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.
Fill in the gaps in the water cycle below, adding arrows.
What (form of energy) powers the water cycle?
> Sun's HEAT energy
What is the life process by which ALL living organisms release water vapour into the air?
Don't forget to add it above.
What is the (much less important) process by which mammals sometimes release water vapour into the air? Why do they do it?
> perspiration > to keep cool / regulate temperature
Why do geographers use the term evapotranspiration?
> combines evaporation & transpiration on an area of land -
difficult to tell the difference (the rest is runfoff or underground)
Apart from water, what else do rivers carry to the sea?
> soluble mineral (inorganic) salts > sediment / silt
What will be the long-term consequences of this?
> sea gets salty (and even saltier!) > silting up (mudflats, deltas etc - and erosion higher up)
List three sources from which water may be obtained.
> bore holes into aquifers > reservoirs > abstraction from rivers
Which of these should, in theory, provide the purest water?
> bore holes
What else might (naturally) be in this water?
What is the purpose of adding chlorine to the water supply?
> disinfection - kills bacteria
What is the purpose of sedimentation tanks?
> remove solid particles
How does the process involving coagulation tanks differ?
> chemicals are added to cause coagulation
Why does water abstracted from rivers need these processes?
> it is more impure/likely to be contaminated
Why do you think we use water from rivers?
> habitations grow up near rivers - flowing water has uses!
How might the activities of Man affect the water from bore holes?
> landfill sites / chemical spillages may contaminate
How might the activities of Man affect the water from reservoirs?
> pollution from sailing/fishing/animals
How might the activities of Man affect the water from rivers?
> sewage works / lowland industries
Some of the processes at the sewage works are based on physical separation, to take the solids out of the water. Others are biological transformations, involving growth of bacteria and protozoa. There is also an anaerobic phase in which different bacteria break down sludge, in the absence of air. This produces a fairly harmless solid substance which may be used as an agricultural fertiliser, as well as methane gas which may be used to generate electrical power in some sewage plants.
Which parts of the process involve aerobically-growing organisms?
> aeration tank (activated sludge)> "biological filter"
It is essential that these wastes are kept separate from the water supply, so there are regulatory bodies which oversee both water supply and sewage disposal.
What sort of things (or, rather, organisms) could theoretically be transferred from sewage to water supply (clue: they must be very small), and what might that cause?
> bacteria > diseases , e.g. diarrhoea
If the effluent from a sewage works discharging into a river is not sufficiently treated, it may also contain organic matter which will be acted on by bacteria in the river. These may then use up all the dissolved oxygen in the water.
What effects might this have on life in the river?
> kill some or most living organisms, leaving only species tolerant of pollution (& low oxygen levels)
Sewage effluent may also contain inorganic (mineral) nutrients which are the same as required by all green plants. Contamination of water itself by sewage effluent is not the main problem, but it may also cause other effects such as EUTROPHICATION which results in the growth of different organisms.
What sort of simple plant organism might be in the river?
Even the growth of simple plants may be a problem, because they sometimes also take in and use up oxygen.
Under what conditions would this occur?
> darkness / cloudy / overcast (insufficient light for photosuynthesis)
List some general categories of substances which may be present as pollutants in water:
> factory waste > farm wastes, e.g. slurry,silage,manure
> fertilisers > oil
> pesticides > paper mill waste, etc.
|Pollution type||Possible source||Apparent ill-effects|
|Soot||> smoke||> prevents photosynthesis by plants|
|Acid rain||> SO2||> kills trees|
|CFCs||> aerosols||> ozone depletion extra UV (skin) cancer|
|"Greenhouse effect"||> CO2||> global warming|
|Lead pollution||> exhaust fumes||> IQ lowering|
|Low level Ozone||> Vehicle engines, esp. in cities||> asthma|