AP Biology Notes Outline Plant Structure, Growth, and DevelopmentChapter 35

FIGURE 35.2 – PLANT STRUCTURE AND GROWTH: Both genes and environment affect plant structure. Plants have three basic organs: roots, stems, and leaves. Plant organs are composed of three tissue systems: dermal, vascular, and ground. Parenchyma, collenchyma, and sclerenchyma are three types of plant cells.

The basic morphology of vascular plants reflects their evolutionary history as terrestrial organisms that draw nutrients from two very different environments: below-ground and above-ground. Why 2 different systems?

• Soil – provides water and minerals, but no light present

• Air – source of CO2• SO, plants developed 2 systems:

– Root systems (subterranean)– Shoot systems (aerial)

Organ Systems in Plants – ROOTS, STEMS, & LEAVES:1. Roots anchor plant, prevent erosion, absorb minerals and

water and store food– The absorption of water and minerals occurs near

the root tips, where vast numbers of tiny root hairs increase the surface area of the root

– Many plants have modified roots such as fibrous or taproots

• Fibrous : mat of thin roots that spread out below ground (monocots).• Taproot : consists of one large, vertical root (dicots).

– Root Hairs – provide surface area for max absorption of H2O– Adventitious Roots – roots that arise above ground from stems or even from leaves…help support

plant.2. Stems

– A stem is an alternating system of nodes, the points at which leaves are attached, and internodes, the stem segments between nodes.

– An axillary bud is a structure that has the potential to form a lateral shoot, or branch– A terminal bud is located near the shoot tip and causes elongation of a young shoot

• The presence of the terminal bud is partly responsible for inhibiting the growth of axillary buds, a phenomenon called apical dominance – an evolutionary adaptation that increases the plant’s exposure to light.

– The stem houses the transport system of plants, stores food, support leaves, and protects tissues3. Leaves

– The leaf is the main photosynthetic organ of most vascular plants– Leaves generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a node of

the stem• Simple leaf - A simple leaf is a single, undivided blade.• Compound leaf - In a compound leaf, the blade consists of multiple leaflets.• Doubly compound leaf - In a doubly compound leaf, each leaflet is divided into smaller

leaflets.

AP Biology Notes Outline Plant Structure, Growth, and DevelopmentChapter 35

FIGURE 35.8 – TISSUE SYSTEMS IN PLANTS: Each plant organ has dermal, vascular, and ground tissues. Each tissue system is continuous throughout the plant body.

Vascular – transport (xylem and phloem) - Carries out long-distance transport of materials between roots and shoots

• Figure 35.10 - Xylem conveys water and dissolved minerals upward from roots into the shoots• The water-conducting elements of xylem, the tracheids and vessel elements, are elongated cells

that are dead at functional maturity. Water passes from one cell to another through pits.• Figure 35.10 - Phloem transports organic nutrients from where they are made to where they are needed

• In the phloem, organic compounds are transported through tubes formed by chains of cells called sieve-tube members which are alive and functional at maturity. Walls between sieve tube members are called sieve plates and they have pores that facilitate the flow of fluid from cell to cell. Non-conducting companion cells are connected to the sieve tube members – they mature into sieve tube elements.

Dermal – tissue that covers and protects the plant. It includes endodermis, epidermis, and modified cells like guard cells, root hairs, and cells that produce a waxy cuticle.

Ground – the most common plant tissue – includes filler, packing material for cushioning - includes various cells specialized for functions such as storage, photosynthesis, and support.

FIGURE 35.11 – PLANT CELL TYPES: Plants are characterized by cellular differentiation, including parenchyma, collenchyma, and sclerenchyma.

Parenchyma cells are unspecialized plant cells that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell types.

Collenchyma cells are flexible plant cells that occurs in strands or cylinders that support young plant parts of the plant without restraining growth.

Sclerenchyma cells are rigid, supportive plant cells usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity.

AP Biology Notes Outline Plant Structure, Growth, and DevelopmentChapter 35

FIGURE 35.11, 35.13, 35.16 & 35.19 – PLANT GROWTH AND DEVELOPMENT: A plant continues to grow as long as it lives because plants have embryonic tissues called meristems that continually divide, generating new cells. The pattern of new cell growth is a function of the location of the meristem.

Primary Growth in Plants:Apical meristems, located at the tips of the roots and in the buds of the shoots, provides primary growth, that is, elongation of the plant down into the soil and up into the air. Growth in length is concentrated near the root’s tip. Three zones of cells at different stages of primary growth are located: the zone of cell division (called apical mersitem), the zone of elongation, and the zone of differentiation.

– The root tip is protected by a root cap, which secretes a substance that helps digest the earth as the root tip grows through the soil (see figure 35.13).

– A shoot apical meristem is a dome-shaped mass of dividing cells at the tips of a terminal bud – they give rise to a repitition of internodes and leaf-bearing nodes (see figure 35.16).

• Zone of Cell Division: These are meristem cells that are actively dividing and are responsible for producing new cells that grow down into the soil.

• Zone of Elongation: Here the cells elongate and are responsible for pushing the root cap downward deeper into the soil.

• Zone of Differentiation: Here cells undergo specialization into three primary meristems that give rise to three tissue systems in the plant. The protoderm becomes the epidermis, the ground meristem becomes the cortex (for storage), and the procambium becomes the primary xylem and phloem.

Secondary Growth in Plants:REVIEW FIGURE 35.19 - Lateral meristem provides secondary growth which is increase in girth. In nonwoody plants, there is only primary growth. In woody plants, secondary growth is responsible for the gradual thickening of the roots and shoots formed from earlier primary growth. Two lateral meristems function in secondary growth:

– vascular cambium (produces secondary xylem – wood, and secondary phloem)– cork cambium (produces tough, thick covering for stems and roots that replaces the epidermis)

FIGURE 35.19 – LEAF ANATOMY: The leaf of a plant is organized to maximize sugar production while minimizing water loss.

The epidermis is covered by a waxy cuticle made of cutin to minimize water loss. The cuticle is transparent to allow light to penetrate.

Guard cells are modified epidermal cells that contain chloroplasts, are photosynthetic, and control the opening of stomates. Stomata are tiny pores flanked by guard cells – they allow gas exchange between the leaf and surrounding air. Guard cell behavior is controlled by turgor pressure. Transpiration is the loss of water through the stomata of plants.

AP Biology Notes Outline Plant Structure, Growth, and DevelopmentChapter 35

The inner part of the leaf consists of palisade parenchyma and spongy mesophyll cells whose function is photosynthesis.

• The cells in the palisade layer are packed tightly, while the spongy cells are loosely packed to allow for diffusion of gases into and out of these cells.

Xylem transport water to leaf tissues. Phloem transports “food” from leaf tissues to sink cells. In phloem, hydrostatic pressure is generated at one side of a sieve tube, forcing sap to the opposite end of the tube (a concept known as bulk flow).

Vascular bundles or veins are located in the mesophyll and carry water and nutrients from the soil to the leaves and also carry sugar from the leaves to the rest of the plant.

• Specialized mesophyll cells called bundle sheath cells surround the veins and separate them from the rest of the mesophyll.

Many leaves have specialized adaptations to various environments:• small leaves found on conifers reduce water loss• succulents have leaves modified for storing water• cacti have spines – modified leaves that reduce water loss• stomata of Xerophytes are concentrated on the lower leaf surface• C4 and CAM plants