Ecosystem Flashcards
What is the ultimate source of energy for ecosystems on Earth?
The sun.
Describe the flow of energy in a food chain.
Unidirectional; energy is lost as heat at each trophic level.
Explain why energy is lost at each trophic level.
Energy is used for metabolic activities and is lost as heat.
What is an ecological pyramid?
A graphical representation of feeding relationships showing the number
What does a pyramid of numbers represent?
The number of individuals at each trophic level in a food chain.
What are the disadvantages of using a pyramid of numbers?
Producers and consumers vary greatly in size
What does a pyramid of biomass represent?
The total wet or dry mass of organisms at each trophic level.
How is biomass measured in a pyramid of biomass?
In grams per square meter (g/m^2).
What does a pyramid of energy represent?
The rate of flow of food energy through each trophic level.
In what units is the rate of energy flow measured?
kJ/m^2/yr (kilojoules per square meter per year).
What percentage of solar energy that reaches the Earth’s surface is available to primary producers?
About 1 to 10%.
What is gross primary productivity?
The rate at which primary producers manufacture food per unit area per unit time.
What is net primary productivity (NPP)?
The amount of food stored by producers after their own energy use.
Give examples of how much of the Net Primary Productivity is consumed by primary consumers
In open seas nearly 90% of photosynthetic plankton is consumed
What happens to the energy that is not consumed by primary consumers?
The rest is broken down when the producers die.
What is the first law of thermodynamics?
Energy cannot be created or destroyed
What is the second law of thermodynamics?
Energy transformations are never completely efficient
What is entropy?
A measure of the degree of disorganization in a system.
What is an important characteristic of living organisms in terms of entropy?
A living organism is highly organized
Are nutrients recycled in an ecosystem?
Yes
Name the main nutrients that are necessary for the maintenance of life
Carbon
Name 3 important processes which bring about the recycling of carbon dioxide between the biotic and abiotic components of an ecosystem
Photosynthesis
What is an ecosystem?
A basic functioning unit of nature
How are the living and non-living components of an ecosystem linked?
By a variety of biological
What are the two main groups of organisms in an ecosystem based on their feeding?
Autotrophs and heterotrophs.
Define autotrophs.
Organisms that use sunlight or chemical energy to manufacture their own food from simple inorganic substances.
Where do autotrophs get their nutrients and energy?
From the non-living (abiotic) component of the ecosystem.
What is the main energy source for autotrophs?
Sunlight
What is the role of autotrophs in an ecosystem?
They form a direct link between the abiotic and biotic components and are primary food producers.
What do autotrophs do with the food they produce?
Use some for their activities and growth
Give examples of autotrophs.
Green plants
Name the main food producers in a terrestrial ecosystem.
Green plants
Name the main food producers in an aquatic ecosystem.
Protists like diatoms and algae like Spirogyra (phytoplankton).
Define heterotrophs.
Organisms that cannot manufacture food and feed on ready-made food from other organisms.
Where does the food of heterotrophs come from?
The tissues of organisms in their environment (biotic component).
Do heterotrophs depend on autotrophs for food?
Yes
What do heterotrophs use the nutrients and energy from their food for?
Their activities and growth.
What happens to excess nutrients and energy in heterotrophs?
They are stored in various parts of their bodies.
Give examples of heterotrophs.
Animals
What two categories can heterotrophs in an ecosystem be divided into?
Consumers and decomposers.
Define consumers.
Heterotrophs that feed on other organisms.
List types of consumers.
Holozoic organisms (herbivores
Give examples of consumers in a terrestrial ecosystem.
Caterpillars
Give examples of consumers in an aquatic habitat.
Copepods
Why do living organisms need to obtain energy and nutrients from their environment?
To remain alive.
What are food relationships or feeding pathways?
The ways organisms obtain energy and nutrients from their environment.
What are trophic levels?
The steps in an ecosystem where energy and nutrients are transferred among organisms.
Describe a simple feeding pathway example.
Grass (primary producer) → Zebra (primary consumer) → Lion (secondary consumer).
What is the role of decomposers in a feeding pathway?
To convert the remains of dead producers and consumers into simple inorganic substances.
How do feeding pathways vary in length?
They can end at the primary consumer level or extend to secondary
What does the arrangement of trophic levels show?
The path of energy (food) flow among functional groups of organisms.
How are trophic levels numbered?
In ascending order
What organisms are in trophic level 1?
Primary producers or autotrophs.
What organisms are in trophic level 2?
Primary consumers.
Give examples of herbivores (primary consumers).
Cows
Give examples of other primary consumers.
Birds and insects that feed on pollen
Name the main types of consumers above trophic level 2.
Carnivores (predators)
Give examples of carnivores (predators).
Dogs
Give examples of scavengers.
Vultures and hyenas.
What happens to the final consumers when they die?
They are fed on by decomposers.
What is a food chain?
A linear sequence that shows the transfer of energy and nutrients from organism to organism in a feeding pathway.
How are organisms identified in a food chain?
By their specific type
Give an example of a simple food chain in a grassland ecosystem.
Grass → Zebra → Lion.
What does a food chain show, similar to a trophic level diagram?
The direction of energy (food) flow through an ecosystem.
What is a food web?
A network of interconnected food chains in an ecosystem.
Give examples of how food chains are linked in a food web.
The same plant may be eaten by different animals
Why is a food web important for the survival of consumers?
It provides alternative food sources if one source is destroyed.
How does a food web differ from a food chain?
A food chain shows one possible energy flow pathway
Describe the energy flow in the food chain: grass → zebra → lion.
Grass traps solar energy
What is the initial source of energy in a food chain?
Solar energy.
What happens to energy as it moves along a food chain?
Some energy is lost as heat at each trophic level.
Is energy flow in a food chain unidirectional or bidirectional?
Unidirectional.
Why must an ecosystem receive a constant supply of energy from outside?
To keep its biotic components alive.
What is the outside energy source for Earth’s ecosystems?
The sun.
What determines the size of populations at each trophic level?
The amount of solar energy trapped by primary producers.
Why are most food chains short?
Because energy is lost at each trophic level.
What are ecological pyramids?
Graphical representations of feeding relationships in an ecosystem.
What three things can ecological pyramids show?
The number
How are trophic levels represented in an ecological pyramid?
As horizontal bars stacked in ascending order.
What does a pyramid of numbers represent?
The number of individuals at each trophic level in a food chain at a particular time.
What does the length of each bar in a pyramid of numbers indicate?
The approximate number of individuals at that trophic level.
What general trend is observed in most ecosystems regarding the number and size of organisms across trophic levels?
The number of individuals decreases
What is the shape of a typical pyramid of numbers?
Upright.
Give an example of an ecosystem with an odd-shaped pyramid of numbers.
A tropical forest ecosystem.
What are the two main disadvantages of using a pyramid of numbers?
It gives the same status to organisms of very different sizes
What does a pyramid of biomass represent?
The total wet or dry mass of organisms at each trophic level.
How is a pyramid of biomass constructed?
By counting and weighing the organisms in a given area.
What are the units for biomass in a pyramid of biomass?
Grams per square meter (g/m^2).
Why is a pyramid of biomass considered more accurate than a pyramid of numbers?
Because it takes into account both the size and number of organisms.
What is the shape of most pyramids of biomass?
Upright
Why do pyramids of biomass in a lake show seasonal changes in shape?
Because of the difference in size and lifespan between producers (diatoms) and consumers (fish).
What does a pyramid of energy represent?
The rate of flow of food energy through each trophic level of a food chain.
What are the units for energy flow in a pyramid of energy?
kJ/m^2/yr (kilojoules per square meter per year).
Why is a pyramid of energy always upright?
Because there is a loss of useful energy as food is transferred between trophic levels.
What are the different forms in which energy exists?
Various forms which are interconvertible.
What are the laws that govern energy transformations?
The laws of thermodynamics.
What is the role of living organisms in energy transformations?
They cause energy to flow through ecosystems unidirectionally.
What is the external source of energy for ecosystems on Earth?
The sun.
What percentage of solar energy that reaches the Earth’s atmosphere is reflected or absorbed?
More than half.
How much of the solar energy that reaches a grassland is reflected by vegetation?
About 20%.
How much of the solar energy that reaches a grassland warms the vegetation, soil and air?
About 40%.
How much of the solar energy that reaches a grassland evaporates water?
About 39%.
What percentage of solar energy that reaches the Earth’s surface is available for use by producers?
About 1%.
What do photosynthetic organisms (primary producers) use to manufacture food?
Light energy from the sun
What energy transformation occurs during photosynthesis?
Light energy is transformed into chemical energy.
Where does photosynthesis occur in green plants?
In the chloroplasts in leaves.
How much of the solar energy absorbed by a leaf is converted into chemical energy?
About a quarter (25%).
What percentage of food energy do plants use for their metabolic activities?
About 30%.
What is net food production?
The amount of stored chemical energy available to the next link in the food chain.
What is the fate of solar energy absorbed by a leaf?
100 units of solar energy is absorbed
What is gross primary productivity?
The rate at which primary producers manufacture food per unit area per unit time.
How much of the food produced by primary producers is used by them?
About 30%.
What is net primary productivity (NPP)?
The remainder of the food produced by primary producers that is stored.
Where is NPP higher: tropical or temperate ecosystems?
Tropical ecosystems.
What does NPP determine?
The food available to consumers in an ecosystem.
Do primary consumers eat all the food produced by producers?
No.
Give examples of the percentage of photosynthetic plankton that are eaten by primary consumers in open waters of the seas
Nearly 90%
Give examples of the percentage of grass that may be eaten by herbivores on a grassland
About 40%
Give examples of the percentage of plant food that may be eaten by the primary consumers in a forest
Only about 3%
What happens to the rest of the NPP that is not consumed by primary consumers?
It is broken down when the producers die.
What percentage of energy consumed by a cow is stored in new tissue and available to the next link in the food chain?
About 7% (which is 1% of the NPP of the grassland).
How efficient are secondary consumers (carnivores) in incorporating available energy into their tissues compared to herbivores?
Almost double the efficiency.
What are the factors that determine the population size of consumers in a food chain?
Net primary productivity of the primary producer
What happens to the amount of energy available as you move up the trophic levels?
It decreases
What happens to the population size as you move up the trophic levels?
It decreases
What do the energy losses at each trophic level explain?
The general upright shapes of ecological pyramids of energy.
What limits the number of links in a food chain?
Energy losses at each trophic level.
By which trophic level is the useful energy incorporated into the body tissues of the primary producers completely dissipated into the surroundings
By the fourth trophic level
Why is it more efficient for humans to eat plant food directly than to eat animals that eat plants?
Because there is less energy loss in a shorter food chain.
What percentage of the maize eaten by hens is converted to stored food (meat) in their bodies?
About 10%.
How can we try to make hens convert more of the maize they eat into stored food?
By keeping them indoors in small cages to minimize heat loss due to movement (intensive rearing).
What does the first law of thermodynamics state?
Energy cannot be created or destroyed but may be transformed from one form into another.
What does the second law of thermodynamics state?
Energy transformations are never completely efficient
What is the role of living organisms in energy transformations?
They are energy converters.
