Plant Biology

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Systematics

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A field of biology that gives scientific names to organisms, describes them, preserves collections, investigates evolutionary histories and environmental adaptations

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Bootstrap value

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shows the relative confidence in the depicted relationship; the higher the number, the greater the confidence

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What are the two phases of a plant life cycle?

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Sporophytic generation (multicellular diploid phase) and the gametophytic generation (multicellular haploid phase)

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Bryophytes

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-nonvascular plant
-no true roots, stems, or leaves
-haploid gametophytic generation is free-living and dominant
-diploid sporophytic generation is small, permanantly attached to the gametophyte, and nutritionally depended on the gametophyte
-3 living groups: liverworts, hornworts, mosses

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Lycophytes

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-vascular plants with green branched stems and scale-like leaves (no flowers or seeds)
-usually grow close to ground
-reproduce by shedding spores
-club mosses, quillworts, spikemosses

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pteridophytes

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-vascular plants that have stems, roots, and leaves (no flowers or seeds)
-spread with spores
-ferns, horsetails, whisk ferns

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gymnosperms

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-vascular plants with cones that bear seeds
-pines, furs, junipers, redwoods

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angiosperms

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-flowering plants that form fruits with seeds
- most crops, garden plants, weeds

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rhizoids

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long tube cells that anchor bryophytes to ground

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What does the activity of class A specify?

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sepal identity

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What does class A + Class B specify?

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petal identity

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What does class B + Class C specify?

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stamen identity

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What does class C specify

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carpal identity

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What is the C function required for?

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floral meristem determinacy

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What does floral induction depend on?

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environmental and endogenous signals

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What is photoperiodism?

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the ability of plants to detect day-length-> allows for seasonal responses

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What is vernalization?

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long exposure to temperatures

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What is the photoperiod signal perceived by?

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leaves

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What regulates flowering?

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shoot apex

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What is the primary photoreceptor in photoperiodism?

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phytochrome

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What is phentypic plasticity?

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Changes in physiology or development-> temporary, non-heritable

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What are abiotic factors?

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non-living factors that influence plant growth, development, reproductive, and survival

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What are primary effects of abiotic factors on plants?

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reduced water potential and cellular dehydration

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What are secondary efects of abiotics on plants?

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reduced metabolic activity, ion cytotoxicity, production of reactive oxygen species that disrput cellular integrity leading to cell death

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What are trichromes and how do they work?

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hair-like epidermal cells; densely packed trichromes on leaf surface reflect light, keeping it cooler

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What is the cuticle and how does it work?

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Multi-layered structure of waxes on the outer cell walls-> reflect light-> reduce heat load-> minimizes water loss

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How do plants reduce leaf area?

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by reducing cell division and/or expansion, altering leaf shape and/or initiating senescence and abscission of leaves

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What is the heat load?

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amount of heat loss required to maintain leaf temperature close to air temperature

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How do primary effects work?

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They directly alter physical and biochemical properties of cells, which then leads to secondary effects

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Functions of a seed

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-seeds can remain dormant in the soil for many years
-aid in dispersal of species in time and place (seed coats can be modified to facilitate dispersal)
-nourishment of developing embryo-> well packaged food source

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Characteristics of gymnosperms

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-woody plant
-naked seeds-> not enclosed within fruit-> ovules and seeds are present on the surfaces of leaflike structures called sporophylls that are aggregated to form cones

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Angiosperms

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-Have flowers (structures that contain the reproductive organs of plants)
-seed enclosed within the carpal
-carpal develops into fruit
-double fertilization results in endosperm formation

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Angiosperm life cycle & double fertilization

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-zygote develops into mature seed
-seed germinates to give rise to seedling
-seedling gives rise to mature sporophyte
-inside flower, the megasporocytes inside ovule (inside the ovary of the carpel) and microsporocytes (inside the anthers) undergo meiosis to generate megaspores and microspores
-megaspores undergoes mitotic divisions to form embryo sac containing the egg cell

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embryo sac

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contains 1 egg cell, 2 synergids, 3 antipodal cells, and a central cell that contains two nuclei; 7 cells with 8 nuclei

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egg cell

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located at micropylar end; egg cell fuses with a sperm nucleus to produce a zygote

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synergids

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located on either side of the egg cell

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central cell

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fuse with each other and then a sperm nuclei to produce triploid endosperm

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antipodal cells

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located at oppsite end of embryo sac from egg cell

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pollen grain

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-inside stamen-> microspore undergoes mitotic divisions to form this
-contains two sperm cells enclosed within a vegetative cell
-consists of 3 cells

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Double fertilization

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one sperm nucleus fuses with egg nucleus to produce the diploid zygote; 2nd sperm nucleus fuses with the two nuclei of central cell to produce triploid endosperm nucleus

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wind-dispersed fruits

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indehiscent fruits of dandelion have modified sepals which form a plume-like structure; parachute-like

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water-dispersed fruits

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large air spaces allow for flotation; coconut

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Reasons for success of angiosperms

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-resistant to cold and drought-> tough leaves
-vessel elements in xylem more efficient than those in gymnosperms
-deciduous habit
-seed coat
-more efficient transport of sugars (sieve tube elements of phloem)
-more effective pollination
-specialized mechanisms of seed dispersal
-secondary metabolism

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Monocotyledons

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(monocots): 65,000 species; include grasses, lilies, irises, orchids; one cotyledon; flower parts usually in threes; parallel leaf venation

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Eudicotyledons

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(eudicots): 165,000 species; include many trees, herbs; two cotyledons; flower parts usually in fours and fives; netlike leaf venation

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____________ meristems are required for primary growth and __________ meristems are required for secondary growth.

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apical; lateral

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Which of the following are common features of plants?

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nonmotile, autotrophic, indeterminate growth

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Which of the following cytoskeletal structure is responsible for building a cell plate at the end of the mitotic phase?

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phragmoplast

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Openings in the cell wall that connect the cytoplasm of one plant cell to another are called _____________________.

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plasmodesmata

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The transcription factor HY5 is ubiquitinated and subsequently degraded by the 26S proteasome. What level of gene regulation is described here?

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posttranslational regulation

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Which of the following covalent modifications can influence the degree of DNA packing in chromatin.

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cytosine methylation and histone methylation

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Which of the following terms is used to describe the attraction of water molecules to a solid phase like plant cell walls?

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adhesion

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Nitrogen, potassium and calcium are examples of ________________ that typically make up 0.1-1.5% of the plant dry mass.

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macronutrients

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Cells in the ______________ of the root apical meristem divide infrequently.

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quiescent center

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__________ is a substance found in secondary cell walls to make them strong and rigid.

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lignin

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What are pores through which plants obtain CO2

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stomata

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what membrane of chloroplasts is chlorophyll embedded into?

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thylakoid

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what is the idea that there is a combination between histone modifications and a particular chromatin structure?

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histone code

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what are the integral membrane proteins that affect the rate of water by facilitating water movement across membranes?

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aquaporins

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what is the waxy strip in the endodermis of the cell wall that prevents seepage of water into the xylem?

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casparian strip

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what is the loss of water vapor from leaves that pulls water up the plant?

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transpiration

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what type of fungi associate with plant roots and aid in nutrient uptake?

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mycorrhizal