Adaptations of plant leaves




Дата канвертавання20.04.2016
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Adaptations of plant leaves


Teaching and technical notes

In this activity students investigate a selection of plant leaves to discover how they are adapted to deter herbivores.


The leaves suggested are generally easy to get hold of in the school grounds or the lab. Some (e.g. holly, ivy and geraniums) will be available throughout the year, while others (e.g. nettle, dock) will not be widely available in winter.
Part 1 can be carried out using only the photos of the plants, as supplied in the accompanying image sheet. If leaves are available, students can also examine those.
Part 2 requires a variety of plant leaves, as available. At least one of these should contain acid (as shown in the table below).
Part 3 requires nettle leaves and dock leaves.

Safety notes
Check for allergies to the leaves involved.
Students should be careful when handling leaves with prickles, spines and stings. We recommend using Marigold gloves or similar, rather than using ordinary latex lab gloves.

Part 1 – Visible adaptations of leaves
Students begin by looking at the visible adaptations of leaves, as shown in the photos, and fill in the table below. If you have the actual leaves available, students can look at those instead, taking care to wear gloves.

Table of plants and leaf adaptations



Leaf

Has sharp prickles or spines

Has stings


Contains acid


Other

Holly

x










Ivy










X (waxy cuticle prevents excess water loss and protects against bacteria and fungal attack)

Geranium







x




Grass










x (low meristem – see ‘answers’ below)

Nettle




x

x




Dock







x




Thistle

x











Plant adaptations – answers
Name a plant with prickles……………holly or thistle………………………….
How does this adaptation help the plant to survive? .........The prickles make it difficult for herbivores to eat the leaves...........................................................
A geranium has very soft leaves. What adaptation does it have to deter herbivores?

…………The leaves contain a large amount of acid which makes it taste unpleasant to herbivores……………………..……………………………..

Why does the nettle have hairs/stings? …………………………………………..

…………To deter herbivores by giving them a painful sting……………………



Extension: Grass does not have sharp spines, stings or contain chemicals to deter herbivores. What adaptations does it have to help it survive rather than being destroyed by grazing animals?
Grass has a very low meristem (zone of the plant where growth can take place) which means it can regrow even if the leaves are grazed by herbivores.


Part 2 - Investigating the pH of plant material
In part 2, students look at the pH of various different leaves. The table of adaptations above indicates which will be find to contain acid.
Apparatus

Full details of the method are given in the student sheet.



Part 3 - Investigating Nettle Stings and Dock Leaves
In part 2, students use Universal Indicator paper to look specifically at nettle stings and dock leaves. In particular, they will consider why dock leaves are traditionally used as an antidote to nettle stings.

Stinging nettles have developed stinging cells as an adaptation to deter herbivores from eating them. The plants contain long, thin, hollow hairs that cover the majority of the stem and the underside of the leaves.

Nettle stings contain acid (formic acid) but they also contain histamine and other chemicals. The exact details are still unknown but it is the histamine that causes the initial reaction when you are stung.

Dock leaf sap contains a natural antihistamine, which helps to ease the stinging sensation. The dock leaves themselves contain oxalic acid, which deters herbivores from eating them.

More images of nettle stings are available from the SAPS Image Collection: http://www.flickr.com/photos/71183136@N08/sets/

Apparatus


  • gloves

  • microscope

  • slides

  • plastic cover slips (small pieces of clear plastic such as acetate can be used if plastic cover slips are not available)

  • Universal Indicator solution

  • Universal Indicator paper

  • nettle leaves

  • dock leaves

  • equipment for pH testing, as in Part 2 (unless students have already tested dock and nettle leaves for their pH)

Full details of the method are given in the student sheet.


Stinging hairs on a nettle leaf A piece of damp universal indicator paper that has been pressed against a nettle leaf. Yellow spots show where acid has been released from the stings.

Science & Plants for Schools: www.saps.org.uk

Adaptations of plant leaves – teacher sheet: p.


This resource may be photocopied for educational use. Revised 2012.




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