photosynthesis : an overview
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Photosynthesis : An Overview. Photosynthesis : An Overview. The key cellular process identified with energy production is photosynthesis . - PowerPoint PPT PresentationTRANSCRIPT
Photosynthesis: An Overview
Photosynthesis: An Overview The key cellular process identified with
energy production is photosynthesis. Photosynthesis is the process in which
green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen.
Investigating Photosynthesis
◦Belgian Jan van Helmont conducted an experiment in the late 1600’s to better understand where a plants mass comes from.
◦Planted a small willow tree in a container filled with soil.
◦After 5 years of watering it, he found that the tree gained 160 pounds while the soil lost only two ounces.
◦Concluded that most of the plants mass came from water, not the soil.
Investigating PhotosynthesisVan Helmont’s experiment accounts for the
“hydrate,” or water, portion of the carbohydrate produced by photosynthesis.
But where does the carbon of the “carbo” portion come from?
We now know that carbon dioxide in the air is also a major contributor of plant mass.
In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates.
In 1772, Joseph Priestley made another important discovery.
Placed a shoot of a green plant into a container of water.
He then covered the container and lit a candle in it until it completely burned out.
Later, Priestley was able to both burn the candle again and keep mice alive in the air.
Priestley became the first person ever to observe the respiration of plants - the fact that they take in carbon dioxide and release oxygen.
Also discovered how to dissolve CO2 in water and invented the first soda pop.
Investigating Photosynthesis
Investigating Photosynthesis
Jan Ingenhouz laid the groundwork for understanding photosynthesis when he demonstrated that green leaves absorb carbon dioxide and release oxygen only in sunlight.
In darkness, he showed, leaves absorb oxygen and give off carbon dioxide, just like animals and non-green plant parts.
Photosynthesis
Light and Pigments◦What is the role of light and chlorophyll
in photosynthesis? How do plants capture the energy of sunlight?
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll.
Plants gather the sun's energy with light-absorbing molecules called pigments.
The main pigment in plants is chlorophyll. There are two main types of chlorophyll:
chlorophyll a chlorophyll b
LightVisible spectrum – ROYGBIVRed = longest wavelengthViolet = shortest wavelengthColor of an object is determined by the color the object reflectsPlants gather light using pigments
Light and Pigments Chlorophyll absorbs light well in the blue-
violet and red regions of the visible spectrum.
Wavelength (nm)
Estim
ated
Abs
orpt
ion
(%) 100
80
60
40
20
0400 450 500 550 600 650 700 750
Chlorophyll b
Chlorophyll a
Wavelength (nm)
Light and Pigments Chlorophyll does not absorb light well in
the green region of the spectrum. Green light is reflected by leaves, which is why plants look green.
Estim
ated
Abs
orpt
ion
(%) 100
80
60
40
20
0 400 450 500 550 600 650 700 750
Chlorophyll b
Chlorophyll a
Wavelength (nm)
Lights and PigmentsCarotenoids are accessory
pigments that allow plants to absorb light in mainly the blue and green regions of the spectrum and reflect red, yellow, and orange.
These pigments are more prominent in the fall.
Light and Pigments Light is a form of energy, so any
compound that absorbs light also absorbs energy from that light.
When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons.
These high-energy electrons are what make photosynthesis work.
Light and Pigments
Plant pigments can be separated by a process called chromatography.
Chromatography is used to separate mixtures of substances
The Photosynthesis EquationThe Photosynthesis Equation
The equation for photosynthesis is:
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugars + oxygen
◦Glucose is theprimary sugarproduced byphotosynthesis
Light
Light
The Photosynthesis Equation
◦Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.
Inside a Chloroplastthylakoids –
saclike photosynthetic membranes
grana – stacks of thylakoids
stroma – space outside the thylakoids
Overview of Photosynthesis
photosynthesis occurs only in producers
endergonic reaction – a chemical reaction that uses or stores energy
Two steps of photosynthesis◦Light Reactions◦Calvin Cycle
Light Reactionsrequire lightuse energy from
light to produce ATP and NADPH
occurs in the grana
energy from “excited electrons” is used to bond ADP and Pi to form ATP
Light Reactions3 main events
◦Light energy is absorbed by the chlorophyll and ATP is made
◦Water is split into hydrogen ions, oxygen and electrons
◦The hydrogen ions are used to make NADPH
Light ReactionsInputs:
◦Light◦Water
Outputs:◦ATP ◦NADPH◦Oxygen (O2)
Calvin CycleAlso called the dark reactions or
light-independent reactionsprocess of synthesizing sugarsoccurs in the stromadoes not require lightconverts CO2 to sugar
Calvin Cycle3-carbon sugars are produced
◦Some used as energy sources◦Some converted to lipids, amino
acids, parts of nucleic acids◦Two can combine to form 6-carbon
sugars
Calvin CycleInputs:
◦ATP◦NADPH◦CO2
Outputs:◦Sugars
Photosynthesis Overview
O2
CO2
+H20
Sugar
ADPNADP+
Light-Dependent Reactions
(thylakoids)H2O
ATPNADPH
Calvin Cycle (stroma)
Light energy
In the end…a single 6-carbon sugar is formed
from 6 molecules of carbon dioxide
plants use the sugar for energy and to build more complex carbohydrates such as starches and cellulose
other organisms eat the plants and use the energy stored in carbohydrates
Photosynthesis Overview
◦In van Helmont's experiment, most of the added mass of the tree came from soil and carbon dioxide. water and carbon dioxide. oxygen and carbon dioxide. soil and oxygen.
Quiz
◦Plants use the sugars produced in photosynthesis to make oxygen. starches. carbon dioxide. protein.
Quiz
◦The raw materials required for plants to carry out photosynthesis are carbon dioxide and oxygen. oxygen and sugars. carbon dioxide and water. oxygen and water.
Quiz
◦The principal pigment in plants is chloroplast. chlorophyll. carotene. carbohydrate.
Quiz
◦The colors of light that are absorbed by chlorophylls are green and yellow. green, blue, and violet. blue, violet, and red. red and yellow.
Quiz