# Identifying Biological Trends and Patterns in Data
ACT Science passages often ask you to describe trends or predict outcomes based on biological data. Recognising common biological patterns — growth curves, enzyme kinetics, predator-prey cycles — helps you answer faster and more accurately.
1. Common Biological Trends
Population Growth Curves
- Exponential growth (J-curve): Population increases rapidly without limits
- \(N_t = N_0 \times e^{rt}\) where \(r\) = growth rate
- Logistic growth (S-curve): Growth slows as population approaches carrying capacity \(K\)
- Lag phase → Exponential phase → Deceleration → Plateau
Enzyme Activity
- Activity increases with temperature up to an optimum, then drops sharply (denaturation)
- Activity increases with substrate concentration, then plateaus (saturation — all active sites occupied)
- pH affects enzyme shape: each enzyme has an optimal pH
Predator-Prey Cycles
- Prey population rises → predator population rises (with a time lag)
- Predator population rises → prey declines → predator declines
- Oscillating pattern with predator peaks lagging behind prey peaks
2. Describing Trends
Use precise language:
- "As temperature increases from 20°C to 37°C, enzyme activity increases"
- "Beyond 37°C, activity decreases sharply"
- "There is a positive correlation between light intensity and photosynthesis rate"
- "The relationship is inversely proportional"
Quantifying Trends
- Calculate rate of change: \(\text{Rate} = \frac{\Delta y}{\Delta x}\)
- Identify where the steepest change occurs
- Note any plateaus or inflection points
3. Worked Example
Passage: A study measured photosynthesis rate (measured as O₂ produced in mL/min) at different light intensities:
| Light Intensity (lux) | O₂ Production (mL/min) |
|---|---|
| 0 | -0.5 |
| 200 | 0.0 |
| 500 | 2.1 |
| 1000 | 3.8 |
| 2000 | 4.5 |
| 4000 | 4.6 |
Q: Describe the trend and explain why O₂ production is negative at 0 lux.
A: O₂ production increases with light intensity but the rate of increase slows at higher intensities (the curve plateaus around 2000–4000 lux). At 0 lux, no photosynthesis occurs but respiration still consumes O₂, so net O₂ production is negative. The compensation point is at approximately 200 lux, where photosynthesis rate equals respiration rate.
4. Practice Questions
Q1. Heart rate was measured before, during, and after exercise: 72, 72, 110, 145, 150, 148, 120, 90, 75 bpm (at 1-minute intervals). Describe the trend.
A1. Heart rate is stable at rest (~72 bpm), increases rapidly during exercise (peaking at ~150 bpm), then gradually returns toward resting level during recovery. The increase is steeper than the decrease, indicating recovery takes longer than the onset of elevated heart rate.
Q2. Yeast cell count doubles every 2 hours starting from 1000 cells. Predict the count at 10 hours.
A2. Number of doublings = \(10 ÷ 2 = 5\). Cell count = \(1000 \times 2^5 = 1000 \times 32 = 32{,}000\) cells.
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Summary
- Recognise standard biological patterns: growth curves, enzyme kinetics, cycles
- Describe trends using precise, directional language
- Calculate rates of change and identify key features (optima, plateaus, inflection points)
- Always relate the trend back to the biological process