What is the lowest level of organization of the biosphere or the one that has the fewest members?

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Segment: 9. Natural Resource Systems, Standard: Apply scientific principles of an ecosystem. (Technical III.A.2)

Ecosystems are organized to better understand the frame of reference in which they are being studied. They are organized from smallest to largest; organism, population, community, ecosystem. An organism is a single living thing, a population is all of the organisms of the same species in the same place at the same time, a community is all populations in the same place at the same time (all living things), and an ecosystem is the reactions between living and nonliving components in a given area. Ecosystems can vary in size depending on the scope of study.

Resources

  • Ecological Organization Overview
  • Biological levels Video

Brainstorming, Lecture Discussion, Paired or Small Group Discussion, Demonstration, Field Trip, Resource People, Supervised Study

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What is the lowest level of organization of the biosphere or the one that has the fewest members?

Figure 1. All molecules, including this DNA molecule, are composed of atoms. (credit: “brian0918″/Wikimedia Commons)

Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells. Examples of organelles include mitochondria and chloroplasts, which carry out indispensable functions: mitochondria produce energy to power the cell, while chloroplasts enable green plants to utilize the energy in sunlight to make sugars. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack the reproductive mechanism of a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled or colonial organisms that do not have membrane-bound nuclei or organelles; in contrast, the cells of eukaryotes do have membrane-bound organelles and a membrane-bound nucleus.

In larger organisms, cells combine to make tissues, which are groups of similar cells carrying out similar or related functions. Organs are collections of tissues grouped together performing a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. Mammals have many organ systems. For instance, the circulatory system transports blood through the body and to and from the lungs; it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms.

All the individuals of a species living within a specific area are collectively called a population. For example, a forest may include many pine trees. All of these pine trees represent the population of pine trees in this forest. Different populations may live in the same specific area. For example, the forest with the pine trees includes populations of flowering plants and also insects and microbial populations. A community is the sum of populations inhabiting a particular area. For instance, all of the trees, flowers, insects, and other populations in a forest form the forest’s community. Keep in mind that the community level only consists of living organisms. The forest itself is an ecosystem; this is the first level that contains non-living aspects of a given area that impact the living things in that environment. An ecosystem consists of all the living things in a particular area together with the abiotic, non-living parts of that environment such as nitrogen in the soil or rain water. At the highest level of organization (Figure 2), the biosphere is the collection of all ecosystems, and it represents the zones of life on earth. It includes land, water, and even the atmosphere to a certain extent.

From a single organelle to the entire biosphere, living organisms are parts of a highly structured hierarchy.

What is the lowest level of organization of the biosphere or the one that has the fewest members?

Figure 2. The biological levels of organization of living things are shown. From a single organelle to the entire biosphere, living organisms are parts of a highly structured hierarchy. (credit “organelles”: modification of work by Umberto Salvagnin; credit “cells”: modification of work by Bruce Wetzel, Harry Schaefer/ National Cancer Institute; credit “tissues”: modification of work by Kilbad; Fama Clamosa; Mikael Häggström; credit “organs”: modification of work by Mariana Ruiz Villareal; credit “organisms”: modification of work by “Crystal”/Flickr; credit “ecosystems”: modification of work by US Fish and Wildlife Service Headquarters; credit “biosphere”: modification of work by NASA)

Which of the following statements is false?

  1. Tissues exist within organs, which exist within organ systems.
  2. Communities exist within populations, which exist within ecosystems.
  3. Organelles exist within cells, which exist within tissues.
  4. Communities exist within ecosystems, which exist in the biosphere.

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The levels of organization from lowest complexity to highest are:
species, population, community, ecosystem, biome and biosphere.

Since you are asking specifically about the levels of organization in an ecosystem, we leave out the levels of biome and biosphere since they are both more complex than ecosystem.

The most inclusive level in an ecosystem is the ecosystem itself.

An ecosystem includes all the living organisms and nonliving (abiotic) factors such as air, water, light etc.

Community is the next level to discuss - a community in an ecosystem includes all of the living organisms which live in the defined area of the ecosystem.

Population is the next least inclusive level - a population includes all the members of one species in a defined area.

Finally the least inclusive level is that of a species. This would be one individual member of a species.