1. Plant Responses and Adaptations
Chapter 25: Biology II

2. Plant Hormones Chemical substances that control:
A plant’s patterns of growth and development
A plant’s responses to environmental conditions
Target Cell: cell affected by a particular hormone

3. Auxins Stimulate cell elongation Produced in the apical meristem
Transported downward into the rest of the plant
Responsible for: phototropism and gravitropism

4. Auxins: Phototropism
Tendency of plants to grow toward a source of light

5. Auxins: Gravitropism
Tendency of a plant to grow in a direction in response to the force of gravity

6. Auxins
Lateral Bud: meristematic area on the side of a stem that gives rise to side branches
Apical Dominance: phenomenon in which the closer a bud is to the stem’s tip, the more its growth is inhibited
Herbicide: auxin-like weed killers; compound that is toxic to plants

7. Cytokinins
Plant hormones that are produced in growing roots and in developing fruits and seeds
Stimulate cell division and the growth of lateral buds
Cause dormant seeds to sprout

8. Gibberellins Growth-promoting substance produced by plants
Causes dramatic increases in size, particularly in stems and fruits
Produced by seed tissue
Responsible for the rapid early growth of many plants

9. Ethylene Plant hormone that stimulates fruits to ripen
Released in small amounts as a response to auxins
Commercial products can use this to control the ripening process; treated with synthetic ethylene

10. Tropisms The response of plants to environmental stimuli Gravitropism
Phototropism
Thigmotropism

11. Thigmotropism Response of plants to touch Examples:
A plant that is touched regularly may be stunted in its growth-sometimes quite dramatically
Vines and climbing plants-tips wrap around objects

12. Rapid Responses
Some responses do not involve growth; they are not tropisms
Examples:
Mimosa pudica: the “sensitive plant”
The Venus flytrap

13. Photoperiodism
Responsible for the timing of seasonal activities such as flowering and growth
Phytochrome: plant pigment responsible for photoperiodism

14. Short-Day Plants Plants that flower when daylight is short
Also called “long-night plants”

16. Long-Day Plants Plants that flower when days are long
Also called “short-night plants”

17. Winter Dormancy
Period of time during which a plant embryo is alive but not growing
As cold weather approaches, deciduous plants:
Turn off photosynthetic pathways
Transport materials from leaves to roots
Seal leaves off from the rest of the plant

18. Abscission Layer
Layer of cells at the petiole that seals off a leaf from the vascular system

19. Aquatic Plants
To take in sufficient oxygen, many aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse

20. Salt-Tolerant Plants
Leaves have specialized cells that pump salt out of the plant tissues and onto the leaf surfaces
Example: mangroves

21. Desert Plants Also called: xerophytes Extensive roots Reduced leaves
Thick stems that can store water

22. Nutritional Specialists
Plants that have specialized features for obtaining nutrients
Carnivorous plants: obtain nutrients from digested prey
Parasites: plants that extract water and nutrients directly from a host plant
The dodder plant Cuscuta

23. Epiphytes Plants that grow directly on the bodies of other plants
Gather their own moisture and produce their own food, unlike parasitic plants
Spanish moss-not a moss, but a bromeliad!

24. Chemical Defenses
Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals