Lecture 24

Question 1

2 sources of carbon

Answer 1

Carbon is fixed into organic molecules during photosynthesis (roughly CO2 + H2O + Sun’s Energy→ C6H12O6 + O2).

Carbon is released during cellular respiration (C6H12O6 + O2 → CO2 + H2O + ATP + Heat Energy), by consumers, decomposers and by the producers (they do cellular respiration too).

It’s also released by the burning of wood and fossil fuels such as coal, peat moss, and oil, all of which are end products of photosynthesis

). It is also found in the atmosphere as CO2 and is also present dissolved in water & rocks.

Question 2

Nitrogen is present in many essential molecules, including

Answer 2

nucleic acids, amino acids, and chlorophyll.

Question 3

the nitrogen present in food webs comes from many sources, including

Answer 3

fixation of N2 by bacteria, nitrate in the soil, & ammonification of nitrogenous waste.

Question 4

can plants use n2? why? what do they use

Answer 4

Earth’s atmosphere is 78% N2, but plants can’t use N2 (it’s too stable to be used in synthesis reactions). So N2 must be converted to ammonia (NH3).

Question 5

cycle of nitrogen?

Answer 5

bacteria are needed for almost all of the steps

1. Nitrogen fixation convert nitrogen gas to ammonia (N2→NH3). Carried out only by certain bacteria
2. Nitrification (ammonia to nitrate: NH3→NO3-). Carried out by certain bacteria and archaeans
3. Assimilation: nitrogen into proteins and DNA.
4. Ammonification: bacteria or fungi convert the organic nitrogen (part of proteins, DNA etc) within the remains of dead organisms back into ammonium.
5. Denitrification: conversion of nitrate (NO3-) to nitrogen gas (N2): returns N2 to the atmosphere

Question 6

Phosphorous is found in

Answer 6

nucleic acids, phospholipids, & ATP

Question 7

major way that phosphorous leaves the abiotic component of the ecosystem to enter the biotic component.

Answer 7

It erodes from rock as inorganic phosphate (PO4), which plant roots absorb.
Animals get the phosphorus they need from their diets. Decomposers release PO4 into the environment.

Question 8

connection between precipitation, evaporation, and transpiration

Answer 8

Precipitation onto land & bodies of water

Evaporation from land & bodies of water

Transpiration from plants