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Cellular Respiration and Photosynthesis

 – Important Concepts, Common Misconceptions, and Learning Activities1

Sections I and II present important concepts and common misconceptions. Section III

recommends activities for learning these concepts and overcoming common misconceptions.

These recommended learning activities are aligned with the Next Generation Science Standards 2,as summarized in the tale provided at

http!""serendip.r#nmawr.edu"exchange"ioactivities"NGSS and descried in more detail in the

Teacher Notes for these activities.

I. Energy, ATP and Cellular Respiration

$. %hat is energy&

'nerg# is a difficult concept to define. 'nerg# can e thought of as a propert# or characteristic of 

things that can ma(e something happen )http!""www.ftexploring.com"energ#"definition.html*http!""www.nmsea.org"+urriculum"rimer"energ#-ph#sics-primer.htm. $lthough this definition

is unsatisfactoril# vague, energ# is nevertheless a valuale concept ecause of the important

 principles related to energ# which help us predict and understand multiple scientific and real/world phenomena. These important principles include!

• 'nerg# can e transformed from one t#pe to another )e.g. chemical energ# stored in $T can

 e converted to (inetic energ# of muscle contraction.

• 0owever, energ# is not created or destro#ed )in iological processes. In other words, energ#

lasts forever. This conservation of energ# principle is the irst aw of Thermod#namics.

• 'ver# energ# transformation is inefficient* i.e. some of the energ# is converted to heat. This

 principle is one implication of the Second aw of Thermod#namics.

To help students understand the concept of energ#, it is useful to introduce them to differentt#pes of energ#, including!

• light energ#

• chemical energ# stored in the onds of molecules such as glucose or $T

• (inetic energ#, e.g. the energ# of a moving leg or cell

• heat 3 the (inetic energ# in the random motion of molecules or other microscopic

 particles.

If energ# is never destro#ed, wh# do we 4run out of energ#4 at the end of a race&

• This 5uestion reflects one of the man# wa#s that the word 4energ#4 is used loosel# rather

than in the strict scientific sense of conservation of energ#. %hen a person runs a race, thetotal amount of energ# remains constant if #ou ta(e into account not onl# the decrease in

chemical energ# stored in molecules in the person6s od#, ut also the increases in heat

energ# that result from the energ# transformations re5uired for running.

• $s our odies use chemical energ# for ph#sical activit# and for necessar# cellular

 processes, we need to replace the molecules that provide chemical energ#. $lso, our

1 7# 8r. Ingrid %aldron, 9niversit# of enns#lvania, : 2;1<. These Teacher Notes and multiple activities for teaching iolog#

are availale at http!""serendip.r#nmawr.edu"exchange"ioactivities"cellrespiration 2 $vailale at http!""www.nextgenscience.org"next/generation/science/standards

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 odies need to dispose of accumulated metaolites and waste products and repair micro/

damage )e.g. to muscles. These changes are ma=or reasons for the su=ective experience

of 4running out of energ#4.

7. The Importance of ATP

8ifferent t#pes of organisms get their energ# input from different sources )e.g. food, sunlight,

 ut all organisms use a two/step process to provide the energ# needed for most of their iological

 processes.

• irst, chemical energ# from organic molecules li(e glucose is transferred to $T

molecules in a process called cellular respiration.

• Then, $T provides the energ# for most iological processes.

>ur cells are constantl# using energ# from organic molecules li(e glucose to ma(e $T and

using the $T molecules to provide the energ# for iological processes )e.g. muscle contraction,s#nthesizing molecules, and pumping ions and molecules into and out of cells. >n average,

each $T molecule in our od# is used and re/s#nthesized more than ?; times per minute when

we are at rest and more than <;; times per minute during strenuous exercise.

+. 0ow does the structure of ATP relate to the function of $T&

$T )adenosine triphosphate has three negativel# charged phosphates. %hen $T rea(s downto $8 )adenosine diphosphate and a phosphate, negativel# charged phosphates are separated

and energ# is released. This energ# is used for cellular processes such as s#nthesizing organic

molecules, pumping ions across the cell memrane, and muscle contraction.

2

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)adapted from @rogh, 7iolog# // $ Guide to the Natural %orld, ifth 'dition

$T is produced # the chemical reaction, $8 A i → $T. 'nerg# is re5uired to add a

negativel# charged phosphate to the two negativel# charged phosphates in $8. The

following pages explain how cellular respiration of organic molecules li(e glucose provides

the energ# needed to produce $T.

8. Cellular Respiration is the ma=or process that transfers some of the chemical energ# in

sugars, fats, or amino acids to chemical energ# in $T, so energ# is availale in a form that is

useful for iological processes. The following pair of chemical e5uations gives a simplifiedoverview of the cellular respiration of glucose!

  +B 012>B A B >2 B +>2 AB 02>C"

  C" D2E $8 A D2E i D2E $T

+ellular respiration consists of a series of multistep processes, as shown in the figure elow.

?

  represents a chemical

reaction 

\/ represents energ# transfer etween

 \/  coupled reactions

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)rom Scott reeman, 7iological Science , ourth 'dition, 2;11

Fecent evidence indicates that in aeroic cellular respiration D2E molecules of $T are produced per molecule of glucose. This is fewer than previousl# elieved and still stated in man#

textoo(s. This revised estimate is ased on newl# discovered complexities and inefficiencies inthe function of the electron transport chain and $T s#nthase enz#me )4$pproximate ield of $T

from Glucose, 8esigned # 8onald Nicholson4 # 7rand, 2;;?, 7iochemistr# and Holecular 7iolog#

'ducation ?1!2/, http!""www.amed.org. $lso, the numer of $T produced per molecule ofglucose is variale ecause of variailit# in the efficienc# of the electron transport chain proton

 pumps and the $T s#nthase. These recent findings are interesting as an example of how

scientific understanding is su=ect to revision ased on ongoing research* science progresses #successive improvements in our understanding and (nowledge.

It should also e mentioned that!• >nl# aout ?;J the energ# released from glucose # cellular respiration is captured in

$T* some of the energ# is converted to heat.

• Input molecules for cellular respiration include not onl# glucose, ut also gl#cerol, fatt#

acids and amino acids.Some additional information is provided in the Teacher Notes for 40ow do iological organisms

use energ#&4 )http!""serendip.r#nmawr.edu"exchange"ioactivities"energ# .

'. $eroic cellular respiration re5uires >2 as an electron acceptor at the end of the electrontransport chain. %hen >2 is not availale, cells use a different process to ma(e $T! gl#col#sis

followed # fermentation This figure illustrates the process of alcoholic fermentation in #east

cells.• 8uring alcoholic fermentation, the sugar glucose is ro(en down to smaller molecules,

resulting in the production of caron dioxide )+>2 and the alcohol ethanol.

• $s the glucose molecule is ro(en down, some of the energ# stored in its chemical onds

is released and provides the energ# to convert 2 $8 A i to 2 $T.

• The last step in alcoholic fermentation restores N$8 to its original form so the process

can continue.

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Glucose

)http!""classconnection.s?.amazonaws.com"<K?"flashcards"L<11?<"=pg"alcohol/fermentation.=pg

This figure shows lactic acid fermentation which occurs in mammalian muscle.

)http!""test.classconnection.s?.amazonaws.com"<2E"flashcards"L<<2E"=pg"lactic/acid/fermentation.=pg

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. ATP supplies energy for many !iological processes via coupled reactions in which the first

reaction provides the energ# re5uired for the second reaction, e.g.!

Huscle +ontraction!

  man# $T man# $8 A man# phosphateC"

  energyC" 

muscle relaxed muscle contracted 

rotein S#nthesis!

  $T $8 A phosphate 

C"

  energyC" 

 pol#peptide with n amino acids pol#peptide with n A1 amino acids

G. To use energ# from food!• arge organic food molecules such as starch and trigl#cerides are digested to small

organic molecules such as glucose and fatt# acids that can e asored from the gut,travel in the lood and enter cells to serve as input for cellular respiration.

• +ellular respiration transfers energ# in organic molecules such as glucose to energ# in

$T.

• Then, $T is used to provide energ# for cellular processes.

+ommon Hisconception! ood 3 calories 3 energ#

ood, calories and energ# are related, ut not e5uivalent concepts. ood contains organic

molecules which have chemical energ# stored in the onds etween atoms. There are man#

other t#pes of energ#, including the (inetic energ# of moving muscles and heat )the (ineticenerg# in the random motion of atoms and molecules. In addition to energ#, food provides

atoms and molecules needed for growth and repair of our odies. $ calorie is a unit of measureof energ#. These concepts are discussed in the activit# 4ood, 'nerg# and 7od# %eight4

)descried in section III.

B

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II. Photosynthesishotos#nthesis converts light energ# to stored chemical energ#. Specificall#, photos#nthesis uses

the sun6s energ#, caron dioxide and water to produce sugar molecules with high stored chemical

energ# and ox#gen.

  sunlightB +>2 A B 02> B >2 A +B 012>B 

hotos#nthesis consists of a series of multistep processes, as summarized in the figure elow.

Summar# of hotos#nthesis in the +hloroplasts of lant +ells)rom @rogh, 7iolog# // a Guide to the Natural %orld, ifth 'dition

• hotos#nthesis egins with light reactions which convert the energ# in sunlight to

chemical energ# in $T and N$80.

• In the second stage of photos#nthesis, (nown as the +alvin c#cle, $T and N$80

 provide the energ# and 0 needed to convert +>2 to a ?/caron molecule which is

converted to glucose and fructose.

• Glucose and fructose can e converted to sucrose which moves throughout the plant and

 provides input molecules for cellular respiration. Glucose can also e used to produce

starch )a storage molecule and cellulose )a ma=or structural molecule in plants and

 provides raw materials for producing lipids and amino acids.

+ommon Hisconceptions!

/ Students often do not understand that most of a plantMs iomass comes from +>2. Thismisconception can e addressed with the learning activit# 4%here does a plant6s mass come

from&4 )descried in the next section.

/ Han# students elieve that onl# animals carr# out cellular respiration and plants onl# carr# out photos#nthesis* the# do not understand that plants also need to carr# out cellular respiration to

 provide $T for cellular processes. This misconception can e addressed with the 5uestion,

L

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4+ells in plant leaves have oth chloroplasts and mitochondria. If plants can carr# out

 photos#nthesis, wh# do plant cells need mitochondria&4

and"or with the learning activit# 4lant Growth uzzle4 )descried in the next section.

III. Learning Activities?

$. Se5uence for learning "asic Concepts

0ow do iological organisms use energ#&

This anal#sis and discussion activit# helps students understand the asic principles of how iological organisms use energ#, with a focus on the roles of $T and cellular respiration. In

addition, students appl# the principles of conservation of energ# and conservation of matter to

avoid common errors and correct common misconceptions. Student 0andout and Teacher Notesare availale at

http!""serendip.r#nmawr.edu"exchange"ioactivities"energ# .

9sing Hodels to 9nderstand hotos#nthesisIn this anal#sis and discussion activit#, students develop their understanding of the asic process

of photos#nthesis and also anal#ze the advantages and disadvantages of different t#pes of models

of photos#nthesis, including chemical e5uations, a chart and a diagram. In addition, studentsanal#ze how photos#nthesis and cellular respiration wor( together to provide the $T that plants

need to carr# out their molecular and cellular processes. Student 0andout and Teacher Notes are

availale at http!""serendip.r#nmawr.edu"exchange"ioactivities"modelphoto

hotos#nthesis Investigation

In the first section of this activit#, students learn how to use the floating leaf dis( method to

measure the rate of net photos#nthesis )i.e. the rate of photos#nthesis minus the rate of cellularrespiration. The# compare the rate of net photos#nthesis in water vs. a solution of sodium

 icaronate. The 5uestions in this section guide students in reviewing the relevant iolog# and

interpreting their results. In the second section of this activit#, student groups develop h#pothesesaout factors that influence the rate of net photos#nthesis, and then each student group designs

and carries out an investigation to test the effects of one of these factors. Student 0andout and

Teacher reparation Notes are availale at

http!""serendip.r#nmawr.edu"sci-edu"waldron"photos#nthesis

$lcoholic ermentation in east

This multi/part minds/on, hands/on activit# helps students to understand oth alcoholicfermentation and the engineering design process. In the first part of this activit#, students learn

aout the process of alcoholic fermentation and test for alcoholic fermentation # assessing +>2 

 production # live #east cells in sugar water vs. two controls. In the ioengineering design

challenge, students wor( to find the optimum sucrose concentration and temperature tomaximize rapid +>2 production, using no more sucrose than needed for maximum +>2 

 production. Structured 5uestions guide the students through the asic engineering steps ofappl#ing the relevant scientific ac(ground, developing and s#stematicall# testing proposed

design solutions, and then using initial results to develop and test improved design solutions.

Student 0andout and Teacher reparation Notes are availale at 

http!""serendip.r#nmawr.edu"sci-edu"waldron"fermentation 

? The learning activities in sections $ and 7 are aligned with the Next Generation Science Standards

)http!""www.nextgenscience.org"next/generation/science/standards.

K

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0ow do muscles get the energ# the# need for athletic activit#&In this anal#sis and discussion activit#, students learn aout the similarities and differences

 etween aeroic cellular respiration and anaeroic fermentation and learn how these processes

contriute to $T production in muscle cells during different t#pes of athletic activit#. Inaddition, students gain understanding of general principles such as the conservation of energ#

and conservation of matter, the constant d#namic activit# in cells, and the importance of

interactions etween od# s#stems to accomplish functions such as suppl#ing the energ# thatmuscles need for ph#sical activit#. Student 0andout and Teacher Notes are availale at

http!""serendip.r#nmawr.edu"exchange"ioactivities"energ#athlete

7. $ctivities to $ddress Common Misconceptions

ood, 'nerg# and 7od# %eight

This anal#sis and discussion activit# reinforces understanding of cellular respiration and helpsstudents to understand the relationships etween food, energ#, ph#sical activit#, and changes in

 od# weight. Student 0andout and Teacher Notes are availale at http!""serendip.r#nmawr.edu"exchange"ioactivities"foodenerg# 

%here does a plant6s mass come from&

This anal#sis and discussion activit# help students to understand that a large part of a plantMs

mass consists of water, most of the iomass comes from caron dioxide, and minerals from thesoil contriute onl# a tin# amount of the plantMs mass. This activit# engages students in

anal#zing and interpreting data and arguing from evidence. Student 0andout and Teacher Notes

are availale at http!""serendip.r#nmawr.edu"exchange"ioactivities"plantmass 

lant Growth uzzle

This anal#sis and discussion activit# presents a structured se5uence of 5uestions to challenge

students to explain wh# a plant that sprouts and grows in the light has a greater iomass than theseed it came from, whereas a plant that sprouts and grows in the dar( has less iomass than the

seed it came from. Student 0andout and Teacher Notes are availale at 

http!""serendip.r#nmawr.edu"exchange"ioactivities"plantgrowth

+. Additional Activities and Resource

hotos#nthesis and +ellular Fespiration

Students use puzzle pieces which represent the components of the chemical e5uations for oth

 photos#nthesis and aeroic cellular respiration and answer 5uestions aout these processes.Student 0andout is availale at

http!""serendip.r#nmawr.edu"exchange"ioactivities"photocellrespir  .

8etailed, clear animations of gl#col#sis, @res citric acid c#cle, mitochondria"electron transport,

and photos#nthesis light and dar( reactions are availale at http!""www.=ohn(#r(.com" .

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