2Preliminary Biology: First Hand Investigations – Part 1

Is anyone else frustrated with the lack of resources for first-hand investigations (experiments) done in Preliminary Biology? Okay, so it is quite a specific frustration, but I am going to try remedy this problem (maybe I’m the only one having it…).

Why do you need to know the experiments?

They are examinable. I often stress this with students – YES, the 2nd column in the syllabus dot points ARE examinable (usually in questions worth 4-6 marks). So importantly, you need to know the method, the results/conclusion.

The problem

  1. Students fail to write down (or to completely write down) the experiment and soon forget it.
  2. The experiments are not conducted – sometimes because of a lack of class time etc.
  3. HSC Online (the comprehensive coverage of the syllabus) only covers the HSC, not Preliminary.
  4. Excel Preliminary Biology only covers some of the experiments (and even then in brief descriptions), because its main focus is on the content-dominant dot points.

Your help

If you can share a more accurate experiment recording of any of the following dot points, please let me know. These are gained from my old Biology book (from 2004), Excel Preliminary Biology, online notes and my student’s lab book.

A Local Ecosystem

No first hand investigations.

Patterns in Nature

2.A

plan, choose equipment or resources and perform a first-hand investigation to gather information and use available evidence to identify the following substances in tissues:
– glucose
– starch
– lipids
– proteins
– chloride ions
– lignin

The tests are as follows:

  • Glucose: add benedict’s solution and heat in a water bath. If it turns orange, then glucose is present.
  • Starch: add iodine solution. If it turns blue/black, then starch is present.
  • Lipid: place on brown paper. If the paper goes clear, then lipids are present.
  • Protein: use the Biuret test (add 2mL sodium hydroxide and few drops of copper sulfate). If it turns violet, then protein is present.
  • Chloride ions: add silver nitrate. If a white precipitate forms, then chloride ions are present.
  • Lignin: add toluidine blue. If it turns blue/green, then lignin is present.

2.B

perform a first-hand investigation to model the selectively permeable nature of a cell membrane

Method:

  1. Fill a cellulose bag with starch solution.
  2. Place the bag in iodine solution.
  3. Leave overnight.

Result:

  1. Starch solution in bag will turn purple overnight.

Rationale:

  1. Iodine, in contact with starch, turns purple.
  2. Iodine moved into the bag – this models how substances move into the cell.
  3. Starch molecules are too large to move out of the bag.
  4. In this model, the bag is the cell membrane and the starch solution is the cytoplasm.

2.C

perform a first-hand investigation to demonstrate the difference between osmosis and diffusion

Rationale:

  1. The dialysis tubing allows the movement of water and glucose molecules. It does not allow starch

Method:

  1. Fill 1 dialysis tube with a glucose solution.
  2. Record the weight of the tube.
  3. Place the glucose tube into a beaker of water.
  4. Leave for 30 minutes.
  5. Test the water in the beaker for glucose by adding Benedict’s solution.
  6. Reweigh the tube.

Results:

  1. The water  turns slightly orange (this means glucose is present).
  2. The tube has increased in weight.

Conclusion:

  1. Water moved by osmosis from the beaker (low concentration of glucose) into the tube (high concentration of glucose).
  2. Glucose moved by diffusion from the tube (high concentration of glucose) into the beaker (low concentration of glucose).

2.D

perform a first-hand investigation to demonstrate the effect of surface area to volume ratio on rate of diffusion

Background:

  1. Jelly is pink because of sodium hydroxide and an indicator.
  2. Indicator goes colourless in acid.

Method:

  1. Cut jelly into 3 different size cubes (eg. 20 mm, 10mm, 5mm).
  2. Place in beaker of sulfuric acid.
  3. Wait until 1st cube goes completely clear.
  4. Remove all cubes and pat dry with paper towel.
  5. Cut cubes in half.
  6. Measure in millimeters the depth of the clear layer in each (ie. how far the acid managed to diffuse in)

Result:

  1. Smallest size cube (eg. 5mm) will be the first to go clear.
  2. The depth of the clear layer will decrease as size increases.

Rationale:

  1. The smaller the cube, the higher the SA/V ratio.
  2. With more SA/V ratio, substances enter in/out more efficiently.

3.A

plan, choose equipment or resources and perform first-hand investigations to gather information and use available evidence to demonstrate the need for chlorophyll and light in photosynthesis

Rationale:

  1. Starch is a product of photosynthesis.
  2. If starch is present, then photosynthesis has taken place.

Need for chlorophyll in photosynthesis.

Method:

  1. Find some variegated leaves (only some parts of leaf are green – have chlorophyll).
  2. Boil the leaves.
  3. Soak in methylated spirits to remove the green colour.
  4. Test for starch using iodine solution – if it turns blue black, starch is present.

Results:

  1. The green parts of the leaf turned blue black, but the non-green parts did not.

Need for light in photosynthesis.

Method:

  1. Place 1 plant in light and 1 plant in the dark.
  2. Boil leaves from both plants separately.
  3. Soak in methylated spirits to remove the green colour.
  4. Test for starch using iodine solution – if it turns blue black, starch is present.

Results:

  1. The leaves from the plant in the light turned blue black, but the leaves from the plant in the dark did not.

3.B

perform a first-hand investigation to demonstrate the relationship between surface area and rate of reaction

Method:

  1. Get 2 tablets that can dissolve in water.
  2. Crush 1 tablet and leave the other tablet whole.
  3. Place the crushed tablet and whole tablet in separate beakers of the same amount of water at the same time.
  4. Using a stop watch, time how long it takes for each tablet to completely dissolve.

Results:

  1. The crushed tablet will dissolve faster than the whole tablet.

Conclusion:

  1. The higher the surface area, the faster the rate of reaction.

4.A

use available evidence to perform a first-hand investigation and gather first-hand data to identify and describe factors that affect the rate of transpiration

Method:

  1. Measure the rate of transpiration using a potometer.
  2. For each below, you can design experiments by changing the environment of the plant or choosing different plants.
    1. For example for number 2, place 1 plant outside in the wind and another inside, sheltered from the wind.
    2. For example for number 5, choose a plant with leaves with a large surface area and a plant with leaves with a small surface area.

Results – factors that affect transpiration:

  1. Temperature: the higher the temperature, the higher the rate of transpiration
  2. Wind: the windier, the higher the rate of transpiration
  3. Humidity: the more humid, the lower the rate of transpiration
  4. Hairy leaves, waxy cuticles: the lower the rate of transpiration
  5. Surface area of leaves:  the greater surface area, the higher the rate of transpiration
  6. Number of stomates: the higher the number of stomates, the higher the rate of transpiration.

4.B

perform a first-hand investigation of the movement of materials in xylem or phloem

Aim: observe movement of water and minerals through xylem tubes.

Method:

  1. Cut the bottom of a small piece of celery at a 45 degree angle.
  2. Place in beaker with water and red dye.
  3. Leave for 1-2 hrs.
  4. Remove and make a longitudinal.
  5. Repeat the above steps, but leave overnight instead.

Results:

  1. After 1-2 hours, the dye can be seen in the xylem tubes.
  2. After being left over night, the dye can be seen in the celery leaves.

Part 2 covering Life on Earth and Evolution of Australian Biota will be coming up next!

7 comments for “2Preliminary Biology: First Hand Investigations – Part 1

  1. Kym
    September 14, 2009 at 9:33 am

    True, the theory component is covered much more carefully compared to the practical component. And students tend to perform poorly at questions beginning with: “Recall a practical investigation you performed in which…”

    But one can borrow or purchase resources such as the Heinemann Activity Manual or NSW Biology. :)

    • tutortales
      September 15, 2009 at 1:29 pm

      Thanks for that – I haven’t come across those books before!

      TT

  2. Tasie
    September 17, 2009 at 9:26 pm

    I use NSW bio (year 12) now, but it only outlines the method and the disscussion is quite limited. Biology in Focus is really good for practicals.

  3. vegtabili
    August 10, 2010 at 6:26 pm

    when is part two coming out?

  4. Laura
    May 18, 2011 at 5:54 pm

    Thankyou!! Lifesaver :)

  5. Elyssa Woods
    September 7, 2011 at 11:53 am

    This is quite good for me. Im a student teacher at the moment and i have been finding it hard to come up with practical activities, so this has at least given me some ideas and i can now build on this. Thankyou soooooo much.

  6. Rose
    June 16, 2012 at 1:12 pm

    YOU MISSED THE VERY FIRST ONE AND THE VERY LAST ONE :(

Leave a Reply

Your email address will not be published. Required fields are marked *