Man’s place in natureClassification 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)

1) hair present2) no eggs laid but young born alive after a        period of development inside the mother’s        body3) 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 temperature

Characteristics of Mammals

Characteristics of Primates1) 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 man1) Upright posture, with head held vertically on the        vertebral column, to free the hands from walking2) 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

Mangrove

Forest

Freshwater stream

Grassland

Various habitats on Earth:

• 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

Ecosystem:A dynamic and self-supporting system where organisms interact with each other and with their environment

The components of an ecosystem

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

Plants and algae

Chemical energy in organic molecules

Eaten byAnimals

Absorbed by

Converted to

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

• 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

What are food chains and food webs?

• 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

ProducersProducers

• All food chains starts with producers.

• Include all autotrophic organisms such as plants and algae.

• Provide energy for the organisms in the ecosystem

ConsumersConsumers• 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.

• 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

DecomposersDecomposers

Secondary consumer

Tertiary consumer

What are trophic levels?• Each level of organisms in a food chain is called a

trophic level• Example:

GrassProducerFirst

RabbitPrimary consumerSecond

SnakeThird

HawkFourth

Example of organism in a food chain

Types of organismTrophic level

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 How energy is transferred between trophic levels?trophic levels?

1. However, a small proportion of energy can be transferred to the next trophic level due to energy loss at each level:

2. Consumed during respiration. The energy released is given off as heat or used to support body activities

3. Lost in the form of wastes and excretory substances

4. 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?

• 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

Pyramid of biomassPyramid of biomass

• 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

Complex organic substances

Other organisms

Synthesize

By feeding

Respiration Faeces, excretory products and dead bodies

Decomposers

Decompose

by

CYCLING OFMATERIALS

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

The carbon cycle

44

Carbon CycleCarbon Cycle

Carbon dioxide in air

organic substances in plants

organic substances in animals

assimilation & photosynthesis

respiration

fossil fuel

feeding

respiration

burningincomplete

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

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

Ways of return of carbon:

• 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?

• Nitrogen is an essential component of proteins, nucleic acids and other nitrogen-containing compounds

• The nitrogen cycle describes the cycling of nitrogen in ecosystems

The nitrogen cycle

45

•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 organismsCycling 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:

Dead organic matter Ammonia or

ammonium compound

Nitrites

Decomposed by

putrefying bacteria and fungi Oxidized by

nitrifying bacteria by a process called

nitrificationNitrates

• 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/index.html

nitrogen in atmosphere

N2

Animal protein

Excretion

Nitrate absorbed by plants

Protein (decay of

dead tissues)

ammonia (NH3) in soil and water

denitrifying bacteria

putrefying bacteriaNO3- by nitrate bacteria

NO2- by nitrite bacteria

lightning

nitrogen-fixing bacteria in soil

and roots

Nitrogen cycle

The oxygen cycle

Atmospheric oxygen is   used up in respiration   and combustion to   form carbon dioxide   and water.

Oxygen is produced in   photosynthesis

The water cycle

snow

evaporation

life processlife processraincloud

evaporation

run-off water

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)

Time

Number

prey

predator

Hare Lynx

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 competitionCompetition 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?

Time

NumberCompetition (competitors) the winner

the loser

Cuckoo displacing the host’s egg

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

Considering the barnacles and the crabs. Which are commensals and which are hosts?

• 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

CommensalismCommensalism

The crab does not gain or lose anything from the association

• 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

MutualismMutualism

- The hermit crab gains camouflage and gains      protection from the sea anemone which possesses      sting cells

• 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

In some cases, the organisms are so dependent on   each other that they cannot live independently

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

• 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

ParasitismParasitism

• The tapeworm:- A parasite living in the small     intestine of humans- Absorbs digested food     through its body surface- The host may suffer from     malnutrition