Lebanese University Faculty of Agronomy Entrance Examination common mistakes
Lebanese University Faculty of Agronomy Entrance Examination · Understand the traps and how to avoid them.
Biology - Stating that sugars in the phloem are pulled upward from root to leaf by transpiration, and treating xylem and phloem as interchangeable conduits.
Transpiration pull is visual and is taught first; both tissues are vascular, so candidates reuse the water-column model for sugar transport without checking tissue anatomy.
What to do instead
Draw a source-to-sink map for a loaded leaf and a storage root. Mark sieve tubes and companion cells as living, ATP-dependent loading, and pressure-flow bulk flow. Test the idea with a girdled stem: phloem sugars accumulate above the girdle while xylem water still moves.
Biology - Applying the 9:3:3:1 dihybrid phenotypic ratio to crosses involving linked genes or epistasis, as if the ratio were universal.
The ratio is memorized as a formula for any two-trait cross; candidates do not check independent assortment, recombination, or gene interaction before using it.
What to do instead
Before using any ratio, state the assumptions: independent assortment, no linkage, no epistasis, equal viability. Write parental gametes, draw a Punnett square or recombination map, and use a chi-square test to compare observed and expected counts. Practice one linked-gene cross and one recessive epistasis cross where the ratio is not 9:3:3:1.
Chemistry - In IUPAC naming, choosing the parent chain or suffix by the most visible group, for example naming a molecule with both C=C and -OH as an alkene and ignoring the alcohol suffix.
Functional-group priority is a table to memorize, but candidates often rely on the first group they notice or on the carbon chain length rather than on the highest-priority suffix.
What to do instead
Memorize the priority order: carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne > alkane; halogens and nitro groups are substituents. For each structure, list all groups, select the highest-priority suffix, then number the parent chain to give that suffix the lowest locant.
Chemistry - In titration calculations, substituting the burette reading in millilitres directly into c = n/V, or using the acid-to-base mole ratio from memory instead of from the balanced equation.
The procedure is familiar, so candidates skip the written equation and unit conversion; millilitres and litres look interchangeable in a hurry.
What to do instead
Write the balanced equation first and extract the mole ratio. Convert all volumes to litres before dividing, carry units through the calculation, and round only at the end. Check the result against the expected order of magnitude and report it with the correct number of significant figures.
Mathematics - Adding probabilities for non-mutually exclusive events, writing P(A or B) = P(A) + P(B) even when A and B can occur together.
The word “or” is learned as “add,” and mutually exclusive events are the first examples, so the overlap term is forgotten.
What to do instead
Use the inclusion–exclusion rule P(A∪B) = P(A) + P(B) − P(A∩B). Draw a Venn diagram, shade the overlap, and check that no probability exceeds 1. Classify each pair explicitly as mutually exclusive or not before calculating.
Mathematics - Dividing both sides of an equation or inequality by a variable expression such as x without considering x = 0 or a change of sign, losing solutions or reversing an inequality incorrectly.
Variables are treated as positive numbers because most early examples use positive coefficients; the zero case and sign cases are not checked.
What to do instead
Move all terms to one side and factor instead of dividing by the variable. For inequalities, build a sign chart with the critical values, including where the expression is zero or undefined. State the domain before simplifying and test one value in each interval.
Physics - Identifying the weight of a block and the normal force from a table as an action–reaction pair, or omitting the component of weight along an incline.
The two forces are equal and opposite in a simple resting case, so they look like a Newton’s third law pair; incline components are skipped when the diagram is drawn hastily.
What to do instead
Draw a free-body diagram for each object separately and label each force by the two bodies involved. Weight is Earth on block; its reaction is block on Earth. Normal is table on block. On an incline, resolve weight into mg sin θ along the slope and mg cos θ perpendicular to it before applying Newton’s second law.
Physics - Mixing sign conventions in the thin-lens equation, for example treating object distance as positive in one problem and negative in another, or giving a diverging lens a positive focal length without justification.
Several sign conventions are used in textbooks, and candidates switch between them mid-problem rather than choosing one and stating it.
What to do instead
Adopt one Cartesian convention and write it at the top of the solution: for example, light travels left to right, object distance is negative for a real object on the left, and focal length is negative for a diverging lens. List knowns with signs, solve algebraically, then confirm with a ray diagram and the meaning of a negative image distance.
Earth sciences - Naming a soil from only its most abundant or smallest particle, for example calling a soil with 40% sand, 40% silt and 20% clay a “clay” because clay particles are smallest.
Texture is confused with particle size alone; the texture triangle is read by following only one axis instead of the intersection of three percentages.
What to do instead
Practice reading the texture triangle by locating the sand, silt and clay percentages and finding their intersection; 40/40/20 is loam, not clay. Separately distinguish cation exchange capacity, which measures the soil’s ability to hold nutrient cations, from soil pH, which measures acidity.
Languages and scientific communication - Translating technical terms word-for-word between Arabic, French and English, for example writing “experience” for “expérience” when the intended meaning is “experiment,” and reporting measurements without SI units or uncertainty.
Cognates and everyday meanings are more familiar than the scientific register; lab reports are written quickly without a terminology or unit check.
What to do instead
Keep a three-column glossary of false friends and technical terms in Arabic, French and English, and use the scientific sense in context. Before submitting a report, check every numerical result for its SI unit, significant figures and stated uncertainty; read the sentence aloud to catch a cognate that changes meaning.