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