Plant Structure

There are many types of plants…. We are going to focus on land plants: - they provide protection for their embryos which has increased over time - they have multicellular haploid and diploid phases - they can be compared by the presence o absence of conductive systems

Types of Land Plants Plant Group Major Features Non-vascular no conducting tissue often grouped together as bryophytes usually small and grow close to the ground include mosses, liverworts, and hornworts Seedless Vascular Plants well-developed vascular tissue do not produce seeds include horsetails, ferns, club mosses, and whisk ferns (were once large specimens, but most of today’s representatives are relatively small) Seeded Vascular Plants most living plant specimens are in this group seeds contain an embryo, a supply of nutrients, and a protective outer coat have extensive vascular tissue and include some of the world’s largest organisms

Seeded Plants The seeded vascular plants are divided into: - Gymnosperms Have seeds that do not develop within an enclosed structure - Angiosperms Have seeds that develop within a protective structure

Although no one species of the 265,000 species of plants can be considered typical, the focus here is on angiosperms.

Plants have two basic organ systems: Shoots and Roots

The Shoot System The shoot system consists of stems, leaves and reproductive structures.

Stems are the framework for upright growth. Terrestrial plants support themselves by means of thickened cellulose, cell turgor and xylem

Water, minerals, and organic substances are transported through the stems

The leaf has evolved to optimize photosynthesis.

The root system usually grows underground. It absorbs water and minerals from soil and conducts them upward It stores food; it also anchors and supports the plant There are taproot and fibrous root systems.

Plant organ are composed of three tissue systems. Vascular Tissue Xylem and Phloem carry out long-distance conduction of water minerals, and nutrients within the plant Provides support Dermal Tissue Outer protective covering Protects against physical agents and pathogenic organisms Prevents water loss May have specialized structures for various purposes Ground Tissue Consists mostly of thin-walled cells that function in storage, photosynthesis, support, and secretion

The vascular tissue distributes water and solutes through the plant body.

XYLEM Conducts water and dissolved ions absorbed from the soil

XYLEM It is formed from two types of cells that are dead at maturity - Tracheids are long cells with overlapping ends - Vessels are shorter cells joined end to end to form a vessel.

Phloem transports sugars and other solutes throughout the plant body

PHLOEM Contains living conducting cells called sieve tube members Companion cells, adjacent to the sieve tube members, help to load sugars produced in leaves and unload them in storage and growth regions.

The dermal tissue system covers and protects the plants surface. The epidermiscovers the primary plant body

Dermal Tissue Epidermal cells are typically non- photosynthetic and are relatively transparent , allowing light to penetrate to deeper tissues.

Dermal Tissue A waxy cuticle covers the external surfaces of the plant to restrict water loss and resist microbial attack

Dermal Tissue The periderm replaces the epidermis when roots and stems increase and become woody.

The ground tissue system makes up the bulk of the plant body Functions are photosynthesis, storage and support

Ground tissues are composed of three basic cells types.

Parenchyma is the most abundant type. Thin walled, pliable cells, found in virtually all plant parts. Various types participate in photosynthesis, storage, secretion, and other tasks.

Collenchyma cells help strengthen the plant (for example, “strings” in celery). They are commonly arranged as strands or cylinders beneath the dermal tissue of stems and stalks Cell walls become thickened with cellulose

Sclerenchyma cells provide mechanical support and protection in mature plants Walls are thick and often impregnated with lignin, which strengthens and waterproofs cell walls Sclerenchyma cells form fibers, such as in hemp and flax