Plant Adaptations

Question 1

shoot growth

Answer 1

• apical meristems (populations of totipotent cells at the tip of each stem and branch) is where growth is initiated
• meristem cells divide and are found in auxiliary buds (remain dormant until triggered to grow) near shoot tips
• cells below meristems do not divide, they elongate
• leaf primordia are umps on the meristems that become leaves (branching)

Question 2

photoreceptors

Answer 2

sense availability of light

Question 3

mechanical receptors

Answer 3

sense physical influences such as gravity and wind

Question 4

chemical receptors

Answer 4

detect the presence of chemicals and chemical gradients

Question 5

receptors…

Answer 5

change metabolism or gene expression

Question 6

tropism

Answer 6

bending or turning of an organism in response to an external signal

Question 7

phototropism

Answer 7

bending in response to light - auxins accumulate in the shaded side so it grows faster and bends

• positive phototropism: stems towards light
• negative: roots move away from light - auxin produces ethylene which reduces elongation - bends away

Question 8

gravitropism

Answer 8

bending in response to gravity - starch sinks to the bottom of cells, presses on cytoskeleton and membranes producing auxin - bent up in leaves and down in roots
positive - roots grow down with gravity
negative - stems up, against gravity

Question 9

statolith

Answer 9

starch-filled organelles in root caps that sense gravity. - heavy statocyst in animals

Question 10

sees can delay germination if they detect plants overhead

Answer 10

leaves absorb red wavelength but not far red light - passes to seeds below. red light triggers germination, far red light inhibits it

Question 11

phytochrome

Answer 11

a photoreceptors for red and far red light that switches back and forth between two stable forms, active and inactive, depending on light

• red = Pfr = active and seeds germinate
• far red = Pfr becomes Pr = inactive form (activated again by red light)
• Pfr converts to Pr slowly in the dark

Question 12

plants grow taller and branch less when in the shade of other plants

Answer 12

seeds that germinate in the dark produce white seedlings with elongated internodes and small leaves - resources into getting tall and reaching light

• in light, intermodal elongation slows and leaves expand
• plants above absorb red light and only far red light goes to seed

Question 13

roots elongate more and branch less when water is scarce

Answer 13

• root cap senses water
• in dry soil, root cap cells produce abscisic acid - roots elongate, stomata close and seeds remain dormant
• abscisic acid surpasses ethylene synthesis (slows root elongation, influences orientation of cellulose in cell wall)

Question 14

exposure to wind results in shorter and stronger stems

Answer 14

tough sensitive genes activated by mechanical perturbation

- produce more ethylene when moved - expand in diameter; shorter, thicker

Question 15

timing of developmental events

Answer 15

important to respond to seasons and temperature is unreliable. day length is used

Question 16

photoperiodism

Answer 16

the effect of photoperiod or daylight on flowering

Question 17

short day plant

Answer 17

a plant that flowers only when the day is shorter than a critical value (late summer)

Question 18

long day plants

Answer 18

opposite, so midsummer

Question 19

day-neutral plants

Answer 19

independent of day length
- allows for plants to flower only when they have resources to support seeds and for seeds to have enough time to mature before winter

Question 20

circadian clock and photoreceptors

Answer 20

• circadian clocks let the plant know how long it has been since the sun came up (affects transcription)
• phytochrome detects dark and light

Question 21

plasmodesmata

Answer 21

connection between the plasma membranes of adjacent plant cells that permit molecules to pass directly from the cytoplasm of one cell to that of another - chemical signals and pathogens are also moved

Question 22

xylem

Answer 22

vascular tissue consisting of lignified conduits that that transport nutrients and water from the roots to the leaves

• parisites in xylem get access to water and nutrients
• evaporation from leaves, draws water from the soil
• hydrogen bonds pull water

Question 23

phloem

Answer 23

the vascular tissue that transports carbohydrates from leaves (source) to the rest of the plant (sink)

Question 24

pathogens

Answer 24

viruses, bacteria, fungi, nematode words and other plants

• fungi spread by growing through cell walls - move (like bacteria) in xylem
• viruses move through plasmodesmata and phloem

Question 25

first line of defence

Answer 25

epidermis (thick walls with waxy cuticle) is the first line of defence

• pathogens enter through wounds or by piercing walls (nematodes)
• enter through stomata
• enzymes weaken walls

Question 26

biotropic pathogen

Answer 26

obtains resources from living cells - viruses, bacteria and fungi

Question 27

necrotropic pathogen

Answer 27

kills cells before drawing resources from them - bacteria and fungi

Question 28

parasitic plants

Answer 28

infect other plants through vascular system to get resources

Question 29

host plants

Answer 29

infected by a pathogen - not always damaged much

Question 30

virulent

Answer 30

a pathogen that overcame defences and lead to disease

Question 31

avirulent

Answer 31

pathogens only damage a small part - can contain disease

Question 32

immune system

Answer 32

protein receptors bind to pathogenic molecules and recognise them - cascade leads to response

Question 33

basal resistance

Answer 33

receptor proteins in plants plasma membrane binds to pathogen molecules
defense response is triggered

Question 34

specific resistance

Answer 34

deal with pathogens that survive basal resistance

• pathogens secrete AVR proteins that enter plant cells and might block defence
• R proteins (resistance receptors) are specific to each AVR
• absence of specific R - AVR blocks basal
• binding prevents AVR from blocking and activates defence system
• race to evolve AVR and R - which is faster?

Question 35

hypersensitive response

Answer 35

uninfected cells surrounding infection produce large numbers of reactive oxygen species, triggering cell wall reinforcement and causing cells to die, creating a barrier
prevents spread of biotropic pathogens

Question 36

other ways to block pathogens

Answer 36

plug xylem

Question 37

mechanical and chemical defence against herbivores

Answer 37

hairs, latex (white sticky light that glues mouth parts and is toxic), chemical irritants, silica plates in epidermal cells wear mouthparts, prickles, spines

Question 38

chemical compounds

Answer 38

• cardenolides
• alkaloids - nitrogen bearing compounds that damage NS and are bitter (caffeine)
• terpene - defence compounds that do not contain nitrogen (for proteins), volatile and vaporising (oils), deter herbivores and obstruct growth and metabolism of fungi and insects
• phenols - tannins (bind to proteins and reduce digestibility, don’t taste good)
• non-protein amino acids cause insects to grow slowly and die
• protease inhibitor - antidigestive protein that binds to enzymes in the herbivore’s digestive system

Question 39

grasses regrow quickly

Answer 39

apical meristem close to the ground to avoid damage and can grow leaves when bitten

Question 40

allocating resources for defence

Answer 40

to preserve resources, some defences can be turned on when needed (inducible)
recognise the pathogen and respond only when present
produce volatile signals that attract insects to prey upon herbivores
nutrient rich environments select for plants that allocate resources to growth than defence - can afford to replace and heal if damaged (trade off)