Introduction to Biology

What is Biology?

Biology is the scientific study of living things and the processes that sustain life. It encompasses the structure, function, growth, origin, evolution, and distribution of living organisms.

• Living things are made of cells, use energy, respond to their environment, grow, develop, reproduce, maintain homeostasis, and evolve over generations.

• The scientific method is used to investigate biological questions.

The Scientific Method

The scientific method is a systematic approach to understanding the natural world through observation and experimentation.

• Observation: Notice something in the world.

• Question: Ask why or how it happens.

• Hypothesis: Make an educated guess.

• Experiment: Test your hypothesis.

• Analyze: Collect and examine data.

• Conclusion: Decide if your guess was right.

• Repeat: Science is ongoing and self-correcting.

Chemistry in Biology

Main Elements of Life

Living organisms are primarily composed of four elements: carbon, hydrogen, oxygen, and nitrogen (CHON).

• Water is a polar molecule, excellent at dissolving substances, and essential for life.

• Cohesion (water sticks to itself) and adhesion (sticks to other things) are important properties.

• Water helps regulate temperature and supports biochemical reactions.

Macromolecules

Macromolecules are large, complex molecules essential for life.

• Carbohydrates: Sugars, energy source.

• Lipids: Fats, oils; store energy, make membranes.

• Proteins: Enzymes, structure, most cellular functions.

• Nucleic acids: DNA and RNA, store genetic information.

Cell Structure and Function

Types of Cells

Cells are the basic units of life. There are two main types:

• Prokaryotes: No nucleus (e.g., bacteria, archaea).

• Eukaryotes: Have a nucleus and organelles (e.g., plants, animals, fungi, protists).

All cells have a cell membrane, cytoplasm, and ribosomes.

Cell Organelles and Their Functions

• Nucleus: Contains DNA.

• Mitochondria: Makes energy (ATP).

• Cytoplasm: Fluid for reactions.

• Ribosomes: Make proteins.

• Cell membrane: Controls what enters and exits the cell.

Plant cells have additional structures:

• Cell wall: Structure and support.

• Chloroplasts: Site of photosynthesis.

• Large central vacuole: Storage of water and nutrients.

Cell Transport and Energy

Cell Transport Mechanisms

Cells move substances across membranes using several mechanisms:

• Diffusion: Movement from high to low concentration; no energy required.

• Osmosis: Diffusion of water across a membrane.

• Active transport: Requires energy (ATP); moves materials from low to high concentration.

Cellular Respiration

Cellular respiration converts glucose and oxygen into ATP, water, and carbon dioxide.

• Equation:

Photosynthesis

Photosynthesis is the process by which plants and algae use sunlight to make glucose and oxygen.

• Equation:

Genetics

DNA and Genes

Genetic information is stored in DNA, which has a double helix structure. The bases are adenine (A), thymine (T), cytosine (C), and guanine (G).

• Genes: Segments of DNA that code for traits.

• Chromosomes: Bundles of DNA; humans have 46 chromosomes.

Cell Division

• Mitosis: Cell division for growth and repair (produces 2 identical cells).

• Meiosis: Cell division for reproduction (produces 4 unique cells).

Evolution and Ecology

Evolution

Evolution is the change in species over generations. Natural selection favors organisms best adapted to their environment.

• Evidence includes fossils, DNA similarities, and comparative anatomy.

Ecology

Ecology studies the interactions between organisms and their environment.

• Levels: Organism → Population → Community → Ecosystem → Biosphere

• Producers: Plants, make their own food.

• Consumers: Animals, eat other organisms.

• Decomposers: Bacteria, fungi, break down dead matter.

• Energy flows from the sun to producers to consumers to decomposers.

Domains and Kingdoms

All life is classified into three domains and several kingdoms: