Tag Archives: experiments

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.


Mitosis – Cell replication

mitosis in an African globe lily endosperm

Photo Source

This week we have started Chapter 4: Cell Replication, looking at how cells divide for growth, maintenance and repair. Watch the Cells Alive animation that shows the four stages of Mitosis – Prophase, Metaphase, Anaphase and Telophase. The in-between phase is Interphase, when the chromosomes are not visible. What stage is shown in the electron micrograph above? How can you tell?

This site, at NOVA Online, shows how mitosis and meiosis compare. The McGraw-Hill site also has a good animation showing mitosis and cytokinesis (division of cytoplasm and formation of two separate cells).

The most recent edition of New Scientist has an interesting article about how bone cells form –  bone marrow cells can be induced to form bone, fat or blood depending on chemical and physical cues. In an experiment performed at the University of Chicago, scientists induced bone marrow cells to form bone cells in angular moulds (star-shaped or rectangular) and fat cells in curvy moulds (circles and flower shapes).

Effect of Temperature on Plasma Membranes

beetroot prac large

Test Tube D (added later than others), Test tube C, test tube B and test tube A

The prac was aimed to show us the effect of different environmental temperatures on a plant plasma membranes.

Test tube A contains a beetroot core placed in 70 degree celcius water,

Test tube B contains a beetroot core placed in a 50 degree celcius water,

Test tube C contains a beetroot core placed in  room temperature water,

and test tube D contains a beetroot core, frozen overnight and then placed in water.

We found that treatments to Test tube A and D had the most  effect on the beetroot core. This is because the temperatures ruptured membranes allowing the red pigments inside the beetroot core to escape! The hotter or colder the temperatures were, the more membranes burst and more colour was released. The colour is contianed in plastids within the cell membranes of the beetroot.

Brilliantly written by Year 11 VCE biology students,

Chloe Wood the fantastic and Emily Huglin the awesome!

Rat Dissection

Source: Biology Online

This Wednesday afternoon we will be dissecting laboratory rats, which are specially bred for scientific purposes. This practical exercise is optional, but an excellent way to gain scientific skills of careful observation, identification of body parts and an understanding of the structure and function of the digestive system of mammals. If you plan to continue your science education at university, you will find this a valuable introduction to laboratory dissections. Make sure you read the practical instructions thoroughly, work slowly and carefully and document your progress with video or a digital camera. Remember that ‘dissection’ does not mean ‘to cut up’, it means ‘to expose to view’ – once something has been cut, it can’t be undone, so know what organ or tissue you are cutting and why.

Rat Dissection – Part 1: Exposing the Abdomen

Rat Dissection – Part 2: The Digestive System (Warning – graphic images)

Rat Dissection – Part 3: Identifying the organs of digestion.

What did you learn about dissection and the digestive system of a mammal? Compared to the length of the rat, how long was it’s alimentary canal? What was the difference in the wall of the stomach and the small intestine? What did you notice about the contents of the alimentary canal as they moved towards the rectum? What surprised you most about the inside of a rat?

Procedure for rat dissection.

Classification of the rat and glossary of terms (dorsal, ventral, thoracic etc.)

Check out Miss Baker’s Biology Blog, “Extreme Biology” for a video of a dogfish shark dissection.

Extract DNA in the science classroom

Image Source 

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.