BIOLOGY CHAPTER 6THE FLOW OF ENERGY

Objectives

Distinguish between endergonic and exergonic reactions.

Explain how ATP is used in linking the two types of reactions.

Compare the processes of aerobic respiration and fermentation.

Questions…

What happens to the oxygen once it is in our lungs?

Why do most living things need oxygen? Where does the carbon dioxide we

exhale come from and how is it produced?

6.1 Energy for Cells

ATP – adenosine triphosphate – the energy currency of our bodies.

free energy – the energy available to do work. needed for the construction of a muscle cell Active transport of molecules Synthesis of proteins.

6.1 Energy for Cells

Chemical reactions that require free energy are called endergonic reactions.

Energy needs to be inputted into the reaction.

Sources of free energy: Must come from energy released by other

chemical reactions in the cell. Exergonic reactions are energy-releasing reactions.

ATP

Can be represented by A-P-P-P, and then A-P-P

P’s represent three bonded phosphate groups.

When the bond between one of the phosphate groups is broken, free energy is released.

ATP + H2O ADP + Pi + energy This energy used to produce heat and

drive some processes throughout the body like active transport

Releasing Free Energy from ATP – reversible reaction

Linking Energy Release with Energy Use

1) ATP + glucose ADP+glucose & P (exergonic)

2) Glucose & P+fructosesucrose + Pi (endergonic)

Net: ATP+glucose+fructosesucrose+ADP+Pi

Respiration with Oxygen

Cells maintain their supply of ATP by rejoining the ADP molecule and the phosphate.

However, this requires energy to happen. Where does this energy come from?

Food is converted to energy through the process of cellular respiration.

Respiration in most cells makes use of oxygen and is called aerobic respiration

Aerobic Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + energy

More specifically:

C6H12O6 + 6O2 + 38 ADP + 38Pi 6CO2 + 6H2O + 38 ATP

Aerobic Respiration

Actually, 2 ATP used up during the reaction so the net is 36 ATP produced from 1 glucose molecule.

And in reality, only about 39% of the energy from a glucose molecule is transferred to the ATP molecules. The rest is given off as heat.

Basic Point: During cellular respiration, the energy of one glucose molecule is given off bit by bit and transferred to many molecules of ATP.

ATP as the Cell’s Currency

$100 bill = glucose ATP = smaller change

This is why scientists often refer to ATP as the cell’s energy currency.

Anaerobic Processes

Lifting weights – increase in reps makes it harder and harder to complete the lift. Why?

Muscle cells are not receiving enough oxygen to carry out aerobic respiration.

Instead, they use the process of anaerobic respiration.

Some bacteria carry out all of their processes using this form (clostridium tetani)

Lactic Acid Fermentation

When muscles run low on oxygen, the early steps of glucose breakdown still occur.

If oxygen remains unavailable, enzymes break down a glucose molecule into two lactic acid molecules. Equation follows:

Glucose + 4ADP + Pi 2CH3CHOHCOOH + 4ATP

Only a net of 2 ATP after 2 used up in reaction.

Alcoholic Fermentation

Many plant cells and microorganisms carry out another type of anaerobic respiration.

In alcohol fermentation enzymes break down a glucose molecule into 2 molecules of ethanol and 2 molecules of carbon dioxide. Equation:

Glucose + 4ADP + 4Pi 2C2H5OH + 2CO2 + 4ATP

Yeast rising is an example of an anaerobic process. The carbon dioxide released is what makes bread rise. As bread is baked, the alcohol evaporates, making bread rise even more.

Anaerobic Processes

Can be faster than aerobic respiration. Some orgs., even though getting less

from a sugar molecule, can produce ATP almost as fast as in aerobic respiration.

What are the advantages of anaerobic respiration?

Section 6.1 Review

Questions 1-3, 5 page 151

Compare and contrast these terms: ATP and ADP Exergonic and endergonic Aerobic and anaerobic Aerobic respiration and alcohol

fermentation Lactic acid fermentation and alcohol

fermentation

Photosynthesis

Light is a form of radiant energy. Other ex: radio, micro, X rays, gamma rays.

All radiant energy travels in waves. Human eye is sensitive to radiant energy

with wavelengths of about 400-700 nm. This is called white light.

When white light passed through a prism, it separates into the visible spectrum.

Photosynthesis – visible spectrum

Why objects appear colored

Molecules in colored objects absorb some wavelengths of light and reflect others.

The color of an object depends on which wavelengths it reflects.

White shirt – reflects all wavelengths in the visible spectrum.

Black shirt – absorbs all. On a cold, sunny day, you can feel this in

the energy absorbed by a black shirt.

Chlorophyll and Other Pigments Light energy can be changed to chemical

energy. Photosynthesis is an example of this. Chlorophyll absorbs light from the visible

spectrum except green wavelengths and converts it to chemical energy.

Other pigments, carotenoids, are yellow, orange, and red. These are present in many plants as well.

Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

Carbon dioxide and water are combined into simple sugars and oxygen is given off as a byproduct.

This is an endergonic reaction, because light energy is needed for the reaction to occur.

Plants and some bacteria take in the light energy and convert it into a form of chemical energy, which consumers can then cycle into ATP.

Photosynthesis

Can be divided into 2 main sets of reactions: Light Reactions – a series of changes that

convert light energy into chemical energy. The Calvin Cycle – the synthesizing of

sugars.

Trapping Energy from Light

Internal membranes in chloroplasts are called thylakoid membranes.

Part of these membranes arranged in stacks called grana – these are the internal membranes where the light reactions occur.

Light absorbed by chlorophyll and carotenoids. When they absorb light, electrons are excited, and their energy increases.

This increased energy from the electrons is used to bond a phosphate group to an ADP molecule.

Splitting of Water

As light is transformed to chemical energy in the bonding of P to ADP, water molecules are split into hydrogen ions, electrons, and oxygen.

The electrons replace those that were excited when the light was converted to chemical energy.

The oxygen is a by-product, and the hydrogen ions are used in a later step of photosynthesis.

Summary of Light Reactions

1) Light energy is absorbed and converted to chemical energy in the bonds of ATP.

2) Water is split into hydrogen ions, oxygen, and electrons.

3) Hydrogen ions from water are attached to carriers for use in later steps.

The Calvin Cycle

Thylakoid membranes are surrounded by a fluid called stroma.

This is where the sugars are manufactured.

The process of synthesizing these sugars is known as The Calvin Cycle.

The Calvin Cycle

Remember hydrogen ions were a product of the light reactions and were used later in the photosynthesis process.

This is where they are used. Calvin Cycle takes place in the stroma.

Sugars are composed of hydrogen, oxygen, and carbon.

The Calvin Cycle takes the hydrogen ions and carbon dioxide, along with free energy, to make sugar molecules.

Energy Relationships

Relating photosynthesis and cellular respiration: Opposites: P=endergonic vs.

CR=exergonic More than this, though, is the fact they are

interdependent. Both rely on the continuous input of energy

from the Sun.

Everyday Application

Read the Leisure Connection box on page 150 of text.

Answer the three exploring further questions in lab notebook.

Thinking Lab page 156: Interpret the data and put answers in your lab notebook.

6.2 Review

Questions 1-5 page 161

List all the foods you consumed yesterday. Divide the list into a) foods formed directly by photosynthesis and b) those foods not formed directly by photosynthesis,

Chapter 6 Review

Questions: 1-5, 13-15 pages 164-165