SEED VASCULAR PLANTS

1. SEED VASCULAR PLANTS • Division Cycadophyta: palms (naked seeds) • Division Ginkgophyta: ginkgo (naked seeds) • Division Gnetophyta: only few species (naked seeds) • Division Coniferophyta: cone plants: pine, spruce, fir, larch, yew (naked seeds) • Division Anthophyta: flowering plants (seeds in fruit)

2. DIVISION ANTHOPHYTA • Flowering plants • Sex organs in flowers • Seeds in ovary that ripens into fruit • Two classes: • Monocotyledoneae (Monocot) • Dicotyledoneae (Dicot)

4. Roots, Stems, and Leaves • Cacti leaves are modified into thin, sharp spines • The reduced-leaf surface area prevents excess water loss

5. Roots, Stems, and Leaves

6. Specialized Tissues in Plants • If you look deep inside a living plant, that first impression of inactivity vanishes • Instead, you will find a busy and complex organism packed with specialized systems and subsystems • Materials move throughout the plant, and growth and repair take place continuously • Plants may act at a pace that seems slow to us, but their cells work together in remarkably effective ways to ensure the plant's survival

7. Seed Plant Structure • The cells of a seed plant are organized into different tissues and organs, as shown in the figure • Three of the principal organs of seed plants are roots, stems, and leaves • These organs are linked together by systems and subsystems that run the length of the plant, performing functions such as transport and protection and coordinating plant activities

8. Tissues in a Vascular Plant  • Vascular plants consist of roots, stems, and leaves • Each of these organs contains dermal tissue, vascular tissue, and ground tissue, as shown by the cross sections of the leaf, stem, and root

9. Tissues in a Vascular Plant 

10. Roots • The root system of a plant absorbs water and dissolved nutrients • Roots anchor plants in the ground, holding soil in place and preventing erosion • Root systems also protect the plant from harmful soil bacteria and fungi, transport water and nutrients to the rest of the plant, and hold plants upright against forces such as wind and rain

11. Stems • A stem has a support system for the plant body, a transport system that carries nutrients, and a defense system that protects the plant against predators and disease • Stems can be as short as a few millimeters or as tall as 100 meters • Whatever its size, the support system of a stem must be strong enough to hold up its leaves and branches • Similarly, the stem's transport system must contain subsystems that can lift water from roots up to the leaves and carry the products of photosynthesis from the leaves back down to the roots

12. Leaves  • Leaves are the plant's main photosynthetic systems • The broad, flat surfaces of many leaves help increase the amount of sunlight plants absorb • Leaves also expose a great deal of tissue to the dryness of the air and, therefore, must contain subsystems to protect against water loss • Adjustable pores in leaves help conserve water while letting oxygen and carbon dioxide enter and exit the leaf

13. Plant Tissue Systems • Within the roots, stems, and leaves of plants are specialized tissue systems • Plants consist of three main tissue systems: • Dermal tissue: is the skin of a plant in that it is the outmost layer of cells • Vascular tissue: is the plant's bloodstream, transporting water and nutrients throughout the plant • Ground tissue: and ground tissue is everything else

14. Dermal Tissue • The outer covering of a plant consists of dermal tissue, which typically consists of a single layer of epidermal cells • The outer surfaces of these are often covered with a thick waxy layer that protects against water loss and injury • The thick waxy coating of the epidermal cells is known as the cuticle • Some epidermal cells have tiny projections known as trichomes, which help protect the leaf and also give it a fuzzy appearance • In roots, dermal tissue includes root hair cells that provide a large amount of surface area and aid in water absorption • On the underside of leaves, dermal tissue contains guard cells, which regulate water loss and gas exchange

15. Vascular Tissue • Vascular tissue forms a transport system that moves water and nutrients throughout the plant • The principal subsystems in vascular tissue are xylem, a water-conducting tissue, and phloem, a food-conducting tissue • Vascular tissue contains several types of specialized cells: • Xylem consists of tracheids and vessel elements • Phloem consists of sieve tube elements and companion cells • As you can see in the figure, both xylem and phloem are made up of networks of hollow connected cells that carry fluids throughout the plant

16. Vascular Tissue in a Stem • Vascular tissue is made up of several different types of cells • Xylem consists of tracheids and vessel elements • Phloem consists of sieve tube elements and companion cells • Xylem tissue (left) conducts water from the roots to the rest of the plant • Phloem tissue (right) conducts a variety of materials, mostly carbohydrates, throughout a plant

17. Vascular Tissue in a Stem

18. Xylem • All seed plants have a type of xylem cell called a tracheid • Recall that tracheids are long, narrow cells with walls that are impermeable to water • These walls, however, are pierced by openings that connect neighboring cells to one another • When tracheids mature, they die, and their cytoplasm disintegrates

19. Xylem • Angiosperms have another kind of xylem cell that is called a vessel element • Vessel elements are much wider than tracheids • Like tracheids, they mature and die before they conduct water • Vessel elements are arranged end to end on top of one another like a stack of tin cans • The cell walls at both ends are lost when the cells die, transforming the stack of vessel elements into a continuous tube through which water can move freely

20. Phloem • The main phloem cells are sieve tube elements • These cells are arranged end to end, like vessel elements, to form sieve tubes • The end walls of sieve tube elements have many small holes in them • Materials can move through these holes from one adjacent cell to another • As sieve tube elements mature, they lose their nuclei and most of the other organelles in their cytoplasm • The remaining organelles hug the inside of the cell wall • The rest of the space is a pipeline through which sugars and other foods are carried in a watery stream

21. Phloem • Companion cells are phloem cells that surround sieve tube elements • Companion cells keep their nuclei and other organelles through their lifetime • Companion cells support the phloem cells and aid in the movement of substances in and out of the phloem stream

22. Ground Tissue • The cells that lie between dermal and vascular tissues make up the ground tissues, shown in figure • In most plants, ground tissue consists mainly of parenchyma • Parenchyma cells have thin cell walls and large central vacuoles surround by a thin layer of cytoplasm • In leaves, these cells are packed with chloroplasts and are the site of most of a plant's photosynthesis • Ground tissue may also contain two types of cells with thicker cell walls: • Collenchyma cells have strong, flexible cell walls that help support larger plants • Collenchyma cells make up the familiar “strings” of a stalk of celery • Sclerenchyma cells have extremely thick, rigid cell walls that make ground tissue tough and strong

23. Ground Tissues  • Ground tissue is made of cells whose cell walls have different thicknesses • Parenchyma cells have thin walls and function mainly in storage and photosynthesis • The root cells shown are filled with purple-staining starch grains • Collenchyma and sclerenchyma cells both function in support • Collenchyma cells have irregularly shaped walls, but the walls of sclerenchymacells are much thicker and harder

24. Ground Tissues 

25. Plant Growth and Meristematic Tissue • Most plants have a method of development that involves an open, or indeterminate, type of growth • Indeterminate growth means that they grow and produce new cells at the tips of their roots and stems for as long as they live • These cells are produced in meristems, clusters of tissue that are responsible for continuing growth throughout a plant's lifetime • The new cells produced in meristematic tissue are undifferentiated—that is, they have not yet become specialized for specific functions, such as transport

26. Plant Growth and Meristematic Tissue • Near the end, or tip, of each growing stem and root is an apical meristem • An apical meristem is a group of undifferentiated cells that divide to produce increased length of stems and roots • The figure at right shows examples of root and shoot apical meristems • Meristematic tissue is the only plant tissue that produces new cells by mitosis

27. Plant Growth and Meristematic Tissue • Meristematic tissue produces new cells by mitosis • Apical meristems, which consist of many actively dividing cells, are located at the tips of shoots (left) and roots (right) • The apical meristem of a root is surrounded by a root cap that protects the root as it grows through the soil

28. Plant Growth and Meristematic Tissue

29. Plant Growth and Meristematic Tissue • At first, the cells that originate in meristems look very much alike: They divide rapidly and have thin cell walls • Gradually, these cells develop into mature cells with specialized structures and functions, a process called differentiation • As these cells differentiate, they produce each of the tissue systems of the plant, including dermal, ground, and vascular tissue

30. Plant Growth and Meristematic Tissue • The highly specialized cells found in flowers, which make up the reproductive systems of flowering plants, are also produced in meristems • Flower development begins when certain genes are turned on in a shoot apical meristem • The actions of these genes transform the apical meristem into a floral meristem, producing the modified leaves that become the flower's colorful petals, as well as the reproductive tissues of the flower • Many plants also grow in width as a result of meristematic tissue that lines the stems and roots of a plant

31. Roots • As soon as a seed begins to grow, it puts out its first root to draw water and nutrients from the soil • Other roots soon branch out from this first root, adding length and surface area to the root system • The overall size of a plant's root system can be astonishing: The total surface area of the root system of a rye plant was measured at more than 600 square meters—130 times greater than the combined surface areas of both the stems and leaves

32. ROOT • Absorbs water and dissolved mineral for the plant • Anchors the plant in the soil • Types: • Fibrous: • Greatly branched • Tap: • Single large root

33. Types of Roots • The two main types of roots are: • Taproots, which are found mainly in dicots • Fibrous roots, which are found mainly in monocots • In some plants, the primary root grows long and thick while the secondary roots remain small • This type of primary root is called a taproot, shown in figure • Taproots of oak and hickory trees grow so long that they can reach water far below Earth's surface • Carrots, dandelions, beets, and radishes have short, thick taproots that store sugars or starches

35. Types of Roots • Plants have taproots, fibrous roots, or both • Taproots have a central primary root and generally grow deep into the soil • Fibrous roots are usually shallow and consist of many thin roots.

36. Types of Roots

37. Types of Roots • In other plants, such as grasses, fibrousrootsbranch to such an extent that no single root grows larger than the rest • The extensive fibrous root systems produced by many plants help prevent topsoil from being washed away by heavy rain

39. Root Structure and Growth • Roots contain cells from the three tissue systems—dermal, vascular, and ground tissue • A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue • Between these two tissues lies a large area of ground tissue • The root system plays a key role in water and mineral transport • Its cells and tissues, as shown in the figure, contain a number of subsystems that carry out these functions • The root's epidermal subsystem performs the dual functions of protection and absorption • Its surface is covered with tiny cellular projections called root hairs • These hairs penetrate the spaces between soil particles and produce a large surface area through which water can enter the plant • Just inside the epidermis is a spongy layer of ground tissue called the cortex • This layer extends to another layer of cells, the endodermis • The endodermis completely encloses the root's vascular subsystem in a region called the vascular cylinder

40. Root Structure and Growth • A root consists of a central vascular cylinder surrounded by ground tissue and the epidermis • Compare how cells in different regions of the root are structurally specialized for different functions • Root hairs along the surface of the root aid in water absorption • Only the cells in the root tip divide • In the area just behind the root tip, the newly divided cells increase in length, pushing the root tip farther into the soil • The root cap, located just ahead of the root tip, protects the dividing cells as they are pushed forward • Dicot roots, such as the one shown in the cross section, have a central column of xylem cells arranged in a radiating pattern • How are root hairs structurally specialized?

41. Root Structure and Growth

42. Root Structure and Growth • Roots grow in length as their apical meristem produces new cells near the root tip • These fragile new cells are covered by a tough root cap that protects the root as it forces its way through the soil • As the root grows, the root cap secretes a slippery substance that lubricates the progress of the root through the soil • Cells at the very tip of the root cap are constantly being scraped away, and new root cap cells are continually added by the meristem • Most of the increase in root length occurs immediately behind the meristem, where cells are growing longer • At a later stage, these cells mature and take on specialized functions • The process by which unspecialized cells change to become specialized in structure and function is known as cell differentiation

43. ROOT GROWTH • Meristem: • Located just behind the root cap • Zone of rapidly dividing cells (become cells in the zone of elongation or root cap) • Root cap: • Tip of root • Protects meristem • As root grows through the soil, cells are rubbed off and replaced by meristematic cells • Zone of elongation: • Cells cease to divide but enlarge • Enlargement of cells pushes the root deeper into the soil • Zone of maturation: • Cells differentiate

45. Root Functions • Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil • How does a root go about the job of absorbing water and minerals from the soil? • Although it might seem to, water does not just “soak” into the root from soil • It takes energy on the part of the plant to absorb water • Our explanation of this process begins with a description of soil and plant nutrients

46. ROOT FUNCTION • Anchors the plant in the soil • Absorption of water and dissolved mineral • Root hair • Fingerlike extension of a single epidermal cell • Greatly increase surface area of the root enabling the root to absorb water and dissolved mineral from the soil • Contains many dissolved substances such as minerals, sugars, and amino acids • Soil contains fewer dissolved substances • Concentration gradient develops between the soil and root hair • Water moves into the root hair by osmosis • Absorbs macronutrients (Nitrogen/Potassium) in large amount and micronutrients (Manganese) in small amounts by active transport • Food storage

47. Uptake of Plant Nutrients  • An understanding of soil helps explain how plants function • Soil is a complex mixture of sand, silt, clay, air, and bits of decaying animal and plant tissue • Soil in different places and at different depths contains varying amounts of these ingredients • Sandy soil, for example, is made of large particles that retain few nutrients, whereas the finely textured silt and clay soils of the Midwest and southeastern United States are high in nutrients • The ingredients define the soil and determine, to a large extent, the kinds of plants that can grow in it

48. Uptake of Plant Nutrients  • To grow, flower, and produce seeds, plants require a variety of inorganic nutrients in addition to carbon dioxide and water • The most important of these nutrients are nitrogen, phosphorus, potassium, magnesium, and calcium • The functions of these essential nutrients within a plant are described in the table • These nutrients are located in varying amounts in the soil and are drawn up by the roots of a plant In addition to these essential nutrients, trace elements are required in small quantities to maintain proper plant growth • Trace elements include sulfur, iron, zinc, molybdenum, boron, copper, manganese, and chlorine • Large amounts of trace elements in the soil can be poisonous

49. Essential Plant Nutrients • Soil contains several nutrients that are essential for plant growth • Each nutrient plays a different role in plant functioning and development, and produces distinct effects when deficient in the soil • If you notice that a plant is becoming paler and more yellow, what nutrient might need to be added?

50. Essential Plant Nutrients