Plant Biology: Hormones, Growth, Transport, and Nitrogen Cycle

What are the 5 major plant hormones?

Auxin, cytokinin, gibberellin, ABA, and ethylene.

What does auxin do?

Cell elongation, apical dominance, and phototropism.

What does cytokinin do?

Promotes cell division and branching.

What does gibberellin do?

Promotes stem growth and seed germination.

What does ABA do?

Maintains dormancy and closes stomata during drought.

What does ethylene do?

Fruit ripening, leaf abscission, and triple response.

Which hormone is associated with elongation?

Auxin.

Which hormone is associated with branching?

Cytokinin.

Which hormone is associated with germination?

Gibberellin.

Which hormone is associated with drought response?

ABA.

Which hormone is associated with fruit ripening?

Ethylene.

What does xylem transport?

Water and minerals.

What does phloem transport?

Sugars and other organic nutrients.

Primary growth does what?

Increases plant length.

Which meristem causes primary growth?

Apical meristem.

Secondary growth does what?

Increases plant thickness.

Which meristems cause secondary growth?

Vascular cambium and cork cambium.

What does vascular cambium produce?

Secondary xylem inward and secondary phloem outward.

What does cork cambium produce?

Protective cork tissue.

How many cotyledons does a monocot have?

One.

How many cotyledons does a eudicot have?

Two.

Monocot leaf veins

Parallel.

Eudicot leaf veins

Netted.

Monocot stem vascular bundles

Scattered.

Eudicot stem vascular bundles

In a ring.

What happens in double fertilization?

One sperm fertilizes egg; one sperm fertilizes two polar nuclei.

Sperm + egg produces what?

Diploid zygote.

Sperm + two polar nuclei produces what?

Triploid endosperm.

What does the zygote become?

Embryo.

What does the ovule become?

Seed.

What does the ovary become?

Fruit.

Trace water from soil to atmosphere.

Soil → root hair → cortex → Casparian strip → xylem → leaf → stomata → air.

What does the Casparian strip do?

Forces water and minerals through membranes before entering xylem.

What is transpiration?

Evaporation of water from leaves.

What mainly pulls water upward through xylem?

Transpiration pull.

What is cohesion?

Water molecules sticking to each other.

What is adhesion?

Water molecules sticking to xylem walls.

How do stomata open?

K+ enters guard cells → water enters → cells become turgid → stoma opens.

What happens when guard cells lose water?

They become flaccid and the stoma closes.

Why are open stomata a tradeoff?

CO2 enters, but water is lost.

Trace phloem transport.

Source → sugar loading → water enters → pressure flow → sink.

What is a source?

An organ that produces or releases sugar.

Example of a source

Mature photosynthesizing leaf.

What is a sink?

An organ that uses or stores sugar.

Examples of sinks

Roots, fruits, seeds, and young leaves.

Why does water enter phloem at the source?

Sugar lowers water potential, so water enters by osmosis.

What drives phloem movement?

Pressure difference between source and sink.

What does nitrogen fixation do?

Converts N2 into ammonia/ammonium.

What does nitrification do?

Converts ammonium → nitrite → nitrate.

What does denitrification do?

Converts nitrate → atmospheric N2.

What nitrogen forms can plants absorb?

NH4+ and NO3-.

Easy nitrogen memory trick

Fixation brings N in; nitrification makes nitrate; denitrification sends N out.

What are the 3 root growth zones?

Division → elongation → differentiation.

What happens in the zone of division?

Cells divide by mitosis.

What happens in the zone of elongation?

Cells increase in length.

What happens in the zone of differentiation?

Cells specialize into mature tissues.

What is apoplast transport?

Movement through cell walls and spaces.

What is symplast transport?

Movement through cell cytoplasm and plasmodesmata.

What is positive gravitropism?

Growth toward gravity.

What plant organ shows positive gravitropism?

Roots.

What is negative gravitropism?

Growth away from gravity.

What plant organ shows negative gravitropism?

Shoots.

How do plants detect gravity?

Statoliths settle inside specialized cells.

What are phytochromes?

Plant receptors for red and far-red light.

What does red light do to phytochrome?

Converts Pr → Pfr.

What does far-red light do to phytochrome?

Converts Pfr → Pr.

Which phytochrome form is usually active?

Pfr.

What does a low red:far-red ratio usually mean?

The plant is shaded by other vegetation.

How do plants often respond to shade?

Increased stem elongation.

What is phototropism?

Growth in response to light direction.

How does phototropism work?

Auxin moves to the shaded side, causing greater elongation there.

Which light is important in phototropism?

Blue light.

Fast xylem vs phloem

Xylem = water/minerals; phloem = sugar.

Fast primary vs secondary growth

Primary = length; secondary = thickness.

Fast monocot vs eudicot

Monocot = 1 cotyledon/parallel veins; eudicot = 2/netted veins.

Fast cohesion vs adhesion

Cohesion = water-water; adhesion = water-xylem.

Fast source vs sink

Source releases sugar; sink uses/stores sugar.

ABA memory trick

ABA = drought + dormancy.

Gibberellin memory trick

Gibberellin = grow + germinate.

Ethylene memory trick

Ethylene = ripening + abscission + triple response.

Auxin memory trick

Auxin = elongation + apical dominance + tropisms.

Cytokinin memory trick

Cytokinin = cell division + branching.