Unit 1: The Living World
1. Characteristics of Living Beings
Living organisms are distinguished from non-living objects by a set of fundamental characteristics. While some of these can be seen in non-living things (like growth in mountains), it is the combination of these traits, especially metabolism and consciousness, that defines life.
- Growth: All living organisms grow. Growth is an irreversible increase in size, mass, or number of cells. In animals, growth is typically definite (stops after a certain age), while in plants, it is often indefinite (continues throughout life).
- Reproduction: The ability to produce offspring (progeny) similar to themselves. This ensures the continuity of a species. It can be asexual (one parent) or sexual (two parents).
- Metabolism: The sum total of all chemical reactions occurring inside a living body. This includes anabolism (building up, e.g., photosynthesis) and catabolism (breaking down, e.g., respiration).
- Cellular Organization: All living organisms are composed of one or more cells. The cell is the basic structural and functional unit of life.
- Consciousness (Response to Stimuli): The ability to sense the surrounding environment (stimuli) and respond to them. This can be a response to physical, chemical, or biological stimuli.
Exam Tip: Which are the
defining features of life?
- Defining Features: Metabolism, Cellular Organization, and Consciousness. These are found *only* in living things.
- Non-Defining Features: Growth and Reproduction. Non-living things can "grow" (e.g., a crystal). Some living things cannot reproduce (e.g., sterile mules, worker bees).
2. Diversity in the Living World
Biodiversity refers to the vast variety of life forms found on Earth. This includes diversity within species, between species, and of ecosystems.
- To date, approximately 1.7 to 1.8 million species have been scientifically described and named.
- This immense diversity makes a system of classification necessary to organize, study, and understand the relationships between different organisms.
- Taxonomy is the science of identifying, naming, and classifying organisms.
3. Levels of organization for Living Beings
Life is organized in a hierarchy, from simple to complex. Each level builds upon the one before it, with new properties (emergent properties) appearing at each step.
- Subatomic Particles: Protons, neutrons, electrons.
- Atoms: The smallest unit of an element (e.g., Carbon, Hydrogen).
- Molecules: Atoms bonded together (e.g., Water, DNA, Protein).
- Organelles: "Little organs" within a cell that perform specific functions (e.g., Nucleus, Mitochondria).
- Cells: The basic structural and functional unit of life.
- Tissues: A group of similar cells working together (e.g., Muscle tissue, Nervous tissue).
- Organs: A structure made of different tissues working together (e.g., Heart, Lung, Stomach).
- Organ Systems: A group of organs working together (e.g., Digestive system, Circulatory system).
- Organism: A complete, individual living being.
This hierarchy continues into ecology: Organism → Population → Community → Ecosystem → Biosphere.
4. Binomial Nomenclature & Rules
This is the formal scientific system of naming species, developed by Carolus Linnaeus. It gives every species a unique two-part name.
Binomial Name = Genus + specific epithet
Example: Homo sapiens (Human) or Mangifera indica (Mango)
Rules of Nomenclature
- Latinized: Scientific names are always in Latin or are Latinized, regardless of their origin.
- Two Parts: The first name is the Genus (always capitalized). The second name is the specific epithet (always lowercase).
- Italics: When typed, the entire name must be written in italics.
- Underlining: When handwritten, both parts of the name must be underlined separately (e.g., Homo sapiens).
Common Mistake: When handwriting, do NOT underline the name as one single line (e.g., Homo sapiens). This is incorrect. They must be underlined separately.
5. Zoological parks and Botanical gardens
These are methods of ex-situ conservation, which means conserving species *outside* their natural habitats.
Zoological Parks (Zoos)
- These are facilities where animals are housed within enclosures, cared for, and displayed to the public.
- Purpose:
- Conservation: They run captive breeding programs for endangered species to save them from extinction.
- Education: They teach the public about wildlife, biodiversity, and conservation.
- Research: They allow for scientific study of animal behavior, biology, and health.
Botanical Gardens
- These are large, curated collections of living plants.
- Plants are often grown in specialized gardens (e.g., rock gardens, medicinal gardens) and greenhouses.
- Purpose:
- Conservation: They maintain collections of rare and endangered plant species, including seed banks.
- Education & Identification: Plants are labeled with their scientific (binomial) name and family, serving as a key reference.
- Research: They are centers for plant taxonomy, genetics, and ecology.