Biology Module 12

Plant tissues are specialized for functions such as

absorption, transport, storage, photosynthesis, and reproduction

Aerial roots

adventitious roots that grow from leaf nodes along stems

Primary growth

all plant growth originating at apical meristems resulting in increases in length, as well as growth in diameter of roots originating at the lateral meristems in the first year of a plant's life

root system

anchors plant, absorbs water and minerals, stores food (anything underground)

Succulents

plants which have thick, fleshy parts due to the presence of large amounts of parenchyma for water storage (cactus)

Apical meristems

regions at the tips of all roots and shoots. They are responsible for the primary growth, which lengthens shoots and roots throughout the life of the plant.

Meristems

regions of the plant where some cells retain the ability to divide repeatedly by mitosis. Plant cells divide by mitosis only in specific regions (meristems).

Taproots

root systems where the primary root remains predominant, though very small secondary roots may be present. If a young root increases in diameter, grows downward, and develops small lateral roots, it is called a taproot. (carrots, beets, dandelions, and oak trees)

Fibrous roots

root systems whose primary roots have disintegrated and have been replaced by adventitious roots

Adventitious roots

roots that develop from a part of the plant other than a root. They often form huge tufts at the base of the stem. There is no main root because most are the same size as the others. However, smaller secondary roots do branch out from these roots. Generally, these fibrous roots do not penetrate as deeply as taproots but their total combined length can be enormous. The fibrous roots of a single rye grass plant were estimated to have a total surface area of over 600 m2 while occupying just 6 L of soil!

Pneumataphores

roots which grow upwards into the air to take in oxygen.

Plant organs

roots, stems, leaves, and flowers (or cones)

Secondary growth in root (structure, center to outside)

secondary xylem, vascular cambium, secondary phloem, pericycle, cortex (with endodermis), epidermis

Runners

slender stem producing roots, sometimes at the nodes. Examples of plants that use runners are strawberries. thin stems which grow along the ground producing roots and shoots at their nodes

Companion cells

small cells lying next to the sieve elements and directing their activities (supply the elements with needed substances).

Secondary root

smaller root branches growing sideways from a primary root (lateral root)

Guard cells

the cells that occur in pairs around each stoma in the epidermis of a leaf or a stem. They regulate the opening and closing of the stoma.

Primary root

the first root developed from the seed

Blade

the flattened main body of the leaf.

Sap

the fluid within any part of a plant, found mostly within the xylem and phloem tissues

Annual ring

the increase in the amount of secondary xylem during one year. The number of annual rings indicates the age of the woody plant. In very wet years, the rings are wider than in very dry years. By counting the number of rings, we can learn the age of a woody plant. In tropical zones, growth in wood is somewhat uniform all year and annual rings do not appear.

Nodes

the locations where leaves are attached to the stem

Transpiration

the loss of water through the surfaces of the plants. Most transpiration occurs through leaf stomata. The water diffuses and evaporates into the air spaces of the leaves and out to the atmosphere through the stomata.

Heartwood

the older, harder, nonliving central wood in tree trunks. It is often darker due to the accumulation of oils and resins and its basic function is to provide support. (As trees age, old xylem cells become plugged with various substances such as oils and resins, which prevent water and dissolved materials from moving up or down.)

Bark

the outer layers on older stems, branches, and trunks. Bark consists of every layer from the vascular cambium outwards: phloem, any remaining cortex, cork cambium, and cork. If the bark is removed, the phloem will be destroyed and no further carbohydrates will be transported to the root for storage. The tree will die, although it may be a slow death taking place over three or more years.

Epidermis

the outermost cell layer of a multicellular plant experiencing primary growth

Pith

the parenchyma tissue at the very centre of roots and stems (The general term for ground tissue in the centre of roots and stems. Consists of spongy parenchyma cells, and it functions in the storage of nutrients, carbohydrates, and water.)

Cortex

the parenchyma tissue, usually with slightly thicker cell walls, surrounding the vascular tissue in roots and stems (tissue that surrounds pith)

Mesophyll

the region of photosynthetic cells between the epidermal layers of leaves. The mesophyll consists of parenchyma cells containing lots of chloroplasts.

Internode

the space between two successive nodes on the same stem

Stomata

A leaf must acquire a constant supply of carbon dioxide and be able to release the oxygen produced. The exchange of these gases is regulated by tiny pores called stomata. Stomata are found in the epidermis of leaves or stems but are mostly found in the lower epidermis of leaves. Stomata also allow water vapour to escape from the leaf. When the stomata are open, the plant can obtain needed carbon dioxide; however, the plant also loses water. When the stomata are closed, water is conserved, but carbon dioxide cannot be obtained. The opening and closing of each stoma is regulated by guard cells.

leaves

Green leaves are the major sites of photosynthesis. They contain chlorophyll, the green pigment necessary to capture light energy. They must also be able to obtain carbon dioxide from the air and water to use as the building blocks for sugars and starches. Leaves must not dry out or be eaten. As a result, leaves occur in a great variety of shapes, sizes, and textures. Leaves also have a variety of internal structures. They are the features which allowed the plants to survive the biotic and abiotic factors of their habitats.

What type of wood gets larger, and what type doesn't?

Heartwood widens, sapwood doesn't.

Leap adaptations to biotic factors

Herbivores - tough, hairy, prickly, or bitter leaves to be unappetizing (reduces photosynthetic efficiency) - producing toxins Modified leaves that exist with normal ones - bulbs for storage of water and nutrients, sharp spines, petals

Parallel venation

If the veins run from the petiole to the leaf tip without joining one another. (usual for monocots)

Net venation

If veins branch and rebranch throughout the whole leaf in a crossing pattern (usual for dicots)

Additional changes that happen to tree as they age:

No new ground tissue is added to the tree, and the primary tissue may be displaced by secondary tissue. As in the root, the cork cambium is formed. The cork cells produced by this layer will accumulate in layers. The actual cells die but the cell walls remain to form cork, which offers protection against mechanical damage and damage caused by bacteria, fungi, and insects. As the stem expands, the cork cracks and is renewed from the inside.

Vascular cambium in roots

Some of the ground tissue within the stele becomes meristematic and begins to divide. This tissue is the vascular cambium. Vascular cambium separates the xylem and phloem. When the cambium divides by mitosis, it produces phloem cells to the outside and xylem cells to the inside. As the xylem increases in size, the cambium is displaced outward, causing an increase in the diameter of the root. Primary xylem and phloem are produced in the first year of the plant's life. After that time, all xylem and phloem that are produced are called secondary.

Stems (functions)

Stems and leaves make up the plant shoot system. Stems provide support for the plant and serve as a transport link to and from leaves, roots, and reproductive parts such as flowers, fruits, and seeds. Stems may also serve to store water and carbohydrates. Some plants have herbaceous stems.

Function of cuticle

The cuticle protects against excessive water loss and infection by microorganisms. The cuticle also restricts gaseous exchange through the surfaces of the epidermal cells.

Dermal tissue

The outermost cell layer of the main plant body is the epidermis. On parts of the shoot system, the epidermis produces on its surface a cuticle. Epidermal tissue often contains highly specialized cells such as root hair cells and leaf guard cells. During secondary growth in roots and stems, the epidermis is replaced by the periderm, another dermal tissue. Some peridermal cells form many layers of special cells that soon die but leave behind a material that waterproofs the roots and stems and protects the inner tissues from structural damage.

Hydrophytes

plants living on or in water

How guard cells are regulated

When a pair of guard cells contains low levels of water, they are limp and rest against each other, closing the stoma. As water builds up in the leaf tissues (night) the guard cells tend to swell. As the cells enlarge, they swell less where their walls are thickened. The pairs of swollen guard cells look like beans and the stomata are open. At sunrise, photosynthesis begins in the chloroplasts. Carbon dioxide levels drop and oxygen levels increase in the leaves relative to the concentration of these gases in air. Because the stomata are open, gaseous exchange occurs by simple diffusion. Water vapour is also lost. Throughout the day, as the water concentration in the guard cells drops, the cells begin to shrink. As the pairs of guard cells become limp and collapse, the stomata close. The opening and closing of the stomata are also related to the concentration of carbon dioxide in the guard cells. In addition, light levels, temperature, and abscisic acid concentrations play a key role in the opening and closing of the stomata.

Xerophytes

plants that survive or thrive in areas with very little moisture

Cork cambium

a lateral meristem formed by the pericycle in dicots over two years old

Vascular cambium

a lateral meristem which is responsible for creating new xylem and phloem tissue

Spongy mesophyll

a layer of irregularly shaped cells containing chloroplasts between the palisade mesophyll and the lower epidermis of most leaves. Many air spaces are randomly distributed within this layer. (fewer chloroplasts) These air spaces promote the rapid diffusion of carbon dioxide into cells and oxygen gas out of them

Endodermis

a layer of rectangular cells surrounding the vascular cylinder. It is the innermost layer of the cortex. Regulates lateral movement of water and minerals.

Compound leaf

a leaf that is divided into two or more leaflets

Simple leaf

a leaf that is not divided into leaflets

Parenchyma

a living ground tissue that makes up the bulk of the plant body. Parenchyma tissues take part in several tasks, including photosynthesis, storage, and regeneration.

Chollenchyma

a living ground tissue that offers flexible support for primary growth. Helps strengthen the plant and is specialized for supporting the plant's primary growth regions. Flexibility to bend to withstand windy conditions.

Root cap

a loose mass of cells forming a protective cap covering the apical meristems of most root tips

Toxin

a poison produced in the body of a living organism. It is not harmful to the organism itself but to other organisms

periderm

a protective covering that replaces the epidermis in plants that show extensive secondary growth

Petiole

a stalk that connects leaf to stem

Pericycle

a thin layer of lateral meristematic cells that surrounds the vascular cylinder

Secondary growth in roots

associated with an increase in diameter of the vascular cylinder and, in much older roots, the formation of bark. Most monocot roots as well as some annual dicots do not exhibit secondary growth. It is, however, a definite characteristic of perennial dicot roots.

Plant leaf adaptations

broad leaves to trap low energy (do well in shade) evergreen (can survive in winter, good for short growing season) the needles are inefficient for photosynthesis but prevent water loss leaves with thick layers of water storage tissue and are covered with a thick, waxy cuticle to prevent water loss (can survive in areas of high salt content or low precipitation) for example, cacti

The oldest xylem is nearest the

centre of the stem; the youngest is next to the cambium.

Lateral meristems

cylindrical regions in roots and stems. They are responsible for all increases in diameters of roots and stems.

three major types of plant tissue

dermal tissue, ground tissue, and vascular tissue

Biotic

describes anything related to living things. Biotic factors are all living things in an area and include interactions within and between species, such as competition and predation

Abiotic

describes anything related to nonliving things. Abiotic factors include temperature, humidity, light availability, and soil conditions such as water content, texture, and mineral composition.

Annual

describes plants that complete their entire life cycle, from seed to reproduction to death, in one year

Perennial

describes plants that grow and reproduce repeatedly for many years

Woody

describes stems of perennial plants. They increase in diameter each year as more and more vascular tissue is created. The xylem cells, even after they have died, create the hard, woody tissue called wood. (grape vines, shrubs, conifers, and dicot trees)

Cork

describes the cells produced by the cork cambium that eventually form a layer of dead cells that provide a protective covering for roots over two years old. Cork also describes the protective layers.

Herbaceous

describes the fleshy stems of annual plants. These stems usually do not survive more than one year, especially if there is a cold winter. They are also called nonwoody stems. They carry out photosynthesis and thus produce some carbohydrates for the plant. Usually, herbaceous stems do not grow more than one metre tall. Exceptions include palm trees, which are not actually trees at all, but huge herbaceous monocots lacking true woody tissue.

Cells produced by meristematic tissue eventually ..

differentiate into all other plant tissues.

Vascular cambium in stems

divide by mitosis to produce secondary phloem to the outside and secondary xylem to the inside. The secondary phloem cells tend to crush the somewhat fragile phloem cells of the previous years as pressure is exerted outwards. The secondary xylem cells do not crush earlier xylem cells because they have thick walls.

Dermal tissue cells are found in the

epidermis and the periderm

Tree layers (center to outside)

heartwood, sapwood, vascular cambium, living phloem, cork cambium, cork (periderm is composed of both cork cambium and cork) (bark is composed of living phloem and periderm)

Mesophytes

plants that thrive with moderate moisture

Ground tissue cells make up all of the

internal nonvascular regions in the plant

Sieve tubes

long tubes formed by many sieve elements to allow easy passage of water and dissolved materials. Sieve tubes provide an obstruction-free pathway for the movement of materials from one cell to the next. Sieve elements are long and thin phloem cells with sieve plates at the end walls. The sieve plates have large pores that allow easy passage of water and dissolved materials. Sieve elements also have pits on their side walls. These cells lack a nucleus, ribosomes, Golgi apparatus, cytoskeleton, and vacuoles.

Vessels

long, continuous tubes of vessel elements for conducting water and dissolved materials in plants. The vessel elements have thickened walls and large perforations in their end walls. dead at maturity

Sclerenchyma

mature cells are dead. These cells have secondary thick walls composed of cellulose and lignin. Supports mature plants and often protects seeds. These cells may occur as a continuous mass, or in small clusters, or may be individually scattered throughout the plant. The thickened walls of sclerenchyma cells strengthen and support various plant parts. They are particularly evident in parts where hardness is an advantage, such as in the shells of nuts and in cactus spines.

Root hairs

microscopic extensions of the epidermal cells near the tip of a root. Root hairs function in the absorption of water and minerals. At the centre of each root is the vascular cylinder (stele), which contains the vascular tissues, xylem and phloem, and some ground tissue.

Root function

often larger than the plant's entire shoot system. Roots absorb water and minerals from the soil, physically support and anchor plants, and store carbohydrates. Water and minerals that enter the roots are transported through vascular tissue up to the stem, leaves, and flowers. Many of the carbohydrates produced in the shoot system are transported down to the roots for storage. Roots are also responsible for producing a variety of compounds, such as hormones, which are used throughout the plant.

Palisade mesophyll

one or two layers of brick-shaped cells, rich in chloroplasts and found tightly packed beneath the upper epidermis of most leaves. The longer sides of the cells are at right angles to the upper epidermis. Primary site for photosynthesis.

Three types of ground tissues

parenchyma, collenchyma, and sclerenchyma

shoot system

photosynthesis and reproduction (anything above ground)

Secondary growth

plant growth originating at lateral meristems which results in increased diameters of roots and stems in the second and all subsequent years of a plant's life

Allelopathy

the suppression of growth and development of neighbouring plants by a plant of a different species. This effect is caused by chemicals secreted by the roots or contained in the leaves of the allelopathic species. Not all surrounding plants will suffer the same effect. (walnut sends out toxins)

Sapwood

the younger, softer, outer wood in tree trunks that is important for transporting water and dissolved materials as well as for support. In sugar maples, the xylem also stores and transports carbohydrates. This area is often somewhat light in colour. Each year some sapwood is changed to heartwood.

Epiphytes

they grow on the stems and branches of other plants. They are not parasitic because they have retained their ability to photosynthesize. Strangler figs and orchids.

Phloem

transports sugars and other solutes throughout the plant body. Unlike mature xylem, which is dead, mature phloem is a living tissue.

Tubers

underground stems which grow along the ground producing shoots and roots at their nodes.White potatoes form an underground stem which is specialized for carbohydrate storage thick underground stems specialized for carbohydrate storage and asexual reproduction

Two major divisions of plants:

vascular plants and nonvascular plants.

Tracheids

xylem cells with tapered, overlapping ends and pits (un-thickened areas) in their cell walls for conducting water and dissolved materials in plants (transfer materials to other cells) dead at maturity

Xylem

xylem is the main tissue in plants for conducting water and minerals. Xylem tissue contains fibres and water-conducting cells called tracheids and vessels.

Wood is comprised almost entirely of

xylem tissue.

Primary growth in root (structure, center to outside)

xylem1, phloem1, pericycle1 (1 - stele), endodermis2, parenchyma2 (2-cortex), epidermis, root hair