Leaf Cross-Section and Photosynthesis Sites — Diagram Note — Notes | NoteTube

Leaf Structure Reference

Leaf Transverse Section (T.S.) Upper Epidermis (cuticle) Palisade Mesophyll air air Spongy Mesophyll Xylem Phloem Bundle Sheath Lower Epidermis Stoma + Guard Cells Stoma + Guard Cells Key: Palisade Spongy Xylem Phloem Guard Cells Epidermis *Wikimedia Commons: Leaf_cross_section.svg — Shows epidermis, palisade mesophyll, spongy mesophyll, vascular bundle, guard cells.*

Annotation: Where Photosynthesis Happens in a Leaf

Cell Type	Location in Leaf	Role in Photosynthesis
Palisade mesophyll	Upper layer (columnar cells, densely packed)	Primary photosynthesis site in C3 plants (most chloroplasts here)
Spongy mesophyll	Lower layer (irregular, air spaces)	Also contains chloroplasts; $CO_{2}$ / $O_{2}$ exchange via air spaces
Guard cells	Epidermis (surrounds stomata)	Regulate $CO_{2}$ entry and $H_{2}O$ exit; contain chloroplasts
Bundle sheath cells	Around vascular bundles	Calvin cycle in C4 plants; not prominent in C3
Mesophyll cells (C4)	Surrounding bundle sheath	PEP carboxylase fixation; initial 4C acid formation

Stomata Reference

Stomatal guard cells — open and closed states Wikimedia Commons: Stomata_guard_cells.jpg — Shows open and closed stomata with guard cells.

Stomatal patterns:

C3/C4: Open during the day ( $CO_{2}$ in), closed at night
CAM: Closed during the day, open at night ( $CO_{2}$ in, stored as malic acid)