Plant Structure and Function

Plant Material Maintenance, chapter 2 in the text

Tree or Shrub?

Acer saccharum Betula nigra Viburnum dentatum

Crown Development

Crown: the branches, twigs and leaves of a tree or shrub.

Shoot: a young, actively growing stem. Bud: an unexpanded shoot or flower (a

dormant meristem)◦ Leaf (Vegetative)◦ Flower◦ Mixed

Meristems:Places in plants where cell division is occurring.◦ Apical meristems

are found in shoot tips and root tips. AM cause shoot and root lengthening.

◦ Vascular cambium causes diameter growth in stems and roots.

Growth: the amount of growth experienced by an individual shoot depends on the rate of and duration of cell division and expansion.

Varies by species.

Short (3-4 weeks) growth flush in the spring.◦ Ex: Coniferous Evergreen plants and many

deciduous plants. Several growth flushes over a growing

season.◦ Ex: Monterey Pine and many species of oak.

Growth continues as long as conditions are favorable.◦ Ex: Sweet Gum, Redwood, and Sugar Maple.

Patterns of Shoot Elongation

Crown Form

Leaves

Photosynthesis:

LightWaterCarbon DioxideChlorophyll (a green pigment found in leaves)

Glucose (sugar; carbohydrate)Oxygen

Holly leaves have a thick, waxy cuticle.

Roots

Anchorage. Absorption of water and mineral nutrients. Storage of food reserves. Synthesis of organic regulatory compounds.

•Tree roots extend radially in every direction to a distance equal to at least the height of the tree (assuming no physical barriers) and grow predominantly near the soil surface.

•Typically 90% of all roots, and virtually all the large structural supporting roots, are in the upper 2-3 feet of the soil. This includes the small, feeder roots.

Taproots are common on the dicots.

Fibrous root systems are common on the monocots.

fibrous root system

Stems (Trunk)

Translocation of water, nutrients, and sugars.◦ Xylem: transports water and dissolved nutrients.◦ Phloem: transports sugars◦ Movement is from “source to sink”; that is from

areas of high concentration to areas of low concentration.

Stems support the leaves and fruit.

Roots that develop from newly organized meristems forming in stems, leaves, and other plant parts.

Adventitious Roots

Adventitious roots developing from the leaf petiole of Peperomia.

Adventitious roots developing from the stem of a Coleus cutting.

Adventitious roots forming on an Iris corm.

Photosynthesis Respiration Transpiration

Basic Physiological Processes

Photosynthesis:Food Producing Reaction

light

Photosynthesis is occurring primarily in the leaves and green stems.

Respiration is occurring in all of the living cells of a plant; leaves, stems, and roots.

Respiration:Food Consuming Reaction

Respiration

OxygenCarbohydrates (sugars)

Carbon dioxideWaterHeatChemical energy (ATP)

PHOTOSYNTHESIS

Light and chlorophyll

Water

Carbon dioxide

Oxygen

RESPIRATIONCarbon dioxide

ATP

Sugars

Soil Minerals Absorbed with water

Lignin

Fats

Proteins

Enzymes

Pigments

Hormones

Vitamins

Starch

Pectin

Cellulose

HEATWater

Waterlogged Soils Soil pore space is filled with water. No oxygen in the pore space. Without oxygen the roots will die. Without roots the plant can’t absorb water.

◦ Low areas◦ Soil compaction◦ Burm up the soil or drain the planting hole.

On sunny, warm days the sun warms up the leaf surfaces.  The water in the cells of a leaf begins to evaporate.  Water vapor collects in the spongy mesophyll tissue of

the leaf.  The water vapor moves out of spongy mesophyll,

through the open stomata, and into the drier air surrounding the leaf.

 As water evaporates from the spongy mesophyll, new water molecules are delivered to the leaf through the xylem in leaf veins.

Transpiration is a “pulling” force drawing water up the stem xylem and into the leaves.

Transpiration

•The rate of transpiration is affected by the following 3 things:• Humidity; during dry, less

humid days the rate of transpiration increases.• Temperature; the rate of

transpiration is greater on hot days than on cooler, cloudy days.• Wind; the rate of transpiration

is greater on windy days than calmer days.

Some other terms to remember: Phototropism: a shoot will always grow

towards a light source. Geotropism: roots always grow down in

response to gravity.

The End