Unit 7--Plants

Chapter 25

Plant Responses & Adaptations

Plant Hormones

• Auxin = first discovered

• located in growing tips of roots/stems

• for stem elongation

• inhibits bud growth

• leaf & fruit drop

Plant Hormones

• Ethylene = for fruit ripening & drop or leaf & flower drop

Place fruits in a brown bag to trap ethylene gas release to speed up ripening

Plant Hormones

• Gibberellins = for seed germination, fruit development & stem elongation

Tropisms

• Growth response toward a stimulus

• Phototropism = toward light

• Ex: sunflower

Tropisms• Gravitropism (or geotropism)

• toward earth’s center

• Ex: roots (positive) & stems (negative)

Tropisms

• Thigmotropism =

• toward a support or something “touched”

• Ex: tendrils on a climbing vine

Modified Leaves

• Cactus spines

• Tendrils

• Carnivorous plants

Specialized Plants

• Parasitic plants

– Ex: mistletoe

• Epiphytes

– Ex: orchids, ball moss

Classification by life span

• Annuals =– entire life cycle

in one growing season

• Ex: tomato plant

Classification by life span

• Biennials – lives through two

growing seasons, separated by dormancy

• Ex: cabbage & carrot

Classification by life span

• Perennials =– live many years

and through many periods of dormancy

– Ex: trees, shrubs– Also, bluebonnets