Cambridge IGCSE Biology: Organism Features & Classifications

An action by an organism or part of an organism that causes a change of position or place.

The chemical reactions that break down nutrient molecules in cells to release energy for life's processes.

The ability to detect or sense stimuli and react.

A permanent increase in size and dry mass by increasing cells.

Making more organisms of the same type.

Removing waste products and extra substances from the body.

Getting materials for energy, growth, and development.

A helpful acronym to remember characteristics of living organisms (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition).

A tool used to identify organisms. It uses a series of questions with two choices to guide you to the organism's name.

Branching into two; used to describe the structure of a dichotomous key.

Organism identification is the core purpose of a dichotomous key. It guides through features.

Choose a starting organism or the one provided in a question, answer the questions.

Each step in a dichotomous key involves a yes/no question, leading you through choices.

Use provided info (text or image) to accurately answer, and find the organism's name.

Repeat the process for another organism, starting at the beginning of the key, to identify it.

An example of a structured key with branching questions leading to an organism's name.

Animals without a backbone.

An invertebrate with jointed legs, a segmented body, and a hard exoskeleton.

Mammals have fur or hair, produce milk to feed their young, and are warm-blooded.

Crustaceans are arthropods with two pairs of antennae.

Insects are arthropods with three pairs of legs and usually wings.

Arachnids are arthropods with eight legs and no antennae.

Myriapods are arthropods with many legs and a long segmented body.

Main features are common to a group, like vertebrates having backbones. Defining features are unique to a group, like mammals having fur.

Using DNA sequences to classify organisms based on similarities.

The degree of similarity in DNA sequences indicates how closely related two species are.

The order of DNA bases (A, T, C, G) in an organism's DNA.

The first major division of living things based on their characteristics.

Mammal DNA shows a higher degree of similarity between mammals compared to other vertebrate groups.

Methods used to categorize and organize living things

Determined by DNA and used to determine relationships between organisms.

The shared ancestor of two or more species.

Leaves with parallel veins running lengthwise, typically narrow and grass-like.

Leaves with a network of veins branching throughout, often broader and varied in shape.

A simple structure consisting of genetic material (RNA or DNA) enclosed within a protein coat.

Viruses rely on host cells to carry out the seven life processes. They cannot do so independently.

Viruses replicate by taking over a host cell's metabolic pathways to create multiple copies of themselves.

The highest level of classification for living organisms: Animals, Plants, Fungi, Protoctists, Prokaryotes.

Multicellular organisms with nuclei and cell walls (not made of cellulose). They don't photosynthesize and get food from decaying matter or living organisms.

Mostly unicellular organisms with nuclei. Some have cell walls or chloroplasts, so they can photosynthesize or feed on other things.

Usually unicellular with cell walls (not made of cellulose) but no nucleus or mitochondria.

Fungi get their food by breaking down dead or decaying organic matter.

Fungi get their food from living organisms, harming them in the process.

A complex sugar that makes up plant cell walls. It's a tough and rigid material.

Organelles in cells that are responsible for generating energy through cellular respiration.