Rule
Cell Tissue (a group of similar cells doing one job) Organ (different tissues working together) Organ system (organs working together) Organism.
A higher level shows emergent properties — abilities that appear only once simpler parts combine, not present in any single component alone.
Definition
The stomach wall contains epithelial tissue (lines the surface, produces digestive secretions), muscle tissue (smooth muscle churns and moves food), and connective tissue (contains blood vessels and nerves, supplies and controls the other layers).
Definition
A leaf's palisade mesophyll (packed with chloroplasts) is the main site of photosynthesis; xylem transports water up from the roots; phloem transports the food made in the leaf to the rest of the plant.
Definition
Root system: absorbs water/minerals, anchors the plant. Shoot system: stem + leaves + flowers, carries out photosynthesis and reproduction. The flower's primary role is reproduction.
Definition
Homeostasis is the maintenance of a stable internal environment despite external changes — organ systems work together to achieve it (e.g. the respiratory and circulatory systems together maintain steady oxygen levels in the blood).
Remember
If one organ system fails, others that depend on it are affected too — homeostasis breaks down because the systems are interdependent, not isolated.
Quick Recap
- ●Levels: Cell Tissue Organ Organ system Organism, each level showing new emergent properties
- ●Stomach wall: epithelial (secretes), muscle (churns), connective (blood vessels/nerves)
- ●Leaf: palisade mesophyll (photosynthesis), xylem (water up), phloem (food transport)
- ●Root system: absorption/anchorage. Shoot system: photosynthesis/reproduction
- ●Homeostasis: stable internal environment, kept by organ systems working together
