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Asia-Pacific Forum
on Science Learning and Teaching, Volume 10, Issue 1, Article 3
(June, 2009) |
To be able to compare the effect of the pre-knowledge on the capability of making meaning of the visualizations, three groups of students were selected; students from an upper secondary school in a medium-sized town in southern Sweden, and university students from the same region. The upper secondary students participating (n=20) came from two upper secondary schools and were in the second (grade 11) or third (grade 12) year of their education. All upper secondary students were studying a natural science program or a combined natural science/social science program. The upper secondary students had studied various combinations of natural science courses, and consequently differed in their pre-knowledge to a relatively high degree. The university students (n=35) were in their first or third year of their tertiary education, studying chemical biology and had a relatively similar background knowledge. Our goal in the study was to choose students representing all levels of achievement (based on their grades in natural science subjects). However, since only a small number of students in each class volunteered to be interviewed, high-achieving students came to be over-represented in the study.
The scientific content of the visualizations used in the study
The following paragraphs describe briefly the content presented by the visualizations used in the study, all of which are highly simplified representations of proteins illustrating common functions of proteins rather than their structure.
The first diagram shows a cross-section of a cell membrane. The cell membrane consists of a bilayer of phospholipids, each of which has a polar part (which collectively forms the inner and outer surfaces) and a non-polar part (which constitutes the interior of the bilayer). The phospholipid bilayer also contains other molecules, primarily proteins. The membrane functions (inter alia) as a barrier that protects the interior of the cell from its surrounding environment. Small, uncharged molecules can readily move through the membrane without aid (via ‘passive transport’), while charged and large molecules are ‘locked out’. However, appropriate metabolites must be taken in and waste products removed. Much of the complex structure of biological membranes is therefore involved in the regulation of transport. In the visualization, three proteins acting as channels or pumps are shown in red. Through proteins such as these, various substances flow into or out of the cell in a controlled manner. The leftmost protein acts as a channel that facilitates transport of a substance (shown in grey), that diffuses in the direction of its concentration gradient. The middle protein allows transport of specific molecules, also in the direction of their concentration gradients, and the protein to the right transports a substance against its concentration gradient, in an energy-consuming process that is coupled to the breaking of energy-rich bonds in ATP molecules (‘active transport’).
The animation (http://nobelprize.org/chemistry/laureates/2003/animations.html) shown both in interviews and in individual exercises and group discussions visualizes the facilitated transport of water through a specialized channel protein, a so called aquaporine. The animation depicts the dynamic and random movement of the water molecules and provides an image of the large number of molecules that are constantly interacting.
The second diagram shows the process of protein synthesis in the cell. The process starts with the transcription of DNA into three types of RNA, which occurs in the nucleus (shown in blue). All three types of RNA are transported out of the nucleus, through the nuclear envelope, and out into the surrounding cytoplasm. The messenger RNA (mRNA) molecule (which carries the code for the corresponding protein) binds to ribosomal subunits which form a ribosome (shown at the right hand bottom of the picture). The other two types of RNA also have functions in the protein synthesis. The ribosomal RNA (rRNA) (shown to the right of the mRNA molecule), is an important constituent of the ribosomal subunits together with certain proteins, while transport RNA (tRNA; shown at the top of the picture) transports the various amino acids to the ribosome. There are multiple species of tRNA, each of which has an ‘anticodon’ (in the case shown three bases shown at the top of the molecule), which are uniquely matched to a specific amino acid. The tRNA molecules bind to the mRNA molecule in the ribosome in an order specified by matches of the sequence of bases in the mRNA to the tRNA’s ‘anticodons’. The amino acids so transported to the ribosome are connected to a growing polypeptide chain, which eventually forms a functional protein. The synthesis of proteins from mRNA is called translation. The information contained in the DNA is hereby expressed in proteins, with mRNA acting as an intermediary.
