Botany - Bio 201
Spring Quarter
Written by: Sue Kloss
Lake Tahoe Community College
Instructor: Ralph Sinibaldi
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Chapter 5 and 6
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I. The functions and organization of shoot systems
A. Shoot functions
1. provide pathways of movement for food synthesized in leaves to move to roots
2. provide pathways of movement of water and dissolved minerals to move from roots to stems
B. a module is a segment of stem- an internode; point of attachment of leaves is a node
C. Shoot apical meristems (SAM) and primary meristems of the stem are located in buds
D. Some plants have secondary meristems further down their stems
E. 2 groups of flowering plants: monocots and dicots
II. Primary growth and stem anatomy
A. primary tissues of dicot stems develop from primary meristems
1. protoderm forms the epidermis
2. ground meristem forms the pith and cortex
3. procambium forms primary xylem and phloem; residual procambium
B. The distribution of the primary vascular bundles depends on the position of leaves
1. vascular bundles network into attached leaves through leaf traces
2. Phyllotaxis is the arrangement of leaves on axis of the stem
a. alternate, opposite, whorled and spiral phyllotaxis
C. Primary growth differs in dicot and monocot stems
1. in monocots, the term ground tissue is used for all the parenchyma tissue surrounding the scattered
vascular bundles; dicot stems have bundles arranged in a ring
2. in monocots, the primary thickening meristem (PTM) maintains the same diameter at stem base as at
apex
3. secondary growth in plant stems increases their width
III. Secondary growth and the anatomy of wood
A. herbaceous (nonwoody) plants (monocots and many dicots) normally complete their life cycle in one growing
season
B. Many other dicots are show secondary growth starting in their first years of growth; in woody plants this
continues for many or even hundreds of years
C. Secondary xylem and phloem develop from vascular cambium
D. Wood is composed of secondary xylem
1. wood sections are made in 3 different planes - tangential, radial, and transverse
2. annual rings are concentric rings of cells in the secondary xylem
a. cells of different diameters distinguish springwood from summerwood
b. ring porous wood has large-diameter vessels in mostly spring wood
c. diffuse porous wood has large diameter vessels in both spring and summerwood
d. in a transverse wood section, sapwood is lighter and functioning; heartwood is darker and
mostly nonfunctional; heartwood vessels are blocked by tyloses
E. Gymnosperm wood differs from angiosperm wood
1. gymnosperm wood is simpler than angiosperm wood; mostly tracheids, simple rays, and resin ducts;
rosin and amber are forms of resin
F. Bark is composed of secondary phloem and periderm
1. concept of bark includes everything between the vascular cambium and the outside of the wood stem
2. secondary phloem and its cell types forms to the outside of the vascular cambium
3. Cells in the outer cortex divide to form the cork cambium (or phellogen)
a. cork cambium divides in two directions: phellem or cork cells toward the outside and
phelloderm to the inside
b. periderm is composed of phellem, the cork cambium, and the phelloderm
c. periderm serves as an impermeable layer, inhibiting water evaporation and protecting inner
tissues from insect and pathogen invasion
d. lenticels are specialized regions of periderm where gases can be exchanged
e. new increments of periderm growth are initiated each growing season; cork oak
f. girdling is the removal of a strip of bark around the circumference of a tree
G. Buds are compressed branches waiting to elongate
1. most buds are covered with hard bud scales, modified leaves; they protect meristems
a. a terminal bud is at the end of a branch
b. lateral buds are found in the leaf axils on the sides of branches
c. flower buds produce flowers instead of leaves
d. bud scale scars are left on the stem when bud scales fall
H. Some monocots have secondary growth
1. most monocots lack a vascular cambium and do not form secondary xylem and phloem
Chapter 6
I. Functions of leaves
A. major functions of leaves are photosynthesis and transpiration
B. leaves are shaped to capture light
1. dicot and monocot leaves have similar functions but different basic design
2. leaves are simple or compound
a. leaves with single blade are simple leaves; form and margins may vary
b. compound leaves have blades divided into separate units called leaflets
c. leaves may palmately compound with leaflets diverging from a single point, or pinnately
compound, with leaflets arranged along an axis
3. the petiole
a. a narrow petiole attaches the leaf blade to the stem and its narrow base
b. by extending the leaf blade away from the stem, the petiole reduces the extent to which the
blade is shaded by other leaves
c. movement of a leaf blade on a petiole disrupts the boundary layer and provides fresh CO2 to
the leaf surface as well as cool the leaf
4. the sheath
a. monocot leaves lack petioles but have sheaths and sin some, a ligule and sometimes auricles
b. intercalary meristems at the base of grass leaves allow for continued mature leaf growth
5. leaf veins
a. leaf veins are actually vascular bundles
b. monocot leaves have parallel venation; dicots have netted venation
C. arrangement of leaf cells depends on their functions
1. epidermis covers the entire surface of the blade, petiole and leaf sheath
a. stomates are openings, each surrounded by two guard cells, that permit exchange of gases
between the environment and the internal cellular structure of leaves
b. stomates are more numerous on the bottom of the leaf than on the top
c. stomatal apparatus has guard cells plus their attached subsidiary cells
d. different types of trichomes occur as part of epidermal leaf surfaces
e. insectivores have specialized structures for snaring and digesting prey (Venus fly trap)
2. mesophyll contains photosynthetic cells
a. packed columnar palisade mesophyll parenchyma cells form the upper layer of mesophyll
b. irregularly shaped parenchyma cells with abundant air spaces between them make up the
spongy mesophyll
c. substomatal chamber is a large air space beneath each stoma that provides a place for
mesophyll cells to exchange gases from their evaporative surfaces
3. veins consist of vascular bundles that transport food and water
a. xylem conducts water and dissolved minerals from roots to leaves
b. phloem transports food made via photosynthesis in the mesophyll from leaves to the rest of
the plant
c. dicot leaves have a large diameter bundle, the midrib
d. xylem forms the upper part of the bundle, phloem makes up the lower part of the bundle;
xylem often has fibers around the outside of the bundle
e. usually a single layer of cells called the bundle sheath surrounds the vascular bundles; cells of
the bundle sheath load sugars into phloem and unload water and minerals out of the xylem
f. monocot leaves have several main bundles running parallel along the length of the leaf rather
than a single midrib with branches
g. C4 photosynthesis occurs in some grasses; this type operates at lower CO2 concentrations
and higher temperatures than regular photosynthesis
D. Where do new leaves come from?
1. leaves have their origin in meristems
a.
b.
c.
d.
young leaves forming early on the very tip of the SAM are crescent shaped bumps
in the early stages of development, they are called leaf primordia
a chemical signal may initiate a new leaf
leaf location depends on the plant’s phyllotaxis
II. leaf form and specialized leaves
A. a leaf’s form may depend on the plant’s age and on the environment
1. the first leaves that form are part of the embryo found in seeds- the cotyledons
2. having different leaf shapes on a single plant is heterophylly; ivy
a. one type of heterophylly is induced by the environment; some buttercups have thin an d
deep lobed water leaves that are much different from reduced lobed, thicker leafed air leaves
b. several tree species exhibit shade leaves that are thin with a relatively large surface area and
sun leaves that tend to be thicker and smaller
3. xerophyte plants grow successfully in dry climates
a. leaves are designed to conserve water, store water and insulate against heat; oleander is a
good example
b. leaves have sunken stomata and a thick cuticle
4. hydrophytes grow in moist environments
a. leaves tend to be thin, have a thin cuticle and are often deeply lobed
b. leaves always have an abundance of water and lack characteristics to conserve water
5. mesophytes are plants that are adapted to moderate climates; characteristics are similar to typical
leaf characteristics discussed in the text
6. some leaves are modified for special functions
a. spines are modified to protect against predators; leaves became spines in cactus and stipules
became spines in black locust
b. tendrils are modified leaflets that wrap around things and support; trumpet flower is an
example
c. bulbs are modified branches with a short thick stem and short thick storage leaves; table
onion is an example
d. environmental cues, such as cold temperature or short days are important cues for abscission
e. these cues induce hormonal changes that in turn affect the formation of the abscission zone;
leaves fall and decompose, their nutrients to be recycled
III. Commercially important fibers from leaves and stems
A. fibers from plants have been used for at least 10000 years
1. cotton fibers are really epidermal seed hairs
2. bundles of elongated schlerenchyma fibers are very strong
3. hard fibers occur in leaves of monocotyledonous plants such as agave
a. course fibers are woven into fabric or raided into ropes
b. manila hemp is used to make huge ropes, tea bags, lightweight fabric
4. soft fibers are found mostly in the stems of dicotyledonous plants
a. linen is from the flax plant
b. ramie has the longest fiber cells known and are stronger than cotton fibers; ramie is used for
clothing
Chapter 5 Lesson Objective/Homework
1. What are the 2 main functions of shoots?
2. What are the components of a module of a shoot?
3. What is the shoot apical meristem (SAM)?
4. What are the other 3 primary meristems found in most plants, and what tissues do they ultimately form?
5. What is plant phyllotaxis? Describe or draw the 4 main types.
6. How are annual rings formed in woody plants? What type of growth is this, and what types of plants exhibit this type of
growth?
7. Distinguish between heartwood and sapwood, and between ring porous and diffuse porous wood.
8. Distinguish between vascular cambium and cork cambium and describe the ways each lays down tissue. What is the
periderm and what is it composed of?
9. Distinguish between terminal, apical, lateral, and axillary buds.
Chapter 6 Lesson Objective/homework
1. What are the 2 major functions of leaves?
2. Distinguish between simple and compound leaves, and describes common types of each.
3. How do you distinguish between a leaf and a leaflet<
4. What is a petiole and what are its functions?
5. What is a sheath? What types of plants typically have sheaths? What are auricles and ligules?
6. What are leaf veins? What types of venation patterns are typical in most plants? Distinguish 2 major groups of plants
by their venation patterns.
7. Describe the types of cells that compose the epidermis. What is a stomate, how is it constructed and how does it
work?
8. What is leaf mesophyll typically composed of and what is the function of various layers? Draw and the interior of a leaf.
9. Describe or draw the structures making up the veins in a leaf. What is a bundle sheath?
10. Where do leaves have their origin? Describe or draw.
11. What are cotyledons? Distinguish between monocots and dicots. What types of plants are all monocots and dicots?
12. Describe a common type of heterophylly.
13. Describe or draw variations in leaf adaptations, depending on the environment of the plant. Distinguish between
xerophytes, mesophytes and hydrophytes.