Lesson 1.2 - Producing More Food: Part II

You learned that scientists have developed two major types of chemicals to help increase food production.  The chemicals are pesticides and synthetic fertilizers. 

To learn about pesticides, read Pesticides on page 292 and the top of page 293 in your textbook. Then, answer the following questions.

Question 1. What is a pesticide?

Question 2. What is an insecticide?

Question 3. What is a herbicide?

Question 4. Answer Reading Check on page 292 of your textbook.

Question 5. What percent of the world's food crops is destroyed by insects?

Question 6. What is DDT?

Question 7. Explain how DDT gets into the bodies of animals that are not insects.

Question 8. What is the scientific name given to the process by which a chemical such as DDT moves up in the food chain and increases in concentration?

Question 9. What is natural resistance?

Question 10. How does natural resistance cause problems when pesticides are used?

Refer to the information in Figure 15.1 to answer questions 6 to 9.

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What is the definition of a pesticide?

A pesticide is a chemical that will kill or control any organism that humans consider to be a pest.  These can include plants, insects, and animals.

Question 2. What is an insecticide?

An insecticide is a chemical that will kill insects.

Question 3. What is a herbicide?

A herbicide is a chemical that will kill plants.

Question 4. Answer Reading Check on page 292 of your textbook.

The difference between insecticides and herbicides is in what they kill.  Insecticides kill insects.  Herbicides kill plants that are normally called weeds.  A weed is any plant that is growing where it is not wanted.  This may sound odd, but look at it from a the perspective of a homeowner in the city and a farmer.  Wheat growing in the city homeowner's lawn will be called a weed by the homeowner.  Grass growing in a farmer's wheat field will be called a weed by the farmer, as will canola in a barley field, for example.

Question 5. What percent of the world's food crops is destroyed by insects?

Scientists estimate that 30% of the world's food crops are destroyed by insects.  This information was found in the text of Figure 15.1.

Question 6. What is DDT?

DDT is a chemical insecticide.

Question 7. Explain how DDT gets into the bodies of animals that are not insects.

DDT is absorbed into the bodies of insects such as grasshoppers.  The insects become sick and die.  Secondary consumers such as mice, rats, snakes, frogs, and small birds eat these sick and dead insects and the DDT is stored in their bodies.  Tertiary consumers such as falcons and hawks eat these secondary consumers, and the DDT is passed into their bodies.

Question 8. What is the scientific name given to the process by which a chemical such as DDT moves up in the food chain and increases in concentration?

Biological magnification is the process whereby a chemical moves up the food chain and increases in concentration.  The bird of prey in the picture will have a very high concentration of DDT in its body compared to the concentration of DDT in the body of the grasshopper.

Question 9. What is natural resistance?

Natural resistance is the characteristic of an individual that prevents a chemical or disease agent from killing that individual.

Question 11. How does natural resistance cause problems when pesticides are used?

Natural resistance causes problems in the following manner.  When a pesticide is used to kill a pest, most of the pests are killed. Now, those remaining reproduce without competition.  That means that the survivors reproduce very quickly. Soon, a new population of pests results against which the pesticide is useless.  Then, new pesticides must be developed to kill these pests.  Often, the new pesticides are stronger and pose even more danger to the other animals that are higher up the food chain. 

Question 12. How do weeds reduce the yield of crops?

Weeds compete with the crop plants for water, nutrients, space, and sunlight.  The crop plants will not produce as much food because of the competition from weeds for important resources.  The result is decreased yield of the crop.

Question 13. What is the most destructive insect pest of potatoes?

The Colorado potato beetle is the most destructive insect pest of potatoes.

Question 2. Answer Reading Check in the middle of page 293 of your textbook.

When pesticides are first applied, not all the pests may be killed.  Those that survive are more resistant to the original pesticide, so new pesticides must be created to get rid of the more resistant strain of pests.

Question 3. Answer Reading Check at the bottom of page 293 of your textbook.

Several nutrients could be mentioned here, such as nitrogen, phosphorus, and potassium.

Question 4. Answer questions 2, 3 and 4 of Check Your Understanding on page 296 of your textbook.

2.    Because pesticides contain chemicals that can harm humans, they should be sprayed away from the eyes, kept away from food, and kept away from children and pets.
3.    These chemicals continue up the food chain so one animal may eat the plant and ingest the herbicide.  This herbicide may end up in the fat of this animal.  The animal that eats this herbivore then has the herbicide.
4.    DDT was very effective at controlling harmful insects; however, as it moved up the food chain, many beautiful birds were affected adversely by DDT.  Herbicides control weeds very well; however, they have been associated with cancer in humans.  The insecticide to control the potato beetle must be made stronger to combat the more resistant strains that develop.  Now, the question is whether pesticides should be banned.  There may be no easy answer.  For instance, suppose that a given pesticide allows a million more people to be fed but causes 100 people to get cancer.  What would you suggest?

 


Go to the next page to continue Lesson 1.