Principles of Biology - Biology 102
Spring quarter
_ Written by: Sue Kloss
Lake Tahoe Community College
Instructor: Ralph Sinibaldi
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Plant Structure, Growth, and Development - Ch. 35
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Intro - Fanwort- plasticity - organisms ability to alter itself to suit local enviro conditions
A. Plasticity
1. underwater leaves feathery - stress of moving water
2. top leaves flat - flotation
3. different environments cause different genes to be turned on/off
4. plasticity is more common in plants than animals, maybe bc plants don't have mobility
B. morphology - external form
1. leaf can be a spine (cactus), a needle (conifers), or large and flattened (oak or maple)
C. Vascular plants are most common on earth, especially angiosperms
1. angios comprise about 90% of all plant species
2. basis of nearly every terrestrial food chain
I. Plant Structure
A. Plant body is hierarchy of organs tissues, cells
1. tissue - group of cells with common structure, function or both
2. organ - several types of tissue that together carry out particular function
B. Three basic plant organs- roots, shoots; shoots = stems and leaves
1. plants body’s reflect below ground and above ground components
2. absorb water/minerals from below ground, sun and CO2 above ground
3. Plant body has roots and shoots
4. roots are nonphotosynthetic, would starve without shoots, shoots would die w/out water/nutrients
5. Fig. 35.2 - roots - anchor, uptake of water/nutrients, transports them, stores food
a. fibrous roots - dense mat of roots; no one root stands out, shallower system vs
b. taproots and root hairs - one main root, may penetrate deeply w/many lateral roots
1. in angios, taproot may store organic nutrients for plant to consume or use in
flower and fruit development; carrots, turnips sugar is harvested before flowering
c. adventitious roots - roots arising from stem or leaves (can mean any plant part that
grows in an unusual location)
d. most absorption in roots takes place in root hairs (Fig. 35.3)
e. modified roots - prop, buttress, storage, pneumatophores, aerial stranglers
6. stems (Fig. 35.2)
a. stems = nodes, internodes, leaves
b. buds = undeveloped shoots
1. terminal bud at tip of stem
2. axillary buds = lateral; every leaf has one; in young plants, most are dormant
a) removing apical bud usually stimulates growth of axillary buds
b) pruning and pinching back will result in bushier plants
c. apical dominance - produces leader
d. modified stems - stolons, rhizomes, bulbs, tubers
7. leaves (fig. 35.2)
a. main photosynthetic organ, though green stems may also Ps
b. blade, petiole joins leaf to stem
c. grasses and other monocots lack petioles but have a sheath; palms have petioles
d. veins - vascular bundles
1. monocots- parallel
2. dicots - net or branched
e. simple vs compound (Fig. 35.6)
1. compound form allows large leaves to withstand wind, etc.
f. modified leaves - tendrils, spines, storage (celery is a petiole), bracts,
reproduction (Fig. 35.7)
C. Tissue Systems: Dermal, Vascular, Ground (Fig. 35.8)
1. tissue system is one or more tissues organized into functional unit connecting the organs of
plant
2. dermal tissue system - outer protective covering like our skin
a. defense vs physical damage, pathogens
b. epidermis - non woody plants
c. periderm in woody plants
d. cuticle prevents water loss
e. stomates, trichomes
3. vascular tissue system - transport of materials thru plant
a. xylem - water, phloem- sugar vascular tissue - stele- can be a vascular cylinder (dicots)
or in separate bundles (monocot)
4. ground - tissues that are neither dermal or vascular
a. innermost to vascular tissue - pith; external to vascular tissue - cortex
5. Differentiated plants cells - (Fig. 35.9)
II. Growth in plants
A. Primary growth lengthens roots and shoots
1. Indeterminate growth - continued growth throughout life
a. Determinate growth - cessation of growth after you reach a certain size
b. Animals generally use determinate growth - move through environments
c. Plants generally use indeterminate growth - grow through environment; indeterminate
growth allows plants to increase exposure to air, sunlight and soil through whole life.
2. Plants have a finite life span
a. annuals - germinate, set seed and die in a single year or growing season; crops
(wheat, corn and rice) and many wildflowers
b. biennials complete life cycle in two years; carrots and beets are biennials, but
flowering usually occurs in second year and we harvest them in the first year
b. perennials - plants that live for many years; trees, shrubs and some grasses
3. Plants live for many years; some of the oldest organisms alive are plants, e.g. oldest Giant
Sequoias are 3000 yrs. old; if not for natural conditions (floods, fires etc), disease, habitat
change by humans, and climate change, more perennial plants might live for thousands of years.
4. meristems - localized, unspecialized growing cells present throughout a plants life
a. apical meristem - terminal and axillary buds, root tips - growth in length (Fig. 35.10)
b. lateral meristems in woody plants (Fig. 35.10) for diameter or width growth
1. vascular cambium - adds vascular tissue that is wood
2. cork cambium - adds bark or periderm
c. cells that remain behind with capability for cell division are initials
d. primary and secondary growth occur simultaneously but in different locations
e. each growing season, primary growth near meristems produces young extensions
of roots and shoots, lateral meristems produce secondary growth that thickens and
and strengthens older parts of plants (Fig. 35.11)
III. Primary growth lengthens roots and shoots.
A. Primary growth of roots (Fig. 35.12)
1. root cap - cone of cells protecting the delicate, actively dividing cells of apical meristem.
a. Root apical meristems provide growth downwards into the soil,
b. and upwards (Primary growth= lengthwise growth produced by apical meristems) in the
shoot portion of the plant.
c. Cells produced by primary growth in root form 3 concentric cylinders of
developing embryonic tissue - outer = epidermis, intermediate = root cortex;
innermost cylinder = vascular tissue
d. apical meristem in root sustains growth by continuously adding cells to three
developing tissue cylinders; zone of cell division (Fig. 35.12)
e. cells also grow by elongation- cellulose fibers have horizontal orientation which keep the
cell from expanding sideways. Instead, cell elongates like an accordion as it takes up
water. Cells in the zone of elongation can undergo a 10x increase in length.
f. differentiation of cells occurs in zone of maturation, above zone of
elongation.
1. vascular tissue cells differentiate, via differential gene expression, into
primary xylem or primary phloem.
g. innermost cortex layer is endoderm; outermost stele layer is pericycle; 1 cell thick
h. Organization differs in dicots and monocots (fig. 35.13)
I. lateral root formation begins in pericycle, near xylem
2. shoot cells - (35.15) long section through shoot apical meristem, domeshaped mass on terminal
bud. Elongation occurs just below this meristem
a. elongating cells push meristem upwards. As apical meristem moves up, some
cells left behind. These become axillary bud meristems at base of leaves.
b. grasses and other monocots have intercalary meristems - meristematic regions at the
base of each leaf. that’s why grass grows after you mow it
3. Tissue organization of stems
a. epidermis covers ground and vascular tissues, as in root (Fig. 35.16)
b. vascular bundles converge into roots vascular cylinder just below ground surface
c. in dicots, stem vascular bundles arranged in a ring, monocots is diffused
d. in most, xylem to the inside of plant, phloem to outside
e. most plants ground tissue consists mostly of parenchyma; collenchyma just below
epidermis in many plants
B. Leaf tissue org
1. (Fig. 35.17) epidermis - stomates for exchanging air; composed of guard cells
2. ground tissue btn epidermal layers, mesophyll
a. palisade
b. spongy
3. veins are vascular tissue - each vein enclosed by bundle sheath cells - load/unload products
III. secondary growth - thickening of stems and roots after apical meristem has produced
1. 3 developing tissue cylinders. Causes increase in girth.
a. most evident in woody plants
b. consist mainly of thick layers of mature dead xylem tissue, called wood.
c. secondary growth results from cell division in 2 meristems:
1. vascular cambium- lateral meristem of actively dividing cells between
primary xylem and primary phloem. top of dicot stem just beginning
secondary growth, which adds cells on in both directions from the
vascular cambium. (Fig. 35.18)
a. 2 new tissues form from secondary growth secondary xylem causes most of increase in thickness of stem
this occurs each year in perennial plants. consists of xylem cells
and fibers with thick walls, rich in lignins. Makes up wood.
Woody stems get thicker each year from secondary xylem
build up = annual growth rings
b. each annual growth ring has spring wood- larger, thicker cells
than summerwood, often colored differently.
c. springwood is surrounded by summerwood.
d. all material to outside of vascular cambium is sloughed off
at same rate it is produced
2. cork cambiuma. mature cork cells are dead and have thick waxy walls, protect
the underlying tissues of the cork cambium, forms
from parenchyma cells in cortex.
b. everything external to the vascular cambium= bark
1. all secondary phloem
2. cork cambium
3. cork
c. older secondary phloem dies. Help protect stem until they
too are sloughed off
d. cork cambium regenerates from young secondary phloem,
and produces steady supply of cork
d. In a tree, the living tissues are vascular cambium, youngest 2dary phloem,
cork cambium, cells in wood rays - parenchyma cells that transport H2O to outer
living tissues in trunk.
e. heartwood - dead cells of 2dary xylem no longer conducting water,
clogged w/resin - resistant to rotting (Fig. 35.20)
f. sapwood - lighter colored wood of 2dary xylem that conducts water.
g. many wood products, including saps and resins
h. wood = unique combo of strength, hardness, lightness, insulating properties,
durability and workability; similar to endoskeleton in animals.
Objectives ch. 35
1. Describe and compare the three basic organs of vascular plants. Explain how these basic organs are
interdependent.
2. List the basic functions of roots. Describe and compare the structures and functions of fibrous roots, taproots,
root hairs, and adventitious roots.
3. Describe the basic structure of plant stems.
4. Explain the phenomenon of apical dominance.
5. Describe the structures and functions of four types of modified shoots.
6. Describe and distinguish between the leaves of monocots and those of eudicots.
7. Describe the three tissue systems that make up plant organs.
8. Describe and distinguish between the three basic cell types of plant tissues. For each tissue, describe one
characteristic structural feature and explain its functional significance.
9. Explain the functional relationship between a sieve-tube member and its companion cell.
10. Distinguish between determinate and indeterminate growth. Give an example of each type of growth.
11. Distinguish among annual, biennial, and perennial plants.
12. Explain this statement: “In contrast to most animals, which have a stage of embryonic growth, plants have
regions of embryonic growth.”
13. Distinguish between the primary and secondary plant body.
14. Describe in detail the primary growth of the tissues of roots and shoots.
15. Describe in detail the secondary growth of the tissues of roots and shoots.
16. Name the cells that make up the tissue known as wood. Name the tissues that comprise the bark.
Ch. 36 - Plant Nutrition and Transport
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Intro – some plants are heavy metal accumulators – e.g brake fern – 200x higher than soil, and thrives in these
conditions.
A. brake fern takes up arsenic.
1. Sunflowers and Italian mustard take up lead
2. Help clean up contaminated soils -phytoremediation
3. Radioactive metals – taken up by sunflowers – 2000 times higher than water levels – chernobyl
4. Problem – plants must then be disposed of, animals may consume them, long time to work
5. Plants evolved these abilities from uptake of compounds that reduce herbivory
B. Transport in plants occurs at 3 scales
1. transport of water and solutes by individual cells, such as root hairs
2. short distance transport of substances from cell to cell at levels of tissues and organs
3. long distance transport within xylem and phloem at level of whole plant (fig 36.2)
I. Physical forces and transport in plants
A. Review
1. passive transport - solutes diffuse down their gradient and diffuse across membrane
2. active transport - use of ATP to pump solutes across membranes against electrochemical
gradient (combination of concentration gradient and voltage or charge difference)
3. Most solutes must cross a membrane aided by a transport protein embedded in membrane
a. eg. membranes of most plant cells have K channels that allow K ions to pass, but not
other ions, like Na+
B. Proton Pumps (Fig. 36.3)
1. proton pump is most active transport protein in plant cells
a. uses energy from ATP to pump H+ ions out of cell, creates H+ gradient across
membrane
b. also contributes to membrane potential, voltage due to separation of opposite charges
across membrane
c. proton pumping makes inside of cell negative in relation to outside
2. plants use energy stored in H+ gradient and membrane potential to drive transport of many
different solutes (Fig. 36.4)
a. eg. membrane potential generated by proton pumps contributes to uptake of K+ by
root cells
b, c. cotransport - transport protein couples downhill passage of one solute (H+) to uphill
passage of another (NO3-) - cell has such a pull on H+ that it pulls it in along with the
other substance which may be across a neutral or uphill gradient
3. Effects of differences in water potential
a. osmosis responsible for net uptake or loss of water in plant cells
b. water potential determines direction of movement of water across a cell
c. Water potential = solute concentration + physical pressure  = p +s
d. Water moves from areas of higher water potential to areas of lower water potential
e. water has the capacity to do work when it moves from areas of higher to lower potential
f. water potential is measured in units called MPa or Bars.
g. car tires inflated to ~ .2 MPa; water pressure in home plumbing = .25 M Pa; plant cells
have about 1 M Pa in them.
4. Solutes and pressure always affect water potential
a. p = pressure potential; can be positive or negative
1. water in living cells usually under positive pressure (turgor pressure);
b. s = solute or osmotic potential; proportional to the amt. of dissolved solute molecules
1. Adding solutes always lowers the water potential as they bind to water
molecules and reduces the capacity of water to do work
5. Quantitative analysis of water potential
a. general model (Fig. 36.5)
b. water relations in plant cell model (fig. 36.6)
6. When dynamic equilibrium reached between cell contents and enviro
a. turgor pressure is important to healthy plant cells, necessary for growth
b. flaccid cells result in wilted condition - drooping of leaves (Fig 36.7)
7. transport/movement btn cells- symplast and apoplast (Fig. 36.8)
8. bulk flow - movement of fluid driven by pressure - redwoods would take a decade to diffuse
material from roots to top of tree
a. e.g. loading of sugar into phloem causes inflow of water to phloem cells, and high
positive pressure at top end of sieve tube forces sap to other end of tube
b. xylem has sucking power (negative pressure) that drives movement from soil to top
of plant
II. Uptake and transport of nutrients
A. Plants acquire nutrients from soil and
1. leaves take in CO2 - about 95% of plant’s dry weight is organic material built
mainly from Carbon acquired in CO2
2. Plants get water, minerals and O2 from the soil.
3. Sugars made by plant- composed of CHO
a. CO come from CO2, H comes from H2O
b. Plants use these sugars to make everything else they need, e.g. wood
made from sugar derivatives
4. Cell respiration breaks down some sugar to provide energy for plant, consuming O2.
5. Plants are net producers of O2, though they also consume some.
a. during Ps, H2O is split, and O2 is released through leaves
b. O2 taken up by roots used in root cellular respiration
6. Plants take up minerals
a. nitrogen becomes part of hormones, coenzymes and ATP, nucleic acids, proteins.
b. N and Mg - components of chlorophyll, light absorbing molecule
c. P - nucleic acids, phospholipids, ATP
B. Plasma membrane of roots control solute uptake
1. root hairs are extensions of epidermal cells that cover roots (Fig. 36.9)
a. add enormous surface area
b. all nutrients enter in solution absorbed by root hairs
2. solutes and nutrients (ions) enter the epidermis and cortex, go to xylem to be transported
3. must pass through plasma membrane of root, selectively permeable
4. intracellular route - blue route
a. cross plasma membrane of epidermal cell (usually root hair)
b. cells interconnected by plasmodesmata, can move cell to cell via cytoplasm
c. endodermal cell discharges the solution into xylem
5. extracellular route - red
a. enters porous walls of root hair, doesn't cross plasma membrane.
b. No selection of solutes until they reach cytoplasm of endodermis;
c. Casparian strip- barrier keeps water and solutes from entering xylem via cell
walls; waxy belt.
d. solutes must enter plasma membrane of endodermal cell; ion selection
occurs here; they can then be discharged into xylem
6. in real life, combo of these routes most likely
7. most plants have mycorrhizal associations (fig. 36.10)
C. Transpiration pulls water up xylem vessels
1. works against gravity - significant adaptation
2. supplies nutrients to stem and leaves - how?
3. two types of cells in xylem
a. tracheids
b. vessels
c. both dead at maturity, consist of cell walls,
d. form of thin, vertical tubes arranged end to end
e. open ends
f. solution of organic nutrients called xylem sap can flow through tubes from roots to
leaves.
g. plant roots exert push via inorganic ions, which cause water to diffuse in (osmosis)
pushing sap ahead of it: root pressure. may result in guttation (Fig. 36.11)
h. works for a few meters; some tall trees don’t use root pressure at all
4. xylem sap is pulled (Fig. 36.13) via tension - cohesion mechanism
a. transpiration- loss of water from leaves and other aerial parts of plants
b. cohesion - stickiness of water; this process works bc of special qualities of waterHydrogen bonding - weak bonds
c. adhesion - stickiness of water to other molecules - cellulose in xylem
d. steep diffusion gradient between interior of leaf and drier surrounding air
e. cohesion resists this, but not strong enough to overcome it - weak hydrogen bonds
f. works like a straw; adhesion resists gravity
g. called transpiration-cohesion-tension mechanism
5. guard cells control transpiration (Fig. 36.15)
a. transpiration works for and against plant
b. plant can lose a lot of water - what type of days? (evaporation) eg. a 60 foot maple
can lose 200l/hr on such a day
c. as long as water is present, no problem; if not, wilting and eventual death of plant
d. stomates help control water balance in leaf; flanked by guard cells
e. guard cells keep stomata open during day and closed at night - why?
f. How do guard cells work? K+ pump., cell walls not uniformly thick, cellulose oriented
horizontally
g. sunlight, low cell conc. of CO2, blue light receptors, circadian rhythms (bio. clock) in
plasma membrane of guard cells stimulates guard cells to take up K+
h. bio. clock, loss of H2O too fast close stomates
i. prevents wilting but decreases productivity
j. plant must balance need for water with need to make sugar
6. Phloem transports sugars, food molecules of the plant made by Ps.
a. food conducting cells are sieve tube members (stm’s) (Fig 36.18), sieve plate btn.
b. phloem sap = sugary solution w/ organic ions, amino acids and hormones too
c. sugar source
1) Ps
2) stored starch
d. sugar sink- sugar is stored or consumed - growing parts, fruits, and non Ps parts
e. storage structures (taproot of beet) may alternately be sources or sinks
f. how does sugar move? pressure flow mechanism
1) sugar moves by active transport into phloem cell
2) conc. gradient - water diffuses in.
3) sugars sink, pushed by water, followed by water (osmosis)
4) sugar moves at same rate as water
5) how do researchers study? aphids
Ch 36 objectives
1. Describe how proton pumps function in transport of materials across plant membranes, using the terms proton
gradient, membrane potential, cotransport, and chemiosmosis.
2. Define osmosis and water potential. Explain how water potential is measured.
3. Explain how solutes and pressure affect water potential.
4. Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have
higher, lower, or the same solute concentration.
5. Define the terms flaccid, plasmolyze, turgor pressure, and turgid.
6. Explain how aquaporins affect the rate of water transport across membranes.
7.
8. Distinguish between the symplast and the apoplast.
9. Describe three routes available for lateral transport in plants.
10. Define bulk flow and describe the forces that generate pressure in the vascular tissue of plants.
11. Relate the structure of sieve-tube cells, vessel cells, and tracheids to their functions in bulk flow
12. Explain what routes are available to water and minerals moving into the vascular cylinder of the root.
13. Explain how mycorrhizae enhance uptake of materials by roots.
14. Explain how the endodermis functions as a selective barrier between the root cortex and vascular cylinder
15. Describe the potential and limits of root pressure to move xylem sap.
16. Define the terms transpiration and guttation.
17. Explain how transpirational pull moves xylem sap up from the root tips to the leaves.
18. Explain this statement: “The ascent of xylem sap is ultimately solar powered.”
19. Describe the role of guard cells in photosynthesis-transpiration.
20. Explain how and when stomata open and close. Describe the cues that trigger stomatal opening at dawn.
21. Explain how xerophytes reduce transpiration.
22. Define and describe the process of translocation. Trace the path of phloem sap from a primary sugar source to
a sugar sink.
23.. Define pressure flow. Explain the significance of this process in angiosperms.