Lecture 3: Coping with Environmental Variation - Energy Flashcards
Autotroph Definition
Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis)
Autotroph Key Step
The energy is converted into chemical energy stored in the bonds of organic molecules
Heterotroph Definition
- Obtain their energy by consuming organic compounds from other organisms
- consume energy-rich organic compounds (food) and convert them into usable chemical energy (ATP)
Holoparasites Definition/ Example
- 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 Definition/Example
- photosynthetic, but obtains nutrients, water, and some of its energy from the host plant
Ex. Mistletoe
Photosynthesis Definition
- most autotrophs
- sunlight provides the energy to take up CO2 and synthesize organic compounds
Chemosynthesis Definition
- Energy from inorganic compounds is used to produce carbohydrates
- important in nutrient-cycling bacteria, and in some ecosystems such as hydrothermal vent communities
- Ex. Ammonium and nitrate
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 - light reaction
- Light is harvested and used to split water and provide electrons to make ATP and NADPH
Photosynthesis - dark reaction
- CO2 fixed in the Calvin cycle
- Carbohydrates are synthesized
Photosynthetic rate
- determines the supply of energy, which in turn influences growth and reproduction
Light Response Curves Definition
- show influence of light levels on photosynthetic rate
- Plants can acclimatize to changing light intensities with shifts in light response curves
Light Compensation Point Definition
- Where CO2 uptake is balanced by CO2 loss by respiration
Saturation Point
- When photosynthesis no longer increases as light increases
- 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
- influences CO2 supply in terrestrial plants
- Low water availability causes stomates to close, restricting CO2 uptake
- 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
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
- Oxygenase reaction
Carboxylase Reaction
photosynthesis
Oxygenase Reaction
O2 is taken up, carbon compounds are broken down and CO2 is released (photorespiration)
Photorespiration under High Light
- Dissipate energy
- protects plants from damage
Photorespiration under Normal Light Conditions
when plants can’t photorespire they die
Photorespiration is a Large Disadvantage if ____
CO2 is low and temperatures are high
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
- 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)
Transpiration Losses are Minimized because ______
- PEPcase can take up CO2 even when stomates are not fully open
Crassulacean Acid Metabolism (CAM)
- minimizes water loss
- At night 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)
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
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
Examples of Animals that Make Tools
- Crows on the South Pacific Island use tools to snag insects from decomposing trees
- Dolphins have a learned behaviour called sponging, using another organism to protect them from getting stung at the bottom of the ocean floor
