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Chlorophyll a and chlorophyll b are made up of a long hydrocarbon chain attached to a large, complex ring made up of nitrogen and carbon. Magnesium is associated with the center of the ring. Chlorophyll b differs from chlorophyll a in that it has a CHO group instead of a CH3 group associated with one part of the ring. Beta-carotene is a branched hydrocarbon with a six-membered carbon ring at each end. Each chart shows the absorbance spectra for chlorophyll a, chlorophyll b, and β-carotene. The three pigments absorb blue-green and orange-red wavelengths of light but have slightly different spectra.
(a) Chlorophyll a , (b) chlorophyll b , and (c) β -carotene are hydrophobic organic pigments found in the thylakoid membrane. Chlorophyll a and b , which are identical except for the part indicated in the red box, are responsible for the green color of leaves. β -carotene is responsible for the orange color in carrots. Each pigment has (d) a unique absorbance spectrum.

Many photosynthetic organisms have a mixture of pigments; using them, the organism can absorb energy from a wider range of wavelengths. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater where light intensity and quality decrease and change with depth. Other organisms grow in competition for light. Plants on the rainforest floor must be able to absorb any bit of light that comes through, because the taller trees absorb most of the sunlight and scatter the remaining solar radiation ( [link] ).

The photo shows undergrowth in a forest.
Plants that commonly grow in the shade have adapted to low levels of light by changing the relative concentrations of their chlorophyll pigments. (credit: Jason Hollinger)

When studying a photosynthetic organism, scientists can determine the types of pigments present by generating absorption spectra. An instrument called a spectrophotometer can differentiate which wavelengths of light a substance can absorb. Spectrophotometers measure transmitted light and compute from it the absorption. By extracting pigments from leaves and placing these samples into a spectrophotometer, scientists can identify which wavelengths of light an organism can absorb. Additional methods for the identification of plant pigments include various types of chromatography that separate the pigments by their relative affinities to solid and mobile phases.

How light-dependent reactions work

The overall function of light-dependent reactions is to convert solar energy into chemical energy in the form of NADPH and ATP. This chemical energy supports the Calvin cycle and fuels the assembly of sugar molecules. The light-dependent reactions are depicted in [link] . Protein complexes and pigment molecules work together to produce NADPH and ATP.

 Illustration a shows the structure of PSII, which is embedded in the thylakoid membrane. At the core of PSII is the reaction center. The reaction center is surrounded by the light-harvesting complex, which contains antenna pigment molecules that shunt light energy toward a pair of chlorophyll a molecules in the reaction center. As a result, an electron is excited and transferred to the primary electron acceptor. A water molecule is split, releasing two electrons which are used to replace excited electrons. Illustration b shows the structure of PSI, which is similar in structure to PSII. However, PSII uses an electron from the chloroplast electron transport chain also embedded in the thylakoid membrane to replace the excited electron.
A photosystem consists of a light-harvesting complex and a reaction center. Pigments in the light-harvesting complex pass light energy to two special chlorophyll a molecules in the reaction center. The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor. The excited electron must then be replaced. In (a) photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product. In (b) photosystem I, the electron comes from the chloroplast electron transport chain discussed below.

The actual step that converts light energy into chemical energy takes place in a multiprotein complex called a photosystem [link] , two types of which are found embedded in the thylakoid membrane, photosystem II (PSII) and photosystem I (PSI) ( [link] ). The two complexes differ on the basis of what they oxidize (that is, the source of the low-energy electron supply) and what they reduce (the place to which they deliver their energized electrons).

Questions & Answers

Black market what is the meaning
Bless Reply
where there is illegal transactions of goods or services. where there illegal goods or services are sold.
Azhar
Scarcity is the major problem of any economy which is the limited resources an economy has in order to produce its country's unlimited wants/needs. Therefore, scarcity is the key term beyond the study of Economics.
Bature Reply
what is supply
Rahul Reply
Like the demand, the supply demonstrates the quantities that will be  sold at a certain price. But unlike the demand, the supply relationship  shows an upward slope. This means that the higher the price, the higher the  quantity supplied.  Producers supply more at a higher
Nazneen
or we can say that By supply we mean various quantatirs of a commodity which a producer will offer for sale at different possible prices over a given period of time
Nazneen
What is scarcity?
Jubille Reply
having unlimited needs and wants in a world of limited resources
William
what are the indicator of over population
Accorobatic Reply
Inefficiency of natural resources
Adekunle
Low PCI .
abhinav
resources are limited and wants are unlimited
Nazneen
limited resources
Nazneen
what product market?
Gayflor Reply
explain demand
Bless Reply
what is economics
Murali
Economics is the social science that studies the production, distribution and consumption of goods and services.Economics focuses on the behaviour and interactions of economic agents and how economies work.
Preeti
ok
SAGAR
Pls what is national income?
Ishmael
demand is the number of buyers. as the price of goods is increase, the buyers will not consider to buy the goods, so the demand will decreases
Pung
National Income is the aggregate monetary value of all final goods and services produced in an economy in an year .
abhinav
Why pecularities of land has no economic significance, What the economic bad, effictive demand?
James
Demand is a quantity of goods that a consumer is willing to buy at different prices over a given period of time
Nazneen
Define law of demand
Nazneen
what is deadweightloss
francis Reply
hi
Bless
deadweight loss is the allocative inefficiency.... when the equilibrium for good or services is not achived.
Azhar
hi
Azhar
hi
azaloo
hii too
Jackson
Hello
Micah
how are you all?
Azhar
I am here been sick but here
Amanda
may you get well soon Amanda
Azhar
What are the implications of classical Economics?
Micah
What are the implications of classical Economics school of thought?
Micah
Dead weight loss is an inefficient allocation of resources, especially through taxation or restrictions.
Ezeigwe
Classical Economics had an influenced by ancient economic principle and theory.
Ezeigwe
yec
Yasinta
nice
Amanda
hello please what is localization of industry
Bless Reply
price is tantalisingly the only factor determining demand which can be analyze the view
Sinit Reply
Price is tantalizingly the only factor determining demand which can be analyze the view
Sinit
what is scarcity
Sharkdanny Reply
the state of being scarce or in short supply; shortage.
Abdirahin
what is meant by an abnormal demand curve?
Samuel Reply
what is microeconomics
Berun Reply
micronomics can be define as that part of Economics that deals with small scale business. e.g. House hold stuff
Amodu
Micro economics is the study of individuals, households and firms' behavior un decision making and allocation of resources
Christian
what is underemployment
Xornam Reply
It is the situation where the available resources are not used to it optimum
Bless
state the law of diminishing returns
Bless
Bless, the law of diminishing returns state that one point, adding a single worker will result in a decrease of production.
David
it is a situation where by people are employ but work under their potential
Akua
David please go into details kk
Bless
Akua pls when you say people alone? what about facilities?
Bless
Definition of underemployment. 1 : the condition in which people in a labor force are employed at less than full-time or regular jobs or at jobs inadequate with respect to their training or economic needs
Boahen
OK that is good
Set
I am new here
Taimoor
what does law of demand says?
Samuel
with a diagram explain fairy elastic demand
Samuel
comprehensive answer for public finance is the money that a government has available to spend from taxes and borrowing.
wilflay Reply
what then comprises of public opinion
Raphael
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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