Specialized Tissues Chapter 23 Section 1 Plant Cells

Specialized Tissues Chapter 23 Section 1

Plant Cells n All organisms are composed of cells. n Three basic types of Plant cells: Parenchyma n Collenchyma n Sclerenchyma n n Small changes in structures make different functions possible n Three types arranged differently in roots, stems, and leaves

Plant Cells

Parenchyma n n Loosely packed cube-shaped or elongated cells with a large central vacuole and thin, flexible cell walls Involved in metabolic functions n n n Photosynthesis Storage of water and nutrients Healing Form the bulk of nonwoody plants Make up the fleshy part of most fruits

Parenchyma Cells

Collenchyma n Thicker cell walls than those of parenchyma—thicker walls provide support for the plant n Cell walls irregular shaped n Typically grouped in strands n Specialized for supporting regions of the

Collenchyma Cells

Sclerenchyma Thick, even, rigid cell walls n Support and strengthen the plant in areas where growth is no longer occurring n Cell typically dead at maturity n The hardness of the shells around nuts is due to the presence of sclerenchyma cells n

Sclerenchyma Cells

Plant Tissue Systems Cells that work together to perform a specific function form a tissue. n Tissues are arranged into systems of plants n Dermal System n Ground System n Vascular System n n These systems are further organized into the three major plant organs-----roots, stems, and leaves

Tissue Systems

Dermal Tissue System forms the outside covering of plants n Epidermis n n n Cuticle n n Outer layer made of parenchyma cells Outside waxy layer which prevents water loss Some epidermal cells of roots develop hairlike extensions that increase water absorption

Stomata Openings in the leaf and stem epidermis n Regulates the passage of gases and moisture into and out of the plant. n

Ground Tissue System n Functions in storage, metabolism, and support n Made up of all 3 types of plant cells n n Parenchyma cells are the most common Non-woody roots, stems, and leaves are made up primarily of ground tissue

Vascular Tissue System n Functions in transport and support n Xylem and Phloem Xylem-conducts water and mineral nutrients primarily from roots upward in the plant n Phloem-conducts organic compounds and some mineral nutrients throughout the plant n Unlike xylem, phloem is alive at maturity. n

Vascular Tissue System (cont. ) n In angiosperms, xylem has two major components n Tracheid Long, thick-walled sclerenchyma cell with tapering ends. n Water moves from one traceid to another through PITS, which are thin, porous areas of the cell wall n n Vessel Element Sclerenchyma cell that has either large holes in the top and bottom walls or no end walls at all n Vessel elements are stacked to form long tubes called VESSELS n Water moves more easily in vessels than in tracheids n

Tracheids and Vessel Elements

Vascular Tissue System (Cont. ) n Conducting parenchyma cell of angiosperm phloem is called a Sieve Tube Members are stacked to form Sieve Tubes. n Compounds move from cell to cell through end walls called sieve plates. n Each sieve tube member lies next to a companion cell, a specialized parenchyma cell that assists in transport n

Sieve Tube Member

Plant Growth n Meristems Regions where cells continuously divide n Plant growth originates mainly here n 2 types n n Apical n n Meristems Located at the tips of stems and roots Growing region at the tips of stems and roots n Lateral n n Meristems Allows stems and roots to increase in diameter Located near the outside of stems and roots

Meristems

Roots n 3 Main Function of Roots Absorb Water n Anchor the Plant to the Ground n Store Food n

Types of Roots n When a seed sprouts, it produces a primary root. n Taproot: root that develops from the radicle of a plant embryo, grows vertically downward, and forms braches called lateral roots n n Ex) Carrots Instead, numerous small roots develop and branch to produce a fibrous root system. n Ex) Grasses

Types of Roots n Specialized roots that grow from uncommon places, such as stems and leaves, are called adventitious roots. n Storage Root: stores food for the plant

Monocot and Dicot Cross Sections

Root Structures n The tip of a root is covered by a protective root cap n Covers the apical meristem. n Root cap produces a slimy substance that functions like lubricating oil, allowing the root to move more easily through the soil as it grows. n Root hairs: Tiny hairs that extend out from the main root n n increase the surface area of the root Increase the plant’s ability to absorb water and minerals from the soil.

Root Structures n Cortex: Layer just inside the epidermis that is made of spongy ground tissue n Endodermis: Layer in roots between the ground tissue (cortex) and the Vascular Tissue n Casparian strip: Waterproof strip between the cortex and vascular cylinder

Plant Reproduction and Tropisms

Gymnosperm Reproduction n Gymnosperms use cones for reproduction n Pollen cones, also known as male cones, make the male gametophyte n Seed cones, also known as female cones, make the female gametophyte

Flower Reproductive Parts n The specialized leaves of a flower form on the swollen tip of a floral “branch”, which is called a receptacle. n Flower parts are usually found in four concentric whorls, or rings. n n Sepals Petals Stamens Pistils

Sepals n 1 st Whorl or Ring n Outermost circle of floral parts n Are typically green and resemble leaves in most plants n Enclose the bud before it opens n Protect the flower while it is developing

Petals n 2 nd Whorl or Ring n Often brightly colored n Found just inside the sepals n Attract insects and other pollinators to the flower n Neither the petals nor sepals produce reproductive cells, thus they are sometimes called the sterile leaves

Stamens n 3 rd Whorl or Ring n Stamens are the entire male reproductive parts n Stamens are made up of two parts n Filament and Anther

Filament and Anther n Filament n n n Long, thin stalk that supports the anther Helps hold the anther out for pollination Anther n n n At the tip of each filament An oval sac where meiosis takes place, producing haploid male gametophytes (pollen grains) Each flower has several stamens

Pistils n 4 th Whorl or Ring; also known as carpels n Female reproductive structure n 3 parts of a Pistil Stigma n Style n Ovary n

Stigma, Style, Ovary n Stigma n n n Style n n n Top of the pistil Structure is stick to catch pollen Stalk that connects the stigma and the ovary Pollen or sperm travels down the tube once caught on the stigma to the ovary Ovary n Structure that contains one or more ovules where the female gametophyte is produced

Pollination n Pollination that involves just one flower, flowers on the same plant, or flowers from two genetically identical plants is called self-pollination. n In contrast, pollination that involves two genetically different plants is called crosspollination.

Cross-Pollination n Bright petals and distinctive odors attract animals that feed on pollen and nectar, a nourishing solution of sugars. n Many different kinds of animals can be pollinators. n Animals gather nectar, pollen sticks to them, and then they transport the pollen to other areas of the plant/plants.

Seed Germination n A seed will not germinate or sprout until it is introduced to the right conditions n Many seeds will not germinate even when exposed to conditions ideal for germination. n Conditions Needed for Germination n Need water Light and Increased Temperatures Oxygen

Germination n Process of Germination Emergence of a Radicle n Radicle breaks the seed coat & the shoot begins to grow. n Shoot will break through the ground n

Plant Movement n Tropisms and nastic movements are plant responses to environmental stimuli. n n Tropisms occur slowly Nastic movements happen more quickly. n Nastic Movements: non-directional responses to a stimuli n A tropism is a response in which a plant grows either toward or away from an environmental stimulus.

Hormones/Auxins n Plant movements occur due to hormones n n Substance that is produced in one part of an organism and affects another part of the same individual Auxins A class of plant growth substance n Auxins play an essential role in coordination of many growth and behavioral processes in the plant life cycle n

Types of Tropisms n Phototropisms n Gravitropisms n Thigmotropisms n Chemotropisms

Phototropism n n n Thought to occur in some plants when auxin moves to the shaded side of a plant This movement causes cells there to elongate more than the cells on the lighted side. Solar tracking n Motion of leaves or flowers as they follow the sun’s movement across the sky.

Thigmotropism n A plant’s growth response to touching a solid object. n For example, tendrils and stems of vines, such as morning glories, coil when they touch an object.

Gravitropism n A plant’s response to gravity n Thought to occur when auxin accumulates on the lower sides of a horizontal root and stem n Accumulation causes: n n Cell elongation on the lower side of the stem Inhibits cell elongation on the lower side of the root.

Chemotropism n Plant growth that occurs in response to a chemical is called chemotropism. n An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

Nastic Movements n Responses to environmental stimuli but are independent of the direction of the stimuli n 2 Types: Thigmonastic n Nyctinastic n

Nastic Movements n Thigmonastic n n n Occur in response to touch Ex) closing of the leaf trap of a Venus’ flytrap around an insect. Nyctinastic n n Occurs in response to the daily cycle of light and dark Ex)the cyclical vertical and horizontal positioning of leaves in prayer plants.