Plant Responses & Adaptations

1. Plant Responses & Adaptations Chapter 25

2. Vocabulary – Chapter 25 • 25.1 • Apical Dominance • Auxin • Cytokinin - stimulate cell division and the growth of lateral buds, and cause dormant seeds to sprout • Ethylene – hormone that stimulates fruits to ripen. • Gibberellin • Gravitropism • Herbicide • Hormone • Lateral Bud (Know where this is located!) • Phototropism • 25.2 • Abscission Layer • Long-day Plant • Photoperiodism • Phytochrome • Short-day Plant • Thigmotropism • Tropism • 25.3 • Epiphyte • Xerophyte

3. Plant Adaptation Intro • Rainforest Plants

4. Plant Adaptation Intro • Desert Plants

5. Plant Adaptation Intro • List 2 characteristics (for each) that distinguish desert plants from rainforest plants. • List any characteristics that observed in both types of plants. • How do these characteristics help desert and rainforest plants survive in their environments?

6. Hormones & Plant Growth Chapter 25.1 EQ: How do plant hormones affect plant growth?

7. Patterns of Plant Growth • Plants follow general patterns of growth that differs among species. • Plant cells send signals to one another that indicate when to divide and when to develop into a new kind of cell. • Hormones are produced in apical meristems, in young leaves, in roots, and in growing flowers and fruits. • Plants grow in response to environmental factors such as light, moisture, temperature, and gravity.

8. Hormones & Target Cells • Actions of plant chemicals direct, control, and regulate plant growth. • Patterns of growth lead to distinct shapes of plants such as a thick trunk. • Hormones control division, growth, maturation, and development of cells • Portion of an organism affected by a particular hormone is its target cell.

9. Plant Hormones • Target cells must contain a hormonereceptor – a protein to which the hormone binds. • If the appropriate receptor is present, the hormone can exert an influence on the target cell by changing its metabolism, affecting its growth rate, or activating the transcription of certain genes. • Cells that do not contain receptors are unaffected by hormones. • Different kinds of cells may have different receptors for the same hormone causing it to behave in different ways • A certain hormone may stimulate growth in stem tissues but inhibit growth in root tissues.

10. Auxins & Phototropism • Auxins are hormones that stimulate cell elongation. • They are produced in the apical meristem and transported downward into the rest of the plant. • When light hits one side of a stem, a higher concentration of auxinsdevelops in the shaded part of the stem causing cells on the shaded side to elongate. • As a result, the stem bends away from the shade and towards the light. • Phototropism is the tendency of a plant to grow towards the source of light.

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13. Gravitropism • Gravitropism is the response of a plant to the force of gravity. • Auxins are responsible for gravitropism by stimulating cell growth on lower sides of roots and stems which helps the trunk turn upright. • The effect of auxins in roots in opposite- causing the root to grow downward. • Auxins are responsible for the way that roots grow around objects in the soil such as rocks.

14. Auxins and Branching • Auxins also regulate cell divisions in meristems such as lateral buds. • Lateral buds are meristematic area on the side of a stem that gives rise to side branches. • The delay of growth a lateral bud is regulated by auxins. • Because auxins move out from the apical meristems, the closer a bud is to the stem’s tip, the more its growth is inhibited. This phenomenon is called apical dominance. • If you snip off the tip of a plant, the growth inhibiting auxins are removed. • This causes the side branches begin to grow more quickly, resulting in a rounder, fuller plant.

16. Figure 25–5 Apical Dominance Lateral buds Auxins produced in the apical meristeminhibit the growth of lateral buds. Apical meristem removed Without the inhibiting effect of auxinsfrom the apical meristem, lateral budsproduce many branches. Apical meristem

17. Herbicides • Herbicides are compounds that are toxic to plants. • Herbicides are manmade chemicals that mimic the effects of auxin by inhibiting growth.

18. Cytokinins • Cytokinins are plant hormones that stimulate cell division and the growth of lateral buds, and cause dormant seeds to sprout. • They also delay the aging of leaves and play an important part in the early stages of plant growth. • They produce the opposite effect of auxins. • Auxins stimulate cell elongation; cytokininsinhibit it. • Auxins inhibit the growth of lateral buds, cytokinins stimulate it.

19. Gibberellins • Gibberellins are plant hormones that produce dramatic increases in plant size, especially in stems and fruits. • They are only produced by seed tissue and are responsible for the rapid early growth of many plants. • They were discovered by a Japanese biologist studying a fungus that caused rice plants to grow unusually tall.

20. Ethylene • Ethylene is an auxinthat stimulates fruits to ripen. • Commercial producers use this hormone to control the ripening process of fruits such as tomatoes and lemons. • They are picked before they are ripe and then treated with synthetic ethylene to cause them to ripen.

21. Plant Responses Chapter 25.2

22. Tropisms • Plants change their patterns and directions of growth in response to external stimuli in their environment • The responses of plants to external stimuli are called tropisms. • Tropisms include, gravitropism, phototropism, and thigmotropism.

23. Thigmotropism • The response of plants to touch is called thigmotropism. • Growth patterns can be changed dramatically if touched regularly. • Vines and climbing plants respond to objects that it encounters by changing direction. • Some plants like grapes grow tendrils that emerge near the base of the leaf and wrap around any object they encounter.

24. Thigmotropism One effect of thigmotropism is that plants curl and twist around objects, as shown by the stems of this grapevine.

25. Plant Responses • Plants can also respond to other types of changes in their environment that do not involve growth. • The leaves of a mimosa plant will fold up when touched. This is due to changes in osmotic pressure caused by the loss of water by osmosis. • The Venus flytrap has sensory cells on the inside of its leaf that signals the leaf to snap shut when it senses a fly.

26. Photoperiodism • The ability of plants to respond to periods of light and darkness is called photoperiodism. • It is responsible for the timing of seasonal activities such as flowering and growth. • Plants that flower when days are short are called short-day plants. • Ex) chrysanthemums and poinsettias • Plants that flower when days are long are called long-day plants. • Ex) spinach and irises

27. Photoperiodism • A plant pigment called phytochrome is responsible for photoperiodism. • Phytochrome absorbs red light and activates a number of signaling pathways within plant cells. • Plants respond to regular changes in these pathways. • These changes determine the patterns of a variety of plant responses.

28. Photoperiodism • Short day plants flower only when exposed to an extended period of darkness every night and a short day. • Long day plants flower when exposed to a short period of darkness and a long period of daylight.

29. Winter Dormancy • Phytochrome also regulates the changes in activity that prepare many plant for dormancy as winter approaches. • Dormancy is the period during which an organism’s growth and activity decrease or stop. • As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant.

30. Leaf Abscission • In early autumn, the shorter days and lower temperatures gradually reduce the efficiency of photosynthesis. • The phytochrome in the leaves absorbs less light as the days get shorter. • Auxin production drops, but the production of ethylene increases. • The change in the relative amounts of these two hormones starts a series of events that gradually shut down the leaf.

31. Leaf Abscission • The chemical process of photosynthesis stop first. • When light destroys the remaining green pigment, other pigments that have been present all the long but masked by chlorophyll, become visible. • The brilliant colors of autumn are a direct result of these processes.

32. Enzymes extract nutrients from the broken-down chlorophyll. • These nutrients are then transported to other parts of the plant, where they are stored until spring. • Much of the leaf’s water is extracted. • A layer of cells called the abscissionlayer, form at the petiole and seal off the leaf from the plant’s vascular system. • Leaves die and fall off and the tree enters a period of dormancy.

33. Figure 25-11 Deciduous plants undergo changes in preparation for winter dormancy. Photosynthetic pathways in leaves shut down. An abscission layer of cells forms at the petiole to seal off the leaf form the rest of the plant. Eventually, the leaves fall off.

34. Overwintering of Meristems • Hormones produce important changes in apical meristems by producing thick, waxy scales that form a protective layer around new leaf buds. • This allows a terminal bud to survive cold winter days. • Xylem and phloem tissues pump themselves full of ions and organic compounds that act like antifreeze in a car • This prevents the tree’s sap from freezing allowing the plant to survive the bitter cold.

35. Exit Slip – 5/1 1. Complete the chart below. 2. List the 4 hormones we have discussed and their functions. 3. What 4-5 steps occur that help plants prepare for winter dormancy?

36. Plant Adaptations Chapter 25.3

37. Aquatic Plants • Aquatic plants live in an muddy water environments that have very little oxygen. • Adaptations: • Many plants have tissues with large air-filled spaces through which oxygen can diffuse. • The reproductive adaptations include seeds that float in the water and delay germination for long periods. • Many grow quickly after germination and extend the growing shoot above the water’s surface.

38. Aquatic Plants • Water lilies have long petioles that extend down into the root system; oxygen diffuses from these open spaces into the roots.

39. Salt-Tolerant Plants • Plants that live in salty water must be able to get rid of excess salt. • Their leaves have specialized cells that pump salts out of the plant tissues and onto the surface of the leaf where it is washed off by the rain.

40. Salt-Tolerant Plants • “Some mangroves remove salt from brackish estuarine waters through ultra-filtration in their roots. Other species have special glands on their leaves that actively secrete salt, a process that leaves visible salt crystals on the upper surface of the leaves.” –NOAA OSE

41. Desert Plants • Plants that live in the desert biome are called xerophytes. • They must be able to tolerate extreme conditions such as strong winds, daytime heat, sandy soil, and infrequent rain. • Desert plants have extensive root systems, reduced leaves, and thick stems that can store water. • Seeds of desert plants can remain dormant for many years and germinate only when sufficient moisture guarantees them a chance for survival. • Other plants have bulbs, tubers, or specialized stems that can remain dormant for years. • These plants can mature, flower, and set seeds in a matter of weeks or even days when water is present.

42. Desert Plants

43. Desert Plants • Cactuses have spiny leaves and have thick green stems that carry out photosynthesis and are adapted to store water.

44. Alternative Ways to Obtain Nutrients • Some plants live in bogs, wet, acidic environments where there is very little or no nitrogen. • Bacteria that normally cause decay and return nitrogen to the soil can not live in acidic environments. • These plants have adaptations to obtain nutrients. • Some plants have specialized features for obtaining nutrients other than photosynthesis.

45. Venus Fly Trap Carnivorous plants trap and digest insects and other small animals. Venus’ flytrap has leaf blades that are hinged in the middle so if an insect touches the trigger, it closes up and traps it inside

46. Pitcher Plant • Pitcher plants drown their prey. • Prey land/fly into the pitcher-shaped leaves where they are trapped and digested.

47. Sundew • Sundews trap insects on leaf hairs tipped with sticky secretions.

48. Parasitic Plants • Parasitic Plants harm their host and can pose a serious threat to its survival by extracting nutrients from the plant. • Examples are Mistletoe and Cuscuta.

49. Mistletoe Cuscuta

50. Epiphytes • Epiphytes are plants that are not rooted in soil but instead grow directly on the bodies of other plants. • They are not parasites because they do not absorb nutrients from the plant. • They gather only moisture from rainfall. • Most are found in tropical rain forests and other moist biomes. • Examples: Bromeliads and orchids.