22 Prescribed Lab Practicals (section A on paper 3)

There are 7 prescribed lab practicals in IB Biology. Information / skills / understanding of these labs will be assessed in section A of the Paper 3 regardless of the option.

Please review these videos and other resources. Thanks, Mr. A

Note: the potometer / plant transpiration lab is HL only.

Prescribed practical lab 1 video and other resources

Z: Prescribed lab 1: calculation of magnification of drawings, actual size of structures from drawings or micrographs.

Written summaries of the following labs to include (where applicable):

1. the research question

2. identification of the independent variable

3. identification of the dependent variable

4. procedure on a step-by-step basis

5. sample results in a data table

6. processed results and data analysis

7. conclusions including biological explanations

The research question for this lab would be as follows:

What is the effect of magnification on the actual size of structure

The independent variable: no independent variable

The dependent variable: no dependent variable

Calculation of Magnification:

To calculate the linear magnification of a drawing or image, the following equation should be used:

• Magnification = Image size (with ruler) ÷ Actual size (according to scale bar)

Calculation of Actual Size:

To calculate the actual size of a magnified specimen, the equation is simply rearranged:

• Actual Size = Image size (with ruler) ÷ Magnification

Light microscopes use visible light and a combination of lenses to magnify images of mounted specimens

• Living specimens can be viewed in their natural colour, although stains may be applied to resolve specific structures

When attempting to draw microscopic structures, the following conventions should be followed:

• A title should be included to identify the specimen (e.g. name of organism, tissue or cell)
• A magnification or scale should be included to indicate relative size
• Identifiable structures should be clearly labelled (drawings should only reflect what is seen, not idealised versions)

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Prescribed practical lab 2 video and other resources

Izmah:

Osmolarity is the concentration of a solution expressed as the total number of solute particles per litre.

The osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities

• The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
• Water loss or gain may be determined by weighing the sample before and after bathing in solution
• Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)

• 1.Peel some epidermis from a red onion.
• 2.Cut a sample approx.. 5 x 5mm in size.
• 3.Mount the sample on a microscope slide with one drop of distilled water and a cover slip.
• 4.Observe the cells using a microscope. Record your observations in an appropriate table.
• 5.Mount a second sample of red onion epidermis, this time use one drop of sodium chloride solution.
• 6.Observe the cells using a microscope and record your observations in the table. You should be able to observe the process
• (when plant cell membranes pull away from the cell wall).
• This technique could be used to investigate osmolarity.

Osmosis is the movement of molecules from a region of high concentration to a region of low concentration. Solutes that are osmotically active include glucose, sodium ions, potassium ions and chloride ions. These ions are able to move because they are able to form bonds with water. There are many solutes within cells that are osmotically active.

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Prescribed practical lab 3 video and other resources

Ali and Ahmad

Prescribed Lab 3

Ali and Ahmad

IB Biology SL

Research Question: What is the effect of temperature on enzyme activity?

Independent Variable: Temperature

Dependent Variable: Rate of enzymatic activity

1. Identify which enzyme and corresponding substrate to investigate. Gather all materials.
2. Put a fixed amount of enzymes into a beaker or other container.
3. Put the corresponding substrate into container, modulating the amounts in order to collect data at different points.
4. Measure the amount of collisions or the amount of output that the enzyme creates.
5. Collect data.

7. Like other chemical reactions, the rate of enzyme-catalysed reactions increase as temperature increases. The reaction rate increases with the temperature to a maximum level known as the optimum level. In humans this is around 37 degrees celsius. Following the optimum level, enzyme activity abruptly declines as temperature continues to rise. This is known as denaturing.

In order to convert substrate into a products, enzymes collide with the substrate and bind to it at the active site. The reason the rate of reaction increases is due to the fact that an increase in temperature causes the number of collisions per unit time to increase. The increase in temperature causes an increase in velocity and kinetic energy which is why the number of collisions increases.

Heat may also be converted into chemical potential energy. If the chemical potential energy increase is large enough, some of the weak bonds which determine the shape of the enzymes will be broken. This is what leads to denaturation of the enzyme. This means that too large of an increase in temperature will lead to the reaction rate to decrease due to inactivity of the enzymes.

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Prescribed practical lab 4 video and other resources

Aafia

Research Question: How can we separate photosynthetic pigments using chromatography?

Variables:

Independent - pigment solubility

Dependent - distance that pigments move on chromatography paper

Method:

• A mixture is dissolved in a fluid (called the mobile phase) and passed through a static material (called the stationary phase)
• The different components of the mixture travel at different speeds, causing them to separate
• A retardation factor can then be calculated (Rf value = distance component travels ÷ distance solvent travels)

Two of the most common techniques for separating photosynthetic pigments are:

• Paper chromatography – uses paper (cellulose) as the stationary bed
• Thin layer chromatography – uses a thin layer of adsorbent (e.g. silica gel) which runs faster and has better separation

Conclusion:

If you did a number of chromatographic separations, each for a different length of time, the pigments would migrate a different distance on each run. However, the migration of each pigment relative to the migration of the solvent would not change. This migration of pigment relative to migration of solvent is expressed as a constant, Rf (Reference front). It can be calculated by using the formula:

Rf = distance pigment migrated distance solvent front migrated

Chromatography is the process of separating chemicals in a mixture, where some pigments are more soluble than others and the distance they travel is contingent upon that.

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Prescribed practical lab 5 video and other resources

Armeen and Asma

Prescribed lab 5: attempting to create a sealed mesocosm

Ecosystems have the potential to be sustainable over long periods of time

Mesocosms emulate ecosystems and how they interact with their biotic and abiotic components.

-The main components include: Energy, nutrient availability, and recycling waste.

Mesocosms are enclosed “ecosystems” that allows a small part of a natural environment to be observed under controlled conditions:

A terrarium is a small transparent container, whether it be glass or plastic, in which selected plants or even animals in some cases are kept and observed

1. Building a foundation

• layer for drainage, Add layer of pebbles, gravel or sand etc.
• second thin layer of activated charcoal to prevent mold and help to aerate the soil
• thin cover of sphagnum moss (or organic coffee filter)
• final layer of pre-moistened growing medium

2. Selecting the right plants

• choose plants that are slow growing and thrive in humidity like ferns, club moss, etc.
• Inspect the plant first to make sure its healthy

3. Maintaining appropriate conditions

• Place in a location with a continuous source of light
• Make sure there are no experience temperature conditions
• Do not over water, ensure that the humidity etc is adjusted before continuing to water
• As level of soil nutrients decrease, plant growth should slow down

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Prescribed practical lab 6 video and other resources

Nabhan and Fatima

The research question:

• What is the effect of vigorous exercise on rate of ventilation?

Identification of the independent variable:

• Intensity of the exercise (duration, type)

Identification of the dependent variable

• Ventilation (frequency of breath or spirometer data)

Procedure on a step-by-step basis

1. Set up a chair and a timer with your spirometer set and ready
2. Record frequency of breath or tidal volume with a spirometer at rest
3. Begin exercise for a set amount of time
4. After time as elapsed, stop the exercise and record frequency of breath or tidal volume with a spirometer.
5. Rest
6. Begin exercise again, increase rate or time
7. Record
8. Rest
9. Begin exercise again, increase rate or time
10. Record
11. Rest

Processed results and data analysis

This graph shows the effect of exercise, which is indicated by treadmill velocity, on ventilation rate. We can see that as the ventilation rate increases so does the ventilation rate, for example, it goes from 20 breaths per minute to 80 breaths per minute by the end. Not only that, but the tidal volume also increases.

Conclusions including biological explanations

As the exercise intensity increases, so does the ventilation rate. Ventilation in humans changes in response to levels of physical activity, as the body’s energy demands are increased. As exercise intensity increases, so does the demand for gas exchange, leading to an increase in levels of ventilation. Exercise will influence ventilation in two main ways: increase ventilation rate (a greater frequency of breaths allows for a more continuous exchange of gases) and an increase tidal volume (increasing the volume of air taken in and out per breath allows for more air in the lungs to be exchanged

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Prescribed practical lab 7 video and other resources

Amir and Sana

Measuring The Rate of Transpiration

1. The research question

How does the rate of transpiration in plants vary between different environmental conditions?

OR

Which environmental conditions allow for the greatest rate of transpiration by plants?

2. Identification of the independent variable

Independent variable: different environments (mist, wind, bright light)

3. Identification of the dependent variable

Dependent variable: transpiration rates (as measured by potometers)

4. Procedure on a step-by-step basis

1. Gather all materials.
2. Assemble 4 potometers. Potometers include:
• A plant cutting
• A calibrated pipette to measure water loss
• A length of clear plastic tubing
• An air-tight seal between the plant and the water-filled tubing
1. Place each potometer in different environments including, room conditions (control group), wind, mist, and bright light.
2. Measure water loss in each potometer every 3 minutes for a total of 30 minutes.
3. Calculate the leaf surface area for each cutting.
4. Compare surface areas of leafs between different environments.

OR

Compare loss of water in pipettes of potometers between different environments.

5. Sample results in a data table

6. Processed results and data analysis

7. Conclusions including biological explanations

Transpiration describes the movement of water through plants, including the process of water loss. A potometer is a device that measures the rate at which a plant draws up water. Since the plant draws up water as it loses it by transpiration, you are able to measure the rate of transpiration. This rate of transpiration will be affected by different environmental factors, and different environmental conditions can be created for these plants, to determine how the rate of transpiration varies with each.

Evaporation of water through the stomata is a most important factor in pulling water toward the top of a tall tree. Light conditions would generally result in the higher rate of transpiration. Stomata are generally open in the light, and solar energy increases evaporation. A dry environment would result in the higher rate of transpiration because the water potential in the surrounding air would be lowest, resulting in more rapid evaporation. Breezy conditions would increase the rate of evaporation of water from the surface of the leaves, lowering the water potential, and resulting in more rapid evaporation. However, if the plant is subjected to very high wind movement, the stomata may actually close, which prevents water loss. Unless a plant is specially adapted for hot conditions, the rate of transpiration will drop in a hot environment because heat stress may cause the stomata to close, which conserves water. Warm, light-breezy conditions provide an environment for the greatest rate of transpiration in plants. In breezy conditions the rate of transpiration would be very high because of evaporative water loss.

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