Man’s place in nature
Classification of man
Animal: cannot make own food but
must obtain food from plants or other
animals
Vertebrate: with backbone
Mammal (same group as cat, cow, horse
& dolphin)
Primate (same group as monkey, tarsier
& chimpanzee)
Characteristics of Mammals
1) hair present
2) no eggs laid but young born alive after
a
period of development inside the
mother’s
body
3) Young fed on milk produced by the
mother’s
mammary glands after birth
4) Parental care well developed (young
dependent
on and protected by the parents
for a period
of time)
5) Homoiotherm - can maintain constant
and
relatively high body temperature to be
active
even at low environmental
Characteristics of Primates
1) Brains relatively larger than those of
other
mammals so that they have great
learning
power and a high intelligence.
2) Both eyes face forward instead of being
situated
at the sides of the head. Hence, good
judgment
of distance.
3) Have a flat face and a short snout
4) Have opposable thumb - thumb touching fingers
of
the same hand to grasp objects with hands
(e.g.
man holding tools and monkey holding
tree
branches). It is also separated from
other
fingers, all of which end at a nail.
Unique biological features of man
1) Upright posture, with head held vertically on
the
vertebral column, to free the hands from
walking
2) Body weight supported on 2 legs during walking
or
standing due to broad and strong pelvic
girdle,
longer and stronger hindlimb (or foot
bones) than
forelimb
3) Better developed opposable thumb to grip
objects
more strongly and to manipulate objects
and tools
precisely and skilfully, aided by the
eyes at the
front of the head
4) Large cerebrum, resulting in development
of
complex tools, languages, culture &
man’s
dominance
Ecology:
• The study of the interaction between
organisms and their physical environment,
and with other organisms.
Habitats:
• They are defined regions in the natural world.
• Each habitat has a particular set of physical
conditions in which an organism lives
• Physical conditions include temperature,
humidity and soil type
Various habitats on Earth:
Freshwater stream
Forest
Mangrove
Grassland
• Each habitat is occupied by a
characteristic community of organisms,
which is made up of different populations
 Habitat:
the place where an organism occurs
 Population:
a group of organisms of the same species
in an area
 Community:
populations of all the different organisms
in the same area
The components
of an ecosystem
Ecosystem:
A dynamic and self-supporting system where organisms
interact with each other and with their environment
What does the environment refer to?
• The environment of an organism made up of:
– an abiotic part (physical environment)
– a biotic part (other organisms in the
surroundings)
• These affect the number, distribution,
behaviour and types of organisms in a habitat
What are abiotic factors?
• The abiotic factors arise from the non-living
components in the environment. They differ
between habitats
• The major abiotic factors are:
–
–
–
–
–
Temperature
Light
Rainfall and humidity
Wind
Soil
What are biotic factors?
• Arise from other organisms in the environment
• Organisms interact with each other in various
ways, and these may be beneficial or harmful to
each other
• The major interactions are
- Predation
- Competition
- Commensalism
- Mutualism
- Parasitism
Energy flow in an Ecosystem
Sunlight
The ultimate source
of energy
Absorbed
by
Plants and algae
Converted to
Animals
Eaten by
Chemical energy in
organic molecules
Energy is transferred in the
form of organic materials
within an ecosystem
• Feeding relationships like this are usually
expressed in a food chain or a food web
What are food chains and food webs?
• A particular feeding relationship and
sequence of energy flow between organisms
in a habitat can be shown as a food chain
• Examples:
– In a grassland
Grass
Rabbit
Snake
Hawk
– In a freshwater pond
Algae
Water flea
Shrimp
Fish
• Food chain: over-simplifies the natural situation.
• Food web: a more accurate representation of the
energy relationship, which shows all the possible
feeding relationships between organisms in a
habitat
• Example: In a grassland:
What are the roles of organisms in an
ecosystem?
• The three main roles of organisms in an
ecosystem: Producer, consumer and decomposer
• Decomposers are not shown in food chains
Producers
• All food chains starts with
producers.
• Include all autotrophic
organisms such as plants
and algae.
• Provide energy for the
organisms in the ecosystem
Consumers
• Consumers are organisms that feed on other organisms
• Primary consumers: Animals that feed on plants (Herbivores)
• Secondary consumers: Animals that feed on primary consumers
(Carnivores)
• Tertiary consumers: Animals that feed on secondary consumers
(Carnivores)
Primary consumer
Secondary consumer
Tertiary consumer
• Humans play various roles in food chains.
• We can be primary, secondary or tertiary consumers
With reference to your daily diet,
try to work out your position as a
consumer in the various food chain.
Decomposers
• Organisms that break down organic materials
(e.g. dead bodies and waste products) into simple,
inorganic substances, which can be used by the
plants again.
• Important in recycling materials in the ecosystem
• Mainly bacteria and fungi
What are trophic levels?
• Each level of organisms in a food chain is called a
trophic level
• Example:
Trophic level
Fourth
Third
Second
First
Types of organism Example of organism in
a food chain
Tertiary consumer
Secondary consumer
Primary consumer
Producer
Hawk
Snake
Rabbit
Grass
How energy is transferred
between trophic levels?
• Producers convert light energy into chemical
energy which is stored in organic molecules.
• When the producers are eaten, this chemical
energy is transferred to the next trophic
level.
• Thus, energy is transferred along the food
chain
How energy is transferred between
trophic levels?
•
However, a small proportion of energy can be transferred
to the next trophic level due to energy loss at each level:
1. Consumed during respiration.
The energy released is given off as heat or used to
support body activities
2. Lost in the form of wastes and excretory substances
3. Lost when the organisms die without being consumed
• Energy loss means that some energy cannot
be transferred to the next trophic level
• The wastes and dead bodies are broken
down by decomposers, and the chemical
energy stored is used by them
Some energy trapped by producers is also released to the environment as
heat.
Hence, a continuous supply
of light energy is essential for
the growth and activities of
organisms in the ecosystem
Investigation of a
Balanced Aquarium
Why is it necessary to use
tap water which has been
standing for a few day ?
Ans: Because fresh tap
water contains
chlorine which is
harmful to
organisms in the
aquarium.
lid
water
water
snail
freshwater
plant
Why is it unsuitable to
introduce large carnivores
into the glass jar ?
Ans: Because they
require more food
to survive and they
will eat up all the
organisms in the
aquarium.
lid
water
water
snail
freshwater
plant
Describe the appearance
of the water snails and
the freshwater plants
after a few days if the
aquarium is balanced ?
Ans: The water snails
and the aquatic
plants will remain
healthy even after
a few weeks.
lid
water
water
snail
freshwater
plant
What will happen to the
aquarium if it is placed in
darkness all the time ?
Why ?
Ans: Both the water
snails and the
freshwater plants
will gradually die
since there is no
light for the aquatic
plants to carry out
photosynthesis to
make food…
lid
water
water
snail
freshwater
plant
What will happen to the
aquarium if it is placed in
darkness all the time ?
Why ?
Ans: The plants cannot
survive without
food supply. As all
aquatic plants died,
the water snails
also die due to
starvation.
lid
water
water
snail
freshwater
plant
What is the relationship between
trophic levels?
• The total amount of energy available to each
trophic level become progressively less along
a food chain
• This relationship can be expressed by using:
- The pyramid of numbers
- The pyramid of biomass
Pyramid of numbers
• The number of organisms in a higher trophic level is
usually smaller because:
- The amount of energy available decreases along
a food chain
- A predator is usually larger than its prey
• In a pyramid of numbers, the width of each bar
represents the number of organisms at a trophic level
Why does a large
body size leads to a
small number of
organisms in a
trophic level?
Drawbacks of the pyramid of number:
• It only considers the numbers of organisms,
but not the amount of energy stored in their
bodies
• An inverted pyramid of numbers can result
from organisms with a very large size
Can you give another example of a
food chain showing an inverted
pyramid of numbers?
Pyramid of biomass
• Biomass:
the total dry mass of organisms at a certain
trophic level.
• The pyramid of biomass is a more accurate
representation of the energy transfer because:
-The amount of energy stored in an organism is
usually proportional to the amount of living
materials in its body
• There is a limit to the length of food chain (< 5
links) because:
- Energy is continuously lost along the food
chain, the energy available to organisms at higher
trophic levels becomes progressively less.
• The pyramid of biomass shows that the lower
trophic levels contain more energy
 we can obtain more food from a piece of land
if we use it for growing crops rather than rearing
cattle
To know more about the energy flow in an
ecosystem, visit:
• http://web.ukonline.co.uk/webwise/spinneret/
eco/ecosys.htm
How are toxic substances accumulated
along a food chain?
• Pests are organisms that can damage our crops
• Pesticides are poisonous chemicals used to kill
pests
• Some pesticides are very stable compounds. They
can stay inside organisms for long periods without
being broken down by metabolism or excreted.
•These will accumulate along
food chains and may reach an
amount high enough to kill
organisms at higher trophic
levels
• Example: the pesticide called DDT (a pesticide)
- Widely used in the past
- It is a large molecule that cannot be
excreted
or broken down by metabolic
processes
Accumulation effect of DDT:
• Consumers feed on a relatively large quantity of
organisms in their lower trophic level
 A higher concentration of DDT accumulated in their body
 DDT became more and more concentrated along the
food
chain
 Reach a toxic level in the bodies of the fish and birds
• Thus, the use of DDT has been banned in many countries
What is the effect of DDT on humans?
Introduction
Producers
Inorganic
substances
Synthesize
Complex organic
substances
CYCLING OF
MATERIALS
Decompose
by
Decomposers
Respiration
By feeding
Other
organisms
Faeces,
excretory products
and dead bodies
How does the cycling of carbon
occur in the ecosystem?
• Carbon is an important component
of carbohydrates, fats, proteins, nucleic
acids and other substances essential to the
life of organisms
• The continuous movement of carbon
between organisms and the physical
environment is the carbon cycle
44
The carbon cycle
Carbon Cycle
Carbon dioxide in air
respiration
respiration
organic substances
in animals
feeding
burning
assimilation &
photosynthesis
organic substances
in plants
incomplete
fossil fuel decomposition
Removal of carbon dioxide from the
atmosphere and water
• In atmosphere:
Carbon is present as carbon dioxide in the
atmosphere
• In water bodies:
Carbon is present as dissolved carbon
dioxide, carbonates and hydrogencarbonates
Ways of removal of carbon in nature:
1. Producers take up carbon by photosynthesis to produce
organic substances.
2. Through feeding, the organic molecules are transferred to
the bodies of different consumers along the food chain
Return of carbon dioxide to the
atmosphere and water
Ways of return of carbon:
1. Respiration carried out by all organisms breaks
down organic compounds, and releases carbon in the
form of carbon dioxide back to the environment
2. Decomposition of the dead bodies and organic
wastes by decomposers released carbon back to
the environment
• Large number of organisms
are buried due to movement
of the Earth’s crust. They
are turned into fossil fuels
such as coal and oil
(petroleum)
Through burning, the
carbon present in fossil
fuels and wood are
returned to the
atmosphere as carbon
dioxide
To know more about the carbon cycle, visit:
• http://www.smy.fi/koulut/carbon/
How does the cycling of nitrogen
occur in the ecosystem?
45
The nitrogen cycle
• Nitrogen is an essential component of
proteins, nucleic acids and other nitrogencontaining compounds
• The nitrogen cycle describes the cycling of
nitrogen in ecosystems
•Though 78% of air is nitrogen, they cannot be
used
directly by most organisms.
•They are made available by the activity of
nitrogen
fixing bacteria living freely in the soil or
in the
root nodules of leguminous plants such as
peas and
beans which convert atmospheric
nitrogen into nitrates. This process is called
nitrogen fixation.
1. Atmospheric nitrogen may also react with oxygen
to form nitrogen oxides by electrical discharges
during lightning. These oxides are dissolved in
rain water and carried to the soil to form nitrite
and nitrate.
Cycling of nitrates among organisms
• Plants obtain nitrogen mainly in the form of nitrates in
the soil water, which they then assimilate into proteins.
• Animals obtain nitrogen compounds through feeding
along food chains, so that plant proteins are assimilated
into animal proteins.
• Nitrate can be recycled due to breakdown of dead organic
matter:
Decomposed by
Dead organic matter
putrefying bacteria
and fungi
Nitrates
Nitrites
Ammonia or
ammonium compound
Oxidized by
nitrifying bacteria by
a process called
nitrification
• Though nitrates can be absorbed by the plants from
the
soil water, some may be:
- Lost from the soil by leaching in rain water
- Changed to atmospheric nitrogen by the action of
denitrifying bacteria, which are active when the soil
is poorly aerated. The process is called denitrification.
To know more about the nitrogen cycle, visit:
• http://web.ukonline.co.uk/webwise/spinneret/
eco/cycles.htm
• In natural habitats:
The processes which remove and replace nitrates in
the soil are in balance.
• In agricultural lands:
A large amount of nitrogen in the organic matter is
removed by harvesting.
Fertilizers must be added to the soil to maintain crop
yield. Actually, fertilizers are made by some industrial
process involving nitrogen reacting with hydrogen
using catalyst.
To know more about the ecosystem, visit:
• http://resources.ed.gov.hk/biology/english/ind
ex.html
nitrogen in
atmosphere
N2
Animal protein
lightning
Excretion
nitrogen-fixing
bacteria in soil
and roots
NO 3- by nitrate bacteria
Nitra te
absorbe d
by plants
Protein
(dec ay of
de ad
tissues)
de nitrifying
ba cteria
ammonia (NH 3)
in soil and water
putrefying bacteria
NO 2- by nitrite bacteria
Nitrogen
cycle
Atmospheric oxygen
is used up in
respiration and
combustion to form
carbon dioxide and
water.
Oxygen is produced
in photosynthesis
The oxygen cycle
cloud
rain
life process
life process
snow
evaporation
evaporation
run-off water
The water cycle
Water evaporates from surface of water
bodies such as oceans, lakes and soil.
The water vapour in clouds condenses in
the atmosphere and is returned to the earth as
rain or snow.
Water is lost by evaporation through the
general body surface and respiratory surface.
Plants absorb water through their roots and
land animals obtain water mainly from food to
replace water lost.
Introduction
• Organisms living in a habitat interact with
each other in various ways. These
interactions directly or indirectly affect
their distribution, abundance and behaviour
• These interactions include:
– Predation
– Competition
– Symbiosis
What is predation?
• When one organism (predator) kills and
feeds on another organism (prey), the
relationship is known as predation
• In predation, the predators are benefited
while the preys are harmed
Consider a caterpillar and a bird.
Which is the predator and which is
the prey? How about the bird and
the hawk?
Predation
(Predator-prey relation)
Hare
Number
prey
Lynx
predator
Time
The predator-prey relationship determines the relative
abundance of the predators and the preys.
The relationship also means that the distribution of
predators and preys are closely related. For example,
grasshoppers are only found where there is abundant grass.
When the number of preys increases, more food
is available to the predators and so they also
increase in number.
Increased predation, however, leads to a decrease
in the number of preys. This in turn causes a drop
in the predator population.
As the predators become less abundant, the
number of preys rises again.
This type of interaction therefore results in
a periodic fluctuation in the number of predators
and preys
What is competition?
• The relationship in which two organisms
compete with each other for certain common
needs
• Common needs: food, water, space, light,
mate, etc.
• Two types of competition:
1. Intraspecific competition
Competition between members
of the same species.
Example: Trees in a woodland
compete for light and water
• Interspecific competition
Competition between
different species.
Example: Different types
of fish compete for prey
in the same habitat
•
•
•
The more similar the needs, the greater is the competition
Intraspecific competition is usually greater than interspecific
competition
All involved organisms are harmed
In a grassland, lizards and toads compete
for insects as their food. If the lizards are
removed from the grassland, what will
happen to the number of toads? Why?
Competition
(competitors)
Number
the winner
the loser
Cuckoo displacing the host’s egg
Time
In the food web of the grassland, both lizards and
toads compete for the same food, the grasshoppers. If
the lizards are removed from the habitat, the number of
toads will increase due to less competition for food.
What is symbiosis?
• The relationship in which two species are so
closely associated with each other that they
actually live together
• 3 types of symbiotic relationships:
– Commensalism
– Mutualism
– Parasitism
Commensalism
• One species (the
commensal) benefits,
the other (the host) is
unaffected
• The attachment of
barnacles on a crab:
- The crab provides
transport and a
surface for
attachment to the
barnacles
Considering the barnacles and the
crabs. Which are commensals and which
are hosts?
The crab does not gain or lose anything from the association
Mutualism
• Both species gain benefits
by living together
• The attachment of sea
anemone on the shell
dwelled by a hermit crab:
- The sea anemone
obtains scraps of
food
from the hermit
crab
and gains mobility
- The hermit crab gains camouflage and
gains
protection from the sea anemone which
possesses
sting cells
In some cases, the organisms are so dependent
on each other that they cannot live
independently
• Nitrogen-fixing bacteria living in
the root nodules of leguminous plants:
- The bacteria obtain
carbohydrates from the
host for energy supply
-The bacteria supply
nitrogenous compounds to
the plant to synthesise
protein
Fungus and alga in lichens:
- Lichens are made up of
these two organisms
- The fungus
depends on
the alga for
the supply
of
carbohydrates
- The alga depends on
the fungus for
inorganic
nutrients,
moisture and
protection
etc
Parasitism
• One species (the parasite) lives inside or on
the body surface of another species (the host)
• The parasite gains advantages while the host
suffers from this association
• The tapeworm:
- A parasite living in the
small intestine of humans
- Absorbs digested food
through its body surface
- The host may suffer from
malnutrition