BIOL 3600 Plant Section - Exam 4 Flashcards

Comprehensive vocabulary flashcards covering plant defenses, sensory systems, reproduction, and biomes based on BIOL 3600 lecture notes.

Tropism

Directional growth responses to an external stimulus such as light, touch, or gravity.

Positive Tropism

Directional growth or movement of an organism usually in plant,TOWARD am external stimulus

Negative Tropism

The growth or movement of a plant (or organism) AWAY from an external stimulus

Phototropism

The directional growth or bending of a plant toward a light source to optimize photosynthesis, driven by the hormone auxin.

Phototropism

Growth or bending of a plant TOWARD a LIGHT source (maximize light capture for photosynthesis)

• Positive: Growth TOWARD LIGHT (stems, leaves)

• Negative: Growth AWAY LIGHT (some roots)

Gravitropism

A growth response to gravity where roots exhibit positive gravitropism (downward) and shoots exhibit negative gravitropism (upward).

Gravitropism

A plants growth response to gravity

• Positive: ensures roots grow DOWNWARDS

• Negative: shoots grow UPWARD

Phytochrome

a class of photoreceptor proteins found in plants, bacteria and fungi

Phytochrome (Pr)

A biologically inactive pigment-containing protein that absorbs red light at $660\,nm$ and is converted to its active form in direct sunlight.

Phytochrome (Pfr)

The active form of phytochrome that absorbs far-red light at $730\,nm$ and can promote or inhibit processes like flowering and seed germination.

The processes phytochrome is involved in

• Seed Germination: process in which a dormant seed wakes up and begins to sprout into a young plant (inhibited by far red-light and stimulated by red light in many plants only germinates when exposed to DIRECT sunlight

• Shoot elongation: rapid lengthening of plant stems driven by cell division at the apical meristem & cell expansion below it (Etiolation is an energy conservation strategy where plants divert energy to internode elongation when growing in the dark caused by a lack of red light)

• Detection of Plant crowding; Not enough space for plants to grow and mature properly( plants measure the amount of far-red light bounced back from

Etiolation

An energy conservation strategy where plants divert energy to internode elongation during growth in the dark due to a lack of red light.

4 steps in plant Gravitropic responses

1. Perception: Gravity is perceived by the cell

2. Intracellular transduction: the perception of gravity must produce a change in the structure or biochemistry of the perceiving cell

3. Translocation: a signal is translocated differentially to the two sides of the organ

4. Reaction: differential cell elongation occurs affecting cells in the “up” and “down” sides of the root or shoot

Gravity sensed in Shoots & Roots

• Shoots: gravity is sensed along the length of the stem in endodermal cells surrounding the vascular tissue (signaling occurs toward the outer epidermis cells)

• Roots: in roots the cap is the site of gravity perception (signaling triggers differential cells elongation and division in the elongation zone

Thigmomorphogenesis

A permanent change in form that occurs in response to mechanical stresses.

Thigmotropism

Directional growth of a plant or plant part in response to contact

Thigmonastic responses

Plant responses to touch that are independent of the direction of the stimulus and are usually produced by changes in turgor pressure.

4 responses to Water & Temperature in plants

• Dormancy: mechanism to survive adverse conditions (cold/drought) by stopping growth

• Abscission: shedding of leaves, fruits or flowers often mediated by ethylene and abscisic acid in response to stress

• Lipid Composition: plants after the saturation of fatty acids in cell membranes to maintain fluidity &stability under cold or heat stress

• Heat Shock Proteins (HSPs) : molecular chaperones synthesized in high numbers under heat stress to prevent protein denaturation & fix damaged proteins

Heat shock proteins (HSPs)

Molecular chaperones synthesized in high numbers under heat stress to prevent protein denaturation and fix damaged proteins.

Auxin

A crucial plant hormone found in apical meristems that regulates development by promoting cell elongation and division.

Cytokinins

a class of plant hormones that primarily stimulate cell division and growth in plant root and shoots (produced in the root apical meristem and developing fruits)

Gibberellins

essential plant hormones that regulate growth and development including stem elongation, seed germination & flowering

Ethylene

Known as the "ripening hormone," it controls fruit ripening, leaf and flower senescence, and abscission.

Abscisic acid (ABA)

A stress hormone that inhibits growth and triggers stomatal closure to conserve water during drought, salinity, or cold conditions.

Jasmonic Acid

A hormone that regulates plant responses to abiotic and biotic stresses and activates the transcription of defense genes like proteinase inhibitors.

Salicylic acid

regulate growth, development , & immune responses against pathogens

What is the life cycle of a typical Angiosperm

Angiosperms exhibit a haplodiplontic life cycle (often described as alternation of generations)

• angiosperms life cycle is characterized by a dominant diploid sporophyte phase (the plant body) produces flowers for sexual reproduction

The pathways to flowering

Flowering pathway: the four flowering pathways lend to an adult meristem becoming a floral meristem

• Light-Dependent: the photoperiodic pathway ( mechanism where plants measure by day length or night length to time seasonal events like flowering)

• Temperature -Dependent: a chemical, physical, or biological where the mechanism or final outcome changes based on temperature

• Gibberellin - Dependent: a plant molecular mechanism that triggers growth by breaking down “repressor” proteins in response to the hormone gibberellin

• Autonomous pathway: is a set of internal genetic mechanism in plants that controls flowering time by ensuring the plant blooms at the right time independent of external environmental cues like day light or winter cold

How are long and short- day plants affected by changes? In the length of night?

• Short Day: (Long night) plants need long nights to flower - short day plants flower when daylight becomes shorter than a critical length

• Long Day: (short night) plants need short nights - long day plants when daylight becomes longer than a critical length

Floral meristem identity genes

Are transcription factors that commit undifferentiated shoot meristem to become flowers

Floral organ identity genes

master regulatory genes that determine the development of specific flower parts, Sepals(protect the bud),Petals(attract pollinators),Stamen(male pollen producing parts),Carpels (female contain gin ovules)

ABC model of flower production

• Class A gene alone: Sepals(outer)

• Class A and B genes together: Petals

• Class B and C together: Stamens

• Class C gene alone: Carpels ( inner)

when any one class is missing aberrant floral organs occur predictable positions

Calyx

The outermost whorl of a flower consisting of flattened sepals, which serve to protect the flower while it is in the bud stage.

Corolla

Consists of petals (often brightly colored& fragment to attract pollinators like insects and bugs)

Androecium

The collective term for all the stamens (male parts) of a flower, consisting of anthers that produce pollen and supporting filaments.

Gynoecium

The collective term for all carpels (female structures) of a flower, consisting of the stigma, style, and ovary.

Abiotic factors

Non-living threats to plants such as extreme temperatures, drought, flooding, soil salinity, nutrient deficiencies, and pollution.

• even greater threats exist in the form of pathogenic viruses, bacteria, fungi, animals and other plants

• can tap into nutrient rescuers of plants

• use DNA- replicating mechanism to self-replicate

• kill plant cells immediately leading to necrosis

Biotic threats

Damages caused by living organisms primarily bacteria, fungi, viruses, insects, nematodes, and weeds which reduce plant growth and survival.

• Fungi, bacteria, viruses: fungi are the most common cause of plant disease leading to rots, bacteria & viruses can cause rapid infections transmitted by insects

• Insects & mites : feed on plants by sucking sap chewing leaves or burrowing into stems & fruits causing physical damage & transmitting pathogens

• Parasitic nematodes: microscopic worms often in the soil that attack plant roots causing deformations gall and inhibiting nutrient uptake

• weed: compete with plants for water, nutrients, light & space

animals: herbivores like Deer, rabbits and birds can cause severe mechanical damage by browsing &eating plants

First line of defense

A physical, structural barrier consisting of the epidermal layer, specifically the cuticle and bark, often reinforced by wax, cutin, or suberin.

Secondary metabolites

A class of chemical defenses including alkaloids (e.g., caffeine, cocaine), tannins (to inactivate proteins), and plant oils (to repel insects).

Static defense

Plant responses to threats that are maintained in both the presence and absence of a threat, which can have an high energetic downside.

Inducible defense

Refers to defensive traits that are activated only when the plant is threatened or stressed, allowing the plant to conserve energy resources.

Systemin

An $18$-amino acid peptide produced by wounded leaves that moves through the phloem to signal the production of defense genes.

Gene-for-gene hypothesis

A model where plant resistance genes ($R$) interact with pathogen avirulence genes ($avr$) to signal the pathogen's presence and mount defenses.

Hypersensitive Response (HR)

A defense mechanism triggered by the $R$ gene product that leads to rapid cell death around the site of attack and provides long-term resistance.

Systemic Acquired Resistance (SAR)

A systemic response that leads to broad-ranging resistance lasting for days, likely induced by long-distance signaling from salicylic acid.

Double fertilization

A complex reproductive mechanism in flowering plants where 2 gametes from a pollen grain fertilize 2 different female cells

Suspensor

An elongated structure formed by the larger basal cell during the first zygotic division that transports nutrients to the embryo.

Vegetative propagation

A form of asexual reproduction where new plants develop from vegetative parts such as stems, roots, or leaves rather than seeds.

• some examples (runners/stolons -strawberries , rhizomes - ginger or turmeric, suckers - roses, lilacs, citrus, apple)

• rhizomes - critical organ for nutrient storage

Biome

A major type of ecosystem on land, defined largely by regional climatic conditions like temperature and precipitation.

Primary productivity

The speed at which a biome builds biomass, which is directly correlated with the availability of heat and water.

Taiga

A cold, coniferous forest biome, also known as boreal forest, that wraps around the Northern Hemisphere.

Tundra

A treeless, cold, arctic/alpine biome characterized by permanently frozen soil.

Both Tundra & Taiga stretch in unbroken circles around the entire globe

Pollen formation

• anthers contain four microsporangia which produce micropore mother cells (2n)

• Microspore mother cells produce microspores (n) through Meiosis

• Microspore develops by Mitosis and wall differentiation into pollen

• Generative cell in the pollen grain will later divide to form two sperm cells

Embryo Sac formation

• within each ovule a diploid megaspore mother cell undergoes meiosis to produce four haploid megaspores'

• usually only one megaspore survives

• Enlarges and undergoes repeated Mitotic divisions to produce eight haploid nuclei

• Enclosed within a seven-celled embryo sac

Self- pollination

pollen from a flower’s anther pollinates stigma of the same flower

Upsides:

• High reproductive success:do not require pollinators or other plants to produce seeds/fruit

• Efficiency:pollen grains are not wasted because they are transferred within the same flower or plant

• Guaranteed progeny: ideal for isolated plants or when environmental conditions are harsh or pollinator are scarce

• Genetic stability: preserves favorable traits/ characteristics over generations

Downsides:

• Lack of diversity: progeny are often clones lowering their adaptability to new diseases or environmental changes

• Inbreeding depression: continuous selfing can lead to weaker,smaller or less fertile offspring over time

• No new varieties: it is impossible to develop new cultivars or improve existing traits

Cross pollination

Pollen from another of one flower, pollinates another flower’s stigma

Upsides:

• Increased genetic diversity: combines genes from 2 different parents leading to healthier more robust offspring

• Higher adaptability: increased potential to adapt to changing environments or pests

• Greater vigor: often results in larger more vigorous progeny

Downsides:

• Reliance on agents: requires pollinators(bee, wind,birds) on manual assistance which can be inconsistent

• Energy inefficient: plants must produce large amounts of pollen and nectar to attract pollinators

• Dependency on proximity: requires close planting with compatible pollinators or other cultivars

Outcrossing

• separations of Stamens and Pistils in pace

- dioecious plants produce only ovules or only pollen

• separation of Stamen and Pistils in time

- monoecious plants produce male & female flowers on the same plant but they may mature at different times(dichogamy)

• Self-incompatibility that precent self-fertilization

Flowers pollinated by Bees

Bees typically visit Yellow or Blue flowers
- many have stripes or line of dots the indicate the location of the nectaries

Flowers pollinated by Other insects ( Butterflies,Moths,Flies)

• Flowers that are visited regularly by Butterflies often have flat “Landing platforms”

• Flowers that are visited regularly by Moths are often White or Pale in color

- also tend to be heavily scented making them easy to locate at night

• skunk cabbage produces an odor many people find unpleasant but that seems to attract a variety of flies that serve as pollinators

Flowers pollinated by Birds

Flowers that are visited regularly by Birds must produce large amounts of nectar

• often have a Red color

• (easy to see)Conspicuous to Birds but usually (not easily seen) Inconspicuous to insects

First zygotic divison

asymmetrical cells with two different fates

• smaller apical cell divides repeatedly forming a ball of cells which will form the embryo

• larger basal cells divides repeatedly forming an elongated structure called suspensor

• transports nutrients to embryo

The root-shoot axis also forms at this time

• cells near suspensor become root

• cells at the other end become shoot

Critical developmental events

Critical developmental events: during embryogenesis ,angiosperms undergo three other critical events

• development of a food supply

• development of seed coat

• development of fruit surrounding seed

Germination

Process where a seed wakes from dormancy and begins to grow into a seedling initiated by water absorption , proper temperature & oxygen

-cannot take place until water and oxygen each the embryo

Hormonal Regulation of seed germination

• seed germination is mainly organized by a balance between 2 opposing hormones

Abscisic acid (ABA): which keeps the seed dormant

Gibberellin: which triggers germination

Annual plant

Grow ,flowers and form fruits and seed within one growing season

• they often die when the process is complete

Biennial plant

Have life cycles that take two years to complete

• store energy in year one, flower in year two

Perennial Plant

Continue to grow year after year

• they may be herbaceous or woody

Chemical defenses

• many plants employ toxins that kill herbivores or least deter their grazing behavior

• some are unique to plants

• others called defensins are found in plants & animals

3 Major classes of secondary metabolites

Alkaloids - Include caffeine ,nicotine, cocaine, and morphine

Tannin - Bind to and inactivate proteins

Plant oils - repel insects with strong odors particularly those found in the mint family

Animals including humans can avoid many of the cumulative toxic effects of a secondary metabolites by eating a varied diet

How secondary metabolites beneficial to humans

• Beneficial to humans by: acting as powerful antioxidants , anti- Flammatory agents and antibiotics

secondary metabolites: organic compounds produced by plants, fungi & bacteria for defense offer significant health & benefits to humans

How Ants are involved in plant defenses

ants: often live in plant structures called domatia protect the host plant

• relationships that benefit both

• acacia tree and ant

• ants protect acacia trees from harmful herbivores

• plant provides ants with food & shelter

Ants & wasps act as crucial, mobile, indirect defenses for plants by attacking herbivores (like caterpillars, and beetles) in exchange for food rewards ( nectar, food bodies) or shelter

How Wasps are involved in plant defenses

wasps: including parasitic species are attracted to chemical signals emitted by damaged plants to hunt herbivores

• as caterpillars chew away a wound response in the plant leads to release of a volatile compound

• females parasitoid wasp is attracted to lays fertilized eggs in caterpillar

• eggs hatch and larvae kill caterpillar

Wound response

occurs when a leaf is chewed or injured

• bind to digestive enzymes in the gut of the herbivore

• signaling pathway involves - systemin, jasmoinc acid, salicylic acid

Wound response signaling

• wounded leaves produce an 18 - amino acid peptide called systemin

• systemin moves throughout the plant in the phloem

• cells with systemin receptors produce jasmonic acid

• jasmonic acid activates the transcription for defense gene including the production of a proteinase inhibitor

Main predictors of biome distribution

predicators of biome distribution: Temperature & Precipitation

8 Major biome (based on predicator graph)

• Desert

• Savanna

• Tropical Rainforest

• Temperate Grasslands

• Temperate Deciduous Forest

• Temperate Evergreen Forest

• Taiga

• Tundra

Characteristics of Tropical rain forests

• 140 to 450 cm rain/yr

• richest ecosystem of land

• high temperature and high rainfall

• very high diversity:1,200 species of butterflies in a single square mile

Characteristics of Savanna

• 50 to 125 cm rainfall/yr

• tropical or subtropical grasslands

• occur as a transition ecosystem between tropical rainforests & deserts

• Serengeti of East Africa

Characteristics of Deserts

• 25 to 40 cm rainfall/year (unpredictable)

• plants and animals cannot depend on any rainfall

• 30 N and S latitudes -due to global air circulation patterns

• due to rain shadows

• vegetation sparse animals adapted to little water availability

Characteristics of Temperate Grasslands or Prairies

• rich soils

• grasses with roots that penetrate deep into the soil

• in North America converted to agricultural use

• adapted to periodic fire

Characteristics of Temperate Forests

Temperate Deciduous forests: mild but seasonal climates (warm summers and cold winters) plus plentiful rains

Temperate Evergreen forests: occur along coastlines with temperature climates