Organisms and their Environment
Each subtopic includes About section, revision page link, 10 preview questions, and practice CTAs.
Energy flow
SubtopicEnergy flow under Organisms and their Environment for Grade 12 IGCSE.
Preview questions (no answers)
- 1.
What is the main source of energy for a secondary consumer?
A.Sunlight
B.Primary consumers
C.Producers
D.Decomposers
- 2.
In a pyramid of biomass, which level is shown at the very top?
A.Producers
B.Primary consumers
C.Secondary consumers
D.The highest level consumer
- 3.
Which of the following is most likely to be at the top of a food chain?
A.A herbivore
B.A primary consumer
C.A carnivore
D.A producer
- 4.
What is the term for a group of different populations living and interacting in the same area?
A.Ecosystem
B.Species
C.Community
D.Habitat
- 5.
If a large portion of a forest is cleared for agriculture, how is the total energy flow of the original ecosystem affected?
A.The total energy flow increases because crops grow faster.
B.The total energy fixed by producers usually decreases due to loss of complex layers.
C.Energy flow remains the same as long as something is growing.
D.The energy transfer efficiency between trophic levels increases.
- 6.
Which of the following defines a 'scavenger'?
A.An organism that produces its own organic molecules.
B.An animal that feeds on the carcasses of dead animals.
C.A bacterium that breaks down cell walls.
D.A plant that grows on other plants for support.
- 7.
In a food web, what does the direction of the arrow represent?
A.Which organism is the larger one.
B.The movement of chemical energy from one organism to another.
C.The evolutionary relationship between species.
D.The migration patterns of the animals.
- 8.
How does an increase in environmental temperature affect the of an ecosystem, assuming moisture is not limiting?
A.It always increases NPP because photosynthesis speed increases with temperature.
B.It may decrease NPP if the rate of plant respiration increases faster than the rate of photosynthesis.
C.It has no effect because and always increase by the same amount.
D.It increases NPP by decreasing the energy lost to herbivores.
- 9.
If of energy is fixed by the of a field, and the primary consumers have an exploitation efficiency of and an assimilation efficiency of , how much energy is actually assimilated by the primary consumers?
A.10,000 J
B.20,000 J
C.5,000 J
D.2,000 J
- 10.
Which ecosystem typically has the highest 'Trophic Transfer Efficiency' ()?
A.A desert with sparse vegetation and high-temperature fluctuations.
B.An open ocean ecosystem with small, fast-growing producers and ectothermic consumers.
C.A temperate forest with large woody producers and many endothermic mammals.
D.An agricultural monoculture with heavy pesticide use.
Download the worksheet for Organisms and their Environment - Energy flow to practice offline. It includes additional chapter-level practice questions.
Food chains and food webs
SubtopicFood chains and food webs under Organisms and their Environment for Grade 12 IGCSE.
Preview questions (no answers)
- 1.
Why is biomass lost between trophic levels?
A.Because organisms do not eat every part of their prey
B.Because all organisms are the same size
C.Because producers have the least biomass
D.Because predators eat more than prey
- 2.
In a food chain, the first consumer is also called a:
A.Secondary consumer
B.Tertiary consumer
C.Primary consumer
D.Quaternary consumer
- 3.
If a disease kills most of the rabbits in a field, what might happen to the foxes that eat them?
A.The fox population will increase
B.The fox population will decrease or find new prey
C.The foxes will start eating grass
D.Nothing will change
- 4.
Which organism is a producer in a pond ecosystem?
A.Dragonfly larva
B.Water lily
C.Tadpole
D.Perch
- 5.
If an ecosystem has a Gross Primary Productivity of and the producers use for their own respiration, what is the Net Primary Productivity available to herbivores?
A.B.C.D. - 6.
Which type of pyramid can never be inverted in a healthy, functioning ecosystem?
A.Pyramid of Numbers
B.Pyramid of Biomass
C.Pyramid of Energy
D.All pyramids can be inverted
- 7.
Which of the following correctly orders organisms from the lowest to the highest trophic level?
A.Hawk, Snake, Mouse, Grass
B.Grass, Mouse, Snake, Hawk
C.Mouse, Grass, Hawk, Snake
D.Grass, Hawk, Mouse, Snake
- 8.
Why is it more energy-efficient for a human population to be supported by a crop of corn than by cattle raised on that same corn?
A.Corn contains more protein per gram than beef.
B.Cattle lose a significant amount of energy through respiration and waste before being consumed by humans.
C.Corn has a higher GPP than any other crop.
D.Humans cannot digest the cellulose found in corn used for cattle feed.
- 9.
In which ecosystem would you expect the 'detritus pathway' to be the dominant route for energy flow over the 'grazing pathway'?
A.An open ocean ecosystem.
B.A managed pasture.
C.A deciduous forest.
D.A coral reef.
- 10.
If a food web is 'highly connected', what does this imply about its 'linkage density'?
A.There are many species but very few predatory interactions.
B.There is a high average number of feeding links per species.
C.Most species are autotrophs.
D.The food web consists mainly of isolated food chains.
Download the worksheet for Organisms and their Environment - Food chains and food webs to practice offline. It includes additional chapter-level practice questions.
Nutrient cycles (Carbon and Nitrogen)
SubtopicNutrient cycles (Carbon and Nitrogen) under Organisms and their Environment for Grade 12 IGCSE.
Preview questions (no answers)
- 1.
Which chemical element is found in all proteins, DNA, and RNA, but is NOT found in simple carbohydrates like glucose?
A.Carbon
B.Hydrogen
C.Oxygen
D.Nitrogen
- 2.
In the nitrogen cycle, which process is inhibited by plowing or turning the soil to add oxygen?
A.Nitrification
B.Denitrification
C.Nitrogen fixation
D.Decomposition
- 3.
Which of these is a biotic factor that moves carbon through an ecosystem?
A.Volcanic activity
B.Weathering of rocks
C.Respiration
D.Combustion of coal
- 4.
What is the effect of deforestation on the carbon cycle?
A.It increases the removal of from the air
B.It decreases the amount of in the atmosphere
C.It reduces the amount of being removed by photosynthesis
D.It has no effect on the carbon cycle
- 5.
Which of these processes is exclusively carried out by prokaryotes?
A.Cellular Respiration
B.Nitrogen Fixation
C.Photosynthesis
D.Decomposition
- 6.
How do deforestation and land clearing specifically affect the global carbon cycle?
A.By increasing the capacity of the land to store carbon.
B.By reducing the amount of removed from the atmosphere via photosynthesis.
C.By increasing the rate of nitrogen fixation in the soil.
D.By decreasing the rate of cellular respiration in soil microbes.
- 7.
In the carbon cycle, how does the process of 'feeding' transfer carbon?
A.As gas dissolved in water.
B.As complex organic molecules like proteins and carbohydrates.
C.As inorganic carbonate ions.
D.As methane gas produced by digestion.
- 8.
What is the effect of increased atmospheric on the stoichiometry (C:N ratio) of plant tissues?
A.The C:N ratio decreases as plants take up more nitrogen to match the carbon
B.The C:N ratio increases as plants accumulate more carbohydrates relative to nitrogen-containing proteins
C.The C:N ratio remains constant due to strict homeostatic controls
D.Plants stop taking up nitrogen entirely in high environments
- 9.
How do mycorrhizal fungi indirectly influence the nitrogen and carbon cycles?
A.They fix nitrogen gas directly from the atmosphere for the plant
B.They increase the surface area for nutrient uptake, allowing plants to sequester more carbon in exchange for nitrogen and phosphorus
C.They perform denitrification in the rhizosphere to protect plant roots
D.They convert atmospheric into soil organic matter without the plant's help
- 10.
Which of the following is a biological source of that returns to the atmosphere?
A.Anaerobic fermentation in yeast
B.Aerobic respiration in plant roots
C.Both anaerobic fermentation and aerobic respiration
D.Neither, is only produced by animals
Download the worksheet for Organisms and their Environment - Nutrient cycles (Carbon and Nitrogen) to practice offline. It includes additional chapter-level practice questions.
Populations
SubtopicPopulations under Organisms and their Environment for Grade 12 IGCSE.
Preview questions (no answers)
- 1.
Which process describes how plants use light energy to make their own food?
A.Respiration
B.Photosynthesis
C.Transpiration
D.Combustion
- 2.
In a food web, if a top predator is removed, what is most likely to happen to the population of its prey?
A.It will decrease immediately
B.It will increase
C.It will stay exactly the same
D.It will become extinct
- 3.
Which of these is a renewable resource?
A.Coal
B.Natural gas
C.Wind energy
D.Oil
- 4.
What is the effect of untreated sewage being dumped into a river?
A.Oxygen levels in the water increase
B.Bacteria multiply and use up dissolved oxygen
C.The water becomes clearer
D.Fish populations increase rapidly
- 5.
The diagram represents the sequential phases of a sigmoid population growth curve in a closed environment with limited resources. Which labeled phase identifies the period where environmental resistance (such as nutrient depletion and waste accumulation) first begins to cause the growth rate to decrease, even though the total population size continues to rise?
A.Phase A (Lag phase)
B.Phase B (Log phase)
C.Phase C (Deceleration phase)
D.Phase D (Stationary phase)
- 6.
Which of the following is a direct consequence of overpopulation in a natural habitat?
A.Habitat degradation and loss of biodiversity
B.An increase in the carrying capacity of the environment
C.A decrease in the transmission of infectious diseases
D.An increase in the amount of resources available per individual
- 7.
A population of aphids on a rose bush increases rapidly in spring. Which limiting factor is most likely to stop this growth eventually?
A.An increase in the population of ladybirds (predators)
B.The arrival of winter and freezing temperatures
C.The exhaustion of sap in the rose bush
D.All of the above
- 8.
In an ecosystem with a 'Bottom-Up' control mechanism, what happens to the secondary consumer population if the primary productivity increases?
A.It remains unchanged because it is only controlled by predators
B.It will likely increase as more energy is available at the base of the food web
C.It will decrease because of increased competition for space
D.It will crash due to the accumulation of toxins in the producers
- 9.
Which phase of the human demographic transition is characterized by falling death rates but high birth rates, leading to rapid population expansion?
A.Stage 1 (Pre-industrial)
B.Stage 2 (Transitional/Early expanding)
C.Stage 3 (Industrial/Late expanding)
D.Stage 4 (Post-industrial/Low stationary)
- 10.
What is the effect of 'Allelopathy' on a plant population?
A.It is a form of mutualism where plants share nutrients via fungal networks
B.It is a form of competition where one plant releases chemicals to inhibit the growth of neighboring competitors
C.It is a reproductive strategy involving the production of very large seeds
D.It is a defense mechanism against herbivory by attracting predatory wasps
Download the worksheet for Organisms and their Environment - Populations to practice offline. It includes additional chapter-level practice questions.