Biology Chapter 13

What are living organisms classified as in any ecosystem?

Producers

Consumers

Decomposers

Producers → Consumers →

Decomposers

What are producers?

A producer is an organism that makes its own food, and it contains chlorophyll that absorbs light to convert carbon dioxide and water into glucose, via photosynthesis

Glucose is a chemical store of energy. (T/F)

True

What are examples of producers?

Plants

Algae

What are consumers?

Consumers are organisms that are not able to make their own food, and obtain energy and nutrients by feeding on other organisms

How can consumers be classified?

Primary consumers, feed on plants only

Secondary consumers, feed on primary consumers

Tertiary consumers, feed on secondary consumers

What are decomposers?

Decomposers are organisms that get their energy by breaking down dead organisms, faeces and excretory products, which returns nutrients like mineral salts to the environment

What are examples of decomposers?

Bacteria

Fungi

What is a food chain?

A food chain is a series of organisms, beginning with the producer, through which energy and nutrients are transferred.

Why is a food chain used?

It can represent feeding relationships between organisms in an ecosystem using a food chain. Each organism in the food chain feeds on the organism before it and provides food for the organism after it. It always begins with the producer.

What is trophic level?

The position an organism occupies in a food chain

How many trophic levels does a food chain usually have?

No more than four trophic levels

What is a food web?

A food web consists of a network of interconnected food chains

What is special about a food web?

An organism can be at more than one trophic level in a food web

How does energy flow in a cycle?

In an ecosystem, energy flow is non-cyclical

What is the the principal source of energy in an ecosystem, and why?

Sun, because energy in the form of light has to be constantly supplied to an ecosystem, and living organisms cannot use heat to do work

How is energy transferred in an ecosystem?

In any ecosystem, the principal source of energy is the Sun. During photosynthesis, energy from the Sun is absorbed by chlorophyll in producers and transferred to chemical stores of energy in glucose molecules. Energy in the producers is passed from one trophic level to another by feeding, The amount of energy at each trophic level decreases as it flows through the ecosystem because only some of the energy from one trophic level gets transferred to the next level. The rest of the energy is largely transferred to the environment as heat, through respiration. Since this energy does not return to the same system as the organisms that produced it, it cannot be recycled in the ecosystem. Hence, the flow of energy through the ecosystem is non-cyclical. Egested and excreted materials and dead organisms contain trapped chemical energy, which is released through the activity of decomposers. Decomposers use some of this trapped chemical energy for their needs. The rest of the energy is transferred as heat to the environment

What are the stages of energy flow?

Sun → Photosynthesis → Feeding → Respiration → Excretion and Egestion → Death

Why are short food chains more efficient?

A large amount of energy does not get passed from one trophic level to the next, as it is lost to the environment as heat, or transferred to uneaten body parts, faeces and excretory products. There will be less and less energy available for the organisms at the next trophic level as we move along the food chain, so food chains are generally short, so that it is more energy-efficient and less energy is transferred to the environment.

The shorter the food chain, …

the greater the amount of energy available to the final consumer

What are the most trophic levels a food chain has?

5

Why do food chains have fewer than 5 trophic levels?

Energy transfer along the food chain is inefficient as about 90% of the energy is lost as it is passed from one trophic level to the next.

Apart from the next trophic level, where is the remaining energy transferred?

The energy is transferred to the environment as heat during respiration

The energy is also transferred to uneaten body parts, faeces and excretory products

What is a predator?

An animal that feeds on another animal

What is a prey?

An animal that is eaten by another animal

What happens when there is an increase in prey?

An increase in the population size of prey means that there is more food available for predators, leading to an increase in the number of predators, which causes a decrease in the population of prey. This leads to a decrease in predators as less food is available, which leads to the increase in the number of prey.

The population of prey will always be higher than the population of predators. (T/F)

True

What does an ecosystem use?

Energy

Inorganic nutrients

How does energy enter an ecosystem?

Energy enters an ecosystem in the form of light and heat from the Sun. Light from the Sun is transferred to chemical stores of energy in glucose molecules, then transferred from organism to organism through the ecosystem. The energy is then transferred to the environment in the form of heat as it flows through the ecosystem

Is energy recyclable?

No, it cannot be recycled, so energy must constantly be supplied to the ecosystem

How are inorganic nutrients obtained?

Inorganic nutrients like carbon and nitrogen need not be supplied from outside the ecosystem. They are obtained from the environment and they flow through the ecosystem in a cycle, so that in a balanced ecosystem, nutrients are not lost as they are continuously recycled

How do ecological pyramids work?

The producers are placed at the bottom, the primary and secondary consumers are placed in the middle and the tertiary consumers at the top.

What are the 2 types of ecological pyramids?

Pyramids of Numbers

Pyramids of Biomass

The pyramids of numbers …

allows us to compare the number of organisms present in each trophic level at a particular time

How is a pyramid of numbers constructed?

The length of each bar in the pyramid represents the number of organisms present at that time.

What are the limitations of using the pyramids of numbers?

It does not consider the size and mass of organisms

It does not consider whether the organism is an adult or a juvenile

The pyramid of biomass…

allows us to compare the mass of organisms present in each trophic level at a particular time

How is a pyramid of biomass constructed?

It is constructed based on the dry mass of organisms in each trophic level at any one time

What is the advantage of using the pyramid of biomass?

It considers the size and mass of organisms, so it is a more accurate representation of energy flow through a food chain than a pyramid of numbers

What are the limitations of using the pyramid of biomass?

Organisms have to be killed to obtain biomass

It has to be constructed at a particular point in time

A pyramid of numbers may be upside down/inverted if:

Organisms of one trophic level are parasitic on organisms of another trophic level

Many small organisms of one trophic level feed on a large organism of another trophic level

Is the pyramid of biomass always upright?

No, it is usually inverted in aquatic systems, but other than that, it is usually like a pyramid

What are the substances that are released back into the soil when organisms die?

Carbon

Oxygen

Nitrogen

Water

Is the concentration of carbon in the environment relatively constant?

Yes, because carbon is constantly being removed and released into the environment in the form of carbon dioxide

What is the carbon cycle?

The various processes by which carbon, in the form of carbon dioxide, is removed from and released into the environment

What are the processes in the carbon cycle

Photosynthesis

Feeding

Respiration

Decomposition

Formation of fossil fuels and combustion

Explain the carbon cycle.

During photosynthesis, plants absorb carbon dioxide and use it to synthesise carbohydrates. Some of the carbohydrates are converted to proteins and fats. Animals obtain carbon compounds by feeding on plants or other animals. Plants and animals respire, releasing carbon dioxide into the atmosphere. Decomposers, like fungi and bacteria, break down dead organic matter and release carbon dioxide. Dead bodies of plants and animals may be buried deep in the earth. They are subjected to high pressure and temperature, where they are converted to fossil fuels like coal, natural gas and oil. Combustion of these fossil fuels releases carbon dioxide into the environment.

What is the importance of the carbon cycle?

Ensures a continuous supply of carbon dioxide for plants to carry out photosynthesis. Plants trap light during photosynthesis for plants synthesise glucose, which is a chemical store of energy

Enables energy to flow through the ecosystem. Carbon compounds carry the stored energy from organism to organism in the food chains of an ecosystem

Regulates the amount of carbon dioxide in the atmosphere

What is a carbon sink?

A carbon sink is an area that stores carbon from the atmosphere for a long period of time. It stores more carbon than it releases. It removed carbon dioxide from the environment

What are natural carbon sinks?

Forests

Oceans

What drives the role of oceans as carbon sinks?

Solubility

Photosynthesis

What happens to carbon dioxide in oceans?

The carbon dioxide that dissolves in the ocean’s water is absorbed and used by aquatic plants in photosynthesis. A portion of the carbon compounds found in oceans is buried in the seabed and is in the form of fossil fuels like natural gas and oil

What happens to carbon dioxide in forests?

Atmospheric carbon dioxide is absorbed by plants and used in photosynthesis. In forests, a large amount of carbon compounds is stored in trees, and when they die, their remains may be buried deep in the ground. After millions of years, these remains form coal, a type of fossil fuel. Studies by Asian, African and South American tropical forests absorb about 20% of all carbon dioxide released by the burning of fossil fuels

How does Canada manage its forests?

Canada has about 10% of the world’s forests, claiming less than 0.5% of its forests are harvested in any given year. The harvested areas are allowed to regenerate into forests again.

What is the Paris Agreement?

It is an international treaty on climate change, which covers climate change mitigation, adaptation and finance. The Agreement was negotiated by 196 parties at the 2015 United Nations Climate Change Conference in France, Singapore joining on 22 Apr 2016. By November 2021, 193 members of the United Nations Framework Convention on Climate Change(UNFCC) are parties to the Agreement

What is the goal of the Paris Agreement?

Its goal is to keep the rise in global average temperature to below 2 degrees. It aims ot limit the temperature increase to 1.5 degrees. It is expected to significantly reduce the effects of climate change

How does Singapore contribute to reducing climate change?

Singapore launched a Climate Action Plan in July 2016, to provide details of the strategies for adapting to the impact of climate change, like implementing coastal and infrastructure protection measures. It also mentions ways to reduce carbon emissions up to 2030, like improving energy effiiency, reducing carbon emissions from power generation and developing cutting-edge low-carbon technologies

What are renewable natural resources and their examples?

Resources that can be replaced in the ecosystem by natural cycles as long as humans do not overuse them. Examples are air, water, soil, forests and wildlife.

What are non-renewable natural resources and their examples?

Resources that take millions of years to form and cannot be replaced quickly enough. One example is fossil fuels

What are the 2 main consequences of humans overusing resources?

Deforestation

Pollution

What is deforestation?

The clearing of forests

Why does deforestation occur?

Land is needed for farming livestock

Land is needed for urban development, such as building houses, roads and factories

Firewood is a source of fuel

Land is needed for growing crops like rice

Wood is used as a construction material, and turned into pulp for making paper

What are the undesirable effects of deforestation

Extinction and reduction of biodiversity

Increase of carbon dioxide in the atmosphere, leading to global warming

How is a loss of biodiversity caused?

Clearing forests leads to habitat destruction for many species of animals, and the remaining land may not be big enough to support a breeding population, making the animals endangered/extinct.

When trees in the forests are growing, …

Photosynthesis occurs at a higher rate than respiration. The excess carbon is stored in tree trunks, roots and in the soil

When trees in the forests are cut down, …

they release all the carbon dioxide they have storing into the atmosphere. The emissions of carbon dioxide are created when the trees are left to rot on the forest floor or when they are burnt.

How does deforestation cause global warming?

It reduces the number of trees which function to remove carbon dioxide from the atmosphere via photosynthesis, so the concentration of carbon dioxide in the atmosphere will increase and cause global warming.

What are the human activities that can cause global warming?

Deforestation

Combustion of fossil fuels like coal and gas

Combustion of plastic waste

Emission from motor vehicles

What are the effects of carbon dioxide pollution?

Greenhouse effect

Effect on aquatic ecosystems

How does carbon dioxide cause the greenhouse effect?

Carbon dioxide is a greenhouse gas that forms a layer over Earth’s surface, trapping heat within this layer around Earth, causing global warming, and even climate change. This would cause sea levels to rise, flooding some countries

How does a rise in seawater result in loss of biodiversity?

It causes coral bleaching and death of corals in coral reefs, which provide a habitat for a large variety of marine organisms. Corals rely on colourful algae which live in their tissue and produce food for the corals. When corals are stressed by the chnages in light, water or temperature, they expel algae that live in them and turn white, and they are unable to support species.

Will mosquito breeding grounds increase with rising temperatures and extreme weather?

Yes, which could cause more mosquito-borne diseases to spread

How do high atmospheric carbon concentrations affect aquatic ecosystems?

More atmospheric carbon dioxide dissolves in the seawater, becoming more acidic. The acid dissolves calcium compounds in the shells of shellfish, weakening their shells and making them more vulnerable to predators

What is the difference between global warming and climate change?

Global warming is the rise of global temperature while climate change refers to the changes in temperature and weather patterns over a long period of time

How can human actions reduce the effects of enhanced global warming?

Reduce the use of fossil fuel. Use renewable sources of energy

Reduce consumption of energy, but using more efficient devices

Replace petrol-powered vehicles with hybrid or electric vehicles

Reduce daily consumption of electrcity,water, paper and plastic

Conserve forests

Indiscriminate felling of trees should be prevented

Reforestation

Control of forest fires

Education programmes should be conducted to make people more aware of the importance of forests to our lives

What is pollution?

Pollution is the process by which harmful substances are added to the environment, making it undesirable or unfit for life

What causes pollution

Pollutants

What are natural pollutants?

Volcanic eruptions and forest fires

What is sewage?

Water-carried waste matter from homes or industries

Should untreated sewage be discharged into rivers or lakes? And why?

No, because they may contain disease-causing organisms, like bacteria that can infect people with diseases.

What are examples of water-borne diseases?

Cholera and Typhoid

How does untreated sewage ruin water quality?

Sewage water contains phosphates and nitrates that are nutrients for algae and water When untreated sewage enters eater bodies, this can excessive growth of algae and water plants, promoting bacterial growth. It can lead to eutrophication

What is eutrophication?

Eutrophication is the process by which water receives excess nutrients like phosphates and nitrates, causing excessive growth of algae and water plants

What is the process and effects of eutrophication?

Untreated sewage and fertilisers that are not absorbed by crops may be washed away by rainwater into nearby rivers or lakes. The nitrates and phosphates in fertilisers or untreated sewage enhance the growth of algae and water plants. They are used in the synthesis of proteins and nucleic acids. This leads to the increased growth and multiplication of algae and floating water plants in rivers or lakes, called eutrophication. Overgrowth of algae and floating water plants prevent sunlight from reaching submerged plants, which could then die due to lack of sunlight. They will be decomposed by aerobic bacteria and fungi. As the bacteria feed on the decaying organic matter, they grow and multiply rapidly, using up the oxygen in the water. Organisms like fish will die due to the lack of oxygen

Why do people use insecticides?

To kill insects that destroy crop plant or transmit diseases, like dengue fever and malaria

What are the disadvantages of using insecticides?

Insecticides may become ineffective after some time as some insects become resistant to them. They pass the favourable genes to their offspring and over time, population of insects will rise again

Insecticides may affect organisms other than insects. If insecticides are carried by rainwater into rivers, lakes or streams, they can accumulate in high concentrations in the bodies of aquatic organisms like fish

What is a common insecticide?

DDT( dichlorodiphenyltrichloroethane) is an insecticide that is non-biodegradable, so it cannot be broken down by microorganisms like bacteria. It remains in soil or water for many years. Since it is non-degradable, it cannot be excreted, instead it is stored in the fatty tissues of organisms that consume it. If consumers continue to consume food that contains DDT, bioaccumulation of DDT will occur.

What is biomagnification?

It occurs when toxins or insecticides are passed from one trophic level to the next with increasing concentration along the food chain.

What are the effects of non-biodegradable plastic waste on the ecosystem?

Burning of plastic causes global warming

Plastic waste is deposited in landfills

Harmful chemicals from the plastic waste buried in the landfills may be leached into rivers and seas. The poison wildlife in the sea or rivers

Harmful to marine life

Can be broken down into micro plastics that can be ingested by marine organisms and accumulate in their bodies, leading to biomagnification of micro plastics along food chain

Why is there a need for conservation?

Many species are going extinct before they can even be discovered, especially due to pollution and the depletion of natural resources

What is biodiversity?

Biodiversity refers to the range of species that are present in a particular ecosystem

What is conservation?

Conservation is the protection and preservation of natural resources in the environment

What are the reasons for conservation

Maintaining biodiversity by preventing the extinction of species

For scientific research

For economic purposes

To maintain a stable and balanced ecosystem

To preserve natural scenery and wildlife for people to appreciate

Why is maintaining biodiversity by preventing the extinction of species important?

Could improve agricultural produce

Sources of medicinal drugs

Diversity can be maintained

Why is it important to maintain a stable and balanced ecosystem?

Prevents disruption of natural cycles like the carbon cycle and prevents global warming

Why is preserving natural scenery and wildlife for people to appreciate important?

Enables outdoor recreational activities

Why is conservation important for economic purposes?

Marine life needs to be conserved, as they are a major food source

Tropical forests provide food and raw materials for industries like rubber from the latex of rubber trees

How can mangrove swamps be conserved?

Some countries have a Mangrove restoration Project, where volunteers plant mangrove seedlings over a portion of the mangrove swamp. The trees will protect low-lying area against strong wind, waves and tides

What is Pulau Ubin doing to conserve mangroves?

Adopt a Mangrove Programmes is a campaign initiated at Pulau Ubin to raise awareness about conservation and restoration of degraded areas to reduce the impact of global warming and climate change