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What is a section in botany based upon?

What is a section in botany based upon?


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I am a bioinformatician working with plant data. Therefore my formation on plant biology and botany is "ok" but not very strong.

When people talk about sections, I know that they talk about a phylogenetic rank that is lower than the genus but higher than the species. It groups subsets of species belonging to a genus together.

What is the thing that puts them together? Morphology, origin, geography, metabolism, genome identity,… ?


Type (biology)

In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon. In older usage (pre-1900 in botany), a type was a taxon rather than a specimen. [1]

A taxon is a scientifically named grouping of organisms with other like organisms, a set that includes some organisms and excludes others, based on a detailed published description (for example a species description) and on the provision of type material, which is usually available to scientists for examination in a major museum research collection, or similar institution. [1] [2]


Graduation Writing Assessment Requirement (GWAR)

Students must earn a C or better in a GWAR course to satisfy the requirement.

Botany, Ecology, and Zoology majors may choose between BIOL 475GW , BIOL 478GW , or BIOL 529GW

The department does not permit multiple concentrations within the Biology degree program. All of the curricula require preliminary work in physics and chemistry because many important biological concepts are based squarely upon principles in the physical sciences. Also, each curriculum includes upper-division work in the biological sciences so that students will receive reasonable breadth and depth in their degree program. Because of the sequential arrangement of courses, students are urged to consult the descriptions for the prerequisites of all their courses.

Although course electives are listed for most of the majors, new electives are always being added to various programs. Therefore, we highly recommend that students seek advisement prior to enrolling in elective courses in their major.


What is a section in botany based upon? - Biology

Course Coordinator: Dr John Conran

Benham 109Benham 109
Name Role Building/Rm Email
Prof Bob Hill Lecturer Benham GO5a [email protected]
Dr John Goodfellow Lecturer Benham 110 [email protected]
Dr John Conran Course coordinator Benham 109 [email protected]
Prof Andy Lowe Lecturer Braggs 210 [email protected]
Course Timetable

The full timetable of all activities for this course can be accessed from Course Planner.

Course Learning Outcomes

1 The structure of terrestrial and aquatic plants
2 The developmental processes involved in growth of plants from seed to flowering
3 The main physiological and biochemical processes that sustain plant life, including the ability to absorb water and nutrients, carry out photosynthesis and respiration, and the role of plant hormones and signalling
4 Generic skills of scientific observation, data recording and be able to write a scientific report
5 The ability to use keys to identify the main groups of plants
6 The ability to interpret visual symptoms of nutrient deficiencies of plants

University Graduate Attributes

This course will provide students with an opportunity to develop the Graduate Attribute(s) specified below:

  • informed and infused by cutting edge research, scaffolded throughout their program of studies
  • acquired from personal interaction with research active educators, from year 1
  • accredited or validated against national or international standards (for relevant programs)
  • steeped in research methods and rigor
  • based on empirical evidence and the scientific approach to knowledge development
  • demonstrated through appropriate and relevant assessment
  • developed from, with, and via the SGDE
  • honed through assessment and practice throughout the program of studies
  • encouraged and valued in all aspects of learning
  • technology savvy
  • professional and, where relevant, fully accredited
  • forward thinking and well informed
  • tested and validated by work based experiences
Required Resources
Recommended Resources

For the physiology and biochemistry section, the following text is recommended, especially for students intending to take related follow-on courses such as Ecophysiology of Plants III or Terrestrial Ecology III.

A more general text covering most of the material in the course is:

All students are expected to be familiar with the basic biochemical processes taught in Level 1 biology courses (e.g. Biology 1101, Molecules, Genes and Cells). The following chapters in the textbook &lsquoBiology&rsquo Campbell, Reece and Meyers 8th Edn (or equivalent textbook) should be revised before coming to the relevant lectures:

  • Ch 7, Membrane structure and function (in relation to nutrient uptake)
  • Ch 9, Respiration
  • Ch 10, Photosynthesis
  • Chs 17 & 18 Gene expression and regulation.

It is recognised that some students will not have done the Level 1 course Biology 1 Organisms and some revision of the relevant material from that course will be provided. However, it is recommended that all students familiarise themselves with the following chapters from &lsquoBiology&rsquo Campbell, Reece and Meyers 8th Edn (or equivalent textbook):

  • Ch 26: Phylogeny
  • Chs 29 & 30: Plant diversity
  • Ch 35: Plant structure
  • Chs 36 &ndash 39: Plant physiology
Online Learning

MyUni: Teaching materials and course documentation will be posted on the MyUni website (http://myuni.adelaide.edu.au/).

Learning & Teaching Modes
Workload

The information below is provided as a guide to assist students in engaging appropriately with the course requirements.

A student enrolled in a 3 unit course, such as this, should expect to spend, on average 12 hours per week on the studies required. This includes both the formal contact time required to the course (e.g., lectures and practicals), as well as non-contact time (e.g., reading and revision).

Learning Activities Summary

This course introduces the biology and evolution of plants through lectures including the core components:

1. General principles of plant biology relating to structure and function
2. Systematics,evolution and diversity
3. The physiology of growth and development
4. Floral biology

These general principles of plant biology may also be explored further through a range of case studies on topics such as plant nutrition, symbioses, responses to biotic and abiotic stress and photosynthesis.

Students will also learn to apply scientific approaches in practicals which will expose them to problem solving skills in the areas of plant structure, function and diversity. The aim is to give the students an insight and experience using approaches and techniques
to study plants and to encourage critical thinking on key issues relating to plants and their interactions with the environment.

  1. Assessment must encourage and reinforce learning.
  2. Assessment must enable robust and fair judgements about student performance.
  3. Assessment practices must be fair and equitable to students and give them the opportunity to demonstrate what they have learned.
  4. Assessment must maintain academic standards.
Assessment Summary
Assessment taskType of assessmentPercentage of total assessment for grading purposesHurdle (Yes/No)Outcome being assessed/achieved
Practical reports Formative/Summative 50% No 1,2,3,4,6
Exam Summative 50% No 1,2,3,6
Assessment Detail
Week Practical Assessment %
1 Mineral Nutrition Data/question sheet 5
2 Rhizosphere enzymes Formal report 5
3 Transpiration Data/question sheet 5
4 Respiration and photosynthesis Data/question sheet 5
6 Hormones Data question sheet 5
7 Stems: structure and functions assessed in week 8
8 Roots: structure and functions Quiz 4
9 Leaves: structure and functions Quiz
Project
3
5
10 Plant ID1 ID of vegetative specimens 4
11 Plant ID2 Plant description and
floral and fruit ID
5
12 Aquatic plants Worksheet 4
Exams Theory exam Short answers 50
Submission

Data sheets and quizzes are to be handed up before you leave the lab.

Late submission of assessments

If an extension is not applied for, or not granted then a penalty for late submission will apply. A penalty of 10% of the value of the assignment for each calendar day that is late (i.e. weekends count as 2 days), up to a maximum of 50% of the available marks will be applied. This means that an assignment that is 5 days or more late without an approved extension can only receive a maximum of 50% of the mark.

Course Grading

Grades for your performance in this course will be awarded in accordance with the following scheme:

M10 (Coursework Mark Scheme)
Grade Mark Description
FNS Fail No Submission
F 1-49 Fail
P 50-64 Pass
C 65-74 Credit
D 75-84 Distinction
HD 85-100 High Distinction
CN Continuing
NFE No Formal Examination
RP Result Pending

Further details of the grades/results can be obtained from Examinations.

Grade Descriptors are available which provide a general guide to the standard of work that is expected at each grade level. More information at Assessment for Coursework Programs.

Final results for this course will be made available through Access Adelaide.

The University places a high priority on approaches to learning and teaching that enhance the student experience. Feedback is sought from students in a variety of ways including on-going engagement with staff, the use of online discussion boards and the use of Student Experience of Learning and Teaching (SELT) surveys as well as GOS surveys and Program reviews.

SELTs are an important source of information to inform individual teaching practice, decisions about teaching duties, and course and program curriculum design. They enable the University to assess how effectively its learning environments and teaching practices facilitate student engagement and learning outcomes. Under the current SELT Policy (http://www.adelaide.edu.au/policies/101/) course SELTs are mandated and must be conducted at the conclusion of each term/semester/trimester for every course offering. Feedback on issues raised through course SELT surveys is made available to enrolled students through various resources (e.g. MyUni). In addition aggregated course SELT data is available.

This section contains links to relevant assessment-related policies and guidelines - all university policies.

Students are reminded that in order to maintain the academic integrity of all programs and courses, the university has a zero-tolerance approach to students offering money or significant value goods or services to any staff member who is involved in their teaching or assessment. Students offering lecturers or tutors or professional staff anything more than a small token of appreciation is totally unacceptable, in any circumstances. Staff members are obliged to report all such incidents to their supervisor/manager, who will refer them for action under the university's student’s disciplinary procedures.

The University of Adelaide is committed to regular reviews of the courses and programs it offers to students. The University of Adelaide therefore reserves the right to discontinue or vary programs and courses without notice. Please read the important information contained in the disclaimer.


Cambium: Origin, Duration and Function (With Diagrams) | Botany

Let us learn about Cambium. After reading this article you will learn about: 1. Origin of Cambium 2. Fascicular and Inter-fascicular Cambium 3. Duration 4. Functions 5. Structure 6. Cell Division 7. Thickening in Palms.

Origin of Cambium:

The primary vascular skeleton is built up by the maturing of the cells of the procambium strands to form xylem and phloem. The plants which do not possess secondary growth, all cells of the procambium strands mature and develop into vascular tissue.

In the plant which have secondary growth later on, a part of the procambium strand remains meristematic and gives rise to the cambium proper. In roots the formation of cambium differs from that in stems because of the radial arrangement of the alternating xylem and phloem strands.

Here the cambium arises as discrete strips of tissue in the procambium strands inside the groups of primary phloem. Later on, the strips of cambium by their lateral extension are joined in the pericycle opposite the rays of primary xylem. The secondary tissue formation is most rapid beneath the groups of phloem so that the cambium, as seen in the transverse section of older roots, soon forms a circle.

Fascicular and Inter-fascicular Cambium:

In stems the first procambium that develops from promeristem is usually found in the form of isolated strands. In some plants these first-formed strands soon become, united laterally by additional similar strands formed between them and by the lateral extention of the first-formed strands.

During further development this procambial cylinder gives rise to a cylinder of primary vascular tissue (xylem and phloem) and cambium. Later on, a cylinder of secondary vascular tissue is formed that arises in strands as does the primary cylinder. In Ranunculus and some other herbaceous plants, the procambium strands, and the primary vascular tissues, do not fuse laterally but remain as discrete strands.

More often in herbaceous stems the cambium extends laterally across the intervening spaces until a complete cylinder is formed. Where such extension occurs, the cambium arises from inter-fascicular meristematic cells derived from the apical meristem.

The strips of cambium that arise within collateral bundles are known as fascicular cambium, and the cambial strips found in between the bundles are known as inter-fascicular cambium.

Duration of Cambium:

The duration of the functional life of the cambium varies greatly in different species and also in different parts of the same plant. In a perennial woody plant the cambium of the main stem lives from the time of its formation until the death of the plant.

It is only by the continued activity of the cambium in producing new xylem and phloem that such plants can maintain their existence. In leaves, inflorescenes and other deciduous parts, the functional life of the cambium is short. Here all the cambium cells mature as vascular tissue. The secondary xylem is directly found upon the secondary phloem in such bundles.

Function of Cambium:

The meristem that forms secondary tissues consists of an uniseriate sheet of initials that form new cells usually on both sides. The cambium forms xylem internally and phloem externally. The tangential division of the cambial cell forms two apparently identical daughter cells.

One of the daughter cells remains meristematic, i.e., the persistent cambial cell, the other becomes a xylem mother cell or a phloem mother cell depending upon its position internal or external to the initial. The cambium cell divides continuously in a similar way one daughter cell always remains meristematic, the cambium cell, whereas the other becomes either a xylem or a phloem mother cell.

Probably there is no definite alternation and for brief periods only one kind of tissue is formed. Adjacent cambium cells divide at nearly the same time, and the daughter cells belong to the same tissue. This way, the tangential continuity of the cambium is maintained.

Structure of Cambium:

There are two general conceptions of the cambium as an initiating layer:

1. That it consists of a uniseriate layer of permanent initials with derivatives which may divide a few times and soon become converted into permanent tissue

2. That there are several rows of initating cells which form a cambium zone, a few individual rows of which persist as cell forming layers for some time. During growing periods the cells mature continuously on both sides of the cambium it becomes quite obvious that only a single layer of cells can have permanent existence as cambium.

Other layers, if present, function only temporarily and become completely transformed into permanent cells. In a strict sense, only the initials constitute the cambium, but frequently the term is used with reference to the cambial zone, because it is difficult to distinguish the initials from their recent derivatives.

Cellular Structure of Cambium:

There are two different types of cambium cells:

1. The ray initials, which are more or less isodiametric and give rise to vascular rays and

2. The fusiform initials, the elongate tapering cells that divide to form all cells of the vertical system.

The cambial cells are highly vacuolated, usually with one large vacuole and thin peripheral cytoplasm. The nucleus is large and in the fusiform cells is much elongated. The walls of cambial cells have primary pit fields with plasmodesmata. The radial walls are thicker than tangential walls, and their primary pit fields are deeply depressed.

Cell Division in Cambium:

With the result of tangential (periclinal) divisions of cambium cells the phloem and the xylem are formed. The vascular tissues are formed in two opposite directions, the xylem cells towards the interior of the axis, the phloem cells toward its periphery. The tangential divisions of the cambium initials during the formation of vascular tissues determine the arrangement of cambial derivatives in radial rows.

Since the division is tangential, the daughter cells that persist as cambium initials increase in radial diameter only. The new cambium initials formed by transverse divisions increase greatly in length those formed by radial divisions do not increase in length.

As the xylem cylinder increases in thickness by secondary growth, the cambial cylinder also grows in circumference. The main cause of this growth is the increase in the number of cells in tangential direction, followed by a tangential expansion of these cells.

Cambium Growth about Wounds:

One of the important functions of the cambium is the formation of callus or wound tissue, and the healing of the wounds. When wounds occur on plants, a large amount of soft parenchymatous tissue is formed on or below the injured surface this tissue is known as callus. The callus develops from the cambium and by the division of parenchyma cells in the phloem and the cortex.

During the healing process of a wound the callus is formed. In this there is at first abundant proliferation of the cambium cells, with the production of massive parenchyma. The outer cells of this tissue become suberized, or periderm develops within them, with the result a bark is formed.

However, just beneath this bark the cambium remains active and forms new vascular tissue in the normal way. The new tissue formed in the normal way extends the growing layer over the wound until the two opposite sides meet. The cambium layers then unite and the wound becomes completely covered.

Cambium in Budding and Grafting:

In the practices of budding and grafting, the cambium of both stock and scion gives rise to callus which unites and develops a continuous cambium layer that gives rise to normal conducting tissue. There is an actual union of the cambium of stock and scion of two plants during the practices of budding and grafting and therefore these practices are not commonly found in monocotyledons.

Cambium in Monocotyledons:

A special type of secondary growth occurs in few monocotyledonous forms, such as Dracaena, Aloe, Yucca, Veratrum and some other genera. In these plants the stem increases in diameter forming a cylinder of new bundles embedded in a tissue.

Here a cambium layer develops from the meristematic parenchyma of the peri-cycle or the innermost cells of the cortex. In the case of roots, the cambium of this develops in the endodermis. The initials of cambium strand in tiers to form a storied cambium as found in the normal cambium of some dicotyledons.

Cambium in Thickening in Palms:

The palm stems do not increase in girth, because of any cambial activity but this thickening is the result of gradual increase in size of cells and of intercellular spaces and sometimes of the proliferation of fibre tissues. This is the type of long continuing primary growth.

The process is as follows:

Most of the monocotyledons lack secondary growth, but with the result of intense and long continuing primary growth they may produce such large bodies as those of the palms. The monocotyledons often produce a rapid thickening beneath the apical meristem by means of a peripheral primary thickening meristem as shown in figure.

The activity of the primary thickening meristem resembles with secondary growth found in certain monocotyledons such as Dracaena, Yucca, etc. The apical meristem also known as shoot apex produces only small part of the primary body, i.e., a central column of parenchyma and vascular strands.

Most of the plant body is formed by the primary thickening meristem. The primary thickening meristem is found beneath the leaf-primordia, which divides periclinally producing anticlinal rows of cells. These cells differentiate into a tissue formed of ground parenchyma traversed by procambial strands.

These procambial strands later on develop into vascular bundles. The ground parenchyma cells enlarge and divide repeatedly, causing increase in thickness. This way, both apical meristem and primary thickening meristem give rise to the main bulk of the stem tissues of monocotyledons.

The thickening takes place in monocotyledons, such as palms, due to the activities of the apical meristem and primary thickening meristem.


What is a section in botany based upon? - Biology

INTERNET LINKS TO USEFUL INFORMATION

Biology of Plants and the Study of Botany

  • Instructor of Record: Dr. Martin Huss.
  • Handed out syllabus/course policy to students.
  • Reviewed course policy, emphasis on grade evaluation, examination format, testing dates, make-up policy, etc.
  • Reviewed general information found in syllabus (e.g., reading assignments, office phone number, office hours, etc.).
  • Read book (reading assignments listed in the syllabus), exams will cover both lecture and reading assignments.
  • Beginning of chapters have an outline and a chapter overview: review these!
  • Bold-faced headings and terms - know these terms or concepts.
  • Read chapter summaries.
  • Review Questions - some test and quiz questions will be based on review questions at the end of the chapter.
  • Look at diagrams and figures given in each chapter that is covered.
  • Re-write your lecture notes the same day these are given.
  • Cross-reference your notes with the ones posted on the internet.
  • Ask questions.
  • The Department of Biological Sciences also offers free tutoring for students who are enrolled in this and other 1000 to 2000 level undergraduate biology courses. Contact LSE 202 for more information.
  1. Plants - common examples (e.g., duckweed, redwood tree, etc.) and biodiversity.
  2. Characteristics of Plants.
  3. Role of plants in the biosphere.
  4. Beneficial Effects of Plants
  5. Brief history of botany.
  6. Botany or Plant Biology and the Nature of Science.
  7. Activities associated with plant life and life in general.

Name a plant! (Duckweed, geranium, apple tree, oak tree, dandelion, algae, redwood tree, carrot, etc.). Lots of biodiversity! Plants come in different shapes, sizes. Some are short-lived, others live for hundreds of years. Plants have adapted to a wide variety of habitats, and methods of reproducing and dispersing themselves.

According to E. O. Wilson in his book, "The Diversity of Life" there are about 248,400 species of higher plants (i.e., ferns, gymnosperms, bryophytes, flowering plants). There are about 26,900 species of algae.

TAKE HOME MESSAGE - Many species biodiversity is high!

III. Role of plants in the biosphere


Energy flow from sun to producers yellow arrow = sunlight. Energy and material flow from producers to other organisms green arrows material flow from environment = gray arrow (e.g., carbon dioxide, water, and nutrients) material flow from consumers and decomposers back to producers = red arrow (e.g., carbon dioxide, water, and nutrients). Of the three (producers, decomposers, and consumers), which two are essential to life on earth? (Answer: producers and decomposers). Least significant are the consumers, although these can be important ecologically for specific plants (e.g., pollination and seed dispersal).

IV. Beneficial Effects of Plants

1. Food
2. Resupply oxygen to atmosphere (11 year supply on earth).
3. Maintain the climate (deforestation is of concern).

CONSIDER DOING THIS: Make a list of plants and plant products that you have come in contact over the course of a single day. List the plant and how it was used by yourself. List a particular usage only once. For example, don't list tomato if you eat the fruit in a salad or on a hamburger twice. But if you eat ketchup then list it again. How does this list relate to the quality of your everyday life?

What kinds of plants/plant products have you come in contact with today? Examples: Food, m edicine, spices, fibers, paper, clothing, lumber, oxygen, fuel (coal and wood), toothpicks, toilet paper, paper money, soft drinks, drugs, and so on.

TAKE HOME MESSAGE - Plants are necessary for our continued existence and quality of life.
V. Brief history of botany.

Early human cultures were hunter/gatherers. One of the first professions was botany (plant taxonomy), because it was important knowledge to be able and distinguish poisonous from edible plants.

About 8,000 -12,000 years ago something happened that changed the heart of human society. What was it? Answer: Agriculture!

Agriculture - fossilized plant remains (e.g., seeds, charred plant remains, pollen) in archaeological digs of human encampments place the discovery of agriculture about 8,000 to 12,000 years ago.

Most ancient civilizations (e.g., Chinese, Egyptians, Assyrian, Inca, Mayan, etc.) practiced agriculture regardless of their geographical location in the world. Indigenous plants (and animals) were domesticated by each respective society.

Two hypotheses about origin of agriculture:

1. Independent discovery in different parts of world.
2. Diffusionist hypothesis - discovery originated in one part of the world and spread from
one civilization to another.

Plants for food/medicine:

In preliterate societies, knowledge of what was good or bad was passed on in oral traditions, usually through religious leaders - the 'medicine man' or shaman among certain North American Indians and their counterparts in other societies (e.g. priests, rabbis, teachers).

  • plant taxonomy and biogeography
  • plant physiology
  • plant ecology
  • plant morphology, anatomy, and developmental biology
  • plant cytology (cell structure and function)
  • plant genetics
  • ethnobotany and economic botany
  • genetic engineering - for crop improvement, insect repulsion, soil reclamation, longer shelf-life of fruits, disease resistance, etc.
  • plant taxonomy and biogeography
  • plant physiology
  • plant ecology
  • plant morphology, anatomy, and developmental biology
  • plant cytology (cell structure and function)
  • plant genetics
  • ethnobotany and economic botany
  • genetic engineering - for crop improvement, insect repulsion, soil reclamation, longer shelf-life of fruits, disease resistance, etc.

TAKE-HOME MESSAGE: The field of botany is a culmination of many historical events and consists of many different scientific disciplines.

VI. Botany or Plant Biology and the Nature of Science.

Science is an organized system of knowledge a obtained by a special method b , the "scientific method", of research and aimed at explaining the causes and behavior of the natural universe c .

a There are different kinds of knowledge a : e.g., knowledge of a language, literature, automotive mechanics, cooking, law, philosophy, the meaning of words.

Science is not about proof or absolute truth. Science is more about reducing uncertainty then stating things as hard cold fact.

1. Problem or question based on observation.
2. Hypothesis - "education guess" to answer or explain the question.
3. Experimentation (to determine if the hypothesis is valid or not).
A. Prediction
B. The test
4. Conclusion

c Natural universe - Science can say how a guitar string creates sound when plucked, but it can say little about the aesthetic value of music. Science can say nothing outside it's realm of expertise, in regard to ethics, morality, and the supernatural.

Disclaimer: When scientists engage in scientific research, most of them don't sit down and think, "Gee, I think I'll make an observation. What kinds of questions come to mind? Perhaps I should write down some potential hypotheses. 1,2,3, 4 etc. Ah, now let's see, I will do an experiment to test one of my hypotheses. I will engage in inductive and deductive reasoning". Scientists don't act like the stereotypic characters on television shows (e.g., Mr. Spock from Star Trek or the Professor from Gilligan's Island). Creativity, personal biases, hard work, hit and miss speculation, experimentation, availability of funds and resources, existence of appropriate technology, and dumb luck all come into play. The reason for outlining the "scientific method" is to try to dissect the essential elements of the process. Also scientists aren't like Bill Nye - the science guy, Mr. Wizard, or Beakman from Beakman's World. These are science educators, but when they do experiments they already know what the outcome of the experiment will be. Not so with scientists. FACT: a confirmed or, at least, agreed-upon empirical observation (or conclusion if referring to an "inferred" fact). For example, a fossil is generally accepted by most biologists as evidence for life in the distant past, even if the apparent life form no longer exist in today's world (e.g., dinosaurs, ammonites - an extinct mollusk, etc.). That fossils are the remnants or the products of something once alive is an inferred fact, even though the living organism is no longer present.

HYPOTHESIS: a proposed explanation of certain "facts" that must be empirically testable in some conceivable fashion.

THEORY: an integrated, comprehensive explanation of many "facts" and an explanation capable of generation additional hypotheses and testable predictions about the way the natural world looks and works. A generally accepted scientific theory is a well-tested hypothesis supported by a great deal of evidence. The scientific definition of theory is different then what is used by the lay person - like a guess. "Oh well, it's only a theory". In fact a theory is well tested, and if consistent with the data, possesses a high degree of certainty (although not equivalent to proof).

VII. Activities associated with plant life (and life in general).

In your mind consider the question of which of the following objects you would consider to be alive and not alive. At beginning of this section, ask the class which of the following objects is alive. A frog, a stone, a virus, a seed, and a tree.

What did you base your answer on? Most people have an intuitive feel or sense for determining what is alive or not alive. But coming up with a precise definition is difficult. In 1994, a conference of scientists argued whether or not viruses, which appear to have properties of both being living and nonliving were alive or not. One scientist, by the name of Stephen Hawking has publicly argued that not only are biological viruses alive, but that computer viruses constitute an artificial life form.


InfoPage

  • Contributed by Melissa Ha, Maria Morrow, & Kammy Algiers
  • Faculty (Biological Sciences) at Yuba College, College of the Redwoods, & Ventura College
  • Sourced from ASCCC Open Educational Resources Initiative

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The LibreTexts libraries are Powered by MindTouch ® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. This material is based upon work supported by the National Science Foundation under Grant No. 1246120, 1525057, and 1413739. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0.

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Collaborating on or copying of tests or homework in whole or in part will be considered an act of academic dishonesty and result in a grade of 0 for that test or assignment. Students are encouraged to share information and ideas, but not their work. : SRJC Writing Center Lessons on avoiding plagiarism


System of Plant Classification: 3 Types

The earliest systems of classification which remained dominant from 300 B.C. up to about 1830 were artificial systems, which were based on one or a few easily observable characters of plants, such as habit (trees, shrubs, herbs, etc.) or floral characters (particularly the number of stamens and carpels).

Such types of classification using some arbitrary or at least easily observable characters, often irrespective of their affinity, is called artificial.

The sexual system of Linnaeus is a good example of artificial classification, which uses only one attribute i.e. the number of stamens for grouping plants into 24 Classes as a result of which, various unrelated taxa, which are not at all related but, similar in one respect only, have been placed under the same Class.

Plant Classification: Type # 2.

Natural Classification:

These systems of classifications are based upon overall resemblances, mostly in gross morphology, thus, utilizing as many taxonomic characters as possible, to group taxa.

Charles Darwin’s proposed theory of evolution (1859) postulates that, the present day plants have descended from those existing in the ancient past, through a series of modifications in response to changing environmental conditions, which means that all present day plants are related to each other in one way or another.

Thus, the closely related plants should naturally be grouped together. This is called natural classification. Thus, larger the number of characters shared by different taxa, the more closely related they are to each other. This is the basis of modern classification.

Plant Classification: Type # 3.

Phylogenetic Classification:

The classification systems proposed after Darwin’s theory are mostly phylogenetic i.e. they use as many taxonomic characters as possible in addition to the phylogenetic (evolutionary) interpretations. These are expressed in the form of phylogenetic trees or shrubs showing presumed evolution of the groups.

The natural systems are two-dimensional i.e. based on the data available at any time and is known as Horizontal Classification, whereas the addition of the third dimension i.e. past history or ancestral history results in phylogenetic classification also known as Vertical Classification or Evolutionary Classification.

According to Radford (1986) however there are four systems of classifications:


Full Life Cycle Diagram

Ferns rely on water for dispersal of the sperm, which must swim into an archegonium to fertilize an egg (Figure (PageIndex<15>)). If moisture is plentiful, the sperm swim to archegonia - usually on another prothallus because the two kinds of sex organs generally do not mature at the same time on a single prothallus.

Another method for promoting cross-fertilization: The first spores to germinate develop into prothallia with archegonia. These prothallia secrete a gibberellin into their surroundings. This is absorbed by younger prothallia and causes them to produce antheridia exclusively.

Fertilization restores the diploid number and begins a new sporophyte generation. The embryo sporophyte develops a foot that penetrates the tissue of the prothallus and enables the sporophyte to secure nourishment until it becomes self-sufficient. Although it is tiny, the haploid fern prothallus is a fully-independent, autotrophic plant. Soon, the sporophyte is nutritionally independent. It is the larger, longer-lived stage of the life cycle. To reproduce, many sori are formed on the undersides of the fronds. Within each sporangium of the sorus, the spore mother cells undergo meiosis producing four haploid spores each.

When the humidity drops, the thin-walled lip cells of each sporangium separate, the annulus slowly straightens out, then the annulus snaps forward expelling the spores. Each of these homospores can then grow into a gametophyte capable of producing antheridia and archegonia.

Figure (PageIndex<15>): The diagram above shows the life cycle of a Polypodium fern. The gametophyte generation (n) is shown in the top half of the diagram and the sporophyte generation (2n) in the bottom half. Starting from the release of haploid homospores, these spores grow by mitosis into bisexual gametophytes. The gametophyte is heart-shaped, thalloid, and produces root-like structures called rhizoids. The antheridium produces many swimming sperm that are dispersed by water into an archegonium. A sperm swims down the neck/venter of an archegonium and fertilizes the single egg produced there. This produces a diploid zygote, which is retained on the gametophyte. The zygote grows by mitosis within the archegonium, producing a sporophyll (frond). When fully developed, the sporophyte will likely have multiple fronds and a rhizome. Fronds start as fiddleheads and uncoil by circinate vernation. The frond on the left is producing sori on the underside of the leaflets. Each sorus is a cluster of sporangia, which is protected by an indusium. Meiosis happens within the sporangia. Each sporangium has an inflated annulus to help release the spores when conditions are right. One of these has torn open to release its haploid homospores, which brings us back to the beginning. Diagram by Nikki Harris CC-BY 4.0 with labels added.


Watch the video: History of botany (May 2022).


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