Chapter 6: Tissues and the Primary Growth of Stems

The body of an herb contains just three basic parts. What are they?

Roots, Stems, and Leaves.

An herb has only a primary plant body. That means it has roots, stems, and leaves, but it never becomes_____and covered with_____.

woody, bark

In general, animals have_____growth with a fixed size and number of organs, whereas plants have_____ growth with no set size and any number of organs. Which parts of our body grow continuously like plants? Which parts of a plant have fixed size such that no matter how well we take care of the plants those organs do not become larger? What is the name of plants that live for just 1 year? For just 2 years?

determinate growth, indeterminate growth.

Our hair and nails grow continuously.

Seeds, Fruits, and Flowers have a fixed size.

Annuals are plants that lice for just one year. Biennials are plants that live for two years.

What are the important differences between parenchyma, collenchyma, and sclerenchyma cells?

Parenchyma are living at maturity, have a thin cell wall, located at cortex in stems and roots

Collenchyma are living at maturity, have a unevenly thick cell wall, located beneath epidermis in stems, shoot tips, leaf stalk

Sclerenchyma are dead at maturity, have a very thick cell wall, located everywhere except growing tip

What is the special name of photosynthetic parenchyma cells? Which organelle is especially abundant in these? How does wall thinness affect carbon dioxide and light?

Chlorenchyma cells (palisade parenchyma and spongy parenchyma).

Chloroplasts are exceptionally abundant in these cells.

Thin cell walls allow CO2 to diffuse rapidly into the cell and allow light to penetrate deeply and easily.

It was previously stated that parenchyma cells are relatively inexpensive to build. What does that mean? How does this relate to most leaves being soft?

They require little metabolic energy and few recourses for the plant to produce parenchyma as they have a thin primary cell wall.

Most of a leaf is made up of parenchyma cells to maximize photosynthesis they are soft pliable and flexible because they cannot have a secondary cell wall. The plant deliberately avoids investing heavy resources into making leaves rigid or permanent, allowing it to quickly build, shed, and replace them as seasons change.

Like clay, walls of collenchyma exhibits plasticity. Does that mean it can or cannot be stretched? If a tissue is supported by collenchyma, can it still grow?

Collenchyma cell walls can be stretched.

Yes it can still grow if a tissue is supported by collenchyma.

How does collenchyma support a tissue? Would it work if the tissue did not have parenchyma also? What happens if the tissue is not turgid (does not have enough water)?

Through flexible mechanical support with unevenly thickened primary cell walls.

This would not work if the tissue did not have parenchyma cells because they work together like air pressure in a tire.

If the tissue is not turgid, it will wilt, and lose its shape.

Collenchyma is plastic, but sclerenchyma is elastic. What does “elastic” mean? If you stretch or deform an elastic object, will it keep its new shape or snap back to its original shape?

As an organ grows, its shape changes, but after it has achieved its mature size and shape, what kind of things would deform it?

Should a mature organ have plastic properties or elastic ones (e.g., if a heavy load of snow bends a branch down, should the branch stay in its bent shape when the snow melts, or should it go back to the shape it grew to before the snow)?

Elastic means a material can bend or stretch under pressure and goes back to original shape and size.

External forces like wind, heavy storms, animals and snow can deform it.

A mature organ should have elastic properties.

It should go back to its original shape after the snow melts.

What are the two types of mechanical, nonconducting sclerenchyma? (Hint: See Table 6-3.) Which tends to be flexible and useful in wood? Which tends to be brittle and inflexible, useful in “pits” and “stones” that protect seeds?

Fiber and Sclerid.

Fibers tend to be flexible and useful in wood.

Sclereids tend to be brittle and inflexible.

Fibers and sclereids have secondary walls that are so thick and tough that the cell cannot grow. If that is true, how do fibers and sclereids grow to their mature size and shape? Do they have a secondary wall even when they are young?

They elongate and expand while only having a flexible primary cell wall and depositing their secondary cell wall after they stopped growing.

Imagine a leaf of a palm tree. When it is fully grown, it must have sclerenchyma to support its size and weight. Do you think it has any sclerenchyma when it is tiny and just starting to grow? Would you expect that it might have collenchyma when it is medium sized and still growing?

When it is tiny, it does not have major sclerenchyma as young tissues need flexible cells that can expand as it grows.

When it is medium sized you would expect it to have collenchyma to offer flexible stretchable support while it lengthens and expands.

The point where a leaf is attached to a stem is called a(n)_______. Just above this point is a(n)_______ bud.

node, axillary bud

Figure 6-13A shows two types of buds. What are the two types and how do they differ?

Terminal buds and axillary buds.

Terminal buds are at the tip of a stem and is responsible for primary growth.

Axillary buds are at the side of the stem where a leaf attaches to the stem and eventually develops into lateral branches, side shoots, or flowers.

After a leaf falls off a stem, it leaves a(n)______just below the axillary bud.

It leaves a leaf scar.

What is phyllotaxy? Corn and irises have two rows of leaves. This is known as______phyllotaxy.

Phyllotaxy is the arrangement of leaves.

distichous is two rows of leaves

When you look at a head of cabbage or lettuce, what are you seeing? Where is the stem? What about when you look at an onion? What are you seeing, and where is the onion’s stem?

Cabbage: A unusually large tightly packed terminal bud made of overlapping leaves and the stem is the short dens core at the bottom center of the head.

Onion: an underground structure called a bulb that is fleshy modified storage leaves in a papery outer skin and the stem is the flat woody disk at the bottom known as the basal plate.

Describe each of the following types of specialized shoots. Be certain to account for modifications of the leaves, internodes, and orientation of growth: stolon, rhizome, tuber, bulb, corm, and tendril. Each provides a plant with a selective advantage. What is the adaptive value of each type of specialized shoot?

Stolon/Runners: Grows horizontally and above or just below the soil surface, they have long and thin internodes, leaves are reduced and are found above ground.

Rhizome: Fleshy horizontal stems that spread underground with leaves reduced to small scale like structures with short thick internodes

Tuber: grows underground with leaves that are “eyes” with short and swollen internodes (with parenchyma tissue for storage)

Bulb: short shoots with thick fleshy leaves that grow vertically with condensed and reduced internodes

Corm: thick stem with papery leaves that grow upright with condensed, massive internodes

Adaptive value:

Stolon: asexual spreading and colonization of new space without expending energy on large leaves or deep roots

Rhizome: underground storage for starch and nutrients allowing perennial plants to survive underground during winter or drought

Tuber: maximizes dense starch storage for long term dormancy

Bulb: stores water and nutrients in fleshy leaves to protect plant through winter dormancy

Corm: provides internal stem storage for nutrients to survive harsh freezes or dry spells

Many scientific words are also ordinary English words. If you read that a plant has a bulb or a tuber, can you always be certain exactly what the botanical structure is?

You cannot always be certain.

What is the outermost surface of an herbaceous stem? The outer walls of this layer are encrusted with a chemical made up of fatty substance that makes the wall impermeable to water. What is the name of the substance, and what is the name of the layer?

The epidermis.

Cutin that forms a layer called cuticle

A stoma allows carbon dioxide to pass through the epidermis. What is the name of the two cells that control the opening and closing of a stoma? What is the name of the hole itself that carbon dioxide passes through?

Guard cells

the hole itself is called the stomatal pore

What is the technical term for a plant hair? Plant hairs make it difficult for animals to do certain things. Name three activities that are more difficult for an animal because of a hairy leaf.

Trichomes

Feeding, laying eggs, and walking across surface

What is the name of the region of cells between a stem’s epidermis and its set of vascular bundles? This is usually a compact parenchyma tissue, but in some aquatic angiosperms that live submerged in lakes or oceans this region has what type of special modification? Would you hypothesize that this region is especially thick or thin in desert plants such as cacti or plants that have succulent water storage tissues (you must think about this yourself, as the answer is not in the text).

The cortex.

Aquatic angiosperms: the cortex is modified into aerenchyma that is filled with large air filled spaces that allow gas exchange and provide buoyancy

Desert Plants and Succulents: especially thick to function primarily as a water storage tissue

All flowering plants have two types of vascular tissues,_______, which conducts water and minerals, and______ , which distributes sugars and minerals. Are vascular systems of plants similar to or different from those of animals? Explain the similarity or differences.

xylem, phloem

They are different as plants have open ended circulation and animals have closed loop circulation, plants have passive forces for pump mechanism and animals have active pump, plants have two separate fluids for xylem and phloem while animals only have blood. They both share the purpose of transporting vital resources throughout the organism.

Like xylem, phloem has two types of conducting cells, _______and______ . The term “ ________ _________” refers to either one. Do these die like tracheary elements, or do they need to remain alive in order to conduct?

sieve cells, sieve tube elements (or members)

sieve element

They must remain Alice in order to conduct sugars and other organic nutrients but when they mature they lose their nucleus vacuoles and ribosomes and Golgi apparatus to allow for freer fluid flow

What is the name of the holes that interconnect conducting cells in phloem, and what are groups of these holes called?

sieve pores and groups of these are called sieve plates

Sieve tube members differ from sieve cells by having very large sieve pores on their end walls, much larger than the ones on their side walls. What is the name of these end-wall sieve areas with big sieve pores?

sieve plates

All vascular bundles are ___________. That is, each contains both xylem and phloem. The xylem of a vascular bundle is _________ xylem because it is part of the primary plant body, and the phloem is________phloem.

conjoint (composed of both xylem and phloem), primary xylem, primary phloem

If you live to be 100 years old, how many sets of organs will you have during your lifetime? How many hearts, stomachs, and livers? If a plant lives to be 100 years old, how many sets of leaves will it probably have? If it begins blooming when it is 10 years old, how many sets of flowers? When you are 70 years old, you will still depend on your digestive system to supply you with energy for another 30 years, but how old is that set of organs? In a 70-year-old tree, how old are the cells of the leaves that supply it with energy?

1 set of organs.

90-100 sets of leaves replacing them in a new set each year

90 sets of flowers by age 100

digestive system is 70 years old

cells in a 70 year old tree is less that one year old

What are the three main types of plant cells? Know the characteristics, location, and functions of each.

Parenchyma, collenchyma, and sclerenchyma.

Parenchyma only have a thin primary wall and it is active metabotically (wound healing and regeneration) and is located in the cortex of stems and roots, pith of stems, mesophyll of leaves

Collenchyma have a primary cell wall that is thicker in the corners, it is readily stretched and flexible and it supports tissue

Sclerenchyma have primary and secondary cell walls, they are thick, hard and elastic and contain lignin and it provides support when dead and found in mature regions of the plant like stems, tree trunks, outer coat of seed, shells of nutsY

Are parenchyma cells typically alive?

Yes at maturity

Are collenchyma and sclerenchyma typically dead?

Collenchyma cells are alive while sclerenchyma cells are typically dead

What are the two types of mechanical sclerenchyma?

Fibers and sclereids

What is the difference between the stems of monocots and herbaceous dicots?

Vascular Bundle arrangement (monocots randomly, eudicots orderly ring)

Pith and cortex (monocots do not have a clear separation between cortex and pith, dicots have a clear cortex and central pith)

Secondary growth (monocots lack vascular cambium (closed bundles) and do not have true secondary growth, eudicots have open bundles that allow for primary growth)

Trichomes (monocots lack trichomes, eudicots have trichomes)

What is found at the center of a eudicot stem?

the pith

Define Alternate:

one leaf per node

Define Whorled:

three or more leaves per node

Define Opposite:

two leaves per node

Define Distichous:

two rows of nodes

Define Spiral:

nodes in a spiral pattern

Define Decussate:

four rows of nodes (rare)

Describe five modifications of stems:

Stolen/runners: long and thin internodes, leaves are reduced and found above ground

Bulb: short roots with thick fleshy leaves

Corm: thick stem with papery leaves

Rhizome: fleshy horizontal stems that spread underground

Tuber: general term is underground storage

What is the function of the epidermis? What is the protoderm?

It prevents against water loss and bacteria, fungus from getting in.

The protoderm is the outermost layer of the root and shoot apical meristems that have cells that are actively dividing and as these cells mature they become the epidermis.

What are the functions of guard cells and trichomes?

Guard cells allow the plant to breathe through the protective epidermis using these guard cells that regulate gas exchange (open permit CO2 to enter and 02 to exit), they also control water loss so that when gas exchange is not needed it won’t let water vapor out.

Trichomes are an elongated epidermal cell that decreases water loss, reflects excessive light, and slows down air flow outside the plant and defend against herbivores either mechanically or chemically.

Where is the cortex of a leaf?

A leaf does not have a cortex but instead have the equivalent ground tissue called the mesophyll located between upper and lower epidermis

Name and describe xylem cells and phloem cells. What are their functions? Which one is parenchyma and which one is sclerenchyma? Know the two types of phloem cells?

They are complex vascular tissues that transport water, minerals and sugars.

Xylem is made up of sclerenchyma but also have a small amount of living parenchyma cells. and transports water and dissolved minerals from the root up the plant. dead hollow cells and make water move by conduction via hydrogen bonds. have primary and secondary cell walls and inside xylem there are tracheids that have pits that slow movement

Phloem is made up of parenchyma cells but also have sclerenchyma cells(phloem fibers) and move sugar solution from the leaves down the plant. alive cells only have primary cell wall

Two types of phloem cells:

Sieve cells

Sieve Tube Members

What are vascular bundles?

Transport water nutrients and sugars throughout the plant, made up of xylem and phloem

Where does primary growth occur?

apical meristem

What specific cells are responsible for transporting the dye in the roses?

Tracherary elements in the xylem

What are the tracherary elements?

Tracheids: have pits that slow movement

Vessel elements: complete holes or perforations that decrease friction