23.4 LEAVES

BLADE

Thin, flattened section of a plant leaf that collects sunlight

PETIOLE

Thin stalk by which a leaf blade is attached to a stem

MESOPHYLL

Specialized ground tissue that makes up the bulk of most leaves; performs most of a plant’s photosynthesis

PALISADE MESOPHYLL

Layer of tall, column-shaped mesophyll cells just under the upper epidermis of a leaf.

SPONGY MESOPHYLL

Loose tissue beneath the palisade layer of a leaf

STOMA

Opening in the underside of a leaf that allows carbon dioxide and oxygen to diffuse into and out of the leaf

GUARD CELL

Specialized cell in the epidermis of plants that controls the opening and closing of stomata by responding to changes in water pressure

TRANSPIRATION

Loss of water from a plant through its leaves

KEY CONCEPT

The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

KEY CONCEPT

Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.