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Ecosystems. Abdulhafez Selim, MD, PhD. Ecosystem. Physical environment. Ecosystem. Organisms. +. =. Earth. The organisms living in a particular area, together with the physical environment with which they interact, constitute an ecosystem.

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Abdulhafez Selim, MD, PhD









  • The organisms living in a particular area, together with the physical environment

with which they interact, constitute an ecosystem.

  • At a global scale, Earth is a single ecosystem.
climate on earth solar radiation
Climate on Earth, Solar Radiation
  • Biological processes on Earth are driven primarily by solar radiation.
climates on earth global air circulation
Climates on Earth; Global Air Circulation

More energy received at

equator than at poles

At equator, warm raising air produces a belt of

low pressure and winds.

  • Rising air expands and cools, releasing moisture.
  • Descending air warms and dries and takes up moisture,
  • Creating rain shadows.
  • Global air circulation is driven by solar radiation and the spinning of Earth on its axis
climates on earth global air circulation6
Climates on Earth; Global Air Circulation

Air circulation around the globe would be simple (and the weather boring) if the Earth did not rotate and the rotation was not tilted relative to the Sun.Please click to enlarge!

climate on earth ocean currents
Climate on Earth, Ocean currents

Poleward-moving currents are warm, and equatorward-moving currents are cold.

Surface ocean currents are driven by global winds and play an important role in

redistributing heat around the globe.

climate on earth ocean currents9
Climate on Earth, Ocean currents

Description: Map showing the seven major ocean currents


Photosynthesis is a process in which green plants use energy from the sun to

transform water, carbon dioxide, and

minerals into oxygen and organic

compounds. It is one example of how

people and plants are dependent

on each other in sustaining life

energy flow
Energy flow

Before 1977, scientists believed that all forms of life ultimately depended on

the Sun for energy.

A few deep-sea and cave ecosystems are powered by chemosynthesis rather

than photosynthesis.

Chemosynthesis is the biological conversion of 1-carbon molecules

(usually carbon dioxide or methane) and nutrients into organic matter using

the oxidation of inorganic molecules (e.g. hydrogen gas, hydrogen sulfide) or

methane as a source of energy, rather than sunlight, as in photosynthesis.


Crops need many things for good growth and maximum productivity- light, carbon dioxide, nutrients, water and a sufficiently long period without frost. What is often forgotten is that another requirement for growth and development of crops is needed - heat. Each crop is very specific as to its heat requirements. the most rapid growth and development takes place at 2 l' C (70' F). The growth rate decreases with the increase in temperature and finally stops at 30 C (86' F).


The amount of energy flowing through an ecosystem depends

on primary production and on the efficiency of transfer of energy

from one trophic level to another

food web
Food Web

Who eats whom in a ecosystem can be diagrammed as a food web.

cycles of materials in ecosystem oceans primary production
Cycles of Materials in Ecosystem, oceans primary production.

Primary production in oceans is highest

adjacent to continents,

where nutrient-rich waters rise to the


cycles of materials in ecosystem layers of atmosphere
Cycles of Materials in Ecosystem, Layers of Atmosphere

Layers of the AtmosphereThe atmosphere is divided into five main

layers plus the ionosphere.

It extends over 430 miles (700 km) into the sky.

layers of atmosphere
Layers of Atmosphere

The two lowest layers of Earth's atmosphere differ

from each other in their circulation patterns,

the amount of moisture they contain,

and the amount of ultraviolet radiation they receive.

cycles of material in ecosystem temperate zone lake
Cycles of Material in Ecosystem, Temperate-Zone Lake

Temperate-zone lakes turn over

twice each year as water cools and warms.

biogeochemical cycles
Biogeochemical Cycles
  • The elements organisms need in large quantities cycle through organisms to the environment and back again.
water cycle
Water Cycle

The cycle of water-the hydrological cycle-is driven by evaporation of water;

most of it from ocean surfaces.

carbon cycle
Carbon Cycle

Atmospheric carbon dioxide is the immediate source of carbon for

earthly organisms, but only a small part of Earth's carbon is in the atmosphere.

nitrogen cycle
Nitrogen Cycle

Although nitrogen makes up 78 percent of Earth's atmosphere, nitrogen can be

converted into biologically useful forms only by a few species of bacteria and



The most striking example of a local effect of altered bio-geochemical cycles is

lake eutrophication.

human alterations of biogeochemical cycles lake eutrophication
Human Alterations of Biogeochemical Cycles, lake eutrophication.
  • Normal lakes that have minimal levels of nutrients are said to be enriched, or oligotrophic. An oligotrophic lake has clear water and supports small populations of aquatic organisms. Eutrophication is the enrichment of water by nutrients; a lake that is enriched is said to be eutrophic. The water in a eutrophic lake is cloudy and usually resembles pea soup because of the presence of of vast numbers of algae and cyanobacteria that are supported by the nutrients.
  • Eutrophication can be markedly accelerated by human activities, and it results from the enrichment of water by inorganic plant and algal nutrients- most commonly in sewage and fertilizer runoff.

A great lake - Lots of birds! Hypertrophic

A great lake - Gin-clear water!Oligotrophic