1. Photosynthesis: Using Light to make Food
Bio Honors
Ch. 7

2. Plants have to create their own food to use for energy.
PHOTOSYNTHESIS Plants convert the energy of sunlight into energy stored in chemical bonds of carbohydrates:
Simple sugars- in the form of glucose
Larger molecules of starches- in the form of cellulose

3. REQUIREMENTS FOR PHOTOSYNTHESIS
Reactants Products
6 CO H2O C6H12O O2
(glucose)
Light

4. REQUIREMENTS FOR PHOTOSYNTHESIS
Light – used as a source of energy by plants and some other autotrophs to make food molecules from simple organic molecules in the environment.
2) Pigments – colored substances that absorb or reflect light
Chlorophyll is the main pigment used in photosynthesis.
This pigment gives plants their green color, by reflecting green light!
Photons of light hits the chlorophyll pigments (P680 and P700) and excites the electrons in chlorophyll.

5. Electromagnetic Spectrum

6. REQUIREMENTS FOR PHOTOSYNTHESIS continued…
3) Energy storing compounds –
ATP (adenosine triphosphate)- Energy storage molecule used by all living things, consisting of adenine (a 5-carbon sugar) and 3 phosphate groups.
Carbon dioxide (CO2) – gas from the surrounding environment are brought into the plant cells through STOMATA, small pores in the leaves.
Water – mostly absorbed through the roots of the plant and transported to the cells.

7. Structure of the Chloroplast (site of photosynthesis)

8. THE LIGHT AND DARK REACTIONS of Photosynthesis

9. Stage 1: Light Reactions
Takes place in the thylakoid membranes, inside the chloroplasts.
Involves an electron transport chain, moving particles across protein channels in the membrane.

10. Stage 1: Four basic step of LIGHT REACTIONS
1) Light absorption-
clusters of pigment molecules (Chlorophyll P680 and P700) absorb photons of light, which excite electrons in the chemical structure of the chlorophyll molecules with energy.
Electrons move from Photosystem II to Photosystem I.
Electron transport – high energy electrons transported along electron carriers, and then to NADP+ to form NADPH.
(Show e- in your foldable diagrams!)

11. Stage 1: Light Reactions continued…
3) oxygen production – splitting 2 water molecules, leaving 4 H+ and O2 .
* REMEMBER: PLANTS PRODUCE THE OXYGEN THAT WE BREATHE!
4) ATP formation- energy is transferred into an ATP molecule. ATP is a stored energy source that plants use to carry out everyday functions.
Move H+ ions through ATP synthase (same as seen in cellular respiration!)
Movement of H+ through the ATP synthase moves energy used to bond a P to ADP, forming ATP

12. Light reactions: Quick Animation)
2) Detailed Animation of Light reactions

13. STAGE 2: Calvin Cycle (Dark Reactions)
Called “dark” because sunlight does not play a role!
Takes place in the STROMA, area around the thylakoids in the chloroplast.
Basic Steps:
Starts with CO2 absorb from atmosphere and ATP and NADPH produced in the light reactions.
CO2 enters and attaches to RuBP with the help of rubisco (enzyme)
As it moves around the cycle, RuBP breaks down into 3-PGA
ATP and NADPH get oxidized and form G3P
2 G3P’s come together to form glucose or other sugars.
RuBP gets recycled Animation of Calvin Cycle (Dark Reactions)

14. Comparing and Contrasting Photosynthesis and Cellular Respiration
Synthesizing energy molecules:
Plants go through photosynthesis to create their own glucose.
Synthesis = Photosynthesis = Chloroplast
Breaking down molecules to release energy:
Plant obtain energy from the glucose and sugar molecules they produce during photosynthesis.
Animals, Fungi and some Protists obtain food from food they consume and break it down into glucose.
Breakdown = Cellular Respiration = in mitochondria

16. C3 plants Stomata video Uses CO2 directly from air
Called C3 because the is first incorporated into a 3-carbon compound.
Stomata in the leaves are open during the day to acquire CO2, but can lose water through stomata as well.
RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2.
PHOTORESPIRATION- happens when CO2 levels decrease and make plant less efficient because it doesn’t produce sugar or ATP.
Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy)
Most plants are C3- soybean, oats, agricultural plants, etc.

17. C4 plants Adaptive Value:
Called C4 because the CO2 is first incorporated into a 4-carbon compound.
When weather is hot and dry, keep stomata closed during the day, to prevent photorespiration.
Photosynthesis takes place in inner cells (requires special anatomy)
Adaptive Value:
Photosynthesizes faster than C3 plants under high light intensity and high temperatures
Better for hot, dry climates
C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbush pictured here, corn, sugarcane.

18. CAM plants (Crassulacean Acid Metabolism)
The CO2 is stored in the form of an acid before use in photosynthesis.
Adaptive Value:
Better water efficiency than C3 plants under dry conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.).
When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis. But this does allow the plant to survive dry spells, and it allows the plant to recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells).
CAM plants include many succulents such as pineapples, cacti, agaves and also some orchids.

20. Photosynthesis and Global Warming

21. How does photosynthesis help regulate global temperatures?

22. So how could we help reduce global warming???
ANSWER:
Photosynthesis absorbs CO2 from the atmosphere.
DECREASES the amount of CO2 in the atmosphere, which can trap radiation and increase temperatures.
So how could we help reduce global warming???

23. PLANT MORE TREES AND OTHER PLANTS!!!
Reminder! Quiz on Ch. 7 and Foldable due Monday 12/6!