WeSolve+ reads the whole document and writes the questions for you
Upload your PDF, photograph your notebook, or point the camera. WeSolve+ writes questions from that material, explains why each answer is right, reads the chapter back to you as a podcast, and remembers every item you missed until you own it.
The tool below is a small browser-only tool and it is not WeSolve+: paste a few lines and text rules turn them into cards on the spot. The real app, the one that uses AI, is behind the link above.
Cell structures, from your notes
This is a browser-only tool, and that is all it isIt splits the text you paste by rule, and nothing else. WeSolve+ is a different thing entirely: it reads your whole PDF with AI, writes the reasoning behind every question, speaks the chapter back to you, and remembers what you missed so it can return it. Try the real app now, free!
This tool splits the text you paste by rule and returns two sided cards. It cannot read a diagram, so photograph the diagrams into the app rather than into this box.
The geometric constraint comes first
Double a cell's radius and surface increases fourfold while volume increases eightfold, so exchange capacity falls behind demand. Everything else in the unit is a response: staying small, flattening, folding the membrane, or dividing the interior into compartments each with its own surface.
Selective permeability is what makes a compartment worth having
A boundary that let everything through would not be a boundary. The membrane admits some things and excludes others, which is what allows the inside to hold conditions different from the outside. That difference is what every organelle exists to maintain.
Transport questions are gradient questions
Ask which way the gradient points, then whether the substance is going with it or against it. With the gradient costs nothing; against it costs energy. Almost every transport question resolves once those two are established, and students who memorise transport types without the gradient step keep guessing.
Osmosis is examined through the surroundings
Water moves towards the more concentrated solution, so the question is always about the environment rather than the cell. Naming the surrounding solution as hypertonic or hypotonic and then stating which way water moves is the reliable two step, and reversing the order is where the confusion starts.
Endosymbiosis is evidence, not a story
Mitochondria and chloroplasts have their own DNA and double membranes, and those are the observations the endosymbiotic account explains. Questions ask what evidence supports it, so learning the two observations matters more than learning the narrative they support.
What to photograph for Cells
The diagrams, because this subject is examined through labelled structures. Related: Unit 1, AI flashcards and pricing.
Sources used on this page
- College Board, AP Biology
- Cell (biology)
- Cell membrane
- Organelle
- Endosymbiotic theory
- Active recall
- Spaced repetition
- Testing effect
- Forgetting curve
- Generation effect
- Judgment of learning
- Metacognition
- Desirable difficulty
- Distributed practice
- Formative assessment
- Flashcard
- Cloze test
- Multiple choice
- Test (assessment)
- Educational assessment
- Advanced Placement
- Curriculum
- Study skills
- Study guide
- Note-taking
- Overlearning
- Instructional scaffolding
- Item analysis
- Mastery learning
| Response | How it helps | Where it appears |
|---|---|---|
| Stay small | Keeps the ratio high | Most cells |
| Flatten | More surface per volume | Epithelial cells |
| Fold the membrane | Adds surface inside | Mitochondrial cristae |
| Compartmentalise | Each part gets its own surface | Eukaryotic organelles |
| Extend projections | Increases contact area | Microvilli, root hairs |
| Divide | Two smaller cells | The cell cycle |
What is AP Biology Unit 2?
Cells: structure and function, membranes, transport across them, compartmentalisation and the origin of organelles.
Why can a cell not just grow bigger?
Because volume grows faster than surface. A larger cell has proportionally less membrane through which to exchange materials, so it starves itself.
What makes a membrane useful?
Selective permeability. A boundary that let everything through would not maintain any difference between inside and outside.
How do I approach a transport question?
Find the gradient direction, then ask whether the substance moves with it or against it. With costs nothing, against costs energy.
What is the reliable way to answer osmosis questions?
Name the surrounding solution first, hypertonic or hypotonic, then state which way water moves. Reversing that order is where confusion starts.
What evidence supports endosymbiosis?
Mitochondria and chloroplasts have their own DNA and double membranes. Questions ask for the evidence rather than for the narrative.
Last updated: 2026-08-15