Plant Structure and Functions PDF

PLANTS: FORM AND FUNCTION PREPARED BY: Divine Grace S. Batenga, MSc., LPT 1. Plant Structure and Function 2 The two major groups of angiosperms are the monocots and the eudicots ◍ Angiosperms have dominated the land of more than 100 million years, and...

PLANTS: FORM AND FUNCTION PREPARED BY: Divine Grace S. Batenga, MSc., LPT 1. Plant Structure and Function 2 The two major groups of angiosperms are the monocots and the eudicots ◍ Angiosperms have dominated the land of more than 100 million years, and there are about 250,000 known species of flowering plants living today. ◍ 2 major groups of angiosperms (names refer to the first leaves on the plant embryo) ○ Monocot – has one seed leaf ○ Eudicot – has two seed leaf ◍ COTYLEDONS (seed leaves) – embryonic leaves MONOCOTS ◍ Includes orchids, bamboos, palms, lilies, and all grasses. ◍ Leaves, stems, flowers, and roots are distinctive. ○ Leaves – have parallel veins ○ Stems – have vascular tissues (interna tissues that transport water and nutrients) organized into bundles that are arranged in a scattered pattern ○ Flowers – have their petals and other parts in multiple of three ○ Roots – form a shallow fibrous system that spreads out below the soil surface; well adapted to shallow soils where rainfall is light MONOCOTS With most of their roots in the top few centimeters of soil, monocots, make excellent ground cover and can g=help reduce soil erosion. EUDICOTS ◍ Most flowering plants including many food corps (nearly all fruits and vegetables), majority of ornamental plants, and most shrubs and trees (except gymnosperms). ◍ Typical eudicot seed have two cotyledons. ○ Leaves – have multibranched network of veins ○ Stem – have vascular bundles arranged in a ring ○ Flowers – have petals and other parts in multiple of four or five ○ Root – large vertical root (taproot) extends deep into the soil; well adapted to soils with deep groundwater and enable a plant to grow tall EUDICOT 8 A typical plant body contains three basic organs: roots, stems, and leaves ◍ The basic structure of plants reflects their evolutionary history as land-dwelling organisms. ◍ Most plants must draw resources from two different environments: They must absorb water and minerals from below the ground, while simultaneously obtaining CO2 and light from above the ground. ○ The subterranean roots and aerial shoots (stems and leaves) perform these vital function.  The body parts of a eudicot plant ◍ ROOT SYSTEM – forms all roots of a plant ○ ROOT – an organ that anchors a plant in the soil, absorbs and transports minerals and water, and store carbohydrates ○ ROOT HAIRS – found near the root tips, a vast number of tiny finger- like projections enormously increase the root’s surface area, allowing for the efficient absorption of water and minerals ◍ SHOOT SYSTEM – is made up of stems, leaves, and structures for reproduction (flowers) ○ STEM – are plant organs that bear leaves and buds; located above the ground and support and separate the leaves (promoting photosynthesis) and flowers (responsible for reproduction) ○ NODES – the points at which leaves are attached ○ INTERNODES – the portions of the stem between nodes ○ LEAVES – the main photosynthetic organs in most plants, green stems also perform photosynthesis ○ BUDS – undeveloped shoots; TERMINAL BUD (apical bud) at the apex (tip) of the stem has developing leaves and a compact series of nodes and internodes; AXILLARY BUDS –ne in each of the crooks formed by a leaf and the stem are dormant; APICAL DOMINANCE when terminal bud produces hormones that inhibit the growth of the axillary buds 10  The body parts of a eudicot plant ◍ In the case of a tree, the stems are the trunk and all the branches, including the smallest twig. 11 Three tissue systems make up the plant body ◍ TISSUE – is a group of cells that together perform a specialized function ○ XYLEM – tissue conveys water and dissolved minerals upward from the roots ○ PHLOEM – tissue transports sugars and other organic nutrients from leaves or storage tissues to other parts of the plant ◍ TISSUE SYSTEM – consists of one or more tissues organized into a functional unit within a plant ◍ DERMAL TISSUE SYSTEM – plant’s outer protective covering; forms the first line of defense against physical damage and infectious organisms ○ EPIDERMIS – consists of a single layer of tightly packed cells found in nonwoody plants ○ CUTICLE – waxy coating secreted by dermal cells from leaves and most stem which helps prevent water loss ◍ VASCULAR TISSUE SYSTEM – second tissue system found in all plant bodies; made up of xylem and phloem tissues and provides long- distance transport between the root and shoot system ○ VASCULAR CYLINDER – found at the center of the root with the cross sections of xylem cells radiating from the center like spokes of a wheel and phloem cells filling in the wedges between the spokes 13 ◍ GROUND TISSUE SYSTEM – tissues that are neither dermal nor vascular; accounts for most of the bulk of a young plant, filling the spaces between the epidermis and vascular tissue system; functions includes photosynthesis, storage and support ○ PITH – ground tissue internal to the vascular tissue ○ CORTEX – ground tissue external to the vascular tissue; cortex cells store food as starch and take up minerals that have entered the root through epidermis ○ ENDODERMIS – innermost layer of the cortex, a one cell thick cylinder; selective barrier that regulates the passage of substances between the cortex and vascular tissue 14 ◍ VASCULAR BUNDLES ○ Monocot stems has a scattered bundles, whereas in most eudicots they are arranged in a ring ◍ STOMATA – tiny pores in the epidermis which allow the exchange of CO2 and O2 between the surrounding air and the photosynthetic cells inside the leaf; most of the water vapor lost by a plant passes through stomata. Each stomata is flanked by: ○ GUARD CELLS – specialized epidermal cells that regulate the opening and closing of the stoma ◍ MESOPHYLL – the ground tissue system of a leaf, sandwich between the upper and lower epidermis; consists mainly of cells specialized for photosynthesis ◍ VEIN – a vascular bundle composed of xylem and phloem tissues surrounded by a protective sheath of cells 15  Plant cells are diverse in structure and function ◍ In addition to features shared with other eukaryotic cells, most plant cells have three unique structures ○ CHLOROPLASTS – the sites of photosynthesis ○ LARGE CENTRAL VACOULE – containing fluid that helps maintain cell turgor (firmness) ○ CELL WALL – made from the structural carbohydrate cellulose that surrounds the plasma membrane; functions as protection PLASMODESMATA – are open channels in adjacent cell walls through which cytoplasm and various molecules can flow from cell to cell  Plant cells are diverse in structure and function ◍ 5 major types of plant cells ○ 1. Parenchyma Cells – Parenchyma cells are the most common and versatile type of plant cell. Function: They are primarily involved in photosynthesis, storage, and secretion. Parenchyma cells also have the ability to divide and regenerate, which makes them important in wound healing and growth. Characteristics: ○ Thin primary cell walls. ○ Large central vacuole. ○ Living at maturity. ○ Found in the ground tissue (e.g., in leaves, stems, and roots).  Plant cells are diverse in structure and function ◍ 5 major types of plant cells ○ 2. Collenchyma Cells Function: Collenchyma cells provide structural support to growing regions of the plant, especially in areas like stems and petioles. They help plants maintain flexibility while providing strength. Characteristics: ○ Unevenly thickened cell walls. ○ Living at maturity. ○ Found in the ground tissue, often under the epidermis in stems and petioles.  Plant cells are diverse in structure and function ◍ 5 major types of plant cells ○ 3. Sclerenchyma Cells Function: Sclerenchyma cells are involved in providing rigid support and protection for Mature plant parts. Their thick secondary cell walls are often lignified, making them very strong. Characteristics: ○ Dead at maturity (lack living contents). ○ Have thick, lignified secondary walls. Two types of sclerenchyma cells ○ Two types: fibers (long, slender cells for FIBER – long and slender and is usually support) and sclereids (shorter, irregularly arranged in strands shaped cells, often found in seed coats and SCLEREIDS – are shorter than fiber nutshells). cells, have thick, irregular, and vert hard ○ Found in both ground tissue and vascular secondary walls tissue.  Plant cells are diverse in structure and function ◍ 5 major types of plant cells ○ 4. Xylem Cells Function: Xylem cells are responsible for the transport of water and minerals from the roots to the rest of the plant. They are an essential part of the vascular system. Characteristics: ○ Includes several cell types: tracheids (elongated cells that conduct water) and vessel elements (larger, wider cells that also conduct water). ○ Dead at maturity, with thick, lignified cell walls that allow for efficient water transport. ○ Found in the vascular tissue of the plant.  Plant cells are diverse in structure and function ◍ 5 major types of plant cells ○ 5. Phloem Cells Function: Phloem cells are involved in the transport of sugars and other organic compounds produced during photosynthesis from the leaves to other parts of the plant. Characteristics: ○ Includes sieve tube elements (the main transport cells) and companion cells (which support sieve tube elements). ○ Living at maturity, but with no nucleus in sieve tube elements (they rely on companion cells for metabolic functions). ○ Found in the vascular tissue of the plant. 2. PLANT NUTRIENTS, SOIL, NUTRITION, AND SYMBIOSIS 22 Plant health depends on obtaining all of the essential inorganic nutrients ◍ In contrast to animals, which require a diet of complex organic (carbon-containing) foods, plants survive and grow solely on CO2 and inorganic substances—that is, plants are autotrophs. ◍ The ability of plants to assimilate CO2 from the air, extract water and inorganic ions from the soil, and synthesize organic compounds is essential not only to the survival of plants but also to the survival of humans and other animals.  Plant health depends on obtaining all of the essential inorganic nutrients ◍ ESSENTIAL ELEMENT – if a plant must obtain it from it environment to complete its life cycle – that is, to grow from a seed and produce another generation of seeds ◍ MACRONUTRIENTS – nine essential elements, plants require relatively large amounts of them ◍ MICRONUTRIENTS – elements that plants require in very small quantities  Fertilizers can help prevent nutrient deficiencies ◍ The quality of soil—especially the availability of nutrients—affects the health of plants and, for crops, the quality of our own nutrition—you are indeed what you eat! ◍ Such mineral shortages can stunt plant growth, and if the stunted plant produces any grain, it is likely to have low nutritional value. In this way, nutritional deficiencies in plants can be passed on to livestock or human consumers.  Fertilizers can help prevent nutrient deficiencies ◍ The symptoms of nutrient deficiencies are often distinctive. ◍ Many growers can therefore make visual diagnoses, which can be confirmed by having soil and plant samples chemically analyzed at a laboratory.  Fertilizers can help prevent nutrient deficiencies ◍ Nitrogen shortage is the most common nutritional problem in plants. ◍ Soils are usually not deficient in total nitrogen, but they are often deficient in the nitrogen compounds that plants can use: ○ dissolved nitrate ions (NO3-) and ammonium ions (NH4+ ). ◍ Signs of nitrogen deficiency include stunted growth and yellow-green leaves, starting at the tips of older leaves. ◍ Other nutrients that are commonly deficient in plants include phosphorus and potassium.  Fertilizers can help prevent nutrient deficiencies Once a nutrient deficiency is diagnosed, treating the problem is usually simple. ◍ FERTILIZERS – compounds given to plants via the soil to promote the plant’s growth.  Fertilizers can help prevent nutrient deficiencies ◍ INORGANIC FERTILIZER ○ Inorganic fertilizers (also called mineral fertilizers) may contain naturally occurring inorganic compounds (such as mined lime- stone or phosphate rock) or synthetic inorganic compounds (such as ammonium nitrate). ○ Inorganic fertilizers come in a wide variety of formulations, but most emphasize their “N-P-K ratio,” the relative amounts of the three nutrients most often deficient in depleted soils: nitrogen (N), phosphorus (P), and potassium (K).  Fertilizers can help prevent nutrient deficiencies ◍ ORGANIC FERTILIZER ○ Organic fertilizers are composed of biologically derived products. ○ COMPOST – a soil-like mixture of decomposed organic matter ○ Many gardeners maintain a free- standing compost pile or an enclosed compost bin to which they add leaves, grass clippings, yard waste, and kitchen scraps (avoiding meat, fat, and bone). Over time, the vegetable matter is broken down by naturally occurring microbes, fungi, and animals  Fertile soil supports plant growth ◍ Fertile soil contains a mixture of small rock and clay particles that hold water and ions and also allow O2 to diffuse into plant roots. ◍ Humus (decaying organic material) provides nutrients and supports the growth of organisms that enhance soil fertility. 31 Most plants depend on bacteria to supply nitrogen ◍ Relationships with other organisms help plants obtain nutrients. Bacteria in the soil convert atmospheric N2 to forms that can be used by plants. 32  Mutually beneficial relationships have evolved between plants and other kinds of organisms ◍ Many plants form mycorrhizae, mutually beneficial associations between roots and fungi. ◍ A network of fungal threads increases a plant’s absorption of nutrients and water, and the fungus receives some nutrients from the plant. ◍ Legumes and certain other plants have nodules in their roots that house nitrogen- fixing bacteria. 33  The plant kingdom includes epiphytes, parasites, and carnivores ◍ EPIPHYTES – plants that grow on other plants ◍ PARASITIC PLANTS – siphon nutrients from host plants ◍ CARNIVOROUS PLANTS – obtain nitrogen by digesting insects 34 3. CONTROL SYSTEMS IN PLANTS (PLANT HORMONES AND RESPONSES TO STIMULI) 35  A series of experiments by several scientists led to the discovery of a plant hormone ◍ Hormones coordinate the activities of plant cells and tissues. ○ Small amounts of hormones regulate plant growth and development ◍ Experiments carried out by Darwin and others showed that the tip of a grass seedling detects light and transmits a signal down to the growing region of the shoot.  PLANT HORMONES ◍ AUXIN ○ Stimulates the elongation of cells in young shoots ○ Plants produce the auxin IAA in the apical meristems at the tips of shoots ○ Auxin acts by weakening cell walls, allowing them to stretch when cells take up water. 37  PLANT HORMONES ◍ CYTOKININS ○ Stimulate cell division ○ Cytokinins, produced by roots, embryos, and fruits, promote cell division. ○ Cytokinins from roots may balance the effects of auxin from apical meristems, causing lower buds to develop into branches. 38  PLANT HORMONES ◍ GEBBERELLINS ○ Affect stem elongation and have numerous other effects ○ Gibberellins stimulate the growth of stems and leaves and the development of fruits. ○ Gibberellins released from embryos function in some of the early events of seed germination. 39  PLANT HORMONES ◍ ABSCISIC ACID ○ Inhibits many plant processes ○ Abscisic acid (ABA) inhibits germination. ○ The ratio of ABA to gibberellins often determines whether a seed remains dormant or germinates. ○ Seeds of many plants remain dormant until their ABA is The Mojave Desert in California after a rain inactivated or washed away. 40  PLANT HORMONES ◍ ETHYLENE ○ Triggers fruit ripening and other aging process. ○ As fruit cells age, they give off ethylene gas, which hastens ripening. ○ A changing ratio of auxin to ethylene, triggered mainly by shorter days, causes autumn color changes and the loss of leaves from deciduous trees. 41  Plant hormones have many agricultural uses ◍ Auxins can delay or promote fruit drop. ◍ Auxins and gibberellins are used to produce seedless fruits. ◍ A synthetic auxin called 2,4-D kills weeds. ◍ There are questions about the safety of using such chemicals. 42 43 44 RESPONSES TO STIMULI ◍ TROPISM – orient plant growth toward or away from environmental stimuli. ○ Plants sense and respond to environmental changes. ○ Tropisms are growth responses that cause a plant to grow toward or away from a stimulus. 45  RESPONSES TO STIMULI ◍ PHOTOTROPISM – bending in response to light, results from auxin moving from the light side to the dark side of a stem in grass seedlings. ◍ GRAVITROPISM – a response to gravity, caused by settling of organelles on the low sides of shoots and roots, which may trigger a change in hormone distribution. ◍ THIGMOTROPISM – a response to touch, causes tendrils and vines to coil around objects. Phototropism 46 RESPONSES TO STIMULI 47  Plants have internal clocks ◍ INTERNAL BIOLOGICAL CLOCK – controls sleep movements and other daily cycles in plants ◍ These cycles, called circadian rhythms, persist with periods of about 24 hours even in the absence of environmental cues, but such cues are needed to keep them synchronized with day and night. 48  Plants mark the seasons by measuring photoperiod ◍ The timing of flowering is one of the seasonal responses to photoperiod, the relative lengths of night and day. 49  Phytochromes are light detectors that help set the biological clock ◍ Light-absorbing proteins called phytochromes may help plants set their biological clock and monitor photoperiod. 50  Defenses against herbivores and infectious microbes have evolved in plants ◍ Plants protect themselves against herbivores using physical barriers (such as thorns), and chemicals that are toxic or that recruit predators. ◍ Defenses against infection include microbe-killing chemicals and alarm signals that travel through the plant body. 51 END…. 52