Plant StructuresLeaves, Roots and

StemsObjectives

1.Describe the structure and function of leaves 2.Describe the structure and function of roots

3.Describe the function of stems

Quick review...The kingdom Plantae is divided into two key

‘sub-kingdoms’ – plants that non-vascular (eg.??) and those that are

Vascular plants are further divided into plants that produce no seeds (eg.??) and those that do – Superdivision Spermophyta

Spermophyta is again divided into further divisions commonly known as angiosperms and gymnosperms (now renamed eg. Coniferophyta and magnoliophyta)

• Spermophyta is again divided into further divisions commonly known as angiosperms and gymnosperms (now renamed eg. Coniferophyta and magnoliophyta)

• Angiosperms used to fall into two major groups – dicots and monocots depending on how many cotyledons the seeds contained. Now there are four groups but the main two are monocots and eudicots (true dicots)

• More than 2/3 of angiosperms are eudicots (e.g. Dandelions) and ¼ are monocots (e.g. Grasses)

Leaves...All leaves are responsible for:

• Absorbing energy from the sun in organelles called ___________

• The majority of photosynthetic production (which can take place in any green part of a plant; eg. Cactus),

• Taking in ____________and releasing __________ and water vapour (gas exchange)

• Offering protection from_______________

• Using osmotic pressure to draw water up from the _______________

Parts of the leaf

Blade: Flattened area of leaf.Petiole: Stalk-like structure that attaches leaf blade to stem.Midrib and veins: Contains the vascular tissue.

*there are many different types of leaves – simple, compound, etc.

** monocots have parallel veins and dicots have branching veins

Photosynthesis

1. Leaves are the major site for photosynthesis

Chlorophyll, found in chloroplasts, is the most common Photopigment, which captures the red and blue lightwaves (they reflect green light) from the sun to make food (sugar).

Photosynthesis is the process in which carbon dioxide (CO2) and water (H2O) are used to produce  carbohydrates and oxygen (O2) in the presence of light and chlorophyll.

Stomata• Photosynthesis require a constant supply of

carbon dioxide. The product of this process – oxygen – must be released.

• Gas exchange in plants occurs in the leaves and is regulated by small pores called stomata.

Typical internal leaf structure

Epidermal Cells

• Tightly packed in a single layer covered by a waxy coating called the cuticle.

• Cuticle: – Prevents water loss– Provides a physical barrier against bacteria,

mould and insects.

• Don’t contain chloroplasts.• But are transparent so light can pass through.

Mesophyll• Located in the mid region of the leaf.• Primary site of photosynthesis in the leaf.• There are two types:1. Palisade mesophyll (note how the cells are

shaped): These cells contain many chloroplasts. Primary site for photosynthesis.

2. Spongy mesophyll (note the irregularly shaped and spaced cells): These cells have fewer chloroplasts. There are many air spaces which allows carbon dioxide to diffuse into cells and oxygen out of cells.

Stoma (stomata)• An opening in the epidermis of a leaf (on the

underside of the leaf in land plants) through which gases pass out and in. It also regulates water loss

• In vascular aquatic plants (e.g. Water lilies) stoma are on the upper epidermis

• Water plants that do not float have no stomata

Stomata continued.....• When stomata are open water is lost

(transpiration) and the plant can exchange oxygen for carbon dioxide through diffusion.

• When stomata are closed the plant conserves water, but can not exchange gases.

• Guard cells located on either side of the stomata regulate the opening and closing of the stomata (open in sunlight and high humidity).

Leaf adaptation/specialization

• Evolution favours plants with leaves adapted to their environment (abiotic)

• Eg. Conifers have thin leaves (needles) to shed snow readily and conserve water; evergreen for short growing season

• Eg. Cacti grow in low rainfall areas – have very reduced leaves (spines) for minimal water loss and very few stomata

• Leaves are vulnerable to being eaten – evolution favours plants with leaves that are less appealing (two main types of defenses – structural and chemical)

• Eg. Leaves that are hairy or modified into spikes like a cactus.

Chemical defense is most common

Eg. Nicotine in tobaccoToxin in milkweedHydrangeaPoison Ivy

Other leaf specializations

• Onion bulb – has modified leaves for water and nutrient storage

• Aloe vera – fleshy leaves to store water

• Sundew leaves – sticky to trap insects

StemsStems are responsible for:

•supporting leaves and flowers physically •Connect the vascular tissue in the leaves to the vascular tissue in the roots.•using xylem and phloem to transport water and nutrients to and from leaves, roots, and reproductive parts like flowers, fruit and seeds.•storing water and nutrients for future use (parenchyma)

Vascular System in Roots• Located at the centre of each root.• Vascular cylinder called a stele contains xylem

and phloem.• A layer of cells called the endodermis surrounds

the vascular tissue and regulates the movement of water and minerals

Stem Structure• Herbaceous plants: Stems don’t contain wood– Vascular bundles (arrangements of vascular

tissue) consists of xylem and phloem– These bundles run from leaves to roots

• Woody plants: Stems contain wood– Vascular cambium: a layer of tissue that separates

xylem from phloem. Produces xylem and phloem– Phloem is on the inside and xylem is on the

outside– ‘Wood’ is actually many layers of xylem cells.

Major Tissues in Stems

Woody Stems (note: pith and cortex contain parenchyma tissue)

More Stem Structures

• Bark: Protective outer layer.– Consists of phloem, cork cambium and cork

• Cork cambium: Layer between layers of bark– Produces cork

• Every year the vascular cambium produces layers of xylem and phloem. (Growth rings)

Plenary...

• Transport in Plants (Take up homework.)• Complete all the questions on the hand out.• There WILL be a quiz on this tomorrow!!!!

RootsRoots are responsible for: •Anchoring the plant to the ground •Extracting water and minerals from the soil • Storage of food (carbohydrates or sugar)

In a typical root we can distinguish the following parts:1. Primary root – first root development from the seed2. Secondary roots – smaller root branches growing sideways from the primary root3. Root cap – a protective cap covering the growing region of the root tip. It is designed to drill the soil and it is able to guide the root growth by perceiving gravity.4. Root hairs - are microscopic extension of the epidermal cells near the tip of a root. They absorb water and nutrients from the soil.