Ultimate IB Biology Revision Deck: Mandatory Pracs

What is the effect of immobilising enzymes?

It increases the range of temperature/pH that give high enzyme activity (decreases risk of denaturing). It also enables re-use, which allows for commercial use.

What variables should be kept constant while measuring enzyme activity at different temperatures?

pH, concentration of enzyme, and concentration of substrate.

How does a bubble potometer measure the amount of water lost by a plant?

In a bubble potometer, the greater distance moved by bubble over time, the higher the transpiration rate.

In a study investigating the effect of pretreating egg white proteins with ultrasound on how they were digested by enzymes, what variables should be kept constant?

Enzyme, substrate, egg white concentration, volume, pH, or temperature.

What are the requirements for sustainability within a sealed mesocosm?

Photosynthetic organisms as producers, light as an energy source for photosynthesis, nutrient and water recycling by saprotrophs, and decomposers to breakdown toxic wastes.

How can carbon dioxide be removed from water used to irrigate a plant?

By boiling and cooling the water, exposing the water to a vacuum, or allowing distillation of water.

How does a plastic bag placed around a plant pot prevent carbon dioxide from reaching the plant's leaves?

It prevents CO2 from organisms in the soil affecting the experiment, and the plastic bag is impermeable to gases.

What measurements would be taken to identify pigment X in a chromatograph of photosynthetic pigments of a leaf of the plant?

Distance moved by pigment relative to distance moved by solvent. This will enable the calculation of the RF (retention factor). Rf depends on density / solubility / polarity of the pigment in solvent.

What is an independent variable that would affect the activity of beta-galactosidase enzyme extracted from the fungus Penicillium simplicissimum?

Temperature, substrate concentration, pH, inhibitors/cofactors.

Outline the measurements that would need to be taken to determine the activity of beta-galactosidase at different pH values.

Test samples for the concentration/amount of products/glucose/fructose/substrate/lactose, take samples of the reaction mixture at regular/timed intervals, repeated measurements at the different pH values, and measure independent/controlled/standardized variables/temperature.

How can you estimate the isotonic values for tissues based on a given graph?

Where the line intercepts with the X axis is the point where the water potential of the solution is the same as the water potential inside the tissue (i.e., the isotonic point).

What could be a reason for the difference in isotonic points for potato and carrot tissues?

The tissues may have different dissolved solutes/sugars/sucrose/salts/molarities or may have been grown in different soils giving their tissues different contents or may have been stored under different conditions or may be more dehydrated/different water content or different types of tissue/different age.

Why is the percentage change in mass calculated in a potato osmosis experiment?

The percentage change in mass is calculated to indicate whether the tissue has gained or lost water, to compare the relative changes in mass, and because the pieces of tissue will not be the same mass at the beginning of the experiment.

What are two variables, other than temperature and light, that should be controlled in the mesocosm experiment to study nutrient removal from water?

Type/number of plants and type of soil/substrate.

What did William Harvey's experiment demonstrate about the circulation of blood?

Blood flows towards the heart and valves prevent backflow, making blood flow unidirectional.

How is O2 consumption measured using a respirometer?

A CO2 absorber is added, a bubble/starting water level is measured, and the rate of movement of the bubble/pressure reduction is a measure of O2 consumption.

What is the role of fungi in nutrient cycling?

Fungi act as saprotrophs/decomposers and break down organic matter/food/organisms, returning nutrients trapped in organic matter to the cycle/soil.

How did electron micrographs from freeze fracturing support the fluid-mosaic model of membrane structure?

The fluid-mosaic model proposed two layers of protein on either side of a lipid bilayer, and micrographs illustrate proteins in and/or crossing the membrane.

How does the amphipathic nature of phospholipids allow them to form bilayers?

Phospholipids are amphipathic, meaning that they are both hydrophilic and hydrophobic. The outside hydrophilic parts are exposed to water, while the hydrophobic parts are away from water in the inside, allowing them to form bilayers.

Which nucleotide base was marked with radioactivity in Cairns' experiment to measure the length of DNA in Chinese hamster fibroblast cells?

Thymine because it is only found in DNA

What is the effect of a change in pH on enzyme activity?

A change in pH can denature the enzyme/protein or affect the 3D structure of the protein/active site.

State one technological improvement, other than enzymatic digestion, that led to the falsification of previous models to determine the current model of membrane structure.

Scanning electronmicrography (SEM) or freeze fracture/etching.

Outline how ventilation rate can be monitored in a study.

Ventilation rate can be monitored by data logging with a spirometer or a chest belt. Tidal volume can be recorded for a given period of time or average tidal volume found and multiplied by the number of breaths per minute. The measurement must include a reference to time.

What is the function of a tap and reservoir in a potometer?

The tap and reservoir in a potometer are used to reset the potometer, move the air column to the right/end, or replace/replenish water in the tube.

How can a potometer be used to demonstrate that transpiration rate is affected by air movement?

A fan can be placed so that air blows on the leaves, a control with no air blowing can be used, the distance moved by the bubble in a given time can be measured, the bubble can be reset to the beginning with the tap, and a greater distance moved by the bubble over time indicates a higher transpiration rate. The experiment should be repeated at the same temperature, and different speeds of the fan can be used to determine the effect of a range of air movement.

How can one variable affecting germination of T. grandiflora seeds be investigated?

By using Petri dishes, absorbent cotton balls, and seeds, and varying one independent variable such as temperature while keeping other variables constant. A large or equal number of seeds should be placed in each Petri dish. Germination can be determined by observing the appearance of the radicle or measuring the germination rate/percentage over time. A control group should be included that provides the seeds with all the necessary factors for germination such as water, oxygen, temperature, pH, light, and salt concentration.

How would the total lung volume at rest differ for a patient with emphysema?

The total resting lung volume would be greater for a patient with emphysema.

How would the action spectrum from the white areas of a leaf differ from the green areas?

The action spectrum from the white areas of the leaf would be a straight line or have no peaks, indicating no photosynthesis.

Why are plants with variegated leaves (i.e., partly green and mixed with another colour like white) rarely found growing wild naturally?

Having the leaf partly white would not provide a selective advantage, making it difficult for the plant to compete in the wild. Natural selection would reduce the frequency of the mutation causing variegated leaves. This trait may occur due to artificial selection.

What is the formula for calculating magnification of a given image?

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

What is the difference between absorption spectra and action spectra?

Absorption spectra show the wavelengths of light absorbed by a pigment, while action spectra show the effectiveness of different wavelengths of light in driving a particular biological process.

How can the mean tidal volume after exercise be determined using a graph?

Measure the volume difference for an individual breath or calculate the maximum - minimum for an individual breath, repeat for several breaths and determine the mean.

How can chi-squared be used to test for an association between the distributions of two species?

In each quadrat, determine the presence/absence of plants of each type. The null hypothesis is that the presence of one is random/independent in relation to the presence of the other plant or the alternate hypothesis is that the presence of one is associated with the presence or absence of the other. Calculate the chi-squared value. Accept the alternative hypothesis/reject null hypothesis if the difference between observed and expected is statistically significant/p<0.05/calculated X2 higher than tabulated X2/critical value or it supports the association between the two species if the difference between observed and expected is statistically significant/p<0.05/calculated X2 higher than tabulated X2/critical value.

How would the variables be controlled in an experiment to estimate the osmolarity of plant tissue?

Weigh all pieces to ensure the same amount of plant material, control surface area by having the same shape/size, carry out the experiment at the same temperature, all samples in solution for the same length of time, all samples from the same plant (to minimize variability), use a range of solutions of the same solute, constant method of removing excess fluid before weighing tissue samples.

What apparatus is used to measure the tidal volume?

Spirometer

What is a possible research question that could be investigated using a potometer?

What is the effect of changing the surface area on the transpiration rate of a particular plant species?

What are the limitations of using a potometer in an investigation?

Not all of the water taken up by the plant is used for transpiration, some water taken up might be used for photosynthesis or cell turgidity. The potometer measures the rate of water uptake, not transpiration directly. The plant or twig may get damaged or may not survive. Conditions in a lab are not equivalent to those in nature, and it is difficult to change only one abiotic factor. It is also difficult to extrapolate values from a twig to the whole plant.

What is the effect of humidity on transpiration?

Increased humidity decreases water uptake (inverse relationship) as the diffusion gradient is reduced. Less water is lost through stomata.

What is a suitable solvent for extracting photosynthetic pigments from plant tissue?

acetone or alcohol

How can pigments in a chromatogram be identified?

They can be identified by their colour/analysis with spectrometer. Measure the distance travelled by the solvent front. Measure the distance travelled by the pigment. Calculate the Rf value. They can be identified by comparing Rf values to known values.