1. Cellular Energy and Metabolism

2. Law of Thermodynamics
In your body, energy is required to assemble/break down molecules, transport molecules, and transmit genetic instructions.
“Energy can be converted from one form to another, but it cannot be created or destroyed.”
Law v. Theory

3. Autotrophs and Heterotrophs
(Review) Some organisms make their own food automatically, while others must obtain it from other organisms (heterotrophs).
Chemoautotrophs – use inorganic substances such as hydrogen sulfide as a source of energy.
Chemo – use this
Talk through food web!

4. Metabolism All chemical reactions in a cell Catabolic v. Anabolic
Catabolic – release energy by breaking down larger molecules into smaller ones.
Anabolic – use this energy to build large molecules from smaller ones.

6. ATP: The Unit of Cellular Energy
When the phosphate group breaks off, energy is released!

7. Photosynthesis: Light and Dark Reactions

8. “Photosynthesis is the anabolic pathway in which light energy from the sun is converted to chemical energy for use by the cell.”
As we will learn in the upcoming classes, energy flows between the metabolic reactions of organisms in an ecosystem.
Anabolic – simpler substances are combined to formed more complex ones (in this case glucose) and energy (light) is stored.
Don’t say anything about ATP! (or that it is produced in light to be used in dark)

9. Pigments
Chloroplasts are full of light-absorbing, colored molecules called pigments.
Different pigments absorb specific wavelengths of light, as illustrated in this image.
Why are plants green? The most common types of pigments are chlorophyll a and b. In general they absorb most strongly in the violet-blue region, and reflect light in the green region (why plant parts appear green to the human eye).
Most photosynthetic organisms also contain accessory pigments that allow plants to trap additional light energy from other areas of the visible spectrum. Carotenoids absorb mainly in the blue-green region and reflect in the yellow, orange, and red region – hence the colors of carrots and sweet potatoes.
Though chlorophylls are more abundant than other pigments (and thus hide them), there are times of the year (fall) when chlorophylls break down allowing the other pigments to shine.

10. Photosynthesis: Two Phases
Light-dependent reactions (Light Reactions)
Transform light energy into chemical energy (ATP and NADPH)
In the thylakoids of the chloroplasts
Light-independent reactions (Calvin Cycle)
Use chemical energy to form glucose
In the stroma (space outside Thylakoids)
Light-dependent absorb light energy (from the sun) and then covert it into chemical energy in the form of ATP and NADPH.
Light independent, these molecules are used to make glucose, which can then be joined to other simple sugars to form larger, more complex molecules.
Chloroplasts are found in the leaves.
We will cover each of these, including some variations on the theme, in more detail next class!

11. Light Reactions – Electron Transport
Ferrodoxin
Why are they called Light v. Dark?

12. Light Reaction – Electron Transport
Light energy excites electrons in Photosystem II causing a water (H2O) molecule to split.
Oxygen gas (O2) released as waste
Electron is caught by an electron acceptor before it is passed down an electron transport system (ETS)
This electron movement AND the movement of Hydrogen through ATP synthase to produces ATP
Electrons (in ETS) are transferred among several electron carriers (cytochromes) to Photosystem I.
Photosystems contain light-absorbing pigments

13. Light Reaction – Electron Transport
Light hits Photosystem I and excites an electron a higher energy level, caught by Ferrodoxin
Ferrodoxin transfers electrons and a Hydrogen to the electron carrier, NADP+ to make NADPH
(Last slide) ATP is made during this process – hydrogen molecules flow down concentration gradient through ATP synthase!
H+ from water split!

14. Light Reaction – Electron Transport
Ferrodoxin
Review!

15. Dark Reactions – Calvin Cycle
RuBP
PGA
G3P
Why does this happen?
Aren’t ATP and NADPH enough? (no they can’t store energy for long periods of time)

16. Dark Reactions – Calvin Cycle
Carbon Dioxide reacts with a five-carbon compound (RuBP) with the help of Rubisco (an enzyme) to form PGA (Carbon fixation)
Energy stored in ATP and NADPH is transferred to PGA to form high energy molecules (G3P)
Some G3P leaves the cycle to be used for formation of glucose and other organic compounds
Some of it undergoes a reaction to produce RuBP

17. Dark Reactions – Calvin Cycle
Why do we care?
RuBP
PGA
G3P
Because it creates sugar!!! Energy, building blocks for complex carbs (cellulose – support/structure)

18. Photosynthesis: Alternative Pathways
The environment in which an organism lives can impact the organism’s ability to carry out photosynthesis.
C4 plants (sugar cane and corn) – during hot days, Calvin Cycle occurs in different types of cells (location) to minimize water loss.
CAM plants (desert and marsh plants) – in dry or saline environments, Calvin Cycle occurs at a different time.
Page 233!