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Unit 1 and Unit 3 Biology Exam Revision

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There are several strategies you can use to revise for mid-year exams – here are just a few:

  • Use the Hawkesdale Biology Quizlet Class to revise terms and definitions for each chapter
  • Copy and revise the Slideshows I have saved in the Year 11 and Year 12 Biology class folders (Student Public Drive)
  • Create a set of study notes with the Chapter headings, diagrams and key concepts. These will be very useful at the end of the year for revision too.
  • Create mind maps that link each of the main concepts – use colour to help you remember.
  • Use the posts in this blog to review YouTube videos and other resources for each chapter.
  • Past exams are a good indication of the standard of questions you will be asked – do as many as you can reasonably cope with! Use questions you find difficult as a guide to what you need to study more of.
  • Create flow charts and posters for the wall at home of concepts that can be represented diagrammatically.

“Body at War” at Federation University, Ballarat

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On Friday 17th April, four VCE Biology students attended the “Your Body at War” program, facilitated by the Gene Technology Access Centre at Federation University. Kiri, Leah, Che and Stephanie travelled to Ballarat to participate in the program, which celebrates the “Day of Immunology”.

Together with about 100 students from three other schools, they had the opportunity to hear from Associate Professor Robyn Slattery (Monash University) about the history of vaccination, current research in immunology and exciting new discoveries about immunotherapy in cancer treatment.

They then donned lab-coats and entered the science laboratories at Federation University, where they learned how to use specialist equipment and techniques, such as the Enzyme-linked Immunosorbent Assay (ELISA). They also had the opportunity to discuss career perspectives in science with staff and Dr Misty Jenkins from the Peter MacCallum Cancer Centre.

One of the sponsors of this event is the Walter and Eliza Hall Institute of Medical Research. Later this year we have three Year 11 students who have been very fortunate to obtain a work experience placement at WEHI in Melbourne. This is an exciting opportunity for them to find about authentic medical research, working with expert scientists in a world-leading facility.

Also in science news, students in Year 10 have the opportunity to attend the Science Experience Ballarat, at Federation University from 29th June to 1st July. This three day, hands-on program is a great introduction to the diverse world of science and it’s connection to a range of interesting careers. Please apply online prior to 8th June. Speak to Mrs Gow for further information.

Photosynthesis by video conference from GTAC

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GTAC – Introduction to Photosynthesis on YouTube

GTAC – Photosynthesis – Light Dependent Cycle and an Animation showing six cycles of the Light Independent Cycle on YouTube

Tony, from GTAC, demonstrated a photosynthesis experiment in which equal quantities of spinach leaves were placed in four clear, closed containers. Each container was subjected to light of the same intensity, but one had no filter (control) and the other three were wrapped in coloured cellophane (red, blue and green, as shown above). The coloured cellophane filters out different wavelengths of light, so the red cellophane reflects red wavelengths and allows other wavelengths to pass through. Each container had two probes, measuring oxygen and carbon dioxide concentrations in parts per million (ppm). What would you expect to happen in the cellophane-covered containers compared to the control?

Tony was also able to answer two questions that students have about DNA transcription.

(1) Where does the mRNA molecule go after transcription? “A single mRNA can be translated many times by ribosomes into polypeptides (it’s one way a cellular response dependent on gene expression can be amplified).  After that mRNA is degraded, releasing individual nucleotides which can then be recycled into new mRNA.  In eukaryotic cells, the mRNA is protected by the 5’ methylguanosine cap and the 3’ poly-A tail.  When these are removed from the ends, presumably in response to an intracellular signal that says the mRNA is no longer required, the mRNA becomes susceptible to degradation.”

 (2) When and where does transcription occur? “I would say transcription (the process by which the mRNA is first made from DNA template) occurs in the nucleus of eukaryotic cells almost continuously but the genes being expressed change throughout the cell cycle and in response to stimuli.  For example, genes relevant to growth may be transcribed during G phases.  A special set of genes relevant to DNA synthesis are transcribed during S phase.  If a (stem) cell received a differentiation signal, a relevant set of genes would be switched on for differentiation into a particular cell type.  I would say the only time transcription ceases is when the chromosomes condense for mitosis and cytokinesis.  Essential proteins are still around to ensure cell division proceeds as intended.  After cell division and the chromosomes de-condense, it’s back to business as usual.”

Thanks Tony for these valuable extensions to our Year 12 Biology program at Hawkesdale P12 College.

Mitosis and cytokinesis

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Image source

When cells divide during mitosis, each daughter cell contains an identical set of chromosomes to the parent cell. How can this occur? Watch these animations to find out:

The Cell Cycle includes these five phases of Mitosis and Cytokinesis:

  • Interphase (chromosomes not visible – replication of DNA)
  • Prophase (chromosomes begin to condense)
  • Metaphase (chromosomes line up along the middle of the cell)
  • Anaphase (spindle fibres begin to draw chromosomes apart)
  • Telophase (Chromosomes are separated into chromatids and two new cells start to form)
  • Cytokinesis (Cell cleaves apart and nuclear membranes form)

Mitosis Worksheet

Energizing Cells

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Image from GTAC

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?

Euglena on YouTube and Euglena – flagellum movement in phase contrast on YouTube

Paramecium on YouTube and Paramecium eating pigmented yeast cells on YouTube and Amazing HD video of a Paramecium eating.

Effect of Temperature and pH on Enzyme Activity

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.

 

Transport across Cell Membranes

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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.