Ch. 12: Plants Flashcards
Four major organs of plants
roots, stems, leaves, flowers
Roots
anchor the plant to ground, store food, absorb water and minerals and transport these materials to other areas of the plant
increase water-absorbing capacity by: root hairs, micorrhizae
Root hairs
extensions of epidermal cells into ground that greatly increase absorbing surface area of roots
Mycorrihizae
fungi that have mutualistic relationship w/ plants
fungal filaments absorb water and nutrients so increase absorbing surface area of plant
in exchange, plants give fungi sugar
Stems
support aboveground parts of plant and serve to transport water, minerals, and sugars between those parts and the roots
many have thorns/ spines to protect from eating
Leaves, Palisades mesophyll, Spongy mesophyll, Stomata
sites for photosynthesis
photosynthesis = palisades mesophyll (chloroplasts) which is at surface bc sun
spongy mesophyll: borders palisades w/ loosely arranged cells w/ many open spaces
stomata = transpiration
Cuticle
wax covering that reduces transpiration
plants that grow in hot/ dry habitats have thicker cuticles
Guard cells (definition)
specialized leaf cells that control closing/ opening of stomata
open to allow gas exchange but close when excessive transpiration from high temp./ low humidity threatens water loss
Stomata
openings in the leaves that lead to air spaces which allow for gas exchange like taking in CO2 and releasing O2
at same time stomata permit loss of water through transpiration
Trichomes
plant hairs that can:
- reduce transpiration by interfering w/ wind movement/ solar reflection
- reduce browsing by predators
- discourage egg laying by insects
- some secrete toxins
Flowers
reproductive organs of plant where gametes (egg and pollen) are produced
pollination occurs when wind/ insects transfer pollen between flowers which then causes fertilization (pollen = egg) to make seeds
How does plant balance needs of photosynthesis with costs of transpiration?
cuticle, guard cells, sunken stomata, trichomes
Sunken stomata
stomata that occur in depressions below surrounding surface of leaf which reduce rate of transpiration caused by wind over leaf’s surface
Photosynthesis gas exchange
CO2 in –> O2 out
Respiration gas exchange
use O2 –> release CO2 and generate ATP from glucose produced in photosynthesis
Gas exchange between plant and external environment (4)
- Stomata allow CO2 to diffuse into leaf: 2 guard cells surround each stomata that open when conditions are suitable (not too hot/ dry) to let CO2 in
- CO2 diffuses into water lining the leaf: CO2 enters spaces in spongy mesophyll then once in water lining diffuses into cells
- CO2 enters photosynthesizing cells: palisades mesophyll, top of leaf to maximize surface exposure to light
- O2 diffuses into roots from gaseous spaces in soil: roots carry out respiration to break down the glucose made
Aquatic plants stomata
little risk of water loss from transpiration so stomata usually remain open
Water movement control in plants (4)
- Electrical gradient is est.: opening of stomata initiated by active pumping of H+ out of guard cells by proton pumps (activated by sunlight) which est. electrical gradient across membrane
- Osmotic gradient is est.: electrical gradient drives uptake of K+ ions into guard cells, Cl- follows bc balance. ions create solute gradient to drive osmosis
- Water enters guard cells and stomata open: osmotic gradient so water enters cells, guard cells expand and stomata open
- Water exits guard cells and stomata close: K+, Cl- and sugars decrease, influences by ABA hormone
Guard cells (method)
opening/ closing of stomata controlled by movement of water in and out of guard cells
each stoma gets two guard cells, which have thick cell wall at area that borders stoma
when water diffuses into guard cell, guard cell expands
bc of nonuniform and radially constructed cell wall, expansion is distorted so most of expansion bulges out of thinner wall away from stoma so two kidney shaped guard cells formed and open stoma between them
when water diffuses out, stoma close
Xylem
vascular tissue in plant that transports water and minerals and also provides mechanical support
cells are basically dead and contain just cell wall (they have 2!) and the material being transported (dedication) which passes by through openings in these cell walls
Phloem
vascular tissue in plants that transports sugars from photosynthesis
cells alive unlike xylem and form fluid-conducting columns whose pores allow movement of organic materials
Cohesion-tension theory
explains water movement through xylem
TACT: transpiration, adhesion, cohesion, tension
Transpiration (TACT
evaporation of water from plants, removes water from leaves
Adhesion (TACT)
adhesion is molecular attraction between unlike substances
water adheres to walls of xylem and defies downward pull of gravity
water is polar covalent so it forms H bonds w/ polar walls of xylem
Cohesion (TACT)
cohesion is attraction between like substances
water is polar covalent so forms H bonds w neighboring water molecules so they bunch up to behave like a single, polymer-like column from roots to leaves
Tension (TACT)
negative water pressure, develops as water transpires from leaf
water molecules leave surface of leaf cells and new molecules pulled in to replace them bc are adhered to the transpiring water molecules and cohered w/ cell walls of xylem
bc transpiration is caused by heating of sun, the sun is driving force for climb of water and dissolved minerals through plant
Plasmolysis
contraction of cell away from cell wall as result of not enough supplies/ water and reduction in cell turgor
basically it shrivels
Cell turgor
cell rigidity in plant cells which give plant cells structure
they want to be kind of overfilled so they can be rigid and keep their shape
Ethylene (fruit ripening)
gas that promotes ripening of fruit
ethylene gas fills intercellular air spaces within fruits and stimulates ripening by enzymatic breakdown of cell walls
positive feedback mechanism: as fruit ripens, more and more ethylene is produces and keeps accelerating
Phototropism
plant leaning towards light, bc of hormone auxin
auxin made in apical meristem then moves down shoot, concentrating on shady side of plant; when plant is equally illuminated it grows straight up; when not equally illuminated, auxin goes to dark side and stimulates growth there so shady side grows more than light side and stem bends towards light
Apical meristem
tip of shoot of plant where cell division and growth occurs
where auxin is produced
Gravitropism
response to gravity by stems and roots
Amyloplasts
specialized, starch-containing cell organelles that sink to the bottom of cells in response to gravity and may be associated w/ the detection of a gravitational field
Gravitropism
response to gravity by stems and roots by ways of amyloplast sinking and auxin action
kinda confusing also scientists don’t get it either
Thigmotropism
plant response to touch
when vines/ climbing plants come in contact w/ object they wrap around it
auxin probs in there somewhere but scientists don’t really get this one either
Dormancy
plant mechanism in response to unfavorable conditions
Ex. abscission, seed dormancy
Environmental stimuli that promote Seed Germination and Breaking of Dormancy
- water is needed for germination of seeds to activate cellular respiration
- oxygen needed for aerobic respiration
- temperature is stimulus bc some enzymes need specific temp. to activate (depends on plant environment)
- photoperiod may be required germination stimulus for some seeds
- scarification (damage to seed coat) to let water in
- gibberellins (!)
Gibberellins
class of plant hormones needed to activate germination during initial stages of germination, gibberellins are produced by embryo and bind to DNA to release transcription factors --> activate genes that produce enzymes needed for germination (like a-amylase to breakdown carbs)
Photoperiodism
response of plants to changes in photoperiod: relative length of daylight/ night
to respond to photoperiodism, plants maintain circadian rhythm controlled by external cues of dawn and dusk
Circadian rhythm in plants mechanism
- Pr is form of phytochrome made in plant cells in cytoplasm
- Pfr is active form of phytochrome
- Pfr accumulates during daylight: Pr – Pfr in red light
- Pr accumulates at night: no sunlight so Pfr breaks down faster than Pr
- At daybreak, light rapidly converts accumulated Pr to Pfr
- Night length is responsible for resetting circadian rhythm clock
(red light shortens night length and far-red light restores night length)
3 groups of flowering plants
- Long-day: flower in spring and early summer when daylight is increasing; flower when light exceeds critical length
- Short-day: flower in late summer and early fall when daylight is decreasing; flower when daylight is less than critical length
- Day-neutral: do not flower in response to daylight changes; some other cue like temp./ water triggers flowering
Florigen
produced in plant leaves and then transported to apical meristem where it initiates flower development
Structural defenses (plants)
- leaves have sharp edges (thorns/ spines) to prevent from being eaten
- irritating trichomes discourage herbivory, some release toxins
- physical barriers like thick tree bark
Chemical defenses (plants)
toxins produced to discourage browsing by other organisms
Ex. nicotine in tobacco/ capsicum in hot peppers toxic to insects after they’ve been eaten so jokes on the bug who tries do some munchin
Phytocrhome
light absorbing protein in plants
Pr and Pfr –> two forms are photo-reversible so Pr – Pfr in red light and Pfr – Pr in far red light
Induced response (plant)
plant produces chemical not usually present in response to wound, like production of volatile substance by one plant to warn another plant that herbivores are near
Hypersensitive response (HR) (plants)
plant recognizes invading pathogen (virus, bacteria, fungi) and initiates death of plant cells at and around invasion site; dead tissue blocks pathogens from spreading
to do this plant needs resistance (R) gene whose product binds to protein of pathogen and initiates death of cells
w/ out R genes the plant gets sick
