Transcript Chapter 6 Photosynthesis
Chapters 6 & 7
Photosynthesis & Cellular Respiration
These processes are opposites!
The equation for photosynthesis:
6CO 2 + 6H 2 O + light energy C 6 H 12 O 6 + 6O 2 Carbon Dioxide + Water + sunlight –make Organic compounds (sugar) + Oxygen
Photosynthesis & Cellular Respiration are related:
• The oxygen (O 2 ) and some of the organic compounds produced by photosynthesis are used by cells in a process called
cellular respiration
.
In which organelles in cells do these process occur?
•
Photosynthesis occurs in the chloroplasts.
•
Cellular respiration occurs in the mitochondria.
Cellular Respiration is basically the opposite of Photosynthesis
•
Photosynthesis creates biomass (organic compounds) by converting light energy into chemical energy (stored as carbohydrate, ATP or other high energy molecule)
•
Cellular respiration is the process by which cells break down organic compounds to produce ATP (energy).
Cellular respiration is essentially photosynthesis in reverse
Photosynthesis
Energy from the sun:
Photosynthetic organisms are vital to the survival of all life on Earth.
For this slide show, Diagrams & information are from Holt biology text
Photosynthesis is vital- because it is beginning of almost all food chains
http://www.umaine.edu/umext/earthconnections/images/foodchain.gif
Discuss the following:
•
Name 3 foods you ate today & think about how this food is related to plants.
•
What is the difference between an organic compound and an inorganic compound?
•
What is a carbohydrate?
•
How does photosynthesis cause inorganic compounds to become organic?
Remember:
• •
Organic Compounds contain Carbon!
Carbohydrates:
– Molecules that are a source of
energy
– Example:
Glucose
–
General formula for a carbohydrate is [CH2O]n where n is a number between 3 and 6.
–
Glucose is C 6 H 12 O 6
Obtaining Energy from the sun to make inorganic compounds into organic compounds:
•
Photosynthesis
- converts
light energy
from the
sun
into
chemical energy
in the form of organic compounds through
a series of reactions called biochemical pathways
.
Part I.
The Light Reactions
A.
All organisms need energy to carry out the functions of life.
Where does this energy come from 1. Directly from the sun-
•
autotrophic organisms make sugar from sunlight, CO2 & H2O (examples- all plants, algae, cyanobacteria, plant-like protists) 2. Indirectly from the sun-
•
heterotrophic organisms – need to eat autotrophs )
There are 2 parts to photosynthesis
•
Light reactions
– Light energy is absorbed form the sun and is converted to chemical energy temporarily stored in the bonds of ATP and NADPH •
Calvin cycle
– organic compounds are formed using CO2 (now using the chemical energy stored from the light reactions)
B. Capturing Light Energy
•
The light reactions
– begin with the absorption of light in-
Chloroplasts
•
organelles found in the cells of plants, some bacteria, and algae.
•
Inside chloroplasts are Thylakoids , a system of membranes inside the chloroplast that look like flattened sacs
Light and Pigments
–
White light from the sun is composed of an array of colors called
th e vi si
ble s
pect rum .
–
Pigments
absorb certain colors of light and reflect or transmit the other colors.
•
Chlorophyll a & b
•
Carotenoids
The sun emits energy at a range of wavelengths: the visible spectrum is a small part of that range.
•
Chloroplast Pigments
– Located in membranes of the
thylakoids
of chloroplasts are several
pigments
, including
chlorophylls
(
chlorophyll a
and
chlorophyll b
) and
carotenoids.
How light is absorbed
Light Energy into Chemical Energy
•
Photosystems-
In the thykaloid membranes of chloroplasts- are the clusters of pigment molecules that harvest light energy for photosynthesis •
There are 2 photosystems:
–
Photosystem II
–
Photosystem I The 2 photosystems have similar pigments but different jobs in the chloroplast:
Photosystems II & I:
• •
Light Energy
is absorbed by
chlorophyll a molecules.
“Excited electrons”
in this higher energy level have enough energy to leave the chlorophyll
a
molecules.
• • the
primary electron acceptor
electrons to the donates the
electron transport chain.
NADPH is produced chemical energy!) . (now Energy is stored as
Water is needed:
•
The electrons are replaced by breaking down water
–
The Hydrogen is used to replace the H+ and the e used in the light reactions
–
Oxygen is a waste product.
Making ATP in Light Reactions
– An important part of the light reactions is the
synthesis of ATP.
–
Chemiosmosis
is the movement of protons through ATP synthase (an enzyme) & then into the stroma (This causes a concentration gradient. It releases energy, which is used to produce ATP.) –
Stroma
-the solution that surrounds the thykaloid membrane in chloroplasts.
II. Calvin Cycle
(The dark reactions) •
Carbon Fixation: The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis, the Calvin cycle.
•
In the Calvin cycle, CO 2 is incorporated into organic compounds, a process called carbon fixation.
The Calvin cycle is the most common way that plants fix carbon
• Occurs in the
stroma
of the
chloroplast
• Is a series of enzyme-assisted chemical reactions that produces
a three-carbon sugar called G3P
– Some G3P sugars are used to make
organic compounds
, (energy is stored for later use.) – Some G3P is converted to a
five-carbon sugar (RuBP) to keep the cycle going.
Alternative “Dark” Pathways
•
The C 4 Pathway
– Some plants that evolved in hot, dry climates fix carbon through the
C 4 pathway
.
These plants have their stomata partially closed during the
hottest
part of the day. •
The CAM Pathway
– Some plants in hot, dry climates fix carbon through the
CAM pathway
.
These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize
water loss
Summary photosynthesis
Chapter 7 is
Cellular Respiration
•
Cellular respiration is the process by which cells break down organic compounds to produce ATP .
• Products of cellular respiration are the reactants in photosynthesis;
they are opposites
!
Plants & Animals:
•
Both autotrophs and heterotrophs use cellular respiration to get energy from organic compounds and O 2 & produce waste products CO 2 and water
Cellular respiration can be divided into 2 stages:
•
glycolysis
•
aerobic respiration.
During
glycolysis
•
One six-carbon glucose
molecule is oxidized to form
two three-carbon pyruvic acid
molecules. • A
net yield of two ATP molecules
is produced for every molecule of glucose that undergoes glycolysis
Glycolysis takes a 6-carbon sugar & breaks it into 2 3-carbon sugars http://terravivida.com/vivida/glyintro/page01.htm
Remember: lysis means to break up
• Breaking up the glucose molecule into 2 smaller sugars (pyruvic acid) provides energy to make ATP which is the principle energy 'currency' in the cell http://terravivida.com/vivida/glyintro/page05.htm
What happens after glycolysis?
•
If no oxygen is available fermentation occurs
•
If oxygen is available the krebs cycle
1. Fermentation
.
• • •
Occurs if oxygen is not present convert pyruvic acid into other compounds For example: 1. Lactic Acid Fermentation
– an enzyme converts pyruvic acid into another three-carbon compound, called
lactic acid.
2. Alcoholic Fermentation
– Some plants and unicellular organisms, (like yeast) convert pyruvic acid to
ethyl alcohol & CO 2 .
2. Aerobic Respiration
• occurs in the
mitochondria.
• occurs
only if oxygen
is present in the cell.
•
Called the Krebs cycle
The Krebs cycle
• Also known as the
tricarboxylic acid cycle (TCA),
• was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs
Krebs happens in the mitochondria • After the glycolysis takes place in the cell's
cytoplasm,
• the pyruvic acid molecules travel into the interior of the
mitochondria.
The Krebs Cycle
: (There are actually 8 steps. Not all are show here) Each turn produces 1 ATP 2 CO2 3 NADH 1 ADH2 http://ncam.wgbh.org/publications/stemdx/images/krebs.jpg
The Krebs Cycle.
• • First,
pyruvic acid
(produced in glycolysis) reacts with coenzyme A to
form acetyl CoA.
Then, acetyl CoA enters the Krebs cycle. • The original glucose becomes completely broken down after
2 turns
of the Krebs cycle.
2 turns produce:
–
four CO 2 molecules,
–
two ATP molecules,
–
and hydrogen atoms that are used to make six NADH and two FADH 2 molecules.
Finally:
Electron Transport Chain
•
High-energy electrons in hydrogen atoms from NADH and FADH 2 are then passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane
Efficiency of Cellular Respiration
•
Cellular respiration can produce up to 38 ATP molecule s from the oxidation of a single molecule of glucose.
•
Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose.
•
Thus, cellular respiration is nearly 20 times more efficient than glycolysis alone
.
Summary of Cellular Respiration
•
Providing cells with energy in the form of ATP
is an important function of cellular respiration. • Also: Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.
Summary diagram- cellular respiration: http://www.chem.uwec.edu/Webpapers2005/mintermm/pages/Intro_media/intro.gif