Cambridge IGCSE Biology (0610) — Past Papers, Revision Notes & Exam Prep

Common mistakes and how to avoid them

1. Digestive organ jobs

   MistakeYou give organs the wrong digestive jobs, such as the gall bladder making bile, acid or enzymes, the wrong places for starch digestion, or the large intestine absorbing most water.

   Fix

   The liver makes bile; the gall bladder only stores it.

   Pasta starch: mouth (amylase starts) → stomach (acid stops it) → small intestine (amylase finishes).

   The small intestine absorbs most water.

2. Xylem and phloem

   MistakeYou swap xylem and phloem, so you say phloem carries water, mineral ions or starch, or you pick the wrong tissue in a root or leaf section.

   Fix

   Xylem: water and mineral ions.

   Phloem: sucrose and amino acids, not starch.

   Root section: xylem is the central star.

   Leaf vein: xylem on top, phloem below.

3. Kidneys, ureters and urethra

   MistakeYou swap the ureter and urethra on a diagram, or name the bladder, urethra, liver or gall bladder as the organ that removes urea from the blood.

   Fix

   The kidneys remove urea from the blood; the bladder only stores urine.

   A drop of urine from the left kidney: left ureter → bladder → urethra → out.

   Two ureters, one urethra.

4. Osmosis

   MistakeYou think tissue in a concentrated sugar solution takes in water and gains mass, or that the sugar itself crosses the membrane by osmosis.

   Fix

   Osmosis moves only water, not sugar, towards the more concentrated solution.

   A 5.0 g cucumber slice in strong sugar solution loses water: its mass falls to 4.6 g.

5. Food tests

   MistakeYou mix up the food tests, such as choosing Benedict's solution as the test for protein, or expecting DCPIP to turn blue when vitamin C is present.

   Fix

   Protein: biuret turns purple, e.g. with egg white.

   Benedict's is for reducing sugars: heat it, blue → brick red.

   Vitamin C: kiwi fruit juice turns blue DCPIP colourless, with no heating.

6. Cell structures

   MistakeYou give root hair cells chloroplasts or animal cells such as sperm a cell wall, or think the cell wall controls what enters and leaves a cell.

   Fix

   Root hair cells get no light, so have no chloroplasts.

   Sperm, an animal cell, has no cell wall.

   Sugar passes freely through the wall; the membrane controls entry and exit.

7. Diffusion

   MistakeYou choose an option saying a steeper concentration gradient or a larger surface area slows diffusion, or that diffusion needs energy from respiration.

   Fix

   Steeper gradient or larger surface area: faster diffusion.

   Food colouring in still water spreads fastest while the gradient is steep.

   No respiration needed: particles move by their own kinetic energy.

8. Anaerobic respiration

   MistakeYou mix up the products of anaerobic respiration, giving muscles carbon dioxide or alcohol, or giving yeast lactic acid.

   Fix

   Yeast in grape juice: glucose → alcohol + carbon dioxide (the bubbles).

   Anaerobic respiration in sprinting muscles: glucose → lactic acid only, no carbon dioxide.

   Neither equation uses oxygen.

More multiple-choice traps: Top 10 IGCSE Biology MCQ Mistakes

Common mistakes and how to avoid them

1. Mitosis and meiosis

   MistakeYou mix up the two divisions, thinking meiosis makes identical cells for repair, or giving a human gamete 46 chromosomes because you swap haploid and diploid.

   Fix

   Mitosis: genetically identical cells for growth and repair.

   Meiosis halves the chromosome number: genetically different haploid gametes.

   Dog: body cell 78 chromosomes, sperm 39.

   Human: body cell 46, gamete 23.

2. Turgid, flaccid, plasmolysed

   MistakeYou call a plant cell plasmolysed when it has gained water by osmosis, or mix up the terms turgid, flaccid and plasmolysed.

   Fix

   Limp lettuce goes crisp in water: its cells gain water, becoming turgid.

   In strong sugar solution, lettuce cells lose water: flaccid, then plasmolysed.

   Plasmolysed: membrane pulled away from the wall.

3. Antibodies

   MistakeYou pick the phagocyte as the cell that makes antibodies, or think an antibody fits any pathogen or has the same shape as its antigen.

   Fix

   Lymphocytes make antibodies; phagocytes engulf pathogens.

   Where an antigen has a dip, its antibody has a matching bump: complementary, not the same shape.

   Mumps antibodies bind only mumps antigens.

4. Active transport

   MistakeYou forget that active transport needs energy from respiration, so you miss why ion uptake falls when respiration slows, or you reverse its direction.

   Fix

   Active transport moves particles from lower to higher concentration, using energy from respiration.

   Roots given 2% oxygen instead of air's 21% respire less, so take up fewer potassium ions.

5. Hydrogencarbonate indicator

   MistakeYou expect the indicator around a plant in bright light to turn yellow, forgetting that photosynthesis then takes in carbon dioxide faster than respiration releases it.

   Fix

   Orange-red = normal CO₂, yellow = more, purple = less.

   Cress in bright light photosynthesises faster than it respires: CO₂ falls, so purple.

   In the dark, cress only respires: CO₂ rises, so yellow.

6. Limiting factors

   MistakeYou name one limiting factor for a whole photosynthesis curve, or think a process has stopped where the line on its rate graph levels off.

   Fix

   Rate against light: light limits wherever the line rises.

   Where the line levels off at 6 cm³ of oxygen per hour, photosynthesis has not stopped.

   CO₂ or temperature limits instead.

7. Transpiration

   MistakeYou think water leaves a leaf as a liquid, or you choose an option where humid, still air speeds up transpiration.

   Fix

   Water evaporates from mesophyll cells, then diffuses out of stomata as vapour.

   Humid, still air reduces the vapour gradient, so transpiration slows.

   Wet clothes dry slowly on damp, still days.

8. Enzymes

   MistakeYou say a high temperature kills an enzyme, or choose a boiled enzyme as if it still works.

   Fix

   Enzymes are proteins, not living things: too much heat denatures them, never kills them.

   Boiled at 100 °C, an enzyme's active site changes shape, so its substrate no longer fits.

More multiple-choice traps: Top 10 IGCSE Biology MCQ Mistakes

Common mistakes and how to avoid them

1. Blood components

   MistakeYou write that white blood cells 'fight disease' or 'protect the body', which is too vague to show what they actually do.

   Fix

   'Fights disease' and 'protects the body' are too vague: name the process.

   White blood cells engulf and digest pathogens: phagocytosis.

   White blood cells also make antibodies.

2. Genetic diagrams

   MistakeYou write a parent's whole genotype as one gamete, so your Punnett square holds the wrong alleles and the ratio comes out wrong.

   Fix

   Each gamete has one allele.

   Split each parent: Mm gives gametes M and m, never Mm.

   Mm × mm then gives Mm, Mm, mm, mm.

   Ratio 1 dominant : 1 recessive phenotype.

3. Key definitions

   MistakeYou give half a definition, such as a gene as 'a unit of inheritance' or a species as 'similar organisms living in one place'.

   Fix

   Gene: 'a length of DNA that codes for a protein', not just 'a unit of inheritance'.

   Species: 'a group of organisms that can reproduce to produce fertile offspring'.

4. Photosynthesis

   MistakeYou mix up chlorophyll, chloroplasts and palisade mesophyll, leave carbon dioxide out of photosynthesis, or write symbols when a word equation is asked for.

   Fix

   Green pigment: chlorophyll.

   Structure holding it: chloroplast.

   Leaf cell with the most chloroplasts: palisade mesophyll cell.

   Word equation, words only: carbon dioxide + water → glucose + oxygen.

5. Describe and explain

   MistakeWhen asked to explain, you only describe what happens or repeat the data, without giving the biological reason behind it.

   Fix

   Describe: what happens, with data.

   'In bright light, the pupil narrowed from 6 mm to 3 mm'.

   Explain: the biological reason why.

   'This lets less light in, protecting the retina'.

Common mistakes and how to avoid them

1. Enzyme action

   MistakeYou explain enzyme action by talking about the enzyme's shape in general, without mentioning the active site or how the substrate fits it.

   Fix

   Name the active site, not just 'shape'.

   Maltase's active site is complementary in shape to maltose.

   Maltose fits and forms an enzyme-substrate complex.

   Glucose is released; maltase is unchanged.

2. Antibiotic resistance

   MistakeYou say bacteria become 'immune' to antibiotics, or that the antibiotic causes the mutation that makes them resistant.

   Fix

   Mutations are random: e.g. one bacterium in a million already has a resistance allele.

   The antibiotic kills the others.

   The survivor reproduces, passing on the allele.

   Say 'resistant', not 'immune'.

3. Energy transfer

   MistakeYou say organisms or mitochondria 'produce energy', or say energy is lost between trophic levels without saying how.

   Fix

   Respiration 'releases energy'; never write 'produces energy'.

   A bush holds 2400 kJ; caterpillars eating it gain 240 kJ.

   The other 2160 kJ is lost: uneaten parts, faeces, heat from respiration.

4. Similar-sounding terms

   MistakeYou mix up paired terms, such as antigen and antibody, antibody and antibiotic, or rods and cones, so a correct idea reads as wrong.

   Fix

   A cold virus carries antigens; lymphocytes make antibodies that bind to them.

   Antibiotics are drugs that kill bacteria.

   Rods work in dim light; cones give colour vision.

5. Calculations and rounding

   MistakeIn a percentage change you divide by the wrong value, or you give the wrong number of significant figures or decimal places.

   Fix

   Percentage change = change ÷ original × 100.

   35 mm to 47 mm: 12 ÷ 35 × 100 = 34.285…%.

   To 2 significant figures: 34%.

   To 1 decimal place: 34.3%.

   Dividing by 47 gives 26%: wrong.

Common mistakes and how to avoid them

1. Recording results

   MistakeYou record some times in minutes and others in seconds, or use a different unit from the one the instructions ask for.

   Fix

   Convert every reading to the unit asked for.

   A reading of 3 min 50 s is 180 + 50 = 230 s.

   Write 230, not 3.50, under 'time taken / s'.

2. Biological drawings

   MistakeYou shade your drawing, sketch with broken or hairy lines, or draw it too small to show the structures clearly.

   Fix

   Sharp pencil, one unbroken line per edge, no shading.

   Show even a dark patch on a leaf by its outline only.

   Fill most of the space, avoiding the printed text.

3. Safety precautions

   MistakeYou give a general precaution like 'wear gloves' without saying how it lowers the risk, or add goggles, gloves or a lab coat where there is no real hazard.

   Fix

   Name the hazard and how your precaution lowers it.

   Scalpel: cut onto a tile, away from your fingers, so a slip misses them.

   Sugar solution needs no gloves or goggles.

4. Drawing graphs

   MistakeYou choose an awkward scale, leave units off the axes, or extend your line beyond the first and last readings.

   Fix

   Readings up to 34 s on 8 large squares: 5 s per square fills over half.

   Axis label: 'time taken / s'.

   Don't extend the line past your points unless asked.

5. Writing conclusions

   MistakeYour conclusion repeats the readings or mentions only what you measured, like 'time', without linking the result to the aim or to the biology being tested.

   Fix

   Link the trend to the process in the aim.

   Not 'the time taken fell as protease concentration rose'.

   Instead: 'as protease concentration rose, the protein was digested faster'.

Common mistakes and how to avoid them

1. Table headings

   MistakeYou head a column with something vague like 'test-tube', or write units next to every number in the table instead of in the heading.

   Fix

   Head each column with the quantity, a slash and its unit.

   Write 'temperature / °C', not 'test-tube'.

   In the cells write 45, not 45 °C.

2. Controlled variables

   MistakeAsked which variable was kept constant, you name one you think should have been controlled, rather than one the method actually kept the same.

   Fix

   Name only what the method keeps the same.

   'Add 3 cm³ of starch solution to each tube' gives 'volume of starch solution'.

   Skip temperature unless the method controls it.

3. Improving a method

   MistakeYou suggest vague improvements like 'cut more carefully' or 'be more accurate', or change a step that already worked well.

   Fix

   Name a weakness and the exact change.

   'Only 3 seeds per dish' → 'use 30 per dish', not 'be more accurate'.

   Keep steps that already work, like a thermostatic water-bath.

4. Making dilutions

   MistakeYou work out a dilution wrongly, so the volumes of stock solution and distilled water do not match the concentration you need or state.

   Fix

   Stock volume = final volume × concentration wanted ÷ stock concentration.

   20 cm³ of 9% from 15% stock: 20 × 9 ÷ 15 = 12 cm³ of stock.

   Add 20 − 12 = 8 cm³ of distilled water.

5. Magnification

   MistakeYou measure the image in centimetres but use the actual size in millimetres, or divide the wrong way round, so your magnification is far too big or small.

   Fix

   Magnification = image size ÷ actual size, same units.

   Image 72 mm, actual 0.4 mm: 72 ÷ 0.4 = ×180.

   Not 7.2 ÷ 0.4 = ×18 (image in cm).

   Not 0.4 ÷ 72 = 0.0056 (wrong way round).