Definitions
What is energy flow?
A) The recycling of nutrients through soil
B) The movement of energy through organisms in an ecosystem
C) The process of photosynthesis in plants
D) The transfer of water between organisms
B
Energy flow specifically refers to how energy moves through an ecosystem from the Sun → producers → consumers. It is not recycled like nutrients are, which is what makes it different from nutrient cycling.
Which of the following is an example of an autotroph?
A) Lion
B) Mushroom
C) Oak tree
D) Human
C
Autotrophs are organisms that produce their own food using sunlight through photosynthesis. Oak trees, like all plants, are autotrophs. Lions and humans are consumers, and mushrooms are decomposers.
Where does energy in most ecosystems originally come from?
A) The soil
B) Water
C) The Sun
D) Decomposers
C
The Sun is the primary source of energy for almost all ecosystems. Producers like plants capture sunlight through photosynthesis and convert it into chemical energy, which then fuels every other trophic level above them.
What unit is productivity most commonly measured in?
A) Litres per second
B) Grams of biomass per square meter per year (g/m²/year)
C) Calories per organism
D) Joules per trophic level
B
Productivity in ecology is measured as the amount of biomass (organic matter) produced per unit area per year. This allows scientists to compare how productive different ecosystems are on a standardized scale.
Which of the following best defines a decomposer?
A) An organism that makes its own food using sunlight
B) An animal that eats only plants
C) A fungus or bacteria that breaks down dead organisms and recycles nutrients
D) An organism that eats both plants and animals
C
Decomposers like fungi and bacteria break down dead organic matter and return nutrients back into the soil, which producers then reuse. They are essential to keeping the nutrient cycle going. Option A describes autotrophs, and B describes herbivores.
What process do autotrophs use to convert sunlight into energy?
A) Cellular respiration
B) Decomposition
C) Fermentation
D) Photosynthesis
D
Photosynthesis is the process by which autotrophs like plants and algae convert sunlight, water, and carbon dioxide into glucose and oxygen. This is the foundation of almost all energy in an ecosystem.
According to the 10% rule, if primary producers have 10,000 kJ of energy, how much energy is available to secondary consumers?
A) 1,000 kJ
B) 100 kJ
C) 10 kJ
D) 5,000 kJ
B
At each trophic level only 10% of energy is passed on. So primary consumers receive 1,000 kJ (10% of 10,000), and secondary consumers receive 100 kJ (10% of 1,000). The remaining 90% is lost as heat at each step.
Which ecosystem would you expect to have the highest Net Primary Production?
A) Arctic tundra
B) Sahara Desert
C) Tropical rainforest
D) Open ocean
C
Tropical rainforests receive abundant sunlight, warmth, and rainfall year-round, making conditions ideal for photosynthesis. This results in extremely high NPP compared to deserts or tundras where temperature, water, or light are limiting factors.
Which statement best defines the Second Law of Thermodynamics as it applies to ecosystems?
A) Energy is equally distributed across all trophic levels
B) Energy can be recycled and reused between organisms
C) Energy is lost as heat at each trophic level making flow unidirectional
D) Producers gain more energy than they receive from the Sun
C
Every time energy is transferred between trophic levels, roughly 90% is lost as heat. This is why energy flow is one-directional and why energy pyramids get smaller toward the top. Unlike nutrients, energy cannot be recycled back down the food chain.
Which of the following best describes a stable ecosystem?
A) An ecosystem with only one species
B) An ecosystem that never changes
C) An ecosystem that can resist or recover from disturbances
D) An ecosystem with no predators
C
A stable ecosystem is not one that never changes, but one that can absorb disruptions and return to balance. Stability comes from biodiversity, balanced energy flow, and healthy populations at every trophic level.
Which of the following correctly describes the role of apex predators in an energy pyramid?
A) They contain the most energy of any trophic level
B) They receive the least amount of energy as they are at the top of the pyramid
C) They produce energy through photosynthesis
D) They receive more energy than primary
B
Apex predators sit at the very top of the energy pyramid and receive only a tiny fraction of the original energy (around 0.01%). Each transfer loses 90% of energy, so by the time it reaches apex predators almost nothing remains, which is why their populations are always the smallest.
A scientist measures a forest's GPP as 8,000 g/m²/year and its respiration as 3,000 g/m²/year. What is the NPP?
A) 11,000 g/m²/year
B) 8,000 g/m²/year
C) 3,000 g/m²/year
D) 5,000 g/m²/year
D
NPP = GPP − Respiration. So 8,000 − 3,000 = 5,000 g/m²/year. NPP represents the energy actually available to consumers after the producers have used some for their own metabolic needs.