Plant Form and Function
Learning Goal:
How are plants structurally adapted for survival?
Analyzing how plants detect and defend themselves against
herbivores and environmental stresses (Ch 39)
Refer to
pg 210-213 in Holtzclaw
Ch 39 in Campbell
Media resources
Try This! (from last year)
In double fertilization, how is the
endosperm formed?
A.
B.
C.
D.
E.
The fusing of two sperm and an egg
From the epidermis
From the fertilization of the egg
From the zygote during development
From the fusing of a sperm with two polar
bodies
Try This!
In double fertilization, how is the
endosperm formed?
A.
B.
C.
D.
E.
The fusing of two sperm and an egg
From the epidermis
From the fertilization of the egg
From the zygote during development
From the fusing of a sperm with two
polar bodies
Analyzing how plants detect and defend
themselves against herbivores and
environmental stresses (Ch 39)
You must know:




The three steps to a signal transduction pathway
The role of auxins in plants
The survival benefits of phototropism and
photoperiodism use changes in environment to
modify plant growth and behaviour
How plants respond to attacks by herbivores and
pathogens
Try This!
Both plants and animals respond to environmental stimuli.
Which of the following statements are true and which
ones are false?
A.
The processes by which plants and animals perceive
environmental changes are equally complex.
B.
The processes by which plants and animals perceive
environmental changes are often homologous.
C.
Unlike animal hormones, plant hormones act only locally.
D.
Both plants and animals have physiological cycles called
circadian rhythms.
Try This!
Both plants and animals respond to environmental stimuli.
Which of the following statements are true and which
ones are false?
The processes by which plants and animals perceive
environmental changes are equally complex.
TRUE
B. The processes by which plants and animals perceive
environmental changes are often homologous.
TRUE
C. Unlike animal hormones, plant hormones act only locally.
FLASE
D. Both plants and animals have physiological cycles called
circadian rhythms.
TRUE
A.
Try This!

What are the morphological differences
in dark-grown plants and light-grown
plants?
Try This!

What are the morphological differences
in dark-grown plants and light-grown
plants?
◦ Dark- grown have




long stems
underdeveloped roots
unexpanded leaves
shoots lack chlorophyll
How does this potato change its growth
when there is light?
How does this potato change its growth
when there is light?


Via the Signal Transduction Pathway!
How does this potato change its growth
when there is light?


Via the Signal Transduction Pathway!
◦ The signal (light) is transduced to a response (greening)
Signal Transduction - Review
Reception
 Transduction
 Response

Signal Transduction - Review

Reception: Receptors undergo changes in shape
due to an environmental stimulus
◦ Ex) phytochrome proteins changing in response to light
Signal Transduction - Review

Transduction: Amplification of signal through a
multistep pathway
◦ Allows small signal to produce large cellular response
 Uses protein kinases (phosphorylation cascade)
and second messengers (Ca2+ and cAMP)
Signal Transduction - Review
Response: Two ways response is accomplished:

1.
Transcriptional Modification:
•
2.
↑ or ↓ mRNA production (turning genes on/off)
Post-Translational Modification:
•
Activates existing enzyme molecules
Signal Transduction

Proteins include:
◦ Photosynthesis enzymes
◦ Plant growth hormones
 Auxin levels lower to slow stem growth
(focus on leaf growth)
So…. What was AUXIN?

A plant hormone…

Yes, plants have hormones too!
Examples of Plant Hormones

Auxins – stimulate elongation of cells within young
developing shoots

Cytokinins – stimulate cell division

Gibberellins – stimulate stem elongation, pollen,
fruit, seed development

Abscisic acid – promotes stomatal closure during
drought stress

Ethylene (gas!) – fruit ripening, leaf abscission
Plant Hormones

Hormones: chemical messengers that
coordinate the different parts of a
multicellular organism

Tropism: Plant growth response toward
or away from a stimulus
◦ Phototropism
◦ Gravitropism

How does this benefit survival?
Phototropism - Mechanism
Phototropism - Mechanism
Phototropism - Mechanism
Actions of hormones…

Photoperiodism – physiological
response to a photoperiod (relative
lengths of day and night)
◦ Example: Flowering
 Short day plants
 Long day plants
 Day-neutral plants

Circadian rhythms – physiological cycles that
have a frequency of about 24 hours
Responses to Mechanical Stimuli

Mimosa Plant
Herbivore Defense
Video Clip
Think:

Illustrate this statement with an example:
“A plant generally responds to
environmental cues by adjusting its
pattern of growth and development.”
How do plants detect and defend themselves
against herbivores and environmental stresses?
Do you know?




The three steps to a signal transduction pathway
The role of auxins in plants
The survival benefits of phototropism and
photoperiodism use changes in environment to
modify plant growth and behaviour
How plants respond to attacks by herbivores and
pathogens
Try
# 1 p. 213, #1-4 p. 215 in Holtz