Grade 7 Interactions and Ecosystems

Topic 5: Cycles in the Environment

Natural Cycles

The air we breathe has been cycled through millions of other living organisms as has the water we drink. When an organism dies, its nutrients return back to the environment. There are many natural cycles in the environment.

The Carbon Cycle

Carbon is necessary for all life to exist. Plants use carbon dioxide (CO2) from the air in order to make their own food. Other organisms eat the plants and release carbon dioxide when they exhale.

Carbon is the basic building block for all living organisms on the earth and although carbon is very abundant, the supply is finite.

The Carbon Cycle

During their lives, all organisms reuse the finite supply of carbon here on the earth. Plants are able to combine carbon and water with energy supplied by the Sun to form their own food through the process of photosynthesis. When the plants are consumed, that carbon-based energy is passed on to the primary consumers and so on through the various food webs all the way to the tertiary consumers.

The Carbon Cycle

The carbon cycle is a cycle in which carbon is used and reused through the ecosystem.

http://www.sciencelearn.org.nz/Contexts/The-Ocean-in-Action/Sci-Media/Animations-and-Interactives/Carbon-cycle

The Carbon Cycle

Carbon is released by the burning of fossil fuels (e.g. natural gas, coal, oil, gasoline, etc.) and wood, volcanic activity as well as the respiration and decomposition of all plants and animals.

Carbon is absorbed into plants (through the photosynthesis of land and ocean plants), into the earth (through decomposition) as well as into the ocean (through algae and dissolving into the water).

The Water Cycle

All living things require water. The human body is 60 – 70 percent water. Water is used for life processes such as supplying food throughout an organism’s body in a form it can use in its cells, and carrying away wastes from those cells.

The Water Cycle

Water moves constantly around the environment, changing form as it moves from the air to the ground to your body. This movement is known as the water cycle, which is the continuous movement of water through- out an ecosystem.

The Water Cycle

Evaporation and transpiration move water up from Earth into the atmosphere.

Condensation and precipitation return water to Earth.

The Water Cycle

Evaporation: liquid water changes into water vapor (invisible, suspended in the air).

Transpiration: water evaporates into air through plants who get the groundwater from their roots.

Condensation: water vapor changes back to liquid. Occurs as air cools forming clouds, fog, and dew.

The Water Cycle

Precipitation: water falls as rain, hail, snow, etc.

Ground water: water in and under the soil. Source for plant roots, human wells, etc.

Run-off: water that runs off the ground into lakes, rivers, streams, oceans

Pollution in the Environment

Matter, energy, carbon and water are constantly being cycled throughout the ecosystems. Other substances can also enter and cycle through the environment. Pollution occurs when materials are released into the environment so quickly that they cannot be broken down, stored, or recycled naturally. Pollutants are substances that cause pollution.

Pollution in the Environment

Many substances that occur naturally become pollutants when they are present in concentrations too high for the environment to absorb without a negative effect. An example would be acid rain which is rain with high levels of acid. It is caused by waste gases (sulphur and nitrogen) that are released into the atmosphere as wastes.

Pollution in the Environment

Pollution in the Environment

Pollution in the Environment

Acidity is indicated on a scale known as the pH scale. It is numbered from zero to fourteen, with the a value of 7 considered neutral. From 0 to 7 is the acidic region. From 7 to 14 is the basic portion of the scale.

Neutral

Acidic Basic

Pollution in the Environment

Acid rain poses serious hazards to the ecosystem. It can destroy the life of lakes because the water becomes too acidic for fish and plants to live.

Pollution in the Environment

Other materials are also pollutants. PCBs (polychlorinated biphenyls) are used for a variety of purposes (i.e. paint, packing material). They leaked into the environment accidentally, and break down very slowly causing harm to organisms.

Pollution in the Environment

Mercury is also damaging to the environment. It was used by many industries including gold mining. It leaks out of disposal sites and dissolves into water and the ground and poisons organisms.

Pollution in the Environment

DDT (dichlorodiphenyltrichloroethane) is a pesticide that was widely used until its toxic effects were discovered. Although it is now banned in Canada and many other countries, it is a very effective insecticide. Used from the 1940s to the 1960’s to control insect populations, it damaged other organisms as well and cycles through the environment. Its effects are still being felt throughout the world.

DDT

DDT weakens egg shells.

This woman has eye cancer. She lives near a DDT factory in India.

DDT was thought to be safe enough that people were sprayed with it to kill pests.

Bioaccumulation

Pollutants move from level to level in a food web. They are stored in organisms in the same way that food energy is stored. This effect is called bioaccumulation: the movement of pollutants through a food chain so they accumulate in higher-level organisms.

Bioaccumulation

Mercury enters the water after leaking out of a waste- disposal site and settles on the bottom of the lake.

Level of Pollutant 1

Bioaccumulation

Mercury enters systems of micro-organisms and algae in water.

Level of Pollutant 2

Bioaccumulation

Small fish eat micro-organisms (lots of them!) and the mercury accumulates in their systems.

Level of Pollutant 3

Bioaccumulation

Large carnivorous fish eat many smaller fish and absorb mercury which is stored in their fatty tissue.

Level of Pollutant 4

Bioaccumulation

Humans eat the large fish and accumulate mercury.

Level of Pollutant 5

Bioaccumulation

Review

The carbon cycle is balanced in stable ecosystems. What events might occur to upset this balance?

Increase in factories, the burning of fuels, etc.

Decrease in vegetation.

Extreme natural activities (e.g. volcanic eruptions).

Review

Explain how pesticides that are directed at killing insects can harm birds.

Birds eat the insects and may absorb pesticides too.