Lab 7 - Plant Form and Function
LAB 7 - PLANT FORM & FUNCTION
Suggested Readings
Concepts 35.1 and 35.3 in Campbell Biology 3rd Canadian Edition.
Introduction
This lab exercise focuses on the examination of tissue types and organs in plants, emphasizing the link between the form and function of sporophyte tissues.
The adaptation of leaf function to different environments will also be explored.
Learning Outcomes
After completing this lab, students should be able to:
Relate form and function for the major sporophyte tissue types.
Describe the three organs of a sporophyte.
Identify leaf structural adaptations to various environments.
Explain the relationships of plant structures in different environments.
Note: All material covered in the lab will be testable!
1. Seed Germination
Definition of Germination: The initial process of growth in plants when a plant emerges from a spore (in seedless plants) or from the seed (in seed plants).
Focus will be on seed germination in this lab.
Factors for germination: Seeds germinate when exposed to specific light and temperature conditions. They may also germinate in response to increased concentrations of gibberellins, a plant hormone promoting stem and root elongation.
Role of Gibberellins: Found in high concentration within the seed embryo, they initiate the germination process.
Figure 7.1: Photographs the different stages of germination in Arabidopsis thaliana:
(A) Ungerminated seed.
(B) Seed with elongating radicle.
(C) Continued radicle elongation.
(D) Distinct hypocotyl.
(E) Emergence of seed leaves (cotyledons).
(F) Greening of the plant.
Classification Task: Classify Arabidopsis as a monocot or eudicot based on the figure and provide rationale.
Experimental Design
Two strains of Arabidopsis were used:
Wild Type (WT): No mutations affecting gibberellin synthesis (GA1).
GA1-mutant: Contains a mutation preventing gibberellin synthesis.
Setup: Nine seeds of each strain placed in two environments (with and without exogenous gibberellins added). Other variables held constant.
Data Collection: Count of germinated seeds over four days for each trial.
Results
Figure 7.2: Displays average number of germinated seeds for WT and GA1-mutant Arabidopsis:
WT (blue line) vs GA1-mutant (orange line)
Condition A: Without gibberellins.
Condition B: With gibberellins (200 µM added).
Analysis Questions
Identify the independent and dependent variables in the experiment.
Evaluate if Figure 7.2 supports the hypothesis that gibberellins are required for seed germination.
Discuss any difficulties in comparison based on the figure.
2. Plant Growth
All plant tissues are produced by meristems during growth.
Primary Growth: Involves increase in length, starting with the Root Apical Meristem (RAM) and Shoot Apical Meristem (SAM) during seed germination.
New apical meristems allow for branching of roots and shoots.
Secondary Growth: Increase in girth; occurs in woody plants, involving cambia that produce secondary tissues.
Vascular Cambium: Produces secondary vascular tissues.
Cork Cambium: Produces secondary dermal tissues.
3. Plant Tissues
Overview of cell types found in three major tissues of angiosperm sporophytes: dermal tissue, ground tissue, vascular tissue.
3.1 Dermal Tissue
Definition: Protective dermal tissue covering the plant.
Epidermis: Covers all organs in nonwoody plants and new growth/leaves in woody plants.
Periderm: Replaces the epidermis during secondary growth, produced by the cork cambium.
Function: Protects against excess water loss.
The Waxy Cuticle: Secreted by epidermis; restricts water loss; regulates transpiration through stomata (openings between guard cells).
Trichomes: On leaves, reduce transpiration by slowing air movement at the leaf surface.
3.2 Vascular Tissue
Definition: Circulatory system for plants.
Types of vascular tissue:
Xylem: Transports xylem sap (minerals and water).
Phloem: Transports phloem sap (sugars and organic substances).
Figure 7.4: Shows xylem (A) and phloem (B) in cross-section.
Xylem Structure: Composed of tracheids and vessel elements; secondary cell walls thickened with lignin. Upon maturity, cells die, leaving conduits for water transport.
Phloem Structure: Contains sieve-tube elements connected end to end; alive at maturity but devoid of organelles; supported by companion cells.
3.3 Ground Tissue
Definition: All plant tissues that are not dermal or vascular collectively.
Types include:
Parenchyma: Thin cell walls, large vacuoles; functions in photosynthesis (leaves) and starch storage (roots).
Collenchyma: Elongated cells, irregularly thickened walls; provides flexible support, often found in petioles.
Sclerenchyma: Thick cell walls; provides rigid support, includes sclereids (irregular shapes) and fibers (elongated support cells).
4. Plant Organs
Plants have three organs: roots, shoots (stems), and leaves. Each organ comprises various tissues identified above.
4.1 Roots
Main functions: absorb water and minerals, store nutrients, anchor plant in soil.
Root Growth: Eudicot roots develop from the RAM as a main tap root, lateral roots branch off from parenchyma cells of the pericycle.
Adventitious roots grow from stems to support tall plants in shallow soil.
4.2 Stems
Functions to maximize sunlight exposure for leaves; typical vertical growth above ground.
Shoot Apical Meristem (SAM): produces stem and leaf tissues, as well as axillary buds (dormant SAMs).
4.3 Leaves
Major site for photosynthesis; also aids gas exchange and transpiration.
Leaf architecture varies by species, habitat, and plant region. Eudicots typically have a palisade mesophyll (upper, densely packed) versus spongy mesophyll (lower).
Adaptations: Waxy cuticle to reduce excess water loss, stomata for gas exchange, and variations in stomatal density based on environmental conditions.
Overall Tasks for Figures
Complete diagrams of cross-sections for both eudicot and monocot roots and stems, labeling all tissue types.
Analyze figures depicting leaf structure, identifying dermal, ground, and vascular tissues.
5. Microscopy Observations
5.1 Roots
View various root types under the microscope, noting root apical meristem near the tip and protective root cap.
Observe Allium root tip for actively dividing cells in mitosis.
5.2 Stems
Observe Coleus stem for tissue layers including the shoot apical meristem and axillary buds, and Tilia stem to assess the presence of cambiums.
5.3 Leaves
View cross sections of Syringa and Zea leaves, identifying mesophyll cells and vascular bundles.
6. Summary
This lab analyzed plant structure from germination through tissue production and adaptation in angiosperms.
Students should understand tissue types, their functions, and leaf structure in relation to habitat conditions.
Note: Identify key terminology as part of your learning.
© 2021 Kevin Scott and Cassandra Debets - This material is confidential and intended for personal study only.