1. Cellular Energy 8.1 How Organisms Obtain Energy
All living organisms use energy to carry out all biological processes.
Transformation of Energy
Macromolecules are assembled and broken down.
Substances are transported across cell membranes.
Genetic instructions are transmitted.

2. Cellular Energy All cellular activities require energy.
Energy is the ability to do work.

3. Cellular Energy
Thermodynamics is the study of the flow and transformation of energy in the universe.
Laws of thermodynamics:
1. Law of conservation of energy – energy cannot be created or destroyed.
2. Energy cannot be converted without the loss of usable energy

4. Cellular Energy Examples of Laws of Thermodynamics:
1. stored energy in food is converted to chemical energy when you eat and to mechanical energy when you run or kick a ball.
2. Food chains – a food chain amount of usable energy that is available to the next trophic level decreases.

5. Cellular Energy
Entropy – the measure of disorder, or unusable energy, in a system.
Autotrophs – organisms that make their own food for energy through photosynthesis
Heterotrophs – organisms that need to injest food to obtain energy

6. Metabolism
All of the chemical reactions in a cell are referred to as the cell’s metabolism.
A series of chemical reactions in which the product of one chemical reaction is the substrate for the next reaction is called a metabolic pathway.
Metabolic pathways come in two types:
Catabolic and anabolic

7. Metabolism
Catabolic pathways release energy by breaking down a larger molecule into smaller molecules.
Anabolic pathways use the energy released by catabolic pathways to build larger molecules from smaller particles.

8. Metabolism
The relationship of anabolic and catabolic pathways results in the continual flow of energy within an organism.
Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell.
In photosynthesis, autotrophs use light energy, carbon dioxide, and water to form glucose and oxygen.
This can then be consumed by other organisms for food.

9. Metabolism
Cellular respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cell.
Oxygen is used to break down organic molecules resulting in the production of carbon dioxide and water.
* Note the cyclic nature of these processes – the products of one reaction are the reactants for the other reaction.

10. ATP: The Unit of Cellular Energy
Energy exists in many forms:
*light energy
*mechanical energy
*thermal energy
*chemical energy

11. ATP
In biological molecules, chemical energy is stored and can be converted to other forms of energy when needed.
Example: chemical energy is converted to mechanical energy when muscles contract.
ATP – adenosine triphosphate : the most important biological molecule that provides chemical energy

12. ATP Structure
ATP is a multipurpose storehouse of chemical energy that can be used by cells in a variety of reactions.
ATP is the most abundant energy-carrier molecule in cells and is found in all types of organisms.
ATP is a nucleotide made of an adenine base, a ribose sugar, and three phosphate groups.

13. ATP Function
ATP releases energy when the bond between the second and third phosphate groups is broken, forming a molecule called ADP (adenosine diphosphate) and a free phosphate group.
Energy is stored in the phosphate bond formed when ADP receives a phosphate group and becomes ATP.

14. ATP Function
ATP and ADP can be interchanged by the addition or removal of a phosphate group.
Sometimes ADP becomes AMP (adenosine monophosphate) by losing an additional phosphate group.
There is less energy released in this reaction.
Most of the energy reactions in the cell involve ATP and ADP.

15. Energy Cycles
Sunlight  Photosynthesis (autotrophs)  O2 + Glucose Cellular respiration (heterotrophs)  C02 + H2O Sunlight
ATP energy + phosphate +ADP ATP

16. 8.2 Photosynthesis
Light energy is trapped and converted into chemical energy during photosynthesis.
Most autotrophs – including plants – make organic compounds, such as sugars by a process in which light energy is converted into chemical energy.

17. Photosynthesis Chemical equation for photosynthesis:
6CO2 + 6H2O — light C6H12O6 + 6O2

18. Photosynthesis Occurs in two phases: *Light Reactions
*The Calvin Cycle
Phase One – light-dependent reactions
- light energy is absorbed
- light energy converted into chemical energy
- forms ATP and NADPH

19. Photosynthesis Phase Two: light-independent reactions
- makes glucose using ATP
and NADPH.
- Once glucose is produced, it can be joined to other simple sugars to form larger molecules – complex carbohydrates (starch)

20. Light Reactions First step: Absorbption of light
Plants have special organelles to capture light energy – chloroplasts.
Once energy is captured, two energy storage molecules are produced:
NADPH
ATP

21. Chloroplasts Large organelles Capture light energy
Found mainly in the cells of leaves
Disc-shaped organelles
Contain two main compartments:
*thylakoid – flattened saclike membranes arranged in stacks called grana.
*stroma – fluid-filled space outside the grana

22. Chloroplasts Light-dependent reactions take place in the thylakoids.
Light-independent reactions take place in the stroma.
Light-absorbing colored molecules called pigments are found in the thylakoid membranes.

23. Chloroplasts Different pigments absorb specific wavelengths of light.
The major light-absorbing pigment in plants is chlorophyll.
There are several types of chlorophylls, most important two are:
*chlorophyll a
*chlorophyll b

24. Chloroplasts Structure can differ from one molecule to another.
Enables distinct chlorophyll molecules to absorb light at unique areas of the visible spectrum.
Absorb most strongly in violet-blue region of visible light spectrum.
Reflect light in the green region of the spectrum.

25. Chloroplasts
This is why plant parts that contain chlorophyll appear green to the human eye!

26. Chloroplasts
In addition to chlorophylls, most photosynthetic organisms contain accessory pigments that allow plants to trap additional light energy from other areas of the visible spectrum.
Example: carotenoids (beta-carotene) absorb light mainly in the blue and green regions – reflect light in the yellow, orange and red regions – carrots, sweet potatoes

27. Chloroplasts
What happens to the chlorophyll molecules of trees in the fall?

28. Electron Transport
The structure of the thylakoid membrane is the key to efficient energy transfer during electron transport.
Thylakoid membranes have large surface area, providing the space needed to hold large numbers of electron-transporting molecules and two types of protein complexes called photosystems.

29. Electron Transport
Photosystem I and Photosystem II contain light-absorbing pigments and proteins that play an important role in the light reactions.
1. light energy excites electrons in photosystem II causing a water molecule to split, releasing an electron into the electron transport chain
A hydrogen ion (H+) goes into the thylakoid space and oxygen (O2) becomes a waste product
The breaking down of water is essential for photosynthesis to occur.

30. Electron Transport
2. The excited electrons move from photosystem II to an electron-acceptor molecule in the thylakoid membrane.
3. The electron-acceptor molecule transfers the electrons along a series of electron-carriers to photosystem I.
4. In the presence of light, photosystem I transfers the electrons to a protein called ferrodoxin.
The electrons lost by photosystem I are replaced by electrons shuttled from photosystem II.

31. Electron Transport
Ferrodoxin transfers the electrons to the electron carrier NADP+, forming the energy-storage molecule NADPH.

32. Chemiosmosis
ATP is produced in conjunction with electron transport by the process of chemiosmosis – the mechanism by which ATP is produced as a result of the flow of electrons down a concentration gradient.
Essential – the breakdown of water – provides the electrons that initiate the electron transport chain and also provides the protons (H+) necessary to drive ATP synthesis during chemiosmosis.

33. Chemiosmosis
The H+ released during electron transport accumulate in the interior of the thylakoid.
High concentration of H+ in the thylakoid interior and low concentration of H+ in the stroma causes H+ to diffuse down their concentration gradient out of the thylakoid interior into the stroma through ion channels. Figure 8.8 pg. 225
These channels are enzymes called ATP synthatases.
As H+ moves through ATP synthatase, ATP is formed in the stroma.

34. The Calvin Cycle

35. The Calvin Cycle
NADPH and ATP provide cells with large amounts of energy – but not stable enough to store chemical energy for long periods
Calvin Cycle allows for energy storage in the form of glucose
Light-independent

36. The Calvin Cycle
Step 1: Carbon fixation – six CO2 molecules combine with six 5-carbon compounds to form twelve 3-carbon molecules called 3-phosphoglycerate (3-PGA)
Step 2: Chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules to form high-energy molecules called glyceraldehyde 3- phosphates (G3P) ATP supplies the phosphate groups for forming G3P, while NADPH supplies H+ and electrons.

37. The Calvin Cycle
Step 3: Two G3P molecules leave the cycle to be used for the production of glucose and other organic compounds
Step 4: Final stage – An enzyme, rubisco, converts the remaining 10 G3P molecules into 5-carbon molecules called ribulose 1 , 5-bisphosphates (RuBP) which combine with new CO2 molecules to continue the cycle

38. The Calvin Cycle
Rubisco – one of the most important biological enzymes
Plants use sugars formed during Calvin Cycle both as a source of energy and as building blocks for complex carbohydrates
Complex carbohydrates include cellulose providing structural support for plants.

39. Alternative Pathways
If plants do not have sufficient water, CO2, or sunlight, they use adaptive pathways.
C4 plants: occurs in plants, such as sugar cane and corn
*they fix CO2 into 4-carbon compounds instead of 3-carbon molecules
*have significant structural modifications in arrangement of leaves
*keep their stomata closed on hot days
*carbon compounds are transferred to special cells where CO2 enters the Calvin Cycle
*allows for sufficient CO2 uptake, while minimizing water loss

40. Alternative Pathways CAM plants: crassulacean acid metabolism
Occurs in water-conserving plants
Allow CO2 to enter leaves only at night
Fix CO2 into organic compounds
During day CO2 is released from these compounds and enter the Calvin Cycle
Allows for sufficient CO2 uptake with minimal water loss.