Life Science: Cells, Body Systems, and Ecosystems
What the questions target
Life science items emphasize that cells are the basic unit of life, that structure relates to function at every scale (organelle, tissue, organ, system, organism), that body systems interact to maintain stable internal conditions, and that organisms interact with each other and their environment through food webs, competition, and matter/nutrient cycling. Genetics basics - traits inherited through genes, with environment also influencing expression - appear at an introductory level.
Traps that cost points
- Reversing photosynthesis and respiration. Plants photosynthesize (light energy to stored chemical energy, taking in carbon dioxide and releasing oxygen) and also respire continuously. Only photosynthesis stores energy; respiration releases it in all organisms, plants included.
- Confusing energy flow with matter cycling. Energy flows one way through a food web and is lost as heat at each level; matter (carbon, nitrogen, water) cycles and is reused.
- Treating a food web as a chain. Removing one population affects many others; a predator's decline can cascade to producers.
- Confusing mitosis-style cell division for growth with reproduction of the whole organism, or claiming offspring inherit acquired traits.
- Assuming bigger organisms are always at higher trophic levels, or that decomposers are unimportant - they return nutrients to the soil.
Rule of thumb
Ask: What is the function, and what structure supports it? Then check the direction of energy and matter separately. For ecosystem questions, follow arrows in the direction energy moves (toward the consumer).
Worked example
In a meadow, grasses → rabbits → hawks. If hawks are removed, rabbits initially increase, then grass cover declines, and rabbit numbers fall again from reduced food - a chain of effects, not a single outcome. Energy still enters as sunlight and exits as heat; matter from rabbit waste and remains is broken down by decomposers and returned to the soil for grasses.