1. Plants Form and Function Chapter 28 Plants grow only at meristems Leaf anatomy relates to photosynthesis. The role of root hairs and mycorrhizae in resource acquisition. Roots, stems, and leaves

2. Plants grow only at meristems Meristems are perpetually embryonic tissues  Growth occurs only as a result of cell division in the meristems. Apical meristems  Tips of roots and in buds of shoots  Allowing the plant’s stems and roots to extend. Primary growth Lateral meristem  Results in growth that thickens the shoots and roots  Secondary growth

3. Leaf anatomy relates to photosynthesis.

4. How the structures enhance functions, such as, gas exchange, photosynthesis, and reduction of water loss. Stomata  Formed by guard cells which open and close the stomata.  Allows for gas exchange- CO 2 and O 2  Loss of water- Transpiration

5. The role of root hairs and mycorrhizae in resource acquisition. Root system beneath the ground that is a multicellular organ that anchors the plant, absorbs water and minerals, and often stores sugars and starches. Root hairs are located at the tips of roots, which are extension of root epidermal cells.  Increase the surface area, making efficient absorption of water and minerals possible. Symbiotic relationship with fungi at the tips of the roots called mycorrhizae.  Assist in the absorption process

6. Resource Acquisition and Transport in Vascular Plants- Chapter 29 How passive transport, active transport, and cotransport function to move materials across plant cell membranes. The role of water potential in predicting movement of water in plants. How the transpiration cohesion-tension mechanism explains water movements in plants. How bulk flow affects movement of solutes in plants. Mechanisms by which plant cells communicate with other distant cells.

7. Overview of Resource Acquisition and Transport

8. Different Mechanisms Transport Substances Over Short or Long Distances Transport begins with the movement of water and solutes across a cell membrane.  Solutes diffuse down their electrochemical gradients  Electrochemical gradients are the combined effects of the concentration gradient of the solute and the voltage or charge differential across the membrane.  Passive Transport requires NO energy  Example- Diffusion  Active Transport requires energy  Example- Proton pump

9. Different Mechanisms Transport Substances Over Short or Long Distances The uptake of water across cell membranes occurs through osmosis (passive transport)  Water moves from areas of high water potential to low water potential.  Water potential includes the combine effects of solute concentration and physical pressure.

10. Different Mechanisms Transport Substances Over Short or Long Distances Ψ s = solute potential  Ψ s of pure water is O.  Adding solutes to pure water always lowers water potential, therefore, solute potential of a solution is always negative. Ψ p = pressure potential  Pressure potential is the physical pressure on a solution.  An example of positive Ψ p occurs when the cell contents press the plasma membrane against the cell wall, a force termed turgor pressure.  If the cell loses water, the pressure potential becomes more negative, resulting in wilting.

11. Transport of Water Three mechanisms are involved in the movement of water. 1. Osmosis – Concentration gradient (soil to root) Continuous movement of water out of the root by xylem Higher mineral concentration inside the stele maintained by the selective passage of ions through the endodermis. 1. Root pressure (osmotic force)

12. Transport of Water Three mechanisms are involved in the movement of water. 2. Capillary action  Rise of liquids in narrow tubes  Contributes to movement of water up xylem  Adhesion forces Meniscus formation

13. Transport of Water Three mechanisms are involved in the movement of water. 3. Cohesion-tension theory  Transpiration Evaporation of water from plants Removes water from leaves Causing negative pressure or tension to develop within the leaves and xylem tissue  Cohesion Produces a single, polymerlike column of water from roots to leaves

14. Transport of Water Three mechanisms are involved in the movement of water. 3. Cohesion-tension theory  Bulk flow Occurs as water molecules evaporate from the leaf surface. When a water molecule is lost from a leaf by transpiration, it pulls up behind it an entire column of water molecules. In this way, water moves by bulk flow through the xylem by a pulling action generated by transpiration Transpiration is caused by the heating action of the sun, therefore, the sun is the driving force for the ascent of water and minerals through the plants.

15. The Rate of Transpiration is Regulated by Stomata Stomata opening and closing  Influences gas exchange, transpiration, the ascent of water and minerals (sap), and photosynthesis. Closed stomata  Water and carbon dioxide are not available, and photosynthesis cannot occur. Open stomata  Carbon dioxide can enter the leaf.  Water is delivered by the pulling action of transpiration  Problem: the plant risks desiccation from excessive transpiration.

16. Control of Stomata Mechanisms that control the opening and closing of stomata. 1. Close when temperatures are high. – Reduces loss of water – Shuts down photosynthesis 2. Open when carbon dioxide concentrations are low inside the leaf. – Allows photosynthesis to occur 3. Close at night and open during the day 4. Stomata opening occurs by a diffusion of potasium ions into guard cells, creating a gradient for the movement of water into guard cells.

17. Transport of Sugars Translocation  Movement of carbohydrates through the phloem from a source (leaves) to a sink (a site of carbohydrate utilization or storage).  Mechanism = Pressure-Flow hypothesis 1. Sugars enter sieve-tube members 2. Water enters sieve-tube members 3. Pressure in sieve-tube members at the source move water and sugars to sieve-tube members at the sink through sieve-tubes. 4. Pressure is reduced in sieve-tube members at the sink as sugars are removed for utilization by nearly cells.

18. Soil and Plant Nutrition Chapter 29 Mutualistic relationships between plant roots and the bacteria and fungi that grow in the rhizosphere help plants acquire important nutrients. Plants also form symbiotic relationships that are not mutualistic. Interactions between population (such as competition, predation, mutualism, and commensalism) can influence patterns of species distribution and abundance.

19. Plant Nutrition Often Involves Relationships with Other Organisms Mutualistic relationship between nitrogen-fixing bacteria and plants.  Rhizobium bacteria fix atmospheric nitrogen into a form used by the plant.  Plants provide food into the root nodule where bacteria live. Mycorrhizae another example of mutualistic relationships with roots.  Roots and fungi in the soil  Fungus receives sugar from the plant and the fungus increases the surface area for water uptake, selectively absorbs minerals that are taken up by the plant, and secretes substances that stimulate root growth and antibiotics that protect the plant from invading bacteria.

20. Nitrogen Cycle

21. Plants also form symbiotic relationships that are not mutualistic. Parasitic plants  Example- Dodder  They are not photosynthetic  Rely on other plants for their nutrients. Epiphytes  These plants are not parasitic but grow on the surfaces of other plants instead of the soil.  Example-Orchids Carnivorous plants  These plants are photosynthetic, but they get some nitrogen and other minerals by digesting small animals.  Commonly found in nitrogen-poor soil, like bogs.

22. Plant Responses to Internal and External Signals Chapter 31 The three components of a signal transduction pathway and how changes could alter cellular responses. The role of auxins in plants. How phototropism and photoperiodism use changes in the environment to modify plant growth and behavior. How plants respond to attacks by herbivores and pathagens.

23. Signal Transduction Pathway Involves Three Steps: Reception  Cell signals are detected by receptors that undergo changes in shape in response to a specific stimulus.  Two common plasma membrane receptors are G proteins coupled receptors and receptor tyrosine kinase. Transduction  Multistep pathway that amplifies the signal.  This allows a small number of signal molecules to produce a large cellular response. Response  Cellular response is primarily accomplished by two mechanisms:  Turning genes on or off and thereby increasing or decreasing mRNA production.  Activating existing enzyme molecules

24. Signal Transduction Pathway

27. Plant hormones help coordinate growth, development, and responses to stimuli Hormones are defined as signaling molecules produced in small amounts in one part of an organism and transported to other parts.  Act as chemical messengers that coordinate the different parts of a multicellular organism. Tropism: plant growth response that results in the plant growing either toward or away from a stimulus.  Results from hormone production  Phototropism (positive/negative) The growth of a shoot in a certain direction in response to light Hormone = Auxin  Gravitropism

28. Plant hormones help coordinate growth, development, and responses to stimuli Auxins  Stimulate elongation of cells within young developing shoots  Produced in the apical meristems, activates proton pumps in the plasma membrane, which results in a lower pH (acidification of the cell wall)  This weakens the cell wall, allowing turgor pressure to expand the cell wall, resulting in cell elongation. In phototropism, the plant moves towards the sunlight to have its leaves at 90° angles to the light rays.  This response results from cells on the dark side elongating faster than the cells on the light side.  Causes the shoot to grow faster on the shady side, bending it toward the light.

29. Responses to light are critical for plant success Plants can detect not only the presence of light, but also its direction, intensity, and wavelength.  Action spetra reveal that red and blue light are the most important colors in plant responses to light. Blue-light photorecepetors initiate a number of plant responses to light including phototropisms and light-induced opening of the stomata. Light receptors termed phytochromes absorb mostly red light.

30. Photoperiodism Response of plants to changes in the photoperiod (the relative length of daylight and night) Plants maintain a circadian rhythm (a clock that measures the length of daylight and night), in order to respond to changes in the photoperiod. The mechanism is endogenous (it is an internal clock that continues to keep time even if external cues are absent.  External cues, such as dawn and dusk, reset the clock to maintain accuracy.

31. Photoperiodism Mechanism for maintaining the circadian rhythm  Phytochrome = a protein modified with a light- absorbing chromophore  Two forms: Pr (P 660 ) and P fr (P 730 ) Absorb wavelengths of light: red @ 660 nm and far-red @ 730 nm  Photoreversible When Pr is exposed to red light, it is converted to Pfr When Pfr is exposed to far-red light it is converted back to Pr

32. Photoperiodism The following observations have been made for many plants 1. Pfr appears to reset the circadian-rhythm clock 2. Pr is the form of phytochrome synthesized in plants cells. 3. Pfr and Pr are in equilibrium during daylight. 4. Pr accumulates at night 5. At daybreak, light rapidly converts the accumulated Pr to Pfr

33. Photoperiodism 6. Night length is responsible for resetting the circadian- rhythm - If daylight is interrupted with a brief dark period, there is no effect on the circadium-rhythm. - In contrast, flashes of red or far-red light during the night period can reset the clock. - If a plant is exposed to a flash of re light during the night, P r is converted back to P fr, a shorter night period is measured, and the circadium rhythm is reset. - If a flash of far-red light follows the red light, then the effect of the red light is reversed, and the night length is restored to the night length in effect before the far-red flash.

34. Photoperiodism - In a series of alternating flashes of red and far-red light, only the last flash affects the perception of night length. - Thus, red light shortens the night length and far-red restores the night length.

35. Photoperiodism Many flowering plants initiate flowering in response to changes in the photoperiod. Three groups:  Long-day plants flower in the spring and early summer when daylight is increasing.  These plants flower when daylight exceeds a critical length.  Short-day plants flower in late summer and early fall when daylight is decreasing  These plants flower when daylight is less than a critical length  Day-neutral plants do not flower in response to daylight changes.  Some other cues, such as temperature or water, triggers flowering

36. Photoperiodism

37. Plants respond to a wide variety of stimuli other than light Gravitropism  Plant’s response to gravity  Roots show positive gravitropism and grow toward the source of gravity  Shoots show negative gravitropism and grow away from gravity  Auxin plays a key role in gravitropism in both the roots and stems. Thigmotropism  Directional growth in response to touch  Vines display thigmotropism when their tendrils coil around supports.

38. Plants respond to attack by herbivores and pathogens Physical defenses against predators (herbivores)  Thorns  Chemicals such as bitter or poisonous compounds  Airborne attractants to recruit other animals to kill the herbivores Epidermal layer acts as a barrier (like humans) against viruses. Plants immune responses involve both localized, specific responses as well as plant-wide responses.  The lesions or dead spots you may have seen on leaves can be the result of the plant responding to a pathogen by sealing off the pathogen then killing the cells in the area.  This kills the pathogen and prevents the spread of the disease to the rest of the plant.  Both plants and animals immune systems depend heavily on signal transduction pathways.