Pests

• Aims• To study pests in the context of competition,

predator / prey relationships and pyramids of numbers and build up of toxins in food chains.

• To evaluate written text

Learning outcomes • By the end of the lesson • You should have/be able to • worked effectively on your own and in small groups to:• Use food chains and webs and pyramids to model the build up of

pesticides in food chains. (6)• Describe that the organisms living in a habitat compete with each

other (6)• explain that the numbers of a population of predators influence

the numbers of prey organisms• to evaluate conflicting evidence to arrive at a considered

viewpoint (7)

In pairs

Discuss the meaning of the words pests and pesticides, herbicide, fungicide and insecticide. (3 minutes to discuss the difference.)

Match the definitions (2 mins)

Copy correct definitions into your books

Food webs and chains

• Watch the video • Write down 2 key points

Discuss in pairs

• What is the potential impact of different slug control methods on food webs.

How It WorksThis product is a stomach poison which dehydrates snails after they eat the bait. The added taste deterrent is a bittering agent which prevents most cats and dogs from eating the pellets.

PrecautionsStore away from children and pets. Do not heap – it is wasteful and easy for domestic pets to collect. Dogs may find pellets attractive. If eaten, take to vet immediately. Read all safety directions including rear of pack. Dispose of empty container safely.Do not apply Blitzem Pellets to edible plant parts

•Environmentally friendly multi purpose pure wool pellets ideal for organic gardening.•The hygroscopic nature of wool fibres absorb some of the slimy substance underneath the slugs foot •The wool pellet barrier contains abrasive particles irritates and aggravates the slug‘s ‘foot‘

Food Chains recap.Draw a food chain for the organisms below

Pyramids of numbers

quick test

Pyramids of numbers represent the numbers of organisms at each stage in a food chain. Study the four pyramids of numbers A, B, C and D.

For each of the food chains choose the pyramid of numbers which best represents the food chain.

(i) grass → insects → spiders → birds (ii) oak trees → aphids → blue tits → sparrow

hawks (iii) grass → rabbits → foxes → fleas

Explain the difference between persistent and non-persistent pesticides and the concept of bioaccumulation.What does biodegradeble mean?

(Write definitions in your books if not done last lesson)

Page 148-149 may help

If DDT is banned, why is it still in some of the food I buy?

Work in a small group. Read the information on the cards.Then cut them out and sort them into the correct order to answer the questionthat is the title above.Once you have finished the card sort, discuss the following questionswith a partner.

1 Should poor countries be allowed to use DDT when it causes suchlong-term environmental damage?

2 Which is more important, to save lives by reducing malaria or to protecttop predators from a lethal dose of DDT?