called chemoautotrophs, use inorganic substances like inorganic substances like hydrogen sulfide as a source of hydrogen sulfide as a source of energy – sometimes no oxygen energy – sometimes no oxygen is present).is present).

Heterotrophs Heterotrophs are organisms that are organisms that need to eat/ingest food to get need to eat/ingest food to get energyenergy They capture free energy found in They capture free energy found in

carbon compounds produced by carbon compounds produced by other organisms (remember, other organisms (remember, macromolecules make our food, macromolecules make our food, and they all contain carbon)and they all contain carbon)

Autotrophs and Autotrophs and HeterotrophsHeterotrophs

Autotroph or Autotroph or heterotroph?heterotroph?

Autotroph or Autotroph or Heterotroph?Heterotroph?

Autotroph or Autotroph or Heterotroph?Heterotroph?

Autotroph or Autotroph or Heterotroph?Heterotroph?

Autotroph or Autotroph or heterotroph?heterotroph?

Autotroph or Autotroph or heterotroph?heterotroph?

OverviewOverview

Photosynthesis is Photosynthesis is great because it gives great because it gives us two things:us two things:

All of our foodAll of our food All of our oxygenAll of our oxygen Let’s all take a moment Let’s all take a moment

to thank plants and to thank plants and appreciate appreciate photosynthesisphotosynthesis

Also takes place in Also takes place in bacteria, algae, bacteria, algae, protists in addition to protists in addition to plantsplants

ChloroplastsChloroplasts

Photosynthesis has Photosynthesis has been around for a long been around for a long time, so it’s important time, so it’s important that we know how it that we know how it worksworks

The site of The site of photosynthesis in photosynthesis in eukaryotic cells is the eukaryotic cells is the chloroplastchloroplast

There are many There are many chloroplasts in each chloroplasts in each cellcell

Chloroplasts cont.Chloroplasts cont.

Terms you should be Terms you should be familiar with inside of the familiar with inside of the chloroplast:chloroplast:

ThylakoidThylakoid – round, flat – round, flat discs; this is where light discs; this is where light reactions take placereactions take place

GranumGranum – stacks of – stacks of thylakoidsthylakoids

StromaStroma – the fluid – the fluid surrounding the granum surrounding the granum (this is where the Calvin, (this is where the Calvin, or dark cycle takes or dark cycle takes place)place)

ChromatographyChromatography

There isn’t just one There isn’t just one pigment working in pigment working in photosynthesis – there are photosynthesis – there are many working together many working together (carotine, xanthophyls, etc) (carotine, xanthophyls, etc) – these are the colors you – these are the colors you see in the fallsee in the fall

Each pigment absorbs a Each pigment absorbs a different wavelength of different wavelength of light in the visible color light in the visible color spectrumspectrum

Plants hate green – it is Plants hate green – it is rarely absorbed, which is rarely absorbed, which is why plants are greenwhy plants are green

The ReactionThe Reaction

6 CO2 + 6 H2O -> 6 CO2 + 6 H2O -> C6H12O6 + 6 O2C6H12O6 + 6 O2

A plant takes A plant takes waterwater in from it’s in from it’s roots, and roots, and carbon dioxide carbon dioxide in in from it’s leaves (through the from it’s leaves (through the stomata) – these are the stomata) – these are the reactants reactants (6 molecules of (6 molecules of each)each)

Light takes those reactants, Light takes those reactants, causes a chemical change causes a chemical change (they are broken apart and (they are broken apart and put back together) to give us:put back together) to give us:

A molecule of A molecule of glucoseglucose and 6 and 6 molecules of molecules of oxygenoxygen – our – our food that we eat and air that food that we eat and air that we breathe – these are the we breathe – these are the productsproducts..

The reaction cont.The reaction cont.

6 CO2 + 6 H2O -> 6 CO2 + 6 H2O -> C6H12O6 + 6 O2C6H12O6 + 6 O2

Plants are making Plants are making glucose for glucose for themselves, to be themselves, to be used during used during respiration.respiration.

If we take the arrow If we take the arrow and turn it around, we and turn it around, we have the formula for have the formula for respirationrespiration

Steps of PhotosynthesisSteps of Photosynthesis

When you try to remember When you try to remember the steps to the steps to photosynthesis, just break photosynthesis, just break apart the wordapart the word

PhotoPhoto means light, and means light, and synthesis synthesis means to makemeans to make

So there are 2 steps to So there are 2 steps to photosynthesis:photosynthesis:

The light reaction The light reaction (in the (in the thylakoids)thylakoids)

The Calvin Cycle The Calvin Cycle (used to (used to be called the dark cycle, be called the dark cycle, but it doesn’t happen in the but it doesn’t happen in the dark – in the stroma)dark – in the stroma)

Steps cont. - overviewSteps cont. - overview

In the light dependent In the light dependent reaction, water and reaction, water and carbon dioxide go into carbon dioxide go into the thylakoid and the thylakoid and produce oxygen (as produce oxygen (as waste) and NADPH waste) and NADPH and ATP (energy)and ATP (energy)

Oxygen is released as Oxygen is released as wastewaste

The energy transfers The energy transfers to the Calvin Cycle to the Calvin Cycle where carbon dioxide where carbon dioxide comes in, and glucose comes in, and glucose goes outgoes out

Light Reaction DetailsLight Reaction Details In the thylakoidIn the thylakoid Light comes in, and Light comes in, and

water comes inwater comes in Proteins with chlorophyll Proteins with chlorophyll

inside are embedded in inside are embedded in the thylakoid membrane the thylakoid membrane and are called and are called photosystem 2 (PSIIphotosystem 2 (PSII), ), then we go to PS1 (we then we go to PS1 (we go backwards because go backwards because PS1 was discovered 1PS1 was discovered 1stst, , but it comes after PS2)but it comes after PS2)

Light Reaction Cont.Light Reaction Cont. Light enters and powers an electron through Light enters and powers an electron through

an electron transport chain (made of PS1 and an electron transport chain (made of PS1 and PS2) to create NADPH (one product of a light PS2) to create NADPH (one product of a light reaction)reaction)

Water is split right away to become oxygen Water is split right away to become oxygen (that diffuses out of the cell – it’s what you (that diffuses out of the cell – it’s what you breathe in) and protons, which are just breathe in) and protons, which are just Hydrogen ions that have lost their electronHydrogen ions that have lost their electron

That electron moves through the chain That electron moves through the chain (powered by light) of proteins that pump (powered by light) of proteins that pump protons into the cell; creates a high protons into the cell; creates a high concentration of protons on one side, and the concentration of protons on one side, and the only place they can go is out the protein called only place they can go is out the protein called ATP synthaseATP synthase

That ATP synthase acts like a rotor, and every That ATP synthase acts like a rotor, and every time a proton goes through, you make another time a proton goes through, you make another ATPATP

Products: 2 NADHP, ATPProducts: 2 NADHP, ATP Those go to the stroma, and move on to the Those go to the stroma, and move on to the

Calvin CycleCalvin Cycle Energy provided by light, water provides Energy provided by light, water provides

electrons, and our waste product is oxygenelectrons, and our waste product is oxygen

Calvin CycleCalvin Cycle Our ATP and NADPH are providing Our ATP and NADPH are providing

energyenergy CO2 diffuses in through the stomata CO2 diffuses in through the stomata An enzyme called An enzyme called RuBisCoRuBisCo grabs the grabs the

CO2 (a 1 carbon molecule) and CO2 (a 1 carbon molecule) and attaches it to a 5 carbon molecule attaches it to a 5 carbon molecule called called RuBpRuBp; it immediately breaks into ; it immediately breaks into 2 3-carbon molecules and gets energy 2 3-carbon molecules and gets energy from ATP and NADPHfrom ATP and NADPH

When it’s done, it creates a chemical When it’s done, it creates a chemical called called G3PG3P, which can quickly be , which can quickly be assembled into glucose or sucrose or assembled into glucose or sucrose or maltose (whatever it needs)maltose (whatever it needs)

A lot of the G3P is released, but some A lot of the G3P is released, but some of it is recycled to make more RuBp of it is recycled to make more RuBp and used over and over again (which and used over and over again (which is why it’s called a cycle)is why it’s called a cycle)

PhotorespirationPhotorespiration Occurs only when there isn’t Occurs only when there isn’t

enough CO2 enough CO2 - it’s bad (has no - it’s bad (has no benefit for the plant)benefit for the plant)

If there isn’t enough CO2:If there isn’t enough CO2: We couldn’t make G3PWe couldn’t make G3P Oxygen can jump in and combine Oxygen can jump in and combine

with RuBisCo to form another with RuBisCo to form another chemical which doesn’t do chemical which doesn’t do anything and the cell has to break anything and the cell has to break it down (as a result, the plants it down (as a result, the plants don’t get anything out of it)don’t get anything out of it)

Why did this evolve? Remember, Why did this evolve? Remember, oxygen didn’t show up in the oxygen didn’t show up in the atmosphere until after atmosphere until after photosynthesis had been photosynthesis had been occurring, so it wasn’t initially a occurring, so it wasn’t initially a problemproblem

Photorespiration cont.Photorespiration cont.

When would we not When would we not have enough CO2?have enough CO2?

When a plants stomata When a plants stomata is closed (only time it’s is closed (only time it’s closed is when it’s closed is when it’s really hot – it closes to really hot – it closes to keep from losing too keep from losing too much water)much water)

So the plant has a So the plant has a dilemma – lose water dilemma – lose water or CO2?or CO2?

Photorespiration cont. – Photorespiration cont. – evolutionary solutionsevolutionary solutions CAM plants CAM plants (like a jade or (like a jade or

pineapple) – only open stomata pineapple) – only open stomata at night; they then store the CO2 at night; they then store the CO2 in vacuoles in the form of malic in vacuoles in the form of malic acid. During the day they can acid. During the day they can take it and use ittake it and use it

C4 plants C4 plants (corn is an example)– (corn is an example)– take the CO2 in and use take the CO2 in and use enzymes to make a 4 carbon enzymes to make a 4 carbon molecule, which moves to cells molecule, which moves to cells on the inside of the leaf (called on the inside of the leaf (called bundle sheath cells) and from bundle sheath cells) and from there they can reintroduce the there they can reintroduce the CO2 into the Calvin CycleCO2 into the Calvin Cycle

Both solutions take CO2 when Both solutions take CO2 when they can get it, make a chemical they can get it, make a chemical out of it, then use that chemicalout of it, then use that chemical

This requires more energy, so This requires more energy, so you usually only see it in hot you usually only see it in hot areas.areas.

AssignmentsAssignments

Using your Venn Diagram, write Using your Venn Diagram, write at least at least 3 similarities and differences between 3 similarities and differences between respiration and photosynthesisrespiration and photosynthesis

Draw and label a diagram of each Draw and label a diagram of each process on the back process on the back