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Let’s recall some basic facts about plants: • All plants are multicellular, eukaryotic, autotrophic organisms • All plant cells contain cell walls composed of cellulose • All plants are photosynthetic, and contain cellular components with pigments to capitalize on that process • All plants take up water through capillary action Plant Classification Plants can be divided into two main categories •nonvascular Known collectively as phylum bryophyta: These are the simplest terrestrial plants. They lack true roots, stems and leaves. Common bryophytes are mosses and liverworts •vascular Known collectively as phylum tracheophyta: These are the most common and widespread plants, which contain true conducting vascular tissue. Common tracheophytes include ferns, gymnosperms and angiosperms. Tracheophyte Subdivisions Of all the Tracheophytes, ferns are the simplest and most ancient. These are known as “seedless” plants. They do have vascular tissue to transport water and nutrients, but they still need an abundant supply of water for reproduction since they do not possess seeds. These non-seed vascular plants evolved long before dinosaurs. The seeded tracheophytes include the gymnosperms and angiosperms. Gymnosperms contain unenclosed seeds which are often found “naked” on the scales of a cone. Angiosperms contain enclosed seeds located within a fruit or nut. Basic Body Plan: Angiosperms Typical flowering plants have • shoots Aboveground parts such as stems, leaves, and flowers • roots Absorb minerals and water for the plant, and store nutrients as well Shoots and roots consist of three tissue systems. • Ground tissue system Photosynthetic tissue; storage tissue and structural support. • vascular tissue system Distribute water and nutrients around the plant • Dermal tissue system Covers and protects exposed surfaces of the plant Simple Ground Tissues Carry on most of the plant's Parenchyma: typically thin-walled, metabolic functions flexible, and many sided. Makes up most Most parenchyma cells have the of the soft primary growth of roots, ability to differentiate into other stems, leaves, and flowers. Also has cell types under special conditions , storage and secretion functions. Living such as during repair and at maturity. replacement of cells after injury Collenchyma: elongated and stretchable tissue supporting rapidly growing plant parts, including young stems and leaf stalks. Pectin (a polysaccharide) gives flexibility to collenchyma cell walls. Living at maturity Collenchyma Sclerenchyma: Variably shaped, dead at maturity, but lignin in cell wall helps tissue resist compression. (Lignin helped upright plants evolve on land, and resist fungal infections) Fibers and sclerids are typical. Occur in parts of the plant which have quit growing in length Parenchyma Vascular Tissues: As plants evolved to be more and more terrestrial, tube-like structures developed that function to transport materials up, down, and around the plant. While in an aquatic environment, plant tissues are able to transport water and nutrients across membranes through simple osmosis and diffusion. Xylem and phloem are the vascular tissues of complex plants (tracheophytes) which carry water and nutrients around the plant. Xylem: conducts water and minerals up a plant from its roots. There are two types of xylem cells: Tracheids Long and thin Vessel elements Short and thick Xylem is a long narrow tube constructed of dead cells which are strong because of lignin in their cell walls. The water and minerals go in and out of the tubes through the pits on the sides of the tubes. These pits allow easy water transfer to neighbouring cells This lignin also gives the plant an extra strong mechanical support system Phloem vessels carry nutrients, such as glucose, throughout the plant. Made up of: • Sieve tube elements Actually carry the nutrients in the plant •Companion cells Hang around to lend “support” to sieve tube elements. Differences between xylem and phloem… Roots Leaves The growing region of a root includes three regions: • The root tip • The zone of elongation • The zone of maturation Meristematic zones are simply regions of rapid growth, and actively dividing cells. You can find it here in the roots, and at the apical region of the shoot as well. Layers in the Root: If you were to cut a cross section through a root you’d find: •Epidermis (outer protection) • Cortex (mid-region where starches are stored) • Stele (inner cylinder which contains xylems and phloems) Flowers Root hairs provide increased surface area for the absorption of water and minerals Water may enter the root via two methods. The apoplast is a continuous space between the plasma membrane, and the cell wall of all cells. The symplast allows for the flow of water and other nutrients along concentration gradients through a cell’s cytoplasm. While the root’s main function is to anchor the plant, they also come in many different varieties, and have adapted to different circumstances. • Tap Roots: Roots that plunge deep into the Earth to find the water table, and “tap it”, while serving to increase the support of the plant as well. • Fibrous roots: Roots which grow in dense mats to optimally serve the plant in the collection of water, and minerals, as well as to anchor it securely. •Stilt roots: these are support roots, common among mangroves. They grow down from lateral branches, branching in the soil. Pneumatophores: Special stilt roots that are aerating roots which rise above the ground, especially in saturated areas. Prop roots: Special stilt roots that hold tall plants tight in windy areas. Typically, these plants are top-heavy, like corn. Buttress roots: These are large roots on all sides of a tall or shallowly rooted tree, which typically finds itself in poor or low nutrient soil. Aerial roots: roots entirely above the ground, such as in epiphytic orchids. They function as prop roots or anchor roots. Some may be parasitic. • Haustorial roots: roots of parasitic plants that can absorb water and nutrients from another plant, such as in mistletoe Contractile roots: They pull bulbs or corms of monocots deeper in the soil through expanding radially and contracting longitudinally. They help the plant find appropriate soil moisture during seasonal droughts. •Storage roots: These roots are modified for storage of nutrients, such as carrots and beets. Tuberous roots: A special type of storage root where a portion of a root forms into a roundish knob (called a tuber) for food. • Photosynthesis • Protection: modified to form spines, as in cactus • Storage: fleshy leaves allow plants to survive particularly harsh environments. • Consumption: modified to trap prey, as with the insectivorous plants which grow in nitrogen poor soils. • Conservation: tiny hairs to trap water When it comes to plants structures, the one that you will absolutely run into on the AP Biology test, is flowers. The following is what you need to know about the structure of the flower: Male parts collectively called stamen: Male gametes found on the anther are called microspores. (pollen/sperm) Things you should already know: Flowers are colorful and fragrant to attract pollinators. It is a wonderful and foolproof adaptation, that works on humans too! Female parts collectively called pistil: Female gametes are found in the ovary are called megaspores.