IB Biology II
PLANT STRUCTURE LAB
In this lab you will explore plant structures at a variety of levels, from the cellular to the whole organ level. This lab
includes a standard plant histology component (Plant Cell Types, Plant Vegetative Organs), but also includes exercises on leaf
morphology.
PLANT VEGETATIVE ORGANS
For this component of the lab, you will examine prepared
slides of leaves, stems, and roots. In each case the same tissue
types are present; i.e., vascular tissues, dermal tissues and ground
tissues, but their arrangement varies between organ types and
specialized cell types may also be present; i.e., guard cells and
hair cells (trichomes) in the leaf epidermis, etc. Dermal tissues
(epidermis) serve a protective function, but also are involved in
nutrient and gas exchange. Vascular tissues (xylem and phloem)
are specialized for the long-distance transport of water and
carbohydrates. All other tissues present are referred to collectively
as ‘ground tissues’.
A) Leaf Structure:
Leaves are lateral appendages of the shoot that are
specialized for photosynthesis. The ground tissues of leaves,
termed mesophyll, contain photosynthetic parenchyma almost
exclusively. In dicot leaves, the mesophyll is generally organized into two distinct regions based on differences in shape and
arrangement of parenchyma cells. In the palisade mesophyll, located near the upper epidermis, the cells are relatively
closely packed and columnar in shape. In the spongy mesophyll (located on the bottom half of the leaf), the cells are more
irregular in shape and are loosely packed. Since most of the stomata are located in the lower epidermis the loose
arrangement of the spongy parenchyma facilitates gas movement, with carbon dioxide diffusing into the leaves for use in
photosynthesis and water vapor diffusing out (transpiration).
Typical Dicot Leaf Cross-Section
Assignment. Examine the dicot (lilac) leaf cross section provided. Orient the slide such that the upper epidermis is at the top
of your field of view. Avoiding the leaf midvein, draw what you see, identifying the epidermis, palisade and spongy
mesophyll, bundle sheath, veins with xylem and phloem, and stomata. Be sure to note mesophyll organization and bundle
sheath traits; mean cell size, presence/absence of chloroplasts, etc.
B) Stems and Roots:
Axial plant organs (stems and roots) serve a variety of functions, with
roles in transport, storage, and support. In many stems and roots the vascular
tissues are arranged in a cylinder. In such cases the regions of ground tissue
located internal to the vascular tissues are termed pith and those located
towards the exterior are termed cortex. If the vascular tissues (bundles) are
scattered throughout the ground tissues cortex and pith regions cannot be
recognized, and the whole ground tissue is termed a fundamental tissue.
Assignment. Examine cross sections of root and stem from both monocot and
dicot. Draw them and discuss (in your report’s Analysis) how they differ and how
they appear the same. Label the xylem, phloem, epidermis, and ground tissues,
indicating pith and cortex if present. The cross-sectional diagrams of roots to
the right should provide you with a starting point for your analysis. For the stems
phloem fiber caps, groups of fiber cells located just exterior to each phloem
bundle may be present.
Page 1!
IB Biology II
Reminder:
!
Informal and Observational Lab reports include the following components:
I. Introduction
• Purpose (what research question are you answering?)
• Hypothesis (note: observational labs may not have one. e.g. this plant lab does not.)
II. Materials and Methods
• Usually will be written “As indicated in <cite lab protocol source>.”
• Note any deviations from proscribed protocol
III. Results
• Tables (organized reporting of your raw data. Report any margins of error.)
• Calculations
• Graphs (your data transformed on graph paper to make it easier to understand and interpret)
• Any sketches (in pencil, large, correctly labeled)
IV. Analysis
• Conclusion (If there is one, reflect on the hypothesis, interpret the data, and answer the initial
question(s). Was the hypothesis supported or refuted?)
• Evaluate the procedure (weaknesses, limitations, and error)
• Improving the investigation (suggestions in light of the identified weaknesses)
• Further Investigation (What new questions arise because of your results?)
• Discussion Questions (Include any answers to questions posed during the investigation. Include the
question in your answer)
Sheldon Science Sketch Criteria®
1. Use pencil for any sketched data (ink may be used for labeling)
2. Draw within a large field of view (FOV) (approx. 5-8cm is a good diameter for the FOV)
3. Do high quality work; sketch your area of interest perfectly. Make it look exactly as it appears under the
microscope. The remainder of the FOV must be sketched to provide context, but the quality of the sketch may be
quite rough.
4. Label your observations with as much of the following information as possible:
a. Title of the object of interest
b. Use a ruler to draw label lines
c. Include total magnification of the FOV
d. Include size (in µm*) of your object of interest.
e. Label on the right-hand side of the drawing, if possible
*see table below for compound scope scales (note: 1mm = 1000µm)
Page 2!