Lesson 9.3.3. A Growing Concern Science 9 Lesson 9.3.3. A Growing Concern Textbook Reference Science Focus 9 pages 187 to 196

Chemical Use An area of rapid change since the Second World War has been in the field of applied ________. The research laboratories of __________ companies have created a steady stream of new products. __________ has been a major market for the chemical industry. _________ and __________, along with chemical fertilizers, are used in large quantities on modern farms and in many homes.

Chemical Use Selective weed killers (_______________), such as 2-4-D, have revolutionized farming by controlling weeds. Chemical _____________, such as D.D.T., have been used around the world to control the populations of insects that spread disease or that __________ with humans by eating our food crops.

Chemical Use Many chemicals produced and used by humans are toxic. Toxic chemicals are __________. D.D.T. was used in North America until 1969. It was banned on this continent because of the effects it had on ________ and other animals. Even mildly __________ chemicals have to be used with care because they can be extremely hazardous if used incorrectly. All pesticides have the disadvantage of killing more than their intended __________.

Use this model of a food web to answer the following questions.

Trophic Levels The mountain lion in this model of a food chain is in the second __________ level when it eats a rabbit. The mountain lion is a _________ order consumer. Remember that the mountain lion is also called a ____________.

Food Chains 1. Can you identify three other herbivores (first order consumers)? 2. Which organisms on this diagram are decomposers?

Food Chains 3. Which animal would the mountain lion have to eat in order to be a 3rd order consumer? 4. Which scientific model is represented by the sequence: grass -> grasshopper -> shrews -> fox -> mountain?

Pest Resistance Scientists recognize that the wide spread use of ______________ has lead to the development of pesticide-resistant insects. These insects have developed a resistance to the pesticides that we are currently using and their __________ are increasing.

Graph showing what happens to the population of mosquitoes before, during, and after spraying with a chemical pesticide.

Pest Resistance 1. What was the original population of mosquitoes before the spraying program started? 2. Describe what happened to the population of mosquitoes between 30 days and 60 days. What do you think was the cause of this decline?

Pest Resistance 3. Describe what happened to the population of mosquitoes between 30 days and 90 days. 4. Why do you think the insect population increased even though humans were still using chemical sprays to kill the mosquitoes?

Biological Magnification As materials pass through an ecosystem they may become ______________ in the tissues of living creatures. This phenomenon is known as biological magnification or ________________.

This is a model of a salt-water food web. Pesticides accumulate in the fatty tissue of top predators such as killer whales and dolphins. This process is called biological magnification.

Biological Magnification Organisms at the bottom of the food chain, such as microscopic algae, may absorb minute quantities of ________ chemicals such as D.D.T. Many such chemicals are ________ soluble and are not excreted easily. Therefore they become more concentrated toward the top of the _____ ______. In the top ____________, the chemicals may be concentrated enough to have damaging effects.

Science 9.3.3. Assignment Read the Think & Link Investigation 3–B DDT in a Food Chain on pages 189 to190. Do the following questions: (a) Analyze questions 1 to 6 on page 191. (b) Conclude and Apply questions 7 and 8 on page 191 (c) Extend Your Knowledge and Skills question 9 on page 191.