IntroductionIntroduction

Habitat: the place where an organism occurs

Population: a group of organisms of the same species in an area

Community: all population & plants in the same area

IntroductionIntroduction Ecosystem:

a stable, self-supporting system which consists of communities interacting with each other

Ecology: the study of the interactions between living organisms & their environment

Different HabitatsDifferent Habitats

Freshwater Pond

Freshwater Stream

Grassland

Different HabitatsDifferent Habitats

Mangrove Rocky Shore Coral Reef

What is Environment ?What is Environment ?

Composed of 2 components, Physical Factors & Biotic Factors, which influence the lives of organisms

TemperatureLightRainfall & HumidityWind SpeedSoil (esp. for

plants)pH

Physical FactorsPhysical Factors

Biotic FactorsBiotic Factors

Consists of all the other organisms living together in the same habitat

Energy Flow within an Energy Flow within an EcosystemEcosystem

SUN

Producers

Primary Consumers

Secondary Consumers

Tertiary Consumer

s

DEC

OM

PO

SIT

ION

HEA

T

Resp

irati

on

Dead

rem

ain

s, excre

ta, e

tc

Food Chain / Food WebFood Chain / Food Web• shows the feeding

relationship between organisms

green plants

rabbit snake

hawk

grasshopper lizard

toad

DecomposersDecomposersnot shown in food chainconsist of Bacteria & Fungibreak down organic wastes & dead

bodies of other organisms to simpler compounds which are then absorbed by green plants

significance: enable the recycling of materials within an ecosystem

Trophic Level

Green plant ProducerFirst

Rabbit Primary ConsumerSecond

Snake Secondary Consumer

Third

Hawk Tertiary ConsumerFourth

Organism Type

Pyramids of NumbersPyramids of Numbers(Examples)(Examples)

Producers

Primary Consumers

Secondary Consumers

Tertiary Consumers

Pyramids of BiomassPyramids of Biomass

500Producers

Primary Consumers

Secondary Consumers

50

1

• Why is there energy loss ?– Uneaten food– Respiration – Egestion & Excretion

• ∴ solving the food problem by…– consuming organisms in lower trophic levels

– down a level, increase at least 10 times of fo

od available

Energy Lost up a Food ChainEnergy Lost up a Food Chain

Pyramids of BiomassPyramids of Biomass

Biomass is the total dry mass of organisms at a trophic level

500Producers

Primary Consumers

Secondary Consumers

50

1

Effects of DDTEffects of DDT

DDT is an effective pesticide DDT has been used for about 20 years It had been banned for over 20 years But, nowadays, the body of every

people still has DDT

Effects of DDTEffects of DDT Reasons :

– it has excessively long degeneration period (it requires tens of years)

– it is not easy be destroyed by metabolism of living organisms, so it is easily accumulated along the food chain

It killed many predatory birds due to its accumulation to high concentration through the food chain

DDT AccumulationDDT Accumulation

Carbon CycleCarbon Cycle

Carbon dioxide in air

organic substances in plants

organic substances in animals

absorption & photosynthesis

respiration

fossil

feeding

respiration

burningincomplete

decomposition

Nitrogen CycleNitrogen Cycle

nitrate in soil

protein in plantsprotein in animals

ammonia

nitrogenin air

absorption &photosynthesis

feeding

putrefying bacteria

(decomposition)

faeces, urine, dead body

nitrifying bacteria(nitrification)

denitrifyingbacteria

(denitrification)

nitrogen-fixing

bacteria

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

waterwater

snail freshwater plant

Why is it unsuitable to introduce large carnivores into the glass jar ?Ans: Because they requi

re more food to survive and they will eat up all the organisms in the aquarium.

lid

waterwater

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 an

d the aquatic plants will remain healthy even after a few weeks.

lid

waterwater

snail freshwater plant

What will happen to the aquarium if it is placed in darkness all the time ? Why ?Ans: Both the water snail

s and the freshwater plants will gradually die since there is no light for the aquatic plants to carry out photosynthesis to make food…

lid

waterwater

snail freshwater plant

What will happen to the aquarium if it is placed in darkness all the time ? Why ?Ans: so the plants canno

t survive without food supply. As all aquatic plants died, the water snails also die due to starvation.

lid

waterwater

snail freshwater plant

Ecological Ecological Independence of Independence of

OrganismsOrganismsPredation

(Predator-prey relation)

Time

Number

prey

predator

Hare Lynx

Time

NumberCompetition

(competitors)

the winner

the loser

Cuckoo displacing the host’s egg

Ecological Ecological Independence of Independence of

OrganismsOrganisms

CommensalismCommensalism• one gets (physical) benefit, one feels no e

ffect• organism benefited: Commensal• organism with no effect: Host• easy separate from each other• eg. barnacle on crab

(barnacle gets transport)

• both obtain benefits• not easy separate (even cannot be separated)• e.g.1. lichen (mutualism of specific algae & fungi)

– fungi absorb moisture from air and moist the algae– algae provide carbohydrates for the fungi

MutualismMutualism

• e.g.2. Nitrogen-Fixing Bacteria & Leguminous Plants– bacteria fix atmospheric nitrogen to

nitrogenous compounds for the plant– the plant provides carbohydrates to bacteria

MutualismMutualism

ParasitismParasitism

• parasite obtains benefits (food & protection)

• host gets harmful effects• eg. tapeworm in man (endop

arasites)

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