- african... · web viewthey are excellent plants for investigating specialised plant cells using a...

Specialised Cells in Amazing African Violets

Introduction

African Violets (Saintpaulia) are native to Tanzania and Kenya.

They are excellent plants for investigating specialised plant cells using a microscope as you are about to find out.

What you will need:

African Violet plant – preferably one in flower and with reddish undersides to the leaves

A sharp scalpel / razor Microscope slides Cover slips A microscope with x4 , x10 and x40 objective lenses A digital camera or mobile phone with a camera

Safety notes:

Take care when using scalpels / knives / blades. Cut in a direction down and away from your fingers. Glass cover slips are thin and break easily. Handle with care and always

clear away broken glass with a dustpan and brush rather than with your fingers.

Cells and structures that can be viewed:

Guard cells and stomata Hairs (trichomes) and the cells that make trichomes Trichome contents (and cytoplasmic streaming) Xylem vessels Petal Cells Pollen grains

Science & Plants for Schools: www.saps.org.ukAmazing African Violets

This document may be photocopied for educational use in any institution taking part in the SAPS programme. It may not be photocopied for any other purpose. Revised 2012.

http://www.saps.org.uk/

First: Take a look at an African Violet leaf

The leaves are covered in hairs called trichomes. The cells that make up these trichomes are easy to see under a x4 objective lens

Top of the leaf Underside of the leaf

Here’s how to see some specialised cells on the leaves

Take some thin slices from the underside of the leaf using a scalpel or a razor blade.

Mount the slices on a microscope slide in a drop of water and cover with a cover slip

Don’t worry about air bubbles, there will be plenty of other things to see




What you can expect to see

This image was taken through a x10 objective lens and x10 eye piece using an standard digital camera held to the eye piece

TrichomesThe hairs on the leaves are made of several large cylindrical shaped cells. This trichome is made of 5 cells

Stomata and Guard cellsGuard cells do not have any pink pigment unlike the cells around them. So they stand out as white against the pink background.

These yellow arrows above point to two stomata

Close ups of stomata and guard cells

Chloroplasts in the guard cells Bright green chloroplasts



This image below was taken throughthe x40 objective lensYou can see the chloroplasts in theguard cells

This image below was taken throughthe x40 objective lens with the optical zoom used on the cameraYou can see the chloroplasts in theguard cells


More about trichomes

In African Violets trichome cells are large. You can see their cells walls and contents very easily even at low magnifications

These trichome cells were taken down a x40 objective lens

Things moving inside the cells

Look carefully down the microscope using the x40 objective lens at one trichome cell.

Keep your eye focused on one part of the cell. Use the fine focus on the microscope to see grainy particles in the cell. Keep watching – if you are lucky you will see the particles move around the cell

Once you see this, keep adjusting the fine focus – you may be lucky enough to see new streams of particles move. Check out the video on the SAPS website if you want to know what to look for.

Look for movement of grainy particles in the trichome cells




Xylem

If you take a slice from the underside of a leaf, and across one of the leaf veins, you may be lucky enough to see some spirals of lignin in xylem vessels

You can also look at xylem in the leaf stalk (petiole)Both of these images were taken looking down a x40 objective lens

A thin slice was taken along the leaf stalk about 2mm into the tissue.

The microscope needle above is pointing to

a spiral of ligninSpiral of lignin in xylem Notice the chloroplasts as well!

Pollen Cells

Use a scalpel or razor blade to cut open one of the yellow anthers and sprinkle the pollen into a small drop of water on a microscope slide

Cover with a cover slip and look at the cells down a microscope




Petal Cells

Look closely at the petals and they seem to shine / be iridescent

Torn thin edge

Roughly tear a petal so that you obtain some thin tissue where it tears

This ragged torn edge can be looked at down a microscope

You will be surprised at what you might see

Trichomes

Xylem

Dome-shaped petal cells




Petal trichomesThis image was taken looking down a x10 objective lens

Notice that the trichomes have round ends

You may also see the cell contents moving – see the clip on the SAPS website of the cell contents moving in the cell labelled with an arrow

Petal cellsThis image was taken looking down a x40 objective lens

Notice the dome shaped cells

SAPS learned recently from Dr. Beverley Glover, Cambridge University, that this cell shape could have developed to allow insects to grip the petal with their feet more easily

Notice also the thick cell walls with iridescence. We also learned that this could be because there is a mirror-like structure to the cell walls

Acknowledgements

This resource was developed by Vicki Cottrell, Nuffield Teaching Fellow 2011-2012, and a biology teacher at Didcot Girls’ School.

All images by Vicki Cottrell.




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