Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
Name some general categories of organic compound which may
be in a living organism.
> carbohydrate > fats and oils > protein
Name some actual examples of common inorganic carbon compound (with chemical formulae?):
> carbon dioxide > Calcium carbonate/carbonate ion/hydrogencarbonate ion
CO2 CaCO3 CO32- HCO3-
What sort of organisms carry out decay?
> fungi, bacteria (saprophytes)
[decomposers - term describing ecological role]
What sort of organisms carry out respiration?
> plants, animals, fungi, bacteria, i.e. ALL living organisms
What sort of organisms carry out photosynthesis?
> GREEN plants
What other element is being recycled during respiration and photosynthesis?
> Oxygen: ( CO2 = C + O2 !)
What is the normal proportion of carbon dioxide in the air?
> 0.03 % - equivalent to 300 parts per million
to 0.04 400
Below is a representation of the carbon cycle.
Fill it in, and add arrows.
You could use different colour codes to show the quickest routes round the cycle, and the slowest.
What do the capital letters in boxes represent?
> forms of carbon - C compounds
What do the lower case letters on arrows represent?
> processes - transformations
What (form of energy) powers the cycle of conversions above?
> SunLIGHT - NOT heat
According to the simple treatment of the carbon cycle in some books, the amount of carbon dioxide in the air always stays the same. In fact for years many people took this situation for granted, ignoring Biologists' concern over several linked worldwide environmental, agricultural, political and industrial issues.
Explain why it was thought that the amount of carbon dioxide would always stay the same.
> Plants would use up excess carbon dioxide from combustion, etc., by photosynthesis
Which environmentally associated issues do you think fall into the categories mentioned above?
- agricultural > cut & burn - forest clearance
- political > self-sufficiency /
to get foreign currency from cashcrops
- industrial > electrical power needs fuel (coal/oil)
to be burnt
What other carbon compounds contribute to the greenhouse effect?
> methane CH4, chlorofluorocarbons CFCs
(as well as water vapour, nitrous oxide etc.)
Briefly explain some of the consequences which are feared.
> rise in temperature - climatic effects
> rise in sea levels, etc
Name some categories of organic nitrogen compound which may be in a living organism.
> protein > amino acids (& nucleic acids)
Name some (fairly specific) examples of common inorganic nitrogen compound.
> nitrates (NO3-) > nitrogen gas (N2)
Look at the diagram of the nitrogen cycle.
Note that most of the important conversions of nitrogen compounds take place in the soil. Despite being 78% nitrogen, air is only of minor importance as a nitrogen source to most living organisms!.
What is/are the main sort of organisms that use nitrates?
> GREEN plants
What do you understand by "the nitrifying process"?
> processes producing NITRATES
What sort of organisms carry out the nitrifying process?
> (nitrifying) BACTERIA
How are they connected with the carbon cycle? What name was given to the process there?
> the same micro-organisms (decomposers) > decay/ decomposition
What do you understand by "the denitrifying process"?
> processes losing NITRATES
What sort of organisms carry out the denitrifying process?
Denitrifiers and nitrifiers grow in different places. Explain.
> Denitrifiers respire anaerobically i.e live in waterlogged soils - ± no O2
Nitrifiers are aerobic i.e found in ordinary soils
What do you understand by "nitrogen fixation"?
>conversion of gaseous nitrogen to soluble form (which stays "fixed" in soil)
What sort of organisms fix nitrogen?
> (nitrogen fixing) BACTERIA
There are two sorts of these. How do they differ?
> "free living" - in soil "symbiotic" - in root nodules
For what reason might plants benefit from a thunderstorm?
> oxides of nitrogen dissolve to
Thunderstorms are not a very important process in the cycle, but farmers, especially in the Western world, manipulate the nitrogen cycle by adding chemical "fertilisers" in order to improve agricultural productivity. Do not confuse this with fertilisation, which is part of the sexual reproduction process, which may also have a part to play in agricultural productivity!
There is a link between this unit and the topics of Plant mineral nutrition and Soil .
What are the main "chemicals" (as distinct from products of animal origin) by which farmers add nitrogen to the soil?
> nitrates e.g. Ca(NO3)2, NH4NO3
Where does the nitrogen come from, ultimately?
There are several environmental issues connected with the use (or over-use) of fertilisers. For example, nitrates and other plant nutrients may leach or wash out of the soil or into deeper layers.
Briefly mention a few consequences:
> runoff and leaching going to rivers, causing algal blooms, pollution
> nitrates in river and other water enter drinking water system - suspected of link with cancer
Once again, fill in this version of the nitrogen cycle, adding arrows.
You could use different colour codes to show the major routes round the cycle, and the minor routes.
What is the significance of the following on the diagram above?
boxes > forms (compounds) of nitrogen
words on arrows > types of bacteria which transform
Add "leaching" to the cycle above.