Biological Drawings

The CIE AS and A Level Biology (9700) Advanced Practical Skills paper usually requires students to make observations of a photograph or specimen – which will often be on a microscope slide – and to record their observations as a diagram or drawing. A biological drawing looks simple and uncomplicated but it is imperative that students are provided with clear steps to success, lots of WAGOLLs, and plenty of opportunities to develop this important skill throughout the course.

A good biological drawing should:

  • have clear single lines (no ‘fuzzy’ or ‘feathery’ lines)
  • show an accurate overall shape and proportions
  • not include shading or colouring (even the nucleus!)
  • be large, using up most of the space provided but not going outside that space.

Students should use a sharp HB pencil and a good eraser. A ruler should only ever be used for drawing label lines.

Low-power plan diagrams

root 1

This type of diagram only shows the outlines of the different tissues. It should never show individual cells. Students may be familiar with the specimen (e.g. a cross section of a root or stem) but it is important that they only draw what they can see and not what they think they should see. Encourage students to look carefully in order to determine where one tissue ends and another one begins (look for differences in cell shape, size, densities and degree of staining).

For a low-power plan diagram of a microscope slide, CIE require that students are provided with a microscope with a x10 eyepiece lens and low-power objective lens (x10). An eyepiece graticule should also be fitted within the eyepiece and should be visible in focus at the same time as the specimen.

For a low-power plan diagram:

  • do not draw individual cells
  • draw all tissues completely enclosed by pencil lines (no gaps or crossed lines)
  • draw an accurate interpretation of the distribution of the tissues (the eyepiece graticule can be used without calibration to help draw the correct proportions).

High-power diagrams

high power 1

A high-power diagram generally does show individual cells. For a high-power diagram of a microscope slide, CIE require that students are provided with a microscope with a x10 eyepiece lens and high-power objective lens (x40).

For a high power diagram:

  • draw only a few representative cells
  • draw the cell wall of all plant cells (usually as a double line)
  • do not draw the nucleus as a solid blob (this is a particularly common error).

Labelling diagrams

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A ruler should always be used to draw label lines. The label lines should stop exactly at the structure or tissue that is being labelled. A sharp pencil should be used for all label lines and labels.

Workbook

Here is a workbook with checklists (self or peer) that I have produced to help AS and A Level Biology students with their biological drawing skills.

 

 

 

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Squishy Circuits – Electrical Play Dough

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A wonderful idea from the Playful Learning Lab at the University of St. Thomas in Minnesota.

Play dough is a semisolid which contains salt and is naturally electrically conductive. However, replace the salt with sugar and the play dough becomes an insulator! Both can be made easily and cheaply using flour, vegetable oil, water and salt or sugar. Students can then roll the dough into ‘wires’ or build more elaborate shapes into which they can then connect components. Great fun!

The recipes in metric units are available here.

The Squishy Circuits Classroom Guide contains the recipes as well as basic instructions and sample worksheets. There are also lots of fun ideas for using squishy circuits in electronics education on the Tinkering Studio website.

Allopatric Speciation in the Lower Congo River

Central Africa’s Lower Congo River is home to an extraordinary assortment of fish—many truly bizarre. This  video by Science Bulletins, the American Museum of Natural History’s current-science channel, features Museum scientists on a quest to understand why so many species have evolved there. It provides an excellent case study of allopatric speciation and helps to dispel the myth that populations only ever become isolated on islands. A Google Form worksheet to accompany the video is available here.

Modelling Genetic Drift with M&Ms

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Genetic drift is defined as random changes in allele frequencies in a population. It occurs in all populations that are not infinitely large and has a particularly strong effect on small populations over several generations. Because genetic drift is a random rather than deterministic process like natural selection, students often have a difficult time understanding and appreciating its role in evolution.

This simple exercise offers an active learning approach by simulating the founder effect and bottleneck effect (two examples of genetic drift) using M&Ms. A worksheet with full instructions, examples of discussion questions and data sheets is available to download in full from here.