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:
- –Shoot apex
- –Root tip
- 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
- –immediate derivatives
- •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)
- –Large vacuoles
- –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
- Quiescent center–size
- 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
- Apical meristem
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
- Soil Properties–Texture, Aeration, Moisture content
Where does secondary growth in stems occur?
- From lateral meristems
- –Vascular cambium–Cork cambium
- Vascular cambium
- •Origin–Between primary xylem and phloem (fascicular)–From parenchyma (interfascicular)
- •Originates as a thin, circular layer of tissue
- Cork cambium
- •Forms in the cortex, phloem, or epidermis
What are the 2 cell types of the vascular cambium?
- •Ray initials - small, elongate cells, produces ray cells, parenchyma between vascular cells, move food and water between xylem and phloem
- •Fusiform initials - tapered prism shaped cells, produce xylem to inside, produce phloem to outside
What is the periderm?
- •Periderm: replaces the epidermis when stem expands during secondary growth.
- •Cork cambium –differentiates soon after vascular cambium–comes from cells in the cortex and secondary phloem, produced toward the outside of the stem, waterproof cells that protect the stem
- •Phelloderm produced toward the inside of the stem
- •Cork cells–walls lined with suberin and wax–impermeable to water and gas–lignified–dead at maturity
- •Phelloderm –parenchyma–living
- •Lenticels: openings in the periderm that permit oxygen to reach living cells
- •Bark: all tissues outside vascular cambium–secondary phloem + periderm(s)
- •New periderms form after several years
- •Commercial cork–bark of cork oak
Why do trees have growth rings, and what can we find from them?
- •Seasonal activity of vascular cambium leads to growth rings in secondary xylem.
- Annual Rings
- •One season’s growth
- •Two kinds of wood, at least in many trees
- •less dense
- •wider cells
- •thinner walls
- •narrower cells, thicker walls
- We can find
- •Plant age
- •Environmental effects on plant growth
What are the two types of wood?
- •Sapwood–lighter wood, toward outside, still functions in conduction
- •Heartwood–old xylem in the center of the trunk, no longer functions in conduction–dead parenchyma cells may be filled by oils, gums, etc.
- Reaction wood
- •Forms in horizontal stems that are supporting weight
- •Tension wood–upper side of stem–lots of cellulose fibers–dicots
- •Compression wood–lower side of stem–lots of lignin–doesn’t shrink much compared to other wood–conifers
What are the differences of secondary growth in roots compared to in stems?
- Vascular cambium from procambial cells between primary xylem and phloem
- •Dividing cells in cambium–periclinal divisions–derivatives to outside become phloem–derivatives to inside become xylem
- Primary phloem is displaced to outside and forms a ring. Primary xylem and phloem are now separate
- •Forms after initiation of secondary vascular tissue
- •Originates from pericycle
- •Outer cells of pericycle become cork cambium
- Periderm= cork+ cork cambium+phelloderm
- Periderm replaces epidermis and cortex
- After one year, a woody root has, from outside to inside:
- •Remnants of epidermis and cortex
- •Primary phloem
- •Secondary phloem
- •Vascular cambium
- •Secondary xylem
- •Primary xylem