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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
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