Clarification details
Updated February 2014. This clarification has been updated to address issues that have arisen from moderation.
The intent
The intent is for students to investigate biological material at the microscopic level by preparing biological material for viewing (two different plant tissues and one unicellular organism), viewing this using a light microscope to enable detail of cell structures to be determined and recording observations of biological material in three biological drawings.
At Achievement
At Achievement, the student identifies observed specialised features and relates them to the function of the cells or tissues, e.g. in identifying guard cells in a leaf epidermal tear of a named plant, a feature could include their thickened cell walls alongside the stoma.
At Merit
At Merit, the student gives reasons for how or why observed specialised features enable the cells to effectively carry out their specific function(s), e.g. “When guard cells absorb water from surrounding epidermal cells by osmosis and become turgid, they change shape to open the stoma because of the thickened cell walls along the stoma, and allow gas exchange.”
A ‘Class Result Sheet’
A ‘Class Result Sheet’ listing individual performance, identifying specific microscope slide preparation and viewing criteria for each slide, must be submitted for moderation.
Biological drawings
Biological drawings are based on the slides prepared and viewed by the student, rather than on pre-prepared slides and/or projected images of cells or tissues. Teachers need to have seen the student’s specimens during drawing as plant cells can show quite significant phenotypic plasticity.
In judging a biological drawing there is a need to distinguish between errors in conventions and representational errors.
Conventions
Conventions (the accepted guidelines) for biological drawings include:
- an appropriate title that identifies the biological material used
- the magnification used e.g. x 10 x 40 = x 400
- a pencil drawing
- using clear bold lines, no lines crossing over
- having no shading/cross hatching/stipples
- having no gaps between cells
- components or organelles correctly identified by labels.
Consistency of observations or representation
Consistency of observations or representation (i.e. accuracy) includes the:
- cells having a recognisable shape and proportions
- inclusion of typical organelles present in a cell, as seen using a light microscope.
Notes about the specialised features
Notes about the specialised features may be annotated on the drawing or be written out separately. Choosing relatively unspecialised cells, without the use of staining, may make it more difficult for students to achieve at Merit when they need to give reasons for why or how each feature effectively contributes to the function of the cell or tissue.