Difficulty: Beginner | Prerequisites: None
This is your starting point for BIO 101. It covers what biology is, why it matters, and the foundational concepts (evolution, metabolism, ecology) that the rest of the course builds on. If you are joining late or need a refresher, start here before moving on to the Cells unit.
Biology is the study of living organisms, how they work, and how they interact with each other and their environments. The field rests on a few big ideas: evolution explains how species change over time through natural selection, metabolism covers the chemical reactions that keep organisms alive, and ecology looks at how organisms relate to their surroundings. Everything in this course builds on these foundations.
Biology
The scientific study of living organisms and their interactions with each other and their environments. Sub-fields include genetics, evolution, ecology, and physiology. In simple terms, biology is the science of life, from single cells to entire ecosystems.
Evolution
The process by which living organisms change over time, driven by natural selection. Think of it as the mechanism that explains why life on Earth is so diverse and why species share common ancestors.
Natural selection
The process in which traits that improve an organism's ability to survive and reproduce become more common in a population over generations. In simple terms, organisms better suited to their environment tend to leave more offspring, so their traits spread.
Metabolism
The complete set of chemical reactions that occur within an organism to sustain life, including breaking down nutrients for energy and synthesising new molecules for growth and repair. Think of it as the engine that keeps every living thing running.
Ecology
The study of how organisms interact with each other and with their physical environment, at scales from individual behaviour to entire ecosystems. In simple terms, ecology asks: who lives where, with whom, and how do they affect each other?
Homeostasis
The maintenance of a stable internal environment within an organism, despite changes in external conditions. Think of it as the body's thermostat: it keeps conditions (temperature, pH, water balance) within a narrow range so cells can function properly.
Biology investigates the structure, function, and behaviour of living organisms.
It spans multiple levels of organisation: molecules, cells, tissues, organs, organisms, populations, communities, ecosystems, and the biosphere.
Key sub-disciplines include:
Genetics (inheritance and variation)
Evolution (change in populations over time)
Ecology (organisms and their environments)
Physiology (how organisms function)
Evolution is the central unifying concept in biology.
It works through natural selection: individuals with traits better suited to their environment are more likely to survive and reproduce.
Over many generations, advantageous traits become more common in a population.
This explains both the diversity of species and the shared features (homologies) among related organisms.
Evolutionary thinking connects genetics, ecology, and physiology into a single framework.
Every living organism requires energy to grow, reproduce, and maintain itself.
Metabolism has two broad arms:
Catabolism: breaking down complex molecules (e.g. glucose) to release energy.
Anabolism: using energy to build new molecules needed for growth and repair.
These chemical reactions are tightly regulated and occur continuously in every cell.
Ecology examines how organisms interact at multiple scales: individual, population, community, and ecosystem.
Key interactions include:
Competition: two or more species (or individuals) vying for the same resources.
Cooperation / mutualism: species that benefit from working together.
Predation: one organism consuming another.
Human activities (habitat destruction, pollution, climate change) can disrupt these interactions and reshape ecosystems.
Biology underpins modern medicine: understanding how pathogens evolve (evolution) and how the body maintains balance (homeostasis) is the basis for developing vaccines, antibiotics, and treatments for chronic disease.
Ecological principles guide conservation efforts, agriculture, and environmental policy. Knowing how ecosystems respond to disruption helps scientists predict the effects of deforestation, overfishing, or climate change.
Students often think evolution means an individual organism changes during its lifetime. It does not. Evolution describes changes in a population across generations.
"Survival of the fittest" does not mean the strongest or fastest. "Fittest" means best suited to the current environment, which might mean the most cooperative or the most efficient at using scarce resources.
Metabolism is sometimes confused with digestion alone. Digestion is one part of catabolism; metabolism also includes all the building (anabolic) reactions that keep the body growing and repairing.
Students sometimes treat ecology and environmentalism as the same thing. Ecology is a scientific discipline; environmentalism is a social and political movement informed by ecological science.
⚠️ Be able to define evolution and natural selection separately. Exams often ask you to distinguish the mechanism (natural selection) from the outcome (evolution).
⚠️ Know the difference between catabolism and anabolism. A common exam question gives a reaction and asks which category it falls into.
⚠️ Understand that biology operates at multiple levels of organisation, from molecules up to the biosphere. Expect questions that ask you to identify the correct level for a given example.
⚠️ Be ready to explain how human activities affect ecosystems, with a specific example (e.g. deforestation reducing biodiversity).
True or False: Evolution occurs within a single organism's lifetime.
Fill in the blank: The two arms of metabolism are ______ (breaking down) and ______ (building up).
True or False: Natural selection always favours the physically strongest individuals.
Fill in the blank: The study of how organisms interact with each other and their environment is called ______.
True or False: Biology only studies animals and plants.
Answers: 1. False (evolution occurs across generations in populations). 2. Catabolism, anabolism. 3. False (it favours those best suited to the environment). 4. Ecology. 5. False (it also covers bacteria, archaea, fungi, protists, and more).
Q: Define biology and name three of its major sub-disciplines.
A: Biology is the scientific study of living organisms and their interactions. Major sub-disciplines include genetics, evolution, and ecology (also physiology, among others).
Q: Explain how natural selection leads to evolution.
A: Individuals with traits better suited to their environment are more likely to survive and reproduce. Over many generations, these advantageous traits become more frequent in the population, and the population evolves.
Q: What is the difference between catabolism and anabolism?
A: Catabolism is the breakdown of complex molecules to release energy. Anabolism is the use of energy to synthesise new molecules needed for growth and repair. Together they make up metabolism.
Q: Give one example of how human activities can disrupt an ecosystem.
A: Deforestation removes habitat and food sources for many species, reducing biodiversity and disrupting food webs within the ecosystem.
Q: Why is homeostasis important for living organisms?
A: Homeostasis maintains stable internal conditions (temperature, pH, water balance) so that cells and enzymes can function properly. Without it, metabolic processes would fail.
This material connects directly to the Cells unit (next in the course), because cells are where metabolism, homeostasis, and genetic inheritance happen at the physical level.
Evolution and natural selection will reappear throughout the course whenever you study genetics (how heritable variation arises) and ecology (how environmental pressures shape populations).
Understanding energy and metabolism here lays the groundwork for later units on photosynthesis and cellular respiration, where you will trace the specific chemical pathways involved.
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