Biology - B4 (Community Level Systems) *GCSE OCR HIGHER*

Abiotic Factors

The non-living factors of an ecosystem, e.g. temperature, light intensity, moisture, wind direction, wind intensity, soil pH, soil mineral content, carbon dioxide levels and oxygen levels

Aerobic Decomposition

Organisms break down dead or decaying matter (decompose) in the presence of sufficient oxygen

Anaerobic Decomposition

- Organisms carry out decomposition in the absence of oxygen producing carbon dioxide and methane gas
- This usually happens in waterlogged soils

Biomass

The mass of all the living material present in a particular area or particular organism

Biotic Factors

The living factors of an ecosystem, e.g. food availability, pathogens, predators and other species

Carbon Cycle

- The cycle through which carbon (in the form of carbon dioxide) moves between the environment and living organisms
- It involves respiration, photosynthesis, combustion and decomposition
- Carbon can also be trapped in oceans and rocks

Combustion

- The process by which organic matter is burnt to release energy as well as carbon dioxide and water
- It is part of the carbon cycle

Community

All of the populations of different species that are living in a habitat together

Competition

- When different organisms compete for the same resources (e.g. food, shelter and space)
- It limits population size in an ecosystem

Compost

Dead or decaying matter that is often used as fertiliser for crops

Decomposer

- A micro-organism that feeds on dead and decaying matter
- They break down dead organic matter at a microscopic level by releasing enzymes which break down the substrate
- They absorb the nutrients from the decaying matter

Decomposition

- The process of breaking down dead material into simple organic matter
- The decomposition rate is influenced by water availability (helps reactions), oxygen availability (needed for respiration) and temperature (energy for enzymes)

Ecosystem

- The COMMUNITY of organisms (biotic) and non-living (abiotic) components of an area and their interactions
- They live in HABITATS and the total number of organisms of EACH species is the POPULATION

Efficiency of biomass

(Biomass available after transfer / Biomass available before transfer ) x 100

Egestion

The removal of undigested food from the body as faeces

Excretion

The removal of metabolic waste from the body

Food Chain

- Shows the feeding relationships between organisms
- The arrows show the transfer of biomass transfer
- Each step is a trophic level
It follows the structure of: producer → primary consumer → secondary consumer → tertiary consumer

Habitat

- The place where plants, animals and all other living organisms live
- A habitat includes all biotic and abiotic factors

Host

The organism on/in which the parasite lives

Interdependence

- The dependence of organisms on each other in order to survive
- E.g. herbivores rely on plants, birds rely on trees for shelter.

Microorganisms

- Very small organisms that are involved in the recycling of materials in an ecosystem
- They are able to convert carbon into carbon dioxide which is then released into the atmosphere
- They also return mineral ions to the soil.

Mutualism

The interaction between two organisms where both benefit as a result of their relationship

Parasite

An organism which feeds on or in a host organism at the expense of the host

Parasitism

The interaction between two organisms where only one organism (the parasite) benefits whilst the host does not

Food Web

- A network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem
- It is a series of interlocking food chains

Pathogen

A bacteria, virus or any other microorganism that can cause disease

Photosynthesis

- An endothermic reaction that takes place in the chloroplasts, converting carbon dioxide and water into glucose and oxygen using light energy
6CO2 + 6H2O → C6H12O6 + 6O2 Sunlight energy

Precipitation

A part of the water cycle where water returns to land in the form of rain, snow or hail

Predation

A biological relationship in which a member of one species consumes a member of another species (relationship of predator and prey)

Predator

A consumer that preys on and eats other animals

Prey

A consumer that is eaten by a predator

Primary consumer

- An organism that cannot produce its own food, so must obtain energy by feeding on the producer
- They are herbivores which consume at trophic level two of the food chain

Producer

An organism that makes its own food, usually via photosynthesis

Pyramid of Biomass

- A table showing the amount of biomass transferred
- A table showing the number of organisms

Respiration

- The process by which energy is released from glucose molecules.
-This can be done aerobically (in sufficient oxygen) or anaerobically (in an oxygen debt)
- It is part of the carbon cycle and releases carbon dioxide into the air

Secondary consumer

- An organism that cannot produce its own food so must obtain energy by feeding on the primary consumer
- They are carnivores which consume at trophic level three of the food chain

Species

A group of organisms that can interbreed and produce fertile offspring

Tertiary consumer

A carnivore that eats other carnivores

Trophic level

The position of an organism in the food chain

Water cycle

- The cycle of water moving between the environment and living organisms
- It involves precipitation, condensation, transpiration, biomass transfer and evaporation.

Detritivores

They are small animals that speed up decomposition by shredding organic matter into smaller pieces (e.g. earthworm / maggots)

Nitrogen Cycle

- The transfer of nitrogen from the atmosphere to the soil, to living organisms, and back to the atmosphere
- Nitrogen makes up 80% of the atmosphere
- Organisms use nitrogen to make FNA and proteins

Intraspecific

Competition between members of the same species for the same resources (e.g. food or mates)

Interspecific

Competition between members of different species for the same resources (food or nesting spaces)