Lecture Outlines by Gregory Ahearn, University of North Florida
Copyright © 2011 Pearson Education Inc.
Plant Responses to the Environment, Transpiration, Photosynthesis, Respiration
Adapted from
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Plants respond to their environment in sophisticated ways – React to stimuli like touch, gravity, moisture,
light, and day length – They use hormones—chemicals that are
secreted by cells and transported to other cells, where they exert specific effects
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Auxins promote or inhibit elongation in different target cells – Controls positive phototropism (growth toward light) in
shoots and gavitropism (growth toward or away from gravity) in shoots and roots
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Radish Seedlings Show Positive Phototropism
Fig. 45-3
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Auxin is transported to the lower side of theshoot, where it stimulates cell elongationand causes the stem to bend upward
Auxin is transported to the lower side of theroot, where it inhibits cell elongation andcauses the root to bend downward
(b) The shoot and root are orientedhorizontally
Positive Gravitropism
Fig. 45-2b
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Gibberellins are primarily active in plant shoots – Promote stem elongation
by increasing both cell division and cell elongation
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Ethylene is a gas – Recognized as a plant “stress hormone” – Causes certain fruits to ripen
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Ripe Fruit Become Attractive to Animal Seed Dispersers
Fig. 45-11
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Abscisic acid helps plants withstand unfavorable environmental conditions – Causes stomata to close when water is scarce – Promotes root growth and inhibits stem growth under dry
conditions – Maintains dormancy in seeds
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.1 What Are Some Major Plant Hormones?
Florigens control the timing of flowering in response to environmental cues
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
45.2 How Do Hormones Regulate Plant Life Cycles?
Some plants display thigmotropism, a directional movement or change in growth in response to touch
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
A Rapid Response to Touch
Fig. 45-14
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
A Sundew with Its Insect Prey
Fig. 45-14
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Photosynthesis Review
Occurs in two steps: Light reaction and dark reaction (Calvin Cycle)
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Light Reaction
Requires light Converts light energy
into chemical energy (NADPH and ATP)
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Dark Reaction
AKA Calvin cycle Does not require light Makes sugar from CO2
and hydrogen ions carried by NADPH
Energy to do this comes from ATP produced in light reaction
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
C4 and CAM plants separate light and dark reactions
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Cellular respiration in plants?
Yes! Sugar must be converted into ATP for cells to use
Sugar + O2 CO2 + H2O + ATP In mitochondria
Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e
Transpiration
Plants breathe! Gas exchange occurs
through stomata Evaporation from
leaves (transpiration) draws water up the plant – like a straw!
Relies on cohesion and adhesion