Bio 120 lecture 2

Classifying Living Things

1. Why Do We Classify Living Things?

• Classification helps scientists organize and name living things in a systematic way.

• It ensures that all scientists around the world use the same names for organisms.

• Organisms are classified based on how closely related they are to each other.

Scientific Naming (Binomial Nomenclature)

• Each organism is given a scientific name using two Latin or Greek words:

  1. Genus (group of closely related species)

  2. Species (specific organism within that genus)

• Example:

  • Canis familiaris (domestic dog)

  • Canis lupus (wolf)

  • Canis latrans (coyote)

• Scientific names are written in italics or underlined.

Why Use Scientific Names?

• Avoids confusion from common names (e.g., "puma" and "mountain lion" refer to the same animal).

• Helps scientists clearly identify and study organisms.

2. The Tree of Life (How We Organize Living Things)

• All living things are grouped into a hierarchy from broadest to most specific.

• This grouping is based on common ancestry and shared characteristics.

Hierarchy of Classification

From most general to most specific:

1. Domain – The largest category (e.g., Eukarya).

2. Kingdom – Large groups of related organisms (e.g., Animalia).

3. Phylum – Major groups within kingdoms (e.g., Chordata for animals with a backbone).

4. Class – Subdivisions of phyla (e.g., Mammalia for mammals).

5. Order – Further grouping (e.g., Primates for monkeys and humans).

6. Family – Grouping of closely related species (e.g., Hominidae for great apes).

7. Genus – Even smaller group, containing very similar species (e.g., Homo).

8. Species – The most specific group (e.g., Homo sapiens – modern humans).

Examples:

Key Points

• Closely related organisms share a recent common ancestor.

• Distantly related organisms evolved from a common ancestor further in the past.

• Humans and dolphins are both mammals, meaning they share a more recent ancestor compared to humans and lobsters.

3. Types of Cells: Prokaryotes vs. Eukaryotes

All living things are made of cells, but there are two major types:

Prokaryotic Cells (Bacteria & Archaea)

• Simplest, most primitive type of cell.

• Small with no nucleus or complex structures inside.

• DNA floats freely in the cell.

• Example: Bacteria, Archaea (extremophiles living in extreme environments).

Eukaryotic Cells (Plants, Animals, Fungi, Protists)

• More complex and organized cells.

• Have a nucleus and membrane-bound organelles (like mitochondria and chloroplasts).

• Found in: Humans, plants, fungi, algae, and most living things we see.

Types of Eukaryotic Cells

1. Animal Cells – Have a nucleus, mitochondria, but no cell wall.

2. Plant Cells – Have chloroplasts, a cell wall, and a large vacuole for storing water.

4. How Organisms Get Energy: Autotrophs vs. Heterotrophs

Autotrophs ("Self-feeders")

• Organisms that produce their own food using photosynthesis.

• Use sunlight to create glucose (sugar) from carbon dioxide (CO₂) and water (H₂O).

• Examples:

  • Plants

  • Algae (in the ocean)

  • Photosynthetic bacteria

Heterotrophs ("Other-feeders")

• Organisms that cannot make their own food.

• Must consume organic material (plants, animals, or decomposed matter).

• Examples:

  • Herbivores (eat plants – deer, rabbits)

  • Carnivores (eat meat – lions, wolves)

  • Omnivores (eat both plants and meat – humans, bears)

5. Energy and Growth in Living Things

Primary Production (How Energy is Used in Plants)

• Gross Primary Production (GPP): Total organic matter produced by autotrophs.

• Plant Respiration: Some energy is used by the plant itself.

• Net Primary Production (NPP): The remaining organic matter that contributes to growth and reproduction.

Formula:

Gross PP−Plant Respiration=Net PP (Growth)Gross PP−Plant Respiration=Net PP (Growth)

Why is this important?

• More NPP means more growth – plants can grow bigger and reproduce more.

• Ecosystems depend on primary producers to support herbivores and carnivores.

6. Cellular Respiration: How Living Things Use Energy

All organisms break down glucose to release energy in a process called cellular respiration.

Equation for Cellular Respiration

Glucose(C6H12O6)+Oxygen(O2)→Carbon Dioxide(CO2)+Water(H2O)+Energy (ATP)Glucose(C6​H12​O6​)+Oxygen(O2​)→Carbon Dioxide(CO2​)+Water(H2​O)+Energy (ATP)

Key Points:

• This process releases energy (ATP) that cells can use to grow, move, and function.

• All organisms perform respiration, including plants, animals, and bacteria.

7. Characteristics of All Living Things

To be considered alive, an organism must meet all of these criteria:

1. Composed of one or more cells – The basic unit of life.

2. Take in materials & energy – Organisms must consume food or perform photosynthesis.

3. Maintain homeostasis – Keep a stable internal environment (e.g., body temperature).

4. Reproduce using DNA – Life continues through reproduction.

5. Respond to stimuli – React to light, temperature, sound, and other external factors.

6. Evolve over time – Adapt to their environment through natural selection.

7. Highly organized – Cells and systems are structured to function efficiently.

Final Takeaways

• Classification helps scientists organize life and understand relationships.

• Scientific names prevent confusion and provide universally recognized names.

• Life is grouped into domains, kingdoms, and smaller categories based on shared ancestry.

• Organisms are either prokaryotic or eukaryotic and classified by how they obtain energy.

• Living things must meet certain criteria to be considered "alive."