Human population growth
South Tuen Mun Government Secondary School
Biology Revision Note 15

The doubling time becomes much shorter because of better medical care and economic growth, birth rate is faster than the death rate. Moreover, the survival of newborn baby increases.

Increase in human population will use up more the natural resources and cause pollution problems.
Example of renewable resources : timber, fish; non renewable resources : fossil fuels and minerals
Human activity Environmental impact
Fishing

Depletion of fish stock (some human consumed species e.g. humphead wrasse become extinct)

Killing of non target species e.g. juvenile fish

no reproduction

extinction of fish species

Destruction of marine habitats e.g. coral reef (breeding ground of some fishes)

no reproduction / newborn cannot grow up

extinction of fish species

Food resources for other fish species are reduced

affect the food web and
Deforestation
Agriculture
Urbanization and industrialization ecological balance
 Destruction of natural habitat  loss of shelter and food  death and extinction of species  affect the food web and ecological balance
 Soil erosion  removal of top soil  infertile land; soil erosion  blocking of river
 raising the seabed  flooding
 Global warming and greenhouse effect because the decrease in the rate of photosynthesis, less carbon dioxide is taken up  increase in the carbon dioxide concentration in air

Destruction of natural habitat
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Soil erosion

Excess use of chemical fertilizer

leaching to nearby river / sea
 eutrophication

Excess use of pesticide
 accumulation along the food chain + development of pesticide resistant pest

Depletion of certain mineral(s) in the soil due to monoculture

Land clearance

destruction of natural habitat

Reclamation

destruction of coastal habitat

Dredging

reduce light intensity in the water

death of green plants / phytoplankton (producers); dredging

suspended particles

clog the gills of fishes

Air pollution due to burning of fossil fuel

Water pollution due to untreated sewage, solid waste and oil

Global warming and greenhouse effect

When the carbon dioxide concentration in the air increases (due to deforestation + burning of fossil fuel), the infrared radiation is absorbed and trapped in the atmosphere. This is the greenhouse effect. When the infrared radiation is trapped, the temperature of the atmosphere on earth increases. This is global warming.

Global warming

melting of ice at the poles

rise in sea level

flooding of low-lying area

Global warming

unusual weather pattern + spread of infectious disease
Eutrophication by chemical fertilizer (e.g. phosphate, ammonium, nitrate) or detergent (phosphate)

fast growth of algae (algal bloom)

very fast rate of respiration at night

use up oxygen (depletion of oxygen in water)

suffocation of aquatic organisms e.g. fishes

dead bodies of aquatic organisms

food for bacteria

further use up oxygen and release of toxin

death of more aquatic organisms
Accumulation along the food chain
When a pesticide / heavy metal from sewage cannot be broken down and cannot be excreted, it will increase in concentration from one trophic level to another trophic level along the food chain because an organism in the higher trophic level eats many organisms of the lower trophic level. The concentration may reach a very high concentration that poisons living organisms in the top trophic level e.g. man.
Air pollution
Air pollutant
Carbon particles
Harmful effects
Deposit on the air sac

a physical barrier

reduce surface area / increase the distance of diffusion

slower gaseous exchange

diseases e.g. bronchitis, asthma
Lead particles Affect mental development
Carbon monoxide Bind with haemoglobin

haemoglobin cannot carry oxygen

lower oxygen carrying capacity of blood

dizziness, headache or even death
Sulphur dioxide and nitrogen dioxide

Irritate breathing system, eyes

Smog

damages heart and lung + reduce light reaching the earth (reduce rate of photosynthesis)

Dissolve in rainwater

acid rain

damage plants (crops) and stonework
Carbon dioxide
Chlorofluorocarbons
(CFCs)
Global warming
Destroy ozone layer (ozone depletion)

more UV light reaches the earth

damage crops and increase the risk of skin cancer
Water pollution
Causes Harmful effects
Untreated sewage

Domestic sewage

urine, faeces, dirty water

contains bacteria, virus
 infects man e.g. cholera, dysentery, eye and skin diseases

Hot water

increases water temperature

lower oxygen solubility
 suffocation of aquatic living organisms

Chemical poisoning by cyanide and heavy metal (accumulation along the food
Solid waste
Oil chain)

Industrial sewage and domestic sewage (detergent)
 eutrophication

algal bloom
 Plastic bag traps fishes
Prevents dissolving of oxygen

suffocation of aquatic living organisms
Sticks feathers of birds

cannot fly, cannot keep warm and get poisoned after swallowing oil

Human responsibilities for the environment
(i) Pollution control

3R (reduce, reuse, recycle) Principle

To reduce air pollutant by

Set up laws to tighten the fuel sulphur content and vehicle emission standards

Encourage the use of liquefied petroleum gas (LPG) and catalytic converters (to remove air pollutants from exhaust fumes)

Promote better vehicle maintenance and eco-driving (e.g. switching off engine when stopping the car)

Joint plan with Guangdong ( 廣東 ) Government to reduce formation of smog

To reduce water pollution by

Sewage treatment

Primary treatment – remove large solid wastes e.g. plastic bag by the grit and remove suspended solid particles by slow running sewage in the settling tank

Secondary treatment – microorganisms (bacteria, fungi) carry out decomposition of organic wastes in the solution

Tertiary treatment – kill microorganisms by chlorine / UV light; remove inorganic wastes e.g. nitrate, phosphate (very expensive, many countries do not do this)
[solid waste / sludge is broken down in the digestion tank by anaerobic bacteria

biofuel e.g. methane + solid residue as fertilizer]

Polluter pays principle

Harbour area treatment scheme
(ii) Conservation – maintain the natural environment and biodiversity by managing the abiotic and biotic components of the ecosystems

Importance of maintaining biodiversity

(i) economic reason : living organisms provide a lot of valuable goods e.g. food, medicine, materials, genes for improving agricultural products e.g. plant crops and farm animals; (ii) ecological reason : each organism has its role in an ecosystem, this is important to maintain ecological balance; (iii) aesthetic reason : biodiversity in the natural habitat is valuable for recreational activity; (iv) moral reason : it is not moral to destroy the habitat of other living organisms, making them extinct.


Conservation of endangered species

(i) protect wild animals and plants by laws e.g. trading of endangered species is not allowed; (ii) breeding programme in zoos e.g. artificial insemination of endangered species; (iii) gene bank

store the seeds, sperm, ovum, tissues, blood products and DNA of living organisms; (iv) education

to increase the awareness to protect wildlife through exhibition, education centres, competition;
[Examples of endangered species in the world : panda, tiger; examples of endangered species in Hong
Kong : Romer’s Tree Frog ( 盧氏小樹蛙 ), Chinese White dolphin ( 中華白海豚 )]

Conservation of natural habitats by setting up country parks, nature reserves, marine parks, marine reserve, sites of Special Scientific Interest, Ramsar site

Country parks are conserved by (i) tree planting, (ii) hill fire fighting, (iii) bird nest, (iv) visitor centres, (v) nature trail e.g. Tai Lam Country Park ( 大欖郊野公園 )

Nature reserves are conserved by restricting human activities in these area e.g. lighting fire is not allowed in Tai Po Kau Nature Reserve ( 大埔滘自然護理區 )

Marine parks are conserved by recreational activities and restricting human activities such as removal of specimen from the park e.g. Hoi Ha Wan Marine Park ( 海下灣海岸公園 )

Marine reserves are conserved by restricting human activities such as fishing, water sports e.g.
Cape D’Aguilar Marine Reserve ( 鶴咀海岸保護區 )

Site of Special Scientific Interest is set up based on the special collection of animals and plants in the area, new development is not allowed e.g. Ngong Ping ( 昂平 ) – largest collection of
Romer’s Tree Frog

Ramsar site ( 拉娒薩爾濕地 ) + wetland park – wetland areas that are protected e.g. Mai Po Inner
Deep Bay ( 米埔內后海灣 )

Restoration of damaged area by (i) afforestation, (ii) stream restoration and (iii) ecological migration e.g. to construct an artificial wetland to replace a loss of wetland due to the building of Lok Ma Chau
Spur Line ( 落馬洲支線 )
(iii) Sustainable development
 the way of development which meets the present needs without compromising the needs of a good quality of life in our future generation.
 to balance economic development, social development and environmental protection in the development of the society

Examples of sustainable development

Fishing industry : (i) introducing the fishing moratorium – allow fishes to breed, grow and reproduce;
(ii) stopping destructive fishing methods e.g. explosives, cyanide; (iii) carrying out artificial reef project – provide breeding ground for reproduction and development of new born aquatic organisms;
(iv) giving advice on aquaculture

Forestry : (i) afforestation; (ii) hill fire fighting

Agriculture : (i) use organic fertilizer – not easy to leach, replace the humus and reduce soil erosion;
(ii) use organic pesticide – can be decomposed, thus will not accumulate along the food chain + biological control method by introducing natural enemy of the pest; (iii) crop rotation – growing of legume crop that has mutualism with nitrogen fixing bacteria, to increase the nitrogen content in the soil

better growth of other crops