Edexcell ppt Biology 4.1 - 4.17 Used in lessons to scaffold class teaching and as a revision resource for students

1. Ecology & Environment

2. Definitions
4.1 understand the terms population, community, habitat and ecosystem
• Population: all the individuals of a particular
species within a defined area
• Community: a group of different populations
living in the same area
• Habitat: the physical, chemical and biological
environment in which an organism lives
• Ecosystem: a community of living things and
the environment in which they live

3. How to Use a Quadrat (1)
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
• A quadrat can be used to calculate
the total population of a species
(e.g. snails).
• Simply count the number of
individuals in the quadrat.
• This technique only works for large
organisms which can be
distinguished as individuals and do
not move fast (not always easy for
plants, e.g. grass and tigers)

4. How to Use a Quadrat (2)
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
• A quadrat can be used to
calculate the percentage cover
of a species (e.g. moss).
• The quadrat is divided into
100 smaller squares.
• The percentage cover of the
quadrat is simply the number
of squares filled with the
species.

5. How to Use a Quadrat (3)
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
• A quadrat can be used to
calculate the percentage
frequency of a species (e.g.
daisies in a field).
• The quadrat is divided into 100
smaller squares. You simply count
a 1 for each square the species is
in and a 0 for those where it is
absent.
• This gives you an indication of the
frequency of the species, it does
not tell you the total population.

6. USE of A Sample Quadrat
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
The best use of a quadrat is in obtaining a sample
(it is not practical to count all of the species)
e.g. one cannot count all of the grass plants in a field!
Ecologists use quadrats to sample from a habitat.

7. You can use the data to:
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
Compare different species in ONE
area
Compare the same species in TWO
or MORE areas

8. Using a Quadrat
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
Sampling:
1) Sample has to be random (so no bias is
introduced).
2) Samples have to be representative, so we have to
take a large enough sample. At least 5% of
habitat.

9. Using a Quadrat
4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas
4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats.
How to make a quadrat sample?
• Find the boarders of your habitat (measure)
• Divide your habitat into a grid with X and Y coordinates.
• Randomly place your quadrat (use a random numbers for X & Y
coordinates)
• Count number or organism/organisms, percentage cover or
frequency of organisms.
• Record all data in a table.
• Repeat until a large enough sample size is completed
• Average all data
• Scale up average (multiply average per quadrat by number of
quadrats in habitat)
• Compare:
1. Different species in same habitat
2. Same species from a different habitat

10. Review from the past
4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers

11. Feeding Relationships
4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers
Food chains are used to show the relationships
between species in a habitat. E.g.
The secondary Consumer (eats the Primary
Consumer)
The Primary Consumer (eats the producer)
The Primary Producer (all food chains start with this)
FOX
RABBIT
GRASS
Each level in a food chain is called a Trophic Level

12. Definitions of Different Trophic levels
4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers
and decomposers
• Producers:
Plants (use sunlight to obtain nutrients)
• Primary Consumer:
Herbivores (plant eaters)
• Secondary Consumer:
Carnivore (animal / herbivore eaters)
• Tertiary Consumer:
Carnivore (animal / carnivore eaters)
• Decomposers:
Usually a bacterium or fungi, that breaks down the cells of
dead plants and animals into simpler substances.

13. FOOD WEBS
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
Food chains can be built up into complex food
webs. The difference between food chains and
food webs is that food webs have branches,
chains never do.

14. A Pyramid of Numbers
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
In a pyramid of numbers, the length of each bar
represents the number of organisms at each
trophic level in a specified area.

15. Pyramid of numbers (complex)
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

16. Pyramid of Biomass
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
In a pyramid of biomass, the length of each bar represents the
amount of organic matter – biomass – at each trophic level in a
specified area.
At each trophic level, the amount of biomass and
energy available is reduced, giving a pyramid shape.

17. Pyramid of Biomass
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

18. Compare Numbers to Biomass
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy
transfer

19. Pyramid of Energy
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
• It is a graphical representation of the trophic levels,
by which the incoming solar energy is transferred to
the ecosystem.
• It shows the total energy flow in the ecosystem.
• There does not exist an inverted energy pyramid.

20. Pyramid of Energy
4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
4.6 understand the transfer of substances and of energy along a food chain
4.7 explain why only about 10% of energy is transferred from one trophic level to the next.
Energy is never ‘lost’, it is transferred.
Not all the energy is transferred to the next
stage is converted into growth.

21. Pyramid of Numbers, Biomass & Energy
4.5 understand the concepts of food chains, food webs, pyramids of numbers, pyramids of biomass and pyramids of energy transfer

22. Cycles within Ecosystems
4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation (TA)
transpiration

23. Some quick definitions
4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation (TA)
Evaporation: To change from a liquid or solid state
into vapour.
Condensation: To become liquid or solid, as a gas or
vapour.
Precipitation: Rain, snow, sleet, dew, etc, formed
by condensation of water vapour in the
atmosphere.
Transpiration: The passage of watery vapour
through the skin or through any membrane or pore
in plants.

24. CARBON CYCLE
4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

25. Some quick definitions
4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion
• Respiration : The process in living organisms of
taking in oxygen from the surroundings and
giving out carbon dioxide (external respiration).
• Photosynthesis : The synthesis of organic
compounds from carbon dioxide and water (with
the release of oxygen) using light energy
absorbed by chlorophyll.
• Decomposition : To break down (organic matter)
physically and chemically by bacterial or fungal
action.
• Combustion : The process of burning

26. NITROGEN CYCLE
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and
denitrifying bacteria (specific names of bacteria are not required). (TA)

27. NITROGEN CYCLE
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and
denitrifying bacteria (specific names of bacteria are not required). (TA)

28. NITROGEN CYCLE
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and
denitrifying bacteria (specific names of bacteria are not required). (TA)

29. NITROGEN CYCLE
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying
bacteria and denitrifying bacteria (specific names of bacteria are not required). (TA)

30. Nitrogen Cycle
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria
(specific names of bacteria are not required). (TA)
This is not particularly easy to understand. You need to
know the roles of all the different bacteria. There are 4;
• Decomposers – turn nitrogen in protein into ammonium
+)
(NH4
-) into Nitrites
• Denitrifying Bacteria – turn Nitrates (NO3
-) into ammonium (NH4
(NO2
+ ) into Nitrogen gas (N2)
+) into nitrites
• Nitrifying bacteria – turn ammonium (NH4
-) and then nitrates (NO3
(NO2
-)
+)
• Nitrogen-fixing bacteria – turn N2 into ammonium (NH4

31. WAIT!!!
4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of
bacteria are not required). (TA)
There is more that you are not expected to know from
your syllabus, but may be included as additional
information in your exam on the Nitrogen Cycle
• Extension - leguminous plants
• All of the above bacteria are naturally present in the
soil. The only exception to this is that some Nitrogen-fixing
bacteria (e.g. Rhizobium) live in the roots of
some plants. These plants are called legumes (e.g.
peas, clover etc). They have a symbiotic relationship
with the bacteria i.e. both the bacteria and the plant
benefit from working together.

32. Human influences on the environment
4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide
Acid rain:
SO2, CO2 and NOx (oxides of nitrogen) dissolve in
rain to form Sulphuric Acid, Carbonic Acid and
Nitric Acid.
This falls as acid rain, which destroys soil,
pollutes waterways and causes erosion.

33. BIOLOGICAL CONSEQUENCES
4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide
1) Acid rain can 'burn' trees. This stops photosynthesis.
2) Sulphuric acid causes Calcium and Magnesium to be
leached out of the soil. Without Calcium and Magnesium
ions in the soil plant’s leaves turn yellow/wither and the
plant can't grow.
3) Reduce the pH of the streams & lakes. The affect is
that it releases aluminum ions (Al3+) which causes the
thickening of mucus in the fishes gills. Fish have difficulty
in obtaining oxygen. The fish numbers decrease.

34. CO
4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide
Carbon Monoxide (CO) is a gas added to the atmosphere
by the combustion of fossil fuels (particularly coal)
burned with insufficient oxygen.
• Carbon monoxide combines with our hemoglobin
inside our blood and blocks hemoglobin from carrying
oxygen which reduces oxygen circulation.
• This is toxic, too much carbon monoxide can be fatal.

35. Greenhouse Gasses
4.12 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases
4.13 understand how human activities contribute to greenhouse gases

36. Global Warming
4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to
global warming and its consequences
Greenhouse gases trap heat around the surface
of the Earth and are needed to keep the planet
warm enough for life.
1) Incoming shortwave radiation passes through the atmosphere and
hits the Earth, where it is absorbed. (LIGHT)
2) The Earth re-emits the radiation as longer-wavelength Infra-Red
radiation. (HEAT)
This is the problem.
3) Too much IR radiation is absorbed by greenhouse gases on its way
out of the atmosphere. This traps the too much heat in the
atmosphere.

37. GREENHOUSE EFFECT
GOOD
4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to globalwarming and its consequences

38. GREENHOUSE EFFECT
BAD
4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to globalwarming and its
consequences

39. GREENHOUSE EFFECT
4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its
consequences
The theory goes that the greenhouse effect is causing
global warming, which is bad. Global warming might
cause:
a) Polar ice cap melting (Sea levels rising)
b) Extinction of species living in cold climates
c) Changes in rainfall (both droughts and flooding)
d) Changes in species distribution (i.e. tropical species
spreading, like mosquitoes)

40. Eutrophication
4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms
causing depletion of oxygen (TA)
4.16 understand that eutrophication can result from leached minerals from fertiliser
Eutrophication is what happens when too much chemical
fertiliser is used on crops and it washes/leaches into rivers
and streams.
(also nitrates can come from sewage)
1) The nitrates in the fertilisers are essential to get crops to
grow well and increase yields.
NITRATES ADDED
2) However, if too much is used, or it rains soon after it is
added to fields, the fertiliser gets washed away.
RUN OFF
3) The nitrates then help plants in the rivers and streams to
grow very quickly, especially algae.
ALGAL BLOOM

41. 4) But after the initial massive growth in algae
there isn't enough light and water plants die
MASSIVE PLANT DEATH
5) Without sunlight and when the nitrates run
out MOST of the algae die
MASSIVE ALGAL DECAY
6) All those dead plant start to decay. Respiring
bacteria remove oxygen from the water.
ANOXIC CONDITIONS
7) No Oxygen kills fish and other animals.
ANIMAL DEATH AND DECAY

42. 8) Then even more algae and animals die.
MORE DEATH & DECAY
9) pH levels fall as decomposition produces acids
pH DROPS
10) Everything dies and waterway can no longer
support life
TOTAL DEATH
So farmers have to be very careful using fertilisers
so as not to wipe out all river and lake life.

43. Simply but Clearly
4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing
depletion of oxygen (TA)
Nitrates >
Algae Grow >
Algae Die >
Algae Decay >
No Oxygen >
Fish &
Animals Die

44. Deforestation
4.17 understand the effects of deforestation, including leaching, soil erosion, disturbance of the water cycle and of the
balance in atmospheric oxygen and carbon dioxide
Cutting down trees and not replacing causes:
• Leaching of soil minerals
• Soil erosion / washed and blown away (no roots
holding soil together)
• Desertion (new deserts forming)
• Disturbance of the water cycle (less transpiration
can lead to flooding and / or drought)
• Increase in CO2 levels
Less photosynthesis
• Decrease in O2 production
Burning trees