BIOS 7 Angiosperm Adaptations

Auxin

Group of plant hormones. role in plant development.

Apical meristems

shoot tips. where auxin is produced

Phototropism

auxin moves away from light causing shaded side to elongate towards light.

gravitropism

auxin accumulates on lower side.

• shoots promote elongation upwards.

• roots inhibit elongation → downwards

thigmotropism

auxin accumulates away from touch. untouched side elongates to bend around the object

hydrotropism

auxin accumulates to side of root farther from water causing elongation

statoliths

dense, starch filled organelles in statocytes. settle to lower side of cell due to gravity - allows plant to detect orientation

xylem

dead phloem tissue

transports water and minerals upwards

innermost (shoots)

phloem

living tissue

transports nutrients and water unidirectionally

outermost (shoots)

xylem water mechanics

transpiration pull

capillary action

xylem structure

contain lignified walls, allows plant to maintain structure

xylem transportation

translocation

root structure

vascular bundles are in centre - resist forces that pull plant out

stem structure

vascular bundles near edge - resist compression and bending forces

transpiration stream

passive. water moves from areas of high water potential to lower potential.

leaf roles

photosynthesis. maximize light absorbtion, gas exchange and water regulation

Waxy Cuticle

on outer surface of leaves. prevents water loss

stomata

underside of leaves. allow for gas exchange (CO2, O2)

Palisade Mesophyll

contains main chloroplasts. main sight for light absorbtion

Spongy mseophyll

contains air spaces. facilitate gas diffusion

vein

made up of vascular tissues to transport substances

bundle sheath cells

surrounds veins in leaf. regulates movement of substances.

guard cell regulation

takes in gas → stomata opens
lose water → stomata closes

water ______ into the air spaces in ____ mesophyll and _____ through the stomata

evaporates, spongy, diffuses

Spines

modified leaves.

defensive structures, reduce water loss

tendrils

in plants with weak stems. climb nearby sticks or walls for support

cladodes

stems where photosynthesis occurs. in desert plants

fire adaptations

• seed closed until exposure to heat

• insulating bark protects living tissue

• epicormic buds beneath bark

possible reasons for red/purple leaf undersides

• increase internal temperature rates → photosynthesis

• improve light capture

• reduce damage from excess light

phyllodes

modified phtosynthetic structures - look like leaves but aren’t

zygote development

zygote → plant embryo → radicle, plumule, cotyledons

plumule

first shoot → stem and leaves

epicotyl

above cotyledons → true leaves and upper stem

hypocotyl

below cotyledons. connects radicle to cotyledons. pushes shoot above ground during germination

radicle

first root, grows donwards

cotyledons

seed leaves. stores food and helps with early synthesis

seed coat layers

testa, tegmen

testa

tough, outermost layer of seed coat. protection against physical damage and pathogens

tegmen

thinner, inside layer. protects seed and supports embryo

monocot seeds

• endospermic (nutrients)

• single cotyledon

• produce single shoot with no true leaves

eudicot seeds

• non-endospermic

• two cotyledons (nutrients)

• shoots with true leaves

seed dormancy

germination temporarily paused

seed dormancy advantages

• avoid unfavourable conditions

• increases dispersion area

dormancy hormones

abscisic acid, gibberellic acid

abscisic acid

promotes dormancy, prevents germination

gibberellic acid

stimulates enzymes to breakdown food reserves in seed. counteracts effects of abscisic acid.

seed dispersal options (WWAS)

wind, water, animal, self