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 featuresVeins in leaves are parallel to each otherFlower parts are arranged in groups of
threeXylem and phloem are arranged in
bundlesSingle embryonic leaf
Vascular System
XylemTransports water throughout the plant
PhloemTransports food (sugars) throughout
the plant Cambium
Layer of cells that creates new xylem and phloem
Vein arrangementMonocot
The major veins of monocot leaves are generally arranged parallel to each other along the length of the leaf blade.
Convallaria majalis (lily of the valley)
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.
Helianthus (sunflower)
MonocotParallel Leaf Venation
DicotNetted Leaf Venation
Monocot and Dicot Leaf Venation
Convallaria majalis (lily of the valley)
Flower PartsMonocot
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.
Trillium
petal
sepal
stamen
stigma
Dicot Flower Parts
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.
Cydonia oblonga (quince)
petal
pistil
stamen
Monocot and Dicot Flower Parts
MonocotFlower Parts in Multiples
of Three
DicotFlower Parts in Multiples
of Four or Five
petal
sepal
stamen
stigma
Trillium
petal
pistil
stamen
Cydonia oblonga (quince)
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 rootAccess deep waterHold plant in more securelyStore larger quantities of sugars
Types of Roots
FibrousHave 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 Epidermis – Outer
layer of cells, protecting inner cells
Root Hairs – Small hairs that grow from the epidermis, helping water absorption and holding root in place
Parts of Roots
Cortex – Area of storage in the root
Vascular Cylinder – area that contains xylem and phloem tissues
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 RootsAll plants are in competition with
each other for water and nutrientsBy 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
Dicot stem
xylem
phloem
cortex
Primary vs Secondary growth
Primary GrowthGrowing 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 StemsHerbaceous 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
Annuals – Die at the end of the growing season• Fast, frequent reproduction, with
many seeds
Perennials – Live several growing seasons• 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
LeavesLeaves are where plants
conduct photosynthesis to produce most of it’s food.
Leaves come in many shapes and sizes
Parts of a Dicot Leaf
Leaf blade – expanded, usually flat portion of a leaf
Petiole – connects the blade of a leaf to a stem or branch – holds leaf up for better air flow and to catch the light
Parts of a Dicot Leaf
Veins – threads of vascular tissue (xylem & phloem)
Node – place on a stem where leaves or branches normally attach
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 bladeBase – The lower part of the blade,
where the petiole attaches
Base
Blade
Petiole
Midrib Spines
Veins
Margin
Tip
Parts of a Monocot Leaf
Sheath – 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
Node
Collar
Auricle
Ligule
Stem
Monocot Leaf
Picture showing parts of a grass plant.
Two Types of Leaves
Simple leaves – composed of a single blade and a petiole
Two Types of Leaves
Compound leaves – are composed of a blade that includes several leaflets and a petiole Two types:
Two Types of Leaves
Palmately Compound – (chestnut) – the lobes or divisions come together and are attached at one place at the base
Palmately Compound Leaf
Leaf Blade
Petiole
Two Types of Leaves
Pinnately Compound – compound leaf with the leaflets on two sides, usually along a central vein – ex: ferns, ash, hickory
Pinnately Compound Leaf
Leaf Blade
Leaflets
Petiole
Leaf Arrangement
Monocots – have only one type of arrangement – leaf comes off of a node – ex: grasses and grain crops
Leaf Arrangement
Dicots – flowering plantsAlternate – one leaf per nodeOpposite – two leaves per nodeWhorled – three or more leaves
per node
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
Netted veins – are large and small – the small ones connecting to each other to form a net – mostly dicots
Arrangement of Veins
Pinnately veined – with one larger midvein and smaller veins coming off along its length – mostly dicots
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
Dicot Leaf – Vein Arrangement
Vein
Midvein
Smaller lateral vein
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 plantThey 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
Lower Epidermis
Stomata
Guard Cells
Leaf Structure
Palisade CellsElongated cells where most
photosynthesis takes place
Why are they elongated vertically, and not horizontally?
Leaf Structure
Upper Epidermis
Lower Epidermis
Stomata
Guard Cells
Palisade Cells
Leaf Structure
Spongy MesophyllWater storage area of the leaf
Helps to transport wastes out of the leaf through the stomata
Leaf Structure
Upper Epidermis
Lower Epidermis
Stomata
Guard Cells
Palisade Cells
Spongy Mesophyll
Leaf Structure
Vascular SystemXylem – 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
Lower Epidermis
Stomata
Guard Cells
Palisade Cells
Spongy Mesophyll Vascular System
Flowers
Petals – 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.
Flowers
Dicots –have sepals and/or petals in multiples of four or five
Monocots – have sepals in multiples of threes
Parts of a Flower
Petals
Stamens (anther & filaments)
Pistil (stigma,style & ovaries)
Sepals
Pedicel
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