form 4 biology chapter 8

8/11/2019 Form 4 Biology Chapter 8

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8.1 The Abiotic and Biotic Components

of the Environment8.2 Colonisation and Succession in an

Ecosystem

8.3 Population Ecology8.4 Biodiversity

8.5 The Impact of Microorganisms on

Life

8.6 Appreciating Biodiversity


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8.2

Colonisation and Succession inan Ecosystem


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What is an ecosystem ?

1. An ecosystem is a dynamic systemformed by the interactions of organismswith one another and with the non-living

environment.2. It is a dynamic system where the living

organisms are in balance with each otherand with the abiotic components.


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Habitat A habitat is the natural environment in which anorganism lives and obtains its basic resourcessuch as food and shelter.

Species A species is a group of organisms which can interbreedto produce fertile offspring.

Population A population consists of organisms of the same species

living in the same habitat at the same time.

Community A community consists of different populations of plantsand animals living and interacting in the habitat of an

ecosystem.

Niche The niche of an organism is the roles and activities ofthe organism in its habitat. Two organisms sharing thesame habitat may have different niches.


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Colonisation and succession1. Natural phenomena or human activities such as

volcanic eruptions, fires, earthquakes anduncontrolled mining activities leave the land withno living organisms.

2. Later, some organisms will come to occupy the

bare land.3. The process in which living organisms arrive at a

new habitat, live, reproduce and take control ofthe habitat is known as colonisation.

4. The first species of organisms to colonise a newhabitat is called thepioneer species.

5. The pioneer species have special adaptations tosurvive in unfavourable land conditions.


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6. The pioneer species gradually changes theconditions of the habitat, making it no longer

suitable for itself but more suitable for otherspecies, called the successor species. Gradually,the successor species takes over the place of thepioneer species.

7. The process whereby a pioneer species is graduallyreplaced by other successor species is called

succession.


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8. Succession will carry on until a relatively stablecommunity is formed. This type of community is

known as the climax community.9. In Malaysia, the tropical rainforest is the climax

community.

10. It usually takes hundreds of years to form a

climax community. After that it has little or nochanges in its species structure. Therefore, weshould treasure our forests.


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Colonisation and succession in amangrove swamp

1. Swamps are formed by deposition of mud andsilt carried down by the river. It is found at theestuary, that is where the river meets the sea.

2. Only mangrove trees are able to colonise the

soft, waterlogged, muddy soil which has a lowoxygen level but high salt concentration.

3. Mangrove trees have adaptive structures toovercome the harsh conditions in a swampyarea.

A mangrove swamp


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Adaptations of mangrove trees

Problems faced by mangrovetrees

Adaptive structures of mangrovetrees

Ground too soft to providesupport

Have long, branched cable rootsor prop roots to support the plantsin soft ground.

Very little oxygen inwaterlogged mud

Have breathing roots calledpneumatophores which growupwards and protrude out of theground.

Gaseous exchanges also occursthrough lenticels on the bark ofmangrove tress.


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The root systems of mangroves

Pneumatophores ofAvicenniasp.

Prop roots ofRhizophora sp.


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Buttress roots ofBruguiera sp.


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Problems faced by mangrove trees Adaptive structures of mangrovetrees

High salt content of sea water The cell sap in root cells has ahigher salt content. Sea waterenters the roots by osmosis. Excesssalt from the sea water iseliminated through hydathodesfound at the lower epidermis of

leaves.Seeds sink into the mud and die

due to insufficient oxygenHave viviparous seeds. A

radicle grows from the germinatedseed when it is still attached to theparent tree. When the seedling isreleased, the radicle holds the

shoot above the mud.

Exposure to strong sunlight andintense heat leads to a higher rateof transpiration

Leaves with thick cuticle andsunken stomata to reducetranspiration

Store water in succulent leaves


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Viviparity


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4. Avicennia sp. and Sonneratia sp. are the pioneerspecies of a mangrove swamp. Avicennia sp. growsin areas facing the sea while Sonneratia sp. is found

in more sheltered areas.

5. The extensive cable root system of these plantstraps more mud and slit as well as organic matterfrom decaying plant parts.

6. As time passes, the soil becomes more compactand the shore level is slightly raised. The soilbecomes firmer and less waterlogged. Suchconditions favour the growth of another kind of

mangrove tree, namely Rhizophora sp.7. Gradually, Rhizophora sp. replaces the pioneer

species.


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8. The prop root system of Rhizophora sp. continues to

trap more slit and mud. Humus is formed fromthe old pioneer species as well as decaying leaves

of Rhizophora sp. The soil becomes firmer, morecompact and fertile. The shore level is raised and isless saline. The condition now is more suitable forBruguierasp.

9. The buttress root system of Bruguiera sp. Traps more

silt and mud causing the shore to extend further tothe sea.

10. As time passes, coconut trees, Nipah and Pandanussp. gradually replace the Bruguiera sp. when the soil

becomes more like terrestrial ground.

11. Eventually a tropical rainforest, which is the climaxcommunity, is formed.


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Distribution of different mangrove species at

the mouth of a river


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Colonisation and succession in a pond1. Colonisation by pioneer species

(a) Submerged plants such as Hydrilla sp.,Elodea sp. and Cabomba sp. as well as

phytoplankton are the pioneer species in a pond.

(b) These submerged plants have adaptive

features such as long fibrous roots whichpenetrate deep into the soil to absorb nutrientsand hold the sand together. Fine leaves enablethe plants to flow with the water.


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Submerged plants

Hydrilla sp.

Elodeasp.

Cabombasp.


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Floating plantsWater lily

Water hyacinth

Pistiasp.


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3. Succession by emergent (amphibious) plants

(a) The floating plants reproduce rapidly as theyreceive enough sunlight for photosynthesis. Theycover a large area of the surface of the pond. Thisprevents sunlight from reaching the bottom of thepond.

(b) Without sunlight, the submerged plants cannot

perform photosynthesis. As a result, these plantsdie and become humus.

(c) The amount of humus deposited at the bottomof the pond increases. More soil erosion occurs

which results in the pond becoming shallower. Thismakes the pond too shallow for the floating plants.


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Amphibious plants

Cyperus sp.

Scirpus

grossus

Scirpus

mucronatus


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4. Succession by terrestrial plants

(a) The death of emergent plants as well asdeposition of more organic matter make the pond

even shallower. Evaporation of pond water finallydries the pond.

(b) Terrestrial plants such as creepers, grasses,ferns and herbaceous plants begin to grow.

(c) Later, shrubs and woody plants begin to grow.5. Climax community

Over hundreds of years, a tropical rainforestwhich is a climax community is formed.


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Questions 8.2

1. Which of the following describes a population?

A. The function of an organism or the role itplays in an ecosystem

B. The natural environment in which anorganism lives

C. A group of organisms of the same speciesliving in the same habitat at the same time

D. A natural collection of plant and animalspecies living within a habitat in an ecosystem

Answer : C


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2. Phytoplankton, zooplankton and algae are oftenamong the first species to establish themselves ina mining pond. As time passes, submerged and

floating plants will grow, followed by amphibiousplants, grasses, small shrubs, bushes andeventually trees.

This is an example of

A. colonisationB. competition

C. evolution

D. succession

Answer : D


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3. Over many years a forest can be found on aninitially barren piece of land left behind by a

volcanic eruption. What is the correct sequenceof ecological processes that have taken place?

A. Colonisation, succession, climax community

B. Colonisation, climax community, succession

C. Succession, colonisation, climax communiityD. Succession, climax community, colonisation

Answer : A


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4. Which gives the correct sequence of plantsinvolved in the process of succession in a

disused pond?A. Emergent plants floating plants

land plants submerged plants

B. Floating plants submerged plants

land plants emergent plantsC. Submerged plants floating plants

emergent plants land plants

D. Land plants emergent plants

floating plants submerged plant

Answer : C

5 Di 1 h th d f Rhi h hi h


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5. Diagram 1 shows the seed of Rhizophora sp. which

germinates while it is still attached to the parent plant.

Diagram 1

This phenomenon is know asA. double fertilisation

B. oviparity

C. viviparity

D. vegetative reproductionAnswer : C


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8.3 Population Ecology


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1. Populationis a group of organisms of the samespecies living in a habitat. The number of

organisms in a population is called thepopulation size.

2. The study of the measurement of populationsize and the factors affecting the population size

is know aspopulation ecology.3. The quadrat sampling technique is mainly

used to estimate population size, densiity anddistribution of plants and immobile animals.

4. The capture, mark, release and recapturetechnique is used to estimate the populationsizes of mobile animals.


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Capture, mark, release andrecapture technique

1. To estimate the population size ofanimals which move freely such assnails and woodlice, the capture,

mark, release and recapturetechnique is used.


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Capture, mark, release and recapture technique

A number of animals are captured at random andmarked with waterproof paint, ink or a ring.

The marked animals are released.

A second capture is carried out after a few days.

The number of animals captured in the secondsample and the number of marked animals arerecoded.


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2 Th f ll i ti d i


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2. The following assumptions are made inthis technique:

a) The size of the population does not change and isstable throughout the period of investigation.

b) The marked animals are not harmed or predatedupon.

c) The animals are captured at random.

d) The marked animals are able to mix randomlywith the other animals before the secondcapture.

e) Each marked animals has the same probability ofbeing recaptured as an unmarked animals.


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3. To increase the accuracy of thistechnique,

a) more animals must be captured.b) the animals must be captured at random.

c) the markings must be permanent.

d) enough time must be allowed for themarked and unmarked animals to mix.


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Quadrat sampling technique

1. A quadrat sampling technique is used todetermine the distribution of plantswhereby the density, frequency andpercentage coverage of the plants can be

determined.2. A quadrat has a square or rectangular

frame made of wood, metal or rope. It is

subdivided into smaller squares.3. The size of the quadrat depends on the size

and density of the plants sampled.

f


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4. In this technique, a number of quadrats areplaced randomly in the area being studied.

5. The species found within the quadrat arecounted and recorded.


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6. The distribution of the plants can bedetermined in three ways:

a) The percentage coverage is thepercentage of how much of an area iscovered by the plants.


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b) The frequency is the number of times aparticular plant is found from the total

number of quadrats used.


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c) The density is the number of individualsper unit area. This value is difficult todetermine for the population of plants whichreproduce vegetatively.

fl f b f h


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Influence of abiotic factors on thepopulation distribution of an organism

1. Abiotic factors refer to the non-livingcomponents of an ecosystem which include

pH, temperature, light intensity, humidity,topography and climate.

2. The population distribution of an organismis influenced by the changes in the abioticfactors.


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Questions 8.3

1. The quadrat sampling technique can be used inthe study of the populations of

A. birds

B. earthworms

C. grasshoppers

D. rabbits

Answer : B

2 Which of the follo ing steps need to be taken to


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2. Which of the following steps need to be taken toimprove the accuracy of the capture, mark, releaseand recapture technique ?

A. Put a bigger mark.B. Capture more animals.

C. Capture the bigger animals.

D. Do recapture after one month.

Answer : B


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3. The following information is about the capture,mark, release and recapture technique.

P Mark the captured animals.

Q A second sample is captured.

R Release the marked animals.

S An initial sample is captured.

Which of the following is the correct sequence ofthe capture, mark, release and recapturetechnique?

A. P R S Q

B. P S R QC. S P R Q

D. S R Q PAnswer : C


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4. The table shows the results obtained from aninvestigation into the distribution of mimosa plantson a school field.

Table 1

The percentage frequency of the mimosa plants is

A. 25%

B. 36%C. 66%

D. 70%

Quadrat 1 2 3 4 5 6 7 8 9 10

Numberof plants

5 2 0 1 8 2 0 3 4 5

Answer : D

form 4 biology chapter 8

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