PLSC exam 1

cell

fundamental unit of life

prokaryotic

before nucleus, lacks nucleus, lacks organelles, lacks cytoskeleton (bacteria, archaea)

eukaryotes

with true nucleus

nucleus

\-stores DNA

\-controls cellular activity(mRNA, rRNA, tRNA)

nuclear pores

import of proteins into nucleus, exports of RNA to cytoplasm

chloroplast

\-plastids are characteristic of plant cells

\-plastids are classified by their content of pigments (chloroplast, chromoplast, and leucoplast)

\-chloroplast are the site of photosynthesis(contains chlorophyll and carotenoids)

envelopes and thylakoids

\-chloroplast/plastids have two envelope membranes(endosymbiosis)

\-chloroplast have an elaborate system of thylakoid membranes

\-two types of thylakoids (grana stacks and stroma lamellae) are interconnected

plastids are semi-autonomous

\-plastids resemble bacteria(endosymbiosis)

\-plastids contain DNA(found in nucleoids, multiple DNA copies)

\-DNA not associated with histones

\-plastids contain bacteria-type ribosomes

\-plastids replicate by fission

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chromoplasts

\-contain carotenoids, but no chlorophyll

\-may develop from chloroplast

\-often found in fruits and flowers

\-attraction of animals for pollinations and seed dispersal

leucoplasts

\-are the least differentiated mature plastids

\-lack pigments and internal membrane system

\-found in non-green tissues

\-some store oil or protein

\-amyloplasts store starch(found in storage organs such as seeds, roots and tubers)

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plastids development

reproduce by fission(proplastids, mature plastids)

\-proplastids are small undifferentiated plastids

\-found in meristematic/dividing cell

\-develop into other plastids(chloroplasts, amyloplasts, chromoplasts)

etioplasts

\-in light develop into chloroplast(prolamellar body into thylakoids)

\-in the absence of light development of proplastids into chloroplast is arrested instead etioplasts develop

\-contain prolamellar body(semicrystalline tubular membranes)

mitochondria

\-has two surrounding membranes

\-inner membrane has invaginations(called cristae)

\-site of respirations

\-other metabolic processes( biosynthesis of amino acids, fatty acids, vitamins)

\-semi-autonomous organelles(DNA/nucleoids, ribosomes, endosymbiotic)

peroxisomes

\-single membrane, no internal membranes

\-interior may contain crystalline protein

\-self-replicating organelle

\-no DNA and ribosomes(import of proteins)

\-closely associated with other organelles

\-involved in photorespiration

\-glyoxysomes(specialized peroxisomes) conversion of stored lipids into sucrose in germinating seeds

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vacuole

\-single membrane(tonoplast)

\-derived from the ER and Golgi apparatus

\-water storage (makes up large volume of cells, increase of cell size)

\-inorganic ions( Ca2+, K+, Cl-, Na+, HPO4-)

\-at high concentrations some compounds form crystals

\-storage of primary metabolites (sugar, organic acids, amino acids)

\-secondary metabolites(many toxic)

\-pigment deposition(anthocyanins)

endoplasmic reticulum

\-complex three-dimensional membrane(permeates entire cell)

\-represents a system for channeling material within the cell

\-two types of ER with the same cell (smooth ER and Rough ER)

Smooth ER

tubular, lacks ribosomes, involved in lipid biosynthesis

Rough ER

flattened sacs, with ribosomes, involved in protein synthesis(become attached to the ER surface), Newley synthesized proteins are translocated into the ER lumen

endomembrane system

\-interconnected system of membranes and organelles

\-includes (ER/nuclear envelope, Golgi apparatus, Various vesicles, Vacuole/tonoplast, plasma membrane)

Golgi apparatus

\-stacks of cisternae, tubular at their margin

\-dynamic, highly polarized (cis>trans)

\-protein modification (glycoproteins)

\-synthesis of polysaccharides (hemicellulose, pectin)

\-vesicles targeted towards plasma membrane and vacuole

Exocytosis

\-secretory vesicles fuse with plasma membrane

\-discharge their content into the cell wall

Cytoskeleton elements

\-dynamic 3-dimensional network of protein filaments

\-two types of filaments (microtubules(tubulin subunits, arranged in tubular helix) active. filaments (actin proteins)

actin filaments

\-involved in movement of organelles

\-movement of the nucleus

\-vesicle in mediated secretion

\-cytoplasmic streaming

microtubules

\-cortical microtubules, just inside of the plasma membrane

\-involved in orderly growth of cell wall and cell expansion

\-control the alignment of cellulose microfibrils

cell wall

\-constrains expansion of protoplast, determines size and shape of the cell

\-not inactive, but has essential functions (enzymes, transports of substances, defense against pathogens)

\-principle component is cellulose(glucose polymer), bundled into micro-fibrils

\-interlocked by cross-linking matrix(hemicellulose, pectin, glycoproteins)

\-other constituents- lignin(strength, stiffness), fatty substances(cutin, suberin, waxes control of water transport)

plasmodesmata

connection of the protoplasts of two adjacent cells through the cell wall

\-individual or aggregated in pit fields of primary cell wall

\-left out when secondary wall is deposited, forming pit pairs with pit membrane (middle lamella and primary wall)

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plant body plan

\-established during embryogenesis

\-two superimposed patterns

1.apical-basal pattern(along main axis, shoot tip to root tip)

2. radial pattern(concentrically arranged tissues)

meristems

\-plant development occurs through the activity of meristems

\-meristems are populations of cells that retain the potential to divide

\-indeterminate growth(unlimited or prolonged meristematic activity)

-shoot apical meristem

\-root apical meristem

\-generate cells that give rise to

* stems, leaves, and flowers


* roots

shoot and root meristems

\-apical meristems: initials(main meristem) and derivatives(new body cell)

\-cell divisions are not limited o initials

\-primary meristems- protoderm, ground meristem, procambium

primary meristem

\-partially differentiated tissue, remains meristematic for sometime (mitosis and cytokinesis)

\-primary growth: apical and primary meristem(extension of plant body(vertical) and formation of primary tissues)

interphase

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\-G1 phase: intense biochemical activity(synthesis of proteins, ribosomes, membranes, replication of organelles)

\-S phase: DNA replication and synthesis of histones

\-G2 phase: DNA replication complete, preparations for mitosis and cytokinesis

\-G0 phase: temporary arrest in G1 (winter dormancy)

mitosis

prophase, metaphase, anaphase, telophase

prophase

\-chromatin condenses chromosomes with 2 chromatids joined by centromere(kinetochores) nucleolus disappears

metapahse

mitotic spindle(kinetochore microtubules and polar microtubules) chromosomes align in equatorial plane

anaphase

separation of sister chromatids move forwards opposite poles of spindle microtubules become shorter

telophase

nuclear envelopes form from ER vesicles spindle apparatus disappears chromosomes elongate nucleolus reformed

cell division in plant cells

\-formations of a cell plate

\-starts in the middle of the cell and grows outwards

cytokinesis

formation and insertion of new cell wall that separates daughter nuclei after mitosis

phragmoplast

barrel shaped system of microtubules and actin filaments

cell plate

initiated by fusion of Golgi derived vesicles

genetic control

exact path determined by

* location(position with apical-basal and radial patterns)
* as well as environmental factors

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plant development

involves three overlapping processes:

* growth-irreversible increase in size(cell division and cell enlargement)
* morphogenesis-plants assume particular shape(expansion of tissue and subsequent cell division)
* differentiation-initially identical cells become different(gene expression)

differentiation of cells

* depends on control of gene expression
* fate of cell determined by final position in developing organ
* cells communicate positional information

formation of primary tissues

tissues

cells associated to form structural and functional units

three tissue systems

ground tissue, vascular tissue, dermal tissue

* distributed in radial patterns(vascular tissue is embedded in ground tissue covering)
* differences in relative distribution of vascular and ground tissue

parenchyma cells

* most numerous in plant body
* mesophyll in leaves
* cortex and pith of roots and stems
* living at maturirty, primary cell walls
* capable of cell division

collenchyma

* discrete strands or continuous cylinders
* beneath epidermis in stems and petioles
* bordering veins in leaves(dicots)
* typically elongated cells
* unevenly thickened non-lignified primary walls (soft and flexible)
* living at maturity(continue to develop thick flexible cell wall)
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sclerenchyma

xylem elements

* elongated cells, secondary walls, pits lack protoplast at maturity
* two types of elements
* vessel elements
* perforations(lack prim and second wall), form long continuous columns
* tracheids
* less specialized, water must pass through “pit membrane

primary xylem(tracheids)

secondary xylem(tracheid and vessels)

xylem element differentiation

programmed cell death(genetically controlled), total elimination of protoplast

phloem

sieve tubes-companion cell

epidermis

* dermal tissue of leaves, stem, roots, fruits and seeds
* \

epidermis cells

unspecialized and leucoplasts

guard cells

* contain c

trichomes

* hairlike

functions of foots

* anchorage
* absorption
* conduction
* storage

taproots system (dicots)

* tap root(primary root)
* grows dircelty downward
* gives rise to lateral roots
* penetrate deeper into soil

fibrous root system(monocots)

* primary root usually short--lived
* adventitious roots arise from stem
* give rise to lateral roots
* shallow root system

rootcap

* mass of living parencyma cells
* protects the apical meristem
* secrets mucilage, lubricates the root
* rootcap senses and transmits information to the meristem and elongation zone

root apical organization

* rootcap consists of two portions
* central columella
* lateral rootcap
* columella perceives gravity and water potential gradients
* root apical meritem
* only infrequent cell division in “quiescent center”
* most cell division

region of cell elongtation

region of maturation/differentiation

root epidermis

root hairs

* tubular extensions of epidermis cells
* greatly increase absorptive surface
* relatively short-lived
* constantly replaced with new hairs

secondary root growth

\-**Vascular cambium (cells between phloem and xylem meristematic)**

\-**Pericycle cells opposite of xylem also become meristematic**

\-**Thus xylem completely enclosed by cambium**

\-**Cambium produces xylem to the inside and phloem to the outside**

periderm

* The first periderm originates from cortical cells
* Subsequent periderms originate deeper (from phloem parenchyma cells)
* Cork cambium: cell divisions produce cork and phelloderm cells
* Cork cells: cell walls contain suberin, ultimately die
* Phelloderm cells: parenchyma, living cells
* Lenticels: portion of periderm with multiple intercellular spaces, allow gas exchange

Bark

* includes all tissues outside of the vascular cambium
* outer bark: all tissues outside of innermost cork cambium (entirely dead tissue)
* inner bark: all tissue inside innermost cork cambium(living part)

modified stems

tendrils of grape vine

modified leaves

tendrils of garden pea

modified axillary buds/branches

thorns of hawthorn

spiral

* 1 leaf at each node, angle between successive leaves

distichous

* 1 leaf at each node, leaves on opposite side of stem

opposite

* 2 leaves at each node, on opposite side of stem

decussate

* successive pairs of leaves at right angle to previous

whorled

* 3 or more leaves at each node

connection of vascular tissue in leaf and stem

* Leaf and stem procambium is continuous
* Leaf traces:   at each node vascular bundle(s) diverge from strands in the stem
* Leaf trace gap: wide interfascicular region in the vascular cylinder above leaf trace


* A single leaf may have one or more leaf traces
* The arrangement of leaves reflected in the vascular system of the stem

leaf morphology

* Leaf blade or lamina
* Petiole
* Stipules:   attachments at the base of the leaf
* Sessile leaves: lack petiole, leaf base can be expanded into sheath   encircling the stem


* Simple leaves: blade not divided into distinct parts

compound leaves

* The leaf blade divided into leaflets
* Each leaflet has its petiolule
* Pinnately compound leaf:

leaflets arise on either side of the leaf axis (rachis)

* Palmately compound leaf:

leaflets diverge from the tip of the petiole

* How to distinguish leaves and leaflets:

buds are only found on axis of leaves

epidermis of leaves

* Compactly arranged cells
* Covered by cuticle (reduces water loss)
* Stomata:  for controlled gas exchange

  in the lower and/or upper epidermis

  in dicots scattered over the leaf surface

* Trichomes:  found on either or both leaf surfaces