Living Things and Their Diversity - Comprehensive Notes

Unit 5: Living Things and Their Diversity

This unit explores the characteristics of living things, the purpose and methods of classification, and the distinguishing features of the five kingdoms of life: Animalia, Plantae, Protista, Monera, and Fungi.

5.1 Living Things

Introduction

There are at least five million different kinds of living things in the world. These organisms are classified according to their similarities and differences to facilitate identification, study of relationships, origins, development, and understanding of the origin of life.

5.1.1 Characteristics of Living Things

Living things possess characteristics of life, including:

  • Movement: An action by an organism or part of an organism causing a change of position or place. Most single-celled creatures and animals move about as a whole. Fungi and plants may make movements with parts of their bodies.
  • Respiration: The chemical reactions that break down nutrient molecules in living cells to release energy for metabolism.
  • Sensitivity: The ability to detect or sense stimuli in the internal or external environment and to make appropriate responses. Plants can grow toward light, climb, or respond to touch. Bacteria can move toward or away from chemicals or light.
  • Growth: A permanent increase in size and dry mass by an increase in cell number or cell size or both. Living organisms grow from within using food, unlike non-living organisms that grow by addition of new material to the outside surface.
  • Reproduction: The ability to produce more organisms of the same kind, either sexually or asexually.
  • Excretion: The removal of toxic materials and waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements. For example, the process of respiration produces west product, carbon dioxides, which can be harmful in excess and must be removed.
  • Nutrition: The taking in of materials for energy, growth, and development. Plants require light, carbon dioxide, water, and ions; animals need organic compounds, ions, and usually water.
5.1.2 Classification and Scientific Names of Organisms

Classification is the sorting or grouping of things together based on common features/defined characteristics or criteria. The science of classification is called taxonomy.

Why Classify Organisms?

  • To identify those most at risk of extinction and to understand common ancestors.
  • It helps scientists to sort organisms in order and to make easy for study.
  • It helps them to identify new organisms by finding out which group they fit.

Taxonomy includes nomenclature (naming organisms) and systematics (placing organisms into groups based on similarities and differences).

Types of Classification:

  • Artificial Classification: Based on one or a few easily observed characteristics, designed for practical purposes with convenience and simplicity.

    • Example: Grouping animals that fly together (birds, bats, insects) or animals that live in water and have streamlined bodies (fish, whales). These are arbitrary groupings.

  • Natural (Biological) Classification: Uses natural relationships between organisms, considering more evidence, including internal and external features. This classification is hierarchical and reflects evolutionary relationships.

    • Example: Grouping humans and whales in the same class (mammals) because they both feed their young milk, a characteristic inherited from a common ancestor.
5.1.3 Hierarchy in the Classification of Organisms (Kingdom to Species)

Carl Linnaeus extended the binomial system to include more groups than just genus and species, arranging them in a hierarchy:

Kingdom → Phylum → Class → Order → Family → Genus → Species

As you move down the hierarchy (towards the species level), organisms share more specific features.

A species is defined as a group of organisms that can reproduce to produce fertile offspring.

  • Example: Horses and donkeys belong to the same kingdom, phylum, class, order, family, and genus but are different species. Their offspring (mules) are infertile.

Uses of Classification Hierarchy:

  • Sort organisms in order.
  • Identify new organisms.
  • Make it easier to study organisms when they are sorted in groups.

5.2 Kingdoms of Life

The five-kingdom system, developed by Robert H. Whittaker in 1969, is a common way of grouping living things based on distinctive characteristics:

  • Kingdom Animalia
  • Kingdom Plantae
  • Kingdom Fungi
  • Kingdom Protista
  • Kingdom Monera (Bacteria)
5.2.1 Kingdom Animalia

Major Characteristics: Eukaryotic, multicellular, no cell wall or photosynthetic pigments, mostly motile, heterotrophic (must feed on other organisms), reproduce sexually or asexually, store carbon as glycogen and fat.

Major Groups:

  • Invertebrates (lack backbones):

    • Insects (Arthropods): Segmented bodies with a firm exoskeleton, three pairs of jointed legs, compound eyes, typically two pairs of wings. Body divided into head, thorax, and abdomen. Examples: bees, butterflies, mosquitoes, houseflies, earwigs, greenfly, beetles.
    • Worms: Tube-like, flattened, or leaf-like bodies with hydro skeleton, no limbs, no eyes. Includes Platyhelminthes (flatworms), Annelida (segmented worms), Nemertea (ribbon worms), Nematoda (roundworms, pinworms). Live in marine, freshwater, and terrestrial habitats. Some are parasitic, others are free-living.

  • Vertebrates (have backbones):

    • Fish: Poikilothermic (cold-blooded), smooth, wet scales on skin, streamlined shape, breath by gills, reproduce sexually with external fertilization, fins. Live only in water.
    • Amphibians: Poikilothermic (cold-blooded), moist skins with capillaries, have lungs and skin for breathing, external fertilization, jelly-covered eggs in water, four limbs (back feet often webbed). Live both in water and on land.
    • Reptiles: Poikilothermic (cold-blooded), dry skin with scales, four legs (except snakes), produce eggs with a rubbery, waterproof shell laid on land, have lungs for breathing. Most live in warm habitats.
    • Birds: Homoeothermic (warm-blooded), feathers, scales on legs, two wings and two legs, produce eggs with a hard shell laid on land, lungs for breathing, beak. Live in water and on land.
    • Mammals: Homoeothermic (warm-blooded), produce live young, lungs for breathing, females have mammary glands to produce milk, four types of teeth. Live on land.
5.2.2 Kingdom Plantae

Major Characteristics: Eukaryotic, multicellular, cell wall made of cellulose, cells organized into tissues, contain plastids and chlorophyll, non-motile, autotrophic (make their own food by photosynthesis), reproduce sexually and asexually, store food as starch.

Major Groups:

  • Mosses & Liverworts (Bryophytes): Non-vascular plants (lack vascular tissue), lack true leaves, stem, and roots, live in moist places, reproduce through spores, help minimize erosion.

    • Bryophytes includes mosses, liverworts, and hornworts.

  • Ferns (Pteridophytes): Vascular plants (possess xylem and pholem), have well-developed xylem and phloem, seedless, reproduce through spores on the underside of leaves (sporophylls), adapted to aquatic, terrestrial, and cold-resistant habitats.

  • Gymnosperms (Conifers): "Naked seed", have cones instead of seeds, seeds are not enclosed in fruit, have wood and green needle-like or scale-like foliage, good sources of wood and paper, widely distributed in temperate and arctic regions.

  • Angiosperms (Flowering Plants): Have true root, stem, leaves, and flowers, seeds are enclosed in fruit, reproduce by seeds formed in flowers, divided into monocotyledons and dicotyledons, leaves usually broad with branched veins, good sources of food, medicine, clothing fiber, and wood.

5.2.3 Kingdom Protista

Major Characteristics: Eukaryotic, unicellular, diverse group classified by nutrition. They reproduce sexually or asexually.

Examples include Plasmodium (malaria), Amoeba, Euglena, Trypanosomes.

Major Groups:

  • Protozoans: Animal-like protists without cell walls, take in and digest solid food (Amoeba, Paramecium), unicellular 'animals.'
  • Protophyta: Plant-like protists with cell walls, have chloroplasts and make food by photosynthesis (Euglena, Chlamydomonas), unicellular 'plants.'
5.2.4 Kingdom Monera

Major Characteristics: Prokaryotic, unicellular, no nuclear membrane or membrane-bound organelles, cell wall of protein plus polysaccharide but not cellulose, reproduce asexually by binary fission.

Major Groups:

  • Blue-Green Algae (Cyanobacteria): Prokaryotic, singled celled photosynthetic organisms containing blue pigment, occur singly or in colonies in diverse habitats, produce oxygen as a byproduct of photosynthesis.
  • Bacteria: Very small organisms consisting of single cells, lack organized nucleus and chlorophyll pigments, cell walls made of peptidoglycan, various shapes (spherical, rod-shaped, spiral), have flagella, DNA in cytoplasm (nucleoid), found everywhere and are the most numerous organisms on Earth.
5.2.5 Kingdom Fungi

Major Characteristics: Eukaryotic, multicellular or unicellular, cell wall made of chitin, non-motile, heterotrophic (require organic compounds for nourishment), important as decomposers (saprophytes) and can be parasitic, store carbon as glycogen, reproduce sexually and asexually by spore formation.

Examples: Mushrooms, molds (multicellular), yeast (unicellular).

  • Yeast: Single-celled fungi used for baking and alcohol production.
  • Mould: Fungi which grow on decayed bread, cheese, fruit, or other food; many live in soil or dead wood. Example: Penicillium (used to make penicillin).
  • Mushroom: Flush, spore-bearing fruiting body produced above ground, on soil, or on food sources. Edible mushrooms are harvested wild or cultivated.