Coping with Environmental Variation pt.2 Flashcards
Autotrophs
Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis)
Heterotrophs
Obtain their energy by consuming organic compounds from other organisms.
Energy
Key step: The energy is converted into chemical energy stored in the bonds of organic molecules
This energy originated with organic compounds synthesized by autotrophs
Some consume nonliving organic matter
consume energy-rich organic compounds (food) and convert them into usable chemical energy (ATP)
The energy gain depends on the chemistry of the food, and how much effort is need to find and ingest the food
have tremendous diversity in morphological and physiological feeding adaptations
Parasites and herbivores consume live hosts but do not necessarily kill them
Predators capture and consume live prey animals
Holoparasites
They have no photosynthetic pigments and get energy from other plants (heterotrophs)
Ex. Dodder- is an agricultural pest and can significantly reduce biomass in the host plant
Hemiparasite
photosynthetic, but obtains nutrients, water, and some of its energy from the host plant
Ex. Mistletoe
Photosynthesis
(most autotrophs): sunlight provides the energy to take up CO2 and synthesize organic compounds
Chemosynthesis (chemolithotrophic)
Energy from inorganic compounds is used to produce carbohydrates.
important in nutrient-cycling bacteria, and in some ecosystems, such as hydrothermal vent communities
Key molecule for most Photosynthesis
Chlorophyll
Leaves are green because chlorophyll, the green pigment in leaves, absorbs blue and red light (allowing us to see green)
Photosynthesis
Most of the biologically available energy on Earth is derived from photosynthesis
Photosynthetic organisms include some archaea, bacteria, and protists, and most algae and plants
Photosynthetic rate determines the supply of energy, which in turn influences growth and reproduction
Environmental controls on photosynthetic rate are therefore an important topic in physiological ecology
2 Major Steps of Photosynthesis
- Light Reaction: light is harvested and used to split water and provide electrons to make ATP and NADPH.
- Dark reaction: CO2is fixed in the Calvin cycle, and carbohydrates are synthesized
Light response curves
Show the influence of light levels on the photosynthetic rate.
Light compensation point
Where CO2 uptake is balanced by CO2 loss by respiration
Saturation Point
When photosynthesis no longer increases as light increases.
Plants can acclimatize to changing light intensities with shifts in light response curves
Shifts in light saturation point involve morphological and physiological changes
Leaves at high light intensity
may have thicker leaves and more chloroplasts
When light hits the leaf it is absorbed by the top layer, and by the time the light reaches the bottom of the thick layer there isn’t much light energy left
Water Availability
Water availability influences CO2 supply in terrestrial plants
Low water availability causes stomates to close, restricting CO2 uptake
This is a trade-off: water conservation versus energy gain
Closing stomates increases the chances of light damage
If the calvin cycle isn’t operating, energy builds up in the light-harvesting arrays and can damage membranes
Plants have various mechanisms to dissipate this energy, including carotenoids
Plants deal with excess energy through other pigments
Plants from different climate zones have enzyme forms with different optimal temperatures allowing them to operate in that climate
Plants can acclimatize by synthesizing different enzyme forms
Nutrients
Can affect photosynthesis
Most nitrogen in plants is associated with photosynthetic enzymes (e.g. rubisco)
Higher nitrogen levels in a leaf are correlated with higher photosynthetic rates
Low Nitrogen Supply: relative demand for growth and metabolism
Increasing Nitrogen Content of Leaves increases the risk that herbivores will eat them, as plant-eating animals are also nitrogen-starved
Some metabolic processes decrease photosynthetic efficiency
Rubisco
the key enzyme for carbon fixation can catalyze two competing reactions:
Carboxylase reaction: photosynthesis
Oxygenase reaction: O2 is taken up, carbon compounds are broken down and CO2 is released (photorespiration)
Photorespiration is: Sensitive to oxygen concentration and temperature
Does Photorespiration Have Benefits
Under high light, dissipate energy
Under normal light conditions, when plants can’t photorespire, they die
Experiments with arabidopsis thaliana plants with a mutation knocks out photorespiration
Plants die under normal light and CO2 conditions
Photorespiration is a large disadvantage if CO2 is low and temperatures are high
Such conditions existed 7 million years ago when C4 photosynthesis first appeared
C4 photosynthetic pathway: reduces photorespiration and evolved independently several times
Many grass species use this pathway (corn, sugarcane, and sorghum)
Involves biochemical and morphological specialization
Calvin Cycle
Calvin cycle is vulnerable to low CO2 conditions
CO2 uptake and the Calvin cycle occur in different parts of the leaf
CO2 is taken up in the mesophyll by PEPcase
which has greater affinity for CO2 , and does not take up O2
CO2 concentration is increased in bundle sheath cells where rubisco is operating in the Calvin cycle
which reduces O2 uptake by rubisco
More ATP is required for the C4 pathway
higher photosynthetic efficiency gives these plants an advantage at high temperatures
Transpiration losses are minimized because PEPcase can take up CO2 even when stomates are not fully open
Crassulacean Acid Metabolism
(CAM) minimizes water loss
Nighttime is the best time to open stomata because it’s cooler and more humid
During the day, stomates are closed because it is too hot
CO2 uptake and the calvin cycle are separated temporally
CAM plants are often succulent, with thick, fleshy leaves or stems
Common in arid environments
Some occur in the humid tropics—mostly epiphytes that grow on tree branches and have less access to water.
Energy Mass Per Unit
Highest: Fats
Carbs
Proteins (but contain N)
Fibre (indigestible)
Lowest: Secondary compounds (can interfere with digestion)
Feeding strategies are very diverse among heterotrophs
Soil microorganisms that feed on detritus invest little energy to find food, but the food has low energy content.
Crossbills
each incipient species shows an adaptive peak in association with the conifer species it preferentially feeds on
Inside cones, there are very valuable, nutrient-rich seeds
Crossbill is used to take the husk off the seed inside cones (such as pinecones)
Therefore the beak of a crossbill is actually an advantage
Multicellular Animals
Have evolved specialized tissues and organs for absorption, digestion, transport, and excretion
Compared with omnivorous humans, herbivorous primates have longer digestive systems
Plant material is harder to digest than animals
Orangutans have a longer digestive system to have more opportunities to absorb nutrients from their plant material (which is poor nutrients/ harder to absorb)
Tools and Energy Gain
Humans view toolmaking as something that differentiates us from other animals
Toolmaking in chimpanzees has been known since the 1920’s
Some birds also make tools:
Ex. Crows on the South Pacific Island use tools to snag insects from decomposing trees
Ex. Dolphins have a learned behaviour called sponging, using another organism to protect them from getting stung at the bottom of the ocean floor
Knowing the isotopic composition of food sources provides a tool to infer the diet
