Plant Organs – Organs composed of one or more tissues. – Three major types: • Roots • Stems • leaves – Flowers and fruits evolved from stems and leaves
Function of Plant Organs LEAVES – Function Photosynthesis STEMS –Function Suppor Transport. ROOTS – Function Anchorage Absorption Storage Conduction
ROOT ROOTS “the hidden half” Functions of roots: Anchorage Absorption of water & dissolved minerals Storage (surplus sugars, starch) Conduction water/nutrients
Structure of RootsLongitudinal section of roots Root cap Zone of cell division Zone of cell elongation Zone of maturationCross section of root Vascular bundle (Stele) contains xylem and phloem Cortex Epidermis Root hairs Absorb water and minerals
Types of Roots– Fibrous, multibranched roots (e.g. lettuce)– Dominant tap root • Tap roots used to absorb water deep in soil • Some tap roots used to store carbohydrates (e.g. carrots)– Adventitious roots • root-like structures arising from stems or leaves • e.g. prop roots (corn) and holdfasts– Tuberous roots • Swollen structure on fibrous root used to store carbohydrates (e.g. sweet potato)
Types of Roots Fibrous roots Tap rootAdventitious roots Tuberous roots
STEMS Above-ground organs. (usually) Support leaves and fruits. Conduct water and sugars throughout plant.
STEM STRUCTURES Stem Structure Nodes: location of leaves on stem Internodes: stem between leaves Buds: undeveloped leaves or flowers – Terminal (apical) – axillary (lateral) – Apical dominance is growth inhibition caused by apical bud
Function of Stems Support leaves, flowers, fruits. Transport of water (xylem) and products of photosynthesis (phloem). Storage of carbohydrates Tubers - swollen underground stems that store carbohydrates (e.g. potato). Corm - swollen base of stem covered in papery leaves. Bulb - cluster of fleshy leaves attached to short, thick stem with basal roots (e.g. onion). Bulbils - tiny bulbs arising in leaf axils. Rhizome - horizontal stem below ground that produces roots and shoots at each node.
Stems Stems used only for asexual reproduction. Stolon (or runner) - horizontal stem that arises from leaf axel and runs above ground (e.g. spider plant) When tip of solon hits ground a new plant forms
Types of StemsTypes of modified stems Spur - stem with short internodes growing from a larger branch of woody plant. Waterspout - stem that arises from latent buds in branches of woody plants. Sucker - stem arising from root tissue, often from cut woody plant.
Types of StemsTypes of modified stems Tendrils - twining stems used to secure climbing plants to vertical surfaces (e.g. peas, grapes). Prickles - tiny, pointed projections of epidermis tissues of stems (e.g. blackberry). Thorns - long, pointed projections produced in leaf axils (e.g. Hawthorn). Cladophylls - stems modified for photosynthesis (e.g. cacti, asparagus).
LEAVES Most leaves are thin and flat An adaptation that helps them capture sunlight for photosynthesis. Although this structure may be typical, it is certainly not universal. Leaves are extremely variable. This variability represents adaptations to environmental conditions.
Leaves structureLeaf parts Blade - Flat expanded area Petiole - stalk that connects leaf blade to stem, and transports materials Pair of stipules
Leaf epidermis Is transparent – so that sun light can go through. Waxy cuticle protects against drying out Lower epidermis: stomata with guard cells – for gas exchange (CO2, H2O in; O2 out) A. Cuticle B. Upper epidermis C. Palisade layer D. Spongy Layer E. Lower epidermis
Leaves functionsLeaves Carry out photosynthesis in order to make glucose. Composed of epidermal, vascular and ground tissue.
Flower A flower is the reproductive organ of angiosperms. Flowering plants reproduce by pollination.
Fruits A fruit is defined as a ripened ovary that contains angiosperm seeds. The function of a fruit is to hold and protect the seeds. Each kernel of corn on a cob is actually an individual fruit In peaches, the fruits are soft and fleshy and contain a single, stony seed. Legumes like beans and peas produce a fruit called a pod that contains many seeds.