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Summary ZOL 3702 study notes
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ZOL 3702 LEARNING UNIT 3RESOURCES
Textbook reference: pg 58-88
Learning outcomes:
Explain the definition of resources.
Discuss CO2 as resource and discuss the three main means of photosynthesis.
Discuss mineral nutrients, oxygen as resource.
Discuss organisms that serve as sources of nutrition for other organisms.
Classify resources and discuss space as resource.
RADIATION pg 58-69
Solar radiation is the only source of energy for plants.
It comes to the plant as radiation from the sun, either directly having been diffused by the atmosphere, or
after being reflected or transmitted by other objects.
The direct fraction is highest at low altitudes.
For much of the year in temperate climates, and for the whole year in arid climate, the leaf canopy in
terrestrial communities does not cover the land surface, so that most of the incident radiation falls on bare
branches or bare ground.
When a plant intercepts radiant energy it may be reflected, transmitted, or absorbed.
The amount of radiant energy that reaches a plant is determined by various factors, and the effective use of
radiation varies from 0.6 - 4.5%.
Part of the fraction that is absorbed may raise the plant's temperature and be reradiated at much longer
wavelengths; in terrestrial plants a fraction may contribute latent heat of evaporation of water and power the
transpiration stream. A small part may reach the chloroplasts and drive photosynthesis.
Radiant energy is converted during photosynthesis into energy rich chemical compounds of carbon which will
be broken down during respiration.
Unless the radiation is captured and chemically fixed as soon as it falls on the leaf, it is lost for photosynthesis.
Radiant energy that has been fixed in photosynthesis passes just once through the world - this is in contrast to
an atom of nitrogen or carbon or a molecule of water that may cycle repeatedly.
Solar radiation is a spectrum of different wavelengths , however photosynthesizing plants are able to gain
access to energy in only a restricted band of the spectrum.
All green plants depend on chlorophyll and other pigments for the photosynthetic fixation of carbon, and
these pigments fix radiation in a waveband between 400 and 700 nm.
This is the band of photosynthetically active radiation (PAR).
About 56% of the radiation incident on earth surface lies outside the PAR range and is therefore unavailable
as a resource for green plants.
In other organisms there are pigments comment such as bacteriochlorophyll in bacteria, that operate in
photosynthesis outside the PAR range of green plants.
CARBON DIOXIDE pg 69-73
Carbon dioxide used in photosynthesis is mostly obtained from the atmosphere.
In a terrestrial community, CO2 at night increases from soil and vegetation to the atmosphere, and on sunny
days above a photosynthesizing canopy there is a flow of carbon dioxide from the atmosphere downward.
Above a vegetation canopy, the air becomes rapidly mixed.
However, beneath canopies the situation is different.
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