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Chapter 31 Plant structure and function
1) 17.1 What is a plant?
a) Plants
i)
multicellular eukaryotes that make organic molecules
by photosynthesis
(1) problem: multicellular algae also fits this description
(a)plants adapted for terrestrial life
(b) multicellular algae
(i) supported by surrounding water
(ii) anchored by a hold fast
(iii)obtain CO2 and minerals from water
(iv) almost entire organisms can do photosynthesis
(c)plant adaptations
(i) part of body underground
(ii) hold itself upright (rigid cell walls)
(iii)obtain chemicals from air and soil
(iv) roots, stems, leaves
(v) roots
1. absorb water and nutrients (N, P, etc) from soil
2. provide anchorage
3. mycorrhizae enhance absorption in most plants
(vi) cutlicle
1. waxy covering of aerial parts that prevents
water loss (no gas exchange)
(vii)
stomata – for gas exchange
(viii)
vascular tissue
1. network of cells joined in narrow tubes
throughout body
2. twp types
a. xylem
i. dead cells forming microscopic pipes
ii. convery water and minerals up from roots
b. phloem
i. living cells that distribute sugars from
leaves throughout plant
3. neither type are in algae
(ix) plants must keep gametes from drying out in air
1. produce gametes in gametangia
a. protective jacket of cells surrounding
gamete-producing cells
b. egg is fertilized within the gametangium
c. sperm either swim to egg in film of water or
sperm arrive as sperm-producing cells in
pollen
(x) embryophytes
1. embryo develops attached to and nourished by
parents in all plants
2. not present in algae
3. embryo contained in seeds with food supply
a. most seed plants rely on wind and animals to
diseperse
(xi) some plants produce haploid spores with tough
walls to resist harsh environments
2) 17.3 Plant diversity provides a clue to the evolutionary history
of the plant kingdom
a) origin of plants from multicellular green algae (likely
Charophyceans)
b) Four major groups of plants (Figure 17.3A)
i)
non-vascular plants (bryophytes)
(1) mosses
(a)similarities to other plants
(i) have cuticle, embryo retained on parent
(b) differences
(i) no vascular tissue
(ii) generally
lack internal support provided by rigid
cell walls of vascular tissue
1. they hold each other up in tight mats (Fig.
17.3B)
(c)have flagellated sperm very similar to Charophyceans
(i) swim to eggs so moss must be covered with a film
of water
ii) vascular plants
(1) have xylem and phloem, which provide support
(a)upright, tall growth
(2) Seedless vacular plants
(a)ferns
(i) well-developed roots and rigid stems
(ii) leaves = fronds (Fig. 17.3)
1. sprout from stems that grow along ground
(iii)common in shady areas of forest and diverse in
tropics
(iv) flagellated sperm requiring layer of water
(v) rely on tough spores for disperal
1. spore = haploid cell that develops into haploid
multicellular organism without fusing with
another cell
(3) seed plants
(a) 90% of 280,000 species of plants today
(b) make seeds
(c)do not require a water layer for fertilization
(d) produce pollen instead of sperm
(e)pollen
(i) vehicle that transfers nonflagellated spermforming cells to female parts of plants
(ii) carried passively (wind or animals)
(f) pollination
(i) arrival of pollen at the female
(ii) fertilization occurs later
(g) Two types
gymnosperms
1. first to appear
2. gymnos = naked, sperma = seed (Greek)
a. naked because no made in specialized
chamber
3. pines, fir, spruce, etc… - seed-bearing cones
and needle-like leaves = largest group of
gymnosperms (conifers)
(ii) angiosperms
1. flowering plants
2. angeion = vessel, sperma = seed (Greek)
3. Flowers – complex reproductive structures
a. seeds develop within protective chambers
4. majority of modern plants (250,000 species)
are angiosperms
c) summary of key adaptations
i)
dependent embryos (all)
ii) vascular tissue
iii) seeds
iv) flowers
3) Chapter 31 Plant Structure and Function
a) angiosperms can be classified into two groups: monocot and
dicots
i)
names refer to the first leaves that appear on plant
embryo
ii) cotyledons
(1) embryonic leaves (seed leaves)
iii) monocots
(1) one seed leaf
(2) 65,000 species
(3) orchids, bamboos, palms, lilies, grains and other grasses
(4) leaves with parallel veins
(5) vascular bundles in stem arranged in complex array
(6) flowers have petals in multiples of three
(i)
(7) roots form a mat of threads – most in top few cm, great
for erosion prevention
iv) dicots
(1) two seeds leaves
(2) 170,000 species
(3) most shrubs and trees (except conifers)
(4) most ornamental plants and many food crops
(5) branched network of veins in leaves
(6) vascular bundles arranged in rings within stems
(7) flower petals in multiples of 4 or 5
(8) taproot
(a)large vertical root going deep into soil
b) plant body consists of roots and shoots
i)
root system
(1) anchors plant to soil
(2) absorbs minerals and water
(3) stores food
(4) root hairs
(a)near tip of roots
(b) increase surface area
(c)outgrowth of an epidermal cell
ii) shoot system
(1) made up of stems, leaves and adaptations for
reproduction
(2) stems – above ground part, support leaves and flowers
(a)trunk and branches of tree
(b) nodes
(i) point where leaves are attached
(c)internodes
(i) portion of stem b/w nodes
(3) leaves – main sites of photosynthesis
(a)solar panels
(b) some species have green, photosyn. stems
(c)Two parts
(i) blade
– attaches blade to stem
(4) Terminal bud
(a)at apex (tip) of stem
(5) axillary bud
(a)one at each angle formed by leaf and stem
(b) some will develop into shoots with own terminal bud
(c) some develop into shoots with flowers
(6) Apical dominance
(a) axillary bud inhibited in many plants by hormones
produced by terminal bud
(b) evolutionary adaptation to focus resources on
growing taller to get more light
(c) remove terminal bud and what may happern?
c) Many plants have modified roots and shoots
i)
storing food in modified roots
(1) carrots, turnips, sugar beets, sweet potatoes
(a)all unusually large tap roots storing starch
(b) use sugar during active growth (flowers and fruit)
(c)all have been artificially selected
ii) modified stems
(1) runners
(a)strawberry plant
(b) grow along ground surface
(c)means of asexual reproduction
(2) rhizomes
(a)store food
(b) have buds
(c)spread and form new plants
(3) tubers
(a)at end of some rhizomes
(b) food stored as starch
(c)white potato
(d) eyes of potato are dormant buds
iii) plant leaves
(1) long leaves without petioles
(ii) petiole
(a)grasses
and most monocots
(2) enormous petioles
(a)celery (dicot)
(3) tendril (Fig. 31.4C)
(a)modified leaf
(b) help plants climb
(4) spines of barrel cactus
(a)modified leaves for protection
(b) stem of cactus is adapted for photosyn and water
storage.
d) Plant cells are diverse in structure and function
i)
unique in several ways
(1) chloroplasts with chlorophyll a and b
(2) large vacuole filled with fluid to maintain tugidity
(firmness)
(3) cell wall
(a)mainly cellulose
(b) many have two-parts for structural support
(i) primary wall
(ii) secondary wall (more rigid)
1. b/w primary and PM
(4) middle lamina
(a)sticky layer that holds cell walls of adjacent cell
together
(5) pits
(a)regions where cell wall is unusually thin
(b) allow cells to get really close
(6) plasmodesmata
(a)channels of communication and circulation b/w cells
(b) found in pits
ii) Five major types of plants cells
(1) Parenchyma cells
(a)most abundant in most plants
(b) only primary/thin walls
(c)functions
food storage
(ii) photosynthesis
(iii)aerobic respiration
(d) often multisided (Fig. 31.5B)
(e) like stem cells of plant
(i) can divide and become other types of cells
(ii) great for repair
(2) Collenchyma cells (31.5C)
(a)also lack secondary walls
(b) unevenly thickened primary walls
(c)function
(i) provide support in parts of plant still growing
1. young stems have them just below surface
2. elongate with growing stem
(3) Sclerenchyma cells (31.5D)
(a)rigid secondary cell walls
(i) hardened with lignin
1. lignin = main chemical component of wood
(b) cannot elongate
(i) found in region that no longer grow in length
(c)most are dead when mature
(d) cells walls form rigid scaffold that support plant
(e)Two types of these cells
(i) fiber
1. long and slender, occurs in bundles
2. plants abundant in fiber cells commercially
important – hemp fibers to make rope
(ii) sclereid (stone cell)
1. shorter than fiber
2. thick, very hard secondary wall (stone)
a. nut shells and seed coats
b. scattered in pears – feel gritty when you eat
(4) Water conducting cells
(a)two types – both with rigid, lignin containing
secondary cell walls
(i)
both dead when mature
(i) tracheids
1. long with tapered ends
(ii) vessel elements
1. wider, shorter, and less tapered
(iii)function
1. xylem
a. chains of each type with overlapping ends
b. cells are hollow (dead)
c. water passes through the cells itself, they
don’t make a tube like blood vessels
d. hole in ends of cells allow continuous flow
2. support – thick, rigid walls
(5) Food-conducting cells (sieve-tube members)
(a)also arrange end to end
(b) very thin primary wall, no secondary wall
(c)remain alive at maturity
(d) lose nucleus, ribosomes and other organelles
(e)sieve plates
(i) ends perforated with large plasmodesmata
(f) function
(i) phloem – conduct sugar, other organic molecules
and some minerals
(g) each flanked by at least 1 companion cell
(i) connected by many plasmodesmata
(ii) makes certain proteins for sieve-tube member
iii) Tissue Level - cells grouped into tissues with specific
function like photosynthesis
(1) simple tissue
(a)made of one cell type
(i) parenchyma tissue
(2) complex tissue
(a)more than one cell type
(i) vascular tissue
(b)
xylem and phloem also have sclerenchyma
cells for support and parenchyma for storing
materials
e) Three tissue systems make up the plant body
i)
tissues combine to make tissue systems
ii) Roots, stems, and leaves are made of three tissue
systems
(1) epidermis
(2) vascular tissue system
(3) ground tissue system
iii) each tissue system continuous throughout plant
(1) epidermis (skin of plant)
(a)covers and protects leaves, young stems, young roots
(b) first line of defense against physical damage and
microorganisms
(c)cuticle
(i) waxy coating secreted by epidermal cells on
leaves and some stems
1. water retention
(2) vascular tissue system
(a) xylem and phloem
(b) provide support
(c)transport water and nutrients
(3) ground tissue system
(a)bulk of young plant
(b) fills spaces b/w epidermis and vascular tissue
(c)photosynthesis storage and support
(d) mostly parenchyma cells, but some collen- and
sclerenchyma
iv) Figure 31.6B – cross section through dicot (buttercup)
root
(1) cortex
(a)ground tissue of root
(b) mostly parenchyma tissue
(c)store food
1.
purple granules are starch
(d) endodermis
(i) innermost layer of cortex
(ii) one cell thick
(iii)selective barrier to vascular tissue (Chapter 32)
(2) minerals and water pass through layers to vascular tiss.
v)
Figure 31.6C – STEM of dicot (sunflower) vs.
monocot (corn)
(1) vascular bundles
(a) bunches of vascular tissue
(2) monocot
(a)vascular bundles distributed all around
(3) dicots
(a)bundles form ring around edge
(b) two-part ground tissue system
(i) cortex
(ii) pith
1. food storage
vi) Figure 31.6D – three tissue system in dicot leaves
(1) stomata
(a)pores in epidermis of leaves
(b) guard cells
(i) pair of epidermal cells that regulate size of
stomata
(c)allow gas exchange
(d) major avenue for water loss (remember CAM, C4
plants…)
(2) mesophyll
(a)ground tissue system of leaf
(b) mainly parenchyma with chloroplasts (photosyn)
(c)lower mesophyll
(i) loosely arranged, many air spaces
(ii) chief site of gas exchange
(iii)most stomata in lower epidermis (adaptation to
minimize water loss – sun hits top of leaf)
(i)
(3) vein
(a)a
vascular bundle
(i) xylem and phloem
(ii) sheath
1. parenchyma cells wrapping xylem and phloem
2. site of Calvin cycle in C4 plants (remember
that separation of light reactions and Calvin)
(iii)drop off water and minerals, pick up sugars
4) Plant growth
a) primary growth lengthens roots and shoots
i)
indeterminate growth
(1) grow as long as you live (most plants)
(2) increases exposure to sun and soil
(3) does NOT mean they are immortal
ii) determinant growth
(1) cease growth after reaching certain size (animals)
iii) animals MOVE through environment, plants GROW
through environment
iv) plant life span
(1) annuals
(a)complete life cycle in a single year or growing season
(b) grow, flower, seed, death
(c)wheat, corn, rice, wild flowers, etc…
(2) biennials
(a)complete life cycle in 2 years
(b) flower during second year
(c)beets and carrots (harvested in first year)
(3) perennials
(a)live and reproduce for many years
(b) trees, shrubs, some grasses
(c) some among oldest organisms alive
(i) some giant sequoias are 3000 years old
(ii) some shrubs reach 10,000 years old
v)
meristem (meristos = divide (greek))
(1) makes growth possible in plants
(2) local, unspecialized cells that divide
(3) apical meristems
(a)location
tips of roots
(ii) terminal and axillary buds
(b) primary growth
(i) lengthwise grow by apical meristems
(4) root growth
(a)Figure 31.7B – longitudinal section of onion root tip
(i) primary growth helps push root through soil
(ii) root cap
1. tip of root
2. protects apical meristem
3. roles of apical meristem in root (blue oval)
a. replace cells lost from root cap
b. produce cells for primary growth
(iii)zone of elongation
1. cells in this zone elongate in one direction
2. 10-fold increase in length
3. cellulose fibers expand apart as cells fill with
water (Fig. 31.7B) – expanding accordian
a. can’t expand in width, cellulose fibers do
not stretch well
4. what forces root down through soil
(iv) zone of differentiation
1. differentiation – caused by differential gene
expression
2. vascular cylinder differentiate into primary
xylem and phloem
3. epidermis and cortex take shape here
(5) shoot growth
(a)Figure 31.7C primary growth of a shoot
(i) apical meristem
(ii) zone of elongation just below meristem
(i)
pushes apical meristem upward (instead of
downward like the root)
(iii)some of apical meristem cells left behind
1. form the axillary meristems
(iv) differentiation into three tissue types occur below
zone of elongation
b) secondary growth – increases girth of woody plants
i)
how do stems and roots thicken?
ii) secondary growth
(1) increase in girth (thickening)
(2) obvious in woody plants (trees)
(a)stems consist mainly of thick layers of dead xylem
tissue (wood)
(3) two meristems (discussing a woody stem)
(a)vascular cambium (lateral meristem) (Fig. 31.8A)
(i) ring b/w primary xylem and primary phloem
(ii) cells added to either side of vasc. cambium
(iii)eventually gives rise to secondary xylem and
secondary phloem
(iv) wood
1. layers of secondary xylem are added year after
year
2. xylem cells with lignin rich walls
3. growth rings of a tree are layers of secondary
xylem
a. ringed because of interruptions (winter)
b. rings have two parts
i. spring wood – early xylem cells laid
down are usually larger and thinnerwalled (made in spring)
ii. summer wood – smaller, thicker walls
(made in summer)
(v) external to vascular cambium
1. cells are lost as quick as they are made
2. no accumulation over years
1.
cork cambium
(i) forms from parenchyma cells in cortex
(ii) produces cork
(iii)cork
1. replaces cortex and epidermis
2. mature cells are dead, thick/waxy walls
3. protect underlying cells
(iv) original cork cambium and cork are pushed
outward and sloughed off
(v) new cork cambium forms from parenchyma cells
in secondary phloem
(c)bark
(i) everything external to vascular cambium
(ii) secondary phloem, cork cambium, cork
(iii)youngest secondary phloem
1. next to vascular cambium
2. sugar transport
(iv) older secondary phloem dies along with cork
cambium
1. pushed outward and sloughed off
2. cork cambian keeps regenerating from young
secondary phloem
(d) logs – result of several decades of secondary growth
(i) living tissues
1. vascular cambium
2. youngest secondary phloem
3. cork cambium
4. cell in the wood rays
a. transport water to outer living tissue in trunk
(ii) heartwood
1. center of trunk
2. old layers of secondary xylem
3. no longer transport water
a. clogged with resins and other metabolic
byproducts – make resistant to rotting
(b)
(iii)sapwood
younger secondary xylem
2. conducts water
5) Plant reproduction
a) Overview: The sexual life cycle of a flowering plant
i)
flower
(1) structure specific to reproduction
(2) compressed shoot with modified leaves (petals, sepals,
stamens, carpels)
(3) sepals
(a)green, look more like leaves
(b) enclose and protect flower bud before opening
(4) petals
(a)bright and colorful
(b) advertise flower to pollinators
(5) reproductive organs of flower
(a)stamen
(i) male organs
(ii) anther
1. at tip of each stamen
2. site of meiosis where pollen grains develop
3. pollen house cells that develop into sperm
(b) carpel (can be more than one)
(i) female organ of flower
(ii) stigma
1. tip of carpel
2. receives pollen
(iii)ovary
1. base of carpel
2. houses ovules
(iv) ovule
1. contains developing egg and cells that support
it
(6) fertilization
1.
(a)occurs
in the ovule, then matures into a seed
containing embryo
(b) ovary develops into a fruit
(c)fruit
(i) protects seed
(ii) aids in dispersal
(7) germination
(a) begins to grow in suitable habitat
(b) embryo -> seedling -> mature plant
b) The development of pollen and ovules culminates in
fertilization
i)
all plants life cycles alternate between haploid (n) and
diploid (2n) generation (Chapter 17)
ii) all angiosperm and gymnosperms are diploid
iii) sporophyte
(1) diploid plant body
(2) produce special structures in which cells undergo
meiosis
(a)produce haploid spores
(i) gametophyte
1. produced by repeated mitosis of spores
2. the plants haploid generation
3. can think of this as a new organism
4. produces gametes by mitosis
5. fertilization occurs generating a new
sporophyte
6. microscopic in angio and gymnosperms
7. we can only see sporophyte and some pollen
(male gametophytes) by eye – yes, pollen is
haploid
iv) formation of male gametophytes = pollen grain
(1) occurs in anthers (Fig. 31.10)
(2) steps
(a)cell undergoes meiosis -> make 4 haploid cells
(spores)
a spore divides by mitosis forming
(i) one tube cell
(ii) one generative cell
(c)thick wall forms around these two cells (done)
v)
formation of the female gametophyte (Fig. 31.10)
(1) several ovules per ovary in most species
(2) ovule
(a)large central cell surrounded by smaller protective
cells
(b) central cell
(i) enlarges and undergoes meiosis
(ii) four haploid spores produced
(iii)3 degenerate
(iv) surviving cells enlarges, undergoes mitosis
producing embryo sac
(v) embryo sac
1. female gametophyte
2. contains
a. large central cell with two haploid nuclei
b. haploid egg cell
vi) pollination
(1) delivery of pollen to stigma of carpel
(a)animals or wind
vii) pollen grain germinates on stigma
(1) tube cell forms pollen tube
(2) generative cell divides by mitosis producing two sperm
(a)double fertilization
(i) one fertilized egg forming zygote
(ii) other contribute nucleus to central cell forming a
triploid nucleus (3n)
1. forms tissue that will nourish embryo
c) The ovule develops into a seed
i)
endosperm
(1) develops from the triploid (3n) cell
(2) nourishes embryo until it is self-supporting seedling
(b)
ii)
zygote
(1) divides into two cells
(2) one of cells continues division to become ball of cells
(embryo)
(3) other cell divides to form thread of cells
(a)pushes embryo into endosperm
iii) seed
(1) seed coat
(a)ovules coat lost most of water
(2) endosperm
(a)food supply for embryo
(3) seed dormancy
(a)embryo stops dividing and becomes dormant
(b) evolutionary adaptation to give time for dispersal
(i) begin growing when conditions favorable (temp.
and moisture)
(4) dormant embryo
(a)miniature root and shoot
(b) meristems
(c)three immature tissue types
(5) bean seed (Fig. 31.11B)
(a)cotyledons absorb endosperms nutrients during seed
formation
(6) corn kernal
(a)actually a fruit with one seed
(b) outer coating is dried fruit
(c)cotyledon absorb endosperm nutrients during
germination
(d) protective sheath around root and shoot
d) The ovary develops into a fruit
i)
fruit
(1) matured ovary
(2) houses and protects seeds, helps disperse them
(a)peach, orange, tomato, cherry, pea pod, corn kernel…
(3) Figure 31.12A – formation of pea pod
(a)pollination
petals drop
(c)ovary expands, walls thicken cued by hormonal
changes
(4) Fig. 31.12B – matches flower to pea pod
(a)wall of ovary  pod
(b) ovules (multiple)  seeds (peas)
(c) upper part of carpel
(d) sepals
(5) pods will become dry and brownish, split open
releasing peas
ii) fruits are sometimes more than developed ovaries
(1) apples
(a)core is the developed ovary (true fruit)
(b) part we eat develop from parts of flower base and
fuse with ovary
(i) becomes softer as enzymes weaken cell walls
(ii) change color
(iii)become sweeter as molecules like starch or
organic acids are converted to sugar
(iv) enticement to animals to help spread seeds
iii) simple fruits
(1) develop from a flower with a single carpel and ovary
(a)apples, pea pods, cherries
iv) aggregate fruit
(1) develops from a flower with many carpels
(a)raspberry
(i) each small part develops from a single ovary
v)
multiple fruit
(1) develops from group of separate flowers tightly
clustered
(a)walls of many ovaries fuse as they thicken
(i) pineapple
1. each part develops from separate flower
e) seed germination continues the life cycle (Fig. 31.13A)
(b)
i)
germination is NOT the beginning of life for a seed
ii) just resumes growth from dormancy
iii) usually begins with uptake of water
(1) seed expands, coat ruptures, metabolic changes
triggered
(2) enzymes in cotyledons or endosperm
(a)digest stored nutrients
(i) transported to growing regions of embryo
iv) root emerges first
v)
peas
(1) then embryonic shoot emerges
(a)hook shape to protect shoot tip (meristem)
(b) straightens with exposure to light
(c)foliage leaves emerge and begin photosynthesis
(2) cotyledons in peas
(a)food reserves during germination
(b) remain in soil and decompose
vi) corn
(1) no hook formed
(2) protective sheath pushes through soil instead
(3) shoot tip grows up through sheath tunnel
(4) cotyledon remain in soil and decompose
f) asexual reproduction produces plant clones
i)
vegetative reproduction (propagation)
(1) asexually reproduction in plants
(2) often involves fragmentation
(a)separation of parts from parent that regenerate into
new plants
(3) Figure 31.14A – garlic buld
(a)underground stem for storage
(b) single bulb fragments into several
(c)each is a clone
(4) Fig. 31.14B
(a) small trees are sprouts from roots of larger trees
(5) Fig. 31.14C
ring of plants is clone of creosote bushes – Mojave
desert
(6) Fig. 31.14D
(a)sprouting shoots and roots from runners
(i) many grasses can do this
ii) advantages
(1) make more of a successful geno/phenotype
(2) clones are hardier than seedlings, better chance of
survival
g) vegetative propagation is a mainstay of modern agriculture
i)
because plants reproduce asexually in nature, it is
cheap and easy to do it for agriculture, etc…
(1) most fruit trees, ornamental trees and shrubs, and
houseplants are propagated from stem or leaf cuttings
(2) other plants from root sprouts (like raspberries) or
pieces of underground stems (potatoes)
(3) In the lab
(a)Figure 31.15A
(i) apple seedling grown from a few meristem cells
(ii) make 1000s of copies from a single plant
1. orchids and pine trees for mass plantings
(b) protoplast fusion
(i) remove cells walls with enzymes
(ii) fuse two different species together and culture to
produce a hybrid plant
(c)introduce foreign genes into a parenchyma cell and
culture to a new plant (GMO’s)
ii) todays crops have little genetic variation
(1) cloning does not help this problem
(2) monocultures
(a)large areas of land with single plant variety
(3) small number of diseases could wipe us clean (irish
potato famine)
(a)
(a)gene
banks – storage sites for seeds just in case