Chapter 15

Our EnvironmentEnvironment includes all of the external factors affecting an organism. These factors may be other living organisms (biotic factors) or nonliving variables (abiotic factors), such as temperature, rainfall, day length, wind, and ocean currents.What happens when we add waste to our environment?

• Some of this waste may be broken down by Biological processes (eg. Saprophytes like fungi and bacteria) and this waste is called BIODEGRADABLE.

Examples: plant and animal waste, vegetable peels etc.• Some of this waste will not be broken down by Biological Processes and this waste is

called NONBIODEGRADABLE. Examples: Polythene bags, plastics, metal objects etc. Non biodegradable substances can be harmful to the environment.

An ecosystem is a natural system consisting of all plants, animals and microorganisms (biotic factors) in an area functioning together with all the non-living physical (abiotic) factors of the environment.

The abiotic components of an ecosystem include various physical and chemical factors.Physical factors: Eg. Sunlight and shade , average temperature, average precipitation, nature of soil (for terrestrial ecosystems) etc.Chemical factors: Eg. Level of water and air in soil , level of plant nutrients dissolved in soil moisture (for terrestrial) and in the water (for aquatic) etc.Biotic Components: Organisms that make up the biotic component of an ecosystem are usually classified as autotrophs and heterotrophs, based on how they get their food or organic nutrients they need to survive.

Autotrophs (producers)-are organisms that can manufacture the organic compounds they need as nutrients from simple inorganic compounds obtained from their environment. In most terrestrial ecosystems, green plants are the producers. In aquatic ecosystems, most of the producers are phytoplankton, consisting of various species of of floating and drifting bacteria and protist.Some producers , mostly specialized bacteria, can extract inorganic compounds from their environment and convert them into organic nutrient compounds without the presence of sunlight. These producers are called chemosynthesis.

Heterotrophs(consumers)-are organisms which cannot synthesize the organic nutrients they need and get their organic nutrients by feeding on the tissues of producers or other consumers. There are several classes of of consumers, depending on there food source.

1. Primary consumers (herbivores) feed directly on plants or other producers. 2. Secondary consumers (carnivores) feed only on primary consumers. 3. Tertiary or higher level consumers feed only on animal-eating animals. 4. Omnivores can eat both plants and animals.Examples are pigs, rats, cockroaches,

and humans.

5. Detrtivores (decomposers and detritus feeders) live off of detritus, parts of dead organisms and castoff fragments and waste of living organisms. Decomposers digest detritus by breaking down the complex organic molecules in these materials into simpler, inorganic compounds. Decomposers consist of various bacteria and

fungi.

Natural and Artificial EcosystemsNatural ecosystems: Forests, ponds and lakesArtificial Ecosystems (manmade): gardens, crop fields, aquarium

FOOD CHAINS AND FOOD WEBSA food chain is the flow of energy from one organism to the next. Organisms in a food chain are grouped into trophic levels — from the Greek word for nourishment, trophikos — based on how many links they are removed from the primary producers. They usually start with a primary producer and end with a carnivore. A food chain shows how each living thing gets its food. i.e. WHO EATS WHOM. Each link in this chain is food for the next link.

Most animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements. These interconnected food chains form a food web.

A food web extends the food chain concept from a simple linear pathway to a complex network of interactions.

Food webs show how many animals are interconnected by different paths. FOOD WEBS show how plants and animals are connected in many ways to help

them all survive.

Transfer of Energy in Food Chains: Energy and organic compounds are passed from one trophic level to the next. What is the efficiency of the transfer? In a highly efficient transfer almost all of the energy would be transferred -- 80% or more. In a low efficiency transfer very little energy would be transferred -- less than 20%. In a typical food chain, not all animals or plants are eaten by the next trophic level. In addition, there are portions or materials (such as beaks, shells, bones, etc.) that are also not eaten. That is why the transfer of matter and energy from one trophic level to the next is not an efficient one.

One way to calculate the energy transfer is by measuring or sizing the energy at one trophic level and then at the next. Calorie is a unit of measure used for energy. The energy transfer from one trophic level to the next is about 10%. For example, if there are 10,000 calories at one level, only 1,000 are transferred to the next. This 10% energy and material transfer rule can be depicted with an ecological pyramid that looks like this:

Trophic levels are the feeding position in a food chain such as primary producers, herbivore, primary carnivore, etc. Green plants form the first trophic level, the producers. Herbivores form the second trophic level, while carnivores form the third and even the fourth trophic levels.

Grass Deer Lion

To summarize: In the flow of energy and inorganic nutrients through the ecosystem, a few generalizations can be made:

1. The ultimate source of energy (for most ecosystems) is the sun 2. The ultimate fate of energy in ecosystems is for it to be lost as heat. 3. Energy and nutrients are passed from organism to organism through the food chain as

one organism eats another. 4. Decomposers remove the last energy from the remains of organisms. 5. Inorganic nutrients are cycled, energy is not.

Biological magnification Biomagnification, also known as bioamplification, or biological magnification is the increase in concentration of a substance, such as the pesticide DDT, that occurs in a food chain as a consequence of:

Food chain energetics Low (or nonexistent) rate of excretion/degradation of the substance.

Biological magnification is the tendency of pollutants to become concentrated in successive trophic levels. Often, this is to the detriment of the organisms in which these materials concentrate, since the pollutants are often toxic. Biomagnification occurs when organisms at the bottom of the food chain concentrate the material above its concentration in the surrounding soil or water. Pollutants that biomagnify have another characteristic. Not only are they taken up by the producers, but they are absorbed and stored in the bodies of the consumers. This often occurs with pollutants soluble in fat such as DDTThe "best" example of biomagnification comes from DDT. This long-lived pesticide (insecticide) has improved human health in many countries by killing insects such as mosquitoes that spread disease. On the other hand, DDT is effective in part because it does not break down in the environment. It is picked up by organisms in the environment and incorporated into fat. Even here, it does no real damage in many organisms (including humans). In others, however, DDT is deadly or may have more insidious, long-term effects. In birds, for instance, DDT interferes with the deposition of calcium in the shells of the bird's eggs. The eggs laid are very soft and easily broken; birds so afflicted are rarely able to raise young and this causes a decline in their numbers.

HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT?

Environmental Problems: Depletion of Ozone Layer, Waste Disposal

Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole. CFCs and other contributory substances are commonly referred to as ozone-depleting substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths (270–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol banning the production of CFCs and halons as well as related ozone

depleting chemicals such as carbon tetrachloride and trichloroethane. The ozone layer in the stratosphere blocks out the sun’s deadly ultraviolet rays. It acts as our planet’s natural sunblock.It is suspected that a variety of biological consequences such as increases in skin cancer, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.

Waste Disposal

Every year, millions of tons of "trash“ are generated.. Less than one-quarter of it is recycled; the rest is incinerated or buried in landfills. With a little forethought, we could reuse or recycle more than 70 percent of the landfilled waste, which includes valuable materials such as glass, metal, and paper. This would reduce the demand on virgin sources of these materials and eliminate potentially severe environmental, economic, and public health problems.

The Eco friendly mantra is

REDUCE REUSE RECYCLE

Answer the following questions:

1. Why is non biodegradable waste more harmful than biodegradable waste?

2. A crop field is termed as an artificial ecosystem. Why?

3. Why does the same enzyme not break down everything that we eat?

4. Animals like cows can digest cellulose , but humans cannot. Give reasons.

5. Comment on the statement “we will not get any energy if we eat coal.”

6. What is the role of UNEP in protecting the ozone layer?

7. What would happen if there was no ozone in the stratosphere?

8. Classify the following as biotic and abiotic components:

Rainfall, a rose plant, soil, fish, earthworm, fertilizer, temperature, bacteria.

9. Match the following:

Herbivores Producers First Trophic level

Plants Secondary consumers Second Trophic level

Small carnivores Primary consumers Third Trophic level

Large carnivores Tertiary consumers Fourth Trophic level

10.Why does a food chain normally consist of only 4-5 steps?

11.How is the ‘flow of energy’ different from the ‘flow of nutrients’ in an

ecosystem?

12.Wheat , meat and humans will have varying amounts of pesticide residues in

their body. Comment on the statement and explain the phenomenon

involved.

13.How much solar energy is captured by the green plants? Trace this energy in

a food chain till it reaches the lion. The other members of the food chain are

plants and deer. The plants are receiving 1000,000 joules of energy from the

sun.