V ASCULAR PLANTS : STRUCTURE & FUNCTION Monocotyledons (monocots) Dicotyledons (dicots) Taproots Fibrous roots Adventitious roots Root hairs Vascular bundles Senescence Abscission KeywordsMaking connections V ASCULAR PLANTS Plants must capture and store sufficient sunlight, water and minerals to survive. To do so, they have specialised: Root structures Taproots Fibrous roots Leaf structures Seed dispersal mechanisms M ONOCOTYLEDONS & DICOTYLEDONS Vascular plants are classified into 2 types: Monocotyledons Dicotyledons It is suggested that monocots evolved first, since their structures appear less complex. The creation model would argue that God made both unique and that both reproduce after their own kind. M ONOCOTYLEDONS & DICOTYLEDONS T APROOTS A taproot system is characterized by having one main root (the taproot) from which smaller branch roots emerge. When a seed germinates, the first root to emerge is the radicle, or primary root. This radicle develops into the taproot. Taproots can be used for storage of carbohydrates. Example: sugar beet and carrot. Taproots can grow extremely long in their search for deep underground water sources. Dicots mostly have taproot systems T APROOTS Radicle with root hairs F IBROUS R OOTS A fibrous root system is characterized by a mass of similarly sized roots. These roots spread out so that they can soak up as much water as quickly as possible. Adventitious roots may also be present. Adventitious roots form on plant organs other than the root. Some fibrous roots are used as storage. Example: sweet potato Plants with fibrous roots systems are excellent for erosion control, because the mass of roots cling to soil particles. Monocots mostly have fibrous root systems. F IBROUS R OOTS Adventitious roots Fibrous roots R OOT HAIRS Both taproots and fibrous roots have root hairs that grow at the apex or tips of the roots. Root hairs absorb water and nutrients from the soil S TEMS Monocot stemsDicot stems vascular bundles pithcortex L EAF S TRUCTURES The leaves of plants are specialised in many ways: Size Shape Function Leaves can be either deciduous or evergreen. Monocot leaves have parallel veins while dicot leaves have a network of veins D ECIDUOUS VS EVERGREEN LEAVES Deciduous leaves typically have a lifespan of just one season, while evergreen leaves last several seasons. All leaves go through a process of senescence or aging. In deciduous leaves, this may involve a change in colour. The plant recovers minerals and other chemicals from the leaf during senescence. This culminates in leaf abscission or the falling off of the leaf. The falling leaf often carries away toxins from the plant. Abscission is an important mechanism equivalent to excretion. L EAF S TRUCTURE The leaves of many plants limit water loss through adaptation of size, sheen and/or texture. Small leaves or spines limit the amount of surface area exposed to the drying heat. Glossy leaves reflect the sun's radiant heat reducing leaf temperatures and evaporation rates. Waxy leaves prevent moisture from escaping. Water escapes from leaves through the stomata, or leaf pores. L EAF STRUCTURE F LOWERS Monocot flowers have flower parts in 3s. Dicot flowers have flower parts in 4s or 5s It is not always easy to distinguish a monocot from a dicot using their flower parts because sometimes flower parts are fused or reduced S EED DISPERSAL Seed dispersal mechanisms include: by wind by water by explosive action by humans & animals adhesion & food D EFENSIVE MECHANISMS Defensive mechanisms are important adaptations that help plants survive. Defensive mechanisms include: sharp spines, thorns or hairs cellulose - makes them hard to digest chemicals - makes the plant toxic or smell bad. mimicry - helps the plant look like another plant that is poisonous