2.3.1: Plant tissues
Not started yet — this one needs some love.
Epidermis: surface layer; thin; covered by a waxy cuticle to reduce water loss; transparent to allow light through.
Palisade mesophyll: column-shaped cells tightly packed with chloroplasts; near the upper surface; main site of photosynthesis.
Spongy mesophyll: loosely packed cells; large air spaces for gas diffusion; some chloroplasts.
Xylem: hollow dead cells with lignified walls; transports water and mineral ions upward (roots → stems → leaves); forms transpiration stream.
Phloem: living cells with pores (sieve plates) in end walls; transports dissolved sugars (sucrose) in any direction; process = translocation.
Meristem tissue: at growing tips (root and shoot); undifferentiated cells; source of new cells for plant growth.
Guard cells and stomata: control opening and closing of stomata (pores for gas exchange and water loss).
Common exam mistakes
Xylem transports water and mineral ions; phloem transports dissolved sugars (sucrose) — do not swap.
Phloem transports sugars/sucrose — NOT glucose alone; NOT mineral ions.
Meristem tissue is found specifically at the growing tips — not throughout the plant.
Xylem cells are dead — they are hollow tubes. Phloem cells are living.
Do not name 'upper epidermis' as the main photosynthetic tissue; the palisade mesophyll sits just below the upper epidermis and is the main site of photosynthesis.
Meristem tissue is undifferentiated cells at growing tips — do not confuse it with guard cells or stomata.