CIE IGCSE Biology: Characteristics and Classification of Living Organisms Study Notes

Mnemonic (MRS. H. GREN): * Movement: Action causing a change of position or place. * Respiration: Chemical reactions in cells that break down nutrients to release energy for metabolism. * Sensitivity: Detecting and responding to stimuli in the internal or external environment. * Homeostasis: Maintenance of a constant internal environment. * Growth: Permanent increase in size and dry mass (cell number or size). * Reproduction: Processes that make more of the same kind of organism. * Excretion: Removal of toxic materials, waste products of metabolism, and substances in excess of requirements. * Nutrition: Taking in materials for energy, growth, and development (plants require light, $CO_2$ , water, and ions; animals require organic compounds, ions, and water).

Species: A group of organisms that can reproduce to produce fertile offspring.
Binomial System: Named by Linnaeus using Latin; consists of $Genus$ (capitalized) and $species$ (lower case), e.g., Homo sapiens.
Classification Hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, Species. (Mnemonic: King Philip Came Over For Gran’s Spaghetti).
Evolutionary Relationships: * Originally based on morphology (overall form) and anatomy (detailed body structure). * Modern classification uses DNA sequencing (base sequences) and amino acid sequences in proteins. * The more similar the DNA base sequences, the more closely related the species (e.g., Brachinus armiger and Brachinus hirsutus are closely related due to nearly identical sequences).

Common Structures: * All cells: Cytoplasm, cell membrane, and DNA as genetic material. * Extended: Ribosomes (protein synthesis) and enzymes for respiration (often in mitochondria).
The Five Kingdoms: * Animals: Multicellular; nucleus; no cell walls or chloroplasts; feed on organic substances. * Plants: Multicellular; nucleus; chloroplasts; cellulose cell walls; feed by photosynthesis. * Fungi: Usually multicellular; nuclei; non-cellulose cell walls; saprophytic or parasitic nutrition. * Protoctists: Usually unicellular; have a nucleus; some have chloroplasts/cell walls. * Prokaryotes (Bacteria): Often unicellular; no nucleus or mitochondria; contain cytoplasm and non-cellulose cell walls.

Vertebrates (Backbone): * Mammals: Fur/hair, placenta, mammary glands, external ears (pinnas), endothermic. * Birds: Feathers, wings, hard-shelled eggs, beak, endothermic. * Reptiles: Dry, fixed scales, rubbery-shelled eggs. * Amphibians: Moist skin, adults have lungs, larvae have gills, eggs sans shells in water. * Fish: Wet scales, gills, eggs sans shells in water.
Invertebrates (Arthropods - Jointed Legs): * Myriapods: Segmented body, minimum $1$ pair of legs per segment, $1$ pair of antennae. * Insects: Three-part body (head, thorax, abdomen), $3$ pairs of legs, $2$ pairs of wings (may be vestigial), $1$ pair of antennae. * Arachnids: Two-part body (cephalothorax, abdomen), $4$ pairs of legs, no antennae. * Crustaceans: More than $4$ pairs of legs, chalky exoskeleton, gills, $2$ pairs of antennae.

Ferns: Have fronds; reproduce via spores on the underside of leaves.
Flowering Plants: Reproduce via seeds inside an ovary. * Monocotyledons: Petals in multiples of $3$ ; parallel leaf veins. * Dicotyledons: Petals in multiples of $4$ or $5$ ; reticulated (web-like) leaf veins.

Viruses: Not considered living; no metabolic processes; consist of genetic material (RNA or DNA) inside a protein coat.
Dichotomous Keys: Identification tool using a series of two-choice descriptions leading to an organism's name.

Question 1: The image below shows a house mouse, whose scientific name is Mus musculus. Which genus does it belong to? * A: Mammal, B: musculus, C: Mus, D: Vertebrate
Question 2: The image below shows what occurs to a seed during and after germination, the seed has been planted in well-watered soil. Which characteristics of living things are demonstrated by this sequence? * A: Nutrition and reproduction, B: Reproduction and growth, C: Nutrition and sensitivity, D: Sensitivity and growth
Question 3: Which of the following would not be a characteristic seen in all living organisms? * A: Reproduction, B: Respiration, C: Excretion, D: Photosynthesis
Question 4: Four different descriptions about plants are given below. Which statement would apply to a plant that is a dicotyledon? * A: The veins in the leaf are reticulated, B: Each flower has six petals, C: The flowers are all wind-pollinated, D: The leaves have parallel veins.
Question 5: Which row of the following table correctly describes the characteristics (W, X, Y) shown by living organisms in the diagram above? * A: respiration, photosynthesis, respiration; B: respiration, respiration, nutrition; C: photosynthesis, respiration, excretion; D: respiration, excretion, nutrition