1 Characteristics And Classification Of Living Organisms

An action by an organism or part of an organism; causing a change of position or place.

Roots growing downwards / shoots bending towards light.

Chemical reactions; in cells; that break down nutrient molecules and release energy for metabolism.

Respiration is chemical reactions inside cells that release energy from nutrients; breathing is the physical/mechanical movement of air into and out of the lungs.

Cells require energy to carry out life processes such as growth and movement; respiration releases this energy by breaking down nutrient molecules.

The ability to detect changes in the internal or external environment; and respond to those changes.

Animal: pupil constricting in bright light / pulling hand from heat; Plant: shoot growing towards light / roots growing towards water.

A permanent increase in size; and dry mass.

Water content of an organism fluctuates / is variable; dry mass gives a more accurate/reliable measure of permanent increases in biological material.

The processes that make more of the same kind of organism.

Sexual reproduction; asexual reproduction.

The removal of waste products of metabolism; and substances in excess of requirements.

Excretion is the removal of waste products produced by metabolic reactions in cells (e.g. CO₂, urea); egestion is the removal of undigested food that was never absorbed into cells / never part of metabolism.

Carbon dioxide (from respiration); urea (from the breakdown of excess amino acids in the liver).

The taking in of materials for energy, growth and development.

Organisms need materials to release energy through respiration; and to provide substances for growth and development / building new cells.

Organisms are classified into groups by the features they share.

Classification systems aim to reflect evolutionary relationships; organisms that share more features are thought to share a more recent common ancestor.

A group of organisms that can reproduce; to produce fertile offspring.

They produce offspring (mule) that is infertile/cannot reproduce; organisms of the same species must produce fertile offspring.

An internationally agreed system; the scientific name is made up of two parts; the first part is the genus and the second part is the species.

It is internationally agreed/understood, so scientists worldwide can identify the same organism without confusion caused by different common names.

A series of paired/two-choice questions used to identify organisms based on observable features.

Each question/step must offer exactly two choices; based on observable/identifiable features.

Vague features (e.g. "large") are subjective and could be interpreted differently; precise features (e.g. "has six legs") ensure the organism is correctly identified every time.

The sequences of bases in DNA can be compared between organisms; organisms with more similar base sequences are more closely related/share a more recent common ancestor.

Closely related species share a more recent common ancestor; they have had less time for mutations to occur and change the base sequence; distantly related species diverged longer ago, so more differences have accumulated.

Physical features can be similar due to adaptation to similar environments rather than shared ancestry; DNA provides direct evidence of evolutionary/genetic relationships.

Animals do not have cell walls / plants have cellulose cell walls; animals are heterotrophic / plants are autotrophic (photosynthesise).

Animals store carbohydrate as glycogen; plants store carbohydrate as starch.

Body covered in hair/fur; females produce milk to feed young.

Amphibians have moist, permeable skin / reptiles have dry scales; amphibians lay eggs in water without shells / reptiles lay eggs on land with leathery shells.

Whales have hair (not scales); whales breathe using lungs (not gills); whales produce milk to feed their young.

Insects have six legs / three pairs; arachnids have eight legs / four pairs.

More than eight legs; two pairs of antennae.

Myriapods have many legs (more than 20) / insects have only six legs; myriapods have a segmented body without distinct thorax and abdomen / insects have three distinct body sections (head, thorax, abdomen).

Reptile.

Insect.

Check for multicellularity and heterotrophic nutrition to confirm it is an animal; check for a backbone to confirm it is a vertebrate; check for hair/fur and milk production to classify as a mammal.

Cells have no true nucleus / genetic material is not enclosed in a nuclear membrane; cells are microscopic / single-celled / unicellular.

Fungi are saprotrophic / they digest and absorb nutrients from dead organic matter; plants are autotrophic / they photosynthesise to make their own food.

Protoctists are eukaryotic organisms that do not fit the criteria for animals, plants, or fungi; they show varied features including varied nutrition and cell wall presence.

Ferns reproduce by spores (not seeds); ferns do not produce flowers.

Dicotyledons have two cotyledons / monocotyledons have one cotyledon; dicotyledons have network/branching leaf veins / monocotyledons have parallel leaf veins; dicotyledon flower parts are in multiples of 4 or 5 / monocotyledon flower parts are in multiples of 3.

Plant kingdom; fern.

Check for two cotyledons in the seed; check for network/branching venation in the leaves / flower parts in multiples of 4 or 5.

A protein coat; genetic material (DNA or RNA).

Viruses do not have a cellular structure / they are not made of cells; they cannot carry out metabolic processes / life processes independently / they can only reproduce inside a host cell.