Plant Physiology
Roots, Stems,
Leaves and Flowers
Plant Physiology

Physiology – understanding how
parts of an organism work
 We
will learn how roots, stems,
leaves and flowers all work
together to keep a plant alive
Plant Identification
 There
are two main categories
of angiosperms.
 Monocots – grasses, grain
crops, lilies, gladiolas, and
palm trees
Monocots
Mono = Single
 Cot = Short for cotyledon


Cotyledon = embryonic leaf
• Embryo = developing plant offspring
located in the seed
Monocots

Have four distinct features
 Veins in leaves are parallel to each other
 Flower parts are arranged in groups of
three
 Xylem and phloem are arranged in
bundles
 Single embryonic leaf
Vascular System

Xylem


Phloem


Transports water throughout the plant
Transports food (sugars) throughout
the plant
Cambium

Layer of cells that creates new xylem
and phloem
Monocot
Vein arrangement
Convallaria majalis (lily of the valley)
The major veins of monocot leaves are generally arranged
parallel to each other along the length of the leaf blade.
Plant Identification
 Dicots
- most of the other
plants such as the shrubs,
trees, and flowers.
• Veins in leaves are branched
• Flower parts are arranged in groups of
four or five
• Xylem and phloem are arranged in layers
• Two embryonic leaves
Dicot Leaf Venation
Helianthus (sunflower)
The major veins of dicot leaves are generally arranged in a netted (reticulate)
pattern that extends across and down the leaf.
Monocot and Dicot Leaf Venation
Convallaria majalis (lily of the valley)
Monocot
Parallel Leaf Venation
Helianthus (sunflower)
Dicot
Netted Leaf Venation
Monocot
Flower Parts
sepal
petal
stigma
stamen
Trillium
In most monocots, the flower parts are arranged in multiples of
three. This trillium flower has three sepals, three petals, six
stamens, and three stigmas on the pistil.
Dicot Flower Parts
petal
stamen
pistil
Cydonia oblonga (quince)
In most dicots, the flower parts are arranged in multiples of four or
five. These quince flowers have five petals, twenty stamens, and five
pistils. The stamens are too numerous to count in this image.
Monocot and Dicot Flower Parts
petal
sepal
petal
stamen
stigma
stamen
pistil
Trillium
Monocot
Flower Parts in Multiples
of Three
Cydonia oblonga (quince)
Dicot
Flower Parts in Multiples
of Four or Five
Roots
Functions of a root
 Water Absorption
• Most water enters the plant through the roots
 Anchorage
• Holds the plant in one place
 Reproduction
• Some roots allow for asexual reproduction
 Food
Storage
• Store sugars for later use
Roots
 The
type of root will normally
help you identify the plant. It will
place the plant into a monocot
or dicot category.
Types of Roots
 Tap
Root
 Have a main central root and
may have some lateral
branching
 E.g. Carrots

e.g. = exempli gratia = for the sake of example
Tap Roots
 Penetrate
the soil to various
depths - some only a few
inches, others like the
mesquite to as deep as 114
ft.
Tap Roots

Benefits of a tap root
Access deep water
 Hold plant in more securely
 Store larger quantities of sugars

Types of Roots
 Fibrous
 Have
many roots of equal
size and a lot of lateral
branching
 Fibrous roots are generally
much more dense and closer
to the surface
Types of Roots
 This
root system can
effectively prevent any other
plant from becoming
established – e.g.: grasses idea of a healthy lawn is to
compete with weeds
Types of Roots
 Prop
Roots augment regular
roots for
anchorage aid ex: corn - roots
come out above
soil and help
hold plant up
Parts of Roots
– Outer
layer of cells,
protecting inner cells
 Root Hairs – Small
hairs that grow from
the epidermis,
helping water
absorption and
holding root in place
 Epidermis
Parts of Roots
– Area of
storage in the root
 Cortex
Cylinder –
area that contains
xylem and phloem
tissues
 Vascular
Parts of a root

Root Cap – Layer of
cells that protect the
growing area of a root

Apical Meristem –
Meristem – point of new
cell development
 Apical – Tip (end of a
branch)

Why Different Types of
Roots
 All
plants are in competition with
each other for water and nutrients
 By having different types of roots,
the plants can reach different
depths in the soil and still live side
by side with other plants
Stems
Stems
 For
identification: type of stem
(woody or herbaceous),
monocot or dicot,
Monocot stem
phloem
xylem
Dicot stem
cortex
Primary vs
Secondary growth

Primary Growth

Growing from a specific location
• In woody stems, often at the ends of the
branches (apical meristem)
• In herbaceous stems, can be at end or at
the surface of the soil (e.g. grasses)

Secondary growth
• Growing wider around a trunk
Mature Structure of Woody
vs Herbaceous Stems
 Herbaceous
stems
 Lack secondary growth plants only live above ground
during the growing season
• Annuals – plants that live only
one growing season
Mature Structure of Woody
vs Herbaceous Stems
 Stems
remain soft and
flexible.
 Buds lack protective scales
(don’t need to survive harsh
conditions)
Mature Structure of Woody
vs Herbaceous Stems
 Woody
stems
 Plants
living and growing over
multiple seasons have
secondary growth (xylem,
phloem) increasing diameter
of the stems
Mature Structure of Woody
vs Herbaceous Stems
– Die at the end of the
growing season
 Annuals
• Fast, frequent reproduction, with
many seeds
– Live several
growing seasons
 Perennials
• Slower, less frequent
reproduction

Growing season
- The time of the year in which most of
the plant’s growth occurs
 - usually in the summer
 - can be other times

• Wet season
• Spring
• Fall
Specialized Stems
 Rhizomes
- underground
horizontal stems (ex: perennial
grasses, bamboo) - will grow a
plant and roots at a node.

Node – Any growth point on a stem or root

E.g. ‘eyes’ of a potato.
Specialized Stems
 Stolons
- runners - usually
above ground, horizontal
stems; will grow a plant and
roots at a node - ex:
strawberries
Specialized Stems
 Tubers
- several nodes at the
end of a rhizome (ex: potatoes)
- eyes are axillary buds – where
the tuber will grow a plant
Specialized Stems
 Bulbs
- large bud with small
stem at lower end - storage in
the form of numerous, fleshy
leaves - ex: onion, lily, tulip
 Corms - look like bulbs, but are
mostly stem tissue with a few,
papery leaves on the outside ex: gladiolus, crocus
Leaves
Leaves
 Leaves
are where plants
conduct photosynthesis to
produce most of it’s food.
 Leaves come in many shapes
and sizes
Parts of a Dicot Leaf
blade – expanded, usually
flat portion of a leaf
 Leaf
– connects the blade of
a leaf to a stem or branch –
holds leaf up for better air flow
and to catch the light
 Petiole
Parts of a Dicot Leaf
– threads of vascular
tissue (xylem & phloem)
 Node – place on a stem where
leaves or branches normally
attach
 Veins
Parts of a Leaf
 Midrib–
the primary vein that is
seen from the petiole to the tip
 Spine– Large veins that branch
from the midrib
 Margin– the edge of the leaf blade
 Base – The lower part of the blade,
where the petiole attaches
Midrib
Tip
Spines
Blade
Margin
Veins
Petiole
Base
Parts of a Monocot Leaf
– part of leaf that holds
leaf to stem – encases stem
 Ligule – membrane-like tissue
extending up from the sheath
(on inside) – keeps dirt and
moisture out – clear membrane
on leaf where attaches to stem
 Sheath
Blade
Sheath
Monocot Leaf
Node
Collar
Auricle
Stem
Ligule
Picture showing parts of a grass plant.
Two Types of Leaves
leaves – composed of a single
blade and a petiole
 Simple
Two Types of Leaves
leaves – are
composed of a blade that
includes several leaflets and a
petiole
 Compound

Two types:
Two Types of Leaves
Compound –
(chestnut) – the lobes or
divisions come together and
are attached at one place at
the base
 Palmately
Leaf
Blade
Palmately
Compound
Leaf
Petiole
Two Types of Leaves
Compound –
compound leaf with the leaflets
on two sides, usually along a
central vein – ex: ferns, ash,
hickory
 Pinnately
Leaflets
Leaf Blade
Petiole
Pinnately
Compound
Leaf
Leaf Arrangement
– have only one type
of arrangement – leaf comes off
of a node – ex: grasses and
grain crops
 Monocots
Leaf Arrangement
– flowering plants
 Alternate – one leaf per node
 Opposite – two leaves per node
 Whorled – three or more leaves
per node
 Dicots
Leaf Arrangements
Arrangement of Veins
 Four
types of vein arrangements:
 Parallel veins – veins are
small and run more or less
parallel – most are long and
narrow – ex: Buckhorn
Plantain, grasses and Iris –
mostly monocots
Arrangement of Veins
veins – are large and
small – the small ones
connecting to each other to
form a net – mostly dicots
 Netted
Arrangement of Veins
veined – with one
larger midvein and smaller
veins coming off along its
length – mostly dicots
 Pinnately
Arrangement of Veins
 Palmately
veined- with two
or more large veins arising at
or near the base of the leaf
blade (palm) – leaves are
usually broad or fat – mostly
dicots
Parallel Veins
Netted
Veins
Pinnately
Veined
Palmately
Veined
Monocot Leaf -Vein
Arrangement
Vein
Dicot Leaf – Vein
Arrangement
Smaller
lateral vein
Midvein
Leaf Structure
Leaf Structure

Epidermis – Tough outside layer of
cells that protect the inner cells

Divided into Upper epidermis and
Lower Epidermis
Leaf Structure
Upper Epidermis
Lower Epidermis
Leaf Structure

Stomata – Openings in the leaf that
allow the passage of CO2 and water

Stomata can open and close based
on the needs of the plant

They will typically stay closed when
the plant needs to retain moisture, and
will open up when there is enough
water available
Leaf Structure

Stomata open and close due to cells
on the edge of the stomata called
guard cells

Guard cells open and close the
stomata by allowing water to enter
and leave, causing them to swell or
shrink
Leaf Structure
Upper Epidermis
Guard Cells
Stomata
Lower Epidermis
Leaf Structure

Palisade Cells

Elongated cells where most
photosynthesis takes place

Why are they elongated vertically, and
not horizontally?
Leaf Structure
Upper Epidermis
Palisade Cells
Guard Cells
Stomata
Lower Epidermis
Leaf Structure

Spongy Mesophyll

Water storage area of the leaf

Helps to transport wastes out of the
leaf through the stomata
Leaf Structure
Upper Epidermis
Palisade Cells
Spongy Mesophyll
Guard Cells
Stomata
Lower Epidermis
Leaf Structure

Vascular System
Xylem – Transports water from roots
to the leaves (water is necessary for
photosynthesis)
 Phloem – Transports sugars from the
leaves to the rest of the plant

Leaf Structure
Upper Epidermis
Palisade Cells
Spongy Mesophyll
Guard Cells
Stomata
Vascular System
Lower Epidermis
Flowers
– are highly colored portions of
the flower.
 May contain perfume (rose) or
nectar glands –to attract pollinators.
 Number of petals on a flower is
often used in the identification of
plant families and genera.
 Petals
Flowers
–have sepals and/or
petals in multiples of four or
five
 Monocots – have sepals in
multiples of threes
 Dicots
Parts of a Flower
Sepals
Petals
Stamens (anther
& filaments)
Pedicel
Pistil
(stigma,style &
ovaries)
Seeds
Monocot seeds
Contain the embryo (infant plant)
 Cotyledon (part of the embryo)
 Seed Coat (protects the embryo)
 Endosperm (provides nutrients to the
embryo )
 Radicle – The embryonic root tip

Monocot Seed
Dicot Seed