Class Notes Week 3 (Plants) (6)

Class Notes Week 3 (Plants) (6) - Week 3 TERMS AND EXAMPLES...

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Week 3 – TERMS AND EXAMPLES PLANT DEFENCES For 400 million years plants have been under attack from animals. Like an evolutionary arms race or ecological chess game, animals on offensive, plants on defensive 1) PHYSICAL DEFENCES Also called mechanical protection 1) body armour = tough epidermis ("outer skin") = bark and woody stems; trees, shrubs, strengthened with lignin; Vulnerable embryos are often housed inside seed coats fortified with lignin 2) other armour: structures that pierce - Physical or mechanical protection is often enhanced with nasty piercing structures Prickles are epidermal outgrowths: rose stems have prickles, raspberries and blackberries too Thorns are modified branches ; Honey Locust trunks and Hawthorn branches have thorns Spines are modified leaves on a thistle; most spines are dead with highly lignified cells ( sclereids ); thistles have spines Sometimes these are aposematically coloured; Automimicry might explain why rose buds look like prickles 3) Trichomes : small hooked or clubbed hairs = dense tangles impede small animals such as mites and small insects. Mullein leaves have very dense trichomes Some trichomes release sticky glandular secretions = glandular hairs or glandular trichomes One type - separately stored phenols and enzymes, when animal brushes them they break open, contents mix like epoxy, create
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Class Notes Week 3 (Plants) (6) - Week 3 TERMS AND EXAMPLES...

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