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

sugarsGround 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 CO2 inside the plant and O2 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

XylemWater moves upward to the leaves

LeavesCarbohydrates (food) produced via photosynthesis

Transpiration in the leaves causes the plant to lose water.

Roots and StemAbsorb water in the xylem

PhloemTranslocation occurs in phloem to move carbs to roots and stem

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