Biology - Characteristics of Living Organisms

What are the seven characteristics of living organisms?

• Movement: an action by an organism or part of an organism causing a change of position or place.

• Respiration: chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

• Sensitivity: the ability to detect and respond to changes in the internal or external environment.

• Growth: a permanent increase in size and dry mass.

• Reproduction: processes that make more of the same kind of organism.

• Excretion: removal of waste products of metabolism and substances in excess of requirements.

• Nutrition: taking in materials for energy, growth and development.

State what organisms can be classified by.

• Features they share / common features.

• What is meant by a species? *

• A species is a group of organisms that can reproduce to produce fertile offspring.

Describe the binomial system used to name species.

• The binomial system of naming species is an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species.

Describe how to construct and use a dichotomous key.

• Use an identifiable feature to make a pair of contrasting choices.

• Choose the statement that matches the organism and follow the instruction to the next pair of choices.

• Repeat the process until the organism is identified. Each choice should separate the organisms into two groups.

Why do classification systems aim to reflect evolutionary relationships?

• Classification systems aim to group organisms according to their evolutionary relationships.

• Organisms placed closer together are expected to share a more recent common ancestor and therefore more inherited features.

How can DNA base sequences be used to classify organisms?

• Compare the sequence of bases in the DNA of different organisms.

• Similarities and differences in the base sequences provide evidence that can be used to place organisms into classification groups.

How can DNA base-sequence similarity show how closely related organisms are?

• The more similar the DNA base sequences are, the more closely related the organisms are.

• A high degree of similarity suggests a more recent common ancestor; greater differences suggest a more distant common ancestor.

State the main features used to distinguish plants from animals.

• Plant kingdom: multicellular organisms with cellulose cell walls; some cells contain chloroplasts and they make organic substances by photosynthesis.

• Animal kingdom: multicellular organisms whose cells do not have cell walls or chloroplasts; they obtain organic nutrients by feeding on other organisms.

State the main features used to distinguish the major vertebrate and arthropod groups.

• Fish are vertebrates with scaly skin, gills throughout life and fins; their eggs have no shells and are laid in water.

• Amphibians are vertebrates with skin without scales; their eggs have no shells and are laid in water; larvae have gills and adults have lungs.

• Reptiles are vertebrates with scaly skin and eggs with soft shells.

• Birds have feathers, a beak, front limbs modified as wings and eggs with hard shells.

• Mammals have hair on the skin, mammary glands that produce milk, different types of teeth, a pinna and a diaphragm.

• All arthropods have jointed legs and an exoskeleton. Insects have three pairs of jointed legs, one pair of antennae and a body divided into head, thorax and abdomen. Crustaceans have more than four pairs of jointed legs and two pairs of antennae. Arachnids have four pairs of jointed legs, no antennae and a body divided into cephalothorax and abdomen. Myriapods have many similar segments with jointed legs and one pair of antennae.

How can observable features be used to classify an animal into the correct group?

• Identify the observable features of the organism, such as body covering, limbs, antennae, wings or other distinguishing structures.

• Compare these features with the defining features of the vertebrate and arthropod groups, then place the organism in the group whose features match.

State the main features used to distinguish the five kingdoms.

• Animal: multicellular organisms whose cells do not have cell walls or chloroplasts; they feed on organic substances made by other organisms.

• Plant: multicellular organisms with cellulose cell walls; some cells contain chloroplasts and they make organic substances by photosynthesis.

• Fungus: usually multicellular, with nuclei and cell walls; no chlorophyll; feeds by digesting organic material and absorbing the products. Recent mark schemes identify fungal cell walls as containing chitin.

• Prokaryote: usually unicellular; no nucleus; circular DNA is free in the cytoplasm and plasmids may be present; no mitochondria.

• Protoctist: mostly unicellular eukaryotes with nuclei; some are plant-like with chloroplasts and cell walls and some are animal-like.

State the main features used to distinguish ferns, monocotyledons and dicotyledons.

• Ferns have roots, stems and leaves (fronds), do not produce flowers and reproduce by spores on the undersides of fronds.

• Flowering plants have roots, stems and leaves, reproduce using flowers and seeds, and have seeds produced inside an ovary.

• Dicotyledons have two cotyledons, a main root with side roots, a network of leaf veins, flower parts usually in multiples of four or five, and vascular bundles in the stem arranged in a ring.

• Monocotyledons have one cotyledon, roots that grow directly from the stem, parallel leaf veins, flower parts usually in multiples of three, and vascular bundles scattered in the stem.

How can observable features be used to classify an organism into the correct kingdom or plant group?

• Identify the organism's observable features, including cell type and visible plant structures where relevant.

• Compare the features with those that distinguish the five kingdoms and the plant groups, then classify the organism in the group whose features match.

State the main structural features of a virus.

A virus consists of genetic material surrounded by a protein coat. Viruses are not made of cells.