1. Hormones
• Hormones are chemical substances that
control a plant’s patterns of growth,
development, and responses to
environment conditions
• Auxins are produced in the apical
meristem and are transported downward
into the rest of the plant, stimulates cell
elongation

2. Cont.
• Auxins are responsible for the plant
response called gravitropsim and
phototropism
• Auxins are also responsible for lateral
buds (branches)
• Cytokinins are plant hormones that
stimulate cell division and the growth of
lateral buds and cause dormant seeds to
sprout

3. Cont.
• Gibberelinns cause an increase in overall
size of plants and individual plant
structures
• Ethylene is produced in response to
auxins, fruit tissue release small amounts
of the hormone which stimulates fruit to
ripen

4. Plant Response
• Tropism – response to external stimuli
• 3 types:
• Gravitropism – responds to force of gravity
• Phototropism: response to light
• Thignotropism: response to touch

5. Cont.
• Photoperiodism: seasonal activity like
flowering and growth (phytochrome is
plant pigment responsible)
• Dormancy: in winter, deciduous plants turn
off photosynthetic pathways, transport
materials from leaves to roots, and seal
leaves off from the rest of the plant

6. Plant Adaptations
• Aquatic plants: for sufficient oxygen
absorption, aquatic plants have tissues
with large air-filled spaces through which
oxygen can diffuse
• Desert: extensive root systems, reduces
leaves, thick stems that can store water
(xerophytes)

7. Cont.
• Nutritional specialists: specialized features
for obtaining nutrients (carnivorous or
parasites)
• Chemical: manufacture compounds that
are toxic to predators