For Vascular Plant: Form and Function lecture exam 1
What is the Endosymbiosis Theory?
Eukaryotes became photosynthetic by engulfing and domesticating photosynthetic cyanobacteria, which became chloroplasts
The process was repeated in secondary and tertiary endosymbiosis: eukaryotes engulfing smaller photosynthetic eukaryotes, who contained within them the descendants of photosynthetic cyanobacteria
What is the definitive criterion for creating taxonomic categories today?
Phylogeny or relationship – plants are an arbitrarily defined group descending from a particular common ancestor, including all its descendants and only its descendants
What are the characteristics of true plants?
Descended from green algae (eukaryotic with cellulose wall and particular set of photosynthetic pigments)
Complex, multicellular structure adapted for terrestrial life*
Embryos protected in multicellular chambers(true plants are also called embryophytes)
What are some challenges of botany?
Preservation of species
Development of new crops
Basic understanding of plant function and ecology
Understanding the organization of plant genomes
Consequences of using molecular genetic tools to change crop species
Understanding the biology of weedy and invasive plants.
Name the major parts of a flowering plant.
3 basic organs:
–stems, roots and leaves
Stem w/ attached leaves and buds = shoot
Embryonic shoot = bud
New growth occurs:
Axillary buds form in the axil (at the base) of each leaf
The positions along the stem to which leaves, buds and other appendages are attached are called nodes
The sections of stem between nodes are called internodes
What is the difference between primary and secondary growth?
Primary growth at the tip (shoot apex) adds new stem tissues and leaves (new node/internode units); grows lengthwise
Secondary growth is the addition of wood and bark in older stems (and roots); grows laterally
How do stems grow long and thin?
Intercalary growth of the internodes
What are plants called that have suppressed internodes?
Acaulescent plants appear to have no stems at all, because growth of the internodes is suppressed
Leaves of acaulescent plants are relatively large and arranged in a circular pattern called a rosette
Some plants with suppressed internodes grow upward slowly, with thick, rarely branched stems and large leaves. They are called pachycauls (“thick stems”)
What is the similarity between bulbs and corms?
What is the difference between bulbs and corms?
- Bulbs and corms are underground storage structures found in some acaulescent plants that are dormant during cold or dry seasons
- Are incased in papery tissue
- Grow adventitious roots
Bulbs are composed of leafy tissue underground
Corms are composed of stem tissue
What are adventitious roots, and what are some examples?
Roots that originate from the stem instead of from the primary root are called adventitious roots
Some examples are:
- Fibrous root systems - a root system made up of many equal adventitious roots
- Rhizome - a horizontal underground stem that grows at one end and decays at the other (ginger root)
- Stolon - a slender horizontal stem with very elongate internodes, and with a leaf, bud (orplantlet) and adventitious roots at each node (grass)
- an above-ground stolon is a runner(strawberries)
- Prop Roots - provide support for some trees
What is an advantage of having a taproot/taproot system?
- Taproot - used primarily for food storage, but also penetrates deeply into the soil for sources of water
- The entire root system is derived directly from the primary root of the seedling, and is called a taproot system
- A taproot system may develop as a single dominant taproot, with small lateralroots, or it may branch into several main roots
Plants can be classified by growth at different times of the year. What are they?
Annual herbs live for one growing season
Biennial herbs live for two seasons
Perennials live many years
How can you tell between a tuber and a tuberous root?
A tuber is composed of stem tissue
A tuberous root is composed of root tissue
What are xero- and hydrophytes?
Xerophytes are plants adapted to arid conditions; they often have succulent organs suited for photosynthesis and water storage.
Hydrophytes are adapted to living in or next to the water. Some have adapted to be totally submerged or floating on the surface of the water.
How do plant cells differ from animal cells?
cell wall composed of cellulose
Why does a plant wilt when it isn't watered, or "perk up" after being watered?
In a living plant cell the wall resists expansion, and pressure builds up (turgor pressure) in a hypotonic solution.
Turgor pressure serves as a “hydrostatic skeleton” that holds leaves and soft stemsupright. Wilting is the loss of turgor pressure.
Depends on the cell's vacuole.
•Vacuole absorbs and stores water & ions(osmoregulation)
•This results in the turgor pressure
Where and how do plants grow?
Primary Growth–extension of the plant body and formation of primary tissues–cells produced by primary meristems
Secondary Growth–increase in girth of the plant body and formation of secondary tissues (esp. xylem and phloem)–cells produced by secondary meristems (vascular cambium).
Both can occur at the same time–example: tall tree
Primary growth at branch tips secondary growth in the main trunk
What are meristems, and where are they in the plant?
•Meristems contain small, undifferentiated cells
•Contain two types of cells
•Apical meristems produce files of undifferentiated cells that become protoderm, ground meristem, and procambium, depending on their position.
•SAM = shoot apical meristem
What are the meristematic tissues in a plant embryo?
Protoderm – gives rise to epidermis
Ground meristem – gives rise to a variety of cells between epidermis and vascular tissue.
Procambium – gives rise to vascular tissue
After germination, these undifferentiated tissues are all produced by the apical meristem
What are the ground tissue systems?
•Pith–in the center of some roots and stems; soft, low density cells (parenchyma)
•Cortex–between epidermis and vascular tissue (parenchyma, collenchyma and sclerenchyma)
Cross-section of Ground Tissue
What are the basic cell types?
Defined by cell wall characteristics
Parenchyma, Collenchyma, Sclerenchyma
Cell Wall–Primary cell wall: thin layer of cellulose synthesized outside of the cell membrane of the plant cell
Secondary cell wall: thick layer of cellulose with lignin; very stiff and strong.
What is Parenchyma tissue?
•Only a primary wall. Other characteristics:
–Similar sized cells
–Alive at maturity (contrast with sclerenchyma)
–Water storage (in vacuole)
–Food storage (in amyloplasts or other plastids)
–Photosynthesis (in chloroplasts)
–Transport (which tissue?)
–Secretion (as glands)
–Growth and division (can dedifferentiate)
–Pigmentation (in chromoplasts)
Parenchyma with chloroplasts are found in leaves and young stems.
What are the three types of plastids?
A plastid that performs photosynthesis is a chloroplast
A plastid that stores starch is an amyloplast
A plastid that stores pigments is a chromoplast
What is Collenchyma?
living cells with unevenly thickened primary walls
cell walls are plastic, which means they take on new shapes when deformed
cell walls contain much water and often transmit light
typically occurs in soft stems and leaves while they are still growing
Function: Provide support and strength to young growing tissues
Source: differentiate from parenchyma
Plasticity in development.
What is Sclerenchyma?
•In sclerenchyma (and xylem), secondary walls, which are much thicker and denser than primary walls, are laid down between the primary wall and the cell membrane
•Secondary walls are also usually impregnated with a hardening material called lignin
•Thin areas in the secondary wall, called pits, often remain over the primary pit fields
Contain: Fibers or sclereids
Epidermal tissue consists of:
Ordinary epidermal cells, which secrete the cuticle and waxes
Guard cells, which form the opening/closing mechanism for stomata
Specialized cells called trichomes, which may have the form of hairs, scales or glands
Epidermal cells are alive at maturity but have little metabolic activity; walls may be thickened
What are the 4 functions of roots?
What are the primary tissues, and their function, that allow root growth?
•Root cap: produced by distal portion of apical meristem
–protection: as growing root pushes through the soil
–light and pressure responses
- Contains: amyloplasts which might have responses to gravity, columella cells, and peripheral cells that secrete mucigel
•Mucigel: secreted by peripheral cells; is a hydrated polysaccharide
•Functions–protection, lubrication, water absorption, nutrient absorption, habitat for beneficial microbes
Apical Meristem-region of active cell division
•Divides to produce protoderm, ground meristem, procambium
•Open vs closed arrangement of layers
Function: cells replace apical initials if they are damaged
What are the regions of the root tip?
Zone of differentiation: elongated cells differentiate consistent with their tissue type (protoderm, pro-cambium, etc).
Zone of cell elongation: undifferentiated cells elongate along the axis of the root, increasing its length
Zone of cell division: derivatives continue to divide
What is the region of maturation, and why can't root hairs grow before or after this region?
Location: 1-5 cm behind root tip
Function: cells mature into primary tissues
Root hairs can't or unable to grow before this region because the Zone of Elongation is moving and they can't grow after this region for the hairs would be cut off.
What are the primary structures of the root and their functions?
Epidermis: absorbs water and nutrients, grows root hairs, and produces mucigel
Cortex: bulk of root area, has storage parenchyma, intercellular spaces, and many plasmodemata
Endodermis: innermost layer of the cortex; contains the Casparian strip, a layer of suberin along cell walls blocks flow of water around cells that forces all uptake of water and nutrients to pass across a cell membrane; membrane characteristics provide plant with control of materials taken from soil.
What are the pathways for water movement into roots?
Apoplast –through cell walls, not through living cytoplasm
Symplast –through living cytoplasm
What is the pericyle and why is it important in roots?
•Pericycle –helps give rise to vascular cambium, cork cambium, and is a source of lateral roots
•have endogenous (internal) origin
•compare with origin of stem branches from axillary buds
How do lateral roots develop?
Lateral root development initiated by divisions of the pericycle. No nodes/internodes or buds in root!
Lateral roots push out through the endodermis, the cortex and the epidermis as they grow.
1. Primordium of lateral root begins in pericycle,over lobe of xylem; endodermis is ruptured
2. Lateral root pushes through tissues of parent root
3.Xylem and phloem of lateral root connect to xylem and phloem of parent root
What are steles, and what are the different types of steles?
The term stele sums up the vascular system, associated tissues and the enclosed pith.
The protostele is a conductive system of simple organization. It is a simple, unbranched, centrally located axial strand of xylem coated or interspersed with phloem
The siphonostele is composed of several axial vascular bundles that are arranged within the stem in the shape of a tube with enclosed pith
Eustele - in this arrangement, the primary vascular tissue consists of vascular bundles, usually in one or two rings around the pith.
Actinostele - a variation of the protostele in which the core is lobed or fluted found in many species of club moss
What is the function of velamen?
Some epiphytic plants, like orchids, have a specialized multiple epidermis called velamen.
Function: protecting underlying tissues of epiphytic plants
What is guttation, and why do plants have it?
Guttation results from root pressure, & helps keep water & minerals flowing upward in times of high humidity – only in relatively low plants.
What factors influence shoot balance?
Proportion of plant biomass that is roots
Depends on –water availability–nutrient availability
What are some factors affecting root growth?
Light –many roots grow away from light
Temperature –Extremes may limit growth or physiological activity.
Other organisms–competition with other plants, root herbivores,
Gravity–roots sense gravity, respond to grow downward
Developmental Stage–during fruit formation, energy not used for roots