UNIT 5
ENERGY FOR LIVING SYSTEMS
READING:
Chapter 5
Photosynthesis and Cellular Respiration
OBJECTIVES
At the end of this unit of study the student will be able to:
1.
Define energy and list and describe the various types of energy
2.
Distinguish between autotrophs and heterotrophs
3.
Describe adenosine triphosphate, ATP.
4.
Define photosynthesis and write the summary equation of the process
5.
Discuss the role of chlorophyll and chloroplasts in photosynthesis
6.
Describe the events of the light and dark reactions
7.
Define respiration and write the summary equation of aerobic respiration
8.
Distinguish between aerobic and anaerobic respiration
9.
Describe the events of glycolysis, citric acid cycle, and electron transport.
10.
Summarize energy production of aerobic respiration
11.
Distinguish between alcoholic and lactic acid fermentation.
ASSIGNMENTS:
1.
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3.
4.
5.
6.
ENERGY FOR LIVING SYSTEMS
I.
UNIT 5
ENERGY
A. Ability to do work
B. Types of energy
1. POTENTIAL ENERGY
a. Energy of position
b. For living organisms, potential energy is stored in chemical bonds
2. KINETIC ENERGY
a. Energy of motion
b. Breaking of chemical bonds in various life processes.
3. ACTIVATION ENERGY
a. Energy necessary to trigger a chemical reaction
b. Lighted match held to a piece of paper would represent activation energy.
C. All living things require energy.
1. Necessary for carrying out all life processes - building, repairing, growing, and reproducing.
2. Energy comes from food (glucose)
a. Energy is stored in bonds of glucose - potential energy
b. No organism can make energy - has to come from the sun.
c. LAW OF CONSERVATION OF ENERGY - Energy can be neither created nor destroyed, but can
only be changed from one form to another.
3. Organisms divided into 2 groups according to the way they get their food.
a. AUTOTROPHS - organisms that can combine inorganic molecules into organic molecules for
use as food; make their own food
b. HETEROTROPHS - organisms that don't make their own food but depend directly on other
organisms for food.
D. Energy is not recycled, matter is recycled
1. Energy available for use decreases with each transformation
2. Some of the energy used to break bonds and some is lost as heat.
3. New energy must be constantly supplied - must come from sunlight.
4. Materials used in producing new molecules can be reused.
E. Energy processes of living organisms
1. PHOTOSYNTHESIS
a. Process in which carbon dioxide and water is used to form glucose.
b. Process requires light energy from the sun.
1) Radiant energy converted to chemical energy.
c. Takes place in the presence of chlorophyll.
2. RESPIRATION
a. Process in which glucose molecule is broken down and chemical energy it contains is released.
b. Carbon dioxide and water released.
c. Carried on by all cells - essential process that releases energy in order to live.
F. ATP - Adenosine triphosphate
1. Usable energy from by one reaction may be stored by another molecule and used in a later reaction.
2. Many times the storage molecule for the released energy is ATP.
a. Composed of 3 parts
1) Adenine - a nitrogen base
2) Ribose - a 5-carbon sugar
3) Three (3) phosphate groups
b. Adenine joins with ribose to form adenosine
c. Phosphate groups attach in sequence to adenosine
1) Adenosine monophosphate - AMP - 1 phosphate group
2) Adenosine diphosphate - ADP - 2 phosphate groups
3) Adenosine triphosphate - ATP - 3 phosphate groups
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3. High energy bonds form between the phosphate groups - indicated by a wavy line (~)
a. Requires a great deal of energy to form bond.
b. Energy is released when bond is broken.
c. ATP - A - P ~ P ~ P
d. ADP - A - P ~ P
4. Normally reaction is cyclic - moves between ADP and ATP - controls the cell's production through
cycle of energy storage and release.
a. ADP + P + energy ---> ATP - energy is stored
b. ATP ---> ADP + P + energy - energy is released
c. Under normal conditions cell does not use ADP as an energy source; ADP not converted to AMP
II. PHOTOSYNTHESIS
A. Process by which green plants convert the sun's light energy into chemical energy stored as food in the
form of glucose.
1. PHOTO - means "light"
2. SYNTHESIS - means "to build a complex substance from simple substances"
B. Basic process
1. Raw materials - the reactants of the reaction
a. Carbon dioxide - CO2
b. Water - H2O
c. Light energy
2. Products a. Glucose - C6H12O6
b. Oxygen - O2
c. Water - H2O
3. Chlorophyll is necessary - acts as a catalyst - causes the reaction to move forward.
a. Pigment in green plants that gives them their color
b. Primary light absorbing pigment of green plants.
4. Represented by the following reaction:
chlorophyll
6 CO2 + 12 H2O + light ------------> C6H12O6 + 6 O2 + 6 H2O
5. Process is series of reactions that change reactants to the products - divided into 2 main groups
a. LIGHT REACTIONS - require light energy
b. DARK REACTIONS - Do not require light energy
C. Light
1. Sunlight is white light; mixture of different wavelengths of light
a. Each wavelength of light has a characteristic color b. Colors that make up white light can be separated by prism to produce the visible part of the
spectrum - ROYGBIV - Red, Orange, Yellow, Green, Blue, Indigo, Violet
1) Shorter the wavelength of light, the more energy it has; blue end has shorter wavelengths
than red thus blue light has more energy than red light.
2. Objects appear to be a certain color because they transmit or reflect light of that color.
a. Colors absorbed by an object are not seen
b. Color of object is the wavelength of light that is reflected or transmitted by the object.
c. Plants appear green because they reflect green light and absorb other colors of light.
D. Plant Pigments
1. Primary pigment in plants that absorbs light energy is chlorophyll
a. Green in color - reflects green wavelengths
b. Absorbs mainly red and blue wavelengths of light
c. Contains enzymes that act as catalysts to speed the reaction of photosynthesis.
d. Types
1) Chlorophyll a
3) Chlorophyll c
5) Bacteriochlorophyll
2) Chlorophyll b
4) Chlorophyll d
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2. ACCESSORY PIGMENTS - may be used to transfer some energy to chlorophyll
a. Types
1) CAROTENOIDS - yellow, brown and orange pigments of plants
a) Carotene
b) Xanthophyll
2) PHYCOBILINS - accessory pigments of red algae and blue-green bacteria
b. Accessory pigments of trees not normally visible - masked by chlorophyll; appear when chlorophyll
production ceases
E. CHLOROPLASTS
1. Organelle in plant cells where photosynthesis occurs.
2. Contain the CHLOROPHYLL pigment.
3. Structure
a. GRANA - tiny stacked structures within the chloroplasts
1) Portion that contains the chlorophyll
2) Also contains the accessory pigments.
3) Site of light reactions
b. STROMA - protein-rich solution surrounding the grana
1) Site of dark reaction
F. Light Reactions
1. Chlorophyll traps the light energy
a. Light energy causes chlorophyll molecules to become energized; electrons released from molecule
b. Two different photosystems active in photosynthesis
1) Photosystem I
2) Photosystem II
2. Water molecules are split and oxygen is released.
3. Energy is stored in ATP and NADPH2 (electron acceptor)
a. Both compounds are used in the Dark Reactions
b. Supply the energy for the Dark Reactions
G. Dark Reactions - light is not required; energy comes from ATP and NADPH2; Called the Calvin cycle
1. Carbon dioxide bonded to 5-carbon sugar called ribulose diphosphate, RDP - forms unstable 6-carbon
compound
2. 6-carbon compound immediately breaks down into two 3-carbon molecule of phosphoglyceric acid, PGA.
3. Each PGA reacts with hydrogen atoms in NADPH2 to produce 3-carbon molecule of
phosphoglyceraldehyde, PGAL, water reformed
4. Two molecules of PGAL combine to produce glucose molecule.
5. Some PGAL used to reform RDP.
III. RESPIRATION
A. Process in which cells take energy, stored in chemical bonds of food and incorporated it into chemical
bonds of ATP
1. Occurs in the mitochondria
2. Series of chemical reactions
3. Reactants
a. Glucose - C6H12O6
b. Oxygen - O2
4. Products
a. Carbon dioxide - CO2
b. Water - H2O
c. ATP - adenosine triphosphate
5. Overall equation of cellular respiration (aerobic)
enzymes
C6H12O6 + 6 O2 ----------> 6 CO2 + 6 H2O + 36 ATP
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B. Types
1. ANAEROBIC RESPIRATION - doesn't require oxygen
2. AEROBIC RESPIRATION - requires oxygen
C. GLYCOLYSIS
1. First stage of respiration; occurs outside the mitochondria
2. Does not require oxygen.
3. Glucose broken down into two 3-carbon molecules of pyruvic acid
4. Requires two molecules of ATP to supply activation energy
5. Produces four molecules of ATP; net gain of two ATP's
6. Pyruvic acid can go in one of two directions - depends on type of organism and availability of oxygen
a. Most organisms - pyruvic acid breaks down into carbon dioxide and water –
aerobic respiration - oxygen required
b. Anaerobic respiration - oxygen not needed
D. Aerobic Phase
1. Divided into two major reactions
a. Citric acid cycle (Krebs Cycle)
b. Electron Transport Chain
2. CITRIC ACID CYCLE
a. Pyruvic acid loses a carbon dioxide forms 2-carbon molecule that enters cycle.
b. Process takes place in the mitochondria
c. Hydrogen atoms released during the cycle - will carry electrons to the next reactions
d. Two molecules of ATP are produced
3. ELECTRON TRANSPORT CHAIN
a. Involves a series of electron acceptors
b. Accepts electrons and hydrogen ions from NADH
c. 24 hydrogen atoms produce 24 electrons and 24 hydrogen ions form 12 pairs of hydrogen ions
and 12 pairs of electrons
d. Near end of chain 12 molecules of hydrogen bond with 6 oxygen molecules to produce 12
molecules of water.
e. 34 molecules of ATP produced
E. Summary of ATP production in aerobic respiration
1. Glycolysis
2 ATP
2. Citric Acid Cycle
2 ATP
3. Electron Transport
32 ATP
4. Total
36 ATP
F. ANAEROBIC RESPIRATION
1. Occurs when cell obtains energy from breakdown of food molecules in the absence of oxygen
2. Also known as FERMENTATION
3. First process is similar to aerobic respiration - glucose converted to pyruvic acid - glycolysis
4. Types of Fermentation
a. Alcoholic Fermentation
b. Lactic Acid Fermentation
5. ALCOHOLIC FERMENTATION
a. Pyruvic acid is converted to ethyl alcohol - can't enter the citric acid cycle.
b. Most of the energy is still stored in the alcohol.
c. Summary equation
enzymes
C6H12O6 ----------> 2 C2H5OH + 2 CO2 + 2 ATP
glucose
ethyl alcohol carbon energy
dioxide
d. Industries that depend on alcoholic fermentation
1) Baking - carbon dioxide; makes bread rise.
2) Brewing - ethyl alcohol in alcoholic beverages
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6. LACTIC ACID FERMENTATION
a. Occurs in muscle tissue especially during heavy exercise
b. Blood can't bring oxygen fast enough; lactic acid builds up causing soreness (cramps); muscles
go into oxygen debt.
c. Summary equation
enzymes
C6H12O6 -----------> 2 CH3CHOHCOOH + 2 ATP
glucose
lactic acid
energy
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