Transcript Photosynthesis and Cellular Respiration

PHOTOSYNTHESIS
and
RESPIRATION
UNIT 5
CHAPTER 5
SECTION 1
Photosynthesis
Energy and Living Things
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Photosynthesis is the process in
which light energy is converted
into chemical energy.
Autotrophs (plants and some
bacteria) use the sun’s energy to
carry out photosynthesis, and are
therefore the foundation of all
living systems.
Breaking Down Food For Energy
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Autotrophs are
organisms that use
energy from sunlight
or from chemical
bonds in inorganic
substances to make
organic compounds.
Heterotrophs are
organisms that must
consume other
organisms as food to
get their energy.
Photosynthesis
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Photosynthesis is the process by which
plants, algae, and some bacteria use
sunlight, carbon dioxide, and water to
produce carbohydrates and oxygen.
Photosynthesis has 3 stages:
Stage 1: absorption of light energy
Stage 2: conversion of light energy into chemical
energy, temporarily stored in ATP and NADPH
Stage 3: storage of chemical energy in ATP and
NADPH powers the formation of organic molecules
Photosynthesis
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Pigments are light-absorbing substances
that absorb only certain wavelengths of
light and reflect all others.
Chlorophyll is the primary pigment
involved in photosynthesis. Chlorophyll
absorbs mostly blue and red light and
reflects green and yellow light.
This reflection of green and yellow light
makes many plants, especially their
leaves, look green.
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Photosynthesis
occurs in the
chloroplasts
and uses the
pigment
chlorophyll.
Photosynthesis
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The following chemical equation
summarizes photosynthesis:
6H2O + 6CO2 + light 
C6H12O6 + 6O2
REACTANTS: water, carbon dioxide,
light energy
PRODUCTS: glucose, oxygen
Stages of Photosynthesis:
STAGE 1 - The Light-Dependent Reactions
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STAGE 1: These reactions are called the “light
reactions,” or “light-dependent reactions”
because the reactions absorb light energy to
make the organic compounds glucose and oxygen.
STAGE 1 occurs in the chloroplasts on the
thylakoid membrane where clusters of the
pigment chlorophyll are embedded.
Other pigments used are carotenoids that produce
yellow and orange fall leaf colors, as well as the
colors of many fruits, vegetables, and flowers.
Photosynthesis:
Where Does it Occur?
Thylakoid membrane
Photosynthesis: Thylakoids
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Thylakoids are disk-shaped structures found in
the chloroplasts of leaf cells that contain
clusters of embedded pigments.
These pigment molecules in the thylakoids of
chloroplasts absorb light energy.
Electrons in the pigments are “excited” by light,
and jump from the chlorophyll molecules to other
nearby molecules in the thylakoid membrane.
The series of molecules along the thylakoid
membrane that excited electrons pass through
as they jump along the chlorophyll molecules is
called the electron transport chain.
Photosynthesis: Stage 1
Absorption of Light Energy
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The excited electrons that leave chlorophyll molecules
must be replaced by other electrons.
Plants get these replacement electrons from water
molecules, H20.
The water molecules are split by an enzyme inside the
thylakoid.
When water molecules are split, chlorophyll molecules
take the electrons from the hydrogen atoms, H, leaving
hydrogen ions, H+.
The remaining oxygen atoms, O, from the disassembled
water molecules combine to form oxygen gas, O2.
Photosynthesis: Stage 2
Conversion of Light Energy by
Electron Transport Chains
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Excited electrons lose some of their energy as
they pass through these proteins. The energy lost
is used to pump hydrogen ions into the thylakoid.
As the process continues, hydrogen ions become
more concentrated inside the thylakoid than
outside, producing a concentration gradient
across the thylakoid membrane.
The hydrogen ions will diffuse back out of the
thylakoid down their concentration gradient
through specialized carrier proteins, or proton
pumps.
Photosynthesis: Stage 2
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inner thylakoid
membrane
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outer thylakoid
membrane
These proteins act as both
ion channels as well as
enzymes.
As H+ pass through the
channel portion of the
protein, the protein
catalyzes a reaction in
which a phosphate group is
added to ADP molecules to
form ATP (ADP + P = ATP).
Thus, the movement of
hydrogen ions across the
thylakoid membranes
through proton pumps
provide the energy to
produce ATP molecules.
Two Electron Transport Chains
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The first electron transport chain lies between
two large clusters of pigment molecules and is
used to form ATP.
A second electron transport chain lies next to
the sight of the first electron transport chain.
In this second chain, excited electrons combine
with hydrogen ions (H+) and an electron
acceptor called NADP+ to form NADPH.
NADPH is an electron carrier and is important in
photosynthesis because it carries high energy
electrons needed to produce organic molecules.
Photosynthesis: Stage 3
The Light-Independent Reactions
The Storage of Chemical Energy
 Stage 3 of photosynthesis is known as the
Calvin cycle.
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The Calvin cycle creates complex
carbohydrates that store energy.
Stage 3 of photosynthesis is also known as
the “light-independent reactions” or “dark
reactions” because these series of reactions
do not need light to occur.
Photosynthesis:
The Light-Independent Reactions
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Stage 3 of photosynthesis is sometimes
called carbon dioxide fixation because
in a series of enzyme-assisted chemical
reactions within the chloroplasts, CO2
molecules adhere to existing carbon
compounds to form sugars for long-term
energy storage.
The energy used in the Calvin cycle is
supplied by ATP and NADPH that was
made during Stage 2.
Three Factors That Affect
Photosynthesis
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1.) amount of light – The rate of photosynthesis
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2.) concentration of carbon dioxide – Once a
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3.) range of temperature – Like all metabolic
increases as light intensity increases until all the
pigments are being used. At this saturation point,
the reactions of the Calvin cycle cannot proceed any
faster.
certain concentration of carbon dioxide is present,
photosynthesis cannot proceed any faster.
processes, photosynthesis involves many enzymeassisted chemical reactions. Unfavorable
temperatures may inactivate certain enzymes.
SECTION 2
Cellular Respiration
Cellular Respiration
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Before energy from food can be utilized, it must
be transferred to ATP in a process called
cellular respiration.
Cellular respiration is the set of metabolic
reactions and processes that take place in the
cells of organisms to convert biochemical
energy from nutrients into adenosine
triphosphate (ATP), and then release waste
products.
To put it simply, cellular respiration is the
process where cells produce energy from
carbohydrates.
Cellular Respiration
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Cellular respiration is the opposite of photosynthesis.
The reactants of photosynthesis – carbon dioxide
and water – are the products of cellular respiration.
The products of photosynthesis – glucose and
oxygen – are the reactants of cellular respiration.
Cellular respiration releases much of the energy in
food to make ATP.
ATP provides cells with energy they need to carry
out the activities of life.
Cells Transfer Energy
From Food To ATP
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When cells break down food molecules,
some of the energy is released into the
atmosphere as heat, while the rest is
stored temporarily in molecules of ATP.
Adenosine triphosphate (ATP) is a
nucleotide with two extra energy-storing
phosphate groups.
ATP molecules are often called the
“energy currency” of a cell.
Adenosine Triphosphate
RED = ribose (a 5-carbon sugar)
BLUE = adenine (a nitrogenous base)
GREEN = phosphate groups
ATP Stores and
Releases Energy
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The energy from ATP is released when the
bonds that hold the phosphate groups
together are broken.
The removal of a phosphate group from
ATP (3 phosphates) produces ADP
(adenosine diphosphate -- 2 phosphates),
which releases energy in a way that
enables cells to use the energy.
Cells use energy released by this reaction
to power metabolism.
ATP FYI:
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The human body uses about 1 million
molecules of ATP per second per cell.
There are more than 100 trillion cells in
the human body.
That is about 1 X 1020, or
100,000,000,000,000,000,000 ATP
molecules used in the body each
second.
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Cellular respiration can
be aerobic respiration
(with oxygen) or
anaerobic respiration
(without oxygen).
Cellular respiration
begins in the cytoplasm,
and ends in the
mitochondria.
Cellular respiration
takes place in the two
stages of glycolysis,
then aerobic respiration.
Cellular Respiration
The chemical formula for cellular respiration is:
C6H12O6 + 6O2 + ADP + P  6CO2 + 6H2O + ATP
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REACTANTS: glucose, oxygen, ADP, extra
phosphate
PRODUCTS: carbon dioxide, water, ATP
The process summarized by the equation begins
in the cytoplasm of a cell and ends in the
mitochondria.
Cellular Respiration: Stage 1
Glycolysis
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Stage 1 of cellular respiration is called
glycolysis.
Glycolysis is the stage of cellular
respiration where glucose is broken down
in the cytoplasm, converted to pyruvate,
and produces a small amount of ATP and
NADPH.
Glycolysis – uses 2 ATP, but produces 4
ATP – net gain = 2 ATP
Cellular Respiration: Stage 2
The Krebs Cycle
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Stage 2 of cellular respiration is known as
the Krebs cycle and is also called aerobic
respiration.
Cellular respiration is called an aerobic
process because it requires oxygen.
C6H12O6 + 6O2 + ADP + P  6CO2 + 6H2O + ATP
A two-carbon molecule combines with a
four-carbon molecule during the Krebs cycle.
Cellular Respiration: Stage 2
The Krebs Cycle
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Pyruvic acid produced during glycolysis
enters the mitochondria and is
converted into carbon dioxide and
water.
ATP and NADPH are produced.
The Krebs cycle produces 2 ATP for
each molecule of glucose broken down.
Cellular Respiration:
The Electron Transport Chain
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If enough O2 is present, up to 34
ATP molecules can be formed
from a single glucose molecule!
At the end of the electron
transport chain, oxygen (O2) acts
as the final electron acceptor and
combines with H+ ions to form
water molecules (H2O).
Fermentation:
Occurs in the Absence of
Oxygen
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If oxygen (O2) is not present in sufficient
amounts, the electron transport chain in the
mitochondrial membrane cannot function.
Energy molecules (ATP and NADH) cannot
be created in abundance.
So, what does the cell do to continue to
break down organic compounds and release
energy if not enough oxygen is present?
Fermentation:
Occurs in the Absence of Oxygen
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Fermentation is the anaerobic process that
continues the breakdown of carbohydrates when
there is not enough oxygen for aerobic
respiration.
There are two types of fermentation:
1.) lactic acid fermentation and
2.) alcoholic fermentation.
Lactic acid and/or ethanol (alcohol) are the byproducts of fermentation when the breakdown of
carbohydrates occurs without oxygen.
Lactic Acid Fermentation
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Glycolysis occurs without oxygen. However,
the Krebs cycle requires oxygen. In lactic
acid fermentation, NAD+, an electron
acceptor, is recycled and glycolysis can
continue to produce ATP.
Fermentation enables glycolysis to continue
producing ATP as long as the glucose supply
lasts.
Lactate, an ion of lactic acid, can build up in
muscle cells if not removed quickly enough and
can cause “muscle burn” or muscle fatigue.
Alcoholic Fermentation
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Carbon dioxide is released during
alcoholic fermentation by yeast.
Carbon dioxide gas released by the
yeast is what causes the rising of
bread dough and the carbonation of
some alcoholic beverages.
Alcoholic Fermentation
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Alcoholic fermentation is a two-step process: First,
pyruvate is converted, releasing carbon dioxide.
Second, electrons are transferred from a molecule of
NADH to the two-carbon compound, producing ethanol.
Alcoholic fermentation by yeast can be used to produce
food and beverages such as yogurt, cheese, beer, and
wine.
Production of ATP
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The total amount of ATP a cell is able to
harvest from each glucose molecule that
enters glycolysis depends on the
presence or absence of oxygen.
When oxygen is present, aerobic
respiration occurs.
When oxygen is not present, anaerobic
respiration, or fermentation, occurs
instead.
Production of ATP
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Most ATP is made during aerobic respiration.
Glycolysis (Stage 1 of cellular respiration)
can occur with or without oxygen, and
produces a net gain of 2 ATP molecules.
The Krebs cycle (Stage 2 of cellular
respiration) produces 2 ATP molecules for
each glucose molecule broken down.
The electron transport chain can produce up
to 34 ATP molecules from a single glucose
molecule.