Semester 1: Unit 2:
Energy Flow in Ecosystems: Photosynthesis
and
Cellular Respiration
• 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).
•ATP consists of:
-adenine (nitrogenous base)
-a 5-carbon sugar called ribose
- three phosphate groups
• 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
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.
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.
Storing Energy
*ADP into ATP=
stored energy
(fully charged
battery)
• 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
• 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)
•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
•Plants do NOT absorb in the green region
• Leaves reflect green light, which is why plants look green.
• Photosynthesis uses the energy of sunlight to convert water & carbon dioxide into high-energy sugars & oxygen.
•Photosynthesis involves 2 reactions sets:
1- light-dependent reactions
2- light-independent reactions (Calvin cycle)
Light-Dependent Reactions:
•Water & light energy = in
•Oxygen, ATP, & NADPH = out
Light-Independent Reactions (Calvin cycle):
• CO2, ATP & NADPH = in
• high energy sugars/carbohydrates = out
• 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.
Light:
•High light intensity increases rate of PS.
•After light intensity reaches a certain level, plants reach the maximum rate of PS.
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.
•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.
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
Cellular Respiration:
•3 stages (in order) are:
1- Glycolysis
2- Krebs cycle
3- Electron Transport
Chain (ETC)
• 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.
•Photosynthesis & cellular respiration are oppositeprocesses.• 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.
• release of energy by cellular respiration-in plants, animals, fungi, protists, most bacteria.
• Energy capture by photosynthesis-in plants, algae, & some bacteria.
• 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.
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+
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+
• During fermentation, cells convert NADH made by glycolysis back into the electron carrier NAD+, allowing glycolysis to continue producing ATP.
• 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
• 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
• 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
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.
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
• Unlike the 1-way flow of energy, matter is recycledwithin & between ecosystems.
• biogeochemical cycles- pass elements from 1 organism to another & through the biosphere due to energy
• matter involved in biological processes, geologicalprocesses, & 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
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
The Carbon Cycle:
• C enters atmosphere by volcano & human- activity-burning of fossil fuels, forests
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