General Biology lab Lab 14 The Leaves The

General Biology lab Lab 14 The Leaves

• The Leaves – are lateral outgrowth of the stem which develop from the meristematic tissues. • Functions of Plant Leaves – Photosynthesis – Transpiration • The exit of water is through the stomata – Food Storage

Dicotolydonous leaf (dicot. leaf) • Epidermis: - there are some differences between upper and lower epidermis. – Stomata are more distribution in the lower epidermis than the upper epidermis. – Stomata are kidney shape. – Have not bulliform cells. • Mesophyll: - – Palisade parenchymal cell are elongated cells located in many leaves just below the epidermal tissue. – Spongy parenchymal cells occur below the one or tow layers of palisade cells.

• Vascular bundles: - – large bundles enclosed in ground parenchyma of the thickened vein ribs. – Have not bundle sheath. – Xylem in vascular bundles has arm shape. • Venation in the leaf blade: net venation, meaning they have one or a few prominent mid veins, form which smaller minor veins branch into a meshed network.

Typical Dicot Leaf Cross-Section Cuticle Palisade Parenchyma Epidermis Vascular bundles Guard Cells Spongy Parenchyma Stoma

Monocotyledonous leaves (monocot leaves) • Epidermis: This typical of grasses. – Stomata are equally distributed in upper and lower epidermis. – Stomata are damples shape. – Have buliform cells. • Mesophyll: is homogenous and there are some difficult to distinguished between palisade and spongy parenchyma.

• Vascular bundles: – there are more than one vascular bundles. – Have bundle sheath. • Venation in the leaf blade: parallel venation, meaning several prominent and parallel veins interconnect with smaller, inconspicuous veins.

Typical Monocot Leaf Cross-Section Midvein Vein Bundle sheath cell Epidermis Phloem Xylem Bulliform Cells Stoma

Leaves and Habitats • Leaves vary much in both form and internal structure. • They variations in plant structure that are commonly related to the habitat and habit are particularly strongly expressed in the structure of leaves. • Therefore, the leaves in particular may be used to characterize the (ecologic types) of plant, the mesophytes, hydrophytes, and xerophytes.

• Hydrophytes – Hydrophytes are plant that live in an abundance of water and thus display few adaptations to reduce water loss in the leaves. – These leaves display aerenchyma, a loosely- organized parenchymatous tissue with wide intercellular spaces containing air. – The submerged aquatics are exemplified by the leaf of Elodea

• Xerophytes – Zerophytc leaves are adapted to arid condition. – Note thick cuticle, epidermis and hypodermis on the upper and lower surface of the leaf. – Stoma are recessed deeply into the lower surface of the leaf with numerous dermal hairs in the cavity surrounding the stomata. • This reduces air flow across the stoma surface thus reducing water loose from the leaf.

• Mesophytes – Mesophytes represent the remainder of the plants, which typically are found in areas in which water is available in the soil most of the time and droughts are short in duration.

Photosynthesis • Photosynthesis is one of the most fundamentally important biological processes. • All green plant can produce their own food simply by using the energy in sunlight to convert carbon dioxide (present in the surrounding air) into a carbohydrate. 6 CO 2 + 6 H 2 O Carbon dioxide Water C 6 H 12 O 6 + 6 O 2 Carbohydrate Oxygen