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Flashcards · 0610 · Topic 1

Characteristics and classification of living organisms flashcards

22 cards on Topic 1, subtopics 1.1 to 1.3. Pick a subtopic or study them all.

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1.1 Characteristics of living organisms

The seven characteristics of living organisms (MRS GREN)
Movement, respiration, sensitivity, growth, reproduction, excretion, nutrition.
Growth (characteristic of life)
A permanent increase in size and dry mass.
Excretion (characteristic of life)
The removal of the waste products of metabolism and substances in excess of requirements.
Respiration (characteristic of life)
The chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
Sensitivity (characteristic of life)
The ability to detect and respond to changes in the internal or external environment.
Nutrition and movement (characteristics of life)
Nutrition: the taking in of materials for energy, growth and development. Movement: an action by an organism or part of an organism causing a change of position or place.
Why must a definition of growth say "permanent" and "dry mass"?
A plant that absorbs water gains mass without growing. Only a permanent increase in dry mass counts as growth.

1.2 Concept and uses of classification systems

Species
A group of organisms that can reproduce to produce fertile offspring.
The binomial system of naming
Genus then species, e.g. Panthera leo. Genus has a capital letter, species is lower case; both are italicised (or underlined when handwritten). It is used worldwide, so it avoids confusion over common names.
Dichotomous key
A series of paired statements. At each step you choose the one that applies and follow it to the next pair or to a name.
Good practice when constructing a dichotomous key
Use observable, contrasting features, so exactly one statement of each pair applies. Avoid relative terms such as "large" and features that vary with age or season, such as colour or behaviour.
How are DNA base sequences used in classification?Extended
The more similar the base sequences of two species, the more closely related they are and the more recently they shared a common ancestor. Classification systems aim to reflect these evolutionary relationships.

1.3 Features of organisms

Features shared by all arthropods
A hard exoskeleton, jointed legs and a segmented body.
Insect: legs, body parts, antennae
6 legs; 3 body parts (head, thorax, abdomen); 1 pair of antennae.
Arachnid: legs, body parts, antennae
8 legs; 2 body parts; no antennae.
Crustacean and myriapod: key features
Crustacean: many legs, 2 pairs of antennae, chalky exoskeleton. Myriapod: many body segments with one or two pairs of legs per segment, 1 pair of antennae.
Vertebrate groups: the single identifying feature of birds, mammals and reptiles
Birds: feathers (and hard-shelled eggs laid on land). Mammals: hair or fur, and mammary glands. Reptiles: dry scales, and soft leathery-shelled eggs laid on land.
Fish vs amphibians: skin and eggs
Fish: wet scales; eggs laid in water with no shell. Amphibians: moist, smooth skin; jelly-coated eggs laid in water.
Fungus kingdom: key featuresExtended
Mostly multicellular, made of hyphae; cell wall of chitin (not cellulose); saprotrophic nutrition: secrete enzymes and absorb the products.
Prokaryote vs protoctistExtended
Prokaryotes are single cells with no nucleus. Protoctists have a nucleus and are mostly single-celled (some multicellular). The difference is the nucleus, not size.
Monocotyledons vs dicotyledonsExtended
Monocots: one cotyledon, parallel leaf veins, flower parts in threes. Dicots: two cotyledons, branching (net-like) leaf veins, flower parts in fours or fives.
Ferns vs flowering plants; and the features of a virusExtended
Ferns have fronds and reproduce by spores, with no flowers or seeds. Flowering plants reproduce by seeds made in flowers. A virus is only a protein coat and genetic material, and is in none of the five kingdoms.

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