Video Lesson:

Lesson Objective:

• Classify living things based on taxonomic principles,
• Describe taxonomic hierarchies
• State the characteristics of living things.

Characteristics of Living things

Welcome to Unit 2! In this section, we’ll explore the fascinating question: What makes something alive? Biologists study life in many different ways, whether it’s living with wildlife, collecting fossils, or even listening to whale songs. For example, they might count how many times a hummingbird’s wings beat per second. But what truly defines life? While it’s easy to say a galloping horse is alive and a car is not, the distinction isn’t always clear-cut. Movement alone doesn’t define life—cars can move and gelatin can wiggle. Instead, life is characterized by a series of shared properties.

Brainstorming Question

Before we dive into the details, consider this question: If someone places an object in front of you and asks if it’s alive, how would you determine its status?

• Would you poke it to see if it reacts?
• Would you watch it closely to see if it moves or breathes?
• Would you dissect it to examine its parts?

Key Terms

1. Unicellular: Organisms made up of a single cell, such as bacteria.
2. Multicellular: Organisms made up of more than one cell, such as plants and animals.
3. Autotrophs (Producers): Organisms that produce their own food using sunlight, such as plants.
4. Heterotrophs (Consumers): Organisms that cannot make their own food and consume other organisms for energy.
5. Stimuli: Environmental changes that living organisms can detect and respond to.
6. Growth: A permanent increase in size and mass due to an increase in cell number or cell size.
7. Reproduction: The process by which living organisms produce more of their kind.
8. Excretion: The removal of metabolic wastes from the body.
9. Homeostasis: The regulation of an organism’s internal conditions to maintain stability despite changes in the external environment.
10. Adaptations: Traits that evolve over time to help organisms survive and thrive in their environments.

Living things share several fundamental characteristics. These include:

1. All living things are made up of one or more cells:
   • Definition: All living things are composed of cells, the basic units of life.
   • Unicellular Organisms: These organisms, such as bacteria, consist of a single cell. Each cell performs all functions necessary for life, making it a complete organism.
   • Multicellular Organisms: These include plants, animals, and fungi, which are made up of many cells. In multicellular organisms, cells are specialized to perform specific functions and work together to support the life of the organism. For example, in humans, muscle cells contract to enable movement, and nerve cells transmit signals.
2. All living things require energy:
   • Metabolism: All organisms require energy to fuel their metabolic activities. Metabolism refers to the chemical reactions that occur within an organism to maintain life, including breaking down nutrients for energy and building up necessary compounds.
   • Producers (Autotrophs): These organisms, like plants, use sunlight to produce food through photosynthesis. They convert light energy into chemical energy stored in glucose, which serves as food.
   • Consumers (Heterotrophs): These organisms, such as animals, obtain energy by consuming other organisms. They may eat plants, other animals, or decompose organic material.
3. All living organisms respond to stimuli:
   • Definition: Living organisms can sense and respond to changes in their internal or external environment. This ability to respond helps organisms survive and thrive.
   • Examples:
     • Plants: Plants may grow towards light sources (a phenomenon known as phototropism).
     • Animals: Animals may flee from predators or move towards food sources. For example, a dog might bark at an intruder or wag its tail when seeing its owner.
4. All living things can grow:
   • Definition: Growth is a permanent increase in size and mass due to an increase in cell number or size.
   • Unicellular Growth: Even single-celled organisms grow by increasing in size.
   • Multicellular Growth: Multicellular organisms grow by increasing the number of cells. As cells divide and multiply, the organism becomes larger and more complex. This growth can be observed in stages, such as a human growing from a child to an adult.
5. All living things can reproduce:
   • Definition: The process by which organisms produce new individuals, ensuring the survival of their species.
   • Asexual Reproduction: Involves a single organism reproducing without the involvement of another, resulting in offspring that are genetically identical to the parent. Examples include bacteria dividing through binary fission and plants reproducing through vegetative propagation.
   • Sexual Reproduction: Involves the combination of genetic material from two parents, leading to offspring with genetic diversity. Examples include flowering plants reproducing through pollination and animals reproducing through mating.
6. All living things can excrete:
   • Definition: The removal of metabolic wastes produced by cells as a result of chemical reactions. These wastes must be expelled to maintain a stable internal environment.
   • Examples:
     • Respiration: Produces carbon dioxide, which must be expelled from the body.
     • Other Metabolic Wastes: Include urea, ammonia, and excess salts, which are excreted through processes such as urination and sweating.
7. All living things display ordered complexity:
   • Definition: Living things are highly complex and organized, from molecules to cells to entire organisms.
   • Levels of Organization:
     • Atoms and Molecules: The smallest units of matter that form the building blocks of life.
     • Cells: The basic units of life, each with specialized functions.
     • Tissues: Groups of similar cells that perform a specific function.
     • Organs: Structures made up of different tissues working together to perform specific tasks.
     • Organ Systems: Groups of organs that work together to carry out complex functions.
     • Organisms: Individual living entities capable of independent life.
8. Most living things maintain homeostasis:
   • Definition: The maintenance of stable internal conditions despite changes in the external environment. Homeostasis is crucial for the survival of organisms, allowing them to function properly.
   • Examples:
     • Body Temperature: Human bodies maintain a stable temperature around 37°C (98.6°F) despite external temperature fluctuations.
     • Blood Sugar Levels: Insulin and glucagon regulate blood sugar levels to ensure cells receive a constant supply of glucose.
9. All living things possess adaptations that evolve overtime:
   • Definition: Over time, organisms develop traits that help them survive and reproduce in their environments. These traits are passed on to future generations, contributing to the evolution of the species.
   • Examples:
     • Camouflage: Animals like chameleons change color to blend in with their surroundings and avoid predators.
     • Drought Resistance: Plants in arid environments develop deep roots or waxy leaves to conserve water.

By understanding these characteristics, you are expected to gain insight into what defines life and how living things are classified. This section will lay the foundation for exploring the diversity of life and the principles of biological classification, guiding you to appreciate the complexity and interconnectedness of the biological world.

Taxonomy of Living things

Welcome to the world of taxonomy! In this section, you will explore how biologists organize and classify the diverse forms of life on Earth. By understanding the principles of classification, you will see how scientists determine which organisms are related and share common characteristics. Imagine being able to identify and categorize all the living organisms you encounter—this is what taxonomy allows us to do!

Brainstorming Questions:

1. How organized are you in your daily life? Do you organize your clothes or books in some way?
2. Discuss the advantages of being organized. How does this relate to the classification of living things?

Key Terms

• Identification: Identifying organisms using characteristic features.
• Nomenclature: The aspect of taxonomy that deals specifically with naming organisms.
• Taxonomy: The science of naming and classifying species.
• Bacteria: A diverse group of single-celled organisms that lack a nucleus.
• Prokaryotic Cells: Unicellular organisms without a separate nucleus.
• Eukaryotic Cells: Cells with a nucleus and membrane-bound organelles.
• Species: A group of organisms that can reproduce to produce fertile offspring.

What is Taxonomy?

Taxonomy is the science of naming, identifying, and classifying organisms. It is a fundamental tool that biologists use to organize and understand the diversity of life. Taxonomy allows scientists to categorize organisms based on their similarities and differences, helping to reveal their evolutionary relationships.

Principles of Classification

Why Do Biologists Classify Living Things?

Classification is the process of grouping organisms based on their similarities, which helps biologists systematically organize and study the immense variety of life forms. This organization makes it easier to study, understand, and communicate about different forms of life.

Key Reasons for Classification:

1. Identification: Helps in naming and identifying organisms, providing a universal language for scientists.
2. Organization: Systematically organizes the diversity of life into manageable categories.
3. Understanding Relationships: Reveals evolutionary relationships among organisms.
4. Predictive Value: Allows predictions about characteristics shared by members of a group.
5. Communication: Facilitates clear and consistent communication about organisms.

Criteria for Classification

Biologists classify organisms into different categories by judging the degrees of their apparent similarities and differences. Here are the main criteria used in classification:

1. External Structures:
   • Physical Appearance: Includes shape, size, and color of the organism.
   • Example: Birds are grouped together because of their feathers and beaks.
2. Internal Structures:
   • Anatomy and Physiology: Examines bone structure, organ systems, and other internal features.
   • Example: Mammals are classified based on their internal anatomy, such as the presence of a backbone and warm-blooded physiology.
3. Habitat:
   • Ecological Niche: Where the organism lives and how it interacts with its environment.
   • Example: Aquatic animals are grouped based on their adaptation to living in water.
4. Genetic Makeup:
   • DNA and Genetic Similarities: Reveals evolutionary relationships and genetic closeness between organisms.
   • Example: Genetic analysis shows that humans and chimpanzees share a high percentage of DNA, indicating a close evolutionary relationship.

Taxonomic Hierarchies

Taxonomic hierarchies are systems of arranging various organisms into successive levels of biological classification, either in decreasing or increasing order. The primary levels of classification, from broadest to most specific, are:

Historical Perspective

Thousands of years ago, Aristotle developed one of the first classification systems, grouping organisms by simple morphological characteristics. Later, in the 1700s, Carolus Linnaeus introduced a more refined system, establishing the taxonomic hierarchy we use today.

Modern Classification Systems

Modern taxonomists use a variety of characteristics to classify organisms, including:

• Morphological: Physical structure and form.
• Physiological: Functional aspects.
• Molecular: Genetic makeup.
• Behavioral: How organisms act.
• Ecological: Their role in the environment.

Domains of Life

At the highest level, life is divided into three domains:

1. Bacteria: Prokaryotic cells without a nucleus.
2. Archaea: Prokaryotic cells that often live in extreme environments.
3. Eukarya: Eukaryotic cells with a nucleus, including protists, fungi, plants, and animals.

Characteristics of the Three Domains

• Bacteria:
  • Cells with no nucleus or membrane-bound organelles.
  • DNA exists as a circular chromosome.
  • Cell walls contain peptidoglycans.
  • Divide by binary fission.
  • Can be unicellular or colonial.
• Archaea:
  • Similar to bacteria in lacking a nucleus and membrane-bound organelles.
  • Cell walls do not contain peptidoglycans.
  • Often inhabit extreme environments.
  • Divide by binary fission.
  • Can be unicellular or colonial.
• Eukarya:
  • Cells with a nucleus and membrane-bound organelles.
  • DNA arranged as linear chromosomes within the nucleus.
  • Includes a wide range of organisms: unicellular, colonial, and multicellular.
  • Divide by mitosis.
  • Reproduce in various ways, both asexually and sexually.

Understanding Species

A species is the smallest natural group of organisms that can reproduce to produce fertile offspring. Members of a species often resemble each other closely in appearance and share many characteristics. Different definitions of species exist, but the biological species concept focuses on reproductive compatibility. For example, all cats belong to the same species but there are wide variations in the appearance of different breeds.

Lesson Summary

By studying taxonomy, you will gain a deeper appreciation for the complexity and diversity of life, and understand how scientists bring order to the natural world. Dive in and explore the fascinating science of classification.