Plant Form and Function: Introduction

Plant Form and Function: Introduction

• Angiosperms, which are flowering plants containing seeds, are the primary focus.
• Plant body organization, plant body plan diversity, and plant growth are covered.
• Indeterminate growth defines plants' continuous growth throughout their lives

Plant Form Variations

• Large quantities of light, CO2, and water are essential for plants.
• Nitrogen, phosphorus, potassium, and magnesium are required by plants in smaller doses.
• Minerals mostly exist as ions dissolved in soil water.
• Shoots, located above ground, are responsible for harvesting light and CO2.
• Roots, located below ground, are in charge of absorbing water and nutrients.

Surface Area to Volume Relationships

• Absorption efficiency relies on a large surface area relative to the volume.
• Leaves and roots exhibit high surface-area-to-volume ratios.

The Root System

• These systems anchor plants, retrieve water and ions, send water and ions to the shoot system and store sugar.
• Roots derive energy from sugars generated in the shoot system.
• Taproot and lateral roots are variations in root systems.
• Fibrous roots are also variations in root systems.
• Prairie plants are tailored to utilize limited water supplies.
• Various species exhibit unique systems.

Diverse Root Systems

• Plasticity exists within species.
• Shallow root systems are common, particularly in eastern forests
• Plant root can extend depending on phenotypic plasticity
• Depth is limited by wet or rocky soil.
• Tree roots frequently grow outside the canopy.
• Root systems representing over 80% of a plant’s mass is not rare.

The Shoot System

• This system is made up of one or more stems.
• Stems are structures which are vertical and aboveground and have nodes with leaves attached and segments between nodes, called internodes.
• Leaves are appendages projecting from the stem on petioles.

Buds in Shoot Systems

• Apical (terminal) and axillary (lateral) buds are important parts of the shoot systems.
• Apical buds are at the end of the stem and branches.
• Flowers may develop from apical and axillary buds.
• The axillary bud is just above where the leaf is attached.
• A branch may develop from an axillary bud, which forms a lateral shoot system.

Morphological Diversity in Shoots

• All sizes exist in shoot systems.
• Ranging from duckweed to giant sequoias
• Acquisition of light drives this system morphology.
• Gaining an advantage in light competition is aided by shoots.

Modified Stems

• Certain plant stems have unique functions.
• Water storage and photosynthesis are functions performed by succulent stems.
• Stolons are stems that grow horizontally, giving rise to roots and nodes.
• Asexual propagation of stem is achieved through rhizomes.
• Tubers are swollen rhizomes and also carbohydrate-storing organs.
• Thorns are stems that evolved to protect plats.
• The spine of a cactus is a modified leaf.

The Leaf

• Leaves are where most photosynthesis occurs.
• The extensive surface is vital for absorbing photons to aid photosynthesis.
• Expanded blade and petiole are the main components of a basic leaf.
• The blades of compound eaves branch into leaflets.

Morphological Leaf Diversity

• The arrangement of a leaves on a stem may vary.
• Leaves can appear in multiple ways: alternate, paired opposite each other, arranged in a whorl, rosettes with short internodes.

Phenotypic Leaf Plasticity

• Leaves exhibit phenotypic plasticity.
• Alterations are seen in leaves based on sun exposure.
• Sun leaves are typically smaller, so reducing water loss in high light areas.
• Shade leaves are bigger, assisting optimum absorption.

Modified Leaves

• Nutrients are stored in onion bulbs.
• Water is stored in succulent leaves.
• Vines can climb using tendrils.
• Pollinators are attracted by the bright red leaves of poinsettias.
• Insects are trapped by the tubelike leaves of pitcher plants.
• Cactus spines evolved to give stem protection.

Plant Cells

• Despite eukaryotic cells sharing traits, plant cells share some unique plant cell features.
• Cellulose-rich primary cell walls surround plant cells.
• Some plant cells feature firm secondary cell walls.
• Cytoplasm of plant cells nearby connect via plasmodesmata which tube structures connecting cells.

Cell Structures Specific to Plant Cells

• Chloroplasts are a major feature of photosynthetic cells
• Plant cells include a large vacuole containing cell sap, water, and waste and maintain turgor.
• Plastids are metabolic structures that are similar to mitochondria or chloroplasts.
• Amyloplasts store starch and detect gravity.
• Fats are stored in elaioplasts.
• Tannins and polyphenols are synthesized by tannosomes.
• Proteins are stored and modified by proteinoplasts.

Key Plant Tissues

• Tissue refers to a collection of cells performing as one unit..
• Plant tissues are categorized inside plants by structure and position..
• Three tissue systems found in plants: dermal, ground, vascular

Plant Tissue Types

• Epidermis and root hairs comprise the dermal tissue system.
• Parenchyma cells make up ground tissue.
• Collenchyma cells feature unevenly thickened, flexible cell walls
• Sclerenchyma is composed of dead sclereids or fibers with thick primary and secondary cell walls.
• Xylem, which transports water and nutrients, is made of dead tracheids, vessel elements, parenchyma cells, and fibers.
• Phloem transports sugars, amino acids, and hormones and are made of functioning sieve-tube elements, companion cells, and dead fibers.

Dermal Tissue

• The dermal system contains dermal tissue or epidermis.
• Epidermis, the cell's outermost layer, protects shoots against water loss.
• In roots, the epidermis absorbs water and nutrients.

Cuticles

• A cuticle prevents water loss forming a leaf and stem surface with a waxy layer.
• The covering also defends against pathogens.

Stomata

• CO2 and O2 for photosynthesis enter through stomata pores.
• Stomata regulate gas exchange and water loss.
• Stomata, singular, are surrounded by guard cells that open and close.

Trichomes

• Trichomes, appendages made of specialized epidermal cells, block sunlight and reduce water loss while protecting from herbivores and trapping insects.

Ground Tissue

• Most of the photosynthesis and carbohydrate storage occurs here.
• Parenchyma, collenchyma, and sclerenchyma compose the complex ground tissue.

Parenchyma

• Parenchyma is a generic tissue performing multiple tasks with thin primary cell walls.
• They are the most common and versatile cell types.
• Chloroplasts found in parenchyma tissue in leaves for photosynthesis
• Starch granules found in parenchyma roots store starch.
• Many parenchyma cells are totipotent, allowing plant healing and asexual reproduction through division and differentiation.
• Cuttings heal by producing undifferentiated cells(callus) which form roots and establish a new plant.

Collenchyma

• Collenchyma consists of simple tissue with unevenly thickened primary walls.
• Flexible support is give.
• Can be found under epidermis of stem.

Sclerenchyma

• Possess thin primary cell walls and thick secondary.
• Secondary walls consist of tough lignin along with cellulose.
• Fibers provide strength.
• Sclereids, short cells function protective role in nuts.

Vascular Tissue

• Xylem and phloem create the vascular system.
• Xylem brings water and nutrients from root to shoot.
• Phloem carries sugars, amino acids, and hormones from roots and shoots and vice versa.

Vascular Xylem Structure

• The conducting cells in xylem comprise tracheids and, in angiosperms, vessel elements.
• All vascular plants have xylem comprised of tracheids, which allows water transfer from the pits.
• Angiosperms have elements with perforations.
• These cells are either dead or almost dead upon maturity.

Vascular Pholem Structure

• Pholem's complex composition includes sieve-tube elements for transport, and maintenance with companion cells.
• Sieve tubes contain perforated ends, called sieve plates.
• Companion cells lack nuclei are directly connected to sieve ends by plasmodesmata.

Primary Plant Meristems

• Development is set up by meristems.
• Apical meristems create the protoderm, ground meristem, and procambium.
• The primary dermal, ground and vascular tissues are given rise by these meristems.
• Primary growth results in lengthening while secondary occurs during thickening.

Root System Growth

• The root cap, which regularlhy loses cells, which is protected by meristem.
• Gravitational sensing is root cap function which determines direction of growth.
• It reduces soil friction through the secretion of a lubricant.

Secondary Plant Growth

• Wood is created when cambium is present.
• This occurrence rises root and shoot width.
• Structural support is also boosted by the raised amount of conducting tissue provided.

Lateral Meristem (Cambium)

• It differs from an apical meristem.
• Forms cylinders down the trunk or branches.
• Adds to width by cell division.
• Vascular cambium located between phloem and xylem.
• Cork cambium around the outside of the root or trunk.

Vascular Cambium

• Secondary pholem and xylem arise from cambia in roots and stems.
• The inner part of bark makes up secondary pholem and the secondary xylem, which makes up wood.
• Vascular tissue comprises parenchyma cells and sclerenchyma fibers generated across the side.
• Wood creation during asymmetry results from the formation of secondary xylem.

Cork Cambium

• The bark of tree trunks exterior is produced with cork cambium outer cells.
• It comprises secondary pholem and cork cambium where gas exchanges occur near lenticels.