Unit 12: Interactions Within Ecosystems

Question 1

Topics

Answer 1

• Human Impact and Conservation
• Deforestation
• Pollution
  o Bioaccumulation
  o Bioamplification
• Rise in Ocean Temperature
  o Coral Reefs
• Conservation of Species
  o Biodiversity
  o Management of Fisheries
• Sustainable Living
• Interactions in the Ecosystem
• Ecological Terms and Definitions
• Biotic and Abiotic Factors of an Organism’s Environment
• Adaptations of Species
• Interrelationships in an Ecosystem
  o Predator-Prey
  o Parasitism
  o Mutualism
• Processes Involved in the Ecosystem
• Food Chains
• Energy Flow and Energy Loss in the Ecosystem
• Food Web
• Trophic Levels
• Ecological Pyramids
• Number and Biomass of Organisms
  o Pyramid of Numbers and Pyramids of Biomass
• How Nutrients are cycled
• Carbon Cycle
• Carbon Sinks
• Decomposers

Question 2

Human Impact and Conservation (not impt, 3pts)

Answer 2

Human Impact and Conservation
* Human activities can have positive and negative impacts on the environment.
* Examples of positive impacts are reducing the use of single-use plastic bags and using cleaner energy.
* Examples of negative impact are deforestation and pollution.

Question 3

Deforestation

Answer 3

• The action of clearing a wide area of trees.

Causes
* Farming
* Logging
* Building Settlements
* Building Transport Routes

How to reduce the negative effects of Deforestation
* Planting new trees
* Promoting eco-tourism
* Having laws to protect forests (e.g. prohibiting logging)
* Agroforestry (leaving trees to grow beside crops)
* Selective logging
- technique where only trees beyond a certain height are cut, hence allowing the younger trees to grow. This, in turn, allows the forests to reach full maturity again in a shorter time.

• Sewage and insecticides are sources of water pollution which can harm the living environment.
• Pollution caused by human activities introduces toxic chemicals into the environment. These toxic chemicals, such as insecticides or mercury, could enter food chains and end up in the food we eat.
• Water pollution is caused by contamination of water bodies, such as lakes and rivers, with pollutants such as toxic chemicals or organic substances. This affects the water quality which then impacts the aquatic life, as well as, living organisms dependent on these water bodies.

Question 4

Sewage (3pt, 3subpt)

Answer 4

• Sewage is the water-carried waste matter from households.
• e.g. from toilet bowls and showers in toilets, from kitchen sinks and washing machine drainage as well as industries.
• Untreated sewage is harmful because it contains:
  1. nitrates and phosphates, which can lead to eutrophication in water bodies
  2. poisonous heavy metals e.g. mercury, lead, chromium
  3. disease-causing bacteria that can cause diseases like cholera and typhoid
• Eutrophication is the process by which water receives excess nutrients like phosphates and nitrates, causing excessive growth of algae and water plants.
• Eutrophication is one of the possible outcome of water pollution. Aquatic life will eventually die as a result of eutrophication.

Question 5

When excess fertilizers get washed away into nearby lakes (optional):

Answer 5

• When excess fertilizers get washed away into nearby lakes:
  1. Excess fertilizers are washed away into lake
  2. Profused growth and multiplication of algae and water plants
  3. Sunlight is unable to penetrate into water
  4. Submerged aquatic plants are unable to photosynthesis and die
  5. Oxygen levels fall
  6. Bacteria population starts to increase
  7. Aquatic animals die due to low oxygen levels

Question 6

What is Bioaccumulation? (4pt)

Answer 6

• Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism.
• Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated by catabolism and excretion.
• The accumulation of toxic chemicals (e.g. insecticides) at higher concentrations in the bodies of organisms at higher trophic levels is because:
• The toxic chemicals cannot be broken down easily in their bodies.
• Organisms at higher trophic levels feed on many individuals at the lower trophic level.
• Toxic chemicals accumulate in the bodies of organisms when they are absorbed and cannot be broken down or processed by the body easily.

Question 7

What is Bioamplification? (1pt)

Answer 7

Bioamplification is the increase in concentration of a substance.
- e.g a pesticide, in the tissues of organisms at successively higher levels in a food chain.
• This increase can occur as a result of:
- Persistence – where the substance cannot be
broken down by environmental processes
- Food chain energetics – where the substance’s concentration increases progressively as it
moves up a food chain
- Low or non-existent rate of internal
degradation or excretion of the substance – mainly due to water-insolubility

Question 8

Responsible use of insecticides: (2pt)

Answer 8

• Avoid excessive use of insecticides
• Use biodegradable insecticides that are made from natural materials

Question 9

Rise in Ocean Temperatures and Coral Reefs (5pt)

Answer 9

• Physical factors such as air, water, temperature, light, minerals and acidity/alkalinity affect the lives of organisms.
• Coral reefs are no exception and they are affected by the changes in physical factors in their environment.
• The survival of coral reefs are particularly threatened by the rising ocean temperatures.
• Effect on coral reefs: Warmer oceans cause corals to experience stress and this can lead to coral bleaching.
• Physical factors that can be measured using a data logger include amount of oxygen and pH value.

Question 10

Conservation of Species (2pt)

Answer 10

• Conservation is the protection and preservation of materials or substances occurring in nature that are useful to humans
• e.g. water, soil, wood, plants and animals natural resources in the environment.
• Conservation allows the maintenance of Earth’s the variety of living organisms in an ecosystem biodiversity and a healthy ecosystem.

Question 11

Reasons for current decrease in global biodiversity (4pt):

Answer 11

• Degradation of land through soil erosion or deforestation
• Global climate change
• Over-exploitation of resources such as over-fishing and intensive farming
• Introduction of new species into areas that are outside their natural habitat

Question 12

Importance of Conservation
Ecological Reasons
4pt

Answer 12

• Diverse ecosystems can withstand and recover from natural disasters better.
• Natural habitats help to stabilise the climate and slow down climate change.
• Conservation helps maintain natural cycles in the ecosystem, such as the carbon cycle.
• Living things are inter-dependent, conserving animal and plant species help to maintain the ecosystem.

Question 13

Importance of Conservation
Economic/Social Reasons
5pt

Answer 13

• Many plant and animal species provide us with food.
• Many plant and animal species provide us with medicines and pharmaceutical drugs.
• Many plant and animal species provide us with raw materials such as cotton, silk and wood.
• Humans engage in recreation and tourism in nature.
• The natural environment and wildlife provide information for scientific research and education.

Question 14

Importance of Conservation
Ethical Reasons
1pt

Answer 14

• Humans have the moral responsibility to play our part in taking care of our environment.

Question 15

How to conserve species through better management of fisheries and forests

2pt, 5 subpt

Answer 15

• Why fishing practices such as trawl fishing and drift net fishing are irresponsible:
• Many marine creatures that are not intended to be captured are also caught.
• How can fishing practices be better managed to conserve marine organisms:
• Banning the use of drift nets (Drift nets lead to unintentional trapping of many marine animals such as dolphins and seals)
• Cultivating fish species for commercial use within controlled environments in fish farms
• Specifying areas of the oceans where fishing is prohibited
• Rearing young fish in hatcheries, releasing them to grow in the wild as adults before they are harvested

Question 16

Interactions in the Ecosystem
Ecological terms and definitions

Answer 16

Term
Definition

Habitat
A place where organisms live

Population
Organisms of the same species / kind that live in a particular habitat

Community
Made up of the different plant and animal populations living together and interacting in a habitat

Ecosystem
The interactions between a community and its physical environment that make up an ecosystem

Ecology
The study of ecosystems

Ecologist
A person who studies ecology

Question 17

What is a habitat?

Answer 17

A place where organisms live

Question 18

What is a population?

Answer 18

Organisms of the same species / kind that live in a particular habitat

Question 19

What is a community?

Answer 19

Made up of the different plant and animal populations living together and interacting in a habitat

Question 20

What is an ecosystem?

Answer 20

The interactions between a community and its physical environment that make up an ecosystem

Question 21

What is Ecology?

Answer 21

The study of ecosystems

Question 22

What is an Ecologist?

Answer 22

A person who studies ecology

Question 23

Biotic and Abiotic factors (2 impt pt, 4pt total)

Answer 23

• Biotic factor: A living thing in an ecosystem.
• Abiotic factor: A non-living thing (or once-living organism) in an ecosystem.
• The abiotic factors in the environment determine the type of biotic factors that can live in that environment.
• Biotic factors that cannot adapt to the abiotic factors, will not survive in that environment.

Examples of Abiotic Factors include light, temperature, water, air, minerals and pH

Question 24

Adaptations of Species

Answer 24

• When an organism is suited to its environment, it is most likely to survive and reproduce.
• The organism is said to be adapted to its environment.
• Organisms that are poorly adapted will not survive.
• Adaptive traits can be:
  1. Structural
• Structural adaptations are physical characteristics of an organism that help it to survive.

2. Behavioural
   - Behavioural adaptations are the different behaviours of an organism that allows it to survive.

Question 25

What are structural adaptations?

Answer 25

1. Structural
   - Structural adaptations are physical characteristics of an organism that help it to survive.

Question 26

What are behavioural adaptations?

Answer 26

2. Behavioural
   - Behavioural adaptations are the different behaviours of an organism that allows it to survive.

Question 27

What is a biotic factor?

Answer 27

• Biotic factor: A living thing in an ecosystem.
• Biotic factors that cannot adapt to the abiotic factors, will not survive in that environment.

Question 28

What is an Abotic factor:

Answer 28

• Abiotic factor: A non-living thing (or once-living organism) in an ecosystem.
• The abiotic factors in the environment determine the type of biotic factors that can live in that environment.

Examples of Abiotic Factors include light, temperature, water, air, minerals and pH

Question 29

Interrelationships in an ecosystem
Predator-Prey Relationship

4pt, 2 impt pt

Answer 29

Predator-Prey Relationship
* Predators are animals that hunt and kill other animals for food.
* The animals that are killed and eaten are called prey.

• Predators are usually well-adapted to catch and kill their prey.
• These include having good senses, speed, strong jaws, claws and beaks, and camouflage.
• Prey have adaptations to protect them from predators,
• e.g. camouflage, high speed, small size.

Question 30

Interrelationships in an ecosystem
Mutualism (definition?)

Answer 30

Mutualism
* Mutualism is a relationship between two or more organisms in which both organisms support or benefit.

• E.g. Sea anemone and clownfish
• The sea anemone provides shelter and protection for the clownfish.
• The clownfish helps bring food to the anemone.

Question 31

Interrelationships in an ecosystem
Parasitism (definition?)

Answer 31

Parasitism
* Parasitism is a relationship in which one organism benefits while the other is harmed.
* The organism that causes the harm is called a parasite.

• E.g. Mosquitoes are parasites.
• They suck our blood for food and spread diseases, such as malaria and dengue fever which harm us.

Question 32

Processes involved in an Ecosystem
A stable ecosystem
6pt

Answer 32

• Organisms in a habitat cannot survive alone.
• They interact with other organisms, for example, by eating them, by competing with them for food, water and light, or by providing them with shelter and protection.
• Three important kinds of interactions between organisms are the predator-prey relationship, mutualism and parasitism.
• The fate of one organism will affect the survival of other organisms in the environment.
• A stable ecosystem requires the maintenance of interrelationships between different organisms.
• Changes in environmental conditions or removal of any organism disrupts the stability of an ecosystem.

Question 33

Food Chains (8pt, 4-5 impt pt)

Answer 33

Food chains
* A food chain shows the sequence of feeding relationships between organisms.
* Different organisms make up different trophic levels in a food chain.
* Each organism in the food chain is called a trophic(feeding) level. The number of levels varies from one food chain to another.
* During feeding, energy and nutrients are transferred from one organism to another
- 10% of energy is transferred from one trophic level to another.
* Main source of energy for all food chains: The Sun
* (prey) → (predator), ‘→’ means ‘eaten by’
* Flow of energy in an ecosystem: (from sun) Light energy → (in organisms) Chemical energy → (when eaten and is lost by) Thermal energy

Question 34

• During feeding, what percentage of energy is transferred from one trophic level to another?

Answer 34

• 10% of energy is transferred from one trophic level to another.

Question 35

• Main source of energy for all food chains?

Answer 35

The Sun

Question 36

Trophic Levels in a Food Chain

Answer 36

Trophic Level
Type of Organisms

First
Producers

Second
Primary Consumers

Third
Secondary Consumers

Fourth or more
Tertiary Consumers

Question 37

Food Webs (4pt, 1 impt pt)

Answer 37

Food Webs
* Food web shows how one or more food chains are interconnected.
* This is because many animals eat more than one type of food. Each animal or plant is also eaten by more than one type of animal.
* Hence, food web gives and overall picture of all the organisms that are involved in the transfer of energy and nutrients in an ecosystem.
* In a nutshell: a food web is basically a food chain but more complex

Question 38

Energy flow in food chains and food webs (9pt, 4 subpt)

Answer 38

• Energy is harnessed directly from the sun via photosynthesis by the producers which are always the start of every food chain or food web.
• In an ecosystem, the flow of energy occurs together with the flow of nutrients.
• This energy is transferred from one form to another through the food chain, via ecological relationships (biotic factors).
• Thus, the energy that is transmitted from one trophic level to another comes directly/indirectly from the sun.
• Photosynthesis and respiration are involved in the flow of energy and nutrients in the ecosystem.
• Energy is lost to the environment at each trophic level in the food chain.
• During respiration: Energy is used for life processes and for activities such as growth, moving and breathing.
• As faeces: Some of the grass is not digested but passes out of the sheep, along with the energy stored in it.
• The rest is lost as thermal energy to the surroundings.
• The remaining energy is stored in the organism to be used for growth.
• It is this energy that is passed on to the next consumer in the food chain.
• Only about 10% of the energy available at any one link is passed on to the next link. The other 90% is lost.
• As energy passes along a food chain, the amount of energy transferred gradually decreases.

Question 39

Energy Loss (3pt, 4 subpt)

Answer 39

Energy Loss
* Energy is lost to the environment as food is transferred from one trophic level to another.
* About 90% of energy is lost when it is transferred from one trophic level to another.
* Energy is lost to the environment:
1. as thermal energy during respiration,
2. in uneaten body parts,
3. through undigested matter egested by consumers, and
4. through waste products excreted by consumers.

Question 40

Ecological Pyramids

Answer 40

• An ecological pyramid is a graphical representation, in the form of a pyramid, showing the relationship between organisms at different trophic levels.
• There are two kinds of ecological pyramids, the pyramid of numbers and the pyramid of biomass.
• A pyramid of numbers
• represents the number of each organisms at each trophic level in relation to each other.
• A pyramid of biomass
• represents the biomass of the organisms at each trophic level in relation to each other.

Question 41

Number and Biomass of Organisms (7pt, 5 subpt)

Answer 41

• The number of an organism of each trophic level in a given area can be counted.
• Biomass is the total dry mass of organisms in a given area at a given time.
• Unit for biomass: g/m2
• Total mass of individuals = Mass of one individual x Total number of all individuals
• Biomass = Total mass of all individuals divided by Area
• Pyramid of Biomass
• Allows the comparison of the relative level of biomass of organisms present in each trophic level at a particular time.
• Although pyramids of biomass are usually ‘pyramid’ shaped, they can sometimes be oddly shaped if organisms in one trophic level have a high reproductive rate.
• Pyramid of Numbers
• Allows the comparison of the relative number of organisms present in each trophic level at a particular time.
• Constructed based on the number of organisms at each trophic level.
• Illustrated the number of organisms at each trophic level at any one time per unit area of an ecosystem.

Question 42

Pyramid of Biomass (2pt)

Answer 42

• A pyramid of biomass
• represents the biomass of the organisms at each trophic level in relation to each other.
• Pyramid of Biomass
• Allows the comparison of the relative level of biomass of organisms present in each trophic level at a particular time.
• Although pyramids of biomass are usually ‘pyramid’ shaped, they can sometimes be oddly shaped if organisms in one trophic level have a high reproductive rate.

Question 43

Pyramid of Numbers (2pt)

Answer 43

• A pyramid of numbers
• represents the number of each organisms at each trophic level in relation to each other.
• Pyramid of Numbers
• Allows the comparison of the relative number of organisms present in each trophic level at a particular time.
• Constructed based on the number of organisms at each trophic level.
• Illustrated the number of organisms at each trophic level at any one time per unit area of an ecosystem.

Question 44

Drawing of Ecological Pyramids (3pt)

Answer 44

• The shapes of the two pyramids shown above is described as upright.
• However, not all ecological pyramids are upright. (Anomaly)

Drawing of Ecological Pyramids
* A ruler and pencil must be used when drawing the pyramid.
* It should not be drawn as a pyramid but as a series of horizontal bars that are labelled / annotated.
* A pencil or pen may be used to label each horizontal bar representing each trophic level.

Question 45

How nutrients are cycled
The Carbon Cycle
3pt, 5 subpt

Answer 45

• Carbon is recycled in nature in two main ways:
  1. During photosynthesis, green plants absorb carbon dioxide from the atmosphere and use it to make starch, a carbohydrate. This is passed on to animals that eat the plants.
  2. During respiration, both animals and plants release carbon dioxide back into the atmosphere.
• Respiration and photosynthesis are important in the interactions between plants and animals for three reasons:
• Plants make food which animals need.
• Plants produce the oxygen animals need for breathing and respiration.
• The carbon dioxide produced by animals during respiration is used by plants for photosynthesis.
• Comparing photosynthesis and respiration
• At night, respiration but not photosynthesis takes place in plants. (FOO → COW)
• Oxygen from the air diffuses in through the stomata of the leaves while carbon dioxide diffuses out. (COW → FOO (with light and chlorophyll)
• During the day, when photosynthesis also occurs, plants produce more oxygen than they need for respiration. The extra oxygen diffuses out through the stomata.
• The amount of carbon dioxide produced from respiration is not enough for photosynthesis, so carbon dioxide from the air diffuses into the leaves.
• Green plants carry out photosynthesis only during the day when there is light.
• Respiration takes place in all organisms and takes place all the time, both day and night

Question 46

Processes in the Carbon Cycle
Releases carbon dioxide into the atmosphere
3pt

Answer 46

• Respiration
• Decomposition
• Combustion

Question 47

Processes in the Carbon Cycle
Removes carbon dioxide from the atmosphere
2pt

Answer 47

• Photosynthesis
• Fossilisation

Question 48

Carbon Sinks (3pt)

Answer 48

• A carbon sink is a reservoir that stores a large amount of carbon for a long time. It absorbs more carbon from the atmosphere than it releases.
• Both photosynthesis and fossilisation happen in forests and oceans. These processes allow forests and oceans to store carbon, in the form of carbon compounds, for a long period of time. Therefore, forests and oceans are known as carbon sinks.
• How changes in physical factors of the oceans affect marine organisms that live in the coral reefs:

Question 49

Decomposers (6pt, 4 impt pt, 2 subpt)

Answer 49

• A decomposer breaks down dead organisms, faeces and waste products into chemicals.
• E.g. Baterica, Fungi
• A scavenger breaks down dead organisms into smaller pieces which they feed on.
• Carbon and other elements are also recycled by decomposers.
• Decomposers such as bacteria and fungi consume nutrients on a molecular level, and break down dead plant and animal matter, and animal faeces into:
• carbon dioxide (which is used for photosynthesis in plants); and
• minerals (which dissolve in water in the soil, and are absorbed by plant roots for growth).
• Decomposers enrich the soil with nutrients that plants need to grow, and conserve natural resources.
• If nutrients in the soil were used only once, they would soon run out. Recycling ensures that nutrients are always available for plants.

Question 50

Definition of Decomposers?

Answer 50

• A decomposer breaks down dead organisms, faeces and waste products into chemicals.
• E.g. Baterica, Fungi

Question 51

Definition of Scavengers?

Answer 51

• A scavenger breaks down dead organisms into smaller pieces which they feed on.

Question 52

How to answer questions:

Answer 52

• Food chain usually looks at the bioamplification of organisms
• How to answer questions:
• Cause
• Effect
• Reason
• (cause) causes (effect) as (reason).
• Usually asks for ‘what if’ questions, e.g. what happens if a species is added or removed from the food chain/food web.
• Template answer (for food chain/food web questions):
• The population of (species) would increase/decrease as (species) is the predator of (species). The population of (species) would increase/decrease as (species) is predator of (species). …

Question 53

Template answer for food chain/food web questions:

Answer 53

• Usually asks for ‘what if’ questions, e.g. what happens if a species is added or removed from the food chain/food web.
• Template answer (for food chain/food web questions):
• The population of (species) would increase/decrease as (species) is the predator of (species). The population of (species) would increase/decrease as (species) is predator of (species). …