Plant Structure and Function

$ photosynthesis is a cellular process, so this posses some interesting questions:

1. how do plants like angiosperms supply their cells with sunlight, carbon dioxide, water and minerals?

2. how do they distribute food to all of the cells?

3. how do they store food?

$ plants are organized like other complex multicellular organisms, they have tissues, organs, and systems

$ in seed plants, root and shoot tissues begin to form in the embryo that is still within the seed.

$ as the seed germinates, cells at the root and shoot tip divide and elongate

$ this lengthwise growth is called primary growth

$ many dicots and a few monocots also exhibit secondary growth

$ secondary growth originates in tissues at sites other than the root and shoot tips, resulting in an increase to the diameter of stems and roots

$ plants only divide in specific regions, called meristems

$ meristems are tissue regions of plants where some cells retain the ability to divide repeatedly

$ cells produced by meristematic tissue eventually differentiate into all other plant tissues

Plant Tissues

$ plant tissues are adapted or specialized for functions such as absorption, transport, photosynthesis, reproduction, and storage.

Ground Tissue

$ there are three types of ground tissue:

1. Parenchyma- living cells that make up the bulk of the primary plant body. It functions in healing wounds, regenerating plants parts, and is also involved in photosynthesis, food and water storage. Cacti, which store large amounts of water, have large amounts of parenchyma tissue called succulents.

2. Colenchyma- a thick living tissue that helps to strengthen the plant and is specialized for supporting the plant=s growth regions. Allow the plant to remain flexible in the wind. Examples include: celery stalks and herbs.

3. Sclerenchyma- made up of the walls of dead cells. The long tapered walls are called fibers. These fibers provide strength and support to the plant. This tissue is prominent in structures like the shells of nuts, and in cactus spines.

Vascular Tissue

$ this includes the xylem and the phloem along with some other types of cells

$ the main water conducting cells in the xylem are called tracheids and vessels

$ both of these types if cells are found in flowering plants, but gymnosperms have only tracheids

$ the two types of cells are dead at maturity and are pierced by many recesses, or pits

$ vessels are usually shorter than tracheids and are joined end to end.

$ tracheids are longer than vessels and have tapered overlapping ends.

$ phloem tissue transports sugars and other solutes throughout the plant body

$ phloem is mainly living tissues

$ phloem cells are called sieve tubes, because they are long and thin

Dermal Tissue

$ the outer most dermal tissue layer of the primary plant body is the epidermis.

$ on the above ground parts the epidermis forms a waxy noncellular coating called the cuticle

$ cork is another example of a dermal tissue. Cork functions in waterproofing the roots and stems

The Root System

$ roots anchor the plant, absorb minerals and water, conduct water and nutrients, and store food.

$ many dicots have a taproot system, consisting of one large, vertical root (the taproot) that produces many smaller secondary roots

$ examples of taproot plants are: dandelions, carrots, turnips, sugar beets, and sweet potatoes

$ monocots, including grasses, generally have a fibrous root system consisting of a mat of thread-like roots that spread out below the surface of the soil

$ the fibrous root system gives the plant extensive exposure to soil water and minerals and anchors the plant firmly to the ground.

$ fibrous roots are only in the upper few centimeters of the soil, making them good ground cover to prevent erosion

$ some plants have roots arising aboveground from stems or even from leaves. Such roots are said to be adventitious root referring to any plant part that grows in an unusual location

$ examples include corn (monocot) and banyan tree (dicot)

$ each root has a protective root cap at the tip

$ further back on the root are root hairs which increase the root=s surface area

$ the root is made up of a cortex which is a layer of tissue that is between the epidermis and the vascular tissue.

$ the inner layer of the cortex is called the endodermis

$ the endodermis forms a waxy substance called suberin which prevents water and minerals from leaving the vascular cylinder

$ inside the endodermis is a tissue called pericycle which is a meristematic tissue consisting of parenchyma cells and sometimes fibers.

$ this pericycle tissue forms lateral roots off the taproot

The Shoot System

$ stem and leaves make up the plant shoot system

$ stems provide support for the plant, serve as a transport link between roots and leaves, and act as sites for food storage

$ there are two types of plant stems: woody stems and herbaceous (nonwoody) stems

$ herbs contain little or no wood and usually do not grow more than one meter tall. Examples include: weeds, cabbage and lettuce

$ examples of woody stems are: vines, shrubs, conifers, and dicot trees

$ both woody and herbaceous plants undergo secondary growth

$ the stems of herbs are thin, soft, weak, green and short-lived

$ all stems start as buds. Buds first develop on the shoot tip and are called terminal buds. Other buds coming off of this bud are called lateral, or auxiliary buds

$ in the first year of growth both herbaceous and woody stems resemble each other. However, as growth proceeds, the strength, hardness, and size of a woody stem arise from secondary growth

$ the darker wood at the center of the stems is called heartwood and is used for support and does not conduct water and minerals

$ sapwood is the light-colored wood that surrounds the heartwood. This wood conducts water and minerals between the roots and leaves. Each year some of the sapwood is changed into heartwood

$ the outermost layer of a stem or tree trunk is called bark. Its tissues are composed of cork, cork cambium, cortex, and phloem

$ just beneath the bark, and forming the bulk of the stem is the secondary xylem or wood

The Leaf

$ the leaf is important because it is the center of photosynthesis and a basic food source for most heterotrophs

$ typically, leaves have a network of veins that contain the vascular tissue, which is continuous with the xylem and phloem in the stem

$ each leaf is connected to the stem by a leaf stalk called a petiole

$ if the leaf is a single blade it is called a simple leaf

$ a blade divided into two or more parts is called a compound leaf

$ the leaf epidermis is covered by a cuticle and is pierced by tiny pores called stomata

$ each stoma is bounded by a pair of sausage-shaped guard cells

$ water and carbon dioxide concentration levels determine the opening and closing of the stoma

$ the guard cells contain many chloroplasts which begin the process of photosynthesis at sunrise.

$ As photosynthesis continues the carbon dioxide is used up to make sugar, causing the guard cells to open and let in more carbon dioxide

$ between the upper and lower epidermis is a photosynthetic layer called the mesophyll

$ the mesophyll consists of two types of parnechyma cells called palisade on the upper side and spongy mesophyll on the lower side of the leaf

$ palisade cells, which contain many chloroplasts, are brick shaped and are arranged neatly side by side

$ the spongy mesophyll cells, have few chloroplasts and are irregular in shape and arranged haphazardly

$ in the middle of the leaf is xylem and phloem tissue, contained in vascular bundles called veins

Transport in Plants

$ about 90% of water loss in plants occurs through stoma

$ this loss of water to the atmosphere is called transpiration

If a tree is 100 m tall, how do the leaves near the top of the tree receive water that is stored in the roots?

$ several forces are involved

1. As water is lost in a leaf it is replaced by osmosis, which continuously pulls water into the roots

2. The force of attraction of water that pulls the water up the narrow xylem tubes is called capillary action

3. The major force behind water movement in plants is the attraction of water molecules for one another. This is known as the cohesion-tension or transpiration-cohesion theory

$ In this theory it is believed that the water adheres to the sides of the xylem tubes

$ these water molecules that are >stuck= to the sides then stick or attract other water molecules

$ foods produced by photosynthesis are moved from leaf cells to other plant parts through phloem tissue called translocation

$ translocation refers to the conduction of organic compounds throughout the plant by way of phloem vessels