Plants

Transport in plants

• Vascular vessels-– Xylem – water & minerals up to leaves– Phloem – water & food – up & down to parts of

plant (products of photosynthesis)

– http://www.youtube.com/watch?v=w6f2BiFiXiM

• Roots – absorb water & minerals• Mycorrhizae – fungi that live in roots– greatly increase surface area– Increases absorption of water & minerals

• http://www.youtube.com/watch?v=bq1bTduTzC0

• Transpiration • Adhesion• Cohesion• Tension

3. Evaporation of water continue, increased rate of transpiration, so water is pulled from surrounding cells

2. As evaporation occurs, air-water interface becomes more curvedIncreases rate of transpiration

1. Water is lost by transpiration,Evaporation of water film replaces it

• Stomata – CO2 enters, H2O exits

• Guard cells balance need for CO2 with need to conserve water

• Stomatal density varies among species• High light exposure & low CO2 lead to

increased stomatal density

• What features account for the evolutionary success of angiosperms?

• Why are the flowering plants so successful in terms of their ecological dominance and in terms of their great number of species (diversity)?

Seeds

• primary means of reproduction and dispersal; an adaptation shared with gymnosperms

Flowers• the flower

attracts insects, birds, and bats

• has dramatically increased the diversity of flowering plants to specificity of pollinators

• Co-evolution (mutual adaptation) with insects• Uses only a relatively small amount of pollen

compared due

hoverfly• http://www.youtube.com/watch?v=MQlq5Qt

RI9o

Closed carpels

• allow seeds to develop enclosed within a fruit

• protects seeds from drying out as they grow and mature

• aids in the dispersal of seeds

Double fertilization

• results in the production of endosperm, a nutritive tissue that feeds the developing embryo.

Vascular system

• very efficient water conducting cells, called vessel elements, in their xylem, in addition to tracheids

Leaves • Broad, expanded blades are structured for maximum

efficiency in photosynthesis. • Shedding of these leaves during cold or dry spells

reduces water loss– Allows some flowering plants to expand into habitats that

would otherwise be too harsh for survival.

Plant responses• Signal transduction pathways:

• Reception Transduction Response

• hormone or stimulus interacts with receptor molecule

• Relay molecules & secondary messengers

• Cell responds (i.e. turning genes on or off)

Plant responses

• Phytochrome – found in cytoplasm• - photoreceptor - • http://glencoe.mcgraw-hill.com/sites/983409

2339/student_view0/chapter41/animation_-_phytochrome_signaling.html

“Greening”

Etiolation – adaptation for growing in dark

De-etiolation- response to light

Phytochrome – plant pigment

2 subunits – each with polypeptide bound to chromophore

Phytochrome – plant pigment

Chromophore is reversible – from Pr to Pfr Exposure to sunlight shifts Pr to Pfr

Plant hormones

• Hormone – a signaling molecule produced in very small amounts that binds to specific receptors & triggers responses in target cells

Phototropism

• http://www.youtube.com/watch?v=zctM_TWg5Ik

Growth of a plant towards or away from light

Differential growth – due to auxin

Auxin Plant hormone – 1st one discovered

Molecule is Indolacetic acid (IAA)

• Circadian rhythms – an internal clock– Physiological 24 hr cycle– Rhythms continue even under set conditions

– The 24 hr clock is set by environmental cues, such as light

– Phytochromes – – When exposed to sunlight, Pr shift to Pfr– The sudden increase of Pfr at dawn sets the

biological clock

Plant survival depends on timing

• Flowers bloom when pollinators are present• Seed germination needs to occur in right

season

• How do plants know when seasons occur?• Environmental cue – photoperiod, changing of

relative lengths of day & night

Photoperiodism

• Response of plant to photoperiods• - i.e. flowering of plants in response to 24 hour cycle

• Photoperiod is the length of day vs. the length of night

• Critical night length- amount of darkness needed for plant to produce flowers (photoperiod responses controlled by night length, not day length) – must be continuous darkness

Short day (long night) plants- flowers when when night is longer than critical dark period

Long day (short night) plants – flower when night is shorter than critical dark period

* originally the day hours were thought to determine flowering (vs. night), but it is the length of night that is critical

Can disrupt with a flash of red light, can reset with a flash of far red light.