1.4.9Inquiry Process
Cell Types and Structures: Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 10 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Identifying Cells
Work through a micrograph by asking the same short list of questions in the same order each time, so nothing is missed.
Presence of nucleus
- Presence of nucleus A clear dark nucleus indicates a eukaryote;
- no nucleus with scattered DNA suggests a prokaryote.
Cell wall and shape
- Cell wall and shape Rectangular cells with thick walls point to plants, while rounded cells with no wall suggest animal cells.
Chloroplasts
- Chloroplasts Green oval bodies filled with stacked thylakoids confirm a photosynthetic plant or algal cell.
Size clues
- Size clues A bacterium is usually about ten times smaller in length than a typical animal cell.
Mitochondria
- Mitochondria Oval profiles with an inner folded membrane appear in nearly all eukaryotic cells under the electron microscope.
| Observation | Likely conclusion |
|---|---|
| No nucleus, cell about 2 μm, wall visible | Bacterium (prokaryote) |
| Nucleus, cellulose wall, chloroplasts, large vacuole | Plant cell |
| Nucleus, no wall, no chloroplasts, irregular shape | Animal cell |
| Nucleus, chitin wall, no chloroplasts, thread-like hyphae | Fungus |
Section 2 of 5Magnification Method
Always keep the units the same on both sides before dividing.
1
Measure the length of the image using a ruler, working in millimetres for convenience.
2
Convert the image length to micrometres by multiplying by 1000 so units match the actual size.
3
Use the formula magnification equals image size divided by actual size.
4
Rearrange to actual size equals image size divided by magnification when a scale factor is given.
5
Where a scale bar is shown, divide the measured bar length by the stated length it represents.
Section 3 of 5Microscope Types
Microscope Types
Light microscope
- Light microscope Shows living or stained cells at up to about 1500 times, resolving structures larger than roughly 200 nm.
Transmission EM
- Transmission EM Passes electrons through thin slices to reveal internal ultrastructure such as ribosomes and membranes in great detail.
Scanning EM
- Scanning EM Scans a coated surface to give three-dimensional images of the outer surface of cells and tissues.
Section 4 of 5Worked Example
Question
- A drawing of a cell is 60 mm long.
- The actual cell is 25 μm long.
- Calculate the magnification.
- Convert the drawing to micrometres60 mm × 1000 = 60 000 μm.
- Divide image size by actual size60 000 ÷ 25.
- 60 000 ÷ 25 = 2400.
Answer
- Magnification = ×2400.
- As a check, 2400 × 25 μm = 60 000 μm = 60 mm, which matches the drawing.
Section 5 of 5Exam Checklist & Tips
1.4.9 – Key Points for the Exam
- Magnification How many times larger an image is than the real object.
- Scale bar A line on an image representing a known actual length.
- Resolution The ability to distinguish two close points as separate.
- Micrograph A photograph taken through a microscope.
Common Mistakes
- Forgetting to convert units, such as dividing millimetres by micrometres.
- Confusing magnification with resolution; a larger image need not be clearer.
- Measuring the scale bar from the wrong edge or including the thickness of the line.
- Calling any organelle with a double membrane a nucleus.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.