Introduction
Key concepts of plants as living things
The activities in this topic are designed to explore the following key concepts:
Broad concepts of living things
- There is no absolute definition of what we count as a living organism. The definition has changed over time. A living organism generally has a cellular structure, but viruses are currently counted amongst living things, and they do not.
- Living things have a variety of characteristics that will be displayed to different degrees: they respire, move, respond to stimuli, reproduce and grow, and are adapted within a complex of living things within an environment.
- When a plant is picked or cut, or an animal dies, some basic life process will continue to occur. There is no universally agreed answer to the question ‘Is it alive?’.
- The way living things are classified has changed over time. Animals and plants are the main ‘kingdoms’, but fungi, mosses and viruses have their own separate kingdoms.
- Animals are ‘consumers’ in that they ingest food to survive. Food provides the energy for life processes.
- Plants are ‘producers’ and grow through the photosynthetic process by which carbon dioxide and water are used to produce starches (of which the plant material is made). Sunlight provides the energy to drive this process.
- Animals and plants are further divided. A major category of plants is ‘flowering plants’ or angiosperms. These differ from conifers and ferns, for instance, in the way they reproduce. Animals include a multitude of organisms, from microscopic creatures, through insects, reptiles, mammals, and so on. These different organisms are all interconnected through an evolutionary history.
Structure, function, adaptation of living things
- Living things have various ‘structures’ that enable them to survive: transport structures in plants by which water and trace elements move; digestive structures and respiratory structures in animals; and reproductive structures.
- Organism structures and behaviours should be seen in terms of their survival purposes.
- Each organism is adapted to a particular ecological niche involving interdependence with other living organisms as well as dependence on non-biotic factors.
Flowering plants, seeds
- The majority of plants on earth are flowering plants (this includes trees, grasses, cacti and other small plants, as well as the more obvious examples).
- All flowering plants have a similar reproductive cycle.
- The reproductive cycle is an important adaptation, and the formation and dispersal mechanisms for seeds (contained in fruit, pods or nuts) are varied.
- Fruits are the outcome of a fertilised flower and contain seeds.
- Conifers do not have flowers but produce seeds in cones.
- Seeds:
- need water to germinate
- need the right temperature to germinate
- vary in their rate of germination
- form a significant part of the world’s food supply
- are living.
Students’ alternative conceptions of plants as living things
Research into student’s ideas about this topic has identified the following non-scientific conceptions:
- Students associate life with movement or action, so that a bicycle may be alive when it is being ridden.
- Students associate life with power or effectiveness, including such things as the sun, fire, lightning, etcetera.
- Students think that the purpose of flowers is to please or support other organisms, for instance bees, or humans (to make them look pretty).
- Students do not understand the different reproductive (flowers, fruit, seeds), respiration (roots, leaves, stalk) or other structures of plants and can think of parts of the plant as the plant itself (e.g. a carrot is not thought of as the root of a carrot plant that may be flowering).
- Students have a restricted view of which plants are flowering plants.
- Students believe that plants take in food through their roots.
- Students have a narrow concept of plants as things in pots, that may not include trees or grass.