Monthly Archives: March 2009

Revision of Unit 1: Area of study 1: Cells in Action

Use My Studiyo to create your own quiz to revise one of the following concepts:

  • Types of cells (prokaryotic, eukaryotic, plant, animal, bacterial)
  • Mitosis
  • Structure and function of cells
  • Biomacromolecules
  • Photosynthesis and respiration
  • Transport across membranes

Make sure you have at least ten questions.

Extract DNA in the science classroom

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No, it’s not a stawberry cocktail! Did you know that you can extract DNA using simple kitchen equipment and readily available materials? The CSIRO has some great biology experiments, including this one to extract DNA from onions. You could also use kiwi fruit, dried peas, banana, liver or strawberries.

You can see the fine, white strands of DNA on the toothpick. During mitosis, these strands condense and become more visible in the cell (especially when a stain is used like in the image below). The amount of chromatin (DNA or nuclear material) varies between species.

Mitosis in a Lymphoma Cell

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This week we are starting Chapter 4: Cell Division. On Friday we watched a Clickview video showing the process of cytokinesis and mitosis, which included a discussion with a cancer surgeon about the types of treatments (chemotherapy and radiation) used to prevent cells dividing and multiplying, as they do in tumours. All living organisms undergo cell division – in unicellular organisms (such as bacteria and yeast) it is how they reproduce. In multicellular organisms, cells divide and multiply for growth, repair and maintenance.

Certain tissues, such as root tips and bone marrow, actively grow and divide and it is relatively easy to find cells undergoing mitosis. We will look at some prepared slides to see the different stages of mitosis – prophase, metaphase, anaphase and telophase – and cells in which the chromatin is not visible (interphase).

Download and print a Mitosis worksheet here.

Another Mitosis worksheet here.

Introduction to Mitosis worksheet here. (Horton)

Animal cell mitosis video at Cells Alive.

Introduction to cell division – Bio 121

Corny cell mitosis video with a dance and rap song on Google Video.

The Cell Cycle and Mitosis Tutorial from The Biology Project

NOVA Online – Mitosis vs Meiosis interactive

McGraw-Hill – Mitosis and Cytonkinesis animation with commentary

What do bread and ginger beer have in common?

They are both made with yeast (Saccharomyces cerevisiae) – a living organism that produces ethyl alcohol and carbon dioxide when allowed to grow in suitable conditions. This is an example of anaerobic respiration, or fermentation, which produces a small amount of energy (ATP) compared to aerobic respiration. An animation of the process of ATP production during fermentation is here.

In bread making, the carbon dioxide gas is captured in a gluten matrix produced by working the flour together with water into a dough. When the dough is baked, the yeast is killed, the small amount of alcohol evaporates and the carbon dioxide produces a light, fluffy loaf of bread. More about the science of bread making here.

When making beer, sugar is added to ‘feed’ the yeast and carbon dioxide bubbles are produced, along with a small amount of alcohol (less than 0.5% in the bottle we will produce). The lemon juice and ginger added to homemade ginger beer is for taste.

Anaerobic vs aerobic respiration

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If you choose to study microbiology at University, you may be involved with experiments such as this, working in an anaerobic chamber. When you exclude oxygen from the environment, respiration takes place anaerobically – without oxygen. Read more here. Anaerobic respiration is used both in the brewing and baking industries, as alcohol and carbon dioxide are produced when specific organisms respire without oxygen. This is called fermentation. If you have access to YouTube, you can see a quick Food Science video about fermentation here.

This site, from Thomas M. Terry of the University of Connecticut, has some excellent, very detailed animations of cellular respiration. Chapter three also deals with enzymes – proteins that accelerate biological reactions. It is important to remember that enzymes are not reactants or products of a reaction – they are not ‘used up’ during the process. Enzymes facilitate, or speed up, a specific reaction. For a good tutorial check out: “What is an Enzyme?”.

Beetroot and cell membranes

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What’s beetroot got to do with cell biology? Well, today we did a practical experiment to investigate the effect of temperature on the plasma membrane of beetroot tissue. Why beetroot? Because it is relatively easy to identify the amount of damage to cell membranes by observing the pigment leakage from the tissue. We used four 5mm x 15mm cylinders of beetroot and four different treatments – room temperature (control), freezing overnight, 50 degrees Celcius and 70 degrees Celcius for 2 minutes each. Then each sample was placed in a test tube with 5 ml of water. What did our results show?

One of the questions in this practical asks why some people put hessian bags over their garden plants in winter and how some plants can survive freezing temperatures. Hessian bags can help to insulate plants against the effects of freezing – some wineries use large fans to keep air circulating over their crops for the same reason. Some plants are genetically more tolerant of frost. This article, from the CSIRO, describes how some plants can empty water out of the cell into the extracellular spaces, where the water can form ice without damaging the cell membrane. Another method is increasing solute concentration, for example by storing monosacharides in place of disacharides, which effectively lowers the freezing point of the cell contents. This is a bit like using anti-freeze in the car radiator during winter.

Revision questions (with answers!) for cell membranes at Biology-Questions-and-Answers.