Chapter 13: Organisms and their envrionment

Question 1

Producers

Answer 1

• organisms that make their own food
• contains chlorophyll that absorbs light to convert carbon dioxide and water into glucose through photosynthesis
• glucose is a chemical store of energy
• oxygen is also released during the process
• ex: plants and algae

Question 2

Consumers

Answer 2

• organisms that are unable to make their own food
• obtains nutrients by feeding on other animals
• classifies into primary, secondary and tertiary according to position on food chain

Question 3

Decomposers

Answer 3

• bacterial and fungi
• organisms that get their energy by breaking down dead organisms, faeces and excretory products
• their activities return nutrients like mineral salts to the environment & are taken by diatoms/phytoplankton to synthesise into useful substances that sustain the lives of other organisms

Question 4

Food chain

Answer 4

• a series of organisms, beginning with the producers, through which energy and nutrients are transferred
• represent feeding relationships between organisms in an ecosystem
• position of an organism in a food chain is the tropic level, and they do not usually have more than 4 trophic levels

Question 5

Food webs

Answer 5

• consists of a network of interconnected food chains

Question 6

Non-cyclic flow of energy in ecosystem

Answer 6

• in a ecosystem, energy does not flow in a cycle
• energy flow is non-cyclical (linear)
• living organisms cannot use heat to do work
• organisms can only use light and chemical energy
• energy in the form of light has to be constantly supplied to ecosystem
• hence, sun is the principle source of energy input to biological systems
• sun provides energy in the form of light

Question 7

Why short food chains are more efficient in energy transfer

Answer 7

• 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 energy available for the organisms @ the next trophic level as we move along the food chain
• the shorter the food chain, the greater the amount of energy available to the final consumer because less energy is transferred to the environment
• shorter food chains are more energy efficient than long food chains

Question 8

Predator

Answer 8

• an animal that feed on another animal

Question 9

Prey

Answer 9

• an animal that is eaten by another animal

Question 10

Predator-prey relationship

Answer 10

• when prey population increase, more food is available to predactor
• leads to increase in no of predators, hence prey population decrease
• this results in predator population decreasing, leading to prey population to increase
• this cycle repeats
• increase and decrease in predator population follow the corresponding increase and decrease in prey population
• average size of prey population is always larger than population of predator
• predation plays impt role in regulating natural populations

Question 11

Why as we move along the food chain, the number of organisms at each trophic level gets lesser

Answer 11

• only about 10% of energy is transferred to the next trophic level per animal
• due to organisms using energy for activities
• the higher the trophic level, the lesser energy there is to support more animals
• hence numbers decreases

Question 12

Pyramid of numbers

Answer 12

• allows us to compare the number of organisms present in each trophic level @ a particular time
• no of organisms in each trophic level can be used to construct a pyramid of numbers
• length of bar in pyramid represents number of organisms present at that time
• limitations are that they do not consider the mass & size of organism as well as the age of animal

Question 13

Pyramid of biomass

Answer 13

• allows us to compare the mass of organisms present in each trophic level at a particular time
• constructed based in the dry mass of organisms, when all water has been removed from organism
• requires organisms to be killed
• it has to be constructed at a particular period of time
• it is used since it considers the mass of organisms, making it a more accurate representation of energy flow through food chain than pyramid of numbers

Question 14

Variations in ecological pyramids

Answer 14

• most are pyramid shaped, but there are exception
• may be upside down or inverted

Question 15

Nutrient cycling in ecosystem

Answer 15

• carbon, oxygen, nitrogen and water are essential substances in nutrients needed for life
• they are released by into soil when animals die
• decomposer break down dead organisms
• materials locked up in dead organisms hence can be returned to physical environment and used again by plants
• therefore nutrients are never lost but are continuously recycled
• the cycling of nutrients are brought about by physical, chemical and biological processes

Question 16

Carbon cycle

Answer 16

1. Photosynthesis: Plants absorb carbon dioxide and use it to synthesise carbohydrates. Some of the carbohydrates are converted to proteins and fats
2. Feeding: Animals obtain carbohydrates by feeding on other animals / plants
3. Respiration: Plants and animals respire, releasing carbon dioxide into atomosphere
4. Decomposition: Decomposers break down dead organic matter and release carbon dioxide
5. Formation of fossil fuels and combustion: dead bodies of organisms are buried deep into earth. They are subjected to high pressures and temperatures, converting them into fossil fuels, which are combusted, releasing carbon dioxide

Question 17

Importance of carbon cycle

Answer 17

• to ensure that there is a continuous supply of carbon dioxide for plants to carry out photosynthesis
• plants trap light for photosynthesis to synthesise glucose, which is a store of chemical energy
• enables energy to flow through ecosystem
• carbon compounds carry stored energy from organism to organism in food chain
• regulated amount of carbon dioxide in atmosphere

Question 18

Carbon sinks

Answer 18

• an area that stores carbon from the atmosphere for a long period of time. It stores more carbon than it releases

Question 19

Oceans as carbon sinks

Answer 19

• largest carbon sink on earth
• about 1/3 of carbon dioxide released due to human activity is absorbed by oceans
• role as carbon sink is driven by solubility and photosynthesis
• carbon dioxide dissolved in the water is absorbed and used by aquatic plants for photosynthesis
• a portion of carbon is buried in seabed as fossil fuel

Question 20

Forests as carbon sinks

Answer 20

• carbon dioxide is absorbed by plants for photosynthesis
• large amount of carbon is stored in trees
• when trees die, the remains are buried deep in the ground
• after millions of years remains form coal
• forests absorbs about 20% of carbon dioxide released by burning of fossil fuels
• deforestation has negative effects
• efficient forest management is important

Question 21

Why does deforestation occur

Answer 21

1. to meet increasing demand for land and materials such as wood
2. for urban development
3. land is needed for growing crops
4. land is needed for farming livestock
5. firewood is a source of fuel
6. wood is used as a construction material and turned into pulp for making paper

Question 22

Undesirable effects of deforestation

Answer 22

• extinction and reduction in biodiversity as habitats are destroyed and there is not enough remaining land to support a breeding population of animals
• global warming since there are lesser trees to remove CO2 from atmosphere and deforestation releases CO2, increasing CO2 concentration in the atmosphere, leading to global warming

Question 23

Activities that causes global warming

Answer 23

• deforestation
• combustion of fossil fuels
• combustion of plastic waste
• emission from motor vehicles

Question 24

Greenhouse effect due to carbon dioxide

Answer 24

• CO2 forms layer around earth, which creates greenhouse effect
• carbon emissions lead to enhanced greenhouse effect
• ice sheets melt due to global warming
• sea levels rise
• temperatures of the sea will rise, resulting in loss of biodiversity like coral bleaching, which will lead to loss of biodiversity since many organisms rely on corals for food and shelter
• rising atmospheric temperatures as well as extreme weathers create breeding grounds for mosquitoes, leading to outbreak of mosquito-borne diseases

Question 25

Effect of carbon dioxide on aquatic ecosystems

Answer 25

• more carbon dioxide will dissolve in the sea water, which causes sea water to be more acidic
• the acid dissolves calcium compounds in shells of shell fish
• this weaken their shells, making them more vulnerable to predators

Question 26

Diff between global warming and climate change

Answer 26

• global warming the rise in global temperatures
• process is accelerated by human activities that causes increasing concentrations of greenhouse gases in atmosphere
• climate change refers to the changes in temp and weather patterns over a long period of time
• effects of climate change include rising sea levels, melting of ice sheets, shifts in flowering or plant blooming times as well as unpredictable weather changes
• in some countries, there may be more frequent and intense hurricanes and winter storms

Question 27

How can we reduce the effect of enhanced global warming

Answer 27

-reduce the use of fossil fuels and use renewable energy instead
- reduce our consumption of energy by using more energy efficient devices/ reducing our usage of electricity
- replace petrol-powered vehicles with hybrid /electrical vehicles
- reduce daily consumption of water, electricity, paper and plastic
- managing our forests well

Question 28

How can we manage our forest well

Answer 28

• conserving forests, this helps prevent disruption of natural cycles like carbon cycle, preventing global warming
• reducing indiscriminate felling of trees
• reforestation
• control forest fires by preventing man made fires in forests
• conducting education programs to make people aware of the importance of forests and the method of forest conservation

Question 29

Pollution

Answer 29

• the process whereby harmful substance are added to the environment, making it undesirable and unfit for life
• some causes are natural like volcanic eruptions
• however most of it is due to humans
• as human population increases and our technology advances, pollution becomes more serious, threatening lives of organisms
• we need to identify sources of pollution and devise method to prevent and reduce pollution

Question 30

Sewage

Answer 30

• waste-carried water matter from homes or industries
• contains disease-causing orgnaisms
• should not be dumbed into water bodies since it make infect many people who drink the water from the water bodies
• untreated sewage also contains phosphate and nitrate, resulting in excessive growth of algae and water plants, promoting bacterial growth
• other organisms in water bodies die due to lack of oxygen, leading to eutrophication, which can also be caused by inorganic chemicals or fertilisers entering water bodies

Question 31

Eutrophication

Answer 31

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

Question 32

Process of eutrophication

Answer 32

1. untreated sewage and fertilisers that are not absorbed by crops are washed into nearby waterbodies
2. nitrates and phosphates in sewage and fertilisers enhance the growth of floating water plants and algae. the overgrowth of floating water plants and algae prevents sunlight from reaching submerges plants
3. submerged algae and water plants die due to lack of sunlight which are decomposed by bacterial and fungi. the decomposers will grow and multiply, using up oxygen in water
4. other organisms will die due to lack of oxygen

Question 33

Insectisides

Answer 33

• they may be ineffective after a while since some insects become resistant to insectisides
• insects will pass favourable genes to their offspring and population of insects will rise again
• insecticides will also affect other organisms when they accumulate in water bodies due to insecticides being washed away by rainwater

Example: DDT
- Cannot be broken down and is insoluble in water
- Stored in fatty tissues of organism and can accumulate when consumers consume food that contains DDT

Question 34

Bioaccumulation

Answer 34

• accumulation of chemical substances in an organism

Question 35

Biomagnification / bioamplification

Answer 35

• occurs when toxins / insecticides are passed from trophic level to the next with increasing concentration along food chain

Question 36

Effects of non-biodegradable plastic waste

Answer 36

• Chemicals from burning of plastic could leech into rivers and seas, poisoning wildlife
• Can be harmful to marine animals when washed into seas
• Can be broken down to microplastics and be ingested by marine organisms and accumulate in their bodies

Question 37

Biodiversity

Answer 37

• the range of species that are present in a particular ecosystem

Question 38

conservation

Answer 38

• the protection and preservation of natural resources in envrionment

Question 39

Importance of conservation

Answer 39

1. Maintaining biodiversity and a large gene pool to prevent the extinction of species. Many organism have favourable genes and by cross-breeding them, we can improve agriculture reproduce. Many tropical plants are also sources of medicinal drugs
2. For scientific research to provide us useful information
3. To maintain a balanced and stable ecosystem
4. For economic purposes since we depend on ecosystems for food and raw materials
5. To preserve natural scenery and wildlife for people to appreciate

Question 40

Conservation of mangrove swamp

Answer 40

• some countries have a mangrove restoration project
• mangroves will help protect low-lying areas against strong wind, wave and tides
• in sg, we have Adopt a Mangrove programme in Pulau Ubin

Question 41

Conservation of coral reef

Answer 41

• people visiting corals should practice safe and responsible diving
• divers should not touch the reefs and anchor their boats on the reef since they can kill corals and reef animals
• they should avoid using sunscreen as some of its ingredients are harmful to corals
• avoid purchasing live corals
• don’t polluted the corals with trash