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