1
Q
taproot
A
- 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.
2
Q
lateral roots
A
The taproot gives rise to lateral roots, also called branch roots.
3
Q
adventitious
A
- 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.
4
Q
fibrous root system
A
- 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.
5
Q
axillary bud
A
- 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.
6
Q
apical dominance
A
- 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.
7
Q
leaf
A
- 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.
8
Q
veins
A
- The vascular tissue of leaves.
- Monocots: parallel major veins that run the length of the blade.
- Eudicots: branched network of major veins.
9
Q
advantages of compound leaves:
A
- 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.
10
Q
tissue system
A
- Dermal + vascular + ground tissues
- A functional unit connecting all of the plant’s organs.
11
Q
dermal tissue system
A
- 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.
12
Q
epidermis
A
- 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.
13
Q
trichomes
A
- 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.
14
Q
vascular tissue system
A
- 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).
15
Q
stele
A
- 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.
16
Q
ground tissue system
A
- 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.
17
Q
pith
A
Ground tissue that is internal to the vascular tissue.
18
Q
cortex
A
Ground tissue that is external to the vascular tissue.
19
Q
indeterminate growth
A
A type of growth characteristic of plants, in which the organism continues to grow as long as it lives.
20
Q
determinate growth
A
- Stop growing after reaching a certain size.
- Animals and some plant organs (leaves, thorns, flowers).
21
Q
meristems
A
- 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.
22
Q
apical meristems
A
- 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.
23
Q
primary growth
A
- 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.
24
Q
secondary growth
A
- 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.
25
vascular cambium
Adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.
26
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.
27
derivatives
The new cells displaced from the meristem that divide until the cells they produce become specialized in mature tissues.
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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.
29
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.
30
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.
31
zone of differentiation
- AKA zone of maturation.
| - Cells complete their differentiation and become distinct cell types.
32
endodermis
- Innermost layer of the cortex.
| - One-cell-thick cylinder that forms the boundary w/ the vascular cylinder.
33
pericycle
Lateral roots arise from the pericycle, the outermost cell layer in the vascular cylinder, which is adjacent to and just inside the endodermis.
34
leaf primordia
Leave develop from leaf primordia, finger-like projections along the sides of the apical meristem.
35
intercalary meristems
- In some monocots, particularly grasses, meristematic activity occurs at the bases of stems and leaves. These areas, called intercalary meristems, allow damaged leaves to rapidly regrow, which accounts for the ability of lawns to grow following mowing.
36
lateral roots vs lateral shoots
- Lat roots: arise from vascular tissue deep within a root and disrupt the vascular cylinder, cortex, and epidermis as they emerge.
- Lat shoots: develop from axillary bud meristems on the stem's surface and disrupt no other tissues.
- The vascular bundles of the stem converge w/ the root's vascular cylinder in a zone of transition located near the soil surface.
37
stoma
Can refer to:
- The stomatal pore
- The entire stomatal complex consisting of a pore flanked by two GUARD CELLS, which regulate the opening/closing of the pore.
38
parenchyma cells
- Have primary walls that are relatively thin and flexible; lack secondary walls.
- When mature, have a large central vacuole.
- Perform most of the metabolic functions (photosynthesis occurs within the chloroplasts of parenchyma cells; some parenchyma cells in stems and roots have amyloplasts)
- Fleshy tissue of many fruits is composed mainly of parenchyma cells.
- Most parenchyma cells retain the ability to divide and differentiate into other types of plant cells under particular conditions -- it's possible to grow an entire plant from a single parenchyma cell.
39
collenchyma cells
- Grouped in strands.
- Help support young parts of the plant shoot.
- Elongated; have thicker primary walls than parenchyma cells, though the walls are unevenly thickened.
- Young stems and petioles often have strands of collenchyma cells just below their epidermis.
- Provide flexible support w/o restraining growth. At maturity, collenchyma cells are living and flexible, elongating w/ the stems and leaves they support.
40
sclerenchyma cells
- Supporting elements; much more rigid than collenchyma cells.
- Secondary walls are thick and contain large amounts of lignin.
- Mature sclerenchyma cells can't elongate, and they occur in regions of the plant that have stopped growing in length. They're so specialized for support that many are dead at functional maturity, but they produce secondary walls before the protoplast (the living part of the cell) dies. The rigid walls remain as a 'skeleton' that supports the plant, in some cases for hundreds of years.
- 2 types: sclereids and fibers.
41
sclereids
- Type of sclerenchyma cell.
- Boxier than fibers.
- Irregular in shape.
- Very thick, lignified secodary walls.
- Impart the hardness to nutshells and seed coats and the gritty texture to pear fruits.
42
fibers
- Type of sclerenchyma cell.
- Usually grouped in strands.
- Long, slender, and tapered.
- Some are used commercially -- hemp fibers for rope, flax fibers for weaving into linen.
43
water-conducting cells of the xylem
- 2 types: tracheids and vessel elements. Both are tubular, elongated cells that are dead at functional maturity.
- When the living cellular contents of a tracheid/vessel element disintegrate, the cell's thickened walls remain behind, forming a nonliving conduit through which water can flow.
- The 2ndary walls of tracheids and vessel elements are often interrupted by pits, thinner regions where only primary walls are present. Water can migrate laterally btwn neighboring cells thru pits, where it doesn't have to cross thick 2ndary walls.
- The 2ndary walls of both are hardened w/ lignin; this hardening prevents collapse under the tensions of water transport and provides support.
44
tracheids
- In the xylem of nearly all vascular plants.
| - Long, thin cells w/ tapered ends.
45
vessel elements
- Wider, shorter, thinner-walled, and less tapered than the tracheids.
- Aligned end to end, forming long micropipes known as vessels.
- The end walls of vessel elements have perforation plates that enable water to flow freely thru the vessels.
46
sugar-conducting cells of the xylem
- Alive at functional maturity.
- In seedless vasculars and gymnosperms, sugars and other organic nutrients are transported thru long, narrow cells called sieve cells.
- In the phloem of angiosperms, these nutrients are transported thru sieve tubes, which consist of chains of cells called sieve-tube elements, or sieve-tube members.
47
sieve-tube elements
- In the phloem of angiosperms, sugars and other organic nutrients are transported thru sieve tubes, which consist of chains of cells called sieve-tube elements, or sieve-tube members.
- Lack a nucleus, ribosomes, a distinct vacuole, and cytoskeletal elements. This reduction in cell contents enables nutrients to pass more easily thru the cell.
48
sieve plates
The end walls btwn sieve-tube elements that have pores that facilitate the flow of fluid from cell to cell along the sieve tube.
49
companion cell
- Alongside each sieve-tube element is a nonconducting cell called a companion cell, which is connected to the sieve-tube element by numerous channels called plasmodesmata.
- The nucleus and ribosomes of the companion cell serve not only that cell itself but also the adjacent sieve-tube element.
- In some plants, the companion cells in leaves also help load sugars into the sieve-tube elements, which then transport the sugars to other parts of the plant.
50
arrangement of vascular tissue: eudicots
- Vascular bundles arranged in a ring.
| - Xylem in each bundle is adjacent to the pith, and the phloem in each bundle is adjacent to the cortex.
51
arrangement of vascular tissue: monocots
- Vascular bundles are scattered throughout the ground tissue rather than forming a ring.
52
role of -chyma cells in vascular tissue arrangement
- Parenchyma: makes up ground tissue.
- Collenchyma cells just beneath the epidermis strengthen many stems.
- Sclerenchyma cells, esp fiber cells, also provide support in those parts of the stems that are no longer elongating.
53
mesophyll
- The ground tissue of a leaf.
- Sandwiched btwn the upper and lower epidermal layers.
- Consists mainly of parenchyma cells specialized for photosynthesis.
- The mesophylls of many eudicots have 2 distinct layers: palisade mesophyll and spongy mesophyll.
54
palisade mesophyll
Consists of 1 or more layers of elongated parenchyma cells on the upper part of the leaf.
55
spongy mesophyll
- Below the palisade mesophyll.
- Has parenchyma cells that are more loosely arranged, w/ a labyrinth of air spaces through which CO2 and oxygen circulate around the cells and up to the palisade region. The air spaces are particularly large in the vicinity of stomata.
56
bundle sheath
- Each vein is enclosed by a protective bundle sheath, consisting of 1 or more layers of cells, usually parenchyma cells.
- Bundle sheath cells are particularly prominent in leaves of plant species that undergo C4 photosynthesis.
57
dendrochronology
- Science of analyzing tree ring growth patterns.
- In temperate regions, the vascular cambium becomes inactive during winter, and after growth resumes in spring. There's a marked contrast btwn the large cells of the new early wood and the smaller cells of the late wood of the previous growing season. This is why a year's growth appears as a distinct ring in the cross sections of most tree trunks and roots.
- Rings vary in thicknesses, depending on seasonal growth. Trees grow well in wet and warm years and vice versa. Thick ring = warm year; thin = cold.
58
heartwood
- As a tree or woody shrub ages, the older layers of 2ndary xylem no longer transport water and minerals (a solution called xylem sap). These layers are called HEARTWOOD b/c they're closer to the center of a stem or root.
- Generally darker than sapwood b/c of resins and other compounds that permeate the cell cavities and help protect the core of the tree from fungi and wood-boring insects.
59
sapwood
- The newest, outer layers of secondary xylem still transport xylem sap and are therefore known as sapwood.
- That's why a large tree can survive even if the center of its trunk is hollow.
60
secondary phloem
- Only the youngest 2ndary phloem, closest to the vascular cambium, functions in sugar transport.
- As a stem or root increases in circumference, the older secondary phloem is sloughed off, which is 1 reason 2ndary phloem doesn't accumulate as extensively as 2ndary xylem.
61
bark
- Misconception: bark consists only of the protective outer covering of a woody stem or root.
- Actually includes all tissues external to the vascular cambium.
- Moving outward, its main components are the secondary phloem (produced by the vascular cambium), the most recent periderm, and all the older layers of periderm.
62
Some insights into the evolution of 2ndary growth have been achieved by studying the herbaceous plant Arabidopsis thaliana:
- Can stimulate some 2ndary growth in Arabidopsis stems by adding weights to the plant. This suggests that weight carried by the stem activates a developmental program leading to wood formation.
- Several developmental genes that regulate shoot apical meristems in Arabidopsis have been found to regulate vascular cambium activity in Populus.
63
periderm
- In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots.
- B/c cork cells have SUBERIN and are usually compacted together, most of the periderm is impermeable to water and gases, unlike the epidermis.
64
lenticels
- Dotting the periderm are small raised areas called lenticels, in which there's more space btwn cork cells, enabling living cells within a woody stem or root to exchange gases w/ the outside air.
- Often appear as horizontal slits.
65
young vs old roots
- In most plants, water and minerals are absorbed primarily in the youngest parts of roots.
- The older parts anchor the plant and transport water and solutes btwn the soil and shoots.
66
secondary growth: epidermis is replaced by
- 2 tissues produced by the first cork cambium.
- PHELLODERM: a thin layer of parenchyma cells that forms to the interior of the cork cambium.
- The other tissue consists of cork cells that accumulate to the exterior of the cork cambium. As cork cells mature, they deposit a waxy, hydrophobic material called SUBERIN in their walls and then die. The cork tissue then functions as a barrier that helps protect the stem or root from water loss, physical damage, and pathogens. Each cork cambium and the tissues it produces comprise a layer of periderm.
67
periderm vs epidermis
B/c cork cells have SUBERIN and are usually compacted together, most of the periderm is impermeable to water and gases, unlike the epidermis.
68
secondary growth: description
- During early stages, the epidermis is pushed outward, causing it to split, dry, and fall off the stem or root. It's replaced by 2 tissues produced by the first cork cambium.
- The thickening of a stem/root often splits the 1st cork cambium, which loses its meristematic activity and differentiates into cork cells. A new cork cambium forms to the inside, resulting in another layer of periderm. As this process continues, older layers of periderm are soughed off, as you can see in the cracked, peeling bark of many tree trunks.
69
development
The specific series of changes by which cells form tissues, organs, and organisms.
70
developmental plasticity
- The ability to alter form in response to local environmental conditions.
- Dramatic examples of plasticity are much more common in plants than in animals and may help compensate for plants' inability to escape adverse conditions by moving.
71
3 overlapping processes in development:
- Growth: irreversible increase in size.
- Morphogenesis; process that gives a tissue, organ, or organism its shape and determines the positions of cell types.
- Differentiation.
72
cell expansion: animal vs plant cells
- Animal cells grow mainly by synthesizing protein-rich cytoplasm, a metabolically expensive process.
- Growing plant cells also produce additional protein-rich material in their cytoplasm, but water uptake typically accounts for about 90 percent of expansion. Most of this water is packaged in the large central vacuole. Vacuolar sap is very dilute and nearly devoid of the energetically expensive macromolecules that are found in great abundance in the rest of the cytoplasm.
73
orientation of plant cell expansion
- Rarely expand in all directions. Their greatest expansion is usually oriented along the plant's main axis. Cells near the tip of the root may elongate up to 20x their original length, w/ little increase in width.
- The orientation of cellulose microfibrils in the innermost layers of the cell wall causes this differential growth. The microfibrils don't stretch, so the cell expands perpendicular to the main orientation of the microfibrils.
74
pattern formation
- The development of specific structures in specific locations.
- Ex: dermal tissue forms on the exterior, vascular tissue in the interior -- never the other way around.
75
lineage-based mechanisms
- Hypotheses based on lineage-based mechanisms propose that cell fate is determined early in development and that cells pass on this destiny to their progeny. According to this view, the basic pattern of cell differentiation is mapped out according to the directions in which meristematic cells divide and expand.
- Hypotheses based on position-based medchanisms propose that the cell's final position in an emerging organ determines what kind of cell it will become.
76
cell fate in plants
- Cell differentiation depends, to a large degree, on the control of gene expression.
- The fate of a plant cell is determined by its final position in the developing organ, NOT BY CELL LINEAGE. One aspect of plant cell interaction is the communication of positional information from one cell to another.
77
phases
- Plant developmental stages.
- Unlike animal development changes, which take place throughout the entire organism, phases occur within a single region: the shoot apical meristem.
78
phase changes
- The morphological changes that arise from transitions in shoot apical meristem activity.
- During the transition from a juvenile phase to an adult phase, the most obvious morphological changes typically occur in leaf size and shape. Juvenile nodes and internodes retain their juvenile status even after the shoot continues to elongate and the shoot apical meristem has changed to the adult phase. Therefore, any new leaves that develop on branches that emerge from axillary buds at juvenile nodes will also be juvenile, even though the apical meristem of the stem's main axis may have bee producing mature nodes for years.
79
meristem identity genes
- Unlike vegetative growth, which is indeterminate, floral growth is determinate: the production of a flower by a shoot apical meristem stops the primary growth of that shoot.
- The transition from vegetative growth to flowering is associated w/ the switching on of floral meristem identity genes.
80
organ identity genes
- A plant homeotic gene that uses positional information to determine which emerging leaves develop into which types of floral organs.
- Belong to MADS-box family.
- Encode transcription factors that regulate the development of characteristic floral pattern: four whorls, from outer --> inner, Se Pe St Ca
81
ABC hypothesis
- Normally, A genes are switched on in Se Pe, B in Pe St, C in St Ca.
- Se arise where only A active
- Pe: A and B
- St: B and C
- Ca: only C
