Human Influences on Ecosystems: Pollution, Deforestation, Conservation, Climate Change and Sustainable Resources

1. A lake receives run-off containing nitrate fertilisers from nearby farms. Several weeks later, fish begin to die.
   Which sequence best explains this?

A nitrate increases → algae decrease → decomposers decrease → oxygen increases → fish die
B nitrate increases → algal bloom → decomposers respire more → oxygen decreases → fish die
C nitrate decreases → plants photosynthesise more → oxygen decreases → fish die
D nitrate increases → fish absorb nitrate directly → haemoglobin denatures → fish die

2. Which statement best describes eutrophication?

A build-up of toxic pesticides in top carnivores
B enrichment of water with mineral ions causing algal growth and oxygen depletion
C release of carbon dioxide by burning fossil fuels
D destruction of forests causing soil erosion only

3. Why can untreated sewage entering a river reduce oxygen concentration?

A bacteria decompose organic matter and respire aerobically
B fish photosynthesise faster and use oxygen
C sewage absorbs oxygen by osmosis
D nitrates directly convert oxygen into nitrogen gas

4. Which measurement would most directly show that organic pollution has increased in a river?

A lower biochemical oxygen demand
B higher dissolved oxygen concentration
C higher biochemical oxygen demand
D lower bacterial activity

5. Which pollutant is most directly responsible for acid rain?

A sulfur dioxide
B methane
C nitrogen gas
D oxygen

6. Which effect is most likely caused by acid rain?

A increased pH of lakes and faster fish reproduction
B damage to leaves and acidification of lakes
C increased oxygen production by all aquatic plants
D complete removal of all carbon dioxide from air

7. Which gas is a major greenhouse gas released during cattle farming and decomposition in landfill sites?

A methane
B oxygen
C nitrogen
D sulfur dioxide

8. Which human activity most directly increases atmospheric carbon dioxide concentration?

A planting forests
B burning fossil fuels
C using biological control
D recycling paper

9. Which statement about the enhanced greenhouse effect is correct?

A it is caused by less infrared radiation being trapped by greenhouse gases
B it is caused by increased greenhouse gases trapping more infrared radiation
C it is caused by oxygen destroying the ozone layer only
D it reduces global mean temperature immediately

10. Which consequence is most likely linked to climate change?

A rising sea levels due to melting ice and thermal expansion of oceans
B permanent decrease in all global temperatures
C complete stopping of photosynthesis in all plants
D instant removal of all invasive species

11. Which gas is released in large amounts when forests are burned?

A carbon dioxide
B ozone
C nitrogen only
D water as a solid

12. Deforestation can increase atmospheric carbon dioxide because

A fewer trees are available for photosynthesis and burning releases carbon dioxide
B trees absorb oxygen only when alive
C roots convert carbon dioxide into nitrogen gas
D deforestation increases the number of chloroplasts globally

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Which effect of deforestation most directly increases soil erosion?

A reduced leaf litter and fewer roots holding soil together
B increased number of trees absorbing rainwater
C increased transpiration from forest canopies
D greater formation of humus by decomposers

14. Which statement best explains why deforestation can reduce biodiversity?

A many habitats and food sources are destroyed
B all animals immediately become producers
C photosynthesis stops in the oceans
D soil minerals become genetically identical

15. Which human activity most directly causes habitat destruction?

A establishing nature reserves
B clearing forests for agriculture
C captive breeding of endangered species
D replanting native trees

16. Which pollutant can bioaccumulate in food chains?

A persistent pesticide
B oxygen
C nitrogen gas
D water vapour

17. A pesticide enters a pond food chain.

algae → small crustaceans → small fish → heron

Which organism is likely to have the highest pesticide concentration?

A algae
B small crustaceans
C small fish
D heron

18. Why does bioaccumulation usually affect top carnivores most severely?

A they eat many contaminated organisms and the toxin is not easily broken down or excreted
B they photosynthesise faster than producers
C they contain no fat tissue, so toxins dissolve in blood only
D they are always smaller than producers

19. Which statement about DDT is correct?

A it is a biodegradable fertiliser that improves oxygen concentration in lakes
B it is a persistent pesticide that can accumulate along food chains
C it is a greenhouse gas released only by cattle
D it is a hormone used in tissue culture

20. Which method reduces pest damage while avoiding chemical pesticide residues?

A biological control
B burning more fossil fuels
C releasing untreated sewage
D draining wetlands for housing

21. Which risk is linked with biological control?

A the control organism may become invasive or affect non-target species
B it always causes acid rain immediately
C it increases carbon dioxide by combustion
D it always kills only the pest species and then disappears

22. Which example shows biological control?

A using ladybirds to reduce aphid numbers
B spraying persistent pesticide on all crops
C adding nitrate fertiliser to a lake
D burning crop residues to release minerals

23. Which farming practice can reduce soil erosion?

A removing all vegetation from slopes
B ploughing up and down steep slopes
C planting cover crops and using contour ploughing
D overgrazing by livestock

24. Which statement about overgrazing is correct?

A it increases plant cover and reduces erosion
B it removes vegetation, exposing soil to erosion
C it always increases biodiversity
D it converts all soil minerals into glucose

25. Which process is most directly increased by large-scale use of nitrate fertiliser?

A eutrophication after run-off into water
B bioaccumulation of oxygen in eagles
C acid rain from methane only
D ozone formation in roots

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. Which statement about non-biodegradable plastics is correct?

A they are broken down rapidly by decomposers into harmless nutrients
B they may persist in ecosystems and harm organisms by ingestion or entanglement
C they are always converted into oxygen by algae
D they reduce microplastic pollution when thrown into oceans

27. Which action is most sustainable?

A cutting trees faster than they can regrow
B using fish stocks faster than they reproduce
C harvesting resources at a rate that allows replacement
D using only non-renewable fossil fuels for all energy

28. Which statement best describes sustainable development?

A using resources to meet present needs without preventing future generations meeting theirs
B stopping all use of natural resources immediately
C increasing consumption until ecosystems collapse
D replacing biodiversity with one high-yield crop everywhere

29. Which practice supports sustainable fishing?

A catching fish before they reach reproductive age
B using nets with very small mesh sizes
C setting quotas and protecting breeding seasons
D removing all predators from the ocean

30. Why can overfishing damage an ecosystem?

A it may reduce breeding populations and disrupt food webs
B it increases fish reproduction forever
C it prevents carbon dioxide dissolving in water
D it makes all fish become decomposers

31. Which method helps conserve endangered species?

A captive breeding and habitat protection
B removing all protected areas
C hunting the last remaining adults
D introducing random predators into their habitats

32. Which advantage of seed banks is most valid?

A they preserve genetic material of plant species for future use
B they prevent all seeds from ever germinating naturally
C they increase hunting of endangered animals
D they store carbon dioxide gas for respiration

33. Which statement about conservation is correct?

A it only protects individual animals and ignores habitats
B it manages ecosystems and species to maintain biodiversity
C it requires destroying all non-human habitats
D it prevents all natural selection permanently

34. Which action most directly conserves biodiversity?

A protecting habitats such as forests and wetlands
B replacing native forests with one crop species
C releasing untreated industrial waste into rivers
D removing all decomposers from soil

35. Which statement explains why reforestation can reduce climate change impact?

A trees absorb carbon dioxide during photosynthesis and store carbon in biomass
B trees release methane during photosynthesis
C tree roots convert oxygen into sulfur dioxide
D tree leaves stop all infrared radiation escaping Earth

36. Which human activity can cause desertification?

A overgrazing and removal of vegetation
B planting shelter belts and cover crops
C restoring wetlands
D reducing livestock numbers on fragile land

37. Which effect is most likely from desertification?

A soil becomes more fertile and supports more crops
B land becomes less productive and vegetation decreases
C rainfall increases permanently in all regions
D biodiversity always increases

38. Which statement about invasive species is correct?

A they may outcompete native species and reduce biodiversity
B they always increase every native population
C they cannot reproduce in new habitats
D they are always used safely in biological control

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Which human activity is most likely to introduce invasive species?

A transporting organisms between countries accidentally or deliberately
B reducing international trade in plants and animals
C protecting native habitats from disturbance
D preventing movement of ships and cargo

40. Which pollutant is most directly linked with carbon monoxide poisoning?

A carbon monoxide from incomplete combustion
B nitrate ions from fertiliser run-off
C sulfur dioxide from acid rain only
D phosphate ions from detergents

41. Why is carbon monoxide dangerous?

A it binds strongly to haemoglobin and reduces oxygen transport
B it increases oxygen binding to haemoglobin permanently
C it acts as a vaccine against lung disease
D it converts red blood cells into platelets

42. Which pollutant is most directly linked with increased cases of asthma and bronchitis?

A particulate smoke and irritant gases
B oxygen from photosynthesis
C nitrogen gas from air
D water vapour from transpiration

43. Which statement about sewage treatment is correct?

A it reduces organic waste and pathogen levels before water is released
B it adds more untreated faeces to rivers
C it removes all oxygen from rivers intentionally
D it converts all bacteria into viruses

44. Which process in sewage treatment uses microorganisms to break down organic matter?

A biological treatment
B distillation of oxygen
C genetic cloning only
D pollination

45. Which effect can phosphate detergents have if released into lakes?

A they can contribute to eutrophication
B they immediately remove all algae
C they prevent bacterial respiration
D they increase oxygen solubility forever

46. Which statement about recycling is correct?

A it can reduce demand for raw materials and reduce waste sent to landfill
B it always increases extraction of raw materials
C it prevents all energy use in manufacturing
D it works only for living organisms

47. Which action reduces landfill pressure most directly?

A reuse and recycling of materials
B producing more single-use plastics
C burying all waste without sorting
D burning all waste in open air

48. Which statement about renewable resources is correct?

A they can be replaced naturally if used sustainably
B they are always unlimited even if overused
C fossil fuels are renewable within a human lifetime
D renewable resources cannot be damaged by pollution

49. Which energy source produces electricity without direct carbon dioxide emissions during operation?

A solar power
B coal combustion
C petrol combustion
D natural gas combustion

50. Which statement is correct?

A human activities can reduce biodiversity through habitat destruction, pollution and overexploitation
B pollution always increases ecosystem stability
C conservation means using all resources as fast as possible
D climate change is caused only by oxygen released in photosynthesis

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. Answer: B
   A is wrong because algae increase first, not decrease.
   B is correct because nitrate run-off causes algal bloom; dead algae are decomposed by bacteria, which respire aerobically and reduce oxygen, killing fish.
   C is wrong because nitrate does not decrease first.
   D is wrong because fish death is mainly due to oxygen depletion, not nitrate denaturing haemoglobin.

2. Answer: B
   A is wrong because that describes bioaccumulation/biomagnification.
   B is correct because eutrophication is mineral ion enrichment of water causing algal growth and oxygen depletion.
   C is wrong because this describes greenhouse gas release.
   D is wrong because deforestation is not eutrophication.

3. Answer: A
   A is correct because bacteria decompose organic matter in sewage and respire aerobically, using dissolved oxygen.
   B is wrong because fish do not photosynthesise.
   C is wrong because sewage does not remove oxygen by osmosis.
   D is wrong because nitrates do not directly convert oxygen into nitrogen gas.

4. Answer: C
   A is wrong because lower BOD suggests less organic pollution.
   B is wrong because organic pollution usually reduces dissolved oxygen.
   C is correct because higher biochemical oxygen demand shows more oxygen is needed by microorganisms decomposing organic matter.
   D is wrong because bacterial activity usually increases.

5. Answer: A
   A is correct because sulfur dioxide dissolves/reacts in the atmosphere to form acidic compounds that cause acid rain.
   B is wrong because methane is a greenhouse gas, not the main acid rain gas.
   C is wrong because nitrogen gas is mostly unreactive.
   D is wrong because oxygen itself does not cause acid rain.

6. Answer: B
   A is wrong because acid rain lowers pH, not increases it.
   B is correct because acid rain damages leaves and acidifies lakes, harming aquatic organisms.
   C is wrong because acid rain does not increase oxygen production by all aquatic plants.
   D is wrong because it does not remove all carbon dioxide from air.

7. Answer: A
   A is correct because methane is released by cattle farming and decomposition in landfill sites.
   B is wrong because oxygen is not a greenhouse gas in this context.
   C is wrong because nitrogen gas is not a major greenhouse gas.
   D is wrong because sulfur dioxide is linked more with acid rain.

8. Answer: B
   A is wrong because planting forests can reduce carbon dioxide by photosynthesis.
   B is correct because burning fossil fuels releases carbon dioxide.
   C is wrong because biological control targets pests, not carbon dioxide directly.
   D is wrong because recycling paper can reduce resource use and emissions.

9. Answer: B
   A is wrong because enhanced greenhouse effect involves more infrared radiation being trapped.
   B is correct because increased greenhouse gases trap more infrared radiation, raising global temperatures.
   C is wrong because ozone depletion is a different issue.
   D is wrong because enhanced greenhouse effect increases global mean temperature over time.

10. Answer: A
    A is correct because climate change can cause rising sea levels from melting ice and thermal expansion of seawater.
    B is wrong because global warming does not mean all places permanently cool.
    C is wrong because photosynthesis does not completely stop in all plants.
    D is wrong because invasive species are not instantly removed.

11. Answer: A
    A is correct because burning forests releases carbon dioxide.
    B is wrong because ozone is not released in large amounts by forest burning.
    C is wrong because nitrogen is not the main gas released.
    D is wrong because water as a solid is ice, not a gas released from burning.

12. Answer: A
    A is correct because fewer trees photosynthesise, and burning trees releases carbon dioxide.
    B is wrong because trees absorb carbon dioxide for photosynthesis.
    C is wrong because roots do not convert carbon dioxide into nitrogen gas.
    D is wrong because deforestation reduces global chloroplast numbers.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Answer: A
    A is correct because roots bind soil and leaf litter protects the surface; removing them increases erosion.
    B is wrong because fewer trees, not more trees, are present after deforestation.
    C is wrong because transpiration from forest canopies decreases after deforestation.
    D is wrong because humus formation usually decreases when vegetation is removed.

14. Answer: A
    A is correct because deforestation destroys habitats, food sources and breeding sites, reducing biodiversity.
    B is wrong because animals do not become producers.
    C is wrong because ocean photosynthesis does not stop.
    D is wrong because soil minerals do not become genetically identical.

15. Answer: B
    A is wrong because nature reserves protect habitats.
    B is correct because clearing forests for agriculture directly destroys habitats.
    C is wrong because captive breeding helps conservation.
    D is wrong because replanting native trees restores habitats.

16. Answer: A
    A is correct because persistent pesticides can bioaccumulate in food chains.
    B is wrong because oxygen does not bioaccumulate as a toxin.
    C is wrong because nitrogen gas does not bioaccumulate in food chains.
    D is wrong because water vapour is not a persistent toxin.

17. Answer: D
    A is wrong because algae are at the lowest trophic level and have the lowest concentration.
    B is wrong because small crustaceans contain more than algae but less than higher consumers.
    C is wrong because small fish contain more than crustaceans but less than herons.
    D is correct because the heron is the top consumer and receives pesticide from many contaminated prey.

18. Answer: A
    A is correct because top carnivores eat many contaminated organisms and persistent toxins are not easily broken down or excreted.
    B is wrong because top carnivores do not photosynthesise.
    C is wrong because many persistent toxins can accumulate in fat tissue.
    D is wrong because top carnivores are not always smaller than producers.

19. Answer: B
    A is wrong because DDT is not a biodegradable fertiliser.
    B is correct because DDT is a persistent pesticide that can accumulate along food chains.
    C is wrong because methane is the greenhouse gas released by cattle.
    D is wrong because plant hormones are used in tissue culture, not DDT.

20. Answer: A
    A is correct because biological control uses living organisms to control pests, avoiding chemical residues.
    B is wrong because burning fossil fuels increases pollution.
    C is wrong because untreated sewage causes water pollution.
    D is wrong because draining wetlands destroys habitats.

21. Answer: A
    A is correct because biological control organisms may become invasive or harm non-target species.
    B is wrong because biological control does not always cause acid rain.
    C is wrong because it is not combustion.
    D is wrong because control organisms do not always disappear after killing only the pest.

22. Answer: A
    A is correct because ladybirds are natural predators of aphids.
    B is wrong because spraying pesticide is chemical control.
    C is wrong because adding nitrate fertiliser can cause eutrophication.
    D is wrong because burning crop residues is not biological control.

23. Answer: C
    A is wrong because removing vegetation increases erosion.
    B is wrong because ploughing up and down slopes increases run-off and erosion.
    C is correct because cover crops protect soil and contour ploughing slows run-off.
    D is wrong because overgrazing removes vegetation and increases erosion.

24. Answer: B
    A is wrong because overgrazing reduces plant cover.
    B is correct because overgrazing removes vegetation, exposing soil to wind and rain erosion.
    C is wrong because overgrazing usually reduces biodiversity.
    D is wrong because soil minerals are not converted into glucose.

25. Answer: A
    A is correct because nitrate fertiliser run-off can cause eutrophication.
    B is wrong because oxygen does not bioaccumulate in eagles.
    C is wrong because methane is not the main cause of acid rain.
    D is wrong because ozone formation in roots is nonsense.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. Answer: B
    A is wrong because non-biodegradable plastics are not broken down rapidly.
    B is correct because they persist and harm organisms through ingestion, entanglement and microplastic pollution.
    C is wrong because algae do not convert plastics into oxygen.
    D is wrong because dumping plastics into oceans increases microplastic pollution.

27. Answer: C
    A is wrong because cutting trees faster than they regrow is unsustainable.
    B is wrong because using fish faster than they reproduce is overfishing.
    C is correct because sustainable use means harvesting at a rate that allows replacement.
    D is wrong because fossil fuels are non-renewable.

28. Answer: A
    A is correct because sustainable development meets present needs without preventing future generations from meeting theirs.
    B is wrong because sustainability does not mean stopping all resource use.
    C is wrong because ecosystem collapse is the opposite of sustainability.
    D is wrong because monocultures reduce biodiversity.

29. Answer: C
    A is wrong because catching immature fish reduces future breeding.
    B is wrong because very small mesh catches young fish.
    C is correct because quotas and protecting breeding seasons allow fish populations to recover.
    D is wrong because removing all predators disrupts food webs.

30. Answer: A
    A is correct because overfishing reduces breeding populations and disrupts food webs.
    B is wrong because it does not increase reproduction forever.
    C is wrong because carbon dioxide dissolution is not the main issue.
    D is wrong because fish do not become decomposers.

31. Answer: A
    A is correct because captive breeding and habitat protection help conserve endangered species.
    B is wrong because removing protected areas increases extinction risk.
    C is wrong because hunting remaining adults worsens decline.
    D is wrong because random predators may damage the ecosystem.

32. Answer: A
    A is correct because seed banks preserve genetic material of plant species for future use.
    B is wrong because seeds can later be germinated under suitable conditions.
    C is wrong because seed banks are for plant conservation, not hunting.
    D is wrong because they do not store carbon dioxide for respiration.

33. Answer: B
    A is wrong because conservation protects habitats as well as species.
    B is correct because conservation manages ecosystems and species to maintain biodiversity.
    C is wrong because destroying habitats is not conservation.
    D is wrong because conservation does not stop natural selection permanently.

34. Answer: A
    A is correct because protecting habitats protects many species and their interactions.
    B is wrong because replacing forests with one crop reduces biodiversity.
    C is wrong because industrial waste pollutes ecosystems.
    D is wrong because decomposers are essential for nutrient cycling.

35. Answer: A
    A is correct because trees absorb carbon dioxide in photosynthesis and store carbon in biomass.
    B is wrong because trees do not release methane during photosynthesis.
    C is wrong because roots do not convert oxygen into sulfur dioxide.
    D is wrong because leaves do not stop all infrared radiation escaping Earth.

36. Answer: A
    A is correct because overgrazing and vegetation removal expose soil and contribute to desertification.
    B is wrong because shelter belts and cover crops reduce erosion/desertification.
    C is wrong because restoring wetlands supports ecosystems.
    D is wrong because reducing livestock pressure helps prevent desertification.

37. Answer: B
    A is wrong because desertification reduces soil fertility.
    B is correct because land becomes less productive and vegetation decreases.
    C is wrong because rainfall does not permanently increase everywhere.
    D is wrong because biodiversity usually decreases.

38. Answer: A
    A is correct because invasive species may outcompete native species and reduce biodiversity.
    B is wrong because they often reduce native populations.
    C is wrong because invasive species can reproduce successfully in new habitats.
    D is wrong because biological control can be risky if the species becomes invasive.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Answer: A
    A is correct because transporting organisms between countries can introduce invasive species accidentally or deliberately.
    B is wrong because reducing trade lowers introduction risk.
    C is wrong because protecting habitats does not introduce invasive species.
    D is wrong because preventing cargo movement reduces accidental introductions.

40. Answer: A
    A is correct because carbon monoxide is produced by incomplete combustion.
    B is wrong because nitrate ions cause eutrophication, not carbon monoxide poisoning.
    C is wrong because sulfur dioxide is linked with acid rain.
    D is wrong because phosphate ions contribute to eutrophication.

41. Answer: A
    A is correct because carbon monoxide binds strongly to haemoglobin, reducing oxygen transport.
    B is wrong because it reduces oxygen binding, not increases it.
    C is wrong because it is not a vaccine.
    D is wrong because it does not convert red blood cells into platelets.

42. Answer: A
    A is correct because particulate smoke and irritant gases can worsen asthma and bronchitis.
    B is wrong because oxygen from photosynthesis is not a pollutant causing these conditions.
    C is wrong because nitrogen gas is not the main respiratory irritant.
    D is wrong because water vapour from transpiration is not the cause.

43. Answer: A
    A is correct because sewage treatment reduces organic waste and pathogen levels before discharge.
    B is wrong because treatment is meant to prevent untreated faeces entering rivers.
    C is wrong because it should prevent oxygen depletion, not intentionally remove oxygen.
    D is wrong because it does not convert bacteria into viruses.

44. Answer: A
    A is correct because biological treatment uses microorganisms to break down organic matter.
    B is wrong because oxygen is not distilled in sewage treatment.
    C is wrong because genetic cloning is not the main sewage treatment process.
    D is wrong because pollination is plant reproduction.

45. Answer: A
    A is correct because phosphate detergents can enrich water and contribute to eutrophication.
    B is wrong because they can encourage algae, not immediately remove all algae.
    C is wrong because they do not prevent bacterial respiration.
    D is wrong because they do not increase oxygen solubility forever.

46. Answer: A
    A is correct because recycling reduces demand for raw materials and reduces waste sent to landfill.
    B is wrong because recycling usually reduces extraction pressure.
    C is wrong because recycling still uses some energy.
    D is wrong because non-living materials can also be recycled.

47. Answer: A
    A is correct because reuse and recycling reduce the amount of waste going to landfill.
    B is wrong because single-use plastics increase waste.
    C is wrong because burying all waste increases landfill pressure.
    D is wrong because open burning causes air pollution.

48. Answer: A
    A is correct because renewable resources can be replaced naturally if used sustainably.
    B is wrong because renewable resources can still be overused.
    C is wrong because fossil fuels take millions of years to form, so they are not renewable within a human lifetime.
    D is wrong because renewable resources can still be damaged by pollution.

49. Answer: A
    A is correct because solar power produces electricity without direct carbon dioxide emissions during operation.
    B is wrong because coal combustion releases carbon dioxide.
    C is wrong because petrol combustion releases carbon dioxide.
    D is wrong because natural gas combustion releases carbon dioxide.

50. Answer: A
    A is correct because habitat destruction, pollution and overexploitation reduce biodiversity.
    B is wrong because pollution usually destabilises ecosystems.
    C is wrong because conservation means careful protection and management, not rapid resource use.
    D is wrong because climate change is mainly linked to greenhouse gases, not oxygen from photosynthesis.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.