1. Plant Structure, Growth, and Development
Chapter 35 & 36

2. The Cells and Tissues of the Plant Body
Cells of angiosperm embryos differentiate early in development into 3 distinct tissues:
A.  Dermal Tissue: forms the outside covering of plants
Epidermis
Cuticle
Cork
Bark
Stomata
B.  Ground tissue: for storage, metabolism and support. Mostly parenchyma, with specialized support cells of collenchyma and sclerenchyma
C. Vascular tissue: phloem and xylem consists of special conducting cells, along with support fibers & parenchyma

3. The Three Tissue Systems: Dermal, Vascular, and Ground
Figure 35.8
Dermal
tissue
Ground
Vascular

4. “Ground” tissue:
Includes various cells specialized for functions such as storage, photosynthesis, and support
parenchyma: cells which occur in all 3 tissue systems, usually photosynthesis, elongated, loosely packed, thin, flexible cell walls
collenchyma: primary wall (in cells) thickened at corners, irregular shapes, provide support
sclerenchyma: 2 types, support and strengthen the plant, thick, even cell walls, dead cells provide framework for additional cells    1. fibers- elongated, elastic strands or bundles associated with the vascular tissue    2. sclereids- form hard outer covering of seeds, nuts, and fruit stones

5. Parenchyma, collenchyma, and sclerenchyma cells
Figure 35.9
Parenchyma cells
60 m
PARENCHYMA CELLS
80 m
Cortical parenchyma cells
COLLENCHYMA CELLS
Collenchyma cells
SCLERENCHYMA CELLS
Cell wall
Sclereid cells in pear
25 m
Fiber cells
5 m

6. Vascular Tissue Xylem Phloem
Conveys water and dissolved minerals upward from roots into the shoots
Phloem
Transports organic nutrients from where they are made to where they are needed

7. Water-conducting cells of the xylem and sugar-conducting cells of the phloem
Figure. 35.9
WATER-CONDUCTING CELLS OF THE XYLEM
Vessel
Tracheids
100 m
Tracheids and vessels
element
Vessel elements with
partially perforated
end walls
Pits
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Companion cell
Sieve-tube
member
Sieve-tube members:
longitudinal view
Sieve
plate
Nucleus
Cytoplasm
Companion
cell
30 m
15 m

8. Vascular tissue Transports nutrients throughout a plant; such transport may occur over long distances
Figure 36.1

9. A variety of physical processes
Are involved in the different types of transport
Sugars are produced by
photosynthesis in the leaves. 5
Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for
photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration. 4
CO2 O2
Light
H2O
Sugar
Transpiration, the loss of water
from leaves (mostly through
stomata), creates a force within
leaves that pulls xylem sap upward. 3
Sugars are transported as
phloem sap to roots and other
parts of the plant. 6
Water and minerals are
transported upward from
roots to shoots as xylem sap. 2
Roots exchange gases
with the air spaces of soil,
taking in O2 and discharging
CO2. In cellular respiration,
O2 supports the breakdown
of sugars. 7
Roots absorb water
and dissolved minerals
from the soil. 1 O2
H2O
CO2
Minerals
Figure 36.2

10. Transpiration is the evaporation of water from plant leaves
Plants lose a large amount of water by transpiration
If the lost water is not replaced by absorption through the roots
The plant will lose water and wilt
Turgor loss in plants causes wilting
Which can be reversed when the plant is watered
Figure 36.7

11. XYLEM: Several factors are at work in the movement of water and minerals up a plant stem
To survive
Plants must balance water uptake and loss
Water is pulled upward by negative pressure in the xylem, caused by losses by transpiration
Cohesion
Adhesion
Osmosis
Determines the net uptake or water loss by a cell
Is affected by solute concentration and pressure
Water potential
Is a measurement that combines the effects of solute concentration and pressure

12. PHLOEM Organic nutrients are translocated through the phloem
Translocation
Is the transport of organic nutrients in the plant
Phloem sap
Is an aqueous solution that is mostly sucrose
Travels from a sugar source to a sugar sink
A sugar source
Is a plant organ that is a net producer of sugar, such as mature leaves
A sugar sink
Is an organ that is a net consumer or storer of sugar, such as a tuber or bulb

13. Phloem
The pressure flow hypothesis explains why phloem sap always flows from source to sink
Experiments have built a strong case for pressure flow as the mechanism of translocation in angiosperms
Aphid feeding
Stylet in sieve-tube
member
Severed stylet
exuding sap
Sieve-
Tube
EXPERIMENT
RESULTS
CONCLUSION
Sap droplet
Stylet
Sap
droplet
25 m
Sieve- tube member
To test the pressure flow hypothesis,researchers used aphids that feed on phloem sap. An aphid probes with a hypodermic- like mouthpart called a stylet that penetrates a sieve-tube member. As sieve-tube pressure force-feeds aphids, they can be severed from their
stylets, which serve as taps exuding sap for hours. Researchers measured the flow and sugar concentration of sap from stylets at different
points between a source and sink.
The closer the stylet was to a sugar source, the faster the sap flowed and the higher was its sugar concentration.
The results of such experiments support the pressure flow hypothesis.
Figure 36.19

14. Reproductive shoot (flower)
The Plant Body
Three basic organs evolved: roots, stems, and leaves
They are organized into a root system and a shoot system
Figure 35.2
Reproductive shoot (flower)
Terminal bud
Node
Internode
Terminal
bud
Vegetative
shoot
Blade
Petiole
Stem
Leaf
Taproot
Lateral roots
Root
system
Shoot
Axillary

15. Growth in Meristems
When plants grow, they add new cells (cells divide by mitosis) at the tips/ends of branches and roots
Apical meristems
Are located at the tips of roots and in the buds of shoots
Elongate shoots and roots through primary growth
Lateral meristems
Add thickness to woody plants through secondary growth

16. The Root Is an organ that anchors the vascular plant Anchors the plant
Absorbs minerals and water
Often stores organic nutrients
Figure 35.3
In most plants:
The absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root

17. Many plants have modified roots
Figure 35.4a–e
(a) Prop roots
(b) Storage roots
(c) “Strangling” aerial roots
(d) Buttress roots
(e) Pneumatophores

18. Primary Growth of Roots
The root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growth
Figure 35.12
Dermal
Ground
Vascular
Key
Cortex
Vascular cylinder
Epidermis
Root hair
Zone of
maturation
elongation
Zone of cell
division
Apical
meristem
Root cap
100 m

19. Taproot and Fibrous Root Systems
dicot monocot

20. Stems A stem is an organ consisting of
An alternating system of nodes, the points at which leaves are attached
Internodes, the stem segments between nodes

21. STEMS
1) hold leaves up and aloft for maximum sun exposure 2) transport nutrients/water up/down (connects leaves to roots) 3) some stems store food
Figure 35.11
This year’s growth
(one year old)
Last year’s growth
(two years old)
Growth of two
years ago (three
years old)
One-year-old side
branch formed
from axillary bud
near shoot apex
Scars left by terminal
bud scales of previous
winters
Leaf scar
Stem
Bud scale
Axillary buds
Internode
Node
Terminal bud

22. Many plants have modified stems
Figure 35.5a–d
Rhizomes. The edible base
of this ginger plant is an example
of a rhizome, a horizontal stem
that grows just below the surface
or emerges and grows along the
surface.
(d)
Tubers. Tubers, such as these
red potatoes, are enlarged
ends of rhizomes specialized
for storing food. The “eyes”
arranged in a spiral pattern
around a potato are clusters
of axillary buds that mark
the nodes.
(c)
Bulbs. Bulbs are vertical,
underground shoots consisting
mostly of the enlarged bases
of leaves that store food. You
can see the many layers of
modified leaves attached
to the short stem by slicing an
onion bulb lengthwise.
(b)
Stolons. Shown here on a
strawberry plant, stolons are horizontal stems that grow
along the surface. These “runners”
enable a plant to reproduce
asexually, as plantlets form at
nodes along each runner.
(a)
Storage leaves
Stem
Root
Node
Rhizome

23. Tissue Organization of Stems
In gymnosperms and most dicots
The vascular tissue consists of vascular bundles arranged in a ring
Figure 35.16a
Xylem
Phloem
Sclerenchyma (fiber cells)
Ground tissue connecting pith to cortex
Pith
Epidermis
Vascular bundle
Cortex
Key
Dermal
Ground
Vascular
1 mm
(a) A eudicot stem. A eudicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section)

24. In most monocot stems
The vascular bundles are scattered throughout the ground tissue, rather than forming a ring
Ground tissue
Epidermis
Vascular bundles
1 mm
(b) A monocot stem. A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section)
Figure 35.16b

25. Secondary growth adds girth to stems and roots in woody plants
Secondary phloem
Vascular cambium
Late wood
Early wood
Secondary
xylem
Cork
cambium
Periderm
(b) Transverse section of a three-year- old stem (LM)
Xylem ray
Bark
0.5 mm
Figure 35.18b

26. As a tree or woody shrub ages The older layers of secondary xylem, the heartwood, no longer transport water and minerals The outer layers, known as sapwood Still transport materials through the xylem
Growth ring
Vascular
ray
Heartwood
Sapwood
Vascular cambium
Secondary phloem
Layers of periderm
Secondary
xylem
Bark

27. The main photosynthetic organs of most vascular plants
Leaves
The main photosynthetic organs of most vascular plants

28. Leaves generally consist of
A flattened blade and a stalk
The petiole, which joins the leaf to a node of the stem

29. In classifying angiosperms
Taxonomists may use leaf morphology as a criterion
Figure 35.6a–c
Petiole
(a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf.
(b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base.
(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.
Axillary bud
Leaflet

30. Monocots and dicots
Differ in the arrangement of veins, the vascular tissue of leaves
Most dicots
Have branching vein “network”
Most monocots
Have parallel veins

31. Some plant species
Have evolved modified leaves that serve various functions
Figure 35.6a–e
(a) Tendrils. The tendrils by which this pea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.
(b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems.
(c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.
(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.
(e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.

32. Cutaway drawing of leaf tissues
Leaf anatomy
Key
to labels
Dermal
Ground
Vascular
Guard
cells
Stomatal pore
Epidermal
cell
50 µm
Surface view of a spiderwort
(Tradescantia) leaf (LM)
(b)
Cuticle
Sclerenchyma
fibers
Stoma
Upper
epidermis
Palisade
mesophyll
Spongy
Lower
Vein
Xylem
Phloem
Bundle-
sheath
Cutaway drawing of leaf tissues
(a)
Air spaces
Guard cells
100 µm
Transverse section of a lilac
(Syringa) leaf (LM)
(c)
Figure 35.17a–c

33. Leaf anatomy
The outer surface of the leaf has a thin waxy covering called the cuticle. This layer's primary function is to prevent water loss within the leaf. (Plants that leave entirely within water do not have a cuticle).
Directly underneath the cuticle is a layer of cells called the epidermis.
The vascular tissue, xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells called bundle sheath cells, and they create a circle around the xylem and the phloem. In most veins, xylem is the upper layer of cells and the lower layer of cells is phloem. Recall that xylem transports water and phloem transports sugar (food).
Within the leaf, there is a layer of cells called the mesophyll. The word mesophyll is Greek and means "middle" (meso) "leaf" (phyllon). Mesophyll can then be divided into two layers, the palisade layer and the spongy layer.
Palisade cells are more column-like, and lie just under the epidermis,
the spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis. The air spaces between the spongy cells allow for gas exchange.
Mesophyll cells (both palisade and spongy) are packed with chloroplasts, and this is where photosynthesis actually occurs.

34. stomata
Stomata are microscopic pores found on the under side of leaves. You will find the stomata in the epidermal tissue. The stomata is bounded by two half moon shaped guard cells that function to vary the width of the pore.

35. Stomata help regulate the rate of transpiration
About 90% of the water a plant loses escapes through stomata
open
Increase photosynthesis
Increase water loss through stomata
closed
Decrease water loss through transpiration
Decrease gas exchange and reduce photosynthesis
20 µm
Figure 36.14