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A review on Crop Sciences (Plant Biology)


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This is a three chapter review for the Agriculture Major Admission Test conducted by the College of Agriculture of Cavite State University, the topicsare: Plant Bilogy, Crop and Agriculture and basic Physiological processes of plants. Credits to all my sourceswhich include lecture notes from our faculty, online sources and books published in the Republic of the Philippines.

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A review on Crop Sciences (Plant Biology)

  1. 1. By: Mark Lawrence B. Edullantes Cavite State University Indang, Cavite Philippines
  2. 2. Topics to be discussed: • Plant Biology • Agriculture and Crop Science • Basic Physiological processes of crops
  3. 3. Chapter 1: PLANT BIOLOGY
  4. 4. Review Questions to be Answered Define calyx, corolla, receptacle, peduncle, pedicel, pistil, filament, ovary and carpel. Distinguish monocots from dicots. What is the difference between a fruit and a vegetable? What causes an embryo to develop into a fruit? What are the various parts of a fruit? How do fleshy fruits differ from dry fruits?
  5. 5. Distinguish among simple, aggregate and multiple fruits. Distinguish achenes, grains and nuts. What adaptation do seeds and fruits have for dispersal by water and animals? Define plumule, radicle, coleoptile, coleorhizae, hypocotyls, after-ripening, stratification and vivipary.
  6. 6. The Leaves  The leaves are the lateral outgrowth of the plant’s stem.  They are flattened surfaces which are covered by a transparent layer of cell called epidermis, which allows sunlight to enter in the leaf tissues.  Leaves are usually green in color due to the presence of substance called chlorophyll.
  7. 7. Parts of typical leaf: • Blade or lamila • Petiole or leaf stalk Petiolated leaf Sessile leaf • Midrib • Stipule Stipulated leaf Ex-stipulated leaf
  8. 8. Other leaf parts & function • Lower epidermis – outmost tissue on the lower side of the leaf; protects the leaf • Upper epidermis – outmost tissue on the upper side of the leaf; protects the leaf • Palisade layer – rows of elongated cells in the upper center of leaf; site of photosynthesis • Cuticle – waxy layer on the covering the epidermis; holds in moisture, prevents too much absorption of water • Stoma – opening between the guard cells; allows for gas exchange and some water • Guard cells – surround the stoma; control the opening and closing of the stoma • Vein – supply support for the leaf; contain the xylem and the phloem
  9. 9. • Spongy layer – irregular shaped cells in lower center of leaf; absorbs gas & some water • Air space – space in the spongy layer; contain gases • Xylem – found in the vein; transports minerals and water from roots to shoots • Phloem – found in the vein; transports sugar & other products of photosynthesis from leaves to other parts of the plant • Chloroplast – cells in the leaves that contain chlorophyll; trap light energy and convert it to chemical energy • Mesophyll – all of the middle tissue of the leaf
  10. 10. Leaf Phyllotaxy Phyllotaxy refers to the arrangement of leaves in a stem of a plant. Alternate- when there is only one leaf at a node Example. Gumamela Opposite- when there are two leaves at a node Example. Santan Whorled- when there are 3 or more leaves at a node Example. Adelfa
  11. 11. Leaf venation It refers to the arrangement of the veins in a leaf. Parallel venation- veins run parallel to each other from the base to the apex, of from the midrib to the margin (as in corn and banana). Netted venation- veins branch out repeatedly and form a network over the blade Includes: Pinnate venation Palmate venation
  12. 12. Kinds of leaves Simple leaf- the blade is made up of only one piece Compound leaf- the blade is made up of two or more pieces. Each piece is called a leaflet and their individual stalks are called petiolules. • Pinnately compound leaves- when there are two rows of leaflets on both sides of the rachis (odd or evenly pinnate) • Palmately compound- when the leaflets radiate from a common point.
  13. 13. Functions of the leaf 1. Photosynthesis. Leaves make food for the plants in the process called photosynthesis. The collected solar energy from the sunlight together with inorganic substances such as water and carbon dioxide produce a hexose sugar (called glucose) which is used in plant metabolism. 2. Transpiration and Guttation. Leaves take part in other plant functions as well including transpiration and guttation, both of which remove excess water from the plant. 3. Respiration. This is the process by which a plant obtains oxygen and energy. 4. Food and water storage. Leaves may also store food and water. 5. Structural support.
  14. 14. The Stem -It is the part of the vascular plants that commonly bears leaves and buds. -Usually aerial, upright and elongated, but may be highly modified in structure.
  15. 15. Parts of stem: • Nodes- those points on the stem at which leaves or buds arise • Internodes- the regions of the stem between the nodes
  16. 16. Functions of the stem: 1. Production and support of leaves and reproductive structures 2. Conduction of water and nutrients 3. Translocation of food substances to other plant parts 4. Food and water storage (such in cactus) 5. Propagation materials as stem cuttings in cassava and fruit crops through grafting.
  17. 17. Structure of stem Conducting tissues within the plant stems are arranged in columns called vascular bundles. These bundles are composed of xylem, which conducts water up the stem, and of phloem, which transports sugars produced during photosynthesis from leaves down the stem. Vascular bundles extend into leaves, in which they are called veins as the stem grows longer, new cells are added to the vascular system, providing conductive tissues for new leaves and branches
  18. 18. The arrangement of vascular bundles differs in the stems of two major groups of angiosperms or flowering plants: the monocotyledons and dicotyledons. In monocotyledons, such as corn, the vascular tissue occurs in many scattered bundles throughout the cross section of the stem. In dicotyledons, such as the pea, the vascular bundles are arranged in a cylindrical ring.
  19. 19. Cross section of a woody plant
  20. 20. The reminder of the stem constitutes the fundamental tissue and is usually divided into the cortex, or portion outside the ring of vascular bundles, and the pith, the portion inside the cylindrical ring. The outer layer of the stem of herbaceous plants is called epidermis.
  21. 21. Cambium thin layer of cells between the xylem and phloem  During the growing season, these cells divide actively, producing new cells that differentiate into xylem, or wood, toward the inner side of the cambium and phloem toward the outer side As the cambium grows, the diameter of the stem increases, and the new phloem presses outward upon the soft tissues of the cortex, which become distorted and die.
  22. 22. Kinds of stem: 1. Herbaceous stems- stem lacking in woody growth. May derived strength by other means (e.g bamboo by the presence of numerous fibers). 2. Woody stems- are thickened and hard stems covered by periderm.
  23. 23. Xylem and Phloem vessel
  24. 24. Specialized stems: Thorns- rose, citrus Tendrils- cucurbits and some legumes Corms- gladiola and gabi Tubers- white potato Rhizome- ginger Photosynthetic stem- cacti Economic importance of stem: • Source of raw materials for industry (e.g. gummy exudates, rubber sap etc.) • Source of building materials ( e.g. timber) • Source of food (e.g sugarcane, labong)
  25. 25. The Root System • The root is the vegetative part which originally goes into the soil or growing media. It is a cylindrical in structure, normally without chlorophyll, not divided into nodes and internodes and does not bear leaf or floral bed. • Upon seed germination, a part of embryo within it (radicle) grows out and develops into the first root. This may develop either into a thickened taproot, from which thinner branch roots arise, or into numerous adventitious roots.
  26. 26. • A fibrous root system (monocot) with numerous fine roots of similar diameter then develops from the adventitious roots. Many mature plants have a combination of taproot and fibrous root system.
  27. 27. Classification of roots according to origin: 1. Primary root- located at the base of the stem, developed from radicle. 2. Secondary root- arises from the primary root and may give rise to other roots. 3. Adventitious root- those that grow from bulbs (e.g. onion), rhizomes (e.g. ginger), tubers (e.g. potatoes) and plant cuttings (asexual reproduction).
  28. 28. Functions of the root system: Anchorage of the plants into the soil Absorption of water and mineral from the soil For food and water storage (as in sweet potatoes and yams) Provide means for asexual reproduction For hormone production of plants
  29. 29. Kinds of root system: Fibrous (monocot) vs. Taproot (dicot) roots systems: 1. Fibrous root system- composed of a mass of similar- sized roots with numerous smaller root branches. Examples are food staples rice and corn. 2. Taproot system- composed of one, or occasionally, more primary roots which remain dominant from which secondary roots develop. Examples are mango and mongo (legume), If the taproot is enlarged so as to serve as storage for food and water, it is termed fleshy taproot. Examples include carrot and radish.
  30. 30. Specialized roots Metamorphosed or specialized roots are roots which are modified to perform functions other than for absorption or anchorage. 1. For support of other plant organs – Brace roots- when the part of the stem near the ground is very small and incapable of supporting the weight of the whole plant, large roots grow out from the main stem and serve as the brace of the plant (as in corn) – Prop roots- adventitious roots that grow from the branches of the plant and prop them up (as in pandan plant). – Aerial adventitious roots- develop into attach branches to their supporting structures such as trellis or posts. (As in Ivy). – Buttress roots- plant-like extension growing from the upper portion of a large root ( as in narra, and Ficus benjamina)
  31. 31. 2. For photosynthesis  Roots to expose light or aerial roots produce chlorophyll and thus, trough photosynthesis, cam manufacture with them, are called photosynthetic roots. (As in orchids).  For reproduction through asexual propagation  Many plants produce adventitious buds along the roots that grow near the surface of the grounds. The buds grow into aerial stems called suckers which become rooted and thus, develop as new plants. Examples include grasses and weeds.
  32. 32. 3. For food and water storage Underground roots may become very much thickened and enlarged. They serve as storage sits for large quantities of starch and other carbohydrates. Examples include sweet potatoes and yams
  33. 33. Root structure Longitudinal section of a young root a. The root cap- Composed of thimble-shaped mass of parenchyma cells covering the tip of each root, Protects from damage the delicate tissues behind it as the young root tip pushes through the soil particles. b. The meristematic region- This is the region of cell division or mitosis. The root cap is produced by the cells in this region, which is the center of the root tip and surrounded by the root cap. It is composed of an apical meristem. Cells are of then cube-shaped, with relatively large centrally located nuclei and few small vacuoles.
  34. 34. c. The region of elongation- This region is composed of the mass of cell recently formed in the merismatic region and undergoing enlargement, particularly in length. Cell alls also increase in length, new protoplasm is formed and vacuoles merge and increase in size. d. The region of maturation- This region is called the region of differentiation or root-hair one. It is composed of cells which have become differentiated into the mature tissues of the root. Root hairs develop from many epidermal cells in this region.
  35. 35. 2. Cross section of a root through the region of maturation • Epidermis: The outermost region of the root made up of a single layer of non-cutinized cells. The surface tissue absorbs water and minerals from the soil and offer protection to the inner tissues of the root. It has specialized structures that is in work of absorption called root hairs. • Cortex: A tissue composed of parenchyma cells adjacent to the epidermis. It is comprised of irregularly shaped parenchyma cells with many intercellular spaces. This is chiefly a water and food storage site.
  36. 36. • Endodermis: innermost layer of the cortex with inner and side walls thickened with suberin. Such thickenings usually take the form of thin waxy strips called Casparian strips. • Pericycle: a cylinder of parenchyma cells inside the endodermis and immediately adjacent to it. It is composed of cells which retain their capacity to divide even after they have matured. Lateral or branch roots arise from the pericycle.
  37. 37. • Primary xylem: Composed of water conducting cells which form a solid core in the center of the roots of most dicot and conifers. In monocots, the primary xylem forms a cylinder of tissue. • Primary phloem: Composed of food conducting cells. It forms in discrete patches between xylem arms of both monocot and dicot roots.
  38. 38. The Reproductive System of the Plants The Flower Flower- name applied to reproductive organs of certain plants which produce fruits containing seeds. Not all seed plants have flowers; conifers, for example produce seed on scales united to form a cone.
  39. 39. Parts of a Flower • Receptacle or floral axis- terminal branch consisting of a modified stem, the floral axis, or receptacle. The floral axis bears one to four types of specialized appendages, or modified leaves, usually arranged in whorls in the more advanced flowers and spirally arranged in the more primitive ones. • Calyx- the outermost whorl consists of a number of sepals that protect the flower bud before it blooms. • Corolla- composed of a number of petals, often bearing nectar- producing glands that aid in attracting pollinators. The calyx and corolla are collectively known as the perianth.
  40. 40. • Androecium- consists of a number of stamens that produce in anthers the pollen necessary for reproduction. Two whorls of stamens may be present. • Gynoecium- consists of several carpels frequently fused to form a pistil. Each carpel contains at least one ovary to which is attached ovules, or immature seeds.
  41. 41. Flowering plants are divided into two major classes, the dicots and the monocots. In the dicots, floral organ in multiples of five or four predominate, in the monocots, multiples of three are usual.
  42. 42. Types of flower 1. Complete flowers- bear sepals, petals, stamens and pistils 2. Incomplete flowers- lack any of the mentioned parts – Imperfect flower- lack the parts involved in reproduction- the stamens or pistils- – Perfect flower- both pistils and stamens are present but lack the other parts. If only pistils are present the flower is said to be pistillate; with stamens only, staminate. Typical flowers are bisexual. When staminate and pistillate flowers occur on one plant, it is said to be monoecious when they occur on different plants, dioecious.
  43. 43. Forms of Flower 1. Radially symmetrical flowers- sepals and petals are uniform in size and arranged in a star-shaped or radially symmetrical form. 2. Bilaterally symmetrical flowers- have petals that differ in size and shape. The five petals the sweet pea, for example, include a large, showy banner, or standard petal, two smaller wing-like petals at the side of the flower, and between them the keel, two petals that encase the pistils and stamens. These are united along their edges.
  44. 44. Figure 12. Types of flower inflorescence
  45. 45. Pollination The transfer of pollen from the stamen, or male structures of a flower, to the region of the pistil or female structure, of the same or different flower. Kinds of pollination Self-pollination or autogamy- the pollen is transferred from the stamen to the stigma of the same flower. Cross-pollination or allogamy- pollen is transferred from one flower to another on the same plant (geitonogamy) or to a flower of another plant of the same species (xenogamy). Agents of pollination  Wind  Bees and other insects  Birds and bats  Man (hand pollination) Opening of flowers is termed anthesis.
  46. 46. The Fruit A fruit is mature ovary on flowering plants, together with all inseparably connected parts of the flower. It is normally produced only after fertilization of ovules taken place. In some plants, largely cultivated varieties such as seedless citrus fruits, bananas and cucumbers, fruit matures without fertilization, a process known as parthenocarpy. The maturation of the ovary results in the withering of stigmas and anthers and enlargement of the ovary or ovaries. Ovules within fertilized ovaries develop to produce seeds. In unfertilized varieties, seeds fail to develop, and the ovules remain their original size.
  47. 47. Function of the Fruits The major function performed by fruit is the protection of the developing seeds. In many plants fruit also aids in seed distribution as in coconut and other species where fruits themselves function as propagating material.
  48. 48. Structure of Fruit  Pericarp As the ovary matures, its wall develops to form the pericarp, divided into three layers. The outermost, exocarp, is usually a single epidermal layer. The extent of the middle layer, mesocarp, and the inner layer, endocarp, varies widely, but in any single type of fruit one of the layers may be thick, the others thin. In fleshy fruits the pulpy layer is usually the mesocarp, as in peaches or grapes.  Seed/Seeds The seed or seeds, which lie immediately within the pericarp, in some cases constitute the entire edible portion of the fruit. For example, the hard outer husk of a coconut is the complete pericarp, and the edible part inside, including the “milk”, is the seed.
  49. 49. Structure of the fruit wall The fruit consists of the wall and the seed. The wall could be dry (has a very low moisture content) or fleshy (succulent). A dry fruit could be either dehiscent (splits apart when ripe) or indehiscent. Thus beans become dry and dehiscent at maturity while the mango is fleshy. The fruit may show three distinct layers: exocarp or pericarp, the outermost layer; mesocarp, the middle part and endocarp, the inner part.
  50. 50. Caryopsis- the pericarp or seed coat is a very thin layer and is fused with the ovary (e.g corn kernel).
  51. 51. Types of Fruit 1. Simple fruit- formed from a single ovary, developed from the pistil of a single flower which may be single or compound 2. Aggregate fruit- composed of many ovaries attached to a single receptacle, as in soursop and strawberry. 3. Multiple fruit- formed from the coalesced ovaries of an entire inflorescence as in pineapple.
  52. 52. Sub-division of simple fruit  Dry simple fruit  Fleshy simple fruit Ovary walls that develop into simple fruits are succulent when young, but as they mature, those of dry fruits lose most of their moisture, whereas those of fleshy fruits increase in size and moisture capacity. Sub-classes of dry fruits 1. Dry dehiscent fruits- dry fruits that split when ripe 2. Dry indehiscent fruits- those that do not split when ripe
  53. 53. Types of fleshy fruits • Berry- typified by the tomato possesses seeds dispersed throughout the fleshy mesocarp and endocarp; the exocarp is thin and skinlike. • Hesperidium- all citrus fruits. These have leathery rinds composed of exocarp and mesocarp and juicy section of endocarp. • Pepo- fruits of the Cucurbitacae, includes cucumber, pumpkins and melons. The outer layer of the pepo is receptacle tissue covering the exocarp; the pulpy portion of the fruit is mostly endocarp and mesocarp. endocarp, the fleshy portion is mesocarp.
  54. 54. • Pome- fruits with a pericarp limited to the so-called core and the inner fleshy portion of the fruit, as in apples and pears. The outer portion of the fleshy part of a pome is tissue developed from the fusion of the other floral parts and the ovary. • Drupe- the stone fruit of such plants as mango, avocado, plum, cherry and peach. The single seed is surrounded by a stony
  55. 55. The Seed Seed, term applied to the ripened ovule. Seeds of the angiosperms or flowering plant differ from those of the gymnosperms or conifers and related plants, in being enclosed in the ovary that later forms a fruit; gymnosperm seeds lie on exposed scales of the cones.
  56. 56. Parts of a dicot seed: • Seed coat- protective covering • Plumule- embryo shoot • Hypocotyle-radicle axis • Hilum- marks the point at which the ovule was attached to the ovary. • Microphyle- visible pore adjacent to the hilum • Cotyledons- food-storage organs • that also function as the first leaves of the seedling plant.
  57. 57. Parts of a monocot seed: • Pericarp- From the wall of the embryo sack (mother tissue) • Endosperm- Food supply containing 3 sets of chromosomes (2 from the mother and 1 from the father) • Embryo - Immature plant • Cotyledon- Seed leaf • Coleoptile- • Plumule-shoot • Radicle- root • Coleorhiza-
  58. 58. Seeds remain viable for periods that vary greatly, depending on the species and the condition of the storage. Vivipary- the embryo develops from the zygote continues to grow without pause. No dormancy of the seed.
  59. 59. Monocot Vs. Dicot features
  61. 61. Agriculture defined Agriculture is the art, science and business of growing crops and raising livestock for food, shelter and raw materials for processing essential to mankind. It also involves primary processing of farm produce. The science, art, or practice of cultivating the soil, producing crops, and raising livestock and in varying degrees the preparation and marketing of the resulting products (Merriam-Webster).
  62. 62. Crop production defined According to Lantican (2001), Crop production may be defined as the art and science of producing crops, aimed at increasing productivity and quality of the products in order to maximize monetary returns but at the same time minimize, if not completely eliminate, the negative effects on the environment. Crop production covers principles underlying crop growth and development, production practices of economically important agronomic and horticultural crops, harvesting, and primary aspects of crop processing. Long term objective of crop production is to enhance the environment.
  63. 63. Branches of Crop Science • Agronomy Agronomy is a term derived from the Latin words, “Agros”, meaning field or farm and “Nomos”, pertaining to management. It involves annual herbaceous plant grown on large-scale or extensive culture.
  64. 64. Classification of major agronomic crops • Cereal or grain crops- Graminaceae, which are food staples. It includes important grains such as corn, rice, sorghum, wheat, millet and rye. • Grain legumes or pulses – belong to family Leguminoseae, which are consumed in dry seed form. It includes mungbean, peanut and soybean. • Fiber crops- sources of commercial fiber which includes: kenaf, jute, ramie and cotton. • Root crops- which are rich sources of carbohydrates. It inclides cassava and sweet potato. • Forage legumes and grasses for animal fodder- Important grasses are: napier, guinea grass, paragrass, and pangola grass. Important legume forage are cento, ipil-ipil, Townville style and siratro. • Crops for industrial processing- The economic species include sugarcane, tobacco and castor bean.
  65. 65. Horticulture The term horticulture derived from the Latin words, “hortus”, meaning garden and “colore”, meaning to cultivate. It involves annual and perennial species which are grown under a system of “intensive” culture or special care. Intensive cultivation refers to higher unit of input in terms of labor and capital is invested per cultivated land area.
  66. 66. Classification of major horticultural crops: • Olericulture or vegetable group- It consists of broad range of crops including leafy, fruit and root vegetables. • Pomological or fruit crops- Are consumed fresh or processed form. It includes mango, pineapple, papaya, lanzones, rambutan, pummel and durian. • Ornamental plants- Includes cutflowers, cutfoliage, flowering pot plant, landscape plant and dry and processed ornamentals.
  67. 67. • Plantation crops for industrial processing- crops need processing for consumption includes coconut (oil), cacao (chocolate), coffee (beverage), abaca (textile) and rubber. It also includes: - Spice producing crops - black pepper and vanilla - Aromatic or essential-oil producing crops, lemon grass, citronella and ilang-ilang - Medicinal and biocidal plants, are sources of pharmaceutical or insecticidal compounds. It includes lagundi, yerba Buena and sambong.
  68. 68. Crop Protection Encompasses the discipline of 1.) entomology, study of insects; 2.) plant pathology, the study of plant diseases; 3.) weed science, the study of weed; and 4.) the study of other vertebrate pests (e.g. rats and birds).
  70. 70. Crop Growth and Development Growth is the irreversible increase in size and in dry matter due to increase in vegetative or reproductive parts. It includes increase in number of cells, weight and enlargement of the cells in terms of width, length, diameter and area. Development refers to all the changes that the plant undergoes from germination up to before death. Differentiation is the process by which cells become specialized into recognizable tissues and organs.
  71. 71. Photosynthesis Photosynthesis is the process in which carbon dioxide and water, to the presence of light and chlorophyll, are converted to carbon- containing energy rich organic compounds needed for plant metabolism. The process of photosynthesis can be generalized by the following:
  72. 72. Consequences: 1. Conversion of light energy into chemical energy, for metabolic processes by plants; 2. Inorganic compounds are converted into essential foodstuffs and other products useful to man; 3. The release of oxygen into the atmosphere which is used in respiration of both plants and animals.
  73. 73. Two phases of Photosynthesis
  74. 74. Light Dependent Reaction The light dependent reaction happens in the thylakoid membrane and converts light energy to chemical energy. This chemical reaction must, therefore, take place in the light. Chlorophyll and several other pigments such as beta-carotene are organized in clusters in the thylakoid membrane and are involved in the light reaction. Each of these differently-colored pigments can absorb a slightly different color of light and pass its energy to the central chlorphyll molecule to do photosynthesis. The central part of the chemical structure of a chlorophyll molecule is a porphyrin ring, which consists of several fused rings of carbon and nitrogen with a magnesium ion in the center.
  75. 75. Light Independent Reaction (Dark reaction) The energy harvested via the light reaction is stored by forming a chemical called ATP (adenosine triphosphate), a compound used by cells for energy storage. This chemical is made of the nucleotide adenine bonded to a ribose sugar, and that is bonded to three phosphate groups. This molecule is very similar to the building blocks for our DNA.
  76. 76. The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn’t directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Actually, notice that the first product of photosynthesis is a three- carbon compound calledglyceraldehyde 3- phosphate. Almost immediately, two of these join to form a glucose molecule.
  77. 77. C3 and C4 pathways C3 pathway Most plants like rice, wheat, potato cotton and tobacco put CO2 directly into the Calvin cycle. Thus the first stable organic compound formed is the glyceraldehyde 3-phosphate. Since that molecule contains three carbon atoms. On hot summer weather the amount of water that evaporates from the plant increases.
  78. 78. Plants lessen the amount of water that evaporates by keeping their stomates closed during hot, dry weather. Unfortunately, this means that once the CO2 in their leaves reaches a low level, they must stop doing photosynthesis. Even if there is a tiny bit of CO2 left, the enzymes used to grab it and put it into the Calvin cycle just don’t have enough CO2 to use.
  79. 79. C4 pathway Other plants like corn and sugarcane capture CO2 in a different way: they do an extra step first, before doing the Calvin cycle. These plants have a special enzyme that can work better, even at very low CO levels, to grab CO2 and turn it first into oxaloacetate, which contains four carbons.
  80. 80. CAM Plants (Crassulecean acid metabolism) Some plants (for example, cacti and pineapple) that live in extremely hot, dry areas like deserts, can only safely open their stomates at night when the weather is cool. Thus, there is no chance for them to get the CO2 needed for the dark reaction during the daytime. At night when they can open their stomates and take in CO2, these plants incorporate the CO2 into various organic compounds to store it. In the daytime, when the light reaction is occurring and ATP is available (but the stomates must remain closed), they take the CO2 from these organic compounds and put it into the Calvin cycle.
  81. 81. Requirements of photosynthesis Carbon dioxide and water. These are the raw materials for photosynthesis. Carbon dioxide comes from the air and enters trough the stomata of the leaves. On the other hand, water is supplied through the soil in the process called absorption. Sunlight. Photosynthesis requires the expenditure of large amounts of energy. It uses the light energy from the sun (as photo means sun, in the word photosynthesis).the more intense and the longer the light duration the greater the chances to capture adequate light for crop growth and development. Light requirement varies among plant species. Light intensity is the most important factor that affects photosynthesis. Chlorophyll. The green pigment of plants, which is found in the chloroplast of the leaves that traps light energy necessary for photosynthesis. For the synthesis of chlorophyll, carbon, hydrogen, oxygen, nitrogen, magnesium and manganese are needed as building blocks. Enzyme. A protein molecule that is necessary for each complex reaction to proceed during photosynthesis. Each enzyme is specific for a particular reaction. The presence or absence of a specific enzyme tells whether a reaction will proceed or not.
  82. 82. Translocation Translocation refers to the movement of photosynthates within the plant. Photosynthates are most needed in the roots, developing flowers, fruits and seeds and the growing region of the stem and roots.
  83. 83. Respiration In respiration, the stored food from photosynthesis is broken down and energy is released to power necessary processes within the cells. Like photosynthesis, respiration also involves complex reactions.
  84. 84. Energy required for growth and development is released in respiration. The complex carbohydrates are broken down first through a process called glycolysis into an acid with three carbons in its structure. Then, this enters into a cycle (Kreb’s cycle), in which it is changed from one organic acid to another.
  85. 85. In the process, Adenosine triphosphate (ATP) is released as a source of energy, CO2 is given off, and the hydrogen removed from the acids combines with oxygen to form water. Some of the acids formed in the cycle may separate and serve as building blocks for other plant constituents like plant growth regulators.
  86. 86. The process of plant respiration requires 1.) the products of photosynthesis or photosynthates; 2.) oxygen; 3.) enzymes. Enzymes are synthesized in all plant parts.
  87. 87. Transpiration Water in the roots is pulled through the plant by transpiration (loss of water vapor through the stomata of the leaves). Transpiration uses about 90% of the water that enters the plant. The other 10% is an ingredient in photosynthesis and cell growth.
  88. 88. Transpiration serves three essential roles: • Movement of minerals up from the root (in the xylem) and sugars (products of photosynthesis) throughout the plant (in the phloem). Water serves as both the solvent and the avenue of transport. • Cooling – 80% of the cooling effect of a shade tree is from the evaporative cooling effects of transpiration. This benefits both plants and humans. • Turgor pressure – Water maintains the turgor pressure in cells much like air inflates a balloon, giving the non-woody plant parts form. Turgidity is important so the plant can remain stiff and upright and gain a competitive advantage when it comes to light. Turgidity is also important for the functioning of the guard cells, which surround the stomata and regulate water loss and carbon dioxide uptake. Turgidity also is the force that pushes roots through the soil
  89. 89. Factors affecting Growth and Development Internal factors Yield potential. Yield potential is usually a reflection of the ability of the plant to utilize and adapt to its aerial environment in terms of its morphology, anatomy or biochemical nature. Relative susceptibility to unfavorable environmental conditions. Unfavorable environmental conditions include presence of harmful insects and diseases, water logging, drought, too high or low temperature and too much or low of nutrients. Natural size. A plant that is naturally small at maturity either lacks the genes that manufacture the enzyme necessary to convert the initial products of photosynthesis into gibberellins, which is necessary for “normal” or typical plant growth.
  90. 90. External factors External or environmental factors includes: • Physical factors • Includes light, temperature, soil relative humidity and rainfall • Chemical factors • Presence or absence of gases and nutrients • Biological factors • Insects, microorganisms, weeds, animals or even humans
  91. 91. Biotic factors All life forms existing around the immediate vicinity of the crop are considered biotic factors. Most of them compete for space, food, water, light and nutrients such as weeds.