Enduring Understanding 2.E BIG IDEA II Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring Understanding 2.E Many biological processes involved in growth, reproduction and dynamic homeostasis include temporal regulation and coordination. Essential Knowledge 2.E.2 Timing and coordination of physiological events are regulated by multiple mechanisms.

Essential Knowledge 2.E.2: Timing and coordination of physiological events are regulated by multiple mechanisms. Learning Objectives: (2.35) The student is able to design a plan for collecting data to support the scientific claim that the timing and coordination of physiological events involve regulation. (2.36) The student is able to justify scientific claims with evidence to show how timing and coordination of physiological events involve regulation. (2.37) The student is able to connect concepts that describe mechanisms that regulate the timing and coordination of physiological events.

Regulation of Physiological Events in Plants and Animals In plants, physiological events involve interactions between environmental stimuli and internal molecular signals. Illustrative examples include: seed germination, phototropism, photoperiodism, and flower development. In animals, internal and external signals regulate a variety of physiological responses that synchronize with environmental cycles and cues. Illustrative examples include: circadian rhythms, diurnal/nocturnal and sleep/wake cycles, and seasonal responses

Temperature and the availability of water determine seed germination in most plants. http://www.indiana.edu/~oso/animations/barley.html Signal transmission within and between cells mediates gene expression. Many seeds break dormancy and germinate only when the light environment are near optimal. Temperature is also a factor in seed germination as chemical and metabolic processes are sped up at higher temperatures. In addition to light availability and temperature, germination in plant seeds depends on imbibition, the uptake of water due to low water potential of a dry seed. Imbibing water causes the embryo to release gibberellins, a hormone that triggers the seed to expand and rupture its coat and also triggers metabolic changes in the embryo that enable it to resume growth after dormancy. NOTE: gibberellins are a hormone – when released they signal a transduction pathway that leads to cellular response. Following hydration, enzymes begin digesting the storage materials of the endosperm or cotyledons, and the nutrients are transferred to the growing regions of the embryo.

Phototropism in Plants Fig. 39-8 Phototropism in Plants Expansins separate microfibrils from cross- linking polysaccharides. 3 Cell wall–loosening enzymes Cross-linking polysaccharides Expansin CELL WALL Cleaving allows microfibrils to slide. 4 Cellulose microfibril H2O Cell wall Cell wall becomes more acidic. 2 Plasma membrane http://bcs.whfreeman.com/thelifewire/content/chp38/3802001.html The term auxin is used for any chemical substance that promotes cell elongation in different target tissues Responsible for phototropisms due to unequal distribution of auxin Plant stems bend toward light as a result of increased cell elongation on the side of the stem away from the light source Auxins stimulate elongation of cells within young developing shoots: Auxin produced in apical meristems (tip of plant) activate proton pumps in plasma membrane. Increased movement of H+ ions lowers pH and the cell wall and causes it to becomes more acidic. This weakens the cell wall, allowing turgor pressure to expand the cell wall, resulting in elongation. Auxin increases proton pump activity. 1 Nucleus Cytoplasm Plasma membrane Vacuole CYTOPLASM 5 Cell can elongate.

Photoperiodism in Plants http://bcs.whfreeman.com/thelifewire/content/chp39/3902002.html Photoperiod, the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year – this phenomenon results in flowering in long-day and short-day plants. A photoperiod such as flowering, is a physiological response to a change in length of night and day. Long day plants flower only if a period of continuous darkness is shorter than a critical period (summer plants). Short day plants require a period of continuous darkness longer than a critical period in order to flower (early spring and fall plants). Note: Short-day plants are actually long-night plants, meaning what the plant measures is the length of the night. Long-day plants are acutally short-night plants. 6

Apoptosis & Flower Development Programmed cell death (apoptosis) plays a role in the normal development and differentiation of an organism. Flowers have a species-specific life span with an irreversible program of senescence. The life span of the entire flower is regulated for ecological and energetic reasons, but the death of individual tissues and cells within the flower is coordinated at many levels to ensure correct timing. In many species, chemicals released during pollination trigger apoptosis in floral components (overproduction of ethylene). In many species, chemicals released during pollination trigger apoptosis in floral components (overproduction of ethylene) – why would this make sense? Flowers are a substantial sink on a plant’s resources – and programmed cell death following pollination is a necessary, energy conserving, life sustaining process. 7

Circadian Rhythms Circadian rhythms, or the physiological cycle of about 24 hours that is present in all eukaryotes, persists even in the absence of external cues.

Enduring Understanding 2.E BIG IDEA II Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring Understanding 2.E Many biological processes involved in growth, reproduction and dynamic homeostasis include temporal regulation and coordination. Essential Knowledge 2.E.3 Timing

Essential Knowledge 2.E.3: Timing Learning Objectives: (2.38) The student can (2.39) The student is able to (2.40) The student is able to

Response & Natural Selection in Plants Response to information and communication of information are vital to natural selection in plants. In phototropism, changes in the light source lead to differential growth, resulting in maximum exposure of leaves to light for photosynthesis. In photoperiodism, changes in the length of night regulate flowering and preparation for winter. 11