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Biology Tools

Interactive calculators and visualisations for Cambridge Biology.

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Magnification Calculator

M = Image size ÷ Actual size | Works in mm or µm

Calculate:

Magnification (×):

Image Size:

Actual Size:

Unit:

Formula Triangle

Use the triangle: I = M × A where I = Image size, M = Magnification, A = Actual size. Cover the quantity you want to find.

M = I ÷ A A = I ÷ M I = M × A

Always use the same units throughout. Convert µm → mm by ÷ 1000.

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Surface Area : Volume Ratio

Explore how cell size affects exchange efficiency

Shape:

Side length (µm): 10 µm

Length × Width × Height (µm):

Why SA:Volume matters

As a cell grows larger, its volume increases faster than its surface area. A high SA:V ratio means the cell can exchange gases and nutrients efficiently across its membrane.

🔑 Small cells have a larger SA:V ratio — better for diffusion. Large organisms need specialised exchange surfaces (lungs, villi, gills).

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Cardiac Output Calculator

CO = Stroke Volume × Heart Rate

Calculate:

Stroke Volume (cm³):

Heart Rate (bpm):

Cardiac Output (cm³/min):

Cardiac Output

CO = SV × HR where CO is in cm³/min (or dm³/min ÷ 1000), SV is the volume pumped per beat, and HR is beats per minute.

CO (cm³/min) = SV (cm³) × HR (bpm)

A resting adult has CO ≈ 5 dm³/min. During exercise this can reach 20–25 dm³/min.

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Punnett Square Generator

Monohybrid and dihybrid crosses with phenotype ratios

Cross type:

Parent 1 genotype:

Parent 2 genotype:

Dominant allele:

Dominant trait:

Recessive trait:

Mendel's Laws

The Punnett square predicts the probability of offspring genotypes. Uppercase = dominant allele; lowercase = recessive allele.

🔑 Monohybrid Aa × Aa → 1 AA : 2 Aa : 1 aa genotype ratio; 3 dominant : 1 recessive phenotype ratio.

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Photosynthesis Limiting Factors

Explore how light, CO₂, and temperature limit the rate

Light intensity (%): 60%

CO₂ concentration (%): 0.04%

Temperature (°C): 25°C

Limiting Factors

The rate of photosynthesis is controlled by the limiting factor — the factor in shortest supply. Increasing other factors has no effect until that bottleneck is removed.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

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Population Estimation (Mark-Recapture)

Lincoln Index: N = (n₁ × n₂) ÷ m

First catch (n₁):

Second catch (n₂):

Recaptured marked (m):

Lincoln Index

Mark a sample (n₁), release them, then catch a second sample (n₂). Count how many in n₂ are already marked (m).

N = (n₁ × n₂) ÷ m

Population must not change significantly between catches
Marks must not affect survival or behaviour
Marked individuals must mix randomly in the population

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Energy Transfer Efficiency

Trophic level efficiency = (energy out ÷ energy in) × 100

Producers (kJ/m²/yr):

Primary consumers:

Secondary consumers:

Tertiary consumers:

Energy Loss at Each Level

Only about 10% of energy passes from one trophic level to the next. The rest is lost as heat (respiration), movement, indigestible material, etc.

Efficiency (%) = (Energy at next level ÷ Energy at current level) × 100

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Enzyme Kinetics Explorer

Effect of temperature, pH, and substrate concentration on enzyme rate

Variable:

Optimum temperature (°C):

Optimum pH:

Enzyme Activity

Enzymes are biological catalysts. Their activity depends on temperature (optimum ≈ 37°C for human enzymes), pH (specific to each enzyme), and substrate concentration (reaches Vmax at saturation).

🔑 Above the optimum temperature, the enzyme denatures — the active site changes shape permanently and the enzyme stops working.