Trophic Levels in an Ecosystem

The first trophic level contains producers. These are mainly plants that produce their own carbon compounds through photosynthesis.

False. The second trophic level contains primary consumers, which are herbivores that feed on producers. Secondary consumers are found at the third trophic level.

The third trophic level contains secondary consumers, which are carnivores or omnivores that feed on primary consumers.

False. Decomposers occupy all trophic levels apart from the first trophic level which is always occupied by plants and algae.

Food chains show the transfer of energy from one organism to the next.

Food webs show networks of interconnected food chains that show the interdependence between organisms in an ecosystem.

True. Producers absorb light energy from the sun, converting it into stored chemical energy which passes up the food chain. There are one or two very unusual exceptions to this rule, e.g. food chains that gain energy from chemicals

Pyramid of biomass show the mass of living material present at each stage of a food chain.

A decrease in the population of any producers eaten by the population An increase in the population of any secondary consumers that feed on the population A decrease in the population of any other primary consumer populations within the food web

True. Pyramids of biomass are always pyramid-shaped, regardless of what the pyramid of numbers for that food chain looks like.

Energy is transferred up food chains when organisms consume the tissues of other organisms and convert it to biomass.

The first trophic level (the producers) is always found at the base of the pyramid of biomass.

Biomass is the dry mass of an organism (excluding water content).

Energy enters food chains by the process of photosynthesis; light energy from the sun is converted into stored chemical energy in the tissues of producers.

Approximately 10 % of the biomass at each trophic level is passed on to the next.

The biological molecules in the tissues of a primary consumer are broken down during digestion, after which some of them may be used to build the biomass of the secondary consumer and some will be lost in waste products.

False. While some of the chemical energy stored in the producer is transferred to the biomass of the primary consumer when it is eaten, much of it is transferred elsewhere, e.g. to the environment as heat or in waste products.

Organisms rarely eat every part of the consumed organism Some tissues cannot be fully digested by the consumer so any undigested material is egested in faeces Large amounts of glucose are used in respiration Material is lost in metabolic waste, e.g. urea in urine, water and carbon dioxide in respiration

False. When energy is transferred to new biomass it is stored in the tissues; this stored chemical energy is available to the next trophic level.

Food chains are rarely made up of more than five trophic levels because of the energy losses at each trophic level; the total energy available eventually becomes too small to support another trophic level.

True. Energy losses at each trophic level mean that each subsequent trophic level will contain less stored energy in the form of biomass.