Roots, Stems, and LeavesPrinciples of Life ScienceRainier Jr/Sr High SchoolMr. Taylor

Plant Cell TypesLevels of Organization Concept Review:

◦There are many different types of cells and plants have 3 basic types of cells

◦Tissues are made of groups of similar cells that perform a specific function for an organism. Plants have 3 basic types of tissues.

◦Organs are made of different tissues that do a general function for an organism. An example in plants would be a stem or a root.

◦Organisms are made of organ systems made from different organs.

Plant Cell TypesThere are 3 basic cell types in

plants:◦Parenchyma cells:

The most common type of cell Thin walls and large central vacuoles Many have chloroplasts Many have storage vacuoles for starch

and other products of photosynthesis. Continue to divide throughout plant’s life:

can heal wounds or start a new plant from a cutting.

Plant Cell TypesThere are 3 basic cell types in

plants:◦Collenchyma cell:

Cell walls may be thin or thick, but remain flexible.

Provide support while a plant is growing.

Plant Cell TypesThere are 3 basic cell types in

plants:◦Sclerenchyma cells:

Have a cell wall hardened by lignin so they are very strong!

Once mature, these cells do not grow; in fact they often become hollow cells connected to their neighbors

If found in the vascular system of a plant, they provide the rigid tubes that carry materials throughout the plant.

Roots, Stems, and Leaves are only found in vascular plants and are made of 3 basic kinds of tissue:◦Dermal tissue◦Ground tissue◦Vascular tissue

Dermal TissueForms on outer/external surfaces

of plants◦Epidermis: often a single layer of flat

cells.◦Cuticle: a waxy covering to reduce

water loss.◦Plant hairs: on leaves it slows water

loss, on roots it increases surface area

◦Stomata: openings flanked by guard cells that allow for H2O and CO2 exchange.

◦Dead cells make the outer bark of a plant.

Ground TissueA variety of thick- and thin-walled

cells making up the bulk of plant tissue◦This tissue is surrounded by dermal

tissue.◦Thin-walled in leaves carry on

photosynthesis◦Thick-walled often aid in support and

protection (cactus spines are an example). Also serve as storage for water, nutrients, and food.

Vascular TissueCells stack end-to-end to form

little pipes.◦Xylem: thick-walled and conduct

water and minerals. The cells are dead sclerenchyma cells.

◦Phloem: thinner-walled; transport food (sugars) and other nutrients. The cells are living parenchyma cells.

Vascular Tissue: XylemXylem moves water and

dissolved minerals by the cohesion-tension theory.◦Water molecules are attracted to

each other (hydrogen bonding): force is called cohesion.

◦Water molecules are attracted to other materials (xylem walls; by hydrogen bonding, too); force is called adhesion.

◦Transpiration (the loss of water through stomata in the leaves) creates a vacuum in the xylem that pulls water up into the plant.

Vascular Tissue: PhloemPhloem is a living tissue of mostly

sieve-tube elements (a type of parenchyma cell).◦Movement of sugars and starches can

be either from storage or to storage according to the pressure-flow model. Loading of sugars and starches from an area

of high concentration into sieve-tubes (phloem) uses plant energy.

Once loaded into the phloem, movement of the materials is by diffusion to areas of low nutrient concentration.

RootsFunction to

◦Anchor plants into ground◦Absorb water and other “raw”

nutrients◦Store starches and sugars.

Dicots have a taproot with many root hairs

Monocots have a fibrous, highly-branched root system

RootsGeneral cross-sectional structure:

◦Xylem and phloem in a central vascular cylinder.

◦Cortex of ground tissue surrounds the core◦Root hairs grow from epidermal cells to greatly

increase surface area to both anchor the plant and increase water and nutrient absorption.

RootsGeneral cross-

sectional structure:◦Root cap covers and

protects the growing tip of the root.

◦The meristem is an active growing/dividing area of cells that “pushes” the root through the soil.

StemsFunction to support leaves that attach to

stems at nodes.Non-woody stems on herbaceous (flexible)

plants have bunches of xylem and phloem called vascular bundles.◦ Randomly scattered in monocots◦ Arranged in rings in dicots.

Pith: ground tissue surrounds vascular bundles

StemsWoody stems: stiff and non-green

◦Central core of pith.◦Ring of xylem; as it ages it becomes

filled with lignin and becomes wood.◦Xylem cells are larger during periods

of rapid growth, smaller when slowly growing. The difference is seen as tree rings. (One cycle per year = one ring per year.)

◦Outside xylem is phloem; as it ages it dies and becomes part of the bark.

Stems

LeavesPrimary site of photosynthesisPetiole: the central stalkBlade: the flattened part of the

leafThe leaf is mostly ground tissue

(the site of photosynthesis) covered by an upper and lower epidermis covered with cuticle.

Most stomata are on lower surface.

You have to be-”leaf” that it’s time to be done!