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Biology Fundamentals — Cells, Life Processes, Genetics & Ecosystems - Leejohnston - 11-13-2025
Biology Fundamentals — Cells, Life Processes, Genetics & Ecosystems
Biology is the study of life — from microscopic cells to entire ecosystems.
This thread introduces the core ideas that all life sciences are built upon.
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1. What Is Biology?
Biology explores:
• living organisms
• how cells work
• genetics & inheritance
• adaptation & evolution
• ecosystems
• human biology
It connects chemistry, medicine, neuroscience, ecology, and biotechnology.
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2. Cells — The Building Blocks of Life
Two main types of cells:
Prokaryotic cells:
• bacteria
• simple structure
• no nucleus
• circular DNA
Eukaryotic cells:
• plants, animals, fungi
• contain nucleus
• specialised organelles
Basic organelles:
• nucleus → stores DNA
• mitochondria → respiration, energy
• ribosomes → protein synthesis
• cytoplasm → chemical reactions
• cell membrane → controls entry/exit
• chloroplasts (plants) → photosynthesis
• vacuole (plants) → storage & support
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3. Life Processes (MRS GREN)
All living things perform:
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
These processes define what it means to be *alive*.
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4. Enzymes — Biological Catalysts
Enzymes speed up chemical reactions in cells.
Key facts:
• each enzyme works on one specific substrate
• temperature and pH affect enzyme activity
• high heat can denature (break) enzymes
Example:
Amylase breaks starch → glucose.
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5. Genetics & DNA
DNA is the molecule that carries genetic information.
Organised into:
• chromosomes
• genes
Humans have 23 pairs of chromosomes.
Genes encode instructions for proteins.
Alleles are different versions of the same gene.
Inheritance patterns include:
• dominant
• recessive
• codominant
Example:
Bb (brown eyes dominant) → brown eyes.
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6. Evolution & Natural Selection
Charles Darwin’s theory of natural selection:
1. Variation exists
2. Competition for survival
3. Individuals with advantageous traits survive
4. These traits are passed to offspring
Over long timescales, this leads to new species.
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7. Humans — Key Systems Overview
Respiratory system: gas exchange in lungs
Circulatory system: heart pumps blood around body
Digestive system: breaks food into nutrients
Nervous system: electrical messages via neurons
Immune system: protects against pathogens
Endocrine system: hormones regulate processes
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8. Ecology & Ecosystems
Ecology studies how organisms interact with each other and the environment.
Food chains: energy flow
Food webs: interconnected chains
Predator–prey cycles
Biodiversity
Adaptations to environment
Examples:
• cactus stores water
• polar bears have insulating fat
• fish have gills for oxygen extraction
Ecosystem threats:
• climate change
• pollution
• habitat loss
• invasive species
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9. Common Biology Mistakes
❌ Thinking plants don’t respire
✔ they do — day AND night
❌ Saying enzymes “die”
✔ enzymes denature; only living cells die
❌ Confusing chromosomes & genes
✔ chromosomes contain many genes
❌ Thinking adaptations happen because organisms “want” them
✔ adaptations come from natural selection over generations
❌ Mixing up diffusion, osmosis, active transport
✔ diffusion = movement from high → low concentration
✔ osmosis = diffusion of water
✔ active transport = requires energy
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10. Practice Questions
1. Name three organelles found in a plant cell but not an animal cell.
2. Define gene and allele.
3. Explain natural selection in one paragraph.
4. What happens to an enzyme when it is heated too much?
5. Give an example of a structural adaptation.
6. Describe the role of the mitochondria.
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Summary
This guide covered:
• cells
• life processes
• enzymes
• genetics
• evolution
• human body systems
• ecosystems
• common mistakes
• practice questions
Biology helps us understand what life is, how it works, and how it changes — from molecules to entire biospheres.