Matter in Ecosystems&

Pesticides

Science 1206

Cycling of Matter in Ecosystems

• Organic substances – – Contain atoms of Carbon and Hydrogen– Are broken down into simpler forms in living things– Ex. Sugar, carbohydrates, proteins, amino acids

• Inorganic substances – – Does not contain combination of carbon and

hydrogen– Ex. Water (H2O), ammonia (NH3), Carbon dioxide

(CO2)

Matter: Recycled

• The atoms and molecules available to make up organisms on earth is limited

• All the atoms MUST be recycled in order for new organisms to form.– It is very likely that at least one

of the carbon atoms in your body was also in a a 70 million year old dinosaur

The Matter CyclePERSON

COW

GRASS

SOIL

DECOMPOSERS

1. Dead plants and animals are broken down by decomposers – their atoms / molecules are released into the system to be re-used

2. Atoms, molecules accumulate in the soil

3. Nutrients are taken up by grasses

4. Cows eat the grass – nutrients and atoms are passed on to the cow

5. Person eats cow – nutrients and atoms are passed on to person

6. Each of these things can die, the atoms are broken down by decomposers and recycled for the next living things

The Oxygen Cycle

Oxygen (atmosphere)

Respiration from plants and animals

Respiration from decomposers

Combustion

Carbon Dioxide

Photosynthesis by green plants

Note: The complementary processes of photosynthesis and respiration ensure that not only oxygen, but also carbon and hydrogen are repeatedly cycled.

Photosynthesis:

6 CO2 + 6 H2O + light ------> C6H12O6 + 6O2

Respiration:

C6H12O6 + 6O2 ------> 6CO2 + 6H2O + energy

The Carbon Cycle• In the carbon cycle we use CO2 from both biotic and

abiotic sources:

• 1. Biotic: aerobic respiration (in the presence of CO2), and decomposition.

• Note: Here, the organic reservoirs (storage areas) for carbon are the bodies of living things.

• 2. Abiotic: combustion and geological activity

• Note: Here, the inorganic reservoirs for carbon are the atmosphere, the oceans, and the Earth’s crust.

• See page 62, figure 1.

CO2 in the atmosphere

volcanic eruption

CO2 dissolved in water

Ocean sediment

combustion

Fossil fuelsConversion to fossil fuels

Decomposition

Glucose

Photosynthesis - carbon is stored in the biomass

Aerobic respiration

Weathering

The Nitrogen Cycle• The movement of nitrogen through the ecosystems,

the soil, and the atmosphere is called the nitrogen cycle.

• Nitrogen gas composes 79% of the Earth’s atmosphere, but in this inorganic form it can not be used by animals. In order for nitrogen to be useful to organisms, it must be converted to a nitrate ion (NO3

-) by the process of nitrogen fixation, or nitrification, either by lightning or by bacteria in the soil.

• Nitrogen is required to make proteins and DNA which is the genetic material found in every cell.

Atmospheric nitrogen (N2)Plant protein

Animal protein

Death and decompositionExcretions

Ammonification (NH3)

Nitrification to nitrites (NO2-)

Nitrification to nitrates (NO3-)

Denitrifying bacteria

Nitrogen fixing bacteria

Pests and Pesticides

4 Types of Pesticides

• Herbicides : kills plants

• Insecticides : kills insects

• Fungicides : kills fungi

• Bactericides : kills bacteria

First-Generation Pesticides

• metals such as arsenic, lead and mercury.

• These were found to be toxic to humans, polluted water and soil and were not biodegradable (not able to break down naturally).

Second-Generation Pesticides

• 20th century pesticides were generally man made organic chemicals in a lab designed to be less toxic to humans and were capable of breaking down within the ecosystem.

• However, it was found that some of these chemicals were fat soluble and became stored within animal tissues. This created a problem known as bioaccumulation.

Bioaccumulation & Bioamplification

Figure 4 on page 54 in your book

• Bioaccumulation – An increase in the concentration levels of a pesticide within the body of an organism over time.

• Bioamplification – Where a species at a higher trophic level feeds on more that one organism below it, pesticide concentrations tend to increase rapidly the higher up the food chain you look.

For Bioamplification to occur…

• Long-lived - Present for a long time in the system

• Mobile - Easily passed up the food chain

• Soluble in fats - Dissolves in, and is stored in fatty tissue

• Biologically active – Affects biological body tissue

Pesticides - Past and Present

• Past Chemical Pesticides:–Stored in fat tissue–Not soluble in water

• Modern Chemical Pesticides:–Not stored in fat tissue–Soluble in water

Pesticide Resistance:

• Over time some species of ‘pest’ become resistant to the pesticide. Meaning the pesticide no longer effects them.

• The survivors then have offspring which are mostly resistant.

• These individuals survive the next spraying. If a similar pesticide is often used, resistant pests will soon make up most of the population.

• See fig. 5 pg. 55

Dichloro, Diphenyl Trichloroethane (DDT)

• Pesticide that is suitable for bioamplification

• Has a half-life of 15 years – That is, every 15 years the amount left in the system

will be reduced by one half.– If you use 100 kg of DDT, after 15 years it will be

reduced to 50 kg, and after another 15 years it will be 25 kg, and so on..

Effects of DDT in Birds

• Shell thinning1. Carnivorous birds such as ospreys and bald

eagles eat other birds, dead animals and fish which contain a build-up of DDT

2. DDT causes the shells to become too thin to allow the large females to sit on the eggs without them breaking

3. Since eggs are being broken, the over-all population of these birds is declining

• After DDT was banned in the US and Canada in the early 1970’s the bird populations of began to recovered.

• DDT bioaccumulates in humans the same as it would other animals

• Male birds have also become more feminine as the DDT mimics female sex hormones

Questions

1. Not all countries, like Mexico for example, have banned the use of DDT.

– Since birds migrate from winter to summer from one country another, do you think the birds are 100% safe from the presence and the effects of DDT? Why?

2. How do you think a pesticide like DDT would affect the over all biodiversity in an ecosystem?