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Transcript
TOPIC 9 PLANT SCIENCE HL 9.1-9.2-9.3 Page 294 in the Biology book 9.1Plants structure and growth Parts of the plant: Root Shoot Leaf Flower Bud Comparison of moncotyledon and dicotyledon plants Cross section of a dicot leaf Cross section of a dicot stem Cross section of a dicot room Modifications of stems, leaves, Modifications of stems, leaves • Runner, tuber, rhizome PLANTS TISSUES 1- Meristem tissue a. Apical meristem b. lateral meristem 2-Dermal tissue a. Epidermis: b. Periderm: 3- Mesophyll: 4- Vascular tissue: 5- Supporting tissue Apical meristem Provides longitudinal growth Lateral meristem Provides lateral growth Lateral meristem Apical and lateral growth pp308 Occurs at the tip of stems and root Occurs laterally, between primary phloem and xylem Product of embryonic cells Cambium- meristematic cells left over from primary growth Produces initial tissues of actively growing plant from the outset Functions in older stems (and roots) and in woody plants from the outset Forms epidermis, ground tissues, and primary phloem and xylem Forms mainly secondary phloem and xylem Produces growth in length and height of plant Produces growth in girth of stem, plus strengthening of stem The role of auxin in phototropism Growth of plant towards light source Darwin’s experiment WENT’S EXPERIMENT 9.2 Transport in angiospermophytes • Explain the process of mineral ion absorption from the soil into roots by active transport. • State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem. • Define transpiration. • Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation. • State that guard cells can regulate transpiration by opening and closing stomata. • State that the plant hormone abscisic acid causes the closing of stomata. • Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant. Outline how the root system provides a large surface area for mineral, ion and water uptake by means of branching and root hairs. There are two pathways of water uptake. Apoplast and symplast ways. Apoplast route: through space in the cellulose Symplast route: through living cytoplasm Water uptake by roots Mass flow (Apoplas route.) The space between cells are filled by water Diffusion (sypmlast route): through the cytoplas of cells and via the cytoplasmic connections between cells. (this is not the major one) Osmosis: from vacuole to vacuole driven by osmotic pressure difference Ion uptake Active transport: Ions are absorbed against concentration gradient. Nitrate and Calcium Active uptake is a highly selective process: Some ions are more absorbed than others. (Na+ and NO3 present in the soil NO3 can be absorbed more than Na) Membrane protein pumps involve active transport. Transportation of water in the stem Water is transported by xylem tissue. Xylem is long hollow capillary tube. They are made of dead cells. Root: When water molecules are absorbed by apoplast or symplast way, water molecules reach to a waxy layer between cells called (casparian strip) and edodermis cell layer. Leaves Meanwhile in the leaves transpiration occur. Transpiration in the leaves Transpiration: is the evaporation of of water vopour through stomata of green plant leaves and stems. Transpiration can pull xylem sap up a tree because of two special properties of water: 1. Cohesion is the sticking together of molecules of the same kind. 2. Adhesion is the sticking together of molecules of different kinds. OPENING AND CLOSING OF STOMATA Stomata are openings on the surface of the leaves (usually in the lower side). They are made of two guard cells. - can open and close and help plants to adjust their transpiration rates according to changes in the environment - They are open during day light closed in dark (there are exceptions) - They open and close due to change in turgor pressure of the guard cells. Stoma opening Stoma closing Transpiration Apparatus to measure transpiration rate. Transport in phloem Mass flow hypothesis High sugar concentration High water pressure Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic Low sugar tissue and storage concentration organs) to sink (fruits, seeds, roots). Low water pressure Adaptations of Xerophytes - Thick cuticle Layers of hairs on the epidermis Reduction on the number of stomata Stomata in pits or groves Leaf rolled or folded when short of water Superficial roots (collects condensed water at soil surface at night) - Deep and extensive roots (exploit deep water sources in the soil) - C4 photosynthesis - CAM metabolism • C4 photosynthesis: They fix CO2 in day light while stomata open- allowing stomata to be closed in dry conditions. • CAM metabolism: open their stomata at night, retain CO2 in an organic acid then they CO2 are release when stomata are closed during the day. Topic 9.3 REPRODUCTION OF FLOWERING PLANTS © 2012 Pearson Education, Inc. 9.3 Reproduction in angiospermophytes • Draw and label a diagram showing the structure of a dicotyledonous animalpollinated flower. • Distinguish between pollination, fertilization and seed dispersal. • Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed. • Explain the conditions needed for the germination of a typical seed. • Outline the metabolic processes during germination of a starchy seed. • Explain how flowering is controlled in long-day and short-day plants, including the role of phytochro The flower is the organ of sexual reproduction in angiosperms • Flowers typically contain four types of highly modified leaves called floral organs. 1. Sepals enclose and protect a flower bud. 2. Petals are showy and attract pollinators. 3. Stamens are male reproductive structures. 4. Carpels are female reproductive structures. © 2012 Pearson Education, Inc. The flower is the organ of sexual reproduction in angiosperms • A stamen has two parts. 1. An anther produces pollen, 2. A stalk (filament) elevates the anther. • A carpel has three parts. 1. The stigma is the landing platform for pollen. 2. The ovary houses one or more ovules, 3. A slender neck (style) leads to an ovary. © 2012 Pearson Education, Inc. Figure 31.9A Figure 31.9B Stamen Anther Stigma Carpel Style Ovary Filament Sepal Petal Ovule Life Cycle of a flowering plant • In the life cycle of a generalized angiosperm, – fertilization occurs in an ovule, – the ovary develops into a fruit, – the ovule develops into the seed containing the embryo, – the seed germinates in a suitable habitat, and – the embryo develops into a seedling and then mature plant. © 2012 Pearson Education, Inc. Figure 31.9C_s5 Ovary, containing ovule Embryo 3 Seed 2 Fruit (mature ovary), containing seed 1 Mature plant with flowers, where fertilization occurs 5 Seedling 4 Germinating seed • Pollination is the transfer of pollen from anther to stigma. • Pollen may be carried by wind, water, and animals. • As a pollen grain germinates, – the tube cell gives rise to the pollen tube, which grows downward into the ovary, and – the generative cell divides by mitosis, producing two sperm. © 2012 Pearson Education, Inc. • At fertilization, – one sperm fertilizes the haploid egg to produce a diploid zygote, and – another sperm fuses with the diploid central cell nucleus to produce a triploid (3n) cell that will give rise to the endosperm, which nourishes the developing embryo. This formation of a diploid zygote and a triploid nucleus is called double fertilization. © 2012 Pearson Education, Inc. Figure 31.10 Development of male gametophyte (pollen grain) Development of female gametophyte (embryo sac) Anther Ovule Ovary Cell within anther Meiosis Surviving cell (haploid spore) Meiosis Four haploid spores Single spore Pollination Germinated pollen grain on stigma Mitosis Wall Mitosis (of each spore) Nucleus of tube cell Generative cell Embryo sac Pollen grain released from anther Egg cell Two sperm in pollen tube Pollen tube enters embryo sac Two sperm discharged Double fertilization occurs Triploid (3n) endosperm nucleus Diploid (2n) zygote (egg plus sperm) Figure 31.10_1 Development of male gametophyte (pollen grain) Development of female gametophyte (embryo sac) Anther Ovule Cell within anther Meiosis Four haploid spores Ovary Meiosis Surviving cell (haploid spore) Figure 31.10_2 Surviving cell (haploid spore) Four haploid spores Single spore Pollination Germinated pollen grain on stigma Mitosis Wall Mitosis (of each spore) Nucleus of tube cell Generative cell Pollen grain released from anther Embryo sac Egg cell Two sperm in pollen tube Development of male gametophyte (pollen grain) Development of female gametophyte (embryo sac) Figure 31.10_3 Pollen tube enters embryo sac Two sperm discharged Double fertilization occurs Triploid (3n) endosperm nucleus Diploid (2n) zygote (egg plus sperm) The ovule develops into a seed • After fertilization, the ovule, containing the triploid central cell and the diploid zygote, begins developing into a seed. • The seed contains proteins, oils, and starches. • The zygote first divides by mitosis to produce two cells. – One cell becomes the embryo. – The other cell divides to form a thread of cells that pushes the embryo into the endosperm. © 2012 Pearson Education, Inc. The ovule develops into a seed • The result of embryonic development in the ovule is a mature seed, including – – – – – an endosperm, one or two cotyledons, a root, a shoot, and a tough seed coat. © 2012 Pearson Education, Inc. • Seed dormancy – is a period when embryonic growth and development are suspended and – allows for germination when conditions are favorable. © 2012 Pearson Education, Inc. Figure 31.11A Triploid cell Ovule Zygote Cotyledons Endosperm Two cells Seed coat Shoot Embryo Root Seed Figure 31.11B Embryonic leaves Embryonic shoot Embryonic root Seed coat Cotyledons Common bean (eudicot) Fruit tissue Cotyledon Seed coat Embryonic leaf Sheath Corn (monocot) Endosperm Embryonic shoot Embryonic root • Hormonal changes induced by fertilization trigger the ovary to develop into a fruit. • Fruits – house and protect seeds and – aid in their dispersal. How? © 2012 Pearson Education, Inc. • After pollination, a pea plant flower – drops its petals, – the ovary starts to grow, expanding tremendously, and its wall thickens, and – a pod forms, holding the peas, or seeds. © 2012 Pearson Education, Inc. Figure 31.12A 1 2 3 Figure 31.UN04 Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm nucleus) • Mature fruits may be fleshy or dry. – Fleshy fruits include oranges, tomatoes, and grapes. – Dry fruits include beans, nuts, and grains. © 2012 Pearson Education, Inc. Seed germination continues the life cycle • At germination, a seed – takes up water. What is the role of water in seed germination? – Needs oxygen. Why? © 2012 Pearson Education, Inc. Figure 31.13A Foliage leaves Cotyledon Embryonic Cotyledon shoot Embryonic root Seed coat Figure 31.13B Foliage leaves Protective sheath enclosing shoot Embryonic root Cotyledon Figure 31.UN03 Pollen (n) Ovary Embryo sac (n) Fertilization within ovule Ovule Fruit (from ovary) Mature plant (2n) Seed (from ovule) Embryo (2n) Germinating seed (2n) • Plants display rhythmic behavior including the – opening and closing of stomata and – folding and unfolding of leaves and flowers. © 2012 Pearson Education, Inc. Plants have internal clocks • Circadian rhythms (daily) are controlled by internal timekeepers known as biological clocks. • Light/dark cycles keep biological clocks precisely synchronized. • For most organisms, including plants, we know little about – where the clocks are located or – what kinds of cells are involved. © 2012 Pearson Education, Inc. Figure 33.10 Noon Midnight Plants mark the seasons by measuring photoperiod • Biological clocks can influence seasonal events including – flowering, – seed germination, and – the onset of dormancy. • The environmental stimulus plants most often use to detect the time of year is called photoperiod, the relative lengths of day and night. © 2012 Pearson Education, Inc. Plants mark the seasons by measuring photoperiod • Plant flowering signals are determined by night length. • Short-day plants, such as chrysanthemums and poinsettias – generally flower in the late summer, fall, or winter – when light periods shorten. • Long-day plants, such as spinach, lettuce, and many cereal grains – generally flower in late spring or early summer – when light periods lengthen. © 2012 Pearson Education, Inc. Figure 33.11 0 Time (hrs) 24 Plants bloom only with a longer dark period. 1 2 Flash of light prevents flowering. 3 Light Shortday (longnight) plants Darkness Flash of light Plants bloom only with a shorter dark period. 4 5 Flash of light induces flowering. 6 Critical dark period Longday (shortnight) plants Phytochromes are light detectors that may help set the biological clock • Phytochromes – are proteins with a light-absorbing component and – may help plants set their biological clock and monitor photoperiod. • Phytochromes detect light in the red and far-red wavelengths. – One form of phytochrome absorbs red light (Pr). – One form detects far-red light (Pfr). – When Pr absorbs light, it is converted into Pfr. – When Pfr absorbs light, it is converted into Pr. © 2012 Pearson Education, Inc. Figure 33.12A Red light Pr Pfr Far-red light Pr is naturally produced during dark hours, while Pfr is broken down. The relative amounts of Pr and Pfr present in a plant change as day length changes. Figure 33.12B 0 Time (hrs) 24 1 R 2 R FR 3 RFRR 4 RFRRFR Critical dark period Short-day (long-night) plant Long-day (short-night) plant