Pick one that interests you. Ten to fifteen minutes is enough for a first conversation; stop or return later. Paper and a pencil are optional, and no purchase or internet is needed. These are explanations and paper models, not home experiments. A supporter can read the source, listen, ask for a reason and let the learner make the choices. No personal health information is requested. The small “compare afterward” notes are feedback, not a test key to hide.
H01 · A boundary for a bookmark
You need: a scrap of paper or a spoken description. Source: Our typical animal membrane model has water on each side, a phospholipid bilayer with water-interacting heads and water-avoiding tails, a selective channel, and a glycoprotein with carbohydrate facing outside.
Make a bookmark-sized word map. Place heads toward both watery spaces and tails facing inward. Add the channel and glycoprotein. Explain to a listener why they do not have the same job. The listener asks, “Does your bookmark show an actual cell?” Add one caption that limits the drawing. If drawing is inconvenient, direct the listener's placements or describe the map aloud.
Compare afterward: The channel offers a selective route; the glycoprotein may help recognition/adhesion/signalling. A caption such as “Simplified model; no scale or full inventory” is valid. Ask next what would be needed to decide whether a particular protein's transport is active.
H02 · An arrow with a reason
You need: two labelled spaces, outside and inside. Source: Neutral M is 7 mmol/L outside and 2 mmol/L inside. It cannot cross the bare bilayer but has a suitable passive carrier. No cellular energy is supplied to that transport.
Choose an initial net arrow, name the mechanism and explain both concentration and route. A supporter draws two tiny opposing arrows and asks why your net arrow can still point one way. Make a short display line that avoids saying every molecule follows it. Try describing what would change if both sides were 2 mmol/L under stable equal conditions.
Compare afterward: Net inward facilitated diffusion is supported; individual crossing occurs both ways. The equal case has no net concentration-driven movement, not frozen particles. The example gives no amount moved per minute. Your next question could be how changing the number of carriers might affect a measured rate.
H03 · A paper water pouch
You need: a spoken comparison or a pouch outline. Source: A model pouch has 0.35 mol/L of an impermeant neutral solute inside, 0.10 mol/L outside. Water can cross, solute cannot; initial temperature and pressure are equal.
Predict initial net water movement. Name the moving substance and underline the conditions that support your prediction. A listener changes only one condition: pressure is now unknown and may differ. Make a second statement that matches the new information. You can retain the first equal-pressure statement as a valid statement about its original scenario.
Compare afterward: Initial net inward water movement follows in the first scenario. Under unknown pressure, concentration alone cannot make that direction certain; request full water-potential/pressure information. Neither case gives a final pouch volume. No solution preparation or change to anyone's drinking is invited.
H04 · Tell two vesicle stories
You need: three spaces on paper, or words. Source: Story A has an external large particle, a membrane wrapping around it, then a closed vesicle inside. Story B has an internal vesicle, fusion with the boundary, then contents outside.
Give each story a mechanism name. Tell it to someone without saying “a particle diffuses through a hole.” Explain why a whole cargo being enclosed or released by membranes differs from one molecule using a channel. A listener mixes the frames; restore the order using the membrane action, not memorised page positions.
Compare afterward: A is endocytosis; B is exocytosis. These are energy-requiring vesicle processes. The stories do not establish a species, actual event or transport rate. An interesting next question is what additional evidence would identify the cargo without assuming it from the drawing.
H05 · Doubling a tiny model
You need: a calculator if you like. Source: Two cubes have edges 5 µm and 10 µm. Area = 6a²; volume = a³; ratio = area/volume; nearest centre distance = a/2.
Calculate all four quantities for each. Compare how many times the edge, area and volume increase. Write two apparently different but compatible facts: the larger cube has more total area, and the smaller one has more area per unit volume. A supporter asks which fact an exchange-per-volume caption should use.
Compare afterward: Small: 150 µm², 125 µm³, 1.2 µm⁻¹, 2.5 µm. Large: 600 µm², 1,000 µm³, 0.6 µm⁻¹, 5 µm. Doubling gives fourfold area and eightfold volume. Geometry helps explain a constraint; it does not give a maximum size for every real cell.
H06 · A thin shape for a display
You need: optional rectangle sketches. Source: Cube C is 2 × 2 × 2 u. Box D is 1 × 1 × 8 u. Area = 2(lw + lh + wh); volume = lwh; shortest centre-to-face distance is half the smallest dimension.
Compare areas, volumes, ratios and shortest paths. Explain what the long thin shape gains and why you cannot simply announce a measured exchange rate. Choose a caption suitable for a small exhibit. A supporter can record dictated calculations so that the task remains about reasoning.
Compare afterward: C gives 24 u², 8 u³, 3 u⁻¹ and 1 u. D gives 34 u², 8 u³, 4.25 u⁻¹ and 0.5 u. D has equal volume, more surface and a shorter nearest path. Actual permeability, gradients and demand remain open; the model does not say every internal destination is equally close.
H07 · Find the untouched core
You need: paper or a calculator. Source: A supplied idealised cube has edge 5 mm and a reached layer 1 mm deep from every face at 4 min. For this supplied interval, the layer starts at depth d_start = 0 mm when t_start = 0 min. Average front speed = Δdepth/Δtime = (d_end − d_start)/(t_end − t_start). This is the model's interval average, not a constant future speed, intrinsic diffusion coefficient or molecular flux. Central edge = max(a − 2d, 0). Fraction reached = 1 − (central edge/a)³.
Find the central edge, total and central volumes, and fraction reached. Separately find the average front speed using Δdepth/Δtime = (d_end − d_start)/(t_end − t_start). Explain to a listener why “1 out of 5” is not the correct reached volume fraction. Label your two results with their different units or lack of a time unit.
Compare afterward: Core edge 3 mm, total volume 125 mm³, core 27 mm³, reached fraction 98/125 = 78.4%. Average front speed = Δdepth/Δtime = (d_end − d_start)/(t_end − t_start) = (1 − 0) mm / (4 − 0) min = 0.25 mm/min for that interval; d_start = 0 mm and t_start = 0 min. This one supplied layer does not establish a constant speed at all times or a measured molecular flux.
H08 · A claim with repeats
You need: a short spoken or written table. Source: Invented endpoint times for A are 20, 24, 28 s; for B they are 24, 28, 32 s. The hypothetical endpoint rule and conditions match. These are supplied examples.
Calculate each mean and range. Does “every B is slower than every A” survive the actual lists? State a careful conclusion and ask what larger or better evidence would help. A supporter can ask you to point to the exact values that make the universal claim fail.
Compare afterward: Means 24 s and 28 s; both ranges 8 s. B's mean is 4 s higher, but the lists overlap. B's 24 s is below A's 28 s, so “every” fails. More independent samples and uncertainty details would help; three authored values cannot prove a population law or actual investigation success.
H09 · A folded paper metaphor
You need: optionally a scrap of paper; folding is optional. Source: A model smooth patch and a folded patch each have projected footprint 3 cm². Their actual membrane areas are 3 cm² and 9 cm². Other exchange conditions are assumed suitable and equal, but no flux is measured.
Explain footprint versus actual surface. Describe or safely fold a broad scrap to illustrate the distinction; do not try to measure or imitate a real cell. How many times greater is the folded model's membrane area? Make a caption that explains a possible exchange advantage without promising a threefold rate for every substance.
Compare afterward: Actual area is three times greater while footprint is unchanged. More area may help exchange when routes and gradients permit it. Folds do not replace energy or permeability. Your paper illustrates geometry only; it is not an experiment demonstrating biological exchange.
H10 · Two questions a drawing cannot answer
You need: just a listener. Source: A membrane sketch shows one open channel and an ion at 12 mmol/L outside and 3 mmol/L inside. It supplies no ion charge, electrical conditions, channel throughput or time data. A caption says, “The ion moves inward at a fast measured rate.”
Challenge the caption in two different ways: direction and rate. Explain what further information each needs. A listener may ask, “Could an honest caption simply say what is shown?” Make one. End by choosing which missing piece you would request first and why.
Compare afterward: Charged-ion passive direction requires electrochemical information, not concentration alone. A measured rate requires actual amount/time or another explicitly defined rate measure and conditions. A valid caption is “An open channel and a concentration difference are shown; net direction and rate are not established.” No personal or medical example is needed.