Characteristics and Classification of Living Organisms - IGCSE Biology

Introduction

• Biology: Study of living organisms (organisms).
• 7 Characteristics of Living Things (MRS GREN mnemonic):
  • M: Movement
  • R: Respiration
  • S: Sensitivity
  • G: Growth
  • R: Reproduction
  • E: Excretion
  • N: Nutrition

Characteristics Explained

• Movement: Change of position/place by an organism or part of it.
• Respiration: Chemical reactions in cells breaking down nutrients to release energy for metabolism.
• Sensitivity: Ability to detect and respond to environmental changes.
• Growth: Permanent increase in size and dry mass.
• Reproduction: Processes to make more of the same organism.
• Excretion: Removal of metabolic waste and excess substances.
• Nutrition: Intake of materials for energy, growth, and development.

Classification Systems

• Species: Group of organisms that can reproduce to produce fertile offspring.
• Binomial System: Internationally agreed system to name species with two parts (Genus, species).
  • Genus: Group of related species.
  • Example: Homo sapiens

Dichotomous Keys

• Purpose: Identify organisms based on features through branching questions.
• Example: If the body is covered with hair -> Has webbed feet -> Answer: C

Importance of Classification

• Purpose: Make studying organisms easier by grouping them.
• Traditional Method: Based on shared features.
• Modern Method: Based on DNA sequences.
• Five Kingdoms: Animals, Plants, Fungi, Protists, Prokaryotes.

Kingdoms of Living Organisms

Animals

• Features: Multicellular, nucleus, no cell walls/chloroplasts, nutrition from other living things.
• Example: Animal cell (nucleus, cell membrane, mitochondria, ribosomes, cytoplasm).

Plants

• Features: Multicellular, nucleus, chloroplasts, cell walls from cellulose, nutrition via photosynthesis.
• Example: Plant cell (animal cell features + cell wall, chloroplasts).

Fungi

• Features: Usually multicellular, nucleus, cell walls not from cellulose, saprophytic/parasitic nutrition.
• Example: Fungal cell.

Protists

• Features: Mostly unicellular, some multicellular, nucleus, some have cell walls/chloroplasts, varied nutrition.
• Example: Protist cells.

Prokaryotes

• Features: Unicellular, cell walls not from cellulose, no nucleus/mitochondria, cytoplasm.
• Example: Bacterial cell (DNA strands, plasmids).

Animal Kingdom Classification

Vertebrates

• Groups: Mammals, Birds, Reptiles, Amphibians, Fish.
• Mammals: Hair/fur, milk from mammary glands, 4-chambered heart, various teeth types (humans, cats, elephants).
• Birds: Feathers, hard-shelled eggs, beak, wings (toucan, parrot, flamingo).
• Reptiles: Scaly skin, rubbery-shelled eggs (snakes, crocodiles, turtles).
• Amphibians: Moist skin, eggs in water, aquatic larvae with gills, terrestrial adults with lungs (frogs, toads).
• Fish: Live in water, scales, gills, fins.

Invertebrates

• Definition: Animals without backbone.
• Arthropods: Group with jointed legs.
  • Myriapods: Many body segments with legs (centipedes, millipedes).
  • Insects: Body in three parts (head, thorax, abdomen), 3 pairs of legs, 2 pairs wings (grasshoppers, butterflies).
  • Arachnids: Four pairs of legs, book lungs (spiders, scorpions).
  • Crustaceans: 4+ pairs of legs, gills (crabs, lobsters).

Plant Kingdom Classification

• Two Groups: Ferns, Flowering Plants.
• Ferns: Fronds, reproduce by spores.
• Flowering Plants: Reproduce by flowers and seeds, seeds in ovary.
  • Monocotyledons: Branching roots, parallel leaf veins, petals in multiples of three.
  • Dicotyledons: Taproot system, branching leaf veins, petals in multiples of four or five.

Viruses

• Non-living: Cannot perform life processes independently.
• Structure: Genetic material encased in a protein coat.
• Example: Virus illustration.

Summary

• Chapter Focus: Characteristics and classifications of living organisms.
• Key Takeaway: Understanding diverse forms of life and their categorization.

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