Download Unit 4: Cellular Energy Study Guide

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Unit 4: Cellular Energy Study Guide
Brief Overview of Unit
ATP
ATP stands for adenosine triphosphate.
ATP is a high energy molecule composed of a ribose sugar, an
adenine base, and three high energy phosphate groups.
The energy in ATP is found in the bonds that connect each
phosphate. Energy is released when a phosphate is broken off.
ATP – 1 phosphate = ADP (adenosine diphosphate)
ADP – 1 phosphate = AMP (adenosine monophosphate)
(Most Energy)
ATP …………ADP…………AMP (Least Energy)
ATP is the energy currency of the cell. Cell’s use ATP to carry out all biological process, such
as breathing, movement, talking, etc…
Photosynthesis
Introduction
Photosynthesis is a process by which plants, green algae, cyanobacteria, and some protists use to convert sunlight into
chemical energy.
For this biology class we will focus on plant photosynthesis only.
6CO2 + 6H2O + sunlight  C6H12O6 + O2
(memorize this formula)
carbon dioxide + water + sunlight  sugar + oxygen
Cross –Section of a Leaf
Photosynthesis mainly occurs in the leaves of plants inside
the mesophyll cells inside of a leaf, in an organelle called the
chloroplast. Inside the chloroplast is a special pigment called
chlorophyll. Pigments absorb light.
Chlorophyll is capable of
absorbing red, violet, and
blue. Chlorophyll,
however, cannot absorb
green! Whatever is not
absorbed will be reflected.
This is why plants are
mainly green because
green is reflected onto your eyes.
There are two reactions that occur during photosynthesis:
light-dependent reaction and light-independent reaction.
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The light-dependent reaction of photosynthesis occurs within the chloroplast in disk-like structures called thylakoids.
The light-independent reaction of photosynthesis (sometimes called the dark reaction) occurs within the chloroplast’s
jelly-like substance called the stroma.
The general concept of photosynthesis begins in the thylakoids.
Light-dependent
Light-independent
(Light-dependent reaction)
*Water and light enter the thylakoids. The light splits the water into
oxygen gas, which is released as a byproduct, and ATP & NADPH are
formed.
The second part of photosynthesis will now continue in the stroma
(Light-independent reaction)
*The ATP and NADPH made in the light-dependent reaction are used
in conjunction with carbon dioxide to power the Calvin cycle.
* Once the Calvin cycle is powered, sugars are made. Since the energy
in ATP and NADPH has been used, these molecules are recycled as
ADP and NADP+.
Do not confuse the words stroma and stoma
The Light-dependent Reaction: Photoysystem II and Photosystem I
The light-dependent reaction occurs in the thylakoids of the chloroplast and is made possible by a machinery of pigments
and proteins called photosystem II and photosystem I. Notice that photosystem II occurs first.
The products of the light-dependent reaction are oxygen, ATP, and NADPH.
PS II
Light and water enter the thylakoids within the photosystem II machinery. The light is absorbed by a special chlorophyll
pigment which absorbs light at 680 nanometers. We call this pigment P680.
The light splits the water, which causes the release of oxygen. This process also produces hydrogen ions (H+ ions) and
high energy electrons.
The high energy electrons are then passed down an electron transport
chain to produce energy in the form of ATP. As electrons pass down the
electron transport chain, hydrogen ions are pulled into the thylakoids
space. The high concentration of H+ ions are then forced out of an
enzyme called ATP synthase. When H+ ions pass through the ATP
synthase, energy is formed by combining a phosphate group to ADP to
produce ATP. This process of going from ADP to ATP with the help of
light is called photophosphorylation.
PS I
By the time the electrons from photosystem II reach photosystem I, they have very little energy. A second light source
must re-charge these electrons when they reach photosystem I. The pigment that absorbs light in photosystem I is called
P700 because it absorbs light at 700 nanometers.
The electrons are now energized and ready to pass a second and shorter electron transport chain. The electrons are picked
up by NADP+ in the stroma, along with H+. This produces the final product of the light-dependent reaction, NADPH.
Please LOOK at the picture below and try to see what is happening as you read the information above
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The Light-independent Reaction: The Calvin cycle
The light-independent reaction is sometimes called the dark reaction or the
Calvin cycle. We do not call it the dark reaction anymore because it is
misleading. It does not need to be dark for it to happen.
During the light-independent reaction, ATP, NADPH, and carbon dioxide are
used to make high-energy sugars.
The Calvin cycle: C3 Pathway
Carbon dioxide enters the Calvin cycle and mixes with a sugar called
Ribulose Bisphosphate (RuBP). This occurs because of the enzyme
Bisphosphate Carboxylase).
The first organic compound to be formed in the Calvin cycle is
3 carbon molecule.
PGA is then energized by ATP and NADPH to produce a higherenergy molecular state called PGAL or G3P.
Since G3P is the first product made, and it contains 3 carbons,
this form of photosynthesis is called the C3 pathway. Many
plants undergo the C3 pathway.
Notice that glucose is NOT the first sugar made. The first
sugar made is G3P, which is later turned into a variety of
as glucose, sucrose, etc.
Photorespiration
Plants close their stomata when it is too hot in order to conserve water. Therefore,
is not able to enter the plant, and the oxygen made is stuck in the plant. This is not good news.
RuBisCo (Ribulose
PGA, a
sugars, such
carbon dioxide
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At this point, the plant’s enzyme, RuBisCo, will bind to the oxygen. This method does
not produce any energy at all (it actually wastes energy).
No sugars are produced either.
In summary, photorespiration is bad for plants. It takes their energy and does not really
do anything good for plants.
Evolutionarily speaking, some plants have adapted ways to deal with intense light, high
temperatures, and low carbon dioxide levels.
C4 Pathway
The C4 pathway occurs in plants that are under intense light, high temperatures, and
low carbon dioxide.
The C4 pathway requires extra energy in the form of ATP, and it is common in
corn, sugarcane, and sorghum.
The C4 pathway uses two cells to perform photosynthesis: Mesophyll cell and
Bundle-sheath cell.
Carbon dioxide and PEP combine thanks to the enzyme PEP carboxylase to
form a 4 carbon molecule called Oxaloacetate. The Oxaloacetate is later
converted to another 4 carbon molecule called Malate. This all happens in the
Mesophyll cell. Because Malate is a 4 carbon molecule, we call this the C4
pathway.
The Malate is then transferred to the bundle-sheath cell where it is broken
down into carbon dioxide and pyruvate. The carbon dioxide is used to power
the Calvin cycle while pyruvate is recycled back to the Mesophyll cell to later
be turned back into PEP.
Crassulacean Acid Metabolism (CAM) Photosynthesis
CAM plants are similar to C4 plants because they are adapted to very hot and
dry environments.
Examples of CAM plants include pineapple trees and many desert cacti.
CAM plants allow air to go in only at night when they open their stomata. At
night, carbon dioxide is combined with organic acids and stored in the plant.
During the day when the stomata are closed, these acids release the carbon
dioxide into the Calvin cycle to produce carbohydrates.
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Cellular Respiration
Introduction
All organisms get energy from food. The energy in food is expressed in a unit called the calorie.
Cellular respiration is the process by which energy is released from food in the presence of oxygen.
C6H12O6 + O2  6CO2 + 6H2O + ATP
(memorize this formula)
sugar + oxygen  carbon dioxide + water + energy
Notice that the formula for cellular respiration is the same as photosynthesis but backwards. Also notice that the energy in
photosynthesis is solar while in cellular respiration it is chemical energy.
Cellular respiration can occur aerobically (with oxygen) or anaerobically (without oxygen).
The process of glycolysis is always first and is present in aerobic and anaerobic respiration.
Glycolysis
No
OXYGEN
OXYGEN
Fermentation
Krebs cycle (citric acid cycle)
Lactic Acid
Fermentation
Alcoholic
Fermentation
Electron Transport chain
&
Oxidative phosphorylation
Aerobic Respiration (with oxygen)
If oxygen is present, cellular respiration will begin with glycolysis, form an intermediate called acetyl CoA, enter the
Krebs cycle, and finish with the electron transport chain and oxidative phosphorylation.
Technically speaking, glycolysis does not need oxygen to function, so it is anaerobic. Memorize this. It is usually asked
on all tests.
Glycolysis occurs in the cytoplasm of cells where 1 molecule of glucose is broken down into pyruvic acid (aka
pyruvate), ATP, and NADH.
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Notice that in photosynthesis we dealt with NADPH and NADP+, but in cellular respiration we deal with NADH and
NAD+.
After glycolysis, the pyruvic acid is converted into acetyl CoA, which then enters the Krebs cycle.
The Krebs cycle takes place in
the matrix of the mitochondria
of eukaryotic cells.
Acetyl CoA mixes with
Oxaloacetate to produce citric
acid (aka citrate). Since citric
acid is the first product, we
also call the Krebs cycle the
citric acid cycle.
The Krebs cycle produces
very little energy, some carbon
dioxide (which you breathe
out), and a lot of electron
carriers
(NADH, FADH2) which will later be used to make a lot of energy.
The electron carries NADH and FADH2 are ready to dump
their electrons onto the inner membrane of the mitochondria called the cristae.
This is where the electron transport chain is found.
The electrons that are dumped on the electron transport chain are passed on
from protein to protein. As this is happening, the intermembrane space of the
mitochondria becomes filled with hydrogen ions. These hydrogen ions are
then forced to go back
into the matrix through the enzyme ATP synthase. Energy (ATP) is produced
in the process when ADP is attached to a phosphate. This is called
phosphorylation. Since
oxygen is the final electron acceptor in the chain, we specifically call this step oxidative phosphorylation.
The electron transport chain and oxidative phosphorylation together produce the most amount of energy (about 36
molecules of ATP from 1 sugar in eukaryotes).
Notice how the
electrons force the H+
to go to the
intermembrane space.
Then notice how the
H+ is forced back into
the matrix of the
mitochondria by the
“red” enzyme ATP
synthase. This produces
ATP.
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Keep in mind that while not all organisms perform photosynthesis, ALL organisms perform cellular respiration, including
plants (ALL ORGANISMS)
One last thing to note is that while eukaryotes perform cellular respiration in their mitochondria, bacterial cells do not
contain mitochondria! So how do they do cellular respiration? They perform the same functions in their cell membrane.
Anaerobic Respiration (without oxygen)
What happens where there is no oxygen?
Glycolysis will continue to run, since it is an anerobic process. It will produce the same products, pyruvic acid, energy,
and NADH. Unfortunately, we cannot have all this high energy NADH
running around, so we need something to bring it back to its lower energy
state, NAD+.
In alcoholic fermentation, the products of glycolysis are turned into an
alcohol called ethanol, carbon dioxide, and NAD+ (look we managed to
bring that high energy NADH back down to NAD+). Unfortunately, no
ATP is produced =( ….but at least we get alcohol and bread =)
By the way, humans cannot do alcoholic fermentation. This is done by
the fungus yeast.
In lactic acid fermentation, the products of glycolysis are turned into lactic acid and NAD+ (look we managed to bring
that high energy NADH back down to NAD+). The lactic acid may cause muscle soreness after you exercise. More
fascinating though, bacteria use lactic acid fermentation to produce cheese, yogurt, buttermilk, and sour-cream. COOL!
Comparing photosynthesis and cellular respiration
Photosynthesis Equation:
6CO2 + 6H2O + sunlight  C6H12O6 + O2
Cellular Respiration Equation:
C6H12O6 + O2  6CO2 + 6H2O + ATP
Notice that these are the same equations but in reverse
to each other.
In photosynthesis we have solar energy while in
respiration we have chemical energy (ATP)
Photosynthesis removes carbon dioxide from the environment
while cellular respiration puts it back in the environment.
Keep in mind that animals cannot do photosynthesis. Only
plants, some bacteria, and some protists can perform
photosynthesis.
*Also, keep in mind that ALL organisms can perform cellular
respiration. Plants are fortunate because they can do both
photosynthesis and respiration.
Very Important – Remember This!!!!
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Some factors affect the rate of photosynthesis. These factors include light intensity, temperature, and water. If
photosynthesis is affected, so will cellular respiration.
For the most part, high light intensity and temperature increases photosynthesis (and thus respiration). The reverse is also
true. Low light and low temperatures stop photosynthesis (and thus respiration).
One last thing, fungi cannot perform photosynthesis! I know these little guys look like plants but they are not plants.
Fungi are decomposers; they are Heterotrophs (consumers not producers).
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Cellular Respiration Questions
1.Label the following
2. Identify the location in the structure to the left where
the following processes occur:
glycolysis:
fermentation:
Krebs Cycle:
ETC:
3. What is the purpose of cellular respiration?
4. What is ATP and what does it stand for? ____________________________________________________
5. What does ADP stand for? ________________________________________________________________
6. What are the 3 steps of cellular respiration?
_________________________________________________________________________________
7. What molecule does glycolysis start with? ______________________________________
8. What molecules does glycolysis end with? )________________________________
9. Is glycolysis aerobic or anaerobic? _________________________________________
10. What is the final electron acceptor of the ETC of Cellular Respiration? ________________________________
11. Is the ETC of Cellular Respiration aerobic or anaerobic? _____________________________________________
12. Under what circumstances does fermentation occur?
13. Is fermentation aerobic or anaerobic? _____________________________________________________________
14. What are two types of fermentation? _____________________________________________________________
15. Which organism performs alcoholic fermentation? ______________________________________________
16. What is produced by alcoholic fermentation? ___________________________________________________
17. Which types of cells perform lactic acid fermentation? _______________________________________________
18. What is produced by lactic acid fermentation? ____________________________________________________
19. What is the physical result of lactic acid fermentation in humans? _____________________________________
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20. What is the chemical equation for cellular respiration?
Use your notes and/or to read about cellular respiration and glycolysis.
Use each of the terms below only once to complete the passage.
aerobic
anaerobic
ATP
cellular respiration
cytoplasm
glucose
glycolysis
mitochondria
NADH
oxygen
energy
Organisms obtain energy in a process called (21) ___________________________ . This process harvests
electrons from carbon compounds, such as (22) _________________________ , and uses that energy to
make (23) ___________________________ . ATP is used to provide (24) ___________________________
for cells to do work. In (25) __________________________ , glucose is broken down into pyruvate.
Glycolysis is a(n) (26) __________________________ process because it does not require oxygen. Glycolysis
takes place in the (27) _________________________ . Two molecules of ATP and two molecules of
(28) _________________________ are formed for every glucose molecule that is broken down.
(29) _________________________ respiration takes place in the (30) _________________________ .
It is aerobic because the process requires (31) _________________________ .
Refer to the diagram of glycolysis. Label the steps in the
description to match the diagram.
32.Step _______ . Each three-carbon compound is
converted into a three-carbon pyruvate.
33.Step _______ . A six-carbon compound is broken down
into two three-carbon compounds.
34.Step _______ . Phosphate groups from two ATP
molecules are transferred to a glucose molecule.
35.Step _______ . Two NADH molecules and four ATP
molecules are produced.
Respond to each question.
36.Interpret How many total ATP molecules
are produced from the glycolysis of one
six-carbon glucose?
37.Explain Why is there a net gain of only two ATP
molecules in the glycolysis of one six-carbon glucose?
38. What proteins make sure that the release of the energy in glucose happens in a
controlled manner?
Glycolysis
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Use your notes and/or textbook to read about the Krebs
cycle, electron transport, and anaerobic respiration.
Refer to the diagram of cellular respiration. Respond to
each question and statement.
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Cellular Respiration
Glucose
without oxygen
39.Recall What is the net yield of ATP produced by
each of the circled processes in the diagram?
Glycolysis
2 ATP
Glycolysis = ___________ ATP
Krebs cycle = ___________ ATP
Pyruvate
Electron transport chain = ___________ ATP
with oxygen
40.Find the total net yield of ATP from one
molecule of glucose.
Acetyl-CoA
41.Specify Based on the diagram and your
calculations, which process produces more
energy—the anaerobic pathway or the
aerobic pathway?
For each statement below, write true or false.
Krebs cycle
2 ATP
Electron
transport chain
32 ATP
________________ 42. The anaerobic pathway that follows glycolysis in the absence of oxygen
is fermentation.
________________ 43. The hydrogen necessary in the electron transport chain comes from the
splitting of carbon dioxide molecules.
________________ 44. Cellular respiration in eukaryotes is slightly more efficient than in prokaryotes.
________________ 45. The Krebs cycle is sometimes called the TCA cycle or the citric acid cycle.
________________ 46. Fermentation occurs in the mitochondria.
________________ 47. Skeletal muscle produces lactic acid when the body cannot supply
enough oxygen.
________________ 48. Alcohol fermentation is found in some bacteria and in humans.
________________ 49. The two pyruvate molecules formed during glycolysis result in two Krebs cycles.
________________ 50. Electron transport is the first step in the breakdown of glucose.
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Photosynthesis Practice Questions
51. Label the following cross section of a leaf
52. Label the following chloroplast.
53. What is the purpose of chlorophyll?
54. Where is chlorophyll found? ___________________________________
55. In what organisms is chlorophyll found? ______________________________________
Use your notes and/or textbook to read about the light reactions.
Number the following steps of light reactions in the order in which they occur.
__________ 56. The energy lost by electrons as they pass through the electron transport chain is used
to make ATP.
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__________ 57. The electrons pass from the chlorophyll to an electron transport chain.
__________ 58. Sunlight strikes the chlorophyll molecules in the thylakoid membranes.
__________ 59. NADP+ molecules change to NADPH as they carry the electrons to the stroma
of the chloroplast.
__________ 60. Light energy is transferred to the chlorophyll’s electrons.
__________ 61. The electrons are passed down a second electron transport chain.
Refer to the graph. Respond to each statement.
62. Explain why there are usually several types
of pigments present in chloroplasts.
63. State the name of the pigment that absorbs
the most light at about 450 nm__________
Use your notes and/or to read about the Calvin cycle and
alternative photosynthesis pathways.
Complete the table by checking the correct column(s) for each description.
Description
Calvin
C4
CAM
64. The second phase of photosynthesis, in which energy is stored in
glucose
65. Pathway(s) that help(s) plants photosynthesize while minimizing water
loss
66. Pathway that allows carbon dioxide to enter leaves only at night
67. Light-independent reactions
68. Uses the enzyme rubisco to convert carbon dioxide into molecules that
can be used by the cell
69. Type of plant found in hot, dry environments
Comparing Cellular Respiration and Photosynthesis
70. What is the relationship between the equation for the overall photosynthesis reaction and the equation for the cellular
respiration reaction?
71. Do plants carry out cellular respiration? Why or why not?
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72. Two hundred years ago, a very old Native American became ill. To help keep his strength up, his family encouraged
him to eat the corn tortillas and buffalo meat that formed such an important part of their diet. The wise chief ate a little,
then said: “It is my time to go and when I die, I want to be buried beneath the large cottonwood at the bend in the creek.
In this way, I will continue to live in the generations of my great grandchildren.”
Using ideas from the unit, explain what the chief meant by his final instructions. In particular, how could one of his
carbon atoms end up in a great grandchild that he never sees? Trace this atom through decomposers (worms, bacteria,
etc.), through corn and buffalo to a great grandchild.
73. What kind of energy is stored in glucose and ATP? _________________________________________________
74. What are 2 ways in which humans depend on plants in order to stay alive?
75. Why do cells bother to make ATP instead of just using a lot of glucose?
76. How do cells get energy out of ATP? What molecules are left?
77. Fill in the chart comparing and contrasting cell respiration and photosynthesis.
Photosynthesis
Cell Respiration
Organelle for process
Inputs (Reactants)
Cycle of chemical reactions
Outputs (Products)
78. How do the reactants and products of cellular respiration and photosynthesis (other than glucose) get into and out of
cells?