35 Flashcards
taproot
- Most eudicots and gymnosperms have a taproot system, consisting of one main vertical root, the taproot, which develops from an embryonic root.
- Taproot systems generally penetrate deeply and are well-adapted to deep soils where the groundwater isn’t close to the surface.
lateral roots
The taproot gives rise to lateral roots, also called branch roots.
adventitious
- In most monocots, such as grasses, the embryonic root dies early on and doesn’t form a taproot. Instead, many small roots emerge from the stem. Such roots are said to be adventitious, a term describing a plant organ that grows in an unusual location.
- Each small root forms its own lateral roots; the result is a fibrous root system.
fibrous root system
- A mat of generally thin roots spreading out below the soil surface.
- Usually don’t penetrate deeply; best adapted to shallow soils where rainfall is light and doesn’t moisten the soil much below the surface layer.
- Ex: grasses – shallow roots hold topsoil in place; excellent ground cover for preventing erosion.
axillary bud
- In the upper angle (axil) formed by each leaf and the stem is an axillary bud, a structure that can form a lateral shoot, commonly called a branch.
- Most of the growth of a young shoot is concentrated near the shoot tip, which consists of an APICAL BUD, or terminal bud, that is composed of developing leaves and a compact series of nodes and internodes.
apical dominance
- The proximity of the axillary buds to the apical bud is partly resopnsible for their dormancy.
- The inhibition of axillary buds by an apical bud.
- If an animal eats the end of the shoot or if shading results in the light being more intense to the side of the shoot, axillary buds break dormancy; that is, they start growing.
- Removing the apical bud stimulates the growth of axillary buds, resulting in more lateral shoots.
leaf
- Generally consist of a flattened BLADE and a stalk, the PETIOLE, which joins the leaf to the stem at a node.
- Grasses and many other monocots lack petioles; instead, the base of the leaf forms a sheath that envelops the stem.
veins
- The vascular tissue of leaves.
- Monocots: parallel major veins that run the length of the blade.
- Eudicots: branched network of major veins.
advantages of compound leaves:
- May enable leaves to withstand strong wind w/ less tearing.
- May confine pathogens that invade the leaf to a single leaflet, rather than allowing them to spread to the entire leaf.
tissue system
- Dermal + vascular + ground tissues
- A functional unit connecting all of the plant’s organs.
dermal tissue system
- Plant’s outer protective covering; forms the 1st line of defense against physical damage and pathogens.
- Nonwoody plants: it’s a single tissue called the EPIDERMIS, a layer of tightly packed cells. In leaves and most stems, the CUTICLE, a waxy coating on the epidermal surface, helps prevent water loss.
- Woody: protective tissues called PERIDERM replace the epidermis in older regions of stems and roots.
epidermis
- The dermal tissue system of nonwoody plants, usually consisting of a single layer of tightly packed cells.
- Protect plant from water loss and disease; also has specialized characteristics in each organ.
- Ex: a root hair is an extension of an epidermal cell near the tip of a root.
trichomes
- Hairlike outgrowths of the shoot epidermis.
- In some desert species, they reduce water loss and reflect excess light, but their most common function is to provide defense against insects by forming a barrier or by secreting sticky fluids or toxic compounds.
vascular tissue system
- Carries out long-distance transport of materials btwn the root and shoot systems. 2 types:
- Xylem: conducts water and dissolved minerals upward from roots into the shoots.
- Phloem: transports sugars from where they’re made (leaves) to where they’re needed (roots, fruits).
stele
- The vascular tissue of a root or stem.
- Angiosperms: the root stele is a solid central VASCULAR CYLINDER of xylem and phloem.
- Stems and leaves: VASCULAR BUNDLES, separate strands containing xylem and phloem.
ground tissue system
- Located btwn the dermal and vascular tissue in each organ.
- Includes various cells specialized for functions such as storage, photosynthesis, and support; also responsible for most of the plant’s metabolic functions.
pith
Ground tissue that is internal to the vascular tissue.
cortex
Ground tissue that is external to the vascular tissue.
indeterminate growth
A type of growth characteristic of plants, in which the organism continues to grow as long as it lives.
determinate growth
- Stop growing after reaching a certain size.
- Animals and some plant organs (leaves, thorns, flowers).
meristems
- Plants are capable of indeterminate growth b/c they have perpetually undifferentiated tissues called meristems that divide when conditions permit, leading to new cells that can elongate. Cells DIVIDE FREQUENTLY.
- 2 types: apical and lateral.
apical meristems
- Located at the tips of roots and shoots and in axillary buds of shoots.
- Provide additional cells that enable growth in length, a process known as primary growth.
primary growth
- Growth in length.
- Allows roots and shoots to extend.
- In herbaceous (non-woody) plants, primary growth produces all, or almost all, of the plant body.
secondary growth
- Growth in thickness (woody plants’ growth in circumference).
- Caused by lateral meristems called the vascular cambium and cork cambium. These cylinders of dividing cells extend along the length of roots and stems.
vascular cambium
Adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.
cork cambium
- Cylinder of dividing cells that arises in the outer cortex of stems and in the outer layer of the pericycle in roots.
- Replaces the epidermis with the thicker, tougher periderm.
- Produces a tough, thick covering consisting mainly of wax-impregnated cells that protect the stem from water loss and from invasion by insects, bacteria, fungi.
derivatives
The new cells displaced from the meristem that divide until the cells they produce become specialized in mature tissues.
root cap
- The tip of a root is covered by a thimble-like root cap, which protects the delicate apical meristem as the root pushes thru the abrasive soil during primary growth.
- Secretes a polysaccharide slime that lubricates the soil around the tip of the root.
- Growth occurs just behind the tip in the zones of cell division, elongation, and differentiation.
zone of cell division
- Includes the root apical meristem and its derivatives.
- New root cells are produced in this region, including cells of the root cap.
zone of elongation
- A few mm behind the tip of the root.
- Where most of the growth occurs as root cells elongate, sometimes to >10x their original length. Cell elongation in this zone pushes the tip farther into the soil.
- Root apical meristem keeps adding cells to the younger end of the zone of elongation.
- Even before the root cells finish lengthening, many begin specializing in structure and function.
zone of differentiation
- AKA zone of maturation.
- Cells complete their differentiation and become distinct cell types.
endodermis
- Innermost layer of the cortex.
- One-cell-thick cylinder that forms the boundary w/ the vascular cylinder.