lecture 9 - autotrophs and photosynthesis

what do the prefixes “auto” and “hetero” mean in trophic terms

auto = self → make own organic carbon from CO2

hetero = other → use organic carbon made by others

autotrophy and heterotrophy 

autotrophy = derive energy from light (photosynthesis) or oxidation (chemosynthesis) to fix CO2 

heterotrophy = obtain carbon and energy from organic molecules

which groups show the greatest trophic diversity

prokaryotes → can be photo-, chemo-, auto-, or heterotrophic

fungi & animals = heterotrophs only

plants = mostly photoautotrophs

what is electromagnetic radiation

energy behaving as both wave and particle (photon); defined by wavelength and photon energy

what wavelengths are photosynthetically useful

photosynthetically active radiation (PAR) = 400-700 nm (visible light)

blue and red light are absorbed most by chlorophyll

what is PPFD

photosynthetic photon flux density → number of PAR photons hitting 1m² per second (umol m^-2 s^-1) measures light quantity

what environmental factors influence PAR

latitude, cloud cover, landscape shading, and plant position (relative to other plants or water depth)

how does light availability differ in forests

canopy trees = high PAR

understory plants = low PAR

species adapt to specific light niches (sun vs shade plants) 

how does light change with water depth

PAR and wavelength composition decrease with depth

red absorbed first → deep autotrophs use blue light

why do deep water algae appear red

their pigments absorb blue/green light and reflect red - adaptation to low-light, blue shifted environments

draw or describe the photosynthetic response curve

net photosynthesis rises with light until Isat (saturation irradiance)

Pmax = max rate

LCP = light compensation point (photosynthesis = respiration

How do sun and shade plants differ physiologically

sun plants - high Pmax & Isat, poor low-light efficiency

shade plants - lower Pmax, efficient at low light, damaged by full sun

write the overall equation for photosynthesis

6CO2 + 6H2O → C6H12O6 + 6O2

what are the 2 main stages of photosynthesis

light dependent reactions - use photons to make ATP, NADPH, and O2

light independent (Calvin Cycle) - uses ATP & NADPH to fix CO2 into carbohydrates

what enzyme fixes CO2 in C3 plants, and what is it’s limitation

RUBISCO → inefficient at high temperatures; when stomata close to conserve water, CO2 drops → photorespiration

How do C4 and CAM photosynthesis solve Cs plants problem

C4 - separates CO2 fixation and Calvin cycle spatially (different cells)

CAM - separates them temporally (day vs night)

describe C4 photosynthesis briefly

CO2 initially fixed by PEP carboxylase into C4 acids in mesophyll; transported to bundle sheath cells for calvin cycle; reduces photorespiration

Describe CAM photosynthesis briefly

At night, stomata open → CO2 fixed into C4 acids

daytime → acids release CO2 for Calvin cycle white stomata stay closed = saves water

what environments favor C4 and CAM pathways

C4 = hot, sunny, dry climates

CAM = Extremely arid environments (deserts, succulents)

give plant examples for each pathway (C3, C4, CAM)

C3 = wheat, rice

C4 = corn, sugarcane, grasses

CAM = cacti, pineapple, agave

why are few native C4 species found in edmonton

water is not limiting → C3 more energy efficient, C4 advantage appears only in hot dry conditions

compare advantages and trade offs among C3, C4, and CAM

Pros: C3 = high photosynthetic rate, C4 = reduced water loss, CAM = negligible water loss

Cons: C3 = massive water loss, C4 = energy costly, CAM = low rate

Best environment: C3 = cool wet, C4 = hot dry, CAM = hot arid

what is chemosynthesis

CO2 fixation by chemoautotrophs using energy from the oxidation of inorganic molecules instead of light

eg. H2S, NH3