PlantsStems, 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

Human Uses…

What do roots do???

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

Monocots vs. Eudicots

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

Overall…Monocots Eudicots

Embryo with single cotyledon

Embryo with two cotyledons

Pollen with single furrow or pore

Pollen with three furrows or pores

Flower parts in multiples of three

Flower parts in multiples of four or five

Major leaf veins parallel Major leaf veins branched

Stem vascular bundles scattered

Stem vascular bundles in a ring

Roots are adventitious Roots develop from radicle

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