Biology 1A    Oct 22, 1998
Lecture 15 - Water Relations

Page Contents :

• Reading Assignment
• Overview of Lecture
• Overview of Lab
• Lecture Outline
• Vocabulary
• Study Questions

Stern: Chapter 9

Overview of Lecture:

Challenges to life on land.
     Algal water relations
     Bryophyte water relations
     Vascular plant adaptations
Water transport in vascular plants.
     Morphology of the transport system.
     Mechanisms behind the systems.

Overview of Lab:

Review Moss Reproduction.
Finish Charophyceae from "Algae II"
Liverworts - Anatomy and Reproduction
Hornworts - Anatomy and Reproduction

A. Algal water relations
1. Homeostasis -- no problem with water availability
2. UV Protection -- filtered through water
3. Support -- natural bouyancy, gas-filled floats
4. Fertilization -- swimming gametes
B. Bryophyte water relations
1. Homeostasis
a. need to worry about dessication
b. sporopollenin
c. conducting cells -- hydroids & leptoids in mosses
d. surface transport
e. poikilohydry
f. hydronasty
2. Support
a. turgor pressure
b. plasmolysis
3. Fertilization -- still needs water
C. Vascular plant adaptations
1. Homeostasis
a. cuticle
b. must evolve stomata
c. conducting cells -- avoid drying out by moving fluids around
d. transpiration
2. Support
a. turgor
b. lignin
3. Fertilization

A. Morphology of the transport system
1. Differences from transport in vertebrates.
a. not a circulatory system -- not a cycle, but unidirectional
b. two independent systems
c. no "pump"
2. Vascular bundles
a. vascular tissue is arranged in bundles -- groups of transport cells.
b. two types of vascular tissue: xylem and phloem
c. both tissues always occur together.
d. xylem is usually closer to the center of the plant.
e. phloem is usually closer to the epidermis of the plant.
f. despite occurring together, they are separate.
3. Xylem
a. xylem morphology
b. xylem function
4. Phloem
a. phloem morphology
b. phloem function
B. Mechanism behind the transport systems
1. Principles of osmosis
a. diffusion -- movement from area of high concentration to low concentration
b. osmosis -- diffusion of water ("dissolved" in substances)
c. water potential -- pressure required to prevent movement.
2. Mechanisms of xylem function
a. capillary action
b. root pressure
c. transpiration -- Cohesion-Tension Theory
3. Mechanisms of phloem function
a. different principles, since the cells are living
b. measuring flow rate in phloem
c. observations of phloem flow:
i. different rates for different materials
ii. different materials move in different directions
iii. two materials can move in opposite directions simultaneously
d. cyclosis
e. Pressure-Flow Hypothesis

• What problems with water do land plants face that algae do not?
• What are some ways that bryophytes maintain homeostasis with regard to water? What are some ways that vascular plants maintain homeostasis with regard to water? Which of these involve chemical waterproofing? Which involve movement? Which involve specialized cells?
• What is poikilohydry? Which groups of plants use this strategy? What strategy do other plants use?
• Explain how turgor pressure helps to keep plant tissues stiff. Which kinds of plants rely primarily on turgor pressure to support them? In which plants is additional support needed?
• Explain what happens in plasmolysis and why. What are the consequences to cells and tissues when this happens?
• Considering the arrangement and function of both hydroids and leptoids in mosses, could they be homologous to vascular tissue in vascular plants? Which could be homologous with xylem? with phloem?
• What adaptations do land plants have for protecting their gametes from drying out?
• What are cutin, lignin, and sporopollenin? How are the functions of these chemicals similar? Where can each be found in plants? In which plants can they be found?
• How is internal transport in plants different from internal transport in vertebrates?
• Explain the term "vascular bundle". What are the components of such a bundle?
• How are xylem and phloem similar? How are they different? (Consider both physical structure as well as their function.)
• Which tissue conducts water up to the shoot system? Which conducts ions? Which conducts organic materials?
• True or False? : The content of phloem is largely sugar and water.
• Explain the process of diffusion. Explain the process of osmosis. How are these processes different? How are they similar?
• Explain the concept of water potential. What causes water potential? How is it measured?
• What are the processes that contribute to the functioning of xylem? Under what conditions is each important?
• How does root pressure move water upwards in a plant?
• How does transpiration move water upwards in a plant?
• What is the Cohesion-Tension Theory? What does it explain?
• How is flow rate measured in phloem? Why is it so difficult to measure?
• What is cyclosis? How does it explain the movement of substances in phloem? What does it fail to explain about movement of substances in phloem?
• Explain the Pressure-Flow Hypothesis. According to this hypothesis, what drives the movement of substances in phloem?