Chapter 4

Cellular Processes

Cellular Energy

Cells Use Energy• Maintain homeostasis• To perform all cellular processes• To make energy-storing molecules

When they stop using energy,they are dead

Energy Relationships• Energy is a one time commodity –

every time it is used some escapes and becomes unusable

• More energy is needed to build an energy-storing molecule than is stored in the molecule.

How do organisms obtain their food?

• Autotrophs– “auto” = self– “troph” = nourishment

• Heterotrophs– “hetero” = others

Autotrophs• Make their own food

– They capture light energy and convert it into sugar

– Ex: plants, algae, and some bacteria.

Heterotrophs• Depend on other organisms

for their energy source– Ex: humans, animals, fungi,

and most bacteria.

ATP – Adenosine Triphosphate

• Most energy sources (fats, carbohydrates) are large and must be broken down into smaller units (sugar – glucose)

• ATP stores energy in a usable form for all living organisms

• The bonds between the three phosphate groups are unstable high-energy covalent bonds

ATP

Energy Production

• When the bonds are broken, a large amount of energy is released (an exothermic reaction) and is available for use in any cellular function that requires energy (an endothermic reaction).

• ATP ADP + P + Energy 

ATPadenosine triphosphate

Phosphates

1 2 3Adenosine

ATP Production• ADP and P can be reused to form ATP

with the proper enzymes and adequate supply of energy

• ADP + P + Energy ATP

1 2Adenosine

ADPadenosine diphosphate

Phosphates

ATP-ADP Cycle

4A – 2 PHOTOSYNTHESIS

The process of taking light energy and

converting it into stored chemical energy

The sun is the source of energy for living things!

Photosynthesis Reaction

• Reaction converting light energy into stored chemical energy

6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2

(Carbon (water) (glucose) (oxygen)dioxide)

• Green plants and algae perform this energy transformation in large enough quantities to provide stored chemical energy for most living organisms

Photosynthesis is important because…

1) It converts solar energy into usable chemical energy

2) It produces oxygen

Light Absorption• Different wavelengths of

visible light are seen by the human eye as different colors.

• The color we see is actually the color reflected.

Chlorophyll a • Primary catalyst of

photosynthesis• Green pigment in the grana

of chloroplasts• Becomes activated by light

energy

Chlorophyll a• Chlorophyll a is a blue green

pigment – it reflects the blues and greens and absorbs the reds and violets

Chlorophyll b• Is a yellow green pigment – that

absorbs some of the same pigments as chlorophyll a as well as some of the blues not absorbed by chlorophyll a and reflects some of the yellow greens that chlorophyll a absorbs 

Absorption Spectrum

The Process of Photosynthesis

• Requires sunlight and water• Occurs in the grana of the

chloroplast• Produces: Oxygen , ATP and

NADPH (electron carrier that stores energy for later use)

The Light-Dependent Phase

• Light is NOT required • Occurs in the stroma of the chloroplast• Also called:“Dark phase,” “synthetic phase,”

“Calvin cycle,” “carbon fixation cycle”• Is dependent upon the products of the

light phase (ATP and NADPH) and CO2 from the atmosphere

Photosynthesis: The Process

Light-Independent Phase

Conditions for Photosynthesis

• Proper wavelengths of light• Sufficient absorption of

carbon dioxide• Proper temperatures• Proper amount of water

Chemosynthesis: Other autotrophs

• A few bacteria use inorganic chemicals (i.e. ammonia or sulfur) to obtain energy

• Ex. Symbiotic bacteria in tubeworms in hydrothermal vents convert chemical energy in sulfur into usable energy

Cellular Respiration

Cellular Respiration

The breakdown of a food substance into

usable cellular energy in the form of ATP

SummaryKinetic energy (sun)

stored chemical energy (C6H12O6)

= photosynthesis

Summary stored chemical energy (C6H12O6)

= cellular respiration

ready-to-use chemical energy ( )

Cellular Respiration• Aerobic

–Requires oxygen, is the opposite of photosynthesis, combines oxygen with sugar to release energy, carbon dioxide and water

• Anaerobic–Does not require oxygen

Aerobic Cellular Respiration

Aerobic Cellular Respiration

C6H12O6 + O2

H2O + CO2 + energy (ATP)

The Process of Cellular Respiration• Glycolysis• Citric Acid Cycle (Krebs Cycle)• Hydrogen and Electron Transport

System

Glycolysis• All types of cellular

respiration begin with glycolysis.

• Does not require oxygen• Occurs in the cytoplasm

Glycolysis• Breakdown of glucose into

pyruvic acid, H+, and electrons

• 2 net ATP

Aerobic Cellular Respiration

The products from glycolysis are sent to the mitochondria.

Aerobic Cellular Respiration

1. Citric Acid Cycle (Krebs Cycle) = Pyruvic acid is broken down into citric acid.− Pyruvic acid Acetyl CoA− Acetyl CoA Citric acid

2. Hydrogen and Electron Transport System− Occurs in the cristae of

the mitochondria

Aerobic Cellular Respiration

2. Hydrogen and Electron Transport System− At the end of the chain, H

combines with oxygen to form water.

− Oxygen is the rate-limiting factor.

Aerobic Cellular Respiration

Energy Facts• Aerobic Cellular Respiration

results in the net gain of 36 ATP molecules.

GlycolysisCitric Acid

CycleH+ & e-

transport system

Reactants

Products

Location

ATP

Cytoplasm Mitochondria (matrix)

Mitochondria(cristae)

Glucose

Pyruvic acid; H+;

e-

Pyruvic acid

CO2; H+; e-

H+; e-

ATP; water

2 net 2 net 32

Anaerobic Respiration

• Breakdown of food (glucose) without oxygen

• “Cellular fermentation”

2 Types of Fermentation1) Alcoholic fermentation – pyruvic acid +

NADH alcohol + CO2 + NAD+Ex: yeast

 2) Lactic Acid fermentation – pyruvic acid

+ NADH lactic acid + NAD+Ex: produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissue

Energy Facts• Cellular fermentation

supplies no ATP energy beyond glycolysis.

Energy Facts• Cellular fermentation

supplies no ATP energy beyond glycolysis.

• Cellular fermentation results in the net gain of 2 ATP molecules.

Cellular Respiration

Comparison of Photosynthesis and Cellular Respiration

Function Energy Capture Energy release

Location Chloroplasts Mitochondria

Reactants Carbon dioxide and water

Glucose and oxygen

Products Glucose and Oxygen

Carbon dioxide and water

Equations 6CO2 + 6H2O + energy C6H12O6 + 6O2

6O2 + C6H12O6 6CO2 + 6H2O + energy

Match the following: ____1. Organisms that make their own food A. Chloroplasts____2. Site of photosynthesis B. Aneorobic ____3.Process occurs in a mitochondrion C. Aerobic____4. C6H12O6 D. Glucose____5. Process does not require oxygen E. ATP ____6. Process requires oxygen F. Kreb’s cycle____7. Adenosine diphosphate G. Glycolysis

____8. Energy storing molecule H. Energy____9. The anaerobic process of splitting glucose and forming two

molecules of pyruvic acid I. ADP ____10. The ability to do work J. Autotrophs

WORD BANK

2 ATP2 ATP

36 ATP6 NADH2 FADH

Electron transport chainMitochondrion

CytoplasmFermentation

GlycolysisGlucosePyruvate

Lactic acidKreb's Cycle