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Edexcel IGCSE
Human Biology
Chapter 14
Human Influences on the environment

2. Ecosystems
• A distinct, self supporting system of organisms interacting
with each other and with their physical environment
• Can be small, such as wood or large like a tropical rainforest.
• Components of an ecosystem,
– Producers – green plants, that photosynthesis to produce
food.
– Consumers – animals who eat plants or other animals.
– Decomposers – bacteria and fungi, who recycle nutrients.
– Physical environmental – non biological components
(water, soil and air)

3. Plants and Photosynthesis
• This is the
reversed
equation
for the
aerobic
respiration
(see
chapter 1)

4. Conversion of Glucose in plants
• Starch – as a storage in plant leaves, roots and other
organs.
• Sucrose – for transportation.
• Cellulose – as a component of the cell wall.
• Lipids – as a storage in fruits and seeds (peanuts,
sunflower seeds and olives)
• Proteins and DNA – with the help of mineral irons
from soil (nitrates and phosphates)
• Chlorophyll – with the help of magnesium ions in the
soil.

5. Feeding relationships
• Food chain
– simplest way of showing feeding relationship within an ecosystem
– the arrow (→) means “is eaten by”
• Primary consumer – organisms that eats the producer
• Secondary consumer – organisms that feed on the primary consumer
• Trophic levels – the different stages in a food chain
• Tertiary consumer – organisms that feed on the secondary consumers
• Quaternary consumer – organisms that feed on the tertiary consumers
• Top carnivore – the carnivore at the end of a food chain
• Food web – linking several chains together

7. Ecological pyramids
• Ecological pyramids are
diagrams that represent relative
amounts of organisms at each
trophic level.
1. Pyramids of numbers –
represent the number of
organisms in a trophic level
2. Pyramids of biomass – show
the total mass of organisms
in a trophic level
(1)
(2)

8. Why are diagrams of feeding relationships
pyramid shaped?
• Some part of the producer re not digested or absorbed.
• Some of the absorbed materials are excreted.
• Much of the material is respired to release energy and
loss by water and CO2.

9. The flow of energy through ecosystem
• Photosynthesis fixes sunlight energy as
chemical energy ( Ex: Glucose)
• Respiration releases from organic compounds
• Almost all biological processes use energy
released in respiration
– Contraction
– Growth
– Reproduction
– Excretion
– Active transport
• If the energy released in respiration is used to
produce new cells, then the energy remains
fixed in molecules in that organism.
• If the energy released in respiration is used for
other processes then it will eventually escape
as heat from the organism.
• Energy flow diagrams – shows the main ways
in which energy is transferred in an ecosystem

10. Decomposers
• Decomposers (bacteria and fungi) break down complex
organic materials into simpler substances
• Main decomposers are;
– Bacteria
– Fungi
• Respiration of decomposers produce H2O and CO2 which
can be used by the plants for photosynthesis
• Proteins are broken down to ammonia and then to
nitrates which are essential minerals for the plants
• Humans use this natural decomposing process in
treatment of sewage

11. Sewage treatment
• Sewage is wet waste from houses, factories and farms.
• If sewage is discharged untreated it can lead to many problems;
– As aerobic bacteria uses high amount of oxygen, the depletion
of water kills many of the organisms
– Untreated sewage contains pathogenic bacteria which are
health hazards
• As a result of that only anaerobic bacteria will only survive
• As the water flows down it mixes up with oxygen in the atmosphere
and it increases the O2 level in the water
• This allows the clean water species to survive
• Aim of sewage treatment is to remove solid and suspended organic
matter and pathogens and to discharge cleaner effluent to the
water ways

13. Two methods of sewage treatment

14. Sewage treatment contd..
• Fungi and bacteria start the conversion of proteins in to
ammonia and then to nitrates
• Then, protozoa and larger invertebrate animals such as
worms act on the organic matter
• At the end effluent has less organic matter and less
pathogens, but it leads to eutrophication
• The waste sludge in tanks are used in other forms
– The anaerobic digestion produces biogas that can be
used as a fuel in electricity generators
– After anaerobic digestion the dry solid leftovers used
as fertilizer or used for land filling

15. Pit Latrines
• A composting toilet is a simple way of dealing with human waste
• The pit contain a hole in the ground over a sunken pit
• In the pit, faeces and urine are broken down by microorganisms
• An improved version is called ventilated improved pit latrine (VIP)
• VIP has a covered pit and vent pipe
• Vent pipe
– take away odours
– has a suction effect that draws clean air through the latrine
– The fly screen prevent flies leaving the pit (as flies can carry pathogens
outside)
• Sand or sawdust may be added to the pit after use to prevent smells and
discourage flies
• Larger pit latrines does not need emptying and smaller ones need new pit
dug

16. Pit Latrines

17. Eutrophication
• A situation where a larger amounts of inorganic material
(nitrates and phosphates) enter a body of water
• Pollution by these minerals can have very harmful effects
on an aquatic ecosystem
• There are two main sources of excess minerals
– From untreated or treated sewage
– From artificial nitrate or phosphate fertilizers
• Leaching
– Fertilizer highly concentrated with nitrogen and
phosphate washed out by the rain and added to
streams and rivers

18. Process of eutrophication
Death of Fish and other animals
Bacteria use up oxygen
Decomposition of death algae
Death of algae
Rapid growth of algae (Algae bloom)
Increase minerals in rivers or lakes
Leaching
Low oxygen levels inside the lake
Decrease photosynthesis of the plants
Algae growth inhibits light coming inside the lake
Death of Fish and other animals

19. Process of water purification
Treated water is pumped to homes
Chlorination to kill microorganisms
Sending the water through a filter bed of microorganisms for oxidization
Sludge is used as fertilizer or land fillings
Water is pumped to settling tanks for suspension.
Screening for solid objects, weeds and debris.
Water is taken from a source.

20. Process of water purification

21. Pollution
• Pollution takes place
when humans release
substances into the
environment that have
harmful effects and
they are not easily
removed by the
biological processes.
• Pollution is measured
by the amount of
pollutant.

22. Air pollution
• Carbon dioxide
– The reason rise is due to;
• increase burning fossil fuels (coal, oil, natural, petrol
and diesel)
• Cutting down large areas of tropical rainforest
(extensive deforestation)
– Consequences of increased levels of CO2;
• Causes global warming (enhanced greenhouse effect)

23. Greenhouse effect
• Greenhouse
gases,
– CO2
– Water vapour
– Methane (CH4)
– Nitrous oxide
(N2O)
– CFCs
• Describe how
greenhouse gases
increase
temperature?

24. Greenhouse effect
• The rise of Earth’s temperature;
– Melt polar ice caps that would increase sea levels
– Changing major ocean currents that result in warm
water beam redirected into previous cooler areas
– long term climate change
– Change in the nature of ecosystems;
• Species are enable to adapt to their habitat and they may
extinct
– Changes in agricultural practices
• High temperatures might allow some pests to complete their
life cycles more quickly

25. Air pollution contd….
• Carbon monoxide (CO)
– Forms when substances containing carbon are burned with limited oxygen
– Dangerous pollutant as it is colorless, ordourless and tasteless
– Can cause death by aspiration
– Hemoglobin has a strong affinity towards CO than the O2
– So if a person inhales CO he may lose consciousness and will cause death
• Sulphur dioxide
– Formed when fossils fuels are burned
– Cause acid rains that would destroy plants and marine life
• Nitrogen oxides
– Formed when fossils fuels are burned
– Cause acid rains that would destroy plants and marine life

26. Air pollution contd….
• Methane
– Produced when micro organisms ferment larger organic
molecules to release energy
– Significant organic origins of microorganisms
• Decomposition of waste in land fill sites by microorganisms
• Fermentation by microorganisms in rumen of cattle and other
ruminants
• Fermentation by bacteria in rice paddy fields
– Causes Global warming

27. Acid Rain
• Normal pH of rain = 5.5
• Acid rain has a lower pH than 5.5

28. Consequences of deforestation
• ‘Slash and burn’ adding CO2 to the environment which leads to global warming and climate
change
• Less trees to do photosynthesis
– Less Co2 is absorbed
– Less O2 is produced
• Destruction of habitats and bio diversity
• Reduced soil quality
– No trees and plants to return minerals back to soil
– No roots to hold soil together
– Rain washes the minerals out ( leaching)
• Leaching may cause
– Eutrophication
– rising water levels and floods
• Produce climate change by upsetting earth’s water cycle (as a result of reduced
transpiration)
• Many undiscovered drugs and crop plants are lost

29. Reforestation