Living Systems: Cells, Body Systems and Health
Living Systems: Cells, Body Systems and Health tests cell structures, levels of organization, organ-system functions, homeostasis, and health choices. Questions often ask how two systems cooperate or which organelle performs a function.
Core concepts
- Cells are the basic unit of life. Plant cells have a cell wall, chloroplasts, and a large central vacuole; animal cells do not.
- Organelles: the nucleus controls activities and holds DNA; mitochondria release energy from glucose; ribosomes make proteins; the cell membrane controls exchange.
- Organization follows cells, tissues, organs, organ systems, and organism.
- Systems interact: the digestive system absorbs nutrients, the circulatory system transports them, the respiratory system supplies oxygen, and the excretory system removes wastes.
- Homeostasis keeps internal conditions stable, such as temperature, blood glucose, and water balance.
Worked example
A muscle cell contracts during exercise. It needs glucose and oxygen. The digestive system absorbs glucose; the circulatory system delivers glucose and oxygen; the respiratory system supplies oxygen; mitochondria use them in cellular respiration to release energy, producing carbon dioxide and water. Carbon dioxide enters the blood and is removed by the lungs. This shows systems working together, not independently.
Traps that cost marks
Saying plant cells have no mitochondria; confusing cell wall and cell membrane; thinking blood is a single cell; assuming breathing and cellular respiration are the same; ignoring that organ systems must cooperate.