Plants Stems, Roots and Transport (12.3-12.5)
Function of Stems… • Connect vascular tissue in leaves to vascular tissue in roots • Transports water and dissolved nutrients • Raise and support the leaves and reproductive organs • Raising leaves maximizes exposure to sunlight • Raising reproductive organs places them in the ideal position for pollination • Storage- modified stems in cacti can store large volumes of water
Structure • Woody – contain wood and are relatively hard, have bark, and do not usually carry out photosynthesis. • Herbaceous- do not contain wood and are relatively pliable, carry out photosynthesis, and have a thin epidermis. • Monocots do not produce woody stems • All gymnosperms are woody
Herbaceous… • The vascular tissue of herbaceous stems is arranged in distinct vascular bundles in ground tissue. • A vascular bundle is a long, continuous strand of vascular tissue that consists of xylem and phloem. • In monocots, the vascular bundles are found throughout the ground tissue of the stem. In eudicots, the vascular bundles form a ring.
Woody Stems… • Grow thick because of vascular cambium • Vascular cambium is a layer of meristematic cells in the vascular tissue that divide to form new xylem and phloem cells. • So what we call “wood” is actually many layers of xylem tissue • Heart wood- old xylem that gets filled with resin and no longer transports water. Supports the tree
Bark…(protection-herbivores and water loss) • Bark consists of all the tissues found outside the vascular cambium. It includes phloem, cork cambium, and cork. • The phloem transports sugars made in the leaves throughout the plant. • The cork cambium is a layer of meristematic tissue that produces cork, the tough, outer layer of the tree that prevents water loss from the stem.
Growth Rings… • In temperate regions growth happens during spring and summer • In spring growth is fast and light coloured wood is produced • In the summer growth is slower and dark coloured wood is produced
Cell types • Xylem cells are thick walled and dead at maturity. • rich in lignin, a carbohydrate that makes the cells very strong. • Phloem cells are living at maturity and contain cytoplasm. • Both phloem and xylem cells may be stacked to form long, continuous tubes.
Xylem… • tracheid an elongated, tapered xylem cell with thick cell walls containing small pits; tracheids overlap one another at the ends to form continuous tubes from root to shoot • vessel element a shorter, blunt-ended xylem cell with thick cell walls containing small pits; vessel elements are stacked end to end to form vessel tubes that run from root to shoot
Phloem… • Three types of phloem cells are found in vascular plants: sieve cells, sieve tube elements, and companion cells. • Sieve cells have narrow pores in all their cell walls and contain all the organelles found in most cells, including a nucleus. • Sieve tube elements have cytoplasm but lack many cell organelles, including a nucleus. The end walls of these cells are called sieve plates, which are cell walls with perforations to allow sugar solutions to pass to the neighbouring phloem cells. • Companion cell, which is always associated with a sieve tube element. It has a nucleus and all the other organelles that the sieve tube element lacks. The sieve tube elements and their associated companion cells form long conducting tubes
Cell Specialization… • Not all hold a plant upright • Underground modified include • Tubers, Rhizomes, Corms • Above ground modified stems • Stolons grow along the soil instead of upright • Vines
Function… • Anchor • Keep upright • Absorb water and nutrients • Some roots store water and carbohydrates for the plant
Types… • Taproot- a root system composed of a large, thick root; can have smaller lateral roots • Lateral root- a smaller root that branches from a larger root • Fibrous root- a root system made up of many small, branching roots • Both taproots and lateral roots are covered with root hairs. A root hair is a microscopic hair-like outgrowth from an epidermal cell.
Structure… • Tip of root contains root cap and meristem • Root cap-slippery substance • Meristem- produces new cells for growth • Roots hairs above the root tip ( S.A) • The root cortex is a region of parenchyma cells beneath the epidermis. • The root cortex store carbohydrates and transport water from the epidermis to the xylem. • Endodermis is the innermost layer of root cortex are wrapped with a wax-like substance, forming a continuous barrier called the Casparian strip
Vascular cylinder… • Tissue comprised of xylem and phloem. • Central part off root • Eudicots- X shapes vascular cylinder • Monocots- parenchyma at center
Root specialization… • Mutualistic relationships-ex. With micorrhizae(expand roots system and perform external digestion) and nitrogen fixers • Parasitic- Strangler fig- seeds are deposited on a host tree by an animal, the roots grow downward and strangle the host tree • Tuberous roots- carbohydrate storage(e.g. carrots)
Human Root Uses…. • Food- carrots, parsnips, turnips, beets, potato • Beverages-root beer from the sassafras root • Dyes- red(beets or madder), brown (dandelion) • Pesticides- from rotenone • Medicine- ipecac(induce vomiting), kava kava (reduce anxiety), valerian (sleep aid) • Erosion Control-forms mat that holds upper soil layers together
Adventitious root- a root that develops from somewhere other than the root apical meristem • Cotyledon- A cotyledon is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling. • Radicle – part of root meristem