Life Sciences: Ecosystems, Traits, and Life Cycles
Core ideas
An ecosystem includes all living organisms in an area plus the nonliving parts they interact with, such as water, air, soil, sunlight, and temperature. Producers, mainly plants and algae, use sunlight, water, and carbon dioxide to make their own food. Consumers eat other organisms. Decomposers break down dead organisms and waste, recycling matter back into the soil and air. A food chain shows one path of energy flow; a food web shows many connected paths. Energy enters most ecosystems as sunlight and moves from organism to organism, but energy is lost as heat at each step. Matter, unlike energy, is recycled.
Organisms have structures and behaviors that help them survive in their environments. Inherited traits come from parents; learned behaviors come from experience. Life cycles describe how organisms grow, reproduce, and die. Plants need light, water, air, and minerals, but they do not get their food from soil.
Traps to avoid
Arrows in a food chain point in the direction energy flows, toward the eater, not toward the food. Decomposers recycle matter, not energy. Removing one population can affect many others. Plants make food through photosynthesis; soil supplies water and minerals but not the plant's main food. Inherited traits are not the same as learned behaviors.
Worked example
In the chain grass, grasshopper, bird, hawk, the arrows mean energy moves from grass to grasshopper to bird to hawk. If the hawks disappear, birds may increase, grasshoppers may decrease, and grass may increase at first. Rule of thumb: follow the arrows for energy, and expect effects to ripple through the web.