ECOLOGYAS BIOLOGY

TOPICS

A Cell StructureB Biological MoleculesC EnzymesD Cell Membranes and TransportE Cell and Nuclear DivisionF Genetic ControlG TransportH Gas ExchangeI Infectious DiseaseJ ImmunityK Ecology

CONTENT

• Energy flow through ecosystems

• Levels of ecological organization

• Recycling of nitrogen

Candidates should be able to:

Learning Outcomes

(a) define the terms habitat, niche, population, community and ecosystem and be able to recognize examples of each;

(b) explain the terms autotroph, heterotroph, producer, consumer and trophic level in the context of food chains and food webs;

(c) explain how energy losses occur along food chains and discuss the efficiency of energy transfer between trophic levels;

(d) describe how nitrogen is cycled within an ecosystem, including the roles of nitrogen-fixing bacteria (e.g. Rhizobium) and nitrifying bacteria (Nitrosomonas and Nitrobacter);

(e) use the knowledge gained in this section in new situations or to solve related problems.

Terminologies:

ēˈkäləjē/Ecology-the branch of biology that deals with the relations of organisms to one another and to their physical surroundings.

Ecosystem -includes all the organisms living in a particular area and all the non-living (abiotic) conditions.

An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system.

Habitat – The place where an organism lives

Population – A group of organisms belonging to the same speciesCommunity – All the populations of different organisms living and interacting in the same space at the same time

Abiotic – The physical and chemical features of the environment

Biotic – The biological features of the environment (living)Niche – A species role within it’s habitat

Adaptation – A feature that members of a species have to increase their chance of survival

The main route by which energy enters an ecosystem is photosynthesis.(Some energy enters sea ecosystems when bacteria use chemicals from deep sea vents as an energy source.)

During photosynthesis plants convert sunlight energy into a form that can be used by other organisms- plants are called producers (because they produce organic molecules using sunlight energy).

Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms, e.g. producers are eaten by organisms called primary consumers.Primary consumers are then eaten by secondary consumers and secondary consumers are eaten by tertiary consumers.

Each of the stages (e.g. producers, primary consumers) are called trophic levels.

Food chains and food webs show how energy is transferred through an ecosystem

Food chains show simple lines of energy transfer

Food webs show lots of food chains in an ecosystem and how they overlap.

Energy that get locked up in the things that cant be eaten e.g., bones and faeces get recycled back into the ecosystem by microorganism called decomposers -they break down dead or undigested material.

Not energy is transferred to the next energy level

Not all the energy (e.g. from sunlight or food) that's available to the organisms in a trophic level is transferred to the next trophic level - around 90% of the total available energy is lost in various ways.

Some of the available energy (60%) is never taken in by the organisms in the first place. For example:

•Plants can't use all the light energy that reaches their leaves, e.g. some is the wrong wavelength, some is reflected, and some passes straight through the leaves.

•Some sunlight can't be used because it hits parts of the plant that can't photosynthesize, e.g. the bark of a tree.

•Some parts of food, e.g. roots or bones, aren't eaten by organisms so the energy isn't taken in.

•Some parts of food are indigestible so pass through organisms and come out as waste, e.g. faeces.

The rest of the avail able energy (40%) is taken in (absorbed)

- this is called the gross productivity. But not all of this is available to the next trophic level either

•30% of the total energy available (75% of the gross productivity)

is lost to the environment when organisms use energy produced fromrespiration for movement or body heat. This is called respiratory loss.•10% of the total energy available (25% of the gross productivity)becomes biomass (e.g. it's stored or used for growth) - this is calledthe net productivity.

Net productivity is the amount of energy that's available to the next trophic level.