FOOD CHAINS AND WEBS

Food chains and food webs show the feeding relationship between organisms in a habitat or ecosystem. A food chain is the sequence by which energy, in the form of food, passes from plant to animal and then to other animals.

SIMPLE FOOD CHAIN

A food web is a compilation of food chains from the same habitat and is more complex than a food chain.

Removing organisms from or adding organisms to the food chain or web can significantly affect the feeding habits and numbers of the remaining organisms.

The arrows in a food chain and web show the flow of ENERGY and not of food. As we go across the food chain or up the food web, the numbers of organisms must decrease. Prey should always outnumber predators if both are to survive.

KEY WORDS PRODUCER: photosynthetic green plant able to make their own food, thereby not dependent on another organism.

CONSUMER: heterotrophic organism that feeds on other organisms; they cannot make their own food.

Herbivore: an animal that eats mainly plants.

Carnivore: an animal that eats mainly meat.

Omnivore: an animal that eats a variety of foods (both plants and meat).

Predator: an animal that hunts and kills another for food.

Prey: an animal that is hunted and killed for food.

ROLES IN THE FOOD CHAIN AND WEB Organisms may have multiple roles in food chains and webs. Below is an example in the food chain:

If there was another organism feeding on the wolf, the wolf would then also be called prey. The organism feeding on it would be the TERTIARY consumer, carnivore and predator.

Anything else feeding after the tertiary consumer would be called the COMPLEX consumer, along with any other applicable designation.

These designations also appear in the food web.

QUESTIONS

RECYCLING MATERIALS IN NATURE

NUTRIENT CYCLES In a natural ecosystem, energy (passed on as food) decreases when it reaches each consumer. However, materials that actually make up the living organisms and non-living structures, must be recycled. There are no new materials coming to Earth!

DECOMPOSERS When the animals and plants in a habitat die, their bodies decay as they are broken down by decomposers (bacteria and fungi). These substances (carbon, nitrogen, oxygen, phosphrus) are then returned to nature to be reused.

We will look at the following cycles: Water Oxygen Carbon Nitrogen

WATER CYCLE KEY TERMS: Evaporate: liquid changes to a gas Condense: Gas changes to a liquid Precipitation: the fall of water from clouds as rain, sleet, hail or snow etc Transpiration: the evaporation of water from leaves

Energy from the sun warms water on the Earth’s surface. The water then EVAPORATES.

The water vapour rises to the atmosphere. It condenses into water droplets to form clouds.

When the water droplets become heavy enough, they fall to Earth as precipitation. The cycle continues as water evaporates.

OXYGEN CYCLE

Humans affect the carbon and oxygen cycles in similar ways. Cutting down forests, polluting waterways and burning fossil fuels decrease the amount of O2 in the atmosphere while increasing the CO2.

THE CARBON CYCLE

WORDS TO REMEMBER in THE CARBON CYCLE PHOTOSYNTHESIS NUTRITION / FEEDING FOSSILIZATION DECOMPOSITION RESPIRATION COMBUSTION

WHAT IS THE CARBON CYCLE? The carbon cycle is the sequence in which carbon is constantly being used and reused in various forms in nature. Below is a diagram of the carbon cycle. Notice that not only is carbon dioxide being removed from the atmosphere, but it is being returned from the atmosphere.

REMOVAL OF CARBON DIOXIDE FROM THE ATMOSPHERE Carbon dioxide is removed from the atmosphere by the process of PHOTOSYNTHESIS. Plants use the sun’s energy, CARBON DIOXIDE and water to make glucose, starch and other carbohydrates.

REMOVAL OF CARBON DIOXIDE FROM THE ATMOSPHERE Animals then eat the plants as part of their NUTRITION and therefore get carbohydrates into their bodies. 40

REMOVAL OF CARBON DIOXIDE FROM THE ATMOSPHERE Sometimes when the plants and animals die, they become hard deep under the Earth’s crust (FOSSILIZATION) and become fossils that later become fossil fuels like oil and coal. 41

RETURN OF CARBON DIOXIDE TO THE ATMOSPHERE Carbon dioxide is returned to the atmosphere by DECOMPOSITION, RESPIRATION AND COMBUSTION.

ADDITION OF CARBON DIOXIDE TO THE ATMOSPHERE When decomposers feed on dead organisms, they use this food in respiration to make energy releasing carbon dioxide into the atmosphere.

ADDITION OF CARBON DIOXIDE TO THE ATMOSPHERE When animals and plants respire, they also release carbon dioxide into the atmosphere as a by-product.

ADDITION OF CARBON DIOXIDE TO THE ATMOSPHERE Lastly, when fossil fuels such as oil and coal are burned (COMBUSTION) in fireplaces, cars and other modes of transportation, carbon dioxide is released as part of the smoke.

Atmospheric carbon dioxide is currently increasing due to: More combustion of fossil fuels Deforestation has increased so less trees are available to photosynthesize.

THE GREENHOUSE EFFECT Radiation from the sun warms the Earth The Earth radiates heat back into space

As carbon dioxide increases, it traps more heat and this causes an increase in temperature. Eventually Arctic and Antarctic may start melting and this could cause flooding.

THE NITROGEN CYCLE

WHAT IS THE NITROGEN CYCLE? The nitrogen cycle is the sequence by which nitrogen is constantly being used and reused in nature.

WORDS TO REMEMBER in the NITROGEN CYCLE Nitrogen-fixing Nitrifying Denitrifying Absorption Nutrition Decomposition Root nodules Legumes

WHY DO WE NEED NITROGEN? Humans need nitrogen to make proteins. Proteins are essential in the making: Hair fingernails Hormones Enzymes Cell membranes Blood clotting proteins And many other substances found in and on the human body

ATMOSPHERIC NITROGEN Nitrogen atoms are bonded so strongly together in the atmosphere that it takes hundreds of kilojoules of energy to break them. Nitrogen can only be used by animals and green plants when this bond is broken and since they cannot break these bonds, they cannot use atmospheric nitrogen as it is. The nitrogen must first be fixed. 78% of the atmosphere is nitrogen.

HOW NITROGEN IS TAKEN FROM THE AIR Nitrogen-fixation are the processes that can break the bonds of atmospheric nitrogen so that the nitrogen can be converted into a useable form. This is done by lightning and nitrogen-fixing bacteria which both convert nitrogen in the air to nitrates in the soil.

HOW NITROGEN IS PASSED ALONG The plants can then absorb nitrogen into their roots and make plants proteins. Animals then eat these plants and use to plant protein to make animal proteins. When plants and animals die or excrete, decomposers will act on the dead flesh, causing them to break-down and release ammonium compounds which smell very bad.

HOW NITROGEN IS CONVERTED Nitrifying bacteria I in the soil then convert the ammonium compounds to nitrites: NH3 to NO2. Nitrifying bacteria II also in the soil then convert the nitrites to nitrates: NO2 to NO3

HOW NITROGEN IS RETURNED TO THE ATMOSPHERE These nitrates are then either absorbed into plant root for the cycle to continue all over again or Denitrifying bacteria in the soil convert them back to nitrogen in the atmosphere and the cycle continues from there.

BACTERIA IN THE NITROGEN CYCLE As you may have seen there are many bacteria that take part in the nitrogen cycle

NITROGEN-FIXING BACTERIA These bacteria live in the soil or in the root nodules of leguminous plants (peas and beans). These bacteria convert nitrogen in the air to nitrates in the soil.

NITRIFYING BACTERIA These bacteria are of two types: Those that convert ammonium compounds to nitrites Those that convert nitrites to nitrates.

DENITRIFYING BACTERIA These bacteria undo the good works of the other bacteria. They convert nitrates in the soil back to nitrogen in the atmosphere.

DECOMPOSERS What do decomposers do in nature? Name two types of organisms that are known as decomposers?