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?
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)
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.
These are 18th century microscopes from a museum in Paris. Today we have much more sophisticated technology that allows the human eye to observe organelles within cells, viruses and even smaller objects. In the classroom we have light microscopes that allow light to shine through a thin section of tissue or groups of cells and stereo microscopes for observing whole specimens (small flowers, insects and three-dimensional objects). At high magnifications (100x), oil may be used to reduce the loss of light due to refraction, which increases the clarity of the image. In universities and research laboratories you may find more powerful microscopes, such as transmission or scanning electron microscopes. Phase contrast and fluorescence microscopes can also be used to observe different features within cells.
In this double lesson we will learn the different parts of the light microscope, observe plant and animal tissues and measure cells and some organelles within cells. Refer to Activity 1.2 and 1.3 in your Activity Manual.
Unit 3: Area of Study 1: Molecules of Life (Year 12)
In our first week of Year 12 Biology we the chemical nature of cells. All living matter is made up primarily of carbon, hydrogen, oxygen, phosphoros, sulfur and nitrogen (CHOPSN). These elements are combined into compounds, with the four classes of biological macromolecules being carbohydrates, lipids, proteins and nucleic acids. Which are which in the diagram below?
With about five weeks until the final end-of-year examination for VCE Biology on Friday 31st October (9.00am to 11.45am), you still have time to prepare an effective study timetable that will assist you to achieve your best result. It is important to balance your commitments at this time of year and avoid getting stressed and anxious, because that won’t help your revision process. You may like to consider some of the following ways to support your exam revision:
Much of your success in this subject will depend on your knowledge of scientific terms, definitions and concepts and how to apply these concepts in new situations. Spend some time identifying key knowledge in each Area of Study, perhaps using the Exam Revision Audit I sent around recently. I have sent a link to a collaborative Google Document for you to complete a specific section, so that the whole class will have a set of online study notes. Please add some information about the concept, an example and a link to more information for each term.
Quizlet is an online tool where I have created sets of terms and definitions for each area of study. You can use these Quiz sets in different modes (Learn, Flashcards, Scatter, Quiz etc) and edit them to add your own terms.
Mindmaps are great to connect different terms and concepts. Create your own using lots of colour to group ideas. Try completing this mindmap about the evidence for evolution. The benefit for learning is in creating your own – the colour and movement stimulate your brain to remember the text. You can also create them online using Bubbl.us and other free software.
Slideshare is an enormous resource with many of my teaching resources uploaded. You can find slideshows on almost any topic and there are several specifically for VCE Biology revision.
Past Exams are available on the VCAA website, but be aware that there is only one example (2013) of the current format – (120 minutes) with 30 multiple choice questions (worth 1 mark each) and 90 marks worth of short answer questions. Keep working hard and contact me by email, Twitter (@brittgow) or phone if you need assistance.
Humans have had an influence on evolutionary processes for much longer than you may have thought – we have tamed wolves and wild cats to become the many breeds of domestic dogs and cats that share our homes today and we have selected cattle, sheep, goats and pigs over many generations for food characteristics. Our main food crops such as rice, corn, wheat, as well as many fruit and vegetables, are very different to their wild ancestors.
Artificial selection, or selective breeding, is the process by which humans breed other animals and plants for particular traits; for example, increased size, fast muscle growth or sweeter taste. This can be a deliberate process, like when farmers choose to breed animals or plants with particular characteristics or it can be accidental. In Asia and Africa, over many centuries, bull elephants with particularly large tusks have been targeted as trophies and for their valuable ivory. As a consequence, individuals with large tusks produce fewer offspring and become less frequent in the population. (Read more about elephant evolution here and here).
In more recent times, due to greater understanding of genetic inheritance and modern gene technology, we have been able to identify specific genes that code for particular characteristics and create new breeds of organisms with beneficial traits – drought tolerance, increased productivity or improved storage life, for example.