Before Instruction students may be able to associate organisms to certain physical locations and have some understanding that organisms have certain requirements for life. They are not always able to distinguish living from non-living. Students understand that organisms “eat” one another, and they “eat” because they are hungry. Food is considered everything that a plant or animal takes in including water, minerals, and, in the case of plants, carbon dioxide or even sunlight.
Conceptual Stepping Stones
Early Elementary students understand that humans and mammals are living organisms and can associate organisms to physical spaces with respect to general location. They relate organisms to habitat via organism’s needs and ways of satisfying those needs. The relationship is perceived to be unidirectional; the habitat satisfies needs. Students can explain that plants need air, water, and sunlight to grow but consider all of these components as plant food. At this age, the scientific definition of food is often confused with its common usage. Students may think animals found lower in the food chain simply exist so that animals higher in the food chain can eat them.
Later Elementary students understand that the relationships between organisms and ecosystems are complex and interacting (bidirectional). They are able to distinguish between abiotic and biotic components of a habitat and can begin to develop hypotheses about the mechanisms by which abiotic qualities of habitat (such as light & moisture) affect resources required for survival. Students understand that the food of almost all kinds of animals can be traced back to plants. While students understand that people and animals could not exist without plants, students think that plants undergo the process of photosynthesis just so we humans can breathe but they think of photosynthesis as a type of respiration. Students still have difficulties understanding ideas about food, plant, and animal nutrition, and how this relates to the release of energy from food: Students correctly understand that “energy is obtained from food” and have some basic understanding that food is broken down, that acid breaks down the food, and that some kind of “goodness” is taken into the body from the food. However, the process that releases usable energy from food is unclear to students and is not related to the chemical process of acquiring energy from food. Students see food chains as simple and linear.
Middle School students understand that organisms and populations of organisms are dependent on their interactions with other living things (biotic), and their interactions with non-living (abiotic) factors in the environment, which together make up ecosystems. Students understand that ecosystems are complex and dynamic systems; however, middle school students are not always able to distinguish between systems and cycles or to explain how they relate to ecosystem processes. Students are able to distinguish types of interactions between organisms in a given environment as competitive or mutually beneficial and they understand the implications of these relationships to the overall populations of the organisms. Middle school students understand that the basis of all food chains and food webs are organisms that create their own food from processes such as photosynthesis. Students recognize the essential role of sunlight in photosynthesis and understand that all ecosystem processes rely on energy movement from the sun to organisms
Culminating Scientific Ideas
High School students interpret food webs in terms of interconnected food chains and can describe energy transfer and conservation, as well as matter transfer and transformation while accounting for the biotic and abiotic components in an ecosystem. Students understand food in terms of the chemical aspects of the carbohydrates, proteins, and fats, which supply organisms’ cells with matter and energy to support life and can explain the principle that molecules travel in and through the organisms as part of the world’s matter cycle. High School students are able to recognize the cyclical flow of matter and the interdependent relationship of organisms within an ecosystem and are able to differentiate between systems and cycles while recognizing they are not mutually exclusive. Students understand photosynthesis as the process of transforming light energy to chemical energy and stored in chemical compounds. Students are able to describe photosynthesis in terms of a process that leads to the storage of energy in food and they understand that that the food provides energy for the plant’s life processes. Students understand that oxygen is simply a waste product of the process of photosynthesis. Students understand energy transfer in the context of photosynthesis, respiration, and nutrition, and can describe how energy and matter are conserved.