2.2 Energy & Biomass in Ecosystems (DP IB Environmental Systems & Societies (ESS): HL): Flashcards

A producer is an organism, such as a plant, algae, or photosynthetic bacterium, that makes its own food using photosynthesis.

An autotroph is an organism that can produce its own food from inorganic substances, typically through photosynthesis.

False.

Producers form the first trophic level in a food chain.

In photosynthesis, the main inputs are sunlight, carbon dioxide, and water.

During photosynthesis, light energy is transformed into chemical energy stored in glucose.

A respiratory substrate is a molecule, such as glucose, that can be used in respiration to release energy for growth.

Respiration is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy.

The main purpose of respiration in living organisms is to release energy from organic matter to be used in active cellular processes.

Cellular respiration releases energy from glucose by converting it into a chemical form for use in active processes.

Aerobic respiration is the release of energy from glucose using oxygen, producing carbon dioxide and water.

The inputs are glucose and oxygen; the outputs are carbon dioxide, water, and energy.

False.

Some of the chemical energy released during cellular respiration is transformed into heat, which is not used for work.

Heat is generated by cellular respiration because it is not 100% efficient at transferring energy from substrates into the chemical form used in cells.

Heat released from cellular respiration increases the entropy of the ecosystem, as required by the second law of thermodynamics, while allowing organisms to maintain internal order.

A trophic level is the position that an organism occupies in a food chain or food web.

The first trophic level in a food chain is always occupied by producers, such as plants or algae.

Primary consumers feed on producers and are found at trophic level 2.

An apex predator is a carnivore or omnivore at the top of the food chain with no natural predators.

Decomposers break down dead organic matter into simpler substances, recycling nutrients back into the ecosystem.

Herbivores are primary consumers and feed primarily on plants.

True.

Both detritivores and decomposers play roles in breaking down organic matter and recycling nutrients in ecosystems.

A scavenger is an organism that consumes dead animal carcasses, helping to clean up ecosystems.

Detritivores obtain energy by feeding on decomposing organic matter.

Energy in a food chain flows from producers to primary consumers and then to higher-level consumers.

Parasites depend on a host organism for survival, often harming but not immediately killing it, while predators kill and consume their prey.

A trophic level is the position that an organism occupies in a food chain or food web.

A food web is a network of interconnected food chains showing the feeding relationships between organisms within an ecosystem.

Food webs are more realistic because consumers rarely feed on just one type of food source, so food webs show the multiple feeding relationships within an ecosystem.

Food webs give us more information about the transfer of energy in an ecosystem than food chains.

Interdependence is how a change in one population can affect others within the food web, as organisms rely on each other for resources.

The population of grass plants would increase because fewer species would be feeding off them.

If earthworms are the only food source for frogs and mice, a decrease in earthworm population will cause the populations of frogs and mice to decrease significantly.

The arrows in food webs and food chains indicate the direction of energy flow and transfer of biomass.

True.

This is because of interdependence; organisms rely on each other within a food web, so changes can have widespread effects.

A trophic level is a step in a food chain representing organisms that share the same function in the transfer of energy and nutrients.

The transfer of organic matter is never 100% efficient because not all food is harvested, not all of what is harvested is consumed, not all of what is consumed is absorbed, and not all of what is absorbed is stored.

When a caterpillar eats a leaf, some nutrients are not absorbed and are instead egested by the caterpillar.

False.

Some of the energy absorbed by a consumer is lost as heat during cellular respiration, so not all is stored.

Caterpillars may leave behind tougher parts of the leaf or those with toxins, instead eating only the more nutritious sections.

Not all food is harvested because there may be too much food relative to the number of consumers, or some food may be in locations that are difficult for consumers to access.

Gross productivity is the total gain in biomass by an organism or community in a given area or time period, representing all the energy captured by organisms.

Net productivity is the amount of energy or biomass remaining after losses due to cellular respiration, representing energy available for growth and reproduction.

Net productivity is calculated by subtracting energy lost to cellular respiration from gross productivity.

In a pond ecosystem, the total amount of energy captured by aquatic plants and other species represents the gross productivity of that ecosystem.

True.

Consumers have higher energy requirements due to activities like movement and digestion, resulting in greater losses to cellular respiration.

Harvesting beyond net productivity can lead to overexploitation and depletion of resources, threatening ecosystem stability and biodiversity.

The net productivity of any organism or trophic level represents the maximum sustainable yield that can be harvested without decreasing future resources.

Measuring biomass helps to understand the structure and function of an ecosystem by estimating the energy and biomass at each trophic level.

A calorimeter is a piece of equipment used to estimate the chemical energy content of biomass by measuring the heat produced during combustion.

One common method for estimating biomass is to measure the dry mass of organisms after removing all water from tissues.

True.

A bomb calorimeter transfers almost all the heat energy from the burning sample to the water, providing a highly accurate estimate.

Extrapolation involves taking small samples and using their data to estimate the total biomass of a population or trophic level, especially when the population is large or difficult to sample.

An ecological pyramid is a quantitative model that shows the relative amounts of numbers, biomass, or energy at each trophic level for a given time and area.

A pyramid of numbers shows the count of organisms at each trophic level in a food chain, with the width of each level representing the number of organisms.

The width of each box in a pyramid of numbers represents the number of organisms at that trophic level.

In a typical food chain, the number of organisms decreases at each successive trophic level because energy is lost at each stage.

False.

A pyramid of numbers can be inverted when large organisms at lower trophic levels support many organisms at higher levels, such as a single oak tree supporting many insects.

An inverted pyramid of numbers occurs when fewer, larger organisms at a lower trophic level support many smaller organisms at higher levels, like one oak tree supporting many insects.

A pyramid of biomass shows the total dry mass of organisms at each trophic level in a food chain.

Pyramids of biomass are usually pyramid-shaped because the biomass decreases at each higher trophic level, regardless of the number of organisms.

The mass used in a pyramid of biomass is the dry mass of the organisms, known as their ‘dry mass’.

True.

In some ecosystems, such as marine environments with fast-reproducing phytoplankton, the biomass of primary consumers may exceed that of producers, resulting in an inverted pyramid of biomass.

A pyramid of energy (or pyramid of productivity) shows the flow of energy through trophic levels per unit area per unit time.

The units for a pyramid of energy are usually mass or energy per square metre per year (e.g. g m⁻² yr⁻¹ or J m⁻² yr⁻¹).

Pyramids of energy always become narrower at higher trophic levels because energy is lost at each level due to incomplete consumption, incomplete digestion, heat loss during respiration, and excretion.

Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down.

Biomagnification is the increase in the concentration of persistent or non-biodegradable pollutants along a food chain.

Organisms at higher trophic levels accumulate higher concentrations of persistent or non-biodegradable pollutants because these pollutants are passed up the food chain, becoming more concentrated as total biomass decreases at each level.

An example of a non-biodegradable pollutant that bioaccumulates and biomagnifies in birds of prey is DDT.

DDT accumulated in birds of prey, leading to thinning of eggshells and reduced reproductive success due to its persistence and biomagnification in food chains.

True.

Mercury biomagnifies in aquatic food chains, so humans who eat large fish like tuna may be exposed to toxic levels of methylmercury.

Microplastics can absorb non-biodegradable pollutants, increasing their transmission along food chains.

Microplastics can absorb pollutants and be ingested by marine animals, leading to bioaccumulation and biomagnification of toxins, which can negatively affect organisms in the food chain.

Oysters exposed to microplastics containing pollutants showed lower feeding rates, altered growth, and reduced reproductive success.

Burning fossil fuels releases carbon dioxide and other pollutants, which can increase photosynthesis rates but also contribute to global warming, acid rain, and reduced plant productivity due to changes in climate and soil chemistry.

Deforestation reduces the carbon sink capacity of forests, contributing to climate change.

Intensive agriculture can lead to soil degradation, water pollution, and loss of biodiversity due to use of fertilisers, pesticides, and monoculture practices.

An autotroph is an organism that synthesises its own carbon compounds from inorganic sources like carbon dioxide and water.

A heterotroph is an organism that obtains its carbon compounds by consuming other organisms or organic matter.

Autotrophs synthesise their own carbon compounds from inorganic sources, while heterotrophs obtain their carbon compounds by consuming other organisms or decomposing organic matter.

Photoautotrophs use light as their energy source to produce organic compounds through photosynthesis.

Examples of photoautotrophs include green plants, algae, and some bacteria such as cyanobacteria.

A chemoautotroph is an organism that uses energy from exothermic inorganic chemical reactions to produce organic compounds through chemosynthesis.

Chemoautotrophs obtain energy by oxidising inorganic substances such as hydrogen sulphide or ammonia in exothermic chemical reactions.

The giant tube worm relies on a symbiotic relationship with chemosynthetic bacteria to survive in extreme environments.

Chemoautotrophs are the primary producers in hydrothermal vent ecosystems, creating energy-rich compounds like sugars that support other organisms in these food webs.

Herbivores obtain carbon compounds by consuming plants, carnivores by consuming animals, and omnivores by consuming both.

A decomposer is an organism such as fungi, bacteria, or earthworms that breaks down dead organic matter, returning nutrients to the ecosystem.

False.

Autotrophs synthesise their own carbon compounds from inorganic sources, not by consuming other organisms.

Primary productivity is the rate at which biomass is produced by primary producers using an external energy source and inorganic materials.

During photosynthesis, primary producers convert light energy into chemical energy that is stored in biomass.

Primary productivity is measured in kilograms of carbon per square metre per year.

In the laboratory, scientists can estimate primary productivity by measuring the rate of photosynthesis in samples such as plants or phytoplankton.

In field studies, changes in biomass are measured over time to estimate primary productivity.

In grassland ecosystems, researchers sample vegetation at different times to see how much biomass has increased.

Gross primary productivity (GPP) is the rate at which plants store chemical energy or biomass via photosynthesis.

True.

Gross primary productivity may be measured in units of energy (e.g. J m⁻² yr⁻¹) or mass (e.g. g m⁻² yr⁻¹) per area per time.

In aquatic environments, productivity is often measured per unit volume instead of per unit area.

Net primary productivity (NPP) is the rate at which energy is stored in plant biomass after respiratory losses.

The equation for net primary productivity is NPP = GPP - R, where GPP is gross primary productivity and R is respiratory loss.

NPP represents the energy available to primary consumers and decomposers in an ecosystem.

Gross secondary productivity is the total energy or biomass assimilated by consumers, calculated as GSP = food eaten - faecal loss.

Net secondary productivity (NSP) is calculated by subtracting respiratory losses from GSP.

False.

The correct equation is NSP = GSP - R, not addition.

A sustainable yield is the rate at which a resource can be harvested or used without compromising the ability of the system to regenerate or replenish that resource for future use.

The main purpose is to ensure that resources are not over-exploited and remain available for future generations by allowing natural regeneration.

The maximum sustainable yield (MSY) is the highest rate of net primary productivity (NPP) or net secondary productivity (NSP) that can be harvested from a system without depleting it.

In these systems, MSY is the highest amount of biomass (such as crops, livestock, seafood, or trees) that can be sustainably harvested over time without degrading the soil, water or ecosystem.

False.

Sustainable yields are generally higher for organisms at lower trophic levels because less energy is lost from the system at these levels.

Energy is lost as heat during the transfer between trophic levels.

Plant-based foods are at lower trophic levels and require fewer resources to produce, making them more energy-efficient and sustainable for human consumption than animal-based foods.

Growing crops for direct human consumption is more sustainable than raising livestock, which requires plants to be grown as feed.

Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the next level.

Usually around 10% of the energy is transferred to the next trophic level, but this value varies between ecosystems and is not a fixed amount.

Energy is lost to the environment at every trophic level.

Only a small proportion of energy is transferred to the consumer's biomass because much energy is lost as heat, through respiration, excretion, and undigested material.

Not every part of a food organism is eaten, so some stored energy in the uneaten tissues is lost to the environment.

Some energy is not transferred because: (1) not all parts of the organism are eaten (e.g. bones, roots), and (2) some material cannot be digested and is egested as faeces.

False.

Energy is also lost as undigested material in faeces, excreted waste products, and uneaten parts of organisms.

Energy is lost to the environment as heat when consumers respire.

The number of trophic levels is limited because so much energy is lost at each level, eventually leaving insufficient energy to support further levels.

Ecological efficiency = ( energy used for new biomass ÷ energy supplied ) × 100

Divide the energy used for new biomass by the energy supplied to that level, then multiply by 100 to get the ecological efficiency as a percentage.

Biomass is the total mass of living material in an organism or trophic level, usually measured as dry mass.

False.

The 10% value is not fixed or a true average; the percentage of energy transferred varies between ecosystems, trophic levels, and species.