1. Energy Flow in Ecosystems: Photosynthesis and Cellular Respiration
Semester 1: Unit 2:
Energy Flow in Ecosystems:
Photosynthesis
and
Cellular Respiration

2. Energy is the ability to do work.
Without ability to obtain & use energy, life would NOT exist.
One of the most important compounds that cells use to store & release energy is adenosine triphosphate (ATP).

3. ATP consists of:
-adenine (nitrogenous base)
-a 5-carbon sugar called ribose
- three phosphate groups

4. ATP can easily release and store energy by breaking and re-forming the bonds between its phosphate groups.
This characteristic makes ATP very useful as a basic energy source for cells

5. Storing Energy
Adenosine diphosphate (ADP) -has 2 phosphate groups instead of 3.
-contains some energy (not as much as ATP)
When a cell has energy available, it stores small amounts by adding a phosphate group to ADP, making ATP.
ADP is like a rechargeable battery that powers the cell.

6. Releasing Energy
Cells release the energy stored in ATP by breaking the bonds between the 2nd & 3rd phosphate groups.
A cell can add (+) or subtract (-) these phosphate groups giving it an easy way of storing & releasing energy as needed.

7. Storing Energy
*ADP into ATP=
stored energy
(fully charged
battery)

8. During photosynthesis-
organisms convert energy from sunlight into chemical energy stored in the bonds of carbohydrates.
- carried out by autotrophs
Autotrophs- organisms that make their own food
Ex: plants, algae, some bacteria
Heterotrophs- organisms that obtain food by consuming other living things
Ex: humans, insects, cheetah, mushroom, etc

9. Energy from the sun travels to Earth in the form of light
Sunlight is a mixture of different wavelengths & make up a color spectrum. (ROYGBIV)

10. Plants gather the sun’s energy with light-absorbing molecules- pigments.
plants’ main pigment is chlorophyll
2 types in plants: - chlorophyll a
- chlorophyll b
Both chlorophylls absorb light in the blue- violet & red regions of the spectrum

11. Plants do NOT absorb in the green region
Leaves reflect green light, which is why plants look green.

12. Photosynthesis uses the energy of sunlight to convert water & carbon dioxide into high-energy sugars & oxygen.

13. Photosynthesis involves 2 reactions sets:
1- light-dependent reactions
2- light-independent reactions (Calvin cycle)

14. Light-Dependent Reactions:
Water & light energy = in
Oxygen, ATP, & NADPH = out

15. Light-Independent Reactions (Calvin cycle):
CO2, ATP & NADPH = in
high energy sugars/carbohydrates = out

16. The 3 main factors that affect photosynthesis are: Temperature
Light intensity
Availability of water
Temperature:
photosynthesis reactions are due to enzymes that function between 0°C & 35°C
Temps above or below that range may slow down the rate of photosynthesis or stop it entirely.

17. Light:
High light intensity increases rate of PS.
After light intensity reaches a certain level, plants reach the maximum rate of PS.

18. Water: Water shortage can slow or stop PS.
Water loss can also damage plant tissues.
Plants living in dry conditions have waxy coatings on leaves to reduce water loss.

19. Organisms get energy from food.
Food molecules release chemical energy when chemical bonds break.
Cells break down food & use the stored energy to produce ATP to power the cell’s activities.

20. Occurs in the mitochondria of a cell Chemical equation (symbols):
Cellular respiration- releases energy from food in the presence of oxygen.
Occurs in the mitochondria of a cell
Chemical equation (symbols):
6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy
In words:
Oxygen + Glucose Carbon dioxide + Water + Energy

21. Cellular Respiration:
3 stages (in order) are:
1- Glycolysis
2- Krebs cycle
3- Electron Transport
Chain (ETC)

22. Aerobic- process that requires oxygen
Krebs cycle & ETC are aerobic processes.
Krebs & ETC take place inside the mitochondria.
Anaerobic- does not require oxygen
Glycolysis is an anaerobic process.
Glycolysis takes place in the cytoplasm.

23. Photosynthesis & cellular respiration are opposite processes.
PS removes CO2 from the air; CR returns it.
PS releases O2 into the air; CR uses O2 from air to release energy from food.
PS “deposits” energy & CR “withdraws” it.
The reactants of CR are the products of PS & vice versa.

24. release of energy by
cellular respiration-
in plants, animals,
fungi, protists, most
bacteria.
Energy capture by
photosynthesis-
in plants, algae,
& some bacteria.

25. Fermentation - energy is released from food molecules in the absence of oxygen.
occurs in the cytoplasm of cells.
2 types of Fermentation exist:
-Alcoholic Fermentation
-Lactic Acid Fermentation
Under anaerobic conditions, fermentation follows glycolysis.

26. Alcoholic Fermentation:
Yeast & a few other microorganisms use alcoholic fermentation to produce ethyl alcohol & carbon dioxide.
used to produce alcoholic beverages & causes bread dough to rise.
Chemical equation: Glucose→
Pyruvic acid + NADH  Alcohol + CO2 + NAD+

27. Lactic Acid Fermentation:
Most organisms carry out fermentation that converts pyruvic acid to lactic acid.
(including humans during exercise)
Chemical equation: Glucose →
Pyruvic acid + NADH  Lactic acid + NAD+

28. During fermentation, cells convert NADH made by glycolysis back into the electron carrier NAD+, allowing glycolysis to continue producing ATP.

29. Sunlight is the ultimate energy source
autotrophs - capture energy from sunlight or chemicals & convert it into forms that living cells use (primary producers).
primary productivity- rate at which primary producers create organic material.
Heterotrophs (consumers)- get energy & nutrients by ingesting other organism

30. Energy flows in one direction in an ecosystem: producers → consumers
food chain- series of steps in which organisms transfer energy by eating & being eaten.
food web- all food chains in an ecosystem

32. Ecological pyramids- show the relative amount of energy or matter contained within each trophic level in a food chain/web
trophic level- each step in a food chain/web
producers- base of pyramid, 1st level
Pyramid of energy- amount of energy available at each trophic level.
Pyramid of biomass- amount of living organic matter at each trophic level
Pyramid of numbers- number of individual organisms at each trophic level

33. Pyramid of Energy:
most of the energy used on life processes
Remaining energy released as heat
ONLY 10% of the energy available from 1 level is transferred to the next level.

34. Ex: many insects graze on 1 tree: lots of biomass, 1 organism.
Pyramids of Biomass or Numbers:
At times, consumers are smaller in size than the organisms they feed upon.
Ex: many insects graze on 1 tree: lots of biomass, 1 organism.
pyramid of numbers may be upside down

35. **Matter is never created or destroyed, only changed!
Unlike the 1-way flow of energy, matter is recycled within & between ecosystems.
biogeochemical cycles- pass elements from 1 organism to another & through the biosphere due to energy
matter involved in biological processes, geological processes, & chemical processes.
**Matter is never created or destroyed, only changed!
nutrients- chemical substances organism needs to sustain life
limiting nutrient -nutrient whose supply limits productivity because it is scarce or cycles slow

36. The Carbon Cycle:
Plants take in CO2, build carbohydrates, & pass it through food webs
animals release CO2 by respiration
organisms die, decomposers break them down, & release C in environment
Geologic forces turn C into fossil fuels/rock

37. The Carbon Cycle:
C enters atmosphere by volcano & human- activity- burning of fossil fuels, forests