CAIE-IGCSE-Biology - Theory

ZNOTES.ORG Updated To 2023-2025 Syllabus CAIE IGCSE Biology

Purpose

Summarized notes prepared for personal use by Kian.

1. Characteristics and Classification of Living Organisms

1.1. Characteristics of Living Organisms

To remember the key features of living organisms, use the acronym MRS GREN:

• Movement: Involves a change of position by the organism or a part of it, such as the locomotion of animals or the growth movement in plants.

• Respiration: A biochemical process that converts nutrients into energy, crucial for sustaining life processes.

• Sensitivity: Refers to how organisms respond to various stimuli in their environment, such as light, heat, and touch.

• Growth: Indicates a permanent increase in size and mass, which can take place in various forms such as cellular division or enlargement.

• Reproduction: Encompasses all processes that lead to the production of offspring, ensuring the survival of the species.

• Excretion: The mechanism for removing metabolic waste products from the organism, vital for maintaining internal balance.

• Nutrition: The process of taking in materials necessary to produce energy and support growth, including photosynthesis in plants and ingestion in animals.

1.2. Concept and Uses of Classification System

Organisms are systematically grouped based on shared characteristics and evolutionary relationships.

• Species: The most fundamental unit of classification, defined as groups of organisms that can interbreed and produce fertile offspring.

• Sequence of Classification: The hierarchical structure of biological classification from broad to specific:

  1. Kingdom

  2. Phylum

  3. Class

  4. Order

  5. Family

  6. Genus

  7. Species

• Mnemonic: King Philip Came Over For Good Soup.

• Binomial Nomenclature: A two-part naming system for species consisting of the genus name (capitalized) and the species identifier (lowercase), e.g., Homo sapiens.

1.3. Features of Organisms

The Five Kingdoms

• Animals: Complex multicellular organisms that are heterotrophic (obtaining food by ingestion), characterized by a lack of cell walls and a central nervous system (e.g., elephant, butterfly).

• Plants: Also multicellular, but autotrophic, synthesizing their food through photosynthesis and possessing a cellulose cell wall, essential for structure (e.g., pine tree, sunflower).

• Fungi: Can be unicellular or multicellular heterotrophs that absorb nutrients from organic material and have cell walls made of chitin (e.g., molds, mushrooms).

• Prokaryotes: Unicellular organisms without a true nucleus or membrane-bound organelles, primarily bacteria that can be classified further into Archaea and Bacteria (e.g., Streptococcus).

• Protist/Protoctist: Diverse group of mostly unicellular organisms that can exhibit characteristics of animals, plants, or fungi (e.g., Paramecium, algae).

1.4. Vertebrates

Different groups of vertebrates exhibit unique characteristics:

• Mammals: Warm-blooded, possess fur or hair, give birth to live young (most), and have mammary glands for nursing offspring. Examples include humans and dolphins.

• Reptiles: Cold-blooded, characterized by scaly skin, typically lay eggs with leathery shells, and also exhibit internal fertilization (e.g., snakes, turtles).

• Fish: Aquatic animals with gills for breathing, streamlined bodies, and fins, most reproduce through external fertilization (e.g., salmon, goldfish).

• Amphibians: Capable of living both in water and on land, characterized by a life cycle that includes development from larva with gills to adults with lungs (e.g., frogs, toads).

• Birds: Endothermic, characterized by feathers, hard-shelled eggs, and unique respiratory systems allowing for sustained flight (e.g., eagles, penguins).

1.5. Arthropods

Invertebrates with segmented bodies and jointed appendages. Notable features include:

• An external skeleton (exoskeleton) made of chitin that supports and protects the body.

• Diverse classes such as:

  • Insects: Characterized by having six legs and typically two pairs of wings (e.g., ants, butterflies).

  • Arachnids: Possess eight legs and are primarily terrestrial (e.g., spiders, scorpions).

  • Crustaceans: Mostly aquatic, typically have ten or more legs, and include crabs and lobsters.

  • Myriapods: Characterized by a long segmented body with many legs (e.g., centipedes, millipedes).

1.6. Classification of Plants

Plants are commonly classified as follows:

• Ferns: Vascular plants that do not produce flowers or seeds, reproduce via spores.

• Flowering Plants: Characterized by roots, stems, leaves, and reproduce through flowers and seeds, divided into:

  • Monocotyledons: Plants with one seed leaf (cotyledon) such as grasses.

  • Dicotyledons: Plants with two seed leaves like beans and oak trees.

1.7. Viruses

Viruses differ significantly from living organisms and are classified as acellular. They require host cells to replicate and do not carry out metabolic processes independently. They consist of nucleic acid (DNA or RNA) encapsulated in a protein coat, lacking organelles such as mitochondria or ribosomes, which distinguishes them from prokaryotes and eukaryotes.

2. Organisation of the Organism

2.1. Cell Structure

Every living thing is made up of cells, with new cells arising from existing ones through processes such as mitosis. Typical features of eukaryotic cells include:

• Cell Membrane: Semi-permeable membrane that regulates the entry and exit of substances, maintaining cellular homeostasis.

• Cytoplasm: A jelly-like substance where cellular processes occur, containing organelles.

• Nucleus: Control center of the cell housing genetic material (DNA) organized into chromosomes.

• Mitochondria: Organelles known as the powerhouses of the cell, where ATP (energy) is produced through cellular respiration.

• Ribosomes: Locations for protein synthesis, either free in the cytoplasm or attached to the endoplasmic reticulum.

• Endoplasmic Reticulum: Network of membranes aiding in protein and lipid synthesis (Rough ER with ribosomes, Smooth ER without ribosomes).

2.2. Prokaryotes

Examples include bacterial cells that possess a cell wall primarily composed of peptidoglycan, along with a cell membrane, ribosomes, plasmids (small circular DNA), and a nucleoid region containing a single, circular DNA chromosome.

2.3. Levels of Organisation

Hierarchy of biological organization:

• Cells: The fundamental unit of life, specialized for various functions.

• Tissues: Aggregates of similarly structured cells working together for shared functions.

• Organs: Structures composed of different tissues working together for specific functions.

• Organ Systems: Groups of interconnected organs that perform united functions to support the organism's life processes.

2.4. Magnification

To examine microscopic structures, magnification formulae are used:

• Magnification = Image size / Actual sizeCommon units include micrometres (μm) for measuring cells and other small structures.

3. Movement Into and Out of Cells

3.1. Diffusion

Refers to the passive movement of particles from areas of higher concentration to areas of lower concentration, continuing until equilibrium is reached.

3.2. Osmosis

A specific type of diffusion that involves the movement of water across a semi-permeable membrane, from regions of higher water potential (dilute solution) to lower water potential (concentrated solution).

3.3. Active Transport

The process of moving particles against their concentration gradient, requiring energy (ATP) to facilitate the transportation of substances across the cell membrane.