1. Ch. 10 – Photosynthesis Essential Knowledge 2.A.2
Big Idea 2
Ch. 10 – Photosynthesis
Essential Knowledge 2.A.2

2. Autotrophs and Heterotrophs
All energy for life comes from the sun, either directly or indirectly.
Autotrophs are organisms that make their own food- most get their energy from the sun (some, called chemoautotrophs, use inorganic substances like hydrogen sulfide as a source of energy – sometimes no oxygen is present).
Heterotrophs are organisms that need to eat/ingest food to get energy
They capture free energy found in carbon compounds produced by other organisms (remember, macromolecules make our food, and they all contain carbon)

3. Autotroph or heterotroph?

4. Autotroph or Heterotroph?

5. Autotroph or Heterotroph?

6. Autotroph or Heterotroph?

7. Autotroph or heterotroph?

8. Autotroph or heterotroph?

9. Overview Photosynthesis is great because it gives us two things:
All of our food
All of our oxygen
Let’s all take a moment to thank plants and appreciate photosynthesis
Also takes place in bacteria, algae, protists in addition to plants

10. Chloroplasts
Photosynthesis has been around for a long time, so it’s important that we know how it works
The site of photosynthesis in eukaryotic cells is the chloroplast
There are many chloroplasts in each cell

11. Chloroplasts cont.
Terms you should be familiar with inside of the chloroplast:
Thylakoid – round, flat discs; this is where light reactions take place
Granum – stacks of thylakoids
Stroma – the fluid surrounding the granum (this is where the Calvin, or dark cycle takes place)

12. Chromatography
There isn’t just one pigment working in photosynthesis – there are many working together (carotine, xanthophyls, etc) – these are the colors you see in the fall
Each pigment absorbs a different wavelength of light in the visible color spectrum
Plants hate green – it is rarely absorbed, which is why plants are green

13. The Reaction 6 CO2 + 6 H2O -> C6H12O6 + 6 O2
A plant takes water in from it’s roots, and carbon dioxide in from it’s leaves (through the stomata) – these are the reactants (6 molecules of each)
Light takes those reactants, causes a chemical change (they are broken apart and put back together) to give us:
A molecule of glucose and 6 molecules of oxygen – our food that we eat and air that we breathe – these are the products.

14. The reaction cont. 6 CO2 + 6 H2O -> C6H12O6 + 6 O2
Plants are making glucose for themselves, to be used during respiration.
If we take the arrow and turn it around, we have the formula for respiration

15. Steps of Photosynthesis
When you try to remember the steps to photosynthesis, just break apart the word
Photo means light, and synthesis means to make
So there are 2 steps to photosynthesis:
The light reaction (in the thylakoids)
The Calvin Cycle (used to be called the dark cycle, but it doesn’t happen in the dark – in the stroma)

16. Steps cont. - overview
In the light dependent reaction, water and carbon dioxide go into the thylakoid and produce oxygen (as waste) and NADPH and ATP (energy)
Oxygen is released as waste
The energy transfers to the Calvin Cycle where carbon dioxide comes in, and glucose goes out

17. Light Reaction Details
In the thylakoid
Light comes in, and water comes in
Proteins with chlorophyll inside are embedded in the thylakoid membrane and are called photosystem 2 (PSII), then we go to PS1 (we go backwards because PS1 was discovered 1st, but it comes after PS2)

18. Light Reaction Cont.
Light enters and powers an electron through an electron transport chain (made of PS1 and PS2) to create NADPH (one product of a light reaction)
Water is split right away to become oxygen (that diffuses out of the cell – it’s what you breathe in) and protons, which are just Hydrogen ions that have lost their electron
That electron moves through the chain (powered by light) of proteins that pump protons into the cell; creates a high concentration of protons on one side, and the only place they can go is out the protein called ATP synthase
That ATP synthase acts like a rotor, and every time a proton goes through, you make another ATP
Products: 2 NADHP, ATP
Those go to the stroma, and move on to the Calvin Cycle
Energy provided by light, water provides electrons, and our waste product is oxygen

19. Calvin Cycle Our ATP and NADPH are providing energy
CO2 diffuses in through the stomata
An enzyme called RuBisCo grabs the CO2 (a 1 carbon molecule) and attaches it to a 5 carbon molecule called RuBp; it immediately breaks into 2 3-carbon molecules and gets energy from ATP and NADPH
When it’s done, it creates a chemical called G3P, which can quickly be assembled into glucose or sucrose or maltose (whatever it needs)
A lot of the G3P is released, but some of it is recycled to make more RuBp and used over and over again (which is why it’s called a cycle)

20. Photorespiration
Occurs only when there isn’t enough CO2 - it’s bad (has no benefit for the plant)
If there isn’t enough CO2:
We couldn’t make G3P
Oxygen can jump in and combine with RuBisCo to form another chemical which doesn’t do anything and the cell has to break it down (as a result, the plants don’t get anything out of it)
Why did this evolve? Remember, oxygen didn’t show up in the atmosphere until after photosynthesis had been occurring, so it wasn’t initially a problem

21. Photorespiration cont.
When would we not have enough CO2?
When a plants stomata is closed (only time it’s closed is when it’s really hot – it closes to keep from losing too much water)
So the plant has a dilemma – lose water or CO2?

22. Photorespiration cont. – evolutionary solutions
CAM plants (like a jade or pineapple) – only open stomata at night; they then store the CO2 in vacuoles in the form of malic acid. During the day they can take it and use it
C4 plants (corn is an example)– take the CO2 in and use enzymes to make a 4 carbon molecule, which moves to cells on the inside of the leaf (called bundle sheath cells) and from there they can reintroduce the CO2 into the Calvin Cycle
Both solutions take CO2 when they can get it, make a chemical out of it, then use that chemical
This requires more energy, so you usually only see it in hot areas.

23. Assignments
Using your Venn Diagram, write at least 3 similarities and differences between respiration and photosynthesis
Draw and label a diagram of each process on the back