chapter 5 pp-new

8/3/2019 Chapter 5 Pp-new..

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CHAPTER 5

Synthesis and Respiration

(Energy Transformation

Prepared by: Marina L. Dato


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A. Photosynthesis

-is the process by which plants, some bacteria,

and some protistans use the energy from

sunlight to produce sugar, which cellular

respiration converts into ATP (Adenosine

triphosphate), the "fuel" used by all living

things.


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We can write the overallreaction of this process as:

6H2O + 6CO2 ---------->C6H12O6+ 6O2

Most of us don't speakchemicalese, so the abovechemical equationtranslates as:

six molecules of water plussix molecules of carbondioxide produce onemolecule of sugar plus sixmolecules of oxygen


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Leaves and Leaf Structure

Plants are the only photosynthetic organisms

to have leaves (and not all plants have leaves).

A leaf may be viewed as a solar collectorcrammed full of photosynthetic cells.

The raw materials of photosynthesis which

enter the cells of the leaf are:- water

-carbon dioxide


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The products of photosynthesis which leave the leaf are:

-sugar

-oxygen

Cross section of a leaf, showing the anatomical featuresimportant to the study of photosynthesis: stoma, guardcell, mesophyll cells, and vein.

Xylem Water enters the root and is transported up to theleaves through specialized plant cells

Stomata- Land plants must guard against drying out(desiccation) and so have evolved specialized structures toallow gas to enter and leave the leaf.


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Carbon dioxide cannot pass through theprotective waxy layer covering the leaf (cuticle),but it can enter the leaf through an opening (the

stoma; plural = stomata; Greek for hole) flankedby two guard cells. Likewise, oxygen producedduring photosynthesis can only pass out of theleaf through the opened stomata. Unfortunately

for the plant, while these gases are movingbetween the inside and outside of the leaf, agreat deal water is also lost.


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B. Autotrophs and HeterotropsOverview of cycle between autotrophs and

heterotrophs. Photosynthesis is the main meansby which plants, algae and many bacteria produceorganic compounds and oxygen from carbondioxide and water (green arrow).

Autotrophs An autotroph,(self-feeding) or producer, is an

organism that produces complex organiccompounds such as:

a. Carbohydrates

b. fats

c. Proteins

-from simple inorganic molecules using energy from light(by photosynthesis) or

-inorganic chemical reactions (chemosynthesis).

They are the producers in a food chain, such as:

*plants on land or

*algae in water. They are able to make their own foodand can fix carbon. Therefore, they do not use organiccompounds as an energy source or a carbon source.

Autotrophs can reduce carbon dioxide (addhydrogen to it) to make organic compounds. Thereduction of carbon dioxide, a low-energycompound, creates a store of chemical energy.

Most autotrophs use water as the reducing agent,but some can use other hydrogen compounds suchas hydrogen sulfide.


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An autotroph converts

physical energy from sun

light (in case of green

plants) into chemical energy

in the form of reduced

carbon.

Autotrophs can be:

*phototrophs or

*lithotrophs

(chemoautotrophs).

Phototrophs use light

as an energy source

lithotrophs oxidize

inorganic compounds,

such as:

- hydrogen sulfide

- elemental sulfur- ammonium

- ferrous iron


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Phototrophs and lithotrophs use a portion of

the ATP (Adenosine triphosphate) producedduring photosynthesis or the oxidation of

inorganic compounds to reduce NADP+

(

Nicotinamide adenine dinucleotidephosphate) to NADPH (nicotinamide

adenine dinucleotide phosphate-oxidase) in

order to form organic compounds


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Heterotroph

is an organism that cannot fix carbon and uses organic carbon forgrowth.This contrasts with autotrophs, such as plants and algae,which can use energy from sunlight (photoautotrophs) or inorganiccompounds (lithoautotrophs)

to produce organic compounds from inorganic carbon dioxide such

as:

-carbohydrates

-fats

-proteins.

These reduced carbon compounds can be used as an energy

source by the autotroph and provide the energy in food

consumed by heterotrophs.


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Heterotrophs can be divided into two broad

classes:

1. photoheterotrophs2.chemoheterotrophs


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Photoheterotrophs, including most purple bacteriaand green bacteria, produce ATP from light and useorganic compounds to build structures. They consumelittle or none of the energy produced during

photosynthesis to reduce NADP+ to NADPH for use inthe Calvin cycle, as they do not need to use the Calvincycle if carbohydrates are available in their diets.

Chemoheterotrophs produce ATP (Adenosinetriphosphate) by oxidizing chemical substances.

There are two types of chemoheterotrophs:

a. chemoorganoheterotrophs

b. chemolithoheterotrophs


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a. Chemoorganoheterotrophs (or simply organotrophs)

-exploit reduced carbon compounds as energy sources, such ascarbohydrates, fats, and proteins from plants and animals.

b. Chemolithoheterotrophs (or lithotrophic heterotrophs) such ascolorless sulfur bacteria (e.g., Beggiatoa and Thiobacillus) and sulfate-reducing bacteria utilize inorganic substances to produce ATP, includinghydrogen sulfide, elemental sulfur, thiosulfate, and molecularhydrogen.

-They use organic compounds to build structures. They do not fix

carbon dioxide and apparently do not have the Calvin cycle.-Chemolithoheterotrophs can be distinguished from mixotrophs (orfacultative chemolithotroph), which can utilize either carbon dioxide ororganic carbon as the carbon source.


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Heterotrophs, by consuming reduced carboncompounds, are able to use all the energy thatthey obtain from food for growth and

reproduction, unlike autotrophs, which must usesome of their energy for carbon fixation.

Heterotrophs are unable to make their own food,however, and whether using organic or inorganic

energy sources, they can die from a lack of food.This applies not only to animals and fungi butalso to bacteria


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The differences between autotrophs and

heterotrophs in the ecosystem?

The autotrophs have the ability to manufacture their own

food from the inorganic raw materials. They extract them

from the outside source. They reside on the inorganic medium

and require an external source of energy. They are known as

producers and include the plants mainly.

The heterotrophs do not have the ability to manufacture

their own food from the inorganic raw materials. They extract

the organic nutrients from the outside source. They reside

seldom on the organic medium and do not require an external

source of energy. They are known as consumers and include

the animals mainly.


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C. Light Reaction and dark Reaction

1. Light Reaction

- In the Light Dependent Processes (Light Reactions) light strikes chlorophyllin such a way as to excite electrons to a higher energy state. In a series ofreactions the energy is converted (along an electron transport process)into ATP and NADPH.

- Water is split in the process, releasing oxygen as a by-product of thereaction. The ATP (Adenosine triphosphate) and NADPH are used to makeC-C bonds in the Light Independent Process (Dark Reactions).

- In the Light Independent Process, carbon dioxide from the atmosphere (orwater for aquatic/marine organisms) is captured and modified by theaddition of Hydrogen to form carbohydrates (general formula ofcarbohydrates is [CH2O]n). The incorporation of carbon dioxide into organic

compounds is known as carbon fixation. The energy for this comes fromthe first phase of the photosynthetic process.

- Living systems cannot directly utilize light energy, but can, through acomplicated series of reactions, convert it into C-C bond energy that canbe released by glycolysis and other metabolic processes.


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2. Dark Reaction

- Carbon-Fixing Reactions are also known as the DarkReactions (or Light Independent Reactions).

- Carbon dioxide enters single-celled and aquatic autotrophsthrough no specialized structures, diffusing into the cells.

- Land plants must guard against drying out (desiccation) andso have evolved specialized structures known as stomata toallow gas to enter and leave the leaf.

- The Calvin Cycle occurs in the stroma of chloroplasts

- Carbon dioxide is captured by the chemical ribulosebiphosphate (RuBP). RuBP is a 5-C chemical. Six molecules ofcarbon dioxide enter the Calvin Cycle, eventually producingone molecule of glucose.


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What Is the Difference between Light and Dark

Reaction?

These refer to Photosynthesis.

Light reaction converts the sunlight into

chemical energy such as ATP and NADH+H.While dark reaction (light independent

reaction) does not use the sunlight directly

but it uses the ATP and NADH+H and C02 to

produce sugars


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D. Cellular Perspiration

Glycolysis literally means "splitting sugars."

In glycolysis, glucose (a six carbon sugar) is

split into two molecules of a three-carbonsugar.

Glycolysis yields two molecules of ATP (free

energy containing molecule), two molecules

of pyruvic acid and two "high energy" electron

carrying molecules of NADH.


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1: Glycolysis

it can occur with or without oxygen. In the

presence of oxygen, glycolysis is the first stage

of cellular respiration. Without oxygen,

glycolysis allows cells to make small amounts

of ATP. This process is called fermentation.


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2: Krebs Cycle The Citric Acid Cycle or Krebs Cycle begins after the two

molecules of the three carbon sugar produced in glycolysis areconverted to a slightly different compound (acetyl CoA).

Through a series of intermediate steps, several compoundscapable of storing "high energy" electrons are produced alongwith two ATP molecules.

These compounds, known as nicotinamide adeninedinucleotide (NAD) and flavin adenine dinucleotide (FAD), arereduced in the process.

These reduced forms carry the "high energy" electrons to thenext stage. The Citric Acid Cycle occurs only when oxygen ispresent but it doesn't use oxygen directly.


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3: The Electron Transport System

Embedded in the inner membrane areproteins and complexes of molecules

that are involved in the process called

electron transport. The electrontransport system (ETS), as it is called,

accepts energy from carriers in the

matrix and stores it to a form that can beused to phosphorylate ADP.


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The electron transport system occurs in the cristae of

the mitochondria, where a series of cytochromes(cell pigments) and coenzymes exist.

These cytochromes and coenzymes act as carrier

molecules and transfer molecules. They accept high-

energy electrons and pass the electrons to the next

molecule in the system.

At key proton-pumping sites, the energy of the

electrons transports protons across the membraneinto the outer compartment of the mitochondrion.


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Each NADH molecule is highly energetic, which accounts for

the transfer of six protons into the outer compartment of themitochondrion. Each FADH2 molecule accounts for the

transfer of four protons.

The flow of electrons is similar to that taking place in

photosynthesis.

Electrons pass from NAD to FAD, to other cytochromes and

coenzymes, and eventually they lose much of their energy.

In cellular respiration, the final electron acceptor is an oxygen

atom. In their energy-depleted condition, the electrons unite

with an oxygen atom. The electronoxygen combination thenreacts with two hydrogen ions (protons) to form a water

molecule (H2O)


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- the role of oxygen in cellular respiration is

substantial.

- As a final electron receptor, it is responsible for

removing electrons from the system. If oxygen

were not available, electrons could not be passed

among the coenzymes, the energy in electrons

could not be released, the proton pump could not

be established, and ATP could not be produced.

- In humans, breathing is the essential process that

brings oxygen into the body for delivery to the

cells to participate in cellular respiration.


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E. Respiration of different molecules

The term cellular respiration refers to thebiochemical pathway by which cells release energy

from the chemical bonds of food molecules and

provide that energy for the essential processes of

life.

All living cells must carry out cellular respiration.

It can be aerobic respiration in the presence of

oxygen or anaerobic respiration.

Prokaryotic cells carry out cellular respiration within

the cytoplasm or on the inner surfaces of the cells.


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More emphasis here will be placed on

eukaryotic cells where the mitochondria are

the site of most of the reactions. The energy

currency of these cells is ATP, and one way to

view the outcome of cellular respiration is as a

production process for ATP.


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F. The Mitochondrion as a site of

respiration

mitochondria are the sites of respiration,

and generate chemical energy in theform of ATP by metabolizing sugars, fats,

and other chemical fuels with the

assistance of molecular oxygen.


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G. Aerobic respiration

is a process of cellular respiration that uses oxygen in order to break downmolecules, which then release electrons and creating energy.

In the process, aerobic respiration creates a substance known asadenosine triphosphate (ATP). This is responsible for storing and carryingmost of the energy to other body cells, thus making life as we know it

possible. The other type of cellular respiration is known as anaerobic respiration.

When an animal eats food or when a plant makes its own energy throughphotosynthesis, that food is broken down into its most basic form ofsugars. Those sugars are useless to the body in that form, however.Therefore, a process of releasing the sugars contained in the food isneeded in order to be used as energy by a cell. While oxygen may not beneeded at the beginning of this process, in aerobic respiration it will beneeded so that the process can be completed.


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There are two main byproducts of aerobic

respiration. Because cellular structures are

being changed with the transfer of electrons,

there are chemical changes that go along with

cellular respiration.

The two main products coming from such

respiration are water and carbon dioxide.

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