Ecosystems (Edexcel International A Level (IAL) Biology): Flashcards

In photosynthesis, plants convert light energy into chemical energy stored in biological molecules.

Chemical energy stored in plant biomass is passed to primary consumers when the plant is ingested.

Decomposers such as bacteria and fungi break down dead organisms, releasing the chemical energy stored in their tissues back to the environment.

Only about 10% of the energy at one trophic level is available to be stored in the tissues of the next level, because about 90% is lost to the environment.

False.

Not all energy in the food is transferred; much is lost to the environment as heat, in undigested material, or excreted waste.

Energy is lost because not all parts of the organism are eaten or digested, and some energy is lost as heat during respiration.

Energy efficiency = (net productivity ÷ energy received) × 100.

The process of measuring dry biomass involves drying a sample in an oven at low heat and weighing until the mass becomes constant.

Net productivity is the rate at which energy is converted into biomass in the body of a consumer, after losses to the environment.

Efficiency of biomass transfer = (biomass transferred ÷ biomass intake) × 100.

True.

Biomass is a measure of chemical energy stored in an organism, so both efficiencies essentially reflect energy passed along the food chain.

A habitat is the place where an organism lives.

A microhabitat is a small or specialised part of a larger habitat, such as an individual tree.

Some species are habitat specialists, meaning they can only survive in a very specific type of habitat, while others are generalists and can survive in a range of habitats.

An invasive species is a generalist species that can invade and take over a new habitat, often disrupting normal species interactions.

Humans sometimes release new species into a habitat, either accidentally or on purpose; these species can disrupt the normal species interactions and cause serious problems.

A population is all the individuals of one species living in a habitat.

The abundance of a population is the number of individuals of that species in a habitat, while its distribution is the exact location within the habitat.

A community is multiple populations living and interacting in the same area.

False.

A garden pond community includes all populations living and interacting in the pond, such as fish, frogs, newts, snails, insects, and plants.

An ecosystem is a community and its interactions with the non-living parts of its habitat.

Within an ecosystem, there is a flow of energy and nutrients are recycled.

Biotic components are living parts of an ecosystem, while abiotic components are the non-living parts.

A desert is a relatively simple ecosystem, whereas a tropical rainforest is a very complex ecosystem.

True.

Organisms such as birds and aquatic animals can migrate between ecosystems to feed or breed.

Biotic factors are living factors that influence populations within a community as a result of the activity of other organisms.

Abiotic factors are non-living factors that influence populations within their community, such as temperature, light intensity, and soil pH.

Intraspecific competition occurs between individuals of the same species, while interspecific competition occurs between individuals of different species.

The abundance of a species within a habitat is determined by a combination of abiotic and biotic factors.

Predation is a biotic interaction in which one organism (the predator) kills and eats another organism (the prey).

An abiotic factor affecting a population could be temperature, whereas a biotic factor could be predation.

True.

Disease is caused by other living organisms such as bacteria or viruses, so it is considered a biotic factor.

Parasitism is a relationship in which one organism (the parasite) lives on or in another organism (the host), causing it harm.

Light intensity influences the rate of photosynthesis in plants, affecting their growth and abundance.

An example of a biotic factor affecting animal populations is food availability.

Soil pH, turbidity, and humidity are all examples of abiotic factors.

Competition between individuals of the same species is called intraspecific competition, while competition between different species is interspecific competition.

A habitat is the place where a species lives.

An ecological niche is the role of a species within its habitat, including what it eats, where it lives, and when it is active.

No two species can fill the same niche within a habitat; if this happens, one will out-compete the other.

The ecological niche of a species includes what it eats, which other species depend on it for food, what time of day it is active, and exactly where in the habitat it lives and feeds.

False.

If two species occupy similar niches, they compete with each other, so their populations and abundance will be lower.

Distribution is where a species lives within a habitat, determined by how well adapted it is to the habitat's biotic and abiotic factors.

Abundance is the number of individuals of a particular species living in a habitat.

A species can only survive in a habitat to which it is well adapted; if not, it will move elsewhere and its distribution will change.

Sampling is a method used to investigate the abundance and distribution of species and populations.

Sampling is used because in large or complex habitats it is not possible to find, identify, and count every organism, so an estimate is made instead.

The two main types of sampling are random sampling and systematic sampling.

In random sampling, sampling points are chosen at random, which helps to avoid bias.

True.

In systematic sampling, sampling points are located at fixed intervals throughout the sampling site.

A frame quadrat is a square frame placed within a study area to provide a sample for studying the distribution and abundance of sessile organisms.

A quadrat can be used to record the abundance or distribution of a species within a sample area.

Percentage cover is measured by estimating the percentage of the quadrat covered by a species, often by dividing the quadrat into smaller squares.

A point quadrat is a vertical frame with holes through which pins are lowered to record which species are present where each pin touches.

Percentage cover is measured by dividing the number of pins touched by a species by the total number of pins used.

A transect is a line laid across a site to measure abundance and distribution of species across a habitat.

A kite diagram can be used to show both the distribution and abundance of a species along a transect.

Succession is the process of ecosystem change over time, involving changes in biotic and abiotic conditions.

An ecosystem is dynamic if it is constantly changing due to interactions between biotic and abiotic factors.

True.

Both biotic and abiotic factors change as succession progresses in an ecosystem.

Primary succession begins on newly formed or newly exposed land, such as after a volcano forms new rock or a glacier retreats.

Colonisation in succession is when organisms first arrive and begin to inhabit bare land.

Pioneer species are the first organisms to colonise new or bare land, often capable of surviving harsh conditions.

As pioneer species die and decompose, their organic matter forms soil.

The roots of small plants and grasses stabilise the soil and prevent it from being washed away.

The final stable community formed during succession is called the climax community.

Secondary succession is succession that occurs on land where soil is already present, such as after a fire or deforestation.

True.

Human activities such as mowing or grazing can interrupt succession and stop a climax community from developing.

A climax community that develops as a result of human intervention is called a plagioclimax.