Euglena and Paramecium are single-celled organisms with some animal-like characteristics. We will be observing these protozoans at x400 magnification in a sample of pond water. Locate the cell membrane, cytoplasm, nucleus, chloroplasts, ‘eye’ spot and flagellum in a Euglena. Is Euglena autotrophic (‘self feeding’) or heterotrophic (‘other feeder’)? In Paramecium, locate the cilia, cell membrane, cytoplasm, food vacuoles and nucleus. Some of the Paramecium have been placed in a medium with yeast cells, which have been stained with congo red indicator. Are the Paramecium autotrophic or heterotrophic?
Photosynthesis and cellular respiration are ‘opposite’ reactions in the carbon cycle – one is endothermic (requires the input of energy) and one is exothermic (releases energy). Once you have read Chapter 3 and answered the chapter review questions, watch these videos and test your understanding by completing the “Photosynthesis/Respiration” worksheet. Whereas photosynthesis occurs only in the chloroplasts of plants, cellular respiration occurs in the mitochondria of both plants, fungi and animals. You will need to know these biochemical processes in a good deal of detail for the exam.
The Gene Technology Access Centre have some excellent resources for VCE Biology, including this slideshow and activity sheets “exploring protein structure“. The image above is one view of a representation of the enzyme amylase, which breaks starch down into sugars. You can see the green alpha-helices, yellow beta-sheets and blue random coils in the secondary structure of this protein. You may also be able to see the ‘co-factors’ or molecules which assist at the active site of this enzyme. Amylase relies on the co-factors calcium and chloride to function efficiently. What are the dietary sources of calcium and chloride?
View the GTAC Bioinformatics Task 4 Presentation and then complete student worksheets #1 and #2. You will need to download the Cn3D software to view the interactive protein molecules.
Learning Intention: Students will understand that enzymes are proteins and biological catalysts that speed up chemical reactions in living organisms. They will also understand two of the factors that affect the action of enzymes, temperature and pH.
Success Criteria: Students will be able to design, perform, describe and report on an experimental procedure demonstrating the effect of temperature and pH on enzyme activity.
Students used potato, alfalfa sprouts and liver extract (most successful) to demonstrate how catalase (enzyme) breaks down hydrogen peroxide (H2O2) into water and oxygen. This process is essential to maintain a safe and healthy internal environment. When hydrogen peroxide was added to the liver extract and different concentrations of HCl (distilled water, 0.01M, 0.05M, 0.1M, 0.5M and 1.0M hydrochloric acid), only the distilled water and 0.01M HCl tubes released significant quantities of oxygen. At higher acid concentrations (lower pH) no enzyme activity was apparent, because the acid destroys the protein or denatures the enzyme.
Diastase is an enzyme that catalyses the conversion of starch (polysaccharide) into sugars (di- and mono-saccharides). Iodine is an indicator that turns from yellow to blue-black in the presence of starch. Students used two sets of five test tubes with 10 ml of starch solution in each. In the control set, distilled water was added to to each test tube. In the second set, the enzyme diastase was added. One tube from each set was then placed into water baths at different temperatures (room temp, 40C, 60C, 80C and 100C). Iodine was used to indicate which tubes contained active enzyme. If the tube contained starch, the colour was blue-black, indicating that there was little or no enzyme activity (control tubes). The lighter the colour, the greater the conversion, therefor the more enzyme activity. The tubes at room temperature, 40C and 60C showed the most enzyme activity.
In Year 11 we will be concentrating on passive transport across cell membranes, diffusion and osmosis. In Year 12 we will learn more about active transport across cell membranes, which requires the cell to use energy (ATP). There are various forms of active transport across membranes, including:
exocytosis (out of the cell)
endocytosis (into the cell)
phagocytosis (solids, like bacteria or other foreign materials)
pinocytosis (liquids)
Today in Year 11, we completed an experiment using cores of potato in several different concentrations of sugar solution. Weighing the potato discs before and after the experiment, we expected the samples placed in distilled water would increase in mass (due to water moving into the cells by osmosis) and the samples placed in concentrated sugar solution would decrease in mass (due to a net movement of water out of the cells). We also used microscopes to observe thin sections of rhubarb, demonstrating how the cell membrane shrinks away from the cell wall when placed in concentrated sugar solution.
In Year 12, we took identical cores of beetroot and placed them into distilled water in test-tubes in water baths of different temperatures (frozen beetroot core, room temperature, 50C and 70C). After 30 minutes, the beetroot cores are removed and the colour of the remaining water is observed. From this, you can infer that the damage to the cell membrane at 70C is greatest, because the greater amount of pigment has been released from the beetroot cells, giving the water a darker pink colour. Some pigment was also released from the frozen core and at 50C, indicating that the cell membrane has ruptured.
