Biology-Plants Flashcards
Gymnosperm (largest group of living gymnosperms: conifers)
woody cone-bearing plant
Angiosperms (flowering plants)
divided into two groups:
dicotyledons (dicots)
monocotyledons (monocots)
Cotyledons
storage tissue that provides nutrition to the developing seedling
Dicots: 2 cotyledons
Monocots: 1 cotyledon
Leaf Venation
the pattern of veins in leaves
Dicot: netted (branching pattern)
Monocot: parallel
Flower parts
numbers of petals, sepals, stamens, and other flower parts
Dicots: in 4s, 5s, or multiples thereof
Monocots: in 3s or multiples thereof
Vascular bundles
arrangement of bundles of vascular tissue (xylem and phloem) in stems
dicots: organized in a circle
monocots: scattered
Root
form of root
Dicot: taproot (a large single root)
Monocot: fibrous system (a cluster of many fine roots)
Ground tissues include what three kinds of cells?
Parenchyma- synthesis/ storage of sugars and other compounds
Sclerenchyma- support (fixed in size)
Collenchyma- support (expandable in size)
Parenchyma Cells
most common component of ground tissues
- thin primary cell walls
- totipotent
typically unspecialized but they function in storage (such as starch granules), photosynthesis (help out in leaves), and secretion
Ground tissue
fills up everything around the dermal and vascular tissues. In the stems, GT is found in the pith and cortex. In the leaves, GT is found in the mesophyll.
- Most photosynthesis and carbohydrate storage takes place here.
- 3 basic kinds of cells: parenchyma, collenchyma, and sclerenchyma cells
Collenchyma
have only primary cell walls; irregularly shaped due to uneven thickening of cell wall.
- Their cell walls (thick/flexible) can stretch and elongate even at maturity so they can function in support
Sclerenchyma Cells
thicker walls than collenchyma, also provide mechanical support
- has both primary and secondary cell walls that are thicker than collenchyma, are lignified, and contain cellulose.
- Usually dead at maturity and function well for support
- There are four types: fibers, sclereids, tracheids, and vessel elements
seed plants
include gymnosperms (conifers) and angiosperms (flowering plants). Angiosperms are divided into 2 groups: dicotyledon (dicots) and monocotyledons (monocots)
Dermal tissue
epidermis cells that cover outside of plant parts, guard cells that surround stomata, hair cells, stinging cells, and glandular cells; aerial portions of plants, epidermal cells secrete waxy protective substance (cuticle)
Vascular tissue
consists of xylem and phloem => form vascular bundles.
xylem
part of vascular tissue; conduction of water, mineral; mechanical support; have 2nd cell wall for additional strength; some places in walls of xylem cells have pits (absence of 2nd cell wall). Cells are dead at maturity (no cellular component).
Two kinds:
tracheids: long/tapered where water passes from one to another through pits
vessel elements: shorter/wider, have less or no taper at ends. A column of vessel elements (members) is called a vessel. Perforations are where H2O passes through from one vessel member to the next (lack both 1st and 2nd cell wall). Perforations are an advantage to tracheids.
Phloem
transport sugar. made of cells called sieve-tube members (elements) that form fluid-conducting columns (sieve tubes); living at maturity although lack nuclei and ribosomes. Pores on end of member form sieve plates (areas where cytoplasm of one cell makes contact w/ next cell). Sieve tubes are associated w/ companion cells (living parenchyma that lie adjacent to each sieve tube member) and connected by plasmodesmata.
The seed
consists of embryo, seed coat, and some kind of storage material (endosperm or cotyledons-formed by digesting material in endosperm). There are 2 cotyledons in dicot (pea). There is 1 cotyledon in monocot (corn)
embryo
- Epicotyl (top portion of embryo) becomes shoot tip.
- Plumule: young leaves often attached to epicotyl; epicotyl can refer to both together
- Hypocotyl: becomes young shoot (below epicotyl and attached to cotyledons)
- Radicles: develops from hypocotyls into root
- Coleoptiles (in monocot) sheath surrounds and protects epicotyl. In developing young plants, coleoptiles emerge 1st as leaf. True leaves are from Plumule within coleoptiles
germination and development
seed remain dormant at maturity until specific environment cues (water, temp, light, seed coat damage), others may have required dormancy period
germination
begins with imbibition (absorption) of water => enzymes => biochemical processed including respiration.
- Absorbed water causes seed to swell and seed coat to crack => growing tips of radical produce roots that anchor seedling => elongation of hypocotyl => young shoot
development
young seedling: growth occurs at root/shoot tips (apical meristems); actively dividing (meristematic) cells. This kind of growth is called primary growth (produces primary tissues- 1st xylem and 1st phloem => height)
- root cap: root tip, protects apical meristem behind
- Zone of cell division: formed from dividing cells of apical meristem
- Zone of Elongation: newly formed cells absorb water and elongate
- Zone of maturation: differentiation; cells mature into xylem, phloem, parenchyma, or epidermal cells (root hairs may grow here).
meristems
areas in plants where mitosis occurs, due to this cell division, it is also where growth occurs. Lateral Meristems can be at tip of lateral growth in plant. Apical meristems are responsible for vertical growth and found at root and shoot (apex) tips.
primary growth versus secondary growth
conifers and woody dicots undergo 2nd growth in addition to 1st growth (extend length). 2nd growth increases girth and is the origin of woody plant tissues; occurs at 2 lateral meristems (vascular cambium- 2nd xylem and phloem and cork cambium- periderm- protective material that lines outside of woody plant
Primary Structure of Roots
from outside of root to center
- Epidermis: outside surface of root. In zone of maturation (epidermal cells produce root hair), when zone of maturation ages, root hairs die. New epidermal cells from zone of elongation becomes cell of new zone of maturation
- Cortex: makes up root bulk, starch storage, contain intercellular spaces, providing aeration of cells for respiration
- Endodermis: ring of tightly packed cells at inner most portion of cortex. A band of fatty material (suberin) called Caspian Strip creates water-impenetrable barrier between cells => All water passing through endodermis must pass through endodermal cells and not between cells => control movement of water.
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Vascular cylinder (stele): makes up tissues inside endoermis (phloem, xylem, pericycle). Outer part consists of one/several layers of cells (pericycle-from which lateral root arise). Inside pericycle are vascular tissue.
- dicot: xylem cells fill center of vascular cylinder (shape X with phloem (sieve-tube members and companion cells) in spaces of X).
- monocot: groups of xylem and phloem alternate in a ring with the pith in the middle.
Primary Structure of Stems
-Lack endodermis, Casparian strips (not need for water absorption)
- Epidermis: contain epidermal cells covered with waxy (fatty-cutin) which forms protective layer called cuticle.
- Cortex: ground tissue types that lies between epidermis and vascular cylinder (many contain chloroplasts)
- Vascular cylinder: consists of xylem, phloem, and pith. Vascular cambium (dicot) is single layer of cells between xylem (inside) and phloem (outside) may remain undifferentiated and later become vascular cambium.
Secondary Structure of Stems and Roots
Vascular cambium: becomes cylinder of tissue that extends the length of stem and root . Secondary growth in a stem (cambium layer is meristematic, producing new cells on both inside and outside the cambium cylinder).
- Cells on the inside differentiate into 2nd xylem, and those on the outside into 2nd phloem. Over years, 2nd xylem accumulate and increase girth of stem and root.
- Outside of cambium layer, new 2nd phloem are added yearly and pushes tissue outward. These tissues include primary tissue (epidermis and cortex) break apart and shed.
- In order to replace shed cells, cork cambium produces new cells on the outside (cork cells-impregnated with suberin). On the inside, phelloderm may be produced. Together, they are called Periderm. In dicots, cork cambium originates from cortex and in root, it originates from pericycle
Secondary Structure of Stems and Roots: Wood
wood: formed from xylem tissues at maturity (dead), only the recent ones remain active to transport water (sapwood). Older xylem located at center (heartwood) functions only as support.
annual rings: alternation of growth (active vascular cambium divides) and dormancy due to season in secondary xylem tissue. Size of ring => rainfall history. Number of rings => age of tree
Structure of Leaf (out of 5):
- Epidermis
protective, covered with cuticle (protective layer containing cutin-waxy) which reduces transpiration (water loss through evaporation); may bear trichomes (hair, scales, glands).
Structure of Leaf (out of 5):
- Palisade Mesophyll
consists of parenchyma cells with chloroplasts and large surface area (specialized for photosynthesis). Orient at upper surface, but for dry habitat => both surfaces. (leaf photosynthetic occurs here primarily)
Structure of the Leaf (out of 5)
- Spongy mesophyll
parenchyma cells loosely arranged below palisade mesophyll. Numberous intercellular spaces (air chambers-CO2 to photosynthesizing cells and O2 to respiring cells)
Structure of Leaf (out of 5)
- Guard cells
specialized epidermal cells control opening and closing of stomata (allow gas exchange)
Structure of Leaf (out of 5)
- Vascular Bundles
consist of xylem (water for photosynthesis) and phloem (transports sugar and by-product to other parts of plants from photosynthesis). Bundle sheath cell surrouds vascular bundle => no vascular tissue exposed to intercellular space => no air bubbles that can enter to impede movement of water; also provide anaerobic environment for CO2 fixation in C4 plant
How does water enter the root?
through root hairs by osmosis. There are 2 pathways:
a. Apoplast (nonliving portion of cells) water moves through cell walls and intercellular spaces from 1 to another w/o ever entering cells
b. Water moves through cytoplasm of one cells to another (symplast-living portion) through plasmodesmata (small tubes that connect cytoplasm of adj. cells
Once water reaches endodermis, it can only enter by symplast (due to Casparian strips) into (stele-outer most layer is the endodermis) vascular cylinder and is selective permeable (K+ pass, Na+ blocked only common in soil). Once through endodermis, apoplast pathway takes over to reach xylem.
What are the 3 mechanisms involved in the movement of water and dissolved minerals in plants?
- Osmosis moves from soil through root and into xylem by gradient (continuous movement of water out of root by xylem, and high [mineral] inside stele). This osmotic force (root pressure) can be seen as guttation, formation of small droplets of sap (water and minerals) on ends of leaves in morning.
- Capillary action rise of liquids in narrow tubes, contribute to movement of H2O up xylem; results from forces of adhesion (molecular attraction between unlike substances) between H2O and tube => meniscus is formed at top of water column. No meniscus in active xylem.
- Cohesion-tension theory most water movement is explained by this; major contributor (aove two minimal)
a. transpiration: evaporation of water from plants, removes water from leaves => causing negative pressure (tension) to develop within leaves and xylem.
b. cohesion: attraction between like substances (water); within xylem cells behave as single, polymerlike molecule.
c. bulk flow: when a water molecule is lost from a leaf by transpiration, it pulls up behind an entire column of water molecules (generated by transpiration, which is itself caused by heat action of the sun)
Control of Stomata
- When stomata are closed => CO2 not available => cannot photosynthesize
- When stomata are open => CO2 can enter leaf => photosynthesize but plant risks desiccation from transpiration
guard cells
two surrounds the stomata. Cell walls of guard cells do not have the same thickness (thicker when border the stomata). Guard cell expand when water diffuses in. Due to the irregular thickness and radical shape, the sides with thinner cell walls => expand => creates opening (stoma). Water diffuses out =>kidney shape collapses and stoma close.
factors involved in mechanism of opening and closing
- High temp => Close
- Low [CO2] inside => Open => photosynthesis
- Close at night, Open during day. CO2 is low during daylight because used by photosynthesis. CO2 levels are high at night because of respiration.
- Stomata opening (diffusion of K+ into guard cell => create gradient => more water moves in)
- K+ enter => unbalanced charge state. Cl- can come in or H+ gets pumped out.
translocation
movement of carbohydrate through phloem from source (leaves) to sink (site of carb utilization); described by the pressure-flow hypothesis
pressure-flow hypothesis
- Sugars enter sieve-tube members: soluble, move from site of production (palisade mesophyll) to phloem sieve-tube members by active transport => high [solue] at source than at sink [root].
- Water enters sieve-tube members: water diffuses into source by osmosis
- Pressure in sieve-tube members at source moves water and sugars to sieve-tube members at sink through sieve tubes: when water enter, rigid cell walls do not expand => pressure build up. Water and sugar move by bulk flow through sieve tubes (through plates between sieve-tube members).
- Pressure is reduced in sieve-tube members at sink as sugar are removed for utilization by nearby cells: pressure begins to build up at sink (from bulk flow source => sink). However, sink is where sugar are used =>removed from sieve-tube members by active transport => increases [water] at sink => water diffuses out of cell => relieve pressure.
Cells store energy as insoluble starch- benefit of this = any cell can act as a SINK and get the sugar and water transported there
- likewise, by breaking down starch, any cell can act as a source
Plant Hormones: Auxin (IAA-indoleacetic acid
promotes plant growth (elongation of cells) increase [H+] in primary cell walls => activate enzymes loosen cellulose fiber (increase cell wall plasticity) and turgor pressure expands cells to grow.
- Produced at tips of roots and shoots ( apical meristem) (inhibition of lateral buds when it is produced at terminal bud of growing tip).
- It is a modified tryptophan aa.
- After synthesis it is actively transported (ATP) from cell to cell in a specific direction (polar transport) by means of chemiosmotic process.
Plant Hormones: Gibberellins (GA)
promote cell growth (flower and stem elongation), inhibition of aging in leaves, promote fruit development and seed germination. High [] causes bolting (rapid elongation of stems)
Plant Hormones: Cytokinins
stimulate cytokinesis, stimulate (and influence direction of) organogenesis;
- stimulate growth of lateral buds (which weakens apical dominance- dominance growth of apical meristem);
- delay senescence (aging) of leaves. Structurally they are variations of the nitrogen base adenine; include naturally occurring zeratin and artificially produced kinetin
Plant hormones: Ethylene (H2C=CH2)
ripening of fruit; production of flowers; influences leaf abscission (aging [senescence] and dropping of leaves). Together w/ auxin, can inhibit elongation of roots, stems, and leaves. Stimulates ripening by enzymatic breakdown of cell walls.
Plant hormones: Abscisic acid (ABA)
growth inhibitor, in buds delays growth and forms scales (in prep for overwintering), maintains dormancy. Dormancy can be broken by increase in gibberellins or mechanistic response to environmental cues (temp, light)
Plant responses: Tropism
growth pattern in response to an environmental stimulus (due to plants not being able to move)
Plant Responses: Phototropism
response to light (acheived by hormone auxin). Auxin is produced in the apical meristem => move downward by active transport into zone of elongation => generate growth
- stem grows straight when all sides of apical meristem are equally illuminated.
- when not equally illuminated, auxin moves more towards shady side (grow more) => stem bends toward light
Plant hormones: Gravitropism (geotropism)
response to gravity by stems and roots (auxin and gibberellins)
- If stem is horizontal, auxin concentrates on lower side => stem bends upward.
- If root is horizontal, auxin is produced at apical meristem (growing tip) moves up in root and concentrates on lower side, however, auxin inhibits growth in roots due to higher [auxin] at root than stems.
Dissolved ions, auxins, gibberellins, and other hormones do not directly respond to gravity. BUT starch is insoluble in water and does respond to gravity. It’s believed specialized starch-storing plasmids called statoliths, which settle at the lower ends of cells somehow influence the direction of auxin movement
Plant Responses: Thigmotropism
response to touch (e.g. vines on surface)
Photoperiodism
response of plants to changes in photoperiod (relative length of daylight and night); plants maintain circadian rhythm (a clock that measure length of daylight and night); endogenous mechanism (internal clock that continues to keep time even if external cues are absent). External cues (dawn, dusk) reset clock for accuracy
phytochrome
protein modified with light-absorbing chromophore. Two forms: Pr (P660-red) and Pfr (P730-far red). They are reversible. When Pr is exposed to red light => Pfr and vice versa
Photoperiodism observations
- Pfr appears to reset circadian-rhythm clock: Pfr is active form of phytochrome.
- Pr is the form of phytochrome synthesized in plant cells: Pr is made in leaves
- Pr and Pfr are in equilibrium during daylight: red light is present as sunlight Pr => Pfr and far red is also present (Pfr => Pr)
- Pr accumulates at night: cells make Pr at night, no sunlight to convert Pr => Pfr; Pfr is converted back to Pr
- At daybreak, light rapidly converts acccumulated Pr to Pfr: equlibrium is maintained.
- Night length is responsible for resetting clock: flashes of red and far-red reset. Only the last flash affects the night length. Red => shorter night length. Far red => restores night length.
Florigen
when flowering is intiated, this flowering hormone is produced in leaves and travels to shoot tips
flowering plants
initiate flowering in response to changes in photoperiod
- Long-day: plants flower in spring and early summer when daylight is increasing
- Short-day: late summer and early fall when daylight is decreasing
- Day-neutral: do not flower in response to daylight changes but temp. or water
C3 vs. CAM
C3: CO2 levels are relatively low in leaves when photosynthesis is active during the DAY, when stomata are OPEN. At night stomata close and CO2 levels increase
CAM: stomata closed during day but photosynthesis proceeds because CO2 supplied by metabolic conversion of malic acid
