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An ib biology sl experiment investigating the impact of temperature on the permeability of beet root cells. Students will study how environmental stresses affect the membranes, leading to betacyanin leakage and color change. The objectives include describing temperature's effect on permeability and relating membrane structure theory to observations.
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IB Biology SL Performed: Due:
Permeability of a cell to solutes in an aqueous solution depends upon the physical and chemical make-up of the membrane. The maintenance of the living cell depends upon the continued presence and functioning of a selectively permeable membrane. If the nature of the membrane is altered in any way, this may affect it’s permeability and thus the properties of the cell of which it is a part. Irreversible changes in the permeability of the membrane usually lead to the death of the cell. In this experiment, we will study the effects of changes in the environmental conditions on the permeability of living beet root cells. Roots of beet ( Beta vulgaris ) contain large amounts of a reddish pigment called betacyanin , localized almost entirely in the large central vacuoles of the cells. Betacyanin in healthy cells remains inside the vacuoles, surrounded by a vacuolar membrane called a tonoplast. The entire cell is surrounded by a cellular or plasma membrane. Environmental stresses can damage the membranes, allowing betacyanin to leak through the tonoplast and plasma membrane. This leakage of betacyanin will produce a red colour in the water surrounding the stressed beet. Thus the degree of membrane damage can be determined by monitoring the intensity of the colour leakage resulting from a treatment.
By the end of this investigation the student should be able to:
Purpose : (2 marks) Hypothesis : (2 marks) Materials and Apparatus : (each group needs the following) 20 test tubes 2 - 250 ml beakers 1 thermometer 1 test tube holder 1 – 50 ml beaker 4 – 400 ml beakers 2 test tube rack beets 1 - 10 ml pipette 5 thermostatic water bath scalpel glass stirring rod safety goggles watch/clock colorimeter tap water 2 cuvettes GLX data recorder Procedure : [Refer to the procedure below and make note of changes only] (2 marks) Preparation of Beet Root Sections With the aid of a scalpel, remove both top vegetative potion and the base of a beet root (See Figure 1). Carefully bore out several cores of beet root tissue using a cork borer. Use a scalpel to slice the cylindrical cores into 5 mm sections. You will need a total of 3 sections for each temperature used in the lab. (Make every effort to cut the sections accurately). All of the sections should be placed in a beaker of distlled water at room temperature to remove the betacyanin from the injured cells on the surface. Note:. There will be 5 water baths set at different temperatures ( room temperature ( ___° C), 30° C, 40° C, 50°C, and 60 ° C ). Work in groups of 5. One or two members of each group will be responsible for for cutting the beet discs while the others will measure 10.0 ml of distilled water at the appropriate temperature into the labelled test tubes used. Two labelled test tube (2 trials per day) are placed into each of the 5 water baths for each group. Be sure that you can identify your groups test tubes