1. ENERGY RELATIONSHIPS IN ORGANISMS
Biology
Corsicana High School

2. Energy in Living Things
All living things need energy to survive----for building, repairing, growing, reproducing, etc.
The energy for these activities comes ultimately from the sun.

3. Two Fundamental Processes for Energy in Living Things:
Photosynthesis
Respiration

4. Photosynthesis
The process that converts light energy of sunlight into chemical energy and stores that energy in glucose
6CO2 + 6H2O + light energy chlorophyll C6H12O6 + 6O2

5. Respiration
the process that breaks down glucose to release its stored energy for use by a cell
C6H12O6 + 6O CO2 + 6H2O + energy (38 ATPs)

6. Autotrophs can build organic molecules from inorganic substances
“can make their own food”
also called producers
examples: green plants, algae, some bacteria

7. Heterotrophs cannot build organic molecules from inorganic substances
“cannot make their own food”
also called consumers
examples: animals, protists, fungi, most bacteria

8. Ultimately, all life on earth depends on autotrophs!

9. The Cycle of Photosynthesis and Respiration
glucose + oxygen
“The Circle of Life”
PHOTOSYNTHESIS
RESPIRATION
carbon dioxide + water
light energy
chemical energy

10. Biochemical Pathway a complex series of chemical reactions
Photosynthesis and respiration are biochemical pathways.

11. ATP
the molecule in the cell that stores the energy released by chemical reactions (the cell’s “energy currency”)
stands for: adenosine triphosphate

12. Diagram of ATP
mono- P
di- P P
tri-
phosphate
Adenosine

13. How does ATP store and release energy?
the high-energy bond attaching the last phosphate can be easily formed (to store energy) and easily broken (to release energy)
ADP + phosphate + energy ATP

14. Chemiosmosis
the process by which cells make ATP by transporting protons across a membrane
proton pump---active transport of protons (H+) through a membrane

15. Chemiosmosis (continued)
the buildup of H+ (protons) on one side of a membrane results in an electrical charge gradient
Eventually, the protons are forced through ATP synthetase (a protein in the membrane). The energy given off is used to form ATP (ADP + phosphate + energy ----> ATP)

16. Photosynthesis takes place in the chloroplast
consists of two interdependent pathways:
light reactions---light is required (Photosystem I and II)
dark reactions---light is not required (Calvin cycle) Takes place at the same time as light reactions

17. Structure of the Chloroplast
Consists of two membranes
Outer membrane separates the chloroplast from the cytoplasm
Inner membrane is formed into flattened sacs called thylakoids

18. Thylakoids a stack of thylakoids is a granum (pl: grana)
thylakoids are surrounded by a protein-rich solution---the stroma
inside each thylakoid is an internal reservoir---the lumen

19. Light reactions take place in the thylakoid membranes
Dark reactions take place in the stroma

20. Photosynthetic pigments
pigment---a light-absorbing compound
absorbs certain wavelengths of light
reflects other wavelengths that we see as color
when light energy is absorbed, electrons are raised to a higher energy level

21. Chlorophyll green pigment necessary for photosynthesis
absorbs red and blue light
reflects green light
several types of chlorophyll---chlorophyll a and chlorophyll b are the most important

22. Accessory pigments
trap other wavelengths of light and transfer the energy to chlorophyll
carotenoids---yellow, orange, brown
examples: carotenes, xanthophylls
phycobilins---found in red algae and blue-green bacteria

23. Photosystems a cluster of pigments in the thylakoid membrane
Photosystem I (first discovered)---absorbs light with a wavelength of 700 nm (nanometers)
Photosystem II---absorbs light with a wavelength of 680 nm

24. Photosystems (continued)
when light energy strikes a pigment molecule, electrons absorb the energy and are boosted to a higher energy level
the pigments in a photosystem funnel the energy (excited electrons) to chlorophyll a in the reaction center of the photosystem

25. Photosystem II
1. Water molecules are split, providing H+ and electrons. The oxygen is released to the air
2. Excited electron (attached to a hydrogen atom) jumps to a protein in the thylakoid membrane

26. Photosystem II (continued)
3. Electron passes through a series of membrane proteins and pigments----electron transport chain (ETC)
4. One of the proteins in the ETC acts as a proton pump, using energy from the electron to move H+ into the lumen

27. Photosystem II (continued)
5. buildup of H+ in lumen eventually causes electrical charge gradient---H+ leaves through ATP synthetase---chemiosmosis produces ATP
6. electron is finally transferred to Photosystem I

28. Photosystem I
1. light energy strikes molecules, causing electrons to jump to higher energy level
2. excited electrons jump to a protein in the thylakoid membrane

29. Photosystem I (continued)
3. electrons pass down another ETC to a reducing protein
4. NADP+ is reduced (H+ and electrons are added)----takes hydrogen to dark reactions

30. Products of light reactions:
ATP--supplies energy for later reactions
NADPH---supplies hydrogen for later reactions
oxygen---from splitting water, is released to the air

31. Dark reactions light is not used
carbon fixation---carbon atoms (from CO2) are placed (“fixed”) into organic compounds

32. Calvin cycle the most common carbon-fixing pathway
occurs in the stroma of the chloroplast
six CO2 molecules must enter the cycle to produce 1 molecule of glucose

33. Cellular Respiration 2 kinds of cellular respiration:
fermentation
aerobic respiration
both kinds start with glycolysis
“glyco” = glucose
“lysis” = splitting

34. Glycolysis
the breakdown of one glucose molecule into 2 molecules of pyruvic acid
occurs in the cytoplasm
anaerobic--no oxygen is required
net result of 2 ATPs (about 2% of the energy stored in a glucose molecule)

35. Fermentation the breakdown of glucose in a cell without oxygen
2 types:
lactic acid fermentation
alcoholic fermentation

36. Lactic acid fermentation
occurs in animal cells when oxygen is in short supply
cells convert pyruvic acid from glycolysis into lactic acid
buildup of lactic acid in muscle tissues causes muscle fatigue and soreness

37. Alcoholic fermentation
occurs in some plant cells, yeasts
cells convert pyruvic acid from glycolysis into ethyl alcohol and carbon dioxide
used in making beer and wine (formation of ethyl alcohol) and in making bread dough rise (formation of CO2)

38. Aerobic respiration the breakdown of glucose in a cell using oxygen
occurs in the mitochondrion---enzymes that control these reactions are on the inner mitochondrial membrane and in the matrix--dense fluid inside the mitochondrion

39. Steps in aerobic respiration
glycolysis
pyruvic acid is converted to acetyl coenzyme A
Krebs cycle
ETC

40. Krebs cycle the central biochemical pathway of aerobic respiration
also called citric acid cycle
CO2 is released
2 more ATPs are formed

41. Electron transport chain
hydrogen and electrons are moved down the chain from molecule to molecule, releasing energy
oxygen is the final acceptor of the electrons and hydrogen to produce water
34 additional ATPs are produced

42. Total ATPs for aerobic respiration
from one molecule of glucose
aerobic respiration is therefore 19 times more efficient than anaerobic
still only about 1/2 the energy stored in a glucose molecule