Harap Maklum
yikygui
Habitat and Ecosystem
1 There are millions of plant and
animal species on Earth.
2 A species is a group of similar organisms with
common characteristics. They can breed among themselves to produce fertile
offspring.
3 It is estimated that there are about
13.6 million species living on Earth. Some are big, some are small, and some
can only be seen under the microscope. They move on land, swim in water, fly in
the air, and some even live on the body of other organisms.
4 Each species is adapted to live in
specific conditions in certain surroundings. This is referred to as a suitable environment for
that species.
5 Everything surrounding a species
that affects how it lives and survives is known as its environment.
6 A species that is best adapted to
its environment is the most likely to survive and reproduce successfully.
Organisms that are poorly adapted will not survive.
7 You have learnt in the previous
chapter that a place where plants and animals live is called a habitat. It is
the place that provides food, shelter from enemies, protection from bad weather
and opportunities for breeding. 
8. In an environment, there are
different types of habitats. Treetops, tree trunks, ponds, rocks, pools,
rotting logs, burrows in the soil, and even rooms in our homes are a few examples
of habitats.
9. A population is a group of organisms
of the same
species living together and reproducing at the same time. For
example, we have population of tigers, a population of human beings and a
population of ferns.
10 The different populations of plants and animal
which live together in the same habitat make up the community.
For example, a freshwater pond community consists of population water
hyacinths, duckweeds, dragonflies, watersnails, freshwater fish and tadpoles. 
11 The organisms in a community are interdependent
on one another and their environment. An organism cannot live in isolation.
12. An ecosystem consists of several
communities that interact with one another and environment.
13. The environment is made up of living and
non-living
components.
14 (a) Non-living components are physical factors
that affect the organisms’ way of life.
(b) Light, temperature, oxygen, carbon dioxide and water are some
examples of physical factors.
15
The relationships between species, population, community and ecosystem are
shown in Figure 4.1
Figure
4.1 How ecosystem is formed
Figure
4.2 shows the relationships between species,
population and community in a
grassland.
17. Figure 4.3 shows an ecosystem in a
freshwater pond.
18. There is usually more than one
habitat in an ecosystem. For example, there are various habitats in the pond
ecosystem as shown in Table 4.1.
Figure
4.3 An ecosystem of freshwater pond
Table 4.1 The
various species found in the different habitats of the pond
|
Habitat
|
Spesies
|
|
Pond apron
|
Cattails,
rusiga, grasses, frogs, toads, kingfishers, grasshoppers
|
|
Water
surface
|
Water
hyacinths, lotus, duckweeds, water insects, mosquito larvae
|
|
Middle water
level
|
Tadpoles,
fish, algae, daphnia
|
|
Pond base
|
Elodea,
Hydrilla, shrimps, water snails
|
|
Under pebbles or
stones in the pond
|
Worms, bacteria,
Paramecium
|
(a) The different communities found in
the pond ecosystem include cattails, rusiga, grasses, frogs, toads, kingfishers
and grasshoppers on the pond apron.
(b) Water hyacinths, lotus, duckeeds,
water insects and mosquito larvae are the community on the water
surface.
(c) Populations of tadpoles, fish and
algae are found at the middle water level.
(d) There are also communities of
Elodea, shrimps and water snails on the pond base.
(e) A community of worm and bacteria
can found under pebbles or stones in the pond.
(f) In the pond ecosystem, there are
the non-living factors that influence the distribution of the organisms.
These factors are water temperature, air temperature, oxygen content in
water, mineral content in water,
rainfall and light intensity.
19. Forests, grasslands, seashores,
rivers, mountains and deserts are some of the world’s ecosystems.
Interdependence of living Organisms Creates 
A Balanced Ecosystem
1. In a particular ecosystem, various
organisms coexist together. The various organisms live together and are interdependent
on one another for their survival. They interact with one another and the
environment to help
create a balanced ecosystem.
2. A balanced ecosystem is one that does
not change very much over a period of time. The size of each population remains
the same through a steady supply of basic needs like oxygen, food, shelter and
breeding partners.
3. When a population grows too big,
organisms from the same species will compete with each other for their basic
needs. The weaker or may not survive, thus leading to a reduction in the
population.
4. A balanced ecosystem also helps to purify and
recycle gases, water and minerals. It even controls the climate.
5. In the pond ecosystem, as discussed
earlier, the aquatic plants obtain their food from sunlight during photosynthesis.
The plants obtain carbon dioxide from aquatic animals which
release oxygen during respiration.
6. The animals in return obtain their
supply of oxygen
from the plants which release oxygen during photosynthesis.
7. The aquatic plants also obtain
minerals from the soil at the bottom of the pond.
8. The animals cannot make their own
food but depend on other organisms to obtain food. They eat plants or other
animals found in their environment.
9. Some pond animals depend on aquatic
plants for shelter
and protection.
They cling to parts of the plants like the leaves. These animals are able to
camouflage themselves as their body colours match the colours of those parts of
the plants they are attached to.
10. Aquatic plants depend on
non-living compound of the environment and other organisms for reproduction.
These plants rely on water, wind, insects and birds for pollination and
dispersal.
11.
The favourable climatic conditions and the abundance of water may help certain
animals to find breeding partners and to disperse their eggs. The absence of
predators in the pond may also increase their chances of survival. The presence
of plants provides opportunities for the eggs or the young ones to attach
themselves
Figure
4.4 Interdependence among living organisms
12.
Microorganisms like bacteria in the soil help to decompose dead organisms and
release minerals into the soil. These minerals act as nutrients for the plants.
These microorganisms are known as decomposers.
13.
Decomposers play
an important role in the relationships which exist in an ecosystem. They break down dead
organisms, and return the relevant gases and minerals to the
environment. By doing this, they also clean up the environment.
14.
The interdependence among living organisms and their environment creates a balanced
ecosystem. The amount of food, the availability of shelter, breeding
partners and space keep the population of each organism in check. There are
enough decomposers to return gases and minerals to the environment
4.2 Interaction between Living Organisms
1. In any ecosystem, organisms
interact with one another in order to survive.
2.
Interaction between
living organisms helps the organisms to obtain food, shelter, protection,
breeding
partners, regulate their population size and maintain the balance of nature.
3
Organisms interact in many ways (Figure 4.5) |
Types of interaction
|
Effects
|
Examples
|
|
Competition
• Organisms struggle,
fight or search for the same basic needs.
• Competition becomes more intense
when basic needs become limited.
• Normally, they compete for
shelter, nesting sites, food, sunlight, minerals
and breeding partners.
• Organisms that are stronger,
fitter and better adapted to environmental changes
will be successful and survive.
• There are two types of
competition.
(a) Intra-specific competition This
is a competition between organisms of the same species.
(b) Inter-specific competition This
is a competition between organisms of different species.
a
b
Figure 4.7
Polulations of two species of Paramecium cultured
(a)
separately and
(b) together.
|
+
(stronger organism)
—
(weaker organism)
|
Figure 4.6 Competition between the
lion for food
|
|
+
(stronger organism)
—
(weaker organism)
|
• Two male tigers fighting for a
tigress.
• Bitter gourd plants competing for
support to reach sunlight.
Balsam plants competing for sunlight.
|
|
|
+ (stronger organism)
—
(weaker organism)
|
· Two different
species of Paramecium. P. aurelia
and
P
caudatum competing with each other for food. P. aurelia
emerges as the winner (Figure 4.7).
· Graph (a)
shows the population of P. aurelia
and P caudatum species living
separately.
· Graph (b)
shows the two populations living together and therefore competing for the
limited amount of food.
· As a result, P aurelia, the stronger species. kills
P. caudatum.
· The
population of P. cauda turn
decreases. The population of
P. aurelia increases.
· The maize
plants competing with weeds for water and minerals.
· The owl and
the snake competing with each other for food (the rat).
|
|
|
Symbiosis
• The close relationship between two
organisms of different species which live closely together and interact with
each other.
At least one of the two living
organisms benefits from this relationship.
• There are three types of
symbiosis.
(a) Commensalism
A relationship between two organisms
in which one partner benefits (the commensal) while the other does not
receive any benefit or harm (the host).
Figure 4.8 The tiyctroid growing on
a shell occupied by a hermit crab
(b) Mutualism
• An interaction between two
different species of organisms which benefits both organisms.
• This relationship helps the
organisms to survive in harsh conditions. Neither organism will be able to
survive on its own.
(e) Parasitism
• In this relationship, there is a
parasite and a host.
• The parasite benefits from living
outside or in the host.
• The host is harmed or may even be
killed by the parasite.
|
+
(the commensal) O (the host)
|
§ A remora fish
is often found attached under a shark, gets free transportation, and feeds on
food scraps left by the shark without harming it.
§ Hydroids are
found attached to the shells of hermit crabs. The hydroids obtain food
particles from the crab plus a free ride. The crab does not gain anything
from this relationship (Figure 4.8).
§ Barnacles
attach themselves to the skin of whales and get a free ride through
nutrient-rich waters, without the whales being harmed or deriving any benefit
from this relationship.
|
|
+
(both organisms)
|
• An alga and a fungus form a
lichen. The alga produces food and the fungus provides shelter (Figure 4.9).
• A sea anemone attaches itself to a
hermit crab in such a way that the anemone’s mouth and tentacles are close to
the mouth of the hermit crab to obtain food scraps and also free
transportation. The hermit crab gets protection from the anemone’s stinging
cells.
|
|
|
+ (the parasite)
— (the host)
|
Ticks, fleas, lice (singular: louse)
and mosquitoes (parasites) live on the skin of mammals (hosts) and suck the
blood of the host.
Tuberculosis bacteria (parasite)
attack human (host) lungs.
Round worms, tapeworms, hook worms
and thread worms live inside the intestine5 of humans (hosts).
These parasites obtain food and
shelter from the host. The host loses weight and is weakened.
 |
|
|
3 Prey-predator relationship
In this relationship, the predator
which is normally bigger in size, hunts, kills and feeds on the smaller,
hunted animals called the prey. Generally, the predator population is smaller
than the prey population.
|
+ (predator)
--
(prey)
|
Frogs (predators) feed on
grasshoppers (prey).
Lions (predators) hunting deer
(prey) for food.
Bigger fishes (predators) feeding on
smaller
fishes (prey).
|
4 Characteristics of predators
and prey:
(a) Generally, predators are bigger in
size than the prey. However, the population of predators is smaller than the
prey.
(b) The predators are well adapted to
kill their prey. They possess good vision (eagles), sharp claws, strong beaks
(eagles), a good
sense of smell, powerful jaws and sharp teeth (lions).
(c)They have the ability to run faster
than their prey. Their bodies are camouflaged (tigers) to prevent detection.
(d) Predators are carnivores while the prey may
be omnivores
or herbivores.
(e) Prey also have sharp eyes to
detect the presence of predators. They have the ability to run and escape from
predators.
(f) Just like the predators, prey also
have body
colours that blend very well with their surroundings (zebras). This
characteristic helps them to avoid being easily detected by the predators.
(g) Some prey give out unpleasant
odours or harmful chemicals. Some can mimic the colours or smell of other stronger
animals to frighten or confuse the predators.
5 (a) When the number of predators is
low but the number of the prey is high, the population of the predators
increases rapidly.
(b) Then as the number of the
predators increases, the population of the prey decreases.
(c) When the population of prey falls,
competition between predators for food increases. So the predator population
decreases because of death due to starvation.
(d) With a smaller number of
predators, the prey population begins to increase again. This is shown in the
graph in Figure 4.10.
Biological control
1 After knowing how living organisms
interact with one another, it is not difficult (in theory) to think of a method
to control the population of a particular species (X) by using another species
(Y) that feeds on or kills species X.
2 Using a living organism to check the population growth of
another organism is known as biological control.
3 The organism used to control the
population of a pest is known as the biological control agent.
4 The predator-prey interaction is
used widely in biological
control. Other interaction like parasitism and competition are also used.
5 This is in contrast to using
chemicals like pesticides, herbicides, fungicides or insecticides to control
the population of living organisms. This approach is called chemical control.
6 Biological control is used in
agriculture to contain the pest population that attack crops and fruit trees.
Table
4.3 Examples of biological control
|
Organism X that is to be controlled
|
Biological control agent for X
|
|
Cactus Opuntia
in Australia
was a nusisance in the early twentieth century
|
The caterpillar of the mouth Cactoblastus
was introduced in large numbers to eat up the cactus plants
|
|
Larvae of a stem borer feed on the leaves and stems
oil palm trees.
|
A type of fly known as Ichneumon can be
used to control the larvae (Figure 4.11(a)).
|
|
Rats in oil palm
estates are pests.
|
Snakes and owls are used to control the rat population
(Figure 4.11(b)).
|
|
To control the growth of weeds
in rubber and oil palm estates.
|
Grass such as the Imperata
cylindrica is planted to control the weeds.
|
|
Mosquitoes breed in
stagnat ponds.
|
Fishes which eat the mosquito larvae
are reared in the ponds
|
|
Aphids that feed on crops
|
Ladybirds are used to eat up the aphids (Figure 4.11(c)).
|
Figure
4.11 Examples of biological control
8. Biological control is more
effective in controlling pests because it does not damage the ecosystems
although its effects are slower.
9. It should be noted that the
organism that is used to control the pest must be specific to the pest. It must
target the specific pest and no other species.
10. What would happen if other species
are also killed other than the targeted species? The implication can be
serious. For example. in Australia,
a type of toad was introduced to control the beetle that damaged sugar-cane
plantations. The toad also killed non-target organisms like the possum, a
primitive mammal. The death of possums caused an imbalance in the ecosystem.
11 In Malaysia, an increase in the number
of crows has posed a problem to people living in Klang. Crows were used to
control the hawk moths. With the available food scraps in Klang, the crow population
increased and became a nuisance. The state government, the relevant authorities
and the non-government agencies (NGOs) have launched several approaches like
• culling the
crows by shooting them
• trimming big
trees so as to reduce the number of branches and leaves
• clearing
food scraps around coffee shops and hawker centres everyday
• ensuring
refuse bins are closed
1. A food chain demonstrates the feeding
relationship between living organisms in an ecosystem.
2.It
consists of a sequence of organisms starting with the producer (green plant), followed by
the primary
consumer, the secondary consumer and usually ending with the tertiary consumer.
3.
In any ecosystem, animals or consumers will eat more than one type of food. For
example, snakes not only eat frogs but also birds and rats.
4
These food alternatives form a food web as shown in Figure 4.12. To make the
food web more complex, we can extend the food web as in Figure 4.13.
 |
5
The food web in Figure 4.13 is made up of three food chains: (a), (b) and (c).
6 A food web is made up of several food chains.
These individual food chains are interlinked in a complex way to provide a more
complete picture of how animals feed.
7 A
food web helps to maintain a balanced ecosystem by regulating the number of
organisms at each level |
Grass
→ |
Grasshopper
→ |
Toad
→ |
Snake
→ |
Hawk
→ |
Bacteria of decay
|
|
In general
|
|||||
|
Herbivores
(Primary Consumers) → |
Carnivores
(Secondary, tertiary, etc. consumers) → |
Decomposers
|
|||
