Natural Sciences
Natural Sciences
The natural sciences subtest samples biology, chemistry, physics, and basic anatomy/physiology, with health-related applications. High-yield topics include cell transport, homeostasis, body systems, atoms and bonds, acids and bases, energy, and motion.
Core rules
- Cell transport: diffusion moves solutes from high to low concentration; osmosis moves water across a membrane toward the side with more solute.
- Homeostasis: negative feedback reverses a change; positive feedback amplifies it.
- Body systems: arteries carry blood away from the heart; veins return blood; capillaries exchange materials.
- Chemistry: pH below 7 is acidic, above 7 is basic; each whole pH step is a tenfold change in hydrogen ion concentration.
- Physics: speed = distance ÷ time; force = mass × acceleration; energy is conserved but can change form.
Worked example
A red blood cell is placed in a hypertonic solution. The solution has a higher solute concentration than the cell. Water moves by osmosis from the cell, where water is more abundant, to the solution. The cell shrinks. A common wrong answer says the cell swells because “water follows salt” into the cell; in hypertonic conditions, the external solution already has more solute, so water leaves.
Traps
Reversing osmosis; confusing mitosis with meiosis; assuming all arteries carry oxygenated blood (the pulmonary artery does not); and treating pH as a linear scale.