2024 Cambridge IAL Biology (9700) Practice Paper with Answers

Which sequence represents the correct pathway taken by a newly synthesized membrane glycoprotein from its site of synthesis to its final destination in the cell surface membrane?

A student placed cylinders of potato tissue in sucrose solutions of different concentrations. After 24 hours, the percentage change in mass was calculated and plotted. The concentration at which there was no change in mass was determined to be \(0.3\text{ mol dm}^{-3}\). Which statement about the potato cells at this concentration is correct?

Which statements correctly describe the differences between a triglyceride molecule and a phospholipid molecule? 1. Triglycerides have three fatty acid tails, while phospholipids have two fatty acid tails. 2. Triglycerides are completely hydrophobic, while phospholipids have a hydrophilic head and hydrophobic tails. 3. Triglycerides contain only carbon, hydrogen, and oxygen, while phospholipids contain carbon, hydrogen, oxygen, and phosphorus.

Which processes are involved in the loading of sucrose into the phloem sieve tube elements at a source? 1. Active transport of protons (\(\text{H}^+\)) out of the companion cells into the cell wall. 2. Co-transport of protons (\(\text{H}^+\)) and sucrose back into the companion cells down a proton gradient. 3. Diffusion of sucrose through plasmodesmata from the companion cells into the sieve tube elements.

A person consumes a meal with a very high salt (sodium chloride) content but does not drink any water. What are the short-term changes in the concentration of antidiuretic hormone (ADH) in the blood, the permeability of the collecting duct to water, and the volume of urine produced?

In an investigation of the light-independent stage of photosynthesis, algae were exposed to radioactive carbon dioxide (\(^{14}\text{CO}_2\)) in the light. The light was then turned off, but the supply of \(^{14}\text{CO}_2\) was maintained. What happens to the concentrations of ribulose bisphosphate (RuBP) and glycerate 3-phosphate (GP) immediately after the light is turned off?

In a species of bird, individuals with intermediate wing lengths survive better during storms than individuals with very short or very long wings. What type of selection is operating on wing length in this bird population, and what is its effect on the variance of wing length over generations?

The polymerase chain reaction (PCR) is used to amplify DNA. The mixture is cycled through three temperatures: \(95\,^\circ\text{C}\), \(55\,^\circ\text{C}\), and \(72\,^\circ\text{C}\). Which row correctly describes the purpose of each temperature in a cycle of PCR?

A micrograph of a plant cell chloroplast has an image length of \(2.4\text{ cm}\). If the actual length of this chloroplast is \(6\\ \mu\text{m}\), what is the magnification of the micrograph?

A group of plant cells with a water potential of \(-500\text{ kPa}\) is placed in four different sucrose solutions, W, X, Y, and Z. The water potentials of the solutions are: W = \(-200\text{ kPa}\), X = \(-500\text{ kPa}\), Y = \(-800\text{ kPa}\), and Z = \(-1100\text{ kPa}\). In which of these solutions will the cell protoplasts pull away from the cell walls?

Which row correctly describes the types of glycosidic bonds present in cellulose, amylose, and glycogen?

Which features of companion cells are essential for their role in loading sucrose into phloem sieve tube elements? 1: Presence of numerous mitochondria to synthesize ATP. 2: Proton pumps in the cell surface membrane that actively transport hydrogen ions out of the cytoplasm. 3: Plasmodesmata connecting the cytoplasm of the companion cell to the sieve tube element.

Which row correctly describes the physiological responses that occur in a human body when the water potential of the blood plasma is lower than normal?

How many molecules of carbon dioxide, reduced NAD, and reduced FAD are produced in the Krebs cycle during the complete aerobic respiration of one molecule of glucose?

What is the correct sequence of temperatures and their primary purposes during one cycle of the polymerase chain reaction (PCR)?

Which row correctly classifies the type of immunity acquired in each of the given scenarios?

An electron micrograph of a eukaryotic cell shows cross-sections of a cilium and a centriole. Which row in the table correctly describes the arrangement of microtubules in these two structures?

A plant cell with a solute potential (\Psi_s) of -0.8 MPa and a pressure potential (\Psi_p) of +0.2 MPa is placed in a sucrose solution with a water potential (\Psi) of -0.4 MPa. Which statement correctly describes the net movement of water and the subsequent change in the cell?

Which statement correctly describes a structural or functional difference between amylose and cellulose?

During the active loading of sucrose into companion cells, protons (\text{H}^+ ions) and sucrose molecules are transported. Which row correctly identifies the mechanisms and directions of transport for both protons and sucrose?

An increase in the concentration of antidiuretic hormone (ADH) in the blood causes changes in the kidney nephrons. Which processes occur in the cells of the collecting duct in response to ADH binding to its cell-surface receptors? 1. Activation of adenylyl cyclase to produce cyclic AMP (cAMP) 2. Fusion of vesicles containing aquaporins with the luminal membrane 3. Facilitated diffusion of water molecules through aquaporins out of the tubule fluid 4. Active transport of sodium ions from the filtrate into the cytoplasm

Which row correctly matches the infectious disease with its type of pathogen and its primary method of transmission?

What is the primary role of memory B-lymphocytes during a secondary immune response to a pathogen that has been encountered previously?

During the complete aerobic respiration of one molecule of glucose, how many molecules of reduced NAD (NADH) and reduced FAD (\text{FADH}_2) are produced combined in the link reaction and the Krebs cycle?

Which feature of an organelle isolated from a plant leaf cell would confirm that it is a chloroplast and not a mitochondrion?

The fluid mosaic model describes the structure of cell membranes. Which change to the membrane components would increase the fluidity of a mammalian cell surface membrane at low temperatures?

Which level of protein structure is maintained by hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bonds between the R-groups of a single polypeptide chain?

Which statements about the transport of sucrose in the phloem of a plant are correct? 1. Sucrose is loaded into companion cells by active transport of hydrogen ions out of the cell followed by co-transport of sucrose with hydrogen ions back in. 2. Hydrostatic pressure increases at the source due to water entering the sieve tube elements by osmosis. 3. Sucrose moves through the sieve tube elements by diffusion down a concentration gradient.

The concentration of glucose in the glomerular filtrate of a healthy human is 1.0 g dm^-3, while its concentration in the final urine is 0.0 g dm^-3. Which process explains this change in glucose concentration?

Which of the following correctly pairs an infectious disease with its causative pathogen type and its primary method of transmission?

In the production of monoclonal antibodies using hybridoma technology, which cells are fused together, and what is the function of the fusing agent?

For every molecule of glucose that undergoes aerobic respiration, what are the total net yields of reduced NAD and reduced FAD produced specifically during the Krebs cycle?

A student uses a light microscope to measure the size of a stomatal pore. At a magnification of \(\times 400\), the image of the stomatal pore is \(8.0\text{ mm}\) wide. What is the actual width of the stomatal pore?

A plant cell is placed in a solution with a higher solute concentration than the cytoplasm of the cell. Which row correctly describes the changes in the water potential of the cytoplasm and the state of the cell?

Which statement correctly describes a difference between amylose and cellulose?

In a plant, what drives the upward movement of water through xylem vessel elements from the roots to the leaves?

During aerobic respiration, how many molecules of carbon dioxide are produced from the complete oxidation of one molecule of pyruvate?

Which of the following occurs in the kidneys of a human when the water potential of the blood decreases below the set point?

A population of snails exhibits a wide range of shell colorations, from very light yellow to very dark brown. A new predator is introduced to the habitat. This predator hunts by sight and is highly efficient at detecting and consuming snails with intermediate (medium-brown) shell colors against the background of light sand and dark rocks. Which type of natural selection is most likely to occur in this snail population over time?

In genetic engineering, which enzyme is correctly matched with its role?

The epithelial lining of the trachea contains goblet cells and ciliated epithelial cells. Goblet cells synthesize and secrete mucin, which is a large glycoprotein.

(a) Describe the roles of the rough endoplasmic reticulum and the Golgi body in the synthesis and processing of mucin. [4]

(b) Explain how the structure of a ciliated epithelial cell is adapted to its function of clearing mucus from the airways. [3]

(c) Suggest why goblet cells contain a large number of mitochondria. [3]

The movement of substances across cell membranes is essential for cell function. In the small intestine, glucose is absorbed into epithelial cells against its concentration gradient.

(a) Explain why glucose cannot pass directly through the phospholipid bilayer by simple diffusion. [2]

(b) Describe how the co-transport of sodium ions (\(\text{Na}^+\)) and glucose takes place across the apical membrane of these epithelial cells. [5]

(c) State how the active transport of sodium ions across the basolateral membrane into the blood maintains this absorption process. [3]

Collagen is the most abundant structural protein in the mammalian body, found in skin, tendons, and bones.

(a) Describe the primary and secondary structures of a single collagen polypeptide chain. [3]

(b) Explain how the tertiary and quaternary structures of collagen are adapted to its structural role. [4]

(c) Describe the structural differences between collagen and a globular protein such as hemoglobin. [3]

Water and assimilates are transported through specialized vascular tissues in plants.

(a) Explain how companion cells load sucrose into phloem sieve tube elements. [4]

(b) Distinguish between the symplastic pathway and the apoplastic pathway of water transport through the root cortex. [3]

(c) Explain how the structure of xylem vessels is adapted to prevent the collapse of the vessel under tension. [3]

Vaccination is an effective method of controlling the spread of infectious diseases such as measles.

(a) Explain how a vaccine stimulates active immunity against a specific pathogen. [4]

(b) Distinguish between natural active immunity and artificial passive immunity. [3]

(c) Suggest why vaccination programs fail to eradicate some infectious diseases, such as malaria or cholera. [3]

Mitosis is part of the cell cycle that ensures genetic stability in eukaryotic cells.

(a) Describe the events that occur during interphase that prepare a cell for division. [3]

(b) Describe and explain the behaviour of chromosomes during metaphase and anaphase. [4]

(c) Explain the significance of mitosis in producing genetically identical daughter cells. [3]

You are required to investigate the effect of sucrose concentration on the water potential of potato tissue.

You are provided with:
* \(1.0\text{ mol dm}^{-3}\) sucrose solution, labeled **S**
* Distilled water, labeled **W**
* Five identical potato cylinders, cut to approximately \(50\text{ mm}\) in length

### (a) Preparation of dilutions and investigation

(i) You need to prepare \(20\text{ cm}^3\) of five different concentrations of sucrose solution: \(0.8\text{ mol dm}^{-3}\), \(0.6\text{ mol dm}^{-3}\), \(0.4\text{ mol dm}^{-3}\), \(0.2\text{ mol dm}^{-3}\), and \(0.0\text{ mol dm}^{-3}\) (pure distilled water), using the stock solution **S** and distilled water **W**.

Complete Table 1.1 to show the volumes of stock sucrose solution **S** and distilled water **W** needed to prepare each concentration.

**Table 1.1**
| Concentration of sucrose / \(\text{mol dm}^{-3}\) | Volume of stock solution S / \(\text{cm}^3\) | Volume of distilled water W / \(\text{cm}^3\) | Total volume / \(\text{cm}^3\) |
| :---: | :---: | :---: | :---: |
| \(0.8\) | | | \(20\) |
| \(0.6\) | | | \(20\) |
| \(0.4\) | | | \(20\) |
| \(0.2\) | | | \(20\) |
| \(0.0\) | | | \(20\) |

[3 marks]

(ii) Carry out the investigation as follows:
1. Label five test-tubes with the concentrations of sucrose prepared.
2. Transfer \(20\text{ cm}^3\) of the corresponding concentration into each tube.
3. Measure the initial length of each potato cylinder to the nearest \(0.5\text{ mm}\).
4. Place one potato cylinder into each of the test-tubes.
5. Leave the potato cylinders in the solutions for 30 minutes.
6. After 30 minutes, remove the potato cylinders from the test-tubes.
7. Gently blot them dry with a paper towel.
8. Measure the final length of each potato cylinder to the nearest \(0.5\text{ mm}\).
9. Calculate the change in length of each cylinder.

Record all your results in a single, appropriate table.

[6 marks]

(iii) Explain the change in length of the potato cylinder in the \(0.0\text{ mol dm}^{-3}\) solution and in the \(0.8\text{ mol dm}^{-3}\) solution in terms of water potential.

[3 marks]

### (b) Graph plotting and interpretation

In a separate investigation, a student measured the percentage change in mass of sweet potato discs in a range of sucrose concentrations. Their results are shown in Table 1.2.

**Table 1.2**
| Sucrose concentration / \(\text{mol dm}^{-3}\) | Mean percentage change in mass (%) |
| :---: | :---: |
| \(0.0\) | \(+14.5\) |
| \(0.2\) | \(+8.0\) |
| \(0.4\) | \(+1.5\) |
| \(0.6\) | \(-4.0\) |
| \(0.8\) | \(-9.5\) |
| \(1.0\) | \(-13.0\) |

(i) Plot a graph of the data in Table 1.2 on suitable graph axes.

[4 marks]

(ii) Use your graph to find the concentration of sucrose solution that is isotonic to the sweet potato tissue.

[1 mark]

### (c) Evaluation

Identify two sources of error in the practical procedure described in (a)(ii) that could affect the accuracy of the measurements of change in length. For each error, suggest an improvement to reduce its impact.

[3 marks]

Marram grass (*Ammophila arenaria*) is a xerophytic plant commonly found on sand dunes.

### (a) Drawings of Plant Structure

(i) **Fig. 2.1** is a photomicrograph showing a transverse section through the rolled leaf of *Ammophila arenaria*.

Draw a large, clear, low-power plan diagram of the transverse section of the leaf shown in **Fig. 2.1** to show the overall shape of the rolled leaf and the arrangement of its tissues.

*Do not draw any individual cells.*

On your plan diagram, use clear label lines to identify:
1. Cuticle
2. A vascular bundle

[5 marks]

(ii) **Fig. 2.2** is a high-power view showing details of the inner epidermis and hinge cells of the leaf of *Ammophila arenaria*, showing guard cells, stomata, and adjacent epidermal cells.

Make a high-power drawing of three adjacent epidermal cells, including one guard cell flanking a stoma.

On your drawing, use a clear label line to identify:
1. Cell wall

[4 marks]

### (b) Calibration and Measurement

A student calibrated an eyepiece graticule under a light microscope using a stage micrometer.
* The stage micrometer scale has divisions spaced at \(0.1\text{ mm}\) intervals.
* Using the \(\times 10\) objective lens, 40 divisions of the eyepiece graticule coincided with exactly 12 divisions of the stage micrometer.

(i) Calculate the actual distance represented by one eyepiece graticule division (epu) in micrometers (\(\mu\text{m}\)). Show all your working.

[3 marks]

(ii) The student then used the same \(\times 10\) objective lens to measure the total leaf thickness at the midrib in a slide of *Ammophila*. The thickness was measured as 32 eyepiece graticule divisions.

Calculate the actual thickness of the leaf in micrometers (\(\mu\text{m}\)). Show your working and state your answer to an appropriate number of significant figures.

[4 marks]

### (c) Comparison

Table 2.1 is an incomplete table comparing the leaf anatomy of *Ammophila arenaria* (a xerophyte) with that of *Ligustrum* (a mesophyte).

Complete Table 2.1 by describing three anatomical differences between the two leaves.

**Table 2.1**
| Anatomical Feature | *Ammophila arenaria* (Xerophyte) | *Ligustrum* (Mesophyte) |
| :--- | :--- | :--- |
| **Leaf shape / rolling** | | |
| **Location of stomata** | | |
| **Cuticle thickness** | | |

[4 marks]

A biotechnology company aims to produce human antithrombin III, a therapeutic protein, in the milk of transgenic goats.

(a) Explain why the human gene must be paired with a promoter sequence from a mammary gland-specific gene, such as beta-casein, before microinjection. [3]

(b) Outline the steps involved in using a PCR-based method to confirm that the human antithrombin gene has integrated successfully into the goat's genome. [4]

(c) Discuss one social or ethical concern associated with producing pharmaceutical proteins in GM animals. [3]

Xenozin is a chemical compound that acts as an uncoupler of oxidative phosphorylation in mammalian mitochondria. It makes the inner mitochondrial membrane highly permeable to hydrogen ions (\(H^+\)).

(a) Define the term 'oxidative phosphorylation' and state its precise location within a mitochondrion. [2]

(b) An experiment showed that adding Xenozin to respiring liver cells increased oxygen consumption but stopped ATP synthesis. Explain how Xenozin causes these effects. [5]

(c) State the main pathway of respiration that continues to produce ATP when oxidative phosphorylation is blocked, and name its net ATP yield per glucose molecule. [2]

(d) State one physiological hazard of uncoupling agents to mammalian homeostasis. [1]

Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase) is a key enzyme in the light-independent stage of photosynthesis. It can catalyze both the carboxylation and oxygenation of RuBP.

(a) Describe how the first stable product of carbon fixation is converted to triose phosphate (TP) in the Calvin cycle. [4]

(b) Under high temperatures and dry conditions, \(C_3\) crops exhibit high rates of photorespiration.
(i) Suggest why high temperature increases the rate of photorespiration relative to photosynthesis. [2]
(ii) Explain why photorespiration reduces the overall productivity of \(C_3\) crops. [2]

(c) State two structural or anatomical features of \(C_4\) plants that minimize photorespiration. [2]

Antidiuretic hormone (ADH) plays a crucial role in maintaining blood water potential in mammals.

(a) Describe how ADH increases the water permeability of the collecting duct cells. [4]

(b) Nephrogenic diabetes insipidus (NDI) is a genetic disorder where the kidneys fail to respond to ADH due to a mutation in the ADH receptor gene.
(i) Explain why an individual with NDI produces a large volume of dilute urine, even when severely dehydrated. [3]
(ii) Explain why injections of synthetic ADH (desmopressin) are ineffective as a treatment for this patient. [1]

(c) State two physiological responses in a healthy mammal that occur when blood water potential increases above the set point. [2]

Sarin is a highly toxic organophosphate compound that acts as an irreversible inhibitor of the enzyme acetylcholinesterase.

(a) Describe the events occurring at the presynaptic membrane of a neuromuscular junction upon the arrival of an action potential, leading to the release of acetylcholine (ACh). [4]

(b) In the presence of Sarin, acetylcholinesterase is inactivated.
(i) Describe the normal role of acetylcholinesterase at the synapse. [2]
(ii) Explain the consequences of Sarin poisoning on post-synaptic transmission and muscle contraction. [4]

The Great Rift Valley lakes of East Africa contain hundreds of species of cichlid fish, which have evolved through rapid adaptive radiation.

(a) Define the term 'speciation' and distinguish between allopatric and sympatric speciation. [3]

(b) Describe how natural selection can lead to the evolution of a new species of cichlid fish feeding on different food sources within the same lake. [5]

(c) Explain the role of reproductive isolation in maintaining separate gene pools after speciation has occurred. [2]

The regulation of the operon system in Escherichia coli is a classic model of prokaryotic gene control.

(a) Outline the function of the following parts of the lac operon:
(i) Promoter [1]
(ii) Operator [1]
(iii) lacZ gene [1]

(b) Explain the sequence of molecular events that occurs in E. coli cells when lactose is present but glucose is absent. [5]

(c) State why the lac operon is described as an inducible operon, and distinguish this from a repressible operon. [2]

Auxins, such as indole-3-acetic acid (IAA), control plant growth responses including phototropism.

(a) Describe the distribution of IAA in a coleoptile tip exposed to unilateral light and explain how this distribution is achieved. [3]

(b) Explain how IAA stimulates cell elongation in the growing region of a plant shoot according to the acid growth hypothesis. [5]

(c) State the role of gibberellins (GA) in the germination of barley seeds. [2]

An investigation was carried out to study the effect of a synthetic peptide, AMP-4, on the osmoregulatory response of healthy volunteers. Two groups of volunteers, Group A (control) and Group B (experimental), fasted overnight and then drank 500 cm3 of pure water at time = 0 minutes. At time = 0 minutes: Group A received an injection of sterile saline solution; Group B received an injection of AMP-4 dissolved in saline. The urine flow rate and urine osmolarity (concentration of solutes) were monitored over 180 minutes. The results showed: In Group A, the mean urine flow rate increased rapidly from 1.5 cm3 min-1 to a peak of 12.0 cm3 min-1 at 60 minutes, before decreasing back to 1.5 cm3 min-1 by 180 minutes. Urine osmolarity decreased to a minimum of 100 mOsmol kg-1 at 60 minutes. In Group B, the mean urine flow rate remained constant at approximately 1.5 to 2.0 cm3 min-1 throughout the 180 minutes. Urine osmolarity remained high at approximately 800 mOsmol kg-1. (a) Describe the physiological homeostatic mechanism by which an increase in blood water potential leads to the production of dilute urine, as observed in Group A. [4] (b) Suggest and explain how the synthetic peptide AMP-4 could prevent the response seen in Group A, keeping urine flow rate low and osmolarity high. [4] (c) State the precise location of the osmoreceptors that detect changes in blood water potential. [1] (d) Name one hormone, other than ADH, involved in homeostasis in mammals that acts via a second messenger system. [1]

Promoters are essential components of vectors used in genetic engineering. An investigation compared the efficiency of two different eukaryotic promoters, Prom-X and Prom-Y, in driving the expression of a human therapeutic protein (HTP) gene in transgenic host mammalian cells. To monitor expression, a reporter gene encoding Green Fluorescent Protein (GFP) was fused downstream of each promoter inside identical plasmids. Cells transfected with the Prom-X-GFP construct showed a mean fluorescence intensity of 120 arbitrary units (au). Cells transfected with the Prom-Y-GFP construct showed a mean fluorescence intensity of 450 au. To confirm transcription levels, quantitative RT-PCR (reverse transcription polymerase chain reaction) was performed on isolated mRNA using primers specific to the HTP gene sequence. The cycle threshold (Ct) value was determined: Cells with Prom-X had a mean Ct value of 24.5; Cells with Prom-Y had a mean Ct value of 19.1. (a) Explain why a reporter gene, such as the gene for GFP, is useful when transforming cells with a gene of interest. [2] (b) State the role of a promoter in transcription. [2] (c) With reference to the quantitative RT-PCR results, explain which promoter is more efficient at driving the transcription of the HTP gene. [3] (d) PCR involves a repeating cycle of three temperature steps. Outline the temperature and purpose of each step. [3]

A student wants to investigate the effect of different concentrations of copper sulfate (acting as a heavy metal respiratory inhibitor) on the rate of anaerobic respiration in yeast. The student is provided with: 10% yeast suspension, 5% glucose solution, 1.0% methylene blue indicator, 0.10 mol dm^{-3} copper sulfate stock solution, distilled water, and standard laboratory glassware with a thermostatically controlled water bath. Describe a method the student could use to carry out this investigation to obtain quantitative, reliable results. Your description should include: (1) how to vary the independent variable to obtain five different concentrations, (2) how to control two key confounding variables, (3) how to measure the dependent variable, (4) how to ensure reliability of the results, and (5) a safety hazard and corresponding precaution.

A student investigated the stomatal density on the lower epidermis of leaves from a single species of tree grown in two different environments: high light exposure (sun leaves) and shaded exposure (shade leaves). The results are: Sun leaves: mean = 184 stomata mm^{-2}, standard deviation = 15.4, sample size = 15. Shade leaves: mean = 142 stomata mm^{-2}, standard deviation = 12.8, sample size = 15. (a) State a suitable null hypothesis for this investigation. (b) Explain why a Student's t-test is appropriate for analyzing these data. (c) Calculate the t-value using the formula: \( t = \frac{|\bar{x}_1 - \bar{x}_2|}{\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}} \). Show your working and give your answer to two decimal places. (d) State the degrees of freedom for this test. (e) The critical value of t at p = 0.05 for the calculated degrees of freedom is 2.048. Explain what conclusion can be drawn from the calculated t-value.

An ecological survey investigated soil biodiversity near a heavy-metal smelting factory. Species richness of soil macroinvertebrates was measured at six sites at increasing distances from the factory. The raw data and ranks are as follows: Site A (1.0 km, Rank 1; Species richness 4, Rank 1), Site B (2.5 km, Rank 2; Species richness 9, Rank 3), Site C (5.0 km, Rank 3; Species richness 8, Rank 2), Site D (7.5 km, Rank 4; Species richness 14, Rank 4), Site E (10.0 km, Rank 5; Species richness 15, Rank 5), Site F (15.0 km, Rank 6; Species richness 23, Rank 6). (a) Calculate the Spearman's rank correlation coefficient (\( r_s \)) using the formula: \( r_s = 1 - \left( \frac{6 \sum d^2}{n(n^2 - 1)} \right) \). Show your working. (b) State what your calculated \( r_s \) value indicates about the relationship. (c) At p = 0.05 and n = 6, the critical value for \( r_s \) is 0.886. State the conclusion that can be drawn from this statistical test. (d) Identify two abiotic soil factors that should have been controlled or measured at each site, and explain why each factor should be controlled.