13 — organisms n their environment

Question 1

Producers

Answer 1

Organisms that makes its own food, glucose, through photosynthesis by absorbing light energy and converting it to chemical energy in food [1] and synthesising organic food substances from inorganic molecules. [1]
Producers are the first organisms in the food chain or food web and occupies the first trophic level. Examples are the microscopic green plants and water plants. [1].

Question 2

Consumers

Answer 2

Organisms that are not able to make their own food and obtain energy and nutrients by feeding on other organisms. Consumers may be classified as primary, secondary and tertiary according to their position in a food chain.

Question 3

Decomposers

Answer 3

Organisms that take in some energy by breaking down dead organisms, waste matter, faeces and excretory products, releasing the rest of the energy and inorganic nutrients, such as carbon and nitrogen to the environment, for nutrient cycling, during the decomposition process.

Question 4

Population

Answer 4

group of organisms of the same species that live together in a particular habitat.

Question 5

Community

Answer 5

made up of all the populations of different species and various organisms living and interacting with one another in a habitat.

Question 6

Ecosystem

Answer 6

community of living organisms interacting with one another and with their physical environment

Question 7

Food chain

Answer 7

A series of organisms, beginning with the producers, through which energy and nutrients are transferred as the form of food.

Question 8

Trophic level

Answer 8

The feeding position that an organism occupies in a food chain or food web. [1]

With reference to diagram:
Trophic level is the feeding position an organism occupies in a food chain or food web.

Plants eg form the first trophic level as they are producers that can make their own food via photosynthesis and serve as a source of food and energy for other organisms like animals.

Animals which are primary consumers such as y cannot make their own food and feed on plants to obtain energy and forms the second trophic level. And so on.

Question 9

Food web:

Answer 9

consists of a network of 2 or more interconnected food chains

Question 10

Predator

Answer 10

an animal that feeds on another animal

Question 11

Prey:

Answer 11

an animal that is eaten by another animal

Question 12

Non-cyclical energy flow

Answer 12

1. During photosynthesis, energy from Sun absorbed by chlorophyll in producers n transferred to chemical stores of energy in glucose molecules
2. Energy passed from 1 trophic lvl to next by feeding. Amt of energy at each trophic lvl decreases as it flows thru ecosystem. Chemical energy is trapped within carbon compounds in undigested food waste that is egested and in excreted substances such as urine. Chemical energy is also trapped in the uneaten dead body parts of an organism.
3. Rest of the energy is transferred to the env as heat due to cellular respiration n cannot be recycled in ecosystem -> non-cyclical.

Question 13

Pyramid of biomass definition

Answer 13

Shows the dry standing mass of organisms present in each trophic level at a particular time.

Biomass at each trophic lvl = total mass of all individuals of that organism type

Question 14

Accuracy of pyramids of numbers and biomass

Answer 14

POB Considers the size n mass of organisms thus more accurate representation of energy flow thru a food chain than PON

Question 15

Limitations of PON vs POB

Answer 15

PON:
X consider size n mass of organisms
X consider whether the organism is an adult/ juvenile

POB:
Organisms hv to be killed to obtain biomass.
Has to be constructed at a particular pt in time.

Question 16

Importance of carbon cycle

Answer 16

• It ensures a continuous supply of carbon dioxide for photosynthesis. Plants trap light during p~ to synthesise glucose, which is a store of Chem energy.
• Regulates the amount of carbon dioxide
• Enables energy to flow through the ecosystem. Carbon compounds carry stored energy from organism to organism in food chains of ecosystem.

Question 17

Removal of CO2

Answer 17

• Photosynthesis; Green plants absorb CO2 from atmosphere n synthesise carbohydrates n some r converted to proteins n fats.
• Feeding, animals obtain Carbon compounds by feeding on plants/ animals

Question 18

Release of CO2

Answer 18

• Respiration; Plants n animals respire, releasing CO2 into atmosphere
• Formation of fossil fuels n Combustion; Dead bodies of plants n animals may be buried deep inside earth -> subject to high pressure n tempt -> converted to fossil fuels like coal, natural gas n oil. Combustion of FF releases CO2 into atm.
• Decomposition; dead organic matter is broken down & CO2 released by decomposers.

Question 19

Carbon sinks

Answer 19

An area that stores carbon compounds for an indefinite period of time [1] n Stores more carbon than it releases. [1]

Question 20

Examples of carbon sinks

Answer 20

Oceans and forests are carbon sinks as they store carbon as carbon compounds indefinitely and releases less carbon than it takes in.

• Largest on earth: oceans
  
  • CO2 dissolved in ocean’s waters absorbed n used by phytoplankton + algae in photosynthesis
  • C used to make shells of shellfish n exoskeletons of corals which stores C even aft organism dies
  • Portion of the carbon compounds found in oceans is buried in the seabed and is in the form of fossil fuels such as natural gas and oil.
    
    • phytoplankton removes CO2 from the air via photosynthesis, and transfer the carbon to other organisms when they r eaten
• Forests
  
  • Atmospheric carbon dioxide is absorbed by the plants and used in photosynthesis.
  • A large amount of carbon compounds is stored in trees.
  • Remains of dead trees form coal – a type of fossil fuel.

Question 21

Renewable resources

Answer 21

Resources that Can be replaced in ecosystem via natural cycles as long as they are not overused

Question 22

Non-renewable Resources

Answer 22

Are resources that cannot be replaced as quickly once they are used

Question 23

Deforestation definition

Answer 23

refers to the clearing of forests to make land available for agricultural and/or urban development.

Question 24

Causes of deforestation

Answer 24

• Land for urban dev
• Land for growing crops
• Land for farming livestock
• Firewood as a source of fuel
• Wood used as construction materials n turned into pulp for making paper

Question 25

Undesirable effects of deforestation

Answer 25

• Extinction and reduction in biodiversity
  
  • Habitat destruction for many species of animals.
  • Remaining amount of forested land may not be big enough to support a breeding population of these animals -> may become endangered or extinct – resulting in loss of biodiversity.
• Global warming
  
  • Reduced tree population results in less carbon dioxide being removed from the atmosphere via photosynthesis -> ^CO2 concentration in atm, leading to global warming.
  • Carbon dioxide is a greenhouse gas that traps heat within the Earth’s atmosphere and results in warmer climates.
  • Tree trunks, roots n soil store excess carbon from photosynthesis -> CO2 stored released into atmosphere
• Soil erosion due to higher vulnerability of topsoil washed away during heavy rain. Forests prevent soil erosion by:
  
  • providing a leafy canopy that protects the topsoil from the direct impact of rain, and
  • retaining water in the forest through the absorption of water by plant roots.
• Flooding (soil washed into rivers -> ^water lvl -> ^ chance flooding
• Desertification
  
  • Without the leafy canopy, sunlight falls directly onto the ground and causes water to evaporate from the ground creating a desert-like condition that is not suitable for plants to grow.

Question 26

Effect of CO2 pollution

Answer 26

1. Greenhouse effect
   
   1. Carbon dioxide is a greenhouse gas which traps heat, causing enhanced greenhouse effect, resulting in global warming
2. Effect on aquatic ecosystem
   
   1. More atmospheric CO2 dissolves in sea water -> more acidic
   2. Shells that contain calcium carbonate react with the acid r weakened -> ^vulnerable to predators
   3. Coral bleaching & death of corals in coral reefs -> lose their ability to support as many species -> loss in biodiversity

Question 27

Pollution

Answer 27

the process by which harmful substances are added to the environment, making it undesirable/unfit for life.

Question 28

Eutrophication

Answer 28

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

Question 29

Causes of water pollution

Answer 29

• discharge of untreated sewage into water bodies
• excessive use of fertilisers and insecticides
• dumping of non- biodegradable plastic waste in landfills
• dumping of inorganic wastes in water bodies (e.g. mercury poisoning in Minamata Japan)

Question 30

Process of eutrophication

Answer 30

1. Nutrient load up: excessive nutrients like nitrate n phosphates from fertilisers flushed from land into water bodies by rain or thru discharged untreated sewage
2. Causing overgrowth & multiplication of algae n water plants in water bodies, since the nutrients r used in synthesis of proteins n nuclei acids.
3. Overgrowth of algae and water plants block sunlight from submerged plants -> insufficient light for photosynthesis -> die n decomposed by aerobic bacteria + fungi -> depletes oxygen -> other organisms die due to lack of dissolved oxygen

Question 31

Biomagnification

Answer 31

Biomagnification is the process when certain chemicals, e.g. insecticides, are passed along the food chain, increasing in concentration of toxins in the bodies of consumers at each increasing trophic levels.

Question 32

Bioaccumulation definition

Answer 32

Refers to the accumulation of toxins and chemical substances, such as insecticides in the body of an organism as it is non-biodegradable and cannot be excreted and will be stored in the fatty tissues of an organism.

Question 33

Effects of non-biodegradable plastic waste on the ecosystem

Answer 33

• Burning of plastic waste
• Harmful chem from plastic waste deposited in landfills may be leached into rivers n seas, poisoning wildlife
• Plastic waste may be harmful to marine animals
• Plastic waste can be broken down into microplastics and ingested by marine organisms n accumulates in their bodies -> bioaccumulation and biomagnification along food chains.

Question 34

Global warming

Answer 34

Rise in global tempt accelerated by human activities that cause increasing conc of greenhouse gases like CO2 in the atmosphere

Effect: increased concentration of ghg

Question 35

Climate change

Answer 35

Changes in tempt & weather patterns over a long period of time

Effects include rising sea levels, melting of ice sheets, shifts in flowering times, unpredictable weather changes

Question 36

Biodiversity

Answer 36

Biodiversity: The range of species that is presenT in a particular ecosystem.

Question 37

Conservation

Answer 37

The protection and preservation of natural resources in the environment.

Question 38

Reasons for conservation

Answer 38

• Preservation of natural scenery and wildlife
• Maintenance of a stable n balanced ecosystem
  
  • Prevents disruption of natural cycles n global warming
• Scientific research: Studies on wildlife give us insight on human beings
• Economic importance:
  
  • Rainforests are a source of raw materials for industries
  • Marine life are a major source of human food
• Maintenance of biodiversity by preventing extinction of species
  
  • Maintenance of a large gene pool -> cross-breeding favourable gene animals -> ^agricultural produce
  • Plants as sources of medicinal drugs
  • Prevent extinction of species

Question 39

Conservation of forests + mangrove swamps

Answer 39

• creation of laws to regulate logging industry
• Reforestation: planting of new trees/seedlings to replace destroyed trees
• Designation of lands as forest reserves
• Research to improve quality n productivity of forests
• Paris Agreement
• SG 2030 greenplan

Mangroves:
Mangrove Restoration Project
Adopt a mangrove project @ Pulau ubin

Coral reefs:
- Avoid purchasing living corals to deter business of live corals extraction
- Avoid polluting coastline with trash -> marine debris r harmful to coral reefs

Question 40

Describe the importance of respiration , combustion and photosynthesis in the carbon cycle [3]

Answer 40

Process P is respiration from animals which produces and releases carbon dioxide into the atmosphere; [1]

Process Q is photosynthesis of plants which absorbs carbon dioxide from atmosphere; it creates carbon sinks over indefinite/long periods of time such as forests as it stores more carbon than it releases; [1]

Process S is combustion of fossil fuels from factories/ industrial power plants which produces and releases carbon dioxide into the atmosphere which contributes to global warming; [1]

Processes P, Q and S help to maintain the level of carbon dioxide in the atmosphere and is part of the carbon cycle. Aerobic respiration and combustion gives out CO2 to atmosphere while photosynthesis takes in CO2 from atmosphere, maintaining a balanced concentration of CO2 in the atmosphere.

Question 41

Describe the role of bacteria and fungi in the carbon cycle. [3]

Answer 41

Bacteria and fungi are decomposers in the carbon cycle; [1] which feed on dead organisms/ dead organic matter and break them down into simpler substances during decomposition; [1]
Decomposers respire to produce carbon dioxide which is released into the atmosphere and absorbed by plants for photosynthesis; [1]

Question 42

Bioaccumulation and biomagnification answ formula (Explain why a higher proportion of fish-eating birds died compared to other organisms in the food chain) [3]

Answer 42

Insecticides are toxic, inorganic, non-biodegradable and cannot be excreted from the organisms when ingested. Due to bioaccumulation, Insecticides accumulate and store in the fatty tissues of the organisms and increase in concentration in the organisms of that trophic level. [1]
Due to bioamplification/ biomagnification, the concentration of the insecticides increases up the trophic levels as the organisms in the higher trophic level consume more of the organisms in the previous trophic level [1] and
hence the fish-eating birds at the highest trophic level would have accumulated the highest concentration of insecticides and
hence a higher proportion of fish-eating birds would have died as a result. [1]

Question 43

Environmental biotechnology

Answer 43

1. It uses aerobic and anaerobic bacteria to break down organic pollutants and remove nutrients such as nitrates and phosphates
2. before discharging sewage and hence prevents water pollution and eutrophication.

Question 44

Explain why a typical food chain in nature rarely exceeds four levels. [3]

Answer 44

About 90% of the energy is lost as it passed down the food chain, from one trophic level to the next. [1] Energy may be lost between trophic levels as heat energy released to the environment through respiration. [1]
Energy may also be lost between trophic levels as stored chemical energy in the egested and excreted materials. [1]
Thus, most amount of energy is not passed on to the next trophic level.
Insufficient and very little energy left to sustain the next trophic level [1] In a very long food chain, there would be too few tertiary consumers to transfer sufficient energy to sustain large numbers of consumers in the next trophic level.

Question 45

Define carbon sink and explain how forest / oceans can act as carbon sinks. [6] + Suggest why the ocean gives out less carbon than it takes in [5]

Answer 45

A carbon sink stores more carbon than it releases [1] for indefinite period of time [1] such as forests/oceans.

Forest
More carbon dioxide is taken up by plants for photosynthesis than given out during respiration [1] Carbon dioxide taken in is converted to organic substances, which will form part of plant tissue [1] and overtime dead trees and vegetation get buried underground and become fossil fuels after millions of years. [1]

Oceans
Much carbon dioxide is dissolved in the water [1]. The dissolved carbon
dioxide is taken up by aquatic plants and planktons as raw materials for photosynthesis and converted to organic substances which enters into food chain when animals eat aquatic plants and planktons [1]; Dead organisms sink to sea bed and get buried. After many years under great pressure the organic matter will become fossil fuels. [1]

[5]:
More carbon dioxide is taken up by plants for photosynthesis than given out dung respiration. [1]
CO2 is converted to organic substances such as glucose, which enters into food chain when animals consume plants. [1] animals respire to release CO2. [1] the organic substances will form part of skeleton[1] and dead organisms sink to sea bed and become fossil fuels [1].

Question 46

Describe how the carbon in a glucose molecule in the body of an animal is cycled in an ecosystem. [6]

Answer 46

Glucose molecule is oxidised during respiration in mitochondria to release carbon dioxide, water and energy. [1]
The carbon dioxide molecule is transported to the lungs by the blood and released into the atmosphere through exhalation. [1]
Plants will absorb the atmosphere carbon dioxide through the stomata in the leaves. [1]
Carbon dioxide and water, in the presence of sunlight and chlorophyll in the chloroplasts of the leaves are used to produce glucose molecules
during photosynthesis. [1] Excess glucose is converted to starch to be
stored.
Plants are eaten by consumers and the carbon in the starch enters the
animal. The starch is digested into glucose and absorbed by the animal in the alimentary canal. [1]
The absorbed glucose with the carbon can be transported to various tissues to be assimilated to synthesize new protoplasm in the animals. [1]

Question 47

Describe the process of eutrophication. [4]

Answer 47

Nutrient load up: excessive nutrients like nitrate and phosphates from fertilisers flushed from land into water bodies by rain or through discharged untreated sewage promote rapid multiplication and overgrowth of algae and water plants on the surface of the water body (river, lake or sea). [1] The nutrients r used in synthesis of proteins n nuclei acids in algae.

This prevents sunlight from reaching the submerged plants. [1]

Submerged plants absorb insufficient light energy and cannot photosynthesize and dies. [1]

Dead plants are decomposed by aerobic bacteria and fungi. [1]

Excessive decomposition depletes the oxygen in the water. Other organisms die due to lack of dissolved oxygen. [1]

Question 48

Explain how mercury dumped into the river can eventually lead to fish farmers suffering from heavy metal poisoning. [6]

Answer 48

Chemical waste discharged into the seawater contains mercury compounds that are non-biodegradable. Plankton takes in mercury which is toxic, non-biodegradable and cannot be excreted from the organism when ingested. [1] Thus mercury is accumulated and stored in the fatty tissues of the organisms and increase in concentration in organisms of that trophic level, [1]; due to
bioaccumulation [1]. The fishes in the higher trophic level consume many planktons which are in the previous trophic level, thus concentration of mercury increases as trophic level increases [1], causing the concentration of mercury to increase in the small fish, leading to bioamplification. [1]
Humans being highest in the trophic level and in food chain consume the fishes with increasing level of mercury, thus accumulating highest concentration of mercury in our body[1], resulting in severe harmful effects such as death.

Question 49

Explain why the banana plant is described as producer in the food web. [1]

Answer 49

Banana plant is able to photosynthesise to make its own food/ glucose (using energy from the sun) and occupies the first trophic level/ first organisms of a food chain/ is a source of food [1] for consumers in food web.

Question 50

With reference suggest why some farmers restrict the movement of the animals they are growing for food. [3]

Answer 50

50/90 x 100 = 55.6% of energy is lost as heat energy due to aerobic respiration [1], hence restricting the movement of the animals
reduces the rate of respiration in the animals, resulting in less energy consumption [1] and more energy available in the body of the animals for the consumers who feed on them. [1]

Question 51

State one factor that will affect the rate at which a methanogen (microorganism that break down sewage in sewage treatment plants) produces methane [1]

Answer 51

Temperature of sewage mixture/pH of sewage mixture/concentration of small organic compounds in sewage

Question 52

Suggest why having large proportion of fish in the sea with long lengths r positive indicator of fish stocks [3]

Answer 52

It is a positive indicator of fish stocks as it means that there is sufficient food available in the sea to enable the fish to grow big
to a body length of 40 cm or longer; [1]
A higher proportion of fish in the sea that is longer in length indicates a larger percentage of fish population grown to adulthood and therefore capable of reproducing. [1]
Indicating that there is sufficient primary and secondary consumers to support a large number of tertiary consumers which are the fishes; [1]
representing a healthy ecosystem in the sea/ enough fish stocks for harvesting; [1]

Question 53

Explain why scientists r concerned about the suspected poisoning of honeybee colonies by insecticides [4]

Answer 53

Bees are important pollinators for flowers to ensure fruits are produced. [1]
Widespread use of insecticides can disrupt food chains and food webs in the ecosystem. [1]
There will be loss in biodiversity of certain species of bees due to indiscriminate killing. [1]
Excessive usage of insecticides will result in bioaccumulation and bioamplification that may cause an increase in insecticides resistance in the insects. [1]

+ different results in cities and farmland areas reasons [3]:

There is excessive use of insecticides in farmland areas by farmers to increase crop yield whereas there are less usage of insecticides in the cities. [1]
More open space in farmlands for honeybees to be killed by insecticides compared to those in the cities. [1]
More different insecticides used in farmlands than in the cities due to different crops grown. [1]

Question 54

Discuss the possible environmental consequences of natural tropical rainforests getting replaced with plantations of H. Brasiliensis. [4]

Answer 54

Loss of habitat for wildlife animal populations in the rainforest [1] -> decrease in animal biodiversity/ [1]
Loss of wild type plants that may have medicinal benefits. [1]/
Increased risk of soil erosion due to loss of top soil as trees in plantations r usually spaced further apart than tropical rainforests/ [1]
Excessive use of fertilisers and pesticides can lead to water pollution as chemicals can be washed off by rainwater into nearby water bodies/[1]
Plantations have lower plant density than natural rainforests, resulting in less CO2 absorbed from atmosphere via photosynthesis potentially contributing to increased global warming/ [1]
Irrigation systems setup to sustain plantations may disrupt natural water sources in the area [1]

Question 55

Explain the difference between “bioaccumulation” and “bioamplification”. [1]

Answer 55

Bioaccumulation refers to the increase in concentration of toxins within each
individual in the population whereas bioamplification refers to the large increase
in concentration of toxin with the increase in trophic level within a food chain. [1]

Question 56

Suggest why the ocean gives out less carbon than it takes in.

Answer 56

More carbon dioxide is taken up by plants for
photosynthesis than given out during respiration [1]
Carbon dioxide is converted to organic substances/ food/
glucose, which enters into food chain when animals eat/
consume plants [1]; Animals respire to release carbon
dioxide. [1] The organic substances will form part of
skeleton [1] and dead organisms sink to sea bed and
become fossil fuels.[1]

Question 57

Why the drained peat swamp is a carbon source [4]

Answer 57

A carbon source releases more C into the atmosphere than it absorbs. A drained peat swamp contain large amount of dead remains
which consist of carbon compounds stored. [1]
When decomposers such as bacteria and fungi [1] undergo decomposition on peat, carbon dioxide is released. [1] Decomposers will also respire aerobically and release carbon dioxide. [1]

Question 58

Habitat definition

Answer 58

The place where an organism lives

Question 59

Niche

Answer 59

Role played by or position occupied by an organism in its habitat

Question 60

Biotic environment definition

Answer 60

Consists of all the living things that an organism interacts with

Question 61

Abiotic environment definition

Answer 61

Consists of all the physical factors, such as light and temperature, in the environment

Question 62

Pyramid of numbers definition

Answer 62

Shows the number of organisms present in each trophic level at a particular time

Question 63

Explain ow the radioactive carbon in plant could become part of the tissues of a primary consumer such as a cow. [3]

Answer 63

Carbon dioxide and water, in the presence of light energy and chlorophyll in the chloroplasts of the leaves are used to produce glucose molecules during photosynthesis. Excess glucose is converted to starch to be stored. [1]
Plants are eaten by consumers and the carbon in the starch enters the cow. The starch is digested into maltose and then glucose which is absorbed by the cow in the alimentary canal [1]
The absorbed glucose with the radioactive carbon can be transported to various tissues to be assimilated to synthesize new protoplasm in the cow. [1]

Question 64

Suggest why only a small proportion of that energy absorbed from the sun is available in the animal feed from the harvested wheat. [3]

Answer 64

1. Not all solar energy is absorbed by plant for
   photosynthesis to synthesise glucose as some
   is reflected.
2. The plants will use up some glucose
   synthesised for its own cellular activities, hence
   loss of energy through respiration or loss of heat to the surroundings.
3. Not all parts of the wheat harvested is used as animal feed, some parts of the plant like the
   roots are thrown away.

Question 65

Student repeated the investigation and obtained a different set of results. Suggest 2 reasons why. [2]

Answer 65

1. The total solar energy available may differ due to different weather conditions. [1]
2. The growth rate of wheat may differ as it depends on climate conditions / seasons, thus the mass of animal feed made from varying harvested wheat amount may differ. [1]