Which of the following may limit primary productivity (photosynthesis)?
a. nitrogen
b. light
c. temperature
d. water availability
e. all of the above

e. All of the above

Explanation:

The primary productivity (photosynthesis) can be define as the total production of organic matter in the form of carbohydrates from available atmospheric carbon dioxide and water in the presence of sunlight, appropriate temperature, and nutrients by the plants or other autotrophs. The life on earth sustains due to primary productivity as the plants prepare their own food and these plants are consumed by the animals and other living beings.

On the basis of the above description, all of the above is the correct option. As plants or other autotrophs will not be able to synthesize their food in the absence of nitrogen (nutrient) obtain from the soil, light, temperature, and water.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.