BIOL 4120: Principles of Ecology Lecture 3: Adaptation to Physical Environment: Light, Energy and Heat

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BIOL 4120 Principles of Ecology Lecture 3
Adaptation to Physical Environment Light, Energy
and Heat

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Topics

• 3.1 Light is primary source of energy for the
  biosphere
• 3.2 Plants capture the energy of sunlight by
  photosynthesis
• 3.3 Plants modify photosynthesis in high water
  stress environments
• 3.4 Diffusion limits uptakes of dissolved gases
  from water
• 3.5 Temperature limits occurrence of life
• 3.6 Each organism functions best under certain
  temperature
• 3.7 Homeothermy increases metabolic rate and
  efficiency

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• Earth provides highly diverse environments
• 1.7 million known species now

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All species have three common basic functions

• Assimilation acquire energy from external
  environment
• Reproduction to produce new individuals
• Response to external stimuli able to respond to
  both physical (light, temperature etc) and biotic
  (predator etc).
• All organisms acquire energy
• Energy obtained directly from an energy source by
  a living organism is called autotrophy
  (autotroph)
• Plants are autotrophs, primary producers
• So are certain bacteria like Thiobacullus
  ferrooxidans
• Energy obtained indirectly from organic molecules
  by a living organism is called heterotrophy
  (heterotroph)
• All animals are heterotrophs, secondary producers
• Some organisms can be a mixture like lichens
  where you have an alga and a fungus living
  together

Autotrophs obtain solar energy through
photosynthesis.
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3.1 Light is the primary source of energy for the
biosphere

• All life requires energy to sustain itself
• With very few exceptions, all life on earth is
  dependent on solar energy
• Life on Earth exists because its fitness is
  optimal for the environment created by solar
  energy
• Shortwave
• longwave radiation

Earth is a balanced ecosystem in term of solar
energy inputs and outputs
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Light is the primary source of energy for the
biosphere
PAR photosynthetically active radiation 400-700
nm
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Light absorption spectra of plants
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Light absorption spectra of algae Ulva sea
lettuce, shallow water Porphyra red alga,
deep-water
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3.2 Plants capture energy of sunlight by
photosynthesisPhotosynthesis (review)

• All life is built on a framework of carbon atoms
• The ultimate source of carbon for organic
  molecules is CO2
• CO2 is transformed into organic molecules by
  plants (photosynthesis).

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Photosynthesis is the process by which the Suns
energy (shortwave radiation) is used to fix CO2
into carbohydrates (simple sugars) and release O2

• Photosynthesis begins with light reactions
• Absorption of light energy by chlorophyll (a
  pigment molecule)
• Conversion of the light energy into ATP and NADPH
• Photosynthesis continues with the dark reactions
• Incorporation of CO2 into simple (organic) sugars
  using the energy provided by ATP and NADPH
• Carboxylation is catalyzed by the enzyme rubisco
  (ribulose biphosphate (RuBP) carboxylase-oxygenase
  )

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C3

• The Calvin cycle (C3 cycle) initially fixes CO2
  into 3-PGA (phosphoglycerate)
• This cycle is called Calvin-Bensen cycle, or
  C3 cycle. Plants employing it are known as C3
  plants

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RuBP Ribulose biphosphate Rubisco ribulose
biphosphate (RuBP) carboxylase-oxygenase G3P
glyceraldehyde 3-phosphate 3-PGA
phosphoglycerate
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C3 cycle (Calvin cycle)
One major drawback of C3 pathway Rubisco can
catalyze both carbonxylation And RuBP
oxygenation Reduce the efficiency of
photosynthesis.
C3 plant trees, forbs, some grasses
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Cellular respiration
Photosynthesis
Net photosynthesis (Gross) Photosynthesis -
Respiration
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3.3 Other photosynthesis pathways adaptation to
water and temperature conditions

• To increase water use efficiency in a warm dry
  environment, plants have modified process of
  photosynthesis
• C3
• Normal in mesophyll with rubisco
• C4
• Warm dry environment
• Additional step in fixation of CO2
• Phosphoenolpyruvate synthase (PEP) does initial
  fixation into Malate and aspartate
• Malate and aspartate are transported to bundle
  sheath as an intermediate molecule
• Rubisco and CO2 convert there to sucrose

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C4 pathway

• Advantages over C3 pathway
• PEP does not interact with O2 (RuBP react with O2
  and reduce the photosynthesis efficiency)
• Conversion of malic and aspartic acids into CO2
  within bundle sheath cell acts to concentrate
  CO2, create a much higher CO2 concentration.
• C4 plants have a much higher photosynthetic rate
  and greater water-use efficiency.
• C4 plants are mostly grasses native to tropical
  and subtropical regions and some shrubs of arid
  and saline environments (Crop corn, sorghum,
  sugar cane).

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CAM pathway
CAM (Crassulacean acid metabolism) pathway Hot
desert area Mostly succulents in the family of
Cactaceae (cacti), Euphorbiaceae and
Crassulaceae) Similar to C4 pathway Different
times Night open stomata, convert CO2 to malic
acid using PEP Dayclose stomata, re-convert
malic acid to CO2, C3 cycle.
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Comparison of three photosynthetic pathways C3
Dovefoot geranium, C4 sorghum, CAM Sierra
sedium
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