Plants Flashcards
1
Q
plants
A
- multicelled, eukaryotic, photosynthetic autotrophs
- cell walls made of cellulose and surplus carbohydrate stored as starch
- evolved from equatic green algae 500 myo
- gradually colonized land as they evolved adaptations to dry environment
- 300 000 species
- stabilize soil and provides home to other organisms
- release oxygen into atmosphere and absorb CO2
2
Q
how plants moved to land
A
- problems: supporting plant body and absorbing + conserving water
- cell walls of cellulose help maintain shape
- roots + root hairs absorb water + nutrients from soil
- transport tissue, xylem and phloem, move fluid great distances
- stomates open to exchange photosynthetic gases and close to minimize water loss
- waxy coating (cutin) prevents water loss from leaves
- some plants: gametes and zygotes form in protective jacket (gametangia) to prevent drying out
- sporopollenin, tough polymer, resistant to almost all environmental damage and protects plant, found in walls of spores and pollen
- seeds + pollen means of dispersing offspring
- xylem + phloem vessels enable plants to grow tall
- lignin embedded in xylem + other plant cells as support
3
Q
the leaf
A
- organized to +sugar production while -water loss
- epidermis overed by waxy cuticle of cutin to minimize water loss
- guard cells = modified epidermal cells w/ chloroplasts, is photosyntehtic, control opening of stomates
- inner part of leaf w/ palisade + spongy mesophyll cells whose function is photosynthetic
- cells in palisade layer packed tightly, spongy cells loosely packed for diffusion of gases into/out of cells
- vascular bundles or veins located in mesophyll and carry water and nutrients from soil to leaves + sugar from leaves to rest of plant
- specialized mesophyll cells (bundle sheath cells) surround veins and seperate them from rest of mesophyll
4
Q
stomates
A
- 90% of water escapes through stomates which cover 1% of leaf
- guard cells modified epithelium containing chloroplasts that control opening/close of stomates by changing shape
- cell walls of guard cells not uniformly thick
- cellulose microfibrils oriented radially so when guard cells absorb water by osmosis and become turgid, will curve and cause stomate to open, when guard cells lose water and become flaccid, stomate closes
5
Q
transport in plants
A
- selective permeability of plasma membranes control short-distance movement of substances into/out of cells
- both active + passive transport mechanism in plants
- plant cell membranes equipped with same type of pumps, channels, transport proteins that other cells have
6
Q
short-distance transport
A
- osmosis, diffusion of water across membrane
- direction of diffusion by water potential
- aquaporins (special transport proteins) faciliate rapid osmosis
- opening + closing of selective channels affect rate at which water flows and not direction
7
Q
long-distance transport
A
- bulk flow = movement of liquid from high pressure to low pressure in response to pressure gradient
- independent of solute concentration, carries material through xylem and phloem vessel
- phloem transports sugar by translocation, sugar moves from source (leaf) to sink (used/stored), proton pumps create electrochemical gradient that powers loading of sugar into sieve tubes of phloem, requires input of energy
- xylem fluid (water + minerals) rise in plant against gravity but requires no energy, pushed up by root pressure or pulled up by transpirational pull
- root pressure = water flowing into stele from soil from high mineral content in root cells, pushes sap upward a few meters (results in guttation)
- transpirational pull = evaporation of water from leaves causes negative pressure to develop in xylem tissue from roots to leaves, cohesion of water makes it possible to pull column of water from above within xylem
- absorbtion of sunlight drives transpiration by causing water to evaporate from leaf
- transpirational pull-cohesion tension theory: for each molecule of water that evaporates from leaf by transpiration, another molecule of water is drawn in at root to replace it
- rate of transpiration affected by humidity (high = slow, low = fast), wind (affects humidity), increased light intensity (increase amount of water vapor to be transpired and increase rate of transpiration), closing stomates (stops transpiration)
8
Q
hormones
plant responses to stimuli
A
- help coordinate growth, development, responses to environmental stimuli
- produced in small quantities but big effect on plant because hormone signal amplified
- signal transduction pathways amplify hormonal signal and connect to cell responses
- plant’s response to hormone depends not on absolute quantity but relative amount
- can work together or in opposition
9
Q
auxins
A
- unequal distribution responsible for phototropism
- enhance apical dominance, preferential growth of plant upward (toward sun)
- main ingredient in rooting power to develop roots quickly
10
Q
cytokinins
A
stimulate cytokinesis + cell division
11
Q
gibberellins
A
- promote stem + leak elongation
- induce “bolting” (rapid growth of floral staclk in which flower and fruit develop
12
Q
abscisic acid (ABA)
A
- inhibits growth + promotes seed dromancy
- enables plant to withstand drought
- closes stomates during times of water stress
13
Q
ethylene gas
A
- promotes ripening, triggering increased production of ethylene gas
- commercial producers pick fruit before ripe and spray with ethylene gas when fruit gets to market
14
Q
tropisms
A
- growth of plant toward or away from stimulus
- thigmotropisms (touch), geotropisms or gravitropisms (gravity), phototropisms (light)
- growth of plant towards stimulus = positive tropism, growth away = negative tropism
- phototropisms from unequal distribution of auxins which acculumate on side of plant away from light, causes shady side of plant to enlarge and stem bends toward light
- geotropisms from interaction of auxins and statoliths, specialized plastids containing dense starch grains
