Biology 35 IB. Topic 9: Plant Science Starr-Taggard Text - Pages

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1 Biology 35 IB Topic 9: Plant Science Starr-Taggard Text - Pages

2 Plantae is a Diverse Kingdom Estimated that there are over 500, 000 different species of plants 10, 000 monerans, 100, 000 fungi, 60, 000 protista, animalia over 1.5 million species! All plants share similar characteristics: Photosynthetic Multicellular Means of sexual reproduction Eukaryotic

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4 9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.

5 Tissue types of the plant stem: Epidermis: surface of the stem made of a number of layers often with a waxy cuticle to reduce waterloss. Cortex Tissue: Forming a cylinder of tissue around the outer edge of the stem. Often contains cells with secondary thickening in the cell walls which provides additional support. Vascular bundle: contains xylem, phloem and cambium tissue.

6 Xylem: a longitudinal set of tubes that conduct water from the roots upward through the stem to the leaves. Phloem (sieve elements) transports sap through the plant tissue in a number of possible directions. Vascular cambium is a type of lateral meristem that forms a vertical cylinder in the stem. The cambium produces the secondary xylem and phloem through cell division in the vertical plane. In the centre of the stem can be found the pith tissue composed of thin walled cells called parenchyma. In some plants this section can degenerate to leave a hollow stem.

7 9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues

8 Cuticle is a waxy layer which reduces water loss through the upper epidermis. Upper epidermis is a flattened layer of cells that forms the surface of the leaf and makes the cuticle. Palisade Layer: This is the main photosynthetic region of the leaf. Vascular bundle: contains the transport system and vascular meristem tissue (see below: x-xylem, p-phloem). Spongy mesophyll: contains spaces that allows the movement of gases and water through the leaf tissue.. Lower epidermis: bottom surface layer of tissues which contains the guard cells that form each stoma.

9 Cross Section of a Leaf Diagram

10 9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants

11 Monocots vs. Dicots 11

12 Feature Monocotyledonous Dicotyledonous Veins in leaves Vascular tissue in stem Number of cotyledons in seed Number of petals in flower Roots

13 9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils Bulbs: Onions & Lilies Short vertical underground stems. Many fleshy highly modified leaves for the storage of nutrient. Can produce new plants by bulb division or the development of one of the many axillary buds. Stem Tubers: Swollen offshoots from the stem that allow the plant to grow every year (becomes perennial). The plant dies in the winter but the following spring a new set of stems and roots grow from the tuber (if we don t eat it first!) The 'eaten potato' contains the carbohydrate and protein stores for the growth. The 'eyes' are in fact axillary buds. In effect this diagram show the branching axillary buds or a stem.

14 9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils

15 Carrot: Tap Root modification Function: Storage of water. Carrot plants are often associated with very sandy soils. The enlarged root is familiar to those who have eaten the vegetable. The root modification allows the storage of water in the cortex and central stele. The mass of the root stabilizes the plant in the loose sandy soils.

16 9.1.5 State that dicotyledonous plants have apical and lateral meristems Meristems: Plants only grow at the meristems: regions of undifferentiated cells (like stem cells in animals) These can be apical (root or stem tip)or lateral (at axillary buds along stem)

17 Can you determine what each letter is? (a) Shoot apical meristem (b) Leaf primordial (c) Axillary bud (d) leaf (e) Stem tissue

18 Can you determine the names for each of the letters in the diagram? (a) Root cap. (b) Root apical meristem. (c) Ground meristem. (d) Protoderm. (e) Epidermal tissue of the root. (f) Vascular tissue (central stele).

19 9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants Primary Growth Once germination occurs, plants begin primary growth where plants grow taller and roots grow longer The growing regions of the tips are apical meristems The part of the embryo that forms the primary root is called the radicle When the primary root emerges from the seed, germination is complete

20 Primary Root The primary growth of roots involves three steps: cell division, elongation, and differentiation Cell divisions in the apical meristem form new cells Cells grow longer in a region of the root called the zone of cell elongation (pushes the root though soil). Cells become specialized in the zone of differentiation (Ex. Cells may become xylem/ phloem tissue cells) The epidermal cells in the zone of cell differentiation have projections called root hairs (single epidermal cell, increase S.A)

21 Primary Shoot Primary shoot (forms stems and leaves) follows primary root two types of meristems: apical meristems (at tips of stems) and axillary buds (form at base of each leaf) Apical meristems make cells that form the stem and leaves Axillary buds (aka lateral buds), which may remain dormant, can form either a branch or a flower eeman_biosci_1/0,6452, ,00.html Animation of primary growth!

22 9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants Secondary Growth makes stems and roots thicker rather than longer Secondary growth greatly enhances a plant's ability to survive (thicker = stronger and taller reach sunlight) Secondary growth is produced by cell divisions in meristems called lateral meristems located within and parallel to the sides of roots and stems have the shape of a hollow cylinder inside the root or stem two common types of lateral meristems called vascular cambium and cork cambium

23 Vascular cambium is located between the xylem and phloem Cell divisions in the vascular cambium produce secondary xylem (wood) toward the inside and secondary phloem (no common name) toward the outside The secondary growth of stems and roots results from cell divisions of the vascular cambium (several layers of xylem + few of phloem/ yr = prevalent growth ring) Animation of Secondary growth!

24 Cork cambium is the meristem between the phloem and the epidermis Cell divisions in the cork cambium replace the epidermis and cortex with cork, which protects the tree Together, the secondary phloem, cork, and cork cambium form the bark that surrounds the trunk of a tree (non-living/ growing) As a result, continued expansion of the tree trunk splits the outer layers of cork The Structure of Wood Wood consists mostly of secondary xylem Xylem accumulates year after year, but only the outermost layers transport water The outer, light-colored layers of secondary xylem are sapwood Animation of Cork cambium

25 Eventually, xylem cells get clogged and can no longer carry water form dark layers at center called heartwood Heartwood typically contains substances such as oils, gums, resins, and tannins that do not occur in the sapwood A series of concentric rings called growth rings form on wood (each ring represents one year's growth) Growth rings are wider when environmental conditions, such as rainfall and temperature, are favorable for growth and narrower when conditions are unfavorable for growth

26 Figure 35.19a-3 (a) Primary and secondary growth in a two-year-old woody stem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular ray Secondary xylem Secondary phloem Cork First cork cambium Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Most recent cork cambium Cork Bark Layers of periderm

27 Figure Vascular cambium Growth Secondary xylem Vascular cambium Secondary phloem After one year of growth After two years of growth

28 9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth Tropisms: Plant responses to directional external stimuli Plant responses to stimuli can be either positive (towards stimulus) or negative (away from stimulus) Phototropism is an example of a positive tropism the plant will grow towards the light Review of Darwins and Went s Experiments:

29 Plant growth is regulated by hormones called auxins. Auxins promote growth by lengthening cells. Auxins are produced in the coleoptile, a protective sheath around the emerging root or shoot. Under normal conditions, auxin is distributed evenly along the shoot, causing even (vertical) growth. If photoreceptors in the coleoptile detect a light stimulus from one direction, auxin is moved to the opposite side of the growing shoot. The uneven distribution of auxin causes increased growth on one side and the plant grows towards the direction of the light.

30 Part II. 9.2 Transport in angiospermophytes Text Reference: Starr and Taggard Pages

31 9.2.1 Root systems for the uptake of water and minerals. (a) The monocotyledon root has a fibrous highly branching structure which increases the surface area for the absorption of water. (b) Dicotyledon root structure has a main tap root and often a surface branching root system for the absorption of surface run off. Deeper in the soil the tap root branches to access deeper water and mineral.

32 Root hairs: The extension of the cell wall increases the surface area for the absorption of water and minerals at the cellular level. The root hair cell provides both an increase in the cell wall (apoplastic pathway) and the cytoplasmic route (symplastic pathway) for the movement of water.

33 List ways in which mineral ions in the soil move to the root.. There are three ways in which mineral ions can move from the soil to the root. The minerals that need to be absorbed from the soil are Nitrogen, potassium, phosphorus and calcium. Minerals will enter the roots via diffusion; passive transport from an area of high concentration (in soil) to one of low concentration (in plant). Minerals can enter the plant via the water. When a plant takes in large volumes of water that contains the dissolved minerals this is called mass flow.

34 The third way mineral ions can move from the soil to the root is through the help of a fungus via the fungal hyphae. Fungi have specialized threads known as hyphae that grow into the soil and absorb minerals. Some of these hyphae also grow into plant roots and can transfer mineral ions to the root of the plant. In exchange for the mineral ions the plant provides the fungi with simple sugars and this is known as a symbiotic relationship (mutualism)

35 Explain the process of mineral ion absorption from the soil into roots by active transport. Active transport (using energy) of mineral ions occurs at the root hairs. Includes: cations such as K +, Ca 2+ which involve ion channels and proton pumps Anions such as NO3- which involve symport with H+ ions

36 Active Transport of Cations: Ion Exchange Clay particles are negatively charged Cations are easily absorbed in sold and attach to negatively charged particles A proton pump forces H+ ions out of the root airs and into the soil H+ displaces cations (eg. K+) Cations are absorbed down the electrochemical gradient into the root hair They pass through ion channels

37 Active Transport of Anions: Symport An electrochemical gradient is generated by the proton pump: the inside of the root hair becomes more neg than the outside Anions (such as NO3 - ) can t diffuse down the electrochemical gradient as they are also negatively charged Instead, the energy from the H+ gradient is used to actively transport the anions into the root hairs this is called symport

38 State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem. Plants lack a skeleton to keep them upright so they rely on cell turgor, thickened cellulose and lignified xylem to keep them upright. Cell turgor is also known as turgor pressure. It is the resulting pressure in a plant that is exerted on the cell wall due to water stored in the large central vacuole. Turgor pressure decreases if a plant dries or is exposed to salty conditions.

39 Cellulose is a polysaccharide found in plant cell walls of the supporting regions of plants. The cellulose adds strength and support to the cell walls.

40 Lignin is a highly branched polymer found in the xylem cells of terrestrial plants. These lignified cells have significantly increased support capabilities. More than 25% of the mass of dry wood can be lignin. Caption: Xylem tissue. Coloured scanning electron micrograph (SEM) of a section through xylem tissue from a dicotyledon rootlet. Xylem vessels (purple) transport water and mineral nutrients from the roots throughout the plant. Its thick lignin walls also provide structural support. Surrounding the vessels are parenchyma cells. Magnification: x400 when printed 10 centimetres wide.

41 Define transpiration. Transpiration is the loss of water vapor from the leaves and stems of plants. The water is lost through openings called stomata. Water lost via transpiration must be replaced by water uptake from the roots (water absorption). Water will move through the transport system (xylem) from roots to leaves. This is known as the transpiration stream.

42 Think back to your science 10 days Can you describe the following process that moves water from the roots to the leaves?

43 Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation. Xylem vessels transport water through the plant. Recall: water has cohesive properties due to H-Bonds Water is heated in the mesophyll by sunlight and becomes vapour. This vapour transpires out of the stomata (pores in the leaf).

44 Loss of water generates negative pressure and a transpiration pull on water molecules in the xylem. More water is drawn into the leaf.

45 Cohesion between water molecules means that the transpiration pull has a knock-oneffect through the plant. Higher rates o transpiration lead to a faster transpiration stream and higher rates of water uptake. This theory is known as cohesion-tension theory.

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47 How do the Guard Cells open and close the stomata? Stomata opening and closing animation: Gas exchange animation:

48 State that guard cells can regulate transpiration by opening and closing stomata. Stomata ( singular Stoma ) are pores in the lower epidermis. Each stomata is formed by two specialised Guard Cells. The epidermis and its waxy cuticle is impermeable to carbon dioxide and water. During the day the pore opens to allow carbon dioxide to enter for photosynthesis. However the plant will experience water loss. If the water loss is too severe the stoma will close. During the night plants cannot photosynthesis and so the plant closes the pores thereby conserving water.

49 State that the plant hormone abscisic acid causes the closing of stomata Abscisic acid is a plant hormone which causes the potassium ions to rapidly diffuse out of the guard cells surrounding the stoma. When the potassium ions diffuse out the water also leaves which causes the guard cells to collapse and effectively closing the stoma. Abscisic acid is produced in the roots of the plant in response to a lack of water in the soil. The hormone will travel to the leaves where it can have an effect on the guard cells.

50 Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant.

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52 Part III. Reproduction in Angiospermophytes Starr and Taggart Pages

53 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower.

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56 Attracts pollinators (insects/ Small Birds) Pollen landing site Contains pollen Supports anther Cover/protect developing flower Pollen tube grows down style from stigma to ovary Contains Ovules Ovules contain egg nuclei and develop into seeds when fertilized

57 9.3.2 Distinguish between pollination, fertilization and seed dispersal. Pollination Pollen is carried from the anther of one flower to stigma of another Fertilization Pollen tube grows down from the stigma to the ovary, through the style. Pollen is delivered to the ovum and fertilization occurs.

58 Seed Dispersal Once the seed has developed in the ovule, it is ready for dispersal Seed Dispersal Fertilization

59 Summary of Angiosperm Life Cycle: 59 Angiosperm Animation Review! man.com/thelife wire/content/chp 39/ html Angiosperm life cycle review activity p?page=250 Biology 35IB Hillaby

60 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed.

61 Explain the conditions needed for the germination of a typical seed. After the formation of the seeds they go through a maturation process where it dehydrates and then usually enters a dormant period. This period of dormancy includes very low metabolism and no growth or development. In order for germination to occur this dormant period must be broken. Germination is the development of a seed into in functioning plant. Oxygen, water and a suitable temperature is needed for germination. Oxygen is need in aerobic respiration to produce ATP so the plant has the energy needed to germinate.

62 Water is taken in and rehydrates the seed causing it to swell up. This cracks the testa and enzymes are activated which begin breaking down large molecules. Temperature needs to be suitable for the type of seed that is germinating. Some seed require a period of low temperature followed by one of high temperature to break dormancy (ensures seeds do not germinate until winter has passed). ch?v=d26ahckeebe Germination is a very uncertain time in a plant s life cycle and many seeds do not produce a viable plant because of threats to the fragile seedling such as harsh weather, predators and parasites.

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65 Explain how flowering is controlled in long-day and shortday plants, including the role of phytochrome. The purpose of flowering is to allow for pollination, fertilization, and seed dispersal Flowers should only bloom when a suitable pollinator is abundant. Some plants (eg. Irises) bloom in long-day conditions (summer), whereas others (eg. Chyrsanthemums) bloom in short-day conditions (autumn-winter). The control of flowering is achieved through a process called photoperiodism. The critical factor is not actually day length, but night-length

66 Phytochromes Phytochromes are leaf pigments which can be used to measure the length of night. If levels of P fr that are used in determining the length of night Long day plants need high levels of P fr if they are to bloom Short Day Plants need low levels of P fr In daylight, there is a lot of red light from the sun (λ = 660 nm)but not as much far-red light (λ = 730 nm) In darkness, there is neither red nor far red light, so P fr is slowly converted back to P r In long nights, lots of P fr is converted to P r

67 Phytochrome signalling controls plant flowering Phytochromes are plant pigments located in the leaf that act as a biological clock. They measure night length in order to control flowering P r is converted quickly to P fr in daylight P fr is converted slowly back to P r in the darkness Long-day plants, flower when day length reaches a critical period. This allows P fr to build up to a critical level stimulating a release of flowering hormones Short-day plants require a long period of darkness, allowing P fr to fall below a critical level in order to flower _phytochrome_signaling.html

68 The role of Phytochromes has been determined experimentally

69 Yikes, so in summary.

70 Try the following Animation and Questions as a Review:

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