Plant Anatomy and Physiology

• Plants/shoots grow upwards, while roots grow downwards.
• A plant emerges from a seed.
• The first leaf/root emerges during germination.
• Primary growth is growth in length.
• Secondary growth is growth in width.

Main tissues

• Dermal tissue forms the protective outer layer of the plant.
• Vascular tissue consists of the epidermis (outer layer), mesophyll (inner layer), xylem, and phloem.
• Vascular tissue supports plant growth, stems, and branches.
• Ground tissue is made up of xylem and phloem.
• Xylem transports water from the roots to the upper parts of the plant.
• Phloem transports food from photosynthesis to other parts of the plant.
• Ground tissue forms the plant's skeleton.
• Ground tissue contains the epidermis, cortex (support), phloem, xylem, and pith (inner center).

Meristems

• Meristems are found at the tips of plants.
• Primary/apical meristems include the shoot apex, root apex, procambium, protoderm, and ground meristems.
• Primary meristems are responsible for length growth and emerging leaves/flowers in certain plants.
• Secondary/lateral meristems include the vascular cambium (between procambium) and the cork cambium (between protoderm and ground meristem).
• Secondary meristems facilitate width growth and have active cell growth/division.

Shoot

• The shoot contains lateral, apical, and ground meristems.

Root

• The root contains lateral, ground, and apical meristems.
• Root hairs are present on roots.
• The root cap protects the root.
• The root cap protects roots where the soil is harsh and may damage roots during growth.
• The root cap is responsible for roots' downward direction of growth.
• Without a root cap, roots may not grow correctly (i.e., sidewards).

Basic Plant Morphology

• Plants have 2 systems: a shoot system and a root system.
• Plants have 6 organs: vegetative (root, stem, leaf) and reproductive (flower, fruit, seed).

Basic Tissue Types

• Plants have 3 basic tissue types: dermal (outer), ground (center), and vascular (inner).

Botany/Zoology Rule

• Structure determines function.

Simple Tissues

• Simple tissues consist of one cell type.
• An example of simple tissue is dermal tissue.
• Dermal tissue includes stomates/stomata and trichomes.
• Trichomes are found in roots and stems.
• Trichomes serve as extensions of plants.
• Trichomes help capture water and/or nutrients efficiently.
• Some trichomes are visible without magnification.
• Trichomes can be glandular or non-glandular; they act as "extra hands" for catching nutrients..
• Root hairs do help in capturing water and are found only in roots.

Ground

• Parenchyma cells have thin walls and are alive at maturity.
• Parenchyma cells are multifaceted and perform photosynthesis, storage, and secretion (glands and trichomes).
• Parenchyma cells perform mitosis, wound healing, cloning, and protection (epidermis).
• Collenchyma cells have unevenly thickened walls with varying thickness.
• Collenchyma cells are alive at maturity and mainly support primary growth.
• Sclerenchyma cells have evenly thickened cell walls and are dead at maturity.
• Sclerenchyma provides strength/support/protection and includes fiber and sclereid cells.

Vascular

• Xylem mostly conducts water and nutrients.
• Phloem mostly conducts sugars and amino acids (i.e., food).

Complex Tissues

• Complex tissues are comprised of more than one cell type.
• Xylem is a water-conducting tissue that contains parenchyma, vessels (big holes, where water goes in), tracheids (small holes, efficient water transport), and ray cells.
• Phloem is a food-conducting tissue made of sieve-tube cells, companion cells, fibers, parenchyma, and ray cells.
• Mature sieve-tube cells lack a nucleus but have cytoplasm;
• Periderm is protective tissue composed of cork and parenchyma.
• Secretory structures are responsible for making latex, resin, nectar, and other substances produced and stored in channels inside the plant body.
• Vessel members are wider, shorter, thinner walled, and less tapered.
• Vessel members are aligned end-to-end, forming micropipes; walls have perforations.
• Tracheids are long, thin cells with tapered ends.
• Tracheids have secondary walls hardened with lignin.
• Water moves between tracheid cells through pits.
• Sieve-tube cells consist of a sieve-tube member, a companion cell (nucleus), a sieve plate, and it needs a nucleus because the sieve tube lacks its own nucleus

Root Functions

• Roots provide anchorage, anchoring the plant to the soil.
• Roots facilitate absorption, absorbing water and other nutrients for the plant.
• Roots are responsible for conduction via the xylem and phloem..
• Xylem continuously conducts water via roots and also acts as a food reserve for the plant.

Root Characteristics

• Roots are non-green due to a lack of chlorophyll.
• Roots are not divided into nodes and internodes and lack leaves and buds.
• Roots are positively geotropic, growing towards gravity.
• Roots are positively hydrotropic, growing towards water.
• Roots are negatively phototropic, growing away from light.

Tap Root System

• A tap root system consists of one prominent main root with smaller lateral roots branching from it.
• Tap root systems provide very strong anchorage, can go very deep into the ground, and are the main root type of dicot plants.

Fibrous Root System

• A fibrous root system consists of several adventitious roots of approximately equal size that comes from the base of the stem, does not branch profusely, tends to be shallow and spread horizontally.
• Fibrous root systems cannot provide strong anchorage and are the main root systems of monocot plants.

Key Terms

• A root cap is a covering of cells over root tips that protects delicate meristematic tissue directly behind it, contains statocytes/cells involved in gravity perception, and each root tip has it.
• Root caps are protective, thimble-like, consist of many thick cells, cover the delicate root apical meristem, and may orient the root so it grows downward.
• If the cap is removed carefully, the root will grow randomly.
• A root cap may secrete mucilage to ease the movement of the root through the soil and is involved in communication with the soil microbiota.
• A root hair is an extension of an epidermal cell of a root that increases the absorptive capacity of the root, short-lived, unicellular extensions of epidermal cells.
• Root hairs increase surface area in contact with the soil to increase absorptive capacity.

Primary Eudicot Roots

• Primary eudicot roots have an outer protective covering, the epidermis, which protects the root.
• Root hairs help absorb water and dissolved minerals.

Ground Tissues in Eudicot Roots

• Cortex consists of parenchyma cells and usually stores starch.
• Pith is only found in certain roots and only in monocot plants.

Vascular Tissues in Eudicot Roots

• Xylem and Phloem types are always near each other.
• Xylem conducts water and dissolved minerals.
• Phloem conducts dissolved sugar.

Endodermis

• The endodermis is the innermost layer of the cortex of the root that prevents water and dissolved materials from entering the xylem and passing between cells.

Casparian Strip

• The Casparian strip is a band of waterproof material around the radial and transverse cells of the endodermis.
• It ensures that water and minerals enter the xylem only by passing through the endodermal cells.
• It is one layer type of cell and wraps around endodermis.

Pericycle

• The pericycle is a layer of cells just inside the endodermis of the root.
• It gives rise to lateral roots, is another layer after endodermis.

Stele

• In dicot plants, the general structure is: endodermis → pericycle → phloem → xylem.

Monocot Roots

• Monocots often have a pith in the center of the root.
• In herbaceous eudicot plants, the xylem and phloem form a solid mass in the center of the root.
• Monocots lack a vascular cambium and do not have secondary growth.

Water Pathway

• In a primary eudicot root, water moves from the soil into the center of the root via: root hair → epidermis → cortex (symplast/apoplast pathway) → endodermis → pericycle → xylem of root.

Symplast vs Apoplast

• Symplast water transport flows through interconnecting cytoplasm of the living cells and consists of the cytosol of all the living cells in a plant, including the plasmodesmata.
• Apoplast water occurs when water flows in the interconnected cell wall spaces
• Apoplast runs through cell via plasmodesmata.
• Apoplast consists of everything external to the plasma membrane
• Apoplast includes cell walls, extracellular spaces, and the interior of vessel elements and tracheids.
• Water is transported upward through the root xylem into the stem xylem and the rest of the plant.

Modified Roots

• Modified roots include roots modified for: food storage, propagative functions, pneumatophores.
• Pneumatophores are specialized aerial roots produced by certain trees living in swampy habitats and may facilitate gas exchange between the atmosphere and submerged roots.
• Other examples of modified roots include aerial roots, photosynthetic roots, and contractile roots
• Photosynthetic roots are found in orchids, and is sometimes mistaken as orchid's stem
• Contractile roots are specialized aerial roots, found in herbaceous dicots some monocots.
• Contractile roots are often found on bulbs or corn, contracts and pulls the plant down into a desirable depth in the soil
• Other examples of modified roots buttress roots, parasitic roots, symbiotic roots, prop roots, and suckers.
• Buttress roots are swollen bases or braces that hold trees upright. They aid in the extensive distribution of shallow roots and are often found in some tropical rainforest trees. Parasitic roots
• Prop roots are adventitious roots rising from the stem that provide additional support for the plant.
• Suckers are aboveground stems that develop from adventitious buds on the roots and are involved in asexual reproduction of some roots.

Symbiotic Roots

• Symbiotic roots have a relationship with fungi/other plants. Mycorrhiza
• Mycorrhiza is a mutually beneficial association between fungus and root, helping the plant absorb essential minerals from the soil.
• Nodules are small swellings on the root of leguminous plants where beneficial nitrogen-fixing bacteria (e.g., rhizobium) live.
• Mycorrhizae are also known as "fungus roots".
• It supports a symbiotic relationship between plant and fungus.
• In this symbiotic relationship, the fungal components provide protection for the plant against some pathogens and increase the surface area for essential nutrient absorption.
• In this symbiotic relationship, plants provide food for the fungus as sugar and amino acids.

Food and Root Crops

• Roots that store the products of photosynthesis are vital sources of food for human consumption (i.e., root crops.
• Some roots are used as flavorings (e.g., root beer uses dried greenbrier roots).
• Predominantly taproot-based root crops include fruits, beets, sugar beets, parsnips, turnips, rutabagas, and radishes.
• Some root crops utilize fibrous roots such as sweet potatoes and cassava.

Explore plant vascular systems (xylem, phloem), root adaptations, meristems, and tissue repair. Learn about protoderm function, mycorrhizae mutualism, and root crop types for a comprehensive plant biology overview.