Chapter 23 Plant Structure and Function

Plant Tissue Vascular Plants have four basic types of tissue 1.Vascular tissue 2.Ground tissue 3.Epidermis 4.Meristematic Tissue

Plant Tissue Vascular Tissue Xylem – transports water and minerals Phloem – transports sugars Ground tissue – surrounds the vascular tissue some store water or sugars, others lend support to the plant Epidermis – layer of flattened cells secrete the waxy cuticle Meristems – regions of actively dividing cells found in ares that are growing

ROOTS  Roots - anchor plant to the ground and absorb water and minerals. Make up 1/3 of weight of a plant.  Absorption actually takes place in the root hairs. Increases the surface area of a root.  Growth of a root takes place in a root cap by cell division.  Some roots have specialized functions like food or water storage.

STEMS  Shoots - made up of the stem and leaves. In some cases, it also includes the flowers and fruits.  Stems support the leaves so they can capture sunlight.  Stems also connect the roots to the leaves and contain the vascular tissue needed for transport of water and minerals.  Stems can be modified for storage.

LEAVES  Leaves are the main sites for photosynthesis.  Leaves contain chloroplasts which contain the chlorophyll needed for photosynthesis.

LEAVES  Thin and Flat – advantageous for photosynthesis  Cuticle - leaves contain a waxy outer layer that prevents it from losing too much water.  Stomata – tiny pores that allow carbon dioxide to enter and water and oxygen to exit

LEAVES  Inside a leaf are layers of photosynthetic cells Bundles of vascular tissue (veins in leaves) Xylem Phloem

How Plants Function  Transpiration - Water Movement in Plants  occurs in Xylem  Translocation - Food Movement in Plants  Occurs in phloem  Growth and Plants Hormones  Other (Sunlight, Temperature, and Gravity)

Water Movement in Plants  Water travels from roots  trunk/stem  leaves  Travels to all the parts of the plant through the xylem.  Direct result of Transpiration in Plants

Transpiration  The loss of water vapor from a plant through its stomata  More than 90% of water entering plant passes through plant and evaporates through the stomata

Stomata and Transpiration  Stomata - Specialized pores located in plant cuticle that enables plant to exchange gases with the atmosphere

Stomata and Transpiration  Two guard cells surround the stomatal pore and control the opening and closing of the stomata.

The Role of Stomata  Evaporation : Helps cool the plant but sometimes the transpiration is so rapid that the loss of water begins to exceed the intake and the stomata may close to prevent wilting.  Gas Exchange:  The plant must open stomatal pore during photosynthesis to allow CO 2 inside the plant and O 2 out.

Transpirational Pull  As transpiration takes place, it creates a “pull or tension” drawing water from the xylem and ultimately from the soil  When plants transpire, the water potential in cells adjacent to the stomata drop because they lose water into the atmosphere. This cause a chain reaction which pulls water from other cells eventually pulling water from the xylem, root, and soil.

Translocation  The transport of nutrients (food) formed during photosynthesis within the phloem to all parts of the plant.

Flow of Materials in Plants

Plant Growth  Primary Growth – Growth that lengthens Meristems – region where plants grow using cell division, this growth occurs in the tips of roots and shoots and enable the plant to grow in length  Secondary Growth - Growth that thickens Woody plants (trees and shrubs) thicken by producing xylem and phloem. Rings of a tree are layers of xylem and phloem

Plant Hormones  Auxin - produced in the tips of stems, causes cell walls to become more flexible If a stimulus causes auxin to concentrate more on one side of a stem, the cells on that side will elongate. Thus, the stem grows toward light.

Plant Hormones  Gibberellin  Stimulate cell division, elongation, and the sprouting of seeds.  Ethylene  Stimulates fruit ripening. Also promotes the dropping of leaves, flowers, and fruits.

Other Factors - Tropism Photoperiodism – the response of plants to periods of light and dark Geotropism – response of plant to gravity Helps plant determine which way to grow roots. Thigmotropism – response of plants to touch Helps climbing plants find support structures