Layers, Chloroplasts, and Thylakoids

Upper epidermis

Uppermost part of the leaf

• thick, waxy film protects plant and prevents excessive H₂O loss

• lacks chloroplasts to allow maximum light penetration

• few or no stomata

Palisade Mesophyll Layer

2nd uppermost part of leaf

• Columnar (rod-shaped) tightly packed cells to maximize light absorption (few air spaces)

• highest concentration of chloroplast

• receives most sunlight

Spongy Mesophyll Layer

2nd lowermost part of leaf

• irregular, loosely shaped sponges to create interconnected air spaces

• significantly less chloroplasts than palisade layer

• facilitate rapid diffusion of gases (O₂, CO₂, H₂O)

Lower Epidermis

Bottom part of leaf

• thinner, waxy cuticle for protection and gas exchange

• lacks chloroplasts except guard cells in stoma for opening / closing

• large amount of stoma for gas exchange

photosynthesis

Palisade mesophyll layer is the primary site of ?

some

even in spongy mesophyll layer, there’s ? photosynthesis

Stomata

Holes / pores on underside of leaves

• guard cells open and close to regulate gas exchange

less

A desert plant would have ? stomata than a rainforest plant

Chloroplasts

Main site of photosynthesis

• many thylakoids each with many pigment molecules on membrane

Double Membrane

This part of chloroplasts suggests endosymbiosis of a prokaryote

Stroma

inside empty area of chloroplast with appropriate enzymes and suitable pH for Calvin cycle

Thylakoid

has electron transport chain and ATP synthase for photophosphorylation

Granum

flat membrane stacks of thylakoids that increase SA:V

• small volumes quickly accumulate ions

Lamella

Membrane that connects and separates thylakoid stacks (grana)

Lumen

space inside thylakoids

Light Independent Reactions

These type of reactions occur in stroma

light dependent reactions

these type of reactions occur on thylakoid membrane

Pigments

molecules that absorb light

don’t absorb

leaves are green because it’s the only color they ?

Pigments of Leaves

chlorophyll A, chlorophyll B, carotenoids, xanthophylls