ENERGY RELATIONSHIPS IN

ORGANISMS

Biology

Corsicana High School

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.

Two Fundamental Processes for Energy in Living Things:

• Photosynthesis

• Respiration

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

Respiration

• the process that breaks down glucose to release its stored energy for use by a cell

• C6H12O6 + 6O2 6CO2 + 6H2O + energy (38 ATPs)

Autotrophs

• can build organic molecules from inorganic substances

• “can make their own food”• also called producers• examples: green plants, algae,

some bacteria

Heterotrophs

• cannot build organic molecules from inorganic substances

• “cannot make their own food”

• also called consumers

• examples: animals, protists, fungi, most bacteria

Ultimately, all life on earth depends on autotrophs!

The Cycle of Photosynthesis and Respiration

carbon dioxide + water

glucose + oxygen

light energy chemical

energy

RESPIRATIONPHOTOSYNTHESIS“The

Circle of Life”

Biochemical Pathway

• a complex series of chemical reactions

• Photosynthesis and respiration are biochemical pathways.

ATP

• the molecule in the cell that stores the energy released by chemical reactions (the cell’s “energy currency”)

• stands for: adenosine triphosphate

Diagram of ATP

Adenosine mono-

P

di-

P P

tri-

phosphate

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

Chemiosmosis

• the process by which cells make ATP by transporting protons across a membrane

• proton pump---active transport of protons (H+) through a membrane

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)

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

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

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

• Light reactions take place in the thylakoid membranes

• Dark reactions take place in the stroma

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

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

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

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

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

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

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

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

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

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

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

Dark reactions

• light is not used

• carbon fixation---carbon atoms (from CO2) are placed (“fixed”) into organic compounds

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

Cellular Respiration

• 2 kinds of cellular respiration:–fermentation

–aerobic respiration

• both kinds start with glycolysis–“glyco” = glucose

–“lysis” = splitting

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)

Fermentation

• the breakdown of glucose in a cell without oxygen

• 2 types: –lactic acid fermentation

–alcoholic fermentation

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

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)

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

Steps in aerobic respiration

• glycolysis

• pyruvic acid is converted to acetyl coenzyme A

• Krebs cycle

• ETC

Krebs cycle

• the central biochemical pathway of aerobic respiration

• also called citric acid cycle

• CO2 is released

• 2 more ATPs are formed

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

Total ATPs for aerobic respiration

• 38 ATPs• 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