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Botany 202

Developmental and Applied Plant Anatomy Practicals

CEJ Botha 2004

Introduction 3

GROUP ASSIGNMENTS: 4

evaluation 4

Introduction

The developmental and applied plant anatomy course offered as a second year course has several aims and objectives. Chief amongst these is to expose you to use of the compound microscope to examine structures and to make deductions concerning the function or purpose of the structure(s) being examined. We will make use also of very simple histochemical techniques to expose particular molecular compositions – chiefly, pectin cellulose, lignin, as wall components, starch lipids and fats as cell constituents This course focuses attention on the interplay between the structural, ultrastructural, biochemical, ecological and functional interrelationships between the organs and the functioning plant body.

This approach does require the examination of organ structure in some detail. This way, we will gain a clear insight into the myriad and varied forms and the functional changes, which occur during the life of the plant. What is particularly important is understanding changes that occur say, between a plant living in ideal mesophytic conditions, and one that has adapted to extreme xerophytic habitats, such as Arcto-Alphine Tundra, or mid latitude deserts, such as the Atacama, or Namibian Desert. Stop to think about these plants. Obviously, on the macro scale, one would think of them in terms of the ecological niches, and, perhaps, in terms of their ecophysiology, one would think of them in terms of their ability to avoid drought, excess water loss and maybe even how the xanthophyll cycle operates in the leaves.

A good comprehension of anatomy will allow you access to a great deal of information about plant structure. It will give you information regarding survival range and potential, or how plants survive particular habitats, or their potential to survive particular stress, their photosynthetic type and possibly, something about their ability to cope with stress (its avoidance or tolerance). Plant anatomy - at the developmental level - is defined as a study of structure/function relationships between at the cellular level. Plant anatomy is thus central to may disciplines. It forces us to examine and to observe. It is therefore critical that we understand the cellular workings of a plant, observe internal structures, their functions and interrelationships, before we rush off and look at whole communities.

So, does Plant Anatomy conjure up an image of hours of sitting in a laboratory, having to spend a lot of time looking down the microscope, at a specimen that you often cannot see clearly. I really hope not! You should have a little understanding, possible be able to 'sort of recognise' and perhaps 'sort of understand' the function of a particular structural component of a plant. Many subjects start off like this – and remain so, until you have been exposed to them. There is a great deal of information to be gained.

To seek, to wonder, to determine – these are the essence of science. I hope that the plant anatomy course will encourage you to seek knowledge, to strive to understand, to determine the relationships that exist within living cells, at the molecular, the sub-cellular, the cellular and the whole organ level.

Relevance is a word that means different things to different people under different circumstances. You may wonder about the relevance of a course like plant anatomy and I am very happy to debate this with you. “Relevance” is an interesting word which means pertinence, significance, importance, aptness, and relationship. Take your pick what does it mean to you?

The preservation of structural details of cells and tissues is influenced by the condition of the material at the time of collection and by the subsequent preparative steps used for killing and fixing the material. In other words, if you wish to prepare sections in which the structural details are well preserved, one should select healthy plant material. Also take care to follow directions and instructions! Failure to do so will affect the quality of the results you attain. Exceptions to this rule apply only when the researcher is interested in observing the effects of disease, fungal infection, insect damage etc. on the normal structure of the plant material being examined or- where you have to prepare a "quick" sample, and do not have all the necessary paraphernalia needed to prepare top-quality preparations.

Remember that your microscope is a valuable and expensive scientific instrument and that as such, you should treat it with great care and respect. Since the cost of microscopes continues to increase alarmingly, it is important that you develop the ability to care for these instruments. A good student microscope, such as that which you are using, costs over R20, 000-00 to replace. You will have to exercise great care and restraint in the use of your microscopes. I shall refresh your memories as to the correct way in which to care for, and use this instrument, as well as in the proper way in which to use the oil-immersion 100x-objectives.

Hopefully, the plant anatomy course will provide new insight and meaning in your botanical studies. Hopefully, your education will be enriched by the new techniques which will allow not only microscopic orientation, but broaden your mind to the unknown and unseen.

Group Assignments:

Practical assignments are compulsory – unsubstantiated absence can lead to withdrawal of the DP. Absence from a group activity is not acceptable unless negotiated before hand, or if you are ill, reporting in a soon as is possible. The first period of the practical session is vital and as such you must attend this. Your group will be expected to hand in completed assignments. Neat and accurate work is expected. The assignments will be marked by the demonstrator and audited by me - this mark will go towards your year mark. Your group must present your permanent preparations at the end of the course for assessment as well. This preparation counts for 25% of the practical component of the portfolio mark. Clearly, neat, well mounted and useful specimens will attract good marks. There may well be will be a test/examination at the end of the Plant Anatomy module, which combines theoretical with practical knowledge. This will be of approximately 3 hours duration. It will count towards the semester as well as the exam mark (40% semester; 60% exam).

evaluation

Evaluation of your practical component of the course will be undertaken by means of the Practical Criterion Assessment Grid which has been drawn up specifically for the task. You should make sure that your GROUP ASSIGNMENTS (which together with the permanent slides that your group have prepared) make up your work portfolio[1] are complete, and that you are familiar with the criteria against which this work will be judged and graded.

The new strategy -- what is expected of you?

In a word, co-operation! The material that we will explore during the three practical sessions will almost surely be completely new, and therefore somewhat foreign to you. You will have to learn and develop a new vocabulary, to come to grips with new terms and you will have to become comfortable with using a slightly more sophisticated microscope, efficiently, effectively, and correctly. I will go through the setup of the Zeiss microscopes that we have at out disposal in the Senior Laboratory, and I will show you how to use them to maximise what you can see using them.

Practicals, like lectures, are about what you gain from them. Participation at the individual level is thus unconditional. Group participation, where this is required, involves sharing responsibilities between the group members – much like the board of a corporation, each of you has to make input, else the board will not achieve its goals or objectives.

We will make use of several assessment methods – I will assess individually, but you will also be evaluated by your group members – each student in a group will assess the input of another group member and these assessments will be discussed and will then contribute to (and possibly affect) the individual concerned’s mark.

How will this work? Assume that an assignment (practical exercise) is worth 25 points. Each member is thus potentially able to score full marks. What happens if one of the members of the group either does it all, or does very little? The mark would be the same for all members of the group. This is hardly fair, as effort (or the lack of it) is not rewarded in this scenario. What we will do is as follows: A group mark will be assigned and in addition, a peer mark for each individual group member will be assessed and the final mark which will be be taken into account is the average of the group mark and the peer mark.

Assume the following scenario, with four members in the Group:

The Table illustrates quite clearly that ‘Canna’ was thought to be slacking off and marked accordingly. Canna has paid the penalty, because the peer review mark was upheld after discussion with the group and a 20% loss of marks resulted!

The concept is thus very simple. The group is responsible for its own performance. The group also assigns the component parts of the exercise, thus saving time and thus allowing for a more polished product.

PLEASE NOTE:

Groups must be formed at the outset, and the list of names must be given to me to ensure that Moodle is set up correctly, to accommodate the group-wise activities which are planned.

ASSIGNMENT 1: Cell wall histochemistry

Introduction

"There is only one reliable criterion by which we can determine whether the image that we see with the microscope is a good representation of what existed in life, and that criterion is comparison with living cells".[2]

The preservation of structural details of cells and tissues is clearly, influenced by the condition of the material at the time of collection and by the subsequent preparative steps used for killing and fixing the material. In other words, if you wish to prepare sections in which the structural details are well preserved one should select healthy plant material. Exceptions to this rule apply only when the researcher is interested in observing the effects of disease, fungal infection, insect damage etc. on the normal structure of the plant material being examined.

What do you need to do?

Each group will select a single plant from the specimens provided. This will be your group‘pet plant’. All experiments and procedures that are listed under the various assignments must be carried out using this plant, and must also, include the recommended number of ancillary specimens as well, as this is assigned to you.e pet plant You should try to apportion the workload within the group, so that everyone contributes to the required work. As lignification, the distribution of photosynthetic tissue and starch distribution to give but three examples, varies between aerial and underground organs, it is highly desirable that you should examine stem, leaf and root material (if the latter is available) to determine what is happening in terms of development, within the plant.

Table of Contents s285

Introduction

Group Assignments:

evaluation

Recommended Reading

Text Books:

Additional Reading

Objectives:

Outcomes:

The new strategy -- what is expected of you?

PLEASE NOTE:

Groups must be formed at the outset, and the list of names must be given to me to ensure that Moodle is set up correctly, to accommodate the group-wise activities which are planned.

ASSIGNMENT 1: Cell wall histochemistry

Introduction

What do you need to do?