Plant Tissues, Organs and Systems — AQA GCSE Biology

Plants are organised into tissues and organs adapted for photosynthesis and transport.

Plant organs

The main plant organs are the roots, stem and leaves. The leaf is itself an organ made of several tissues.

Epidermal tissue — covers and protects the plant; the upper epidermis is often transparent to let light through.
Palisade mesophyll — packed with chloroplasts; the main site of photosynthesis.
Spongy mesophyll — has air spaces to allow gas exchange (CO₂ in, O₂ out).
Xylem — transports water and mineral ions from the roots upward.
Phloem — transports dissolved sugars (made in photosynthesis) around the plant.
Meristem tissue — found at growing tips; can differentiate into other cell types.

Large surface area and thin shape — maximise light absorption and short diffusion paths.
Stomata (pores, usually on the underside) — allow gas exchange; opened and closed by guard cells.
Waxy cuticle — reduces water loss.

Match each tissue to its function (palisade → photosynthesis, spongy → gas exchange, xylem → water, phloem → sugars).
Explain leaf adaptations for photosynthesis and gas exchange.
Guard cells control the stomata.
Xylem carries water up; phloem carries sugars in both directions.