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You can't have a light without a dark to stick it in
." Arlo Guthrie, American musician

In a previous module, you learned about photosynthesis, the mechanism plants use to convert solar energy into chemical energy. The light energy captured is used to make ATP and NADPH, which is then used to reduce carbon from a simple form (CO 2 ) into a more complex form (sugars). The first step of the Calvin cycle is the fixation of carbon dioxide to RuBP, and the plants that only use this mechanism of carbon fixation are called C 3 plants. About 85% of the plant species on the planet are C 3 plants; some examples are rice, wheat, soybeans and all trees.

The process of photosynthesis has a theoretical efficiency of 30% (i.e., the maximum amount of chemical energy output would be only 30% of the solar energy input), but in reality the efficiency is much lower. It is only about 3% on cloudy days. Why is so much solar energy lost? There are a number of factors contributing to this energy loss, and one metabolic pathway that contributes to this low efficiency is photorespiration. During photorespiration, the key photosynthetic enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase oxygenase) uses O 2 as a substrate instead of CO 2 . This process uses up a considerable amount of energy without making sugars ( [link] ). When a plant has its stomata open (CO 2 is diffusing in while O 2 and water are diffusing out), photorespiration is minimized because Rubisco has a higher affinity for CO 2 than for O 2 when air temperatures are below 30°C (86°F). However, when a plant closes its stomata during times of water stress and O 2 from photosynthesis builds up inside the cell, the rate of photorespiration increases because O 2 is now more abundant inside the mesophyll. So, there is a tradeoff. Plants can leave the stomata open and risk drying out, or they can close the stomata, thereby reducing the uptake of CO 2 , and decreasing the efficiency of photosynthesis. In addition, Rubisco has a higher affinity for O 2 when temperatures increase, which means that C 3 plants use more energy (ATP) for photorespiration at higher temperatures.

comp photorespiration and carbon fixation
A comparison of photorespiration and carbon fixation in C3 plants. During photorespiration, O 2 is bound to RuBP and forms phosphoglycolate (PG) and Phosphoglycerate (PGA), PG then undergoes an number energy requiring reactions releasing CO2. Work by Eva Horne.

Evolutionarily speaking, why is photorespiration still around? One hypothesis is that it is evolutionary baggage from a time when the atmosphere had a lower O 2 concentration than it does today. In other words, when Rubisco first evolved millions of years ago, the O 2 concentration was so low that excluding O 2 from its binding site had little or no influence on the efficiency of photosynthesis. The modern Rubisco retains some of its ancestral affinity for O 2 , which leads to the energy costs associated with photorespiration. However, plant cell physiologists are discovering that there might be some metabolic benefits associated with photorespiration, which would help explain why this seemingly wasteful pathway is still found in plants. Adding to the dilemma is the fact that when plant geneticists “knock out” Rubisco’s ability to fix O 2 , Rubisco also loses its ability to fix CO 2 . It is possible that the active site of this enzyme cannot be engineered, by artificial or natural selection, so that it exclusively binds CO 2 and not O 2 .

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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