the working cell energy from food. sunlight powers life obtaining food all organisms require food...

THE WORKING CELLENERGY FROM FOOD

SUNLIGHT POWERS LIFE

• Obtaining Food• All organisms require food for energy and building

materials.

• Autotrophs• Organisms that make their own food, such as

plants, are autotrophs.• They start with inorganic molecules and make

organic molecules, such as photosynthesis.• Autotrophs are also called producers.

• On land, plants are the major producers.• In oceans, lakes, and streams, algae and photosynthetic

bacteria are the major producers.

SUNLIGHT POWERS LIFE• Heterotrophs

• These are organisms that cannot make their own food and rely on other sources for it.

• They are also called consumers, and obtain their food by eating producers or other consumers.

• Harvesting the Energy in Food• Many organisms harvest the energy in foods

by cellular respiration.• This is a chemical process that uses oxygen

to convert energy stored in organic molecules to another form of chemical energy , ATP (adenosine triphosphate).

SUNLIGHT POWERS LIFE• The cells then use this ATP as their main

energy supply.• Photosynthesis and cellular respiration are

opposites of one another.• They both use water, carbon dioxide, oxygen, and

glucose, an organic compound.

• In photosynthesis:• 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆

• In cellular respiration:• 6O₂ + C₆H₁₂O₆ → 6CO₂ + 6H₂O + energy

REVIEW: CONCEPT CHECK 7.1, page 137

1. Define autotroph and heterotroph, and give an example of each.

2. Explain the role of food (glucose) in both photosynthesis and cellular respiration.

3. Explain how life on Earth depends on the sun.

FOOD STORES CHEMICAL ENERGY• Introduction to Energy

• Energy is the ability to do work and work is performed whenever an object is moved against an opposing force.

• Potential and kinetic energy are the two basic forms.

• Kinetic energy is the energy of motion.• Potential energy is stored energy.• Thermal energy is random molecular motion

or the sum of all the kinetic energy of all the particles.

THERMAL ENERGY

FOOD STORES CHEMICAL ENERGY• Chemical Energy

• How do organic compounds in food provide energy for use?

• These organic compounds have a form of potential energy called chemical energy.

• In this case, the potential to perform work is due to the arrangement of the atoms within the molecules.

• Chemical energy depends on the structure of molecules.

• Potential energy is converted to kinetic energy by motion, chemical energy is released to

CHEMICAL ENERGY

KINETIC vs. POTENTIAL ENERGY

FOOD STORES CHEMICAL ENERGY

potential energy after the rearrangement of atoms during chemical reactions.

• This energy is then available for work in the body.

• Putting Chemical Energy to Work• Complex molecules are broken down into

smaller molecules that possess less chemical energy than the original.

• We can compare organic molecules in food to those in gasoline.

FOOD STORES CHEMICAL ENERGY• Gasoline

• gasoline+oxygen→combustion→carbon dioxide+water • The reaction of mixing oxygen with gasoline results in the

breakdown of gasoline releasing thermal energy as heat, which is then used to power the car.

• Only 25% of this potential energy is converted to kinetic energy with the rest lost as heat.

• Food energy• sugar+oxygen→cellular respiration→carbon dioxide+water• The reaction in our cells is slower than in a gas engine.• Our cells are more efficient, converting 40% of the energy from

the food to kinetic energy.• 60% is converted to thermal energy and lost as heat.

FOOD STORES CHEMICAL ENERGY• Not all the heat generated by cellular

respiration is wasted.• It is used to maintain a constant body temperature.

• Calories: Units of Energy• A calorie is the amount of energy required to

raise the temperature of 1 gram (g) of water by 1 degree Celsius (C⁰).

• Since this measure is so small, most scientists use the kilocalorie (kcal) instead.

• Food labels usually show kilocalories and not calories.

ENERGY CONSUMED BY VARIOUS ACTIVITIES

FOOD STORES CHEMICAL ENERGY• Measurement of energy content can be

done in the lab.• Take a peanut, dry it, and burn it under an

insulated layer of water.• The stored chemical energy is converted to

thermal energy, releasing heat.

• The increased temperature of the water is then measured and knowing the definition of a calorie, the total can be calculated.• The peanut has about 5000 calories, or 5 kcal, or

enough chemical energy to raise the temperature of 1 kg (1000 g) of water by 5⁰C.

FOOD STORES CHEMICAL ENERGY• Cells use enzymes to break down organic

molecules by the process of cellular respiration, and the released energy is more manageable for work.


1. Identify the types of energy you have at the top of a staircase and as you go down the stairs.

2. Explain how your body uses chemical energy during exercise.

3. If a food has 10 kcal of energy, how much could it increase the temperature of 100g of water?

ATP PROVIDES ENERGY FOR CELLULAR WORK

• How ATP Packs energy• ATP, as you remember, contains a

nitrogen containing compound called adenine and a five carbon sugar called ribose; and a triphosphate tail of three phosphate groups.

• The phosphate groups are negatively charged and are trying to repel each other.

• This is the potential energy stored in ATP.

ADENOSINE TRIPHOSPHATE

CELL RESPIRATION


• Overall Equation for Cellular Respiration C₆H₁₂O₆ + 6O₂→6CO₂ + 6H₂O + 38 ATP• Cell respiration’s main job is to generate ATP for

cellular work.• “Falling” Electrons as an Energy Source

• Remember a roller coaster with the greatest potential energy at the top and its change to kinetic energy as gravity pulls it down the tracks.

• An atom’s positively charged nucleus exerts a pull on the negatively charged electrons.


• Potential energy is released as the electron “falls” toward the nucleus.

• Oxygen attracts electrons as gravity pull objects downward.

• Carbon and hydrogen exert much less pull on electrons.

• Sugar molecules have carbon-hydrogen bonds which during cellular respiration, the carbon and hydrogen change partners and bond with oxygen.

OXIDATION OF SUGAR


• C-H bonds are replaced by C-O and H-O bonds.

• The energy is released as the electrons of these bonds ‘fall’ toward the oxygen.

• Performing this in the lab is much quicker than in the cells as ATP is made in the cells rather than the heat and light in the lab.

• Electron Transport Chains• Cellular respiration releases energy in small

amounts that are put to good use in the formation of ATP molecules.

ELECTRON TRANSPORT


• Cellular respiration breaks down glucose in several steps.• Oxygen only enters as an electron acceptor in the

final electron transfer.• In the breakdown of glucose, electron carriers

accept the high-energy electrons from the glucose.

• These carriers pass these electrons to other carriers in a series of transfers called an electron transport chain.• Each subsequent carrier holds the electrons more

strongly than those before.


• At the end of the chain, oxygen-the electron grabber-pulls electrons from the final carrier molecule and joins them with hydrogen ions, forming water.

• Each transfer of electrons in the chain releases a little energy.

• The cell traps this released energy to make ATP.


1. Compare and contrast breathing and cellular respiration.

2. List the reactants and products in cellular respiration.

3. What is meant by the “falling” of electrons to oxygen? How does this process release energy?

4. How does an electron transport result in the gradual release of energy stored in glucose?

CELLULAR RESPIRATION CONVERTS ENERGY IN FOOD TO ENERGY IN ATP

• Structure of Mitochondria• These organelles are found in almost all

eukaryotes and their structure is key to its role in cellular respiration.

• Two membranes enclose the mitochondria.• There are many folds of the inner membrane

to increase surface area with a thick fluid contained within called the matrix.

• The enzymes needed to break down the food for energy are contained within the inner membrane.

MITOCHONDRIA

CELL RESPIRATION


• A Road Map for Cellular Respiration• The chemical processes that take place in the cell

make up it’s metabolism.• Cellular respiration is a series of reactions, and,

therefore, is a metabolic pathway.• Enzymes speed up or facilitate each of these

processes.• There are three main stages to cellular

respiration:• Glycolysis• Krebs cycle• Electron transport and ATP synthase

GLYCOLYSIS

GLYCOLYSISGlycolysis is one of the metabolic process for generating ATP from glucose. ATP is the form of energy used by every cell. ATP inhibits the enzyme phosphofructokinase to stop ATP production. The negative feed back loop helps to regulate the amount of ATP produced.


• Stage I: Glycolysis• This is the first step in breaking down a

glucose molecule (means splitting of sugar).• It takes place in the cytoplasm, outside the

mitochondria.• Two ATP molecules are the initial source of

energy, splitting the 6 carbon glucose in half, resulting in 2 three carbon molecules, each with one phosphate group.

• Each of these three carbon molecules transfers electrons and hydrogen ions to a


carrier molecule, NAD⁺.• With the acceptance of the two electrons and one

hydrogen ion converts the NAD⁺ to a compound called NADH.

• The initial energy, 2 ATP molecules, needs to be paid back, and four new ATP molecules are made, netting two additional ATP molecules.

• In summary, the original glucose has been converted to 2 molecules of pyruvic acid, with 2 ATP molecules used initially for energy but resulting in four ATP molecules being produced,

KREBS CYCLE


and the pyruvic acid retaining most of the energy of the original glucose molecule.

• Stage 2: The Krebs Cycle• This stage complete the breakdown of pyruvic

acid molecules to carbon dioxide.• Remember glycolysis takes place outside the

mitochondria with the production of two pyruvic acid molecules.

• The pyruvic acid molecules do not take part in the Krebs cycle, but in the mitochondria, each molecule of pyruvic acid loses a molecule of


carbon dioxide.• What is left is converted to a two carbon

compound called acetyl coenzyme A, or acetyl CoA.

• The acetyl CoA enters the Krebs cycle and joins a four carbon acceptor molecule.

• Two more CO₂ molecules are produced and one ATP molecule per acetyl CoA molecule.

• The NADH with another electron carrier, FADH₂, trap most of the energy.


• At the end of the Krebs cycle, the four carbon acceptor molecule is regenerated and the process continues.

• The Krebs cycle, turning twice for each glucose molecule, produces 4 CO₂ molecules and 2 ATP molecules.

• Stage 3: Electron Transport Chain and ATP Synthase Action• This stage occurs in the inner membranes of the

mitochondria.

ELECTRON TRANSPORT CHAIN

ATP SYNTASE ACTION


• There are two parts: electron transport chain and ATP production by ATP synthase.

• First, NADH transfers electrons from the original glucose molecule to an electron transport chain.

• Remember, electrons move to carriers that attract them more strongly.

• Thus, the electrons move within the inner membrane from carrier to carrier, being pulled to the oxygen at the end of the chain.

• There, the oxygen and electrons combine with hydrogen producing water.


• With each transfer, a small amount of energy is released, which is used to pump H⁺ ions across the membrane from less concentrated to more concentrated.

• With this pumping action, potential energy is stored similar to a dam holding back water.

• In the mitochondria there are protein structures called ATP synthases.• These are similar to the turbines in a dam.

• Hydrogen ions pumped by electrons proceed through the ATP synthase.


• Then the ATP synthase uses the energy from the flow of H⁺ ions to convert ADP to ATP, generating up to 34 ATP molecules per original glucose molecule.

• Adding Up the ATP Molecules• A cell can convert one glucose molecule to as

much as 38 ATP molecules.• Glycolysis = 4 ATP-2 ATP = 2 ATP• Krebs cycle = 2 ATP• ATP synthase = 34 ATP

• After glycolysis, most ATP production requires O₂.

ADDING UP THE ATP MOLECULES


1. How is the mitochondrion’s structure suited to its function?

2. Identify the three steps of cellular respiration, where in the cell each takes place, and how many ATP molecules it produces.

3. Summarize the use and production of ATP in one cycle of cellular respiration.

SOME CELLS CAN HARVEST ENERGY WITHOUT OXYGEN

• Fermentation in Human Muscle Cells• Exercising depletes ATP, so it must be

replenished.• Under normal circumstances, through cellular

respiration, the cells can produce enough ATP.

• Increasing the exercise load requires more oxygen to meet the muscles’ need for ATP.

• Another process is then used called fermentation, that makes ATP without using oxygen.


• ATP and fermentation work together to produce the ATP but the main source when both are working comes from fermentation.

• This process involves glycolysis only.• No oxygen is used.• Glycolysis produces a net gain of 2 ATP

molecules for each molecule of glucose., which is enough for those short bursts of energy required.

• The waste product from fermentation is lactic acid.

GLYCOLYSIS

FERMENTATION


• With the temporary buildup of lactic acid in the muscles, one feels fatigue or cramping.

• Oxygen is consumed by the body as the lactic acid is converted back to pyruvic acid.

• The heavy breathing after these short bursts of speed or exercise restores the oxygen supply.

• Fermentation in Microorganisms• Yeast, a microscopic fungus, is capable of

both cellular respiration and fermentation.• If they are kept in an anaerobic environment,

FERMENTATION


they will ferment sugar and other foods, producing alcohol and not lactic acid.

• This is alcoholic fermentation, and CO₂ is released.• The CO₂ produces the bubbles in beer and champagne,

and makes bread rise.• Some fungi and bacteria do produce lactic acid

during fermentation, and these are used to make cheese and yogurt from milk, soy sauce from soy beans, and sauerkraut from cabbage.


1. How is fermentation different from cellular respiration?

2. Describe one example of how fermentation in microorganisms produces human food.

3. What is the waste product of fermentation in your muscle cells?

the working cell energy from food. sunlight powers life obtaining food all organisms require food...

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