Angiosperm Anatomy: Monocots vs Eudicots

• This explores plant organization, specifically in angiosperms.

Review of Angiosperms

• Angiosperms are flowering plants.
• Angiosperms are seeded plants that produce flowers and fruits.
• 90% of all living plant species are angiosperms.
• Focus on the two groups that make up 95% of living angiosperms which are monocots and eudicots.

Monocots

• Monocots make up 25% of extant angiosperms.
• Monocots have an embryo with 1 cotyledon (seed leaf).
• Monocots have parallel veins, scattered vasculature and a fibrous root system.
• Monocots have a pollen grain with 1 opening.
• Flowers are often in groups of 3.

Eudicots

• Eudicots make up 70% of extant angiosperms.
• Eudicots have an embryo with 2 cotyledons (seed leaf).
• Eudicots have net-like veins and vasculature in rings.
• Eudicots have a taproot, pollen grain with 3 openings.
• Eudicot flowers often appear in multiples of 4 or 5.
• Plants and animals exhibit a hierarchical organization within multicellular organisms: Molecules → Cells → Tissues → Organs → Organism.
• Tissues consist of groups of cells performing specialized functions, such as dermal tissue forming outer protective layers.
• Organs consist of groups of tissues performing specialized functions, such as: leaves, roots, and heart.
• Roots and shoots, along with their tissues.

Meristems

• Meristems are plant stem cells.
• Meristems are clusters of undifferentiated cells that divide and differentiate into specific types of plant cells.
• When meristem cells divide, one cell remains a meristem cell, ensuring continuous growth and renewal.
• Apical meristems are found at the tips of stems and roots.
• In herbaceous plants, apical meristems are the only type of meristematic tissue.
• Tissue derived from apical meristems is considered primary tissue, which can constitute the entire plant in some species or the young, soft shoots and roots in others, composing the primary plant body.

Tissues from Apical Meristems

• Three tissue systems arise from apical meristems.
• Three tissue systems from apical meristems: Protoderm which forms the epidermis.
• Three tissue systems from apical meristems: Procambium which forms primary vascular tissue.
• Three tissue systems from apical meristems: Ground meristem which differentiates into ground tissues.
• Lateral meristems occur in all woody plants and some herbaceous plants, resulting in increased diameter.
• Peripheral cylinders of meristematic tissues within stems and roots undergo division to increase width.
• Woody plants have two lateral meristems which include the cork cambium and the vascular cambium.
• The cork cambium in the bark contributes to the outer bark.
• The vascular cambium produces secondary vascular tissue; secondary xylem is the main component of wood.
• Lateral meristem-derived tissues form most of the mature trunk, branches, and older roots of trees and shrubs, known as the secondary plant body.

Overview of Plant Tissues in Plant Organs

• Roots, stems, and leaves consist of dermal, ground, and vascular tissue types with varying arrangements.
• Dermal tissue forms the outer protective layer, analogous to skin.

Parts of Dermal Tissue

• The epidermis is a layer of tightly packed epidermal cells covering the plant's entire surface.
• Specialized epidermal cells include root hair cells, trichomes, and guard cells.
• Root hair cells are extensions of epidermal cells near the root tip that increase surface area for absorption.
• Trichomes are cellular or multicellular hair-like outgrowths of the epidermis that reduce evaporation and provide cooling and can secrete toxic substances.
• Guard cells flank stomata and regulate gas exchange and water loss.
• Cuticle in some plants has a waxy coating of fatty cutin on the epidermal surface to prevent water loss.
• Periderm in woody plants continually replaces older epidermis with a protective layer.

Vascular Tissue

• Vascular tissue conducts fluids and dissolved substances throughout the plant.
• Xylem transports water and dissolved minerals, located centrally in the plant axis.
• The Xylem combines vessels (hollow tubes of dead cylindrical cells arranged end to end) and tracheids (tapered ends).
• Xylem also contains ground tissues like fibers and parenchyma.
• Extraction of the fibers in xylem is how paper is made.
• Secondary xylem produced by the vascular cambium is the wood in woody plants.
• Pholem conducts carbohydrates, located peripherally in the plant axis.
• Removing the bark can kill a tree by damaging the underlying phloem.
• Sieve and sieve-tube cells conduct carbohydrates through phloem tissue.
• Sieve and sieve-tube cells are living cells that lack nuclei.

Fluids in Plant Tissue

• Xylem sap is a watery solution of hormones, minerals, and some nutrients transported from the roots to the leaves
• Maple syrup is made from reduced sugar maple xylem sap harvested from the Sugar Maple tree.
• Phloem sap primarily consists of sugars dissolved in water, along with hormones and minerals, and is transported from where carbohydrates are produced/stored to where they are used.
• Latex is a milky fluid found in 10% of angiosperms, as it contains proteins, alkaloids, carbohydrates, lipids, resins, and gums that coagulate when exposed to air.
• Resin is mostly made of terpenes secreted for protection and amber.
• Ground tissue has functions in storage, photosynthesis, secretion, and support.

Ground Tissue Types

• Parenchyma are the most common type of plant cell, with thin walls, many sides, and living protoplasts.
• Parenchyma functions to store food/water, promote photosynthesis, and promote secretion.
• Chlorenchyma describes parenchyma cells that contain chloroplasts and carry out photosynthesis.
• Collenchyma which provides support.

Collenchyma

• Collenchyma is often located underneath epidermis of stems and stalks and along veins
• Collenchyma walls vary in width and cells are often column-shaped.
• Collenchyma cells contain living protoplasts.
• Sclerenchyma which has tough, thick walls that lack living protoplasts when they are mature.
• Sclerenchyma can have secondary cell walls containing lignin.
• Lignin is a highly branched polymer making the cell wall rigid.
• Sclerenchyma is present in fibers which are long, slender cells grouped as strands.
• Sclerenchyma is present in sclereids which vary in shape and give pears their gritty texture.

Overview of Basic Plant Organs: Roots and Shoots

• Roots function to anchor a plant to the ground and also to absorb water and minerals from the soil.
• Roots can store carbohydrates.
• Roots have a root cap which constantly regenerates by apical meristem cells.
• Root caps have cells that act as gravity sensors so that roots always grow downward.
• Cross-section of roots reveals an epidermis which is a single layer of dermal cells.
• Cross-section of roots reveals a cortex, consisting of many layers of parenchyma cells for storage.
• Endodermis contains a Casparian strip with bands of suberin, allowing the plant to control passage of water and nutrients through vascular tissue.
• Stele includes: Pericycle (dividing parenchyma for lateral roots), and Vascular tissue (xylem and phloem).
• Vascular tissue has X-shaped xylem in eudicots and some others.
• Vascular tissue has Parenchyma in monocots.
• Adventitious roots arise from any structure besides a root.
• Tap roots penetrate the soil to provide good anchoring for a plant.
• Tap roots allow the plant to grow taller without toppling over.
• Tap roots rely on lateral root branches to absorb water.
• Fibrous root systems consist of thin networks of roots spreading laterally like a mat under the soil.
• Fibrous root systems prevent soil erosion.
• Root hairs are finger-like extensions at the tips of roots which increase the surface area for absorbing water/minerals.
• Mycorrhizal associations are symbiotic interactions between plant roots and mycelium of a fungus.

Root Adaptions

• Aerial roots have a thick outer layer (epidermis) to reduce water loss.
• Prop roots are thick adventitious roots from the lower stem of some monocots (e.g., corn), to brace against the wind.
• Pneumatophores are spongy outgrowths in swamp plants that are used to facilitate oxygen uptake.
• Parasitic roots penetrate a host plant to extract nutrients.
• Contractile roots spiral to pull the plant deeper into the soil each year.
• Food storage roots (e.g., sweet potatoes, carrots, beets, parsnips, radishes, turnips) have extra parenchyma cells storing large quantities of carbohydrates.
• Water storage roots exist in plants that live in arid regions.
• Stems function as an above-ground support system and provide an axis for leaves and flowers.
• The stem contains vascular tissue to transport substances to and from the rest of the plant.
• The shoot apical meristem divides to form the stem tissue and intermittent primordia (bulges) where flowers or branches develop.
• Phyllotaxy optimizes leaf exposure to the sun.
• Spirals, whorls, and opposite pairs.
• The node is the region of leaf attachment.
• Internodes are the stem between nodes.
• The apical bud is the tip of the shoot where growth occurs.
• Axillary buds are buds that grow from the axil and can become a branch or flower cluster.
• Cross-section of a stem has a major difference between monocots and eudicots which is that the organization of the internal structures vary.
• A cross section of a eudicot is organized in rings: Epidermis, Pith, and Cortex.
• The epidermidis is the outer layer and has collenchyma cells underneath for support.
• Pith is the internal ground tissue for storage.
• The cortex is the external ground tissue.
• Cortex has vascular bundles of xylem and phloem.
• In plants with secondary growth, a vascular cambium develops between the xylem and phloem.
• Lateral meristem growth contributes to the rings in trees (xylem) and pholem growth.
• In woody eudicots, the cork cambium can form in the outer cortex to produce cork cells.
• During secondary growth in stems, This is region is the periderm.
• Cork cells fill with suberin, die, and create the outer bark.
• Lenticels allow air exchange of woody stems.
• Rhizomes are stems that grow underground.
• Stolons are shoots that grow on the surface and produce plantlets.
• Tubers are carbohydrates that accumulate in the tips of rhizomes.
• Tendrils allow climbing plants to attach themselves to a surface.
• Bulbs are underground stems with adventitious roots at their base.
• Corms are similar to bulbs but have no leaves inside.
• Cladophylls are modified stems and the spines.

Leaves

• The leaves are the main location of photosynthesis in the plant.
• Leaves capture light energy to generate sugar, exchange gases (CO2 in, O2 out) through stomata, dissipate heat, and contain toxins to defend from pathogens.
• Leaves are initiated by the apical meristems as primordia – then their growth stops at maturity.
• A leaves structure: blade which is a flattened surface.
• Simple leaves have undivided blades with indentations or lobes.
• Compound leaves have blades divided into leaflets.
• Petiole joins the blade to the stem at the node.
• Stipules are outgrowths at the base of the petiole.
• Veins (vascular bundles in leaves) arrangement.
• Microphyll has parallel veins.
• Megaphyll has branched network.
• The epidermis covers the surface of the leaf and contains guard cells.
• Mesophyll is the tissue between the upper and lower epidermis.
• Eudicots have palisade mesophyll and spongy mesophyll.
• Palisade mesophyll contains chlorenchyma cells close to the upper surface.
• Spongy mesophyll has space for gas exchange and vein distribution.
• Monocots can have bundle sheath cells which are cells that surround veins, for the C4 photosynthetic pathway.

Leaf Adaptions

• Floral leaves (bracts) surround a true flower.
• Spines deter predators.
• Reproductive leaves are leaves that are plantlets and can regenerate the entire plant.
• Window leaves permit sunlight to reach the mesophyll when the leaf surface is covered with sand.
• Insectivorous leaves- capture and digest insects in nutrient-poor or swampy environments.
• Storage leaves- the leaves that have carbs to make the onion bulb