IGCSE Biology Chapter 1 : Characteristics and classification of living organisms
1.1 Characteristics of Living Organisms
Living organisms share several key characteristics:
Movement: Organisms move to find food, escape predators, or reproduce. Plants show movement through growth.
Respiration: A chemical process where organisms break down nutrients to release energy.
Sensitivity: Organisms respond to stimuli in their environment, such as light, temperature, or chemicals.
Growth: Organisms grow by increasing in size and number of cells.
Reproduction: Organisms produce offspring to continue the species.
Excretion: The removal of metabolic waste products, such as carbon dioxide and urea.
Nutrition: The intake of nutrients needed for energy, growth, and repair.
Sample Exam Questions:
Define the term 'respiration'.
Answer: Respiration is the chemical process by which organisms break down nutrients to release energy for various biological functions.
Explain how sensitivity is demonstrated in plants.
Answer: Sensitivity in plants is demonstrated by their ability to respond to environmental stimuli, such as light (phototropism), where they grow towards the light source.
List the characteristics of living organisms and explain the importance of excretion.
Answer: The characteristics are movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition. Excretion is important as it removes harmful metabolic waste products, preventing their buildup in the organism.
1.2 Concept of Classification Systems
Classification systems are used to organize living organisms into groups based on shared characteristics and evolutionary relationships. This system simplifies the study of biodiversity and helps scientists understand how different organisms are related to each other.
Hierarchical Structure:
Kingdom
Phylum
Class
Order
Family
Genus
Species (the most specific level, identifying individual organisms that can interbreed)
Binomial Nomenclature: The naming system developed by Carl Linnaeus, giving each species a two-part Latin name (Genus and species). For example, Homo sapiens (humans).
Natural Classification: Groups organisms based on evolutionary relationships, often reflected in their anatomy and genetics.
Artificial Classification: Groups organisms based on observable features rather than evolutionary history (e.g., grouping based on habitat or shape).
Uses of Classification Systems
Organization of Knowledge: Helps biologists study and reference organisms efficiently by placing them into manageable groups.
Understanding Evolutionary Relationships: Allows scientists to trace the lineage of organisms and understand how they evolved from common ancestors.
Conservation: Helps identify species that may be endangered or at risk of extinction, aiding in conservation efforts.
Medical Research: Informs drug development and treatment by identifying related species that share biological traits with humans.
Sample Exam Questions:
Explain why classification systems are important in biology. Answer: Classification systems help organize the vast diversity of organisms, making it easier for scientists to study and understand their relationships, evolution, and ecological roles.
What is binomial nomenclature, and why is it useful?
Answer: Binomial nomenclature is a system of naming organisms using two names (Genus and species), which provides a unique, universal name for each species, reducing confusion across languages and regions.
Describe the difference between natural and artificial classification systems.
Answer: Natural classification is based on evolutionary relationships and genetics, while artificial classification is based on observable features like appearance or habitat, which may not reflect evolutionary history.
1.3 Features of organisms
Main Features to Classify Animals and Plants into Kingdoms:
Animals: Multicellular, heterotrophic, no cell walls, complex nervous and muscular systems.
Plants: Multicellular, autotrophic (photosynthetic), have cell walls made of cellulose, contain chloroplasts.
Fungi: Usually multicellular, have cell walls made of chitin, heterotrophic (by absorption), lack chlorophyll.
Prokaryotes (Bacteria): Unicellular, no nucleus, cell walls, simpler structure, reproduce by binary fission.
Protoctists: Mostly unicellular, some multicellular, can be autotrophic or heterotrophic, usually have a nucleus.
Main Features for Vertebrate Groups:
Mammals: Warm-blooded, have hair/fur, give birth to live young, feed young with milk.
Birds: Warm-blooded, have feathers, lay hard-shelled eggs, have beaks, wings, and lightweight bones.
Reptiles: Cold-blooded, scaly skin, lay leathery eggs or give birth to live young, breathe with lungs.
Amphibians: Cold-blooded, moist skin, live part of life in water and part on land, lay jelly-like eggs in water.
Fish: Cold-blooded, live in water, breathe through gills, have scales and fins.
Main Features for Arthropod Groups:
Myriapods: Long, segmented bodies with many legs (e.g., centipedes, millipedes).
Insects: Three-part body (head, thorax, abdomen), three pairs of legs, usually two pairs of wings.
Arachnids: Two-part body (cephalothorax and abdomen), four pairs of legs, no antennae or wings (e.g., spiders, scorpions).
Crustaceans: Mostly aquatic, two pairs of antennae, more than four pairs of legs (e.g., crabs, lobsters).
Classifying Organisms into the Five Kingdoms:
Animals: Multicellular, heterotrophic, no cell walls.
Plants: Multicellular, autotrophic, with cell walls containing cellulose.
Fungi: Multicellular or unicellular, heterotrophic, with cell walls containing chitin.
Prokaryotes: Unicellular, no true nucleus.
Protoctists: A diverse group, mostly unicellular with a nucleus.
Classifying Organisms in the Plant Kingdom:
Ferns: Vascular plants that reproduce via spores and have fronds, no flowers or seeds.
Flowering Plants: Have flowers and seeds, divided into:
Monocotyledons: One seed leaf, parallel veins in leaves, fibrous roots (e.g., grasses).
Dicotyledons: Two seed leaves, net-like veins in leaves, taproot system (e.g., trees, beans).
Features of Viruses:
Protein Coat: Protective outer shell.
Genetic Material: DNA or RNA, used to infect host cells for replication.
Sample Exam Questions:
Describe the main characteristics of organisms in the plant kingdom and the fungi kingdom.
Answer:
Plant Kingdom: Multicellular, autotrophic (perform photosynthesis), have cell walls made of cellulose, contain chlorophyll, reproduce sexually or asexually.
Fungi Kingdom: Usually multicellular (except yeasts), heterotrophic (absorb nutrients from their environment), cell walls made of chitin, reproduce by spores.
Question:State two features that distinguish mammals from amphibians.
Answer:
Mammals are warm-blooded and have hair/fur, while amphibians are cold-blooded and have moist, permeable skin.
Mammals give birth to live young and feed their offspring with milk, while amphibians lay eggs in water and undergo metamorphosis.
Question:Identify the group of arthropods to which each of the following belongs:
(a) A creature with eight legs and no antennae
(b) An animal with a segmented body and many pairs of legs
Answer: (a) Arachnid (b) Myriapod
Question:State two features of viruses that make them different from living organisms.
Answer:
Viruses do not carry out metabolic processes like respiration or excretion on their own.
Viruses consist of a protein coat and genetic material, and they require a host cell to reproduce.
Question:Explain how you would distinguish between monocotyledonous and dicotyledonous plants based on their features.
Answer:
Monocotyledonous plants have one seed leaf (cotyledon), parallel leaf veins, and fibrous roots.
Dicotyledonous plants have two seed leaves, net-like leaf veins, and a taproot system.
Question:Using the binomial system of naming organisms, write the correct scientific name for humans. Explain the format of this name.
Answer : The scientific name for humans is Homo sapiens. The name is written in italics, with the Genus name (Homo) starting with a capital letter and the species name (sapiens) in lowercase.
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