Plants

desiccation

desiccation

excess water loss

transpiration

evaporative loss of water from leaves

guard cells

modify water volume through alteration of potassium and chloride ions to swell or shrink

CAM photosynthesis

temporal pathway to limit transpiration where stomata are only open at night

PEP carboxylase

catalyzes addition of bicarbonate (HCO3-) to phosphoenolpyruvate (PEP) forming a 4-carbon acid

photorespiration

O2 acts as the substrate for rubisco instead of CO2

C4 photosynthesis

mechanical pathway to limit photorespiration where the Calvin cycle takes place in bundle sheath cells

epiphyte

plant that grows on another plant and does not touch the soil, not a parasite

parenchyma

thin walled cells that carry out a variety of functions

capable of further cell division

xylem

transports water from root to shoot

contains lignin

no nucleus, organelles, or cytoplasm

phloem

transports carbohydrates from source to sink

sclerenchyma

secondary cell wall which provides mechanical support

typically dead cells

pits

in xylem, allow water to pass

tracheids

unicellular conduits that are small and thin

vessels

multicellular conduits that are long and wide

tensile force

molecules pull on each other

creates negative pressure

negative pressure

created by water molecules being pulled upwards as transpiration occurs

due to tensile force

cavitation

water in xylem conduit is replaced by air

herbivory

consumption of plant tissue

root hairs

outgrowth near root tip which increases a roots surface area

cation exchange capacity

soil particles are negative, minerals are positive

plants release hydronium to bond with the soil, increases the free minerals

cortex

parenchyma cells between epidermis and vascular bundle

endodermis

surrounds vascular bundle and controls movement of nutrients into the xylem

casparian strip

hydrophobic band that encircles each endodermal cell, forcing ions and water to pass through the cell membrane before entering the xylem

rhizosphere

soil that surrounds actively growing roots

mycorrhizae

fungi that form a symbiosis with roots

roots receive phosphorus and nitrogen

fungi receive carbohydrates

endomycorrhizae

fungi is within the root

increases phosphorus uptake

ectomycorrhizae

fungi that surrounds the root tip

provides nitrogen

rhizobia

bacteria that live within the roots forming a node and fix nitrogen for the host plant

sporangium

capsule on top of sporophyte that contains thousands of diploid cells undergoing meiosis to form haploid spores

sporopollenin

protects spores from UV radiation and desiccation as they move through the air

pollen tube

male gametophyte grows through an opening in the sporangium in order to reach the female gametophyte

seed coat

protective tissue that surrounds sporangium

made from parental diploid sporophyte

seed embryo

fusion of gametes from parents forming a zygote, will become the next sporophyte generation

dormancy

delayed germination while waiting for more favourable conditions

stigma

top of carpel where pollen lands

style

stalk between ovary and stigma, where pollen tube grows

carpels

ovule producing organ

stamen

pollen producing organ

anther

top of stamen

several sporangia producing pollen

filament

supports anther

nectar spurs

modified petals that form tubular overgrowth that store nectar

self compatibility

plant can produce viable offspring using its own eggs and pollen

self incompatibility

pollination between the same or closely related plants will not lead to fertilization

S gene

codes for proteins that enable self recognition

double fertilization

zygote (fusion of two haploid nuclei) and endosperm (triploid) are formed from two different sperm from the same pollen tube

apomixis

developing seeds in the absence of fertilization (asexual)

vegetative reproduction

horizontal stems allow for growth and fragmentation (asexual)

node

where leaves are attached

internode

segment between two nodes

apical meristem

group of totipotent cells at the tip that give rise to new tissue

totipotent

can give rise to any time of mature cell and become a full organism

meristem identity gene

expressed near tip so cells maintain ability to divide

elongation zone

cells underneath the apical meristem that no longer express meristem identity gene, but they grow in length

axillary buds

junction between leaf and stem or branch and stem

primordia

beginning of a leaf forms from the shoot apical meristem

bud scale

small modified leaves that protect the shoot apical meristem from desiccation and the cold

procambial cells

give rise to xylem and phloem

retain the capacity for cell division

florigen

protein that triggers flower development

turns shoot apical meristems into floral meristems

auxin

shoot elongation

determines where leaves grow

connects leaves to xylem and phloem

affects directionality of growth

polar transport

auxin is uncharged in the cell wall and negatively charged in the cytoplasm

auxin can only exit the cell though PIN proteins which are only located on the basal end of the cell

gibberellic acid

controls internode elongation

mobilizes seed resources for embryo

cytokinins

stimulate cell division

found at meristems

stimulates root growth

suppresses growth in shoot by auxin and strigolactone

apical dominance

suppression of growth of axillary buds by shoot apical meristem

ethylene

triggers fruit ripening

abscission

detachment of plant parts

senescence

loss of ability to divide and grow

deterioration with age

primary growth

growth in apical meristem resulting in new leaves and increased length

secondary growth

growth in lateral meristems resulting in a larger diameter

lateral meristems

form along length after elongation is complete

source of new cells that allows for growth in diameter

vascular cambium

grow secondary xylem and phloem

derived from procambial cells between bundles

cork cambium

renews and maintains outer layer that protects the stem

formed from regressed cortex cells

sapwood

active xylem that become non-functional after several years

heartwood

inactive xylem used for mechanical support

sapwood renewal

continuous growth of rings while broadening the base as trees grow taller

bark

actively dividing cells that become distant from phloem

suberin

waxy layer formed on non living cells by the cork which impedes the diffusion of oxygen

lenticels

regions of loosely packed cells in the cork that allows for oxygen diffusion into the stem

fibers

narrow cells with thick walls and no lumen that provide support to the vessel elements

root cap

protects root apical meristems

rubbed off as roots elongation

pericycle

single layer of cells inside the endodermis which develop into new root meristems

adventitious roots

formed from non-root tissue in normal development or in response to stress

pneumatophores

breathing roots

tropism

bending/turning of an organism in response to external signals

phototropism

movement in response to light

towards light in shoot tip

away from light in root tip

heliotropism

movement in response to the sun

gravitropism

movement in response to gravity

hydrotropism

movement in response to water

chemotropism

movement in response to chemicals

thigmotropism

movement in response to touch/contact

contact promotes cells to expand

statolith

starch filled organelle in the root cap that senses gravity

phytochrome

photoreceptor that changes states depending on type of red wave lengths present

phytochrome far-red (Pfr)

triggered by red light, leads to germination

phytochrome red (Pr)

triggered by excessive far-red in comparison to red wavelengths, stalls seed germination

abscisic acid (ABA)

triggers stomata to close

stimulates root elongation

maintains seed dormancy

photoperiodism

effect of day length on flowering

short day plants

flower when day is less than critical value

flower in autumn

long day plants

flower when day light is more than critical value

flower in the spring

day neutral plants

flowering is independent of change in day length

vernalization

prolong exposure to the cold