Plants

Transport in plants

Vascular vessels- – Xylem – water & minerals up to leaves – Phloem – water & food – up & down to parts of plant (products of photosynthesis) –

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

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

Stomata – CO 2 enters, H 2 O exits Guard cells balance need for CO 2 with need to conserve water Stomatal density varies among species High light exposure & low CO 2 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 RI9o 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 - hill.com/sites/ /student_view0/ch apter41/animation_- _phytochrome_signaling.html hill.com/sites/ /student_view0/ch apter41/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 g5Ik g5Ik Growth of a plant towards or away from light Differential growth – due to auxin

Auxin Plant hormone – 1 st 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.