Coping With Environmental Variation: Energy Lecture PDF

Coping with Environmental Variation: Energy September 12, 2024 Under what climate conditions would you expect pubescence to be common? Hot and dry conditions? Hot and wet conditions? Hot and windy conditions? Hot and calm conditions? Cool and wi...

Coping with Environmental Variation: Energy September 12, 2024 Under what climate conditions would you expect pubescence to be common? Hot and dry conditions? Hot and wet conditions? Hot and windy conditions? Hot and calm conditions? Cool and windy conditions? Under what climate conditions would you expect pubescence to be common? Hot and dry conditions? – yes: evaporative cooling is not a good option Hot and wet conditions? – probably not: evaporative cooling is a good option Hot and windy conditions? – probably not: convective cooling is possible Hot and calm conditions? – yes: convective cooling is not an option Cool and windy conditions? – possibly yes to reduce water loss and heat conduction or convection Energy sources  Energy sources Autotrophs: Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis). The energy is converted into chemical energy stored in the bonds of organic molecules. Heterotrophs: Obtain their energy by consuming organic compounds from other organisms. This energy originated with organic compounds synthesized by autotrophs.  Not all plants are autotrophs Some plants are holoparasites: They have no photosynthetic pigments and get energy from other plants (heterotrophs). Dodder is a holoparasite that is an agricultural pest and can significantly reduce biomass in the host plant. Not all plants are autotrophs Mistletoe is a hemiparasite – it is photosynthetic, but obtains nutrients, water, and some of its energy from the host plant.  Not all animals are heterotrophs Sea slugs have functional chloroplasts that are taken up from the algae that the slug eats.  Means of autotrophy Photosynthesis - sunlight provides the energy to take up CO2 and synthesize organic compounds. Chemosynthesis (chemolithotrophy): Energy from inorganic compounds is used to produce carbohydrates.  Two major steps of Photosynthesis Note: this is not a biochemistry class. You are not expected to memorize chemical names in this lecture 1. Light reaction—light is harvested and used to split water and provide electrons to make ATP and NADPH. 2. Dark reaction—CO2 is fixed in the Calvin cycle, and carbohydrates are synthesized. Ecological physiologists want to understand factors that affect photosynthetic rate.  Studying photosynthesis Light response curves show the influence of light levels on photosynthetic rate. Light compensation point is where CO2 uptake is balanced by CO2 loss by respiration (zero net photosynthesis) Saturation point: When photosynthesis no longer increases as light increases. Light response curve  Factors affecting photosynthetic rates Acclimatization to local environment Plants can acclimatize to changing light intensities with shifts in light response curves. Shifts in light saturation point involve morphological and physiological changes. Light response curve - acclimatization Leaves at high light intensity may have thicker leaves and more chloroplasts. (the rich get richer)  Factors affecting photosynthetic rates Local adaptations Plants from different climate zones have enzyme forms with different optimal temperatures that allow them to operate in that climate.  Figure 5.9 Photosynthetic Responses to Temperature (Part 2) Local adaptations Blue line: plants collected from coast Plants can acclimatize by synthesizing different enzyme forms (isozymes). Red line: plants collected from desert Factors affecting photosynthetic rates Nutrients Most nitrogen in plants is associated with Rubisco and other photosynthetic enzymes. Thus, higher nitrogen levels in a leaf are correlated with higher photosynthetic rates.  Trade-offs: nitrogen content But nitrogen supply is low relative to 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.  Factors affecting photosynthetic rates Rubisco: an enzyme with two activities Carboxylase reaction: Photosynthesis. Oxygenase reaction: O2 is taken up, carbon compounds are broken down, and CO2 is released (photorespiration).  Potential benefits to photorespiration Hypothesis: Photorespiration may protect plants from damage at high light levels. Altered tobacco plants with high rates of photorespiration showed less light damage than plants with normal or lowered photorespiration rates  Potential benefits to photorespiration But photorespiration is not advantageous if CO2 is low and temperatures high. Such conditions existed 7 million years ago, when C4 photosynthesis first appeared.  Plants do photosynthesis in different ways… Mechanism is often defined by niche: the abiotic and biotic conditions a species needs to grow, survive, and reproduce.  C4 pathway? The C4 photosynthetic pathway reduces photorespiration, and evolved independently several times. Carbon dioxide is ‘fixed’ in plants to form a molecule with 4 carbon atoms. In C3 plants, the molecule has 3 carbon atoms. Many grass species use this pathway CO2 uptake and the Calvin cycle C4 leaf occur in different parts of the leaf (spatial isolation). CO2 is taken up in the mesophyll by PEPcase, which has greater affinity for CO2. CO2 concentration is increased in bundle sheath cells (where Rubisco is), which reduces O2 uptake by Rubisco.  C4 pathway Trade-off: More ATP is required for the C4 pathway, but higher photosynthetic efficiency gives these plants an advantage at high temperatures. Transpiration losses are minimized because PEPcase can take up CO2 even when stoma are not fully open.  C4 pathway If photosynthetic rates determine ecological success, climatic patterns should predict regions where C4 plants will dominate.  CAM plants Crassulacean acid metabolism (CAM) minimizes water loss. CO2 uptake and the Calvin cycle are separated temporally. CAM plants open their stomates at night when it is cooler and humidity is higher, and close them during the day. CAM plants  Heterotrophs Heterotrophs 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. Fats Carbohydrates Energy Proteins (but contain N) per unit mass Fibre Secondary Compounds (can interfere with digestion)  Heterotroph feeding Multicellular animals have evolved specialized tissues and organs for absorption, digestion, transport, and excretion. They have tremendous diversity in morphological and physiological feeding adaptations. Crossbills – each variety shows an adaptive peak in association with the conifer species on which it preferentially feeds Compared with omnivorous humans, herbivorous primates have longer digestive systems to extract nutrients Plants and animals get their energy in many different ways, and their physiology and morphology are influenced by their environment. Next day: Evolutionary Ecology