Science: Cells & Organisms: Standard Practice

# Medium Level Guide Grade-level practice aligned to typical classroom expectations and unit assessments. # Cell Theory All living things are made of cells. Cells are the basic unit of life. New cells come from existing cells. Cells may be prokaryotic (no nucleus) or eukaryotic (with a nucleus and membrane-bound organelles). # Plant and Animal Cells Both have a nucleus, mitochondria, ribosomes, and a cell membrane. Plant cells also have a rigid cell wall and chloroplasts for photosynthesis. Large central vacuoles store water in plant cells. # Organelle Functions The nucleus controls cell activities and stores DNA. Mitochondria produce energy (ATP). Ribosomes build proteins. The endoplasmic reticulum and Golgi apparatus process and ship materials. Lysosomes break down waste. # Levels of Organization Cells form tissues, tissues form organs, organs form systems, and systems form organisms. Each level has emergent properties. Unicellular organisms carry out all life functions in one cell.