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ENVS 1500 Lecture 2.docx

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York University
Environmental Studies
ENVS 1500
Gail Fraser

Lecture Two:  Assignment 2 due date has changed to Oct 21  Assignment 1 part 1 for tmrw. 1) Energy and Nutrients 2) Populations 1) Energy sources: a. Autotrophs – self feeders b. Heterotrophs – other feeders i. Where does the carbon come from? Photosynthesis Photons hitting pigments of plants and those pigments focus electrons that generate ATP/NADPH and with them they create sugars with the C02 that is in the atmosphere. Considering two types of plants: C3 plants & C4 plants – dif. evolutions of photosynthesis. C3: most trees are C3plants. Carbon is taken in and it is C3 because the product has 3 carbons in it. It all happens in the mesophyll cell (outer layer of plant). The Stoma must be open to create energy (sugar/ATP) but in the process it loses water – so temperature and moisture is very important: high transpiration – the process of moving water through the plant (costs involved – lose water through stoma). Lower productivity C4: In the case of C4 plants they’ve evolved an additional pathway that allows them to create C4 molecules (4 C). The making of the sugars happens somewhere eles & this allowed C4 plants to exist and undergo photosynthesis is got climates without losing water (stoma can stay open w/o losing water). Low transpiration and higher productivity. The exponential increase in CO2 output by industry has only stopped 3 times in the 20 C. High C: N ration shows that plants are relatively rich in carbon and poor in nitrogen Low C: N rations shows that animals, fungi and bacterial are relatively rich in nitrogen Detritivore: key in nutrient cycling food – rich C, low N. Soil moisture and temperature are very important to detritivores Heterotrophs: herbivores eat plants and eat a lot of plants to get the energy they need (low in N)  Nutrition and plant defenses (thorns, etc). Bottom on the sea: chemosynthetic organisms get hydrogen sulfide and transfer it into energy. Carnivores: eat other things and depending on the carnivore the C;N ratio varies widely. The difference
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