General Biology: Life, Its Levels and Basic Principles
What you must understand
General biology sets the vocabulary the whole exam leans on. Be sure you can define life by its shared properties (organisation, metabolism, growth, reproduction, irritability/response to stimuli, adaptation, evolution) and distinguish living from non-living. Learn the levels of organisation in order: atom → molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere. Understand that metabolism splits into anabolism (building, energy-consuming) and catabolism (breaking down, energy-releasing), and that homeostasis is the maintenance of a stable internal state. Know the difference between prokaryotic and eukaryotic cells at a general level, and the idea that all organisms share a common chemical basis (water, proteins, nucleic acids, carbohydrates, lipids).
Traps candidates fall into
- Mixing up the levels of organisation: a population is a group of one species, a community includes several species, an ecosystem adds the non-living environment.
- Treating a virus as a cell - it lacks metabolism and independent reproduction, so it is not a cell even though it is studied in biology.
- Confusing growth (increase in size/mass) with development (change in form and function).
- Assuming "living" requires movement - plants are clearly alive without moving from place to place.
Worked example / rule of thumb
When a question asks "at which level is X?", ask what is the smallest unit described. A single heart is an organ; a group of muscle cells is a tissue; all the frogs in a pond are a population; the pond with its frogs, fish, water and mud is an ecosystem. Rule of thumb: cell → tissue → organ → system → organism is the internal ladder; organism → population → community → ecosystem is the ecological ladder.