Mid-September 2026: lessons began only a few weeks ago, and in Year 2 of the Italian technical school (istituto tecnico) the integrated sciences course — Chemistry and Biology — leaves behind the chemistry of the first year and moves mostly to biology. It starts with biomolecules, and by mid-October it reaches the cell, prokaryotic and eukaryotic. The first test falls in four to seven weeks, so between the end of October and the beginning of November. Later in the year come mitosis, meiosis and Mendel’s laws: they are the destination, but the body of this post is what you need to get there, biomolecules and the cell.
How you are really assessed: a structured test, not an oral test
Integrated sciences has a particularity that is worth understanding right away: the grade is a single one, shared between chemistry and biology, and the assessment comes in two different forms, almost never a long oral test at the board.
The first is a structured written test: multiple choice, gap-fills, term-definition matching, a few open questions but short ones. It completely changes how it pays to prepare: you do not need to build a fluent speech on a topic, you need precision with terms and speed of recognition. Whoever studies by repeating aloud as for an oral test arrives ready to explain, but often slow to recognise the right answer among four similar alternatives — and that is where time is lost on test day.
The second form is the lab report, which weighs as much as the written test. A report has a fixed structure — aim, materials, procedure, observations, conclusions — and there the grade depends much more on form than on content: a well-described and well-drawn microscope observation of a plant cell, with the parts correctly labelled, is worth more than a page of theory copied from the book. Whoever comes to the lab already knowing what they should see (wall, chloroplasts, vacuole) writes a more precise report in half the time.
Why a functional approach pays
At technical school, first-two-years biology is not an end in itself: those who go on to the agricultural, chemistry-and-biology or health-and-social-care tracks meet these same notions again, applied, from the following three years. For this reason the most useful approach is not to learn the structure of every molecule by heart, but to understand what it is for: why a carbohydrate is ready energy and a lipid is a reserve, not only how they are made.
The four classes of biomolecules
Biomolecules are the organic substances that build the cell and make it work. They divide into four classes, each with a function, a monomer (the repeating unit) and an example.
| Class | Function | Monomer | Example |
|---|---|---|---|
| Carbohydrates | Ready energy and short-term reserve | Monosaccharide (e.g. glucose) | Starch, glycogen |
| Lipids | Long-term energy reserve, cell membranes | Fatty acids + glycerol | Triglycerides, phospholipids |
| Proteins | Structure (e.g. collagen) and enzymes (catalysis) | Amino acid | Haemoglobin, insulin |
| Nucleic acids | Storing and passing on genetic information | Nucleotide | DNA, RNA |
The first three classes share the same building mechanism: monomers join through a condensation reaction (a bond forms and a water molecule comes out) and separate through a hydrolysis reaction (a water molecule breaks the bond, the reverse process). It is the same mechanism that digests starch into glucose and proteins into amino acids: once you have understood it once, it holds for all three classes.
Why water matters: polarity, hydrophilic and hydrophobic
Water is a polar molecule: oxygen attracts the bonding electrons more than hydrogen does, so the molecule has a slightly negative side and a slightly positive one. Substances that interact well with water (sugars, many proteins) are hydrophilic; those that repel it, like lipids, are hydrophobic. This distinction is not a chemical detail: it is the reason why the cell membrane is made the way it is, and it is the key to answering half of the questions on membrane transport.
Prokaryotic cell and eukaryotic cell
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Nucleus | Absent (DNA free in the cytoplasm) | Present, bounded by a membrane |
| Size | Smaller (1-10 µm) | Larger (10-100 µm) |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi…) |
| Cell wall | Present (different from the plant one) | Present only in some (plants, fungi) |
| Example | Bacteria | Animal and plant cells |
Animal cell and plant cell
Both are eukaryotic, but the plant cell has three structures that the animal cell does not: the cell wall (rigid, outside the membrane, made of cellulose), the chloroplasts (where photosynthesis takes place) and a very large central vacuole, which takes up much of the cell’s volume and regulates the internal pressure. The animal cell has a flexible plasma membrane with no wall, has no chloroplasts, and any vacuoles are small and not central.
The organelles, one by one
- Nucleus: contains the DNA and coordinates the activity of the cell.
- Ribosomes: synthesise proteins, free in the cytoplasm or attached to the ER.
- Rough endoplasmic reticulum: has ribosomes attached, synthesises proteins destined to be exported or inserted into membranes.
- Smooth endoplasmic reticulum: without ribosomes, synthesises lipids and disposes of toxic substances.
- Golgi apparatus: modifies, packages and sorts proteins towards their destination.
- Mitochondria: produce energy (ATP) through cellular respiration.
- Lysosomes: contain digestive enzymes, dispose of waste material.
- Chloroplasts: only in plant cells, site of photosynthesis.
The plasma membrane: a bilayer with a precise reason
The plasma membrane is made of a double layer of phospholipids. Each phospholipid has a hydrophilic head (attracted to water) and two hydrophobic tails (which repel it). With water both inside and outside the cell, the most stable arrangement is the one with the heads facing the watery outside and inside, and the tails hidden in the middle, away from the water: it is the same hydrophilic/hydrophobic principle seen above, applied to explain the most important structure of the cell.
Transport across the membrane
- Diffusion: the spontaneous movement of a substance from where it is more concentrated to where it is less concentrated, with no energy consumption.
- Osmosis: the diffusion of water across a semipermeable membrane, always from the less concentrated solution (more free water) towards the more concentrated one.
- Active transport: the movement of a substance against its own concentration gradient, which requires energy (ATP) and transport proteins.
The example that comes back in almost every test: a cell in a hypotonic solution (less concentrated than the cell) absorbs water by osmosis, and a cell that is hypertonic relative to the outside environment means that it is the environment that is less concentrated than it is — the terminology must always refer to the comparison between the two sides of the membrane, never be read on its own.
Two exercises in the test format
1. A multiple-choice set
Which organelle produces energy in the form of ATP?
A) Ribosomes B) Mitochondria C) Golgi apparatus D) Lysosomes
Correct answer: B. Ribosomes synthesise proteins, they do not produce energy; the Golgi apparatus modifies and sorts proteins already made; lysosomes digest waste material. Only the mitochondrion has as its specific function the production of ATP through cellular respiration: it is the keyword “energy” that should trigger the association, not the name of the organelle on its own.
A plant cell immersed in distilled water (hypotonic relative to the cytoplasm):
A) dehydrates B) bursts C) swells but does not burst, thanks to the wall D) stays unchanged
Correct answer: C. Distilled water is hypotonic relative to the cytoplasm, so water enters by osmosis and the cell tends to swell; dehydration (A) is the opposite, and “stays unchanged” (D) ignores osmosis. The difference from an animal cell is that here the rigid cell wall stops the membrane from expanding beyond a certain limit and the cell does not burst: it is exactly the next exercise.
2. A short open question
Explain why a plant cell in distilled water does not burst, while an animal cell in the same conditions does.
Answer: distilled water is hypotonic relative to the cytoplasm of both cells, so in both cases water enters by osmosis. The animal cell has only the plasma membrane, flexible and with no external support: the continuous entry of water makes it swell until the membrane can no longer hold, and it bursts (lysis). The plant cell instead has a rigid cell wall outside the membrane: when the cell swells, the wall resists and stops the expansion before the membrane breaks, creating an internal pressure (turgor) that keeps the cell rigid but intact.
Note the format: two sentences of mechanism (why the water enters) plus one sentence of structure (why the wall changes the outcome). It is the scheme that holds up most of the short open questions of this test.
Typical mistakes and how to spot them
| Typical mistake | How you notice it |
|---|---|
| Confusing mitochondria and chloroplasts | Mitochondria consume in order to produce energy (respiration), chloroplasts capture light to produce it (photosynthesis) — and they are only in plant cells |
| Saying the plant cell has no mitochondria | It has both: chloroplasts and mitochondria. Chloroplasts do photosynthesis, mitochondria respire — a plant needs both |
| Swapping hypotonic and hypertonic | The term always describes a comparison between two solutions: ask yourself “relative to what?” before answering |
| Calling the membrane the “wall” | The wall is rigid and found only in some cells; the plasma membrane is in all cells, animal ones included |
| Confusing rough and smooth ER | The rough one has ribosomes and makes proteins; the smooth one does not and makes lipids — “rough” because of the ribosomes is the memory key |
A three-step study method, tuned to the structured test
- Blank diagram of the organelles. Draw (or print without labels) a cell and try to name every organelle from memory, then check. It trains the visual recognition that the multiple-choice test requires.
- Redo the biomolecule table from memory. Close the book and rewrite the four classes with function, monomer and example: if a box stays empty, it is your priority for the next day.
- Timed self-test. In the last days, give yourself a set of ten multiple-choice questions and time yourself: the real test rewards whoever recognises quickly, not whoever gets to the end with the right reasoning but with time up.
Where to find more, and where not yet
On the site you will find the high school test practice papers, but at the moment they cover only maths and physics: we do not yet have a dedicated practice test on first-two-years biology, and it is not something I can promise for now — if you want to train against the clock, the multiple-choice format of this post is still a good starting point to reproduce with other questions from the book.
If the first year of integrated sciences, with Year 1 chemistry at technical school, is not yet quite solid, it is worth reviewing: the topics overlap less than they seem to, but the study method for a structured test is the same. If instead balancing reactions does not add up for you, I wrote a dedicated guide: balancing chemical equations in Year 2. And if in future you find yourself preparing an admission test for medical and health degrees, these same topics — cell, membrane, metabolism — will come back in a more in-depth form: I wrote about it in cell and molecular biology for medicine admission tests. Cell division, which comes straight after, has its own post with worked exercises: Mitosis and meiosis: differences, phases and exercises.
For the rest of the science syllabus you will find the full picture on the science tutoring page. If you want to set this chapter up properly before the end-of-October test, write to me from the contact page: the first introductory call is free and lasts half an hour.
