Diversity of Life Revision > Diversity of life practice exam > Flashcards
Diversity of life practice exam Flashcards
To completely prepare for any question in the diversity of life quiz
What is the learning objective of unit 1?
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What do all organisms require?
All organisms require energy; they also require a source of organic carbon and a range of other nutrients. All organisms use the organic carbon, nutrients and energy to produce building blocks for new tissues and to maintain tissues.
Do all food chains depend on organisms that photosynthesize?
Yes.
Why do organisms require energy?
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How much more energy do you require when you are exercising hard compared to when you are sleeping?
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Why do resting cells still require energy?
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How do animals get their energy?
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How do plants get their energy?
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Why does it matter that we eat different types of food if all the foods that we eat contain energy?
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Compare an average 6 month old baby, an average 5 year old child, an average 15 year old teenager and an average 40 year old. Which person requires more energy?
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The average weight of the adult only increases marginally between age 30 and age 40. Why does the 40 year old require so much energy?
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Which digestive feature do animals in the Phyla Platyhelminthes and Cnidaria have in common?
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Which of the following BEST describes how the coelem works as a hydrostatic support.
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Which of the following is the most likely way in which multicellular invertebrates arose?
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What is a medusa?
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What are the features of animals in the Phylum Annelida are
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What is a polyp?
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What are the advantages of a partial shell?
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What is the best reason for considering termites to be invertebrates?
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What is the special material all animals in Phylum Cnidaria use to support their tissues called?
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What features contribute to the success of insects?
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What kingdom are invertebrates best classified as being under?
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In increasing order of specialisation for parasitism, what are the classes of the Phylum Platyhelminthes?
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Most animals in the Phylum Cnidaria, capture their food using special cells best called…
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What are the bodies of animals in Phylum Porifera like?
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What is the best reason for classifying termites as arthropods?
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What is the characteristic feature of animals in Phylum Cnidaria?
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The animals in the Phylum Platyhelminthes are usually classified into four classes which are the…
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What is the characteristic feature of animals in the Phylum Mollusca?
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What are the classes of the Phylum Cnidaria?
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What animals fall under the Phylum Echinodermata?
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What are the reasons for the success (many species in great abundance) of insects?
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What are the classes of animals in the Phylum Echinodermata?
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What are animals in the Phylum Porifera commonly known as?
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Does it take energy to build a living organism?
Yes.
Do plants, algae and some bacteria capture the energy of visible sunlight through photosynthesis and is it energy to assemble and maintain their complex structures?
Yes.
What are autotrophs?
An organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide.
What are heterotrophs?
They obtain energy by consuming autotrophs and metabolising energy-rich molecules in this food source, or eat other heterotrophs.
How many organisms are heterotrophs?
95%, including animals, fungi, many protists and most bacteria.
What do organisms convert the chemical energy of fuel molecules into?
ATP (adenosine triphosphate)
What is ATP made through?
It’s made through metabolism of energy rich molecules, such as carbohydrates and fats.
What are carbohydrates which are covered into glucose processed by?
Glycolysis.
What are lipids processed by?
B-oxidation.
What can the products of B-oxidation and Glycolysis as a substrate for?
Cellular respiration, the major process of energy extraction.
What do photosynthesis and respiration provide?
Energy and structural molecules for growth and maintenance.
What is the overview of the metabolic pathways?
p.126
Do organisms all require a source of organic carbon as well as a range of other nutrients?
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Are all living organisms are largely made up of carbon substances and water.
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Do most animals, including humans, gain organic carbon compounds by consuming the living or dead tissues of other animals or plants.
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This new source of organic compounds is due to photosynthetic organisms, like plants:
they capture sunlight and use some of that sunlight to convert the carbon in atmospheric carbon dioxide into sugars.
the plant then uses these sugars to provide energy and to build the plant body.
the plant body might then be consumed by other organisms.
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Photosynthetic organisms -
Organisms that capture energy from sunlight and use that energy to convert carbon dioxide gas to produce high energy organic compounds and oxygen.
Prescribed reading for unit 1
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Chlamydomonas is a tiny organism that inhabits pond water. Like an animal, it can move around through the water but, like a plant, it gets energy and carbon from the sun by photosynthesis.
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Chlamydomonas is a simple organism: it is a single unit of living material surrounded by a membrane. This is called a cell.
Most of the concepts that apply to this tiny organism also apply to large complex organisms, such as trees and animals (including humans). Large organisms are composed of very small, microscopic cells that are linked and are coordinated in function and structure.
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Is the cell the basic unit of life?
Yes
Humans reproduce via sperm and ova; these are cells. All other organisms also reproduce and they all reproduce as cells.
Thus, cell theory is a central tenet of biology.
• The cell is the smallest organisational unit.
• All organisms are made of cells and cell products.
• All cells come from pre-existing cells.
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Chlamydomonas shares many of its features with all other organisms. The cells of your body have membranes, mitochondria and cytoplasm and cellular processes are controlled by a nucleus. Cells in the leaf of a gum tree have these features and so does Chlamydomonas. The gum tree shares another similarity with Chlamydomonas, both organisms have chloroplasts to carry out photosynthesis.
However, while Chlamydomonas is a single cell, both your body and that of the gum tree, are made up of many small cells joined together. Each of these cells is about the size of Chlamydomonas.
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Photosynthesis
Chlamydomonas carries out photosynthesis, producing sugars that can be used for energy. Or these organic sugars produced by photosynthesis can be combined with other nutrients absorbed from the water that surrounds it to produce other chemicals that the cell requires.
This energy and building blocks may then be utilised for many purposes:
provide energy to move the organism,
grow larger,
repair damage,
for reproduction by cell division.
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Chloroplasts
The chloroplast contains the mechanisms for carrying out photosynthesis.
Chloroplasts are surrounded by a membrane and also have special internal membrane structures that contain chlorophyll molecules, the molecules that enable light energy to be captured and used for photosynthesis.
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Organelles
Chloroplasts are one of many different types of organelles; organelles are specialised structures within the cell that are surrounded by their own membrane.
These membranes contain special structures and chemicals to carry out particular functions. Gathering associated structures and functions together within a cell increases the efficiency of a cell’s functioning, e.g. processes can happen faster. It’s rather like organizing a factory: putting related and dependent operations close to each other.
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Food chains and webs
Chlamydomonas may be consumed by another organism and provide organic material and energy for that organism. Thus the energy and carbon initially fixed by Chlamydomonas can flow from organism to organism. This is called a food chains or a food web. You will learn more about food webs in the ecology section of this subject.
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Other structures
The animation also introduced you to mitochondria, the nucleus the plasma membrane and the cell wall. All organisms have these structures while only photosynthetic organisms have chloroplasts.
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Mitochondria
The mitochondria are involved with providing energy for many cellular functions. Like the chloroplast they are membrane-bound organelles.
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Nucleus
As you can see, even in simple life, cells are complex, so a fair bit of information is required to construct a new cell. This information is encoded in a molecule in the nucleus of the cell. That molecule is DNA. DNA is made of thousands to millions of small molecules joined together to form a chain. There are four types of these small molecules and it is variation in the order of these small molecules that make up the DNA chain that allows the DNA to store genetic information.
The DNA contains a genetic blue print (or sequence of genes) for constructing the organism. The DNA also controls the production of templates for the manufacture of proteins the entire cell. These RNA templates pass through pores in the nuclear membrane into the cellular cytoplasm.
The nucleus controls the operations of the cell.
The nucleus is a membrane-bound organelle that contains the DNA of the cell.
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Cytoplasm
The cytoplasm is the fluid and organelles of the cell, excluding the nucleus. By regulating protein manufacture, the nucleus affects how the cell develops and interacts with its environment. These proteins carry messages to other parts of the cell, controlling how they function (like the factory manager).
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Plasma membrane
The cell is contained within a plasma membrane. Imagine the nucleus, mitochondria and chloroplast as tiny sealed plastic bags containing water. Place these plastic bag organelles into a balloon and fill the balloon with water before sealing it. The balloon is holding in all the cellular contents and providing a barrier to the outside environment. This is also the role of the plasma membrane, which surrounds the cell.
Actually, the plasma membrane has tiny valves in it that are made of protein. These allow substances to enter and exit the cell but generally under the control of the cell.
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Cell wall
The animation also mentions that Chlamydomonas has a cell wall. This is a structure of inert material (called cellulose) built by the cell that surrounds the cell. It provides the cell with added protection and with structural support.
Cell walls are not found in animals but are a feature of plant cells. We will discuss cell walls further when we investigate plants.
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The need for reproduction
Cells die, they may be eaten or just accumulate faults (= mutations) in their functioning and no longer be able to function.
In multicellular animals, the cells can be replaced by
repeated cell divisions, replacing the damaged cells with new cells. This happens all the time on the surface of your skin. In single-celled organisms, the whole organism needs to be replaced to produce a new cell.
Even multicellular organisms will eventually accumulate so many faults in cells that repair and cell replication processes fail.
Therefore, individuals of all types of organisms need to be able to produce new cells and new individuals.
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Mutation
At each cell division, there is the possibility of errors (called ‘mutations’) in one or more of the thousands of genes that define an organism. The cell division system of cells is very effective so that the probability of those errors is very low but it is finite, i.e. errors DO occur. And when they do, the errors are passed on to at subsequent divisions of that cell’s descendents. And at each of those subsequent divisions, there is still the chance of more errors!
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Types of reproduction
All cells are produced by other cells. New cells are produced by cell division.
There are two types of cell division:
cells may divide and produce identical copies, a process called asexual reproduction, or
they may undergo sexual reproduction, a process in which two individuals contribute information about the make-up of the offspring.
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Mitosis
Most cell reproduction is asexual and occurs by mitosis. It is the type of cell division that:
took us from single cells in our mothers’ wombs to the large, multicellular organisms we are now,
is responsible for repairing the tissues of your hand that you cut with a knife yesterday.
Organisms grow by the production of new cells and new cells have to be produced to replace old or damaged cells. This process of cell division is called mitosis.
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The process of mitosis
When a cell divides the DNA in the cell is duplicated.
The two sets of DNA occur as separate chromosomes or groups of genetic material.
The nucleus divides, with each new nucleus having a full set of identical DNA.
The plasma membrane ‘heals’ around each half of the cell, thereby forming two new cells.
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Diploidy
DNA is grouped into chromosomes and most organisms have two sets of chromosomes, one that they have inherited from their father and one set from their mother. Thus every cell has two copies of each gene. Such an organism with two sets of chromosomes is termed diploid.
Diploidy is an advantage if one copy is damaged or faulty. Also the two copies of the gene may vary slightly. For example, the two genes could provide a template for constructing a particular protein but the protein may vary very slightly:
one copy may function better at warm temperatures, and
the other may function better at cool temperatures.
Thus, having two copies of each gene (which may vary slightly) can provide a diploid organism with greater flexibility to changes in environmental conditions.
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Meiosis
Sexual reproduction occurs following a type of cellular division called ‘meiosis’.
In this type of cellular reproduction, the DNA is duplicated prior to cell division similarly to mitosis. However two divisions of the cell then occur without any further production of DNA. Thus four cells are produced but each cell ends up with half the genetic material of the parent cell.
Whereas the diploid parent cells had two sets of genetic material, each of the resulting gamete cells only has one set of chromosomes. Such a cell with only one set of genetic material is termed ‘haploid’.
Each of these haploid cells is (or will form) a gametophyte and gametes.
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Fertilization
Sexual reproduction occurs when two gamete cells (e.g. sperm and ovum) fuse together to form an zygote, or new diploid organism. When the nuclei combine the zygote will again have two sets of chromosomes. Thus new combinations of DNA can occur in new organisms.
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What is biodiversity?
How many types of organisms are there in Australia?How many in the world?
Well, we really don’t know as many organisms, particularly plants, invertebrates and fungi, have not been described.
However, we can make educated guesses about the numbers of organisms in different groups.
Biodiversity is the term used to describe the abundance of different types of organisms that are present in an area. A wheat paddock may have many individual organisms but is not very diverse. A rainforest may have 500 different types of plants growing in a small area, it is very biodiverse.
Organisms that are distinctly different from each other are called different species.
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What is classification?
What terms do you use to describe an organism – for example a dingo. It is an animal, it is a vertebrate, it is a mammal, it is a carnivore, it is a type of dog.
All these terms assist in describing the dingo. By describing it as a mammal, someone who was not familiar with a dingo would expect that it was covered with hair rather than scales or feathers.
An early focus of biology was to group organisms on the basis of similarity.
A system was developed that was hierarchical with terms to describe broad groupings of organisms (e.g. order and family) and other terms to describe subsets of organisms within those broad groupings (e.g. genus and species).
Such a system arranging organisms in groups and subgroups is called classification.
Out of the system of classification, comes the system of naming.
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Naming system
The formal classification system that is used today was devised by the Swiss botanist, de Candolle.
Organisms are given a two word latinised name, i.e. Homo sapiens for humans. The scientific name is always typed in italics or underlined when written and the genus always has the first letter written as a capital.
In this binomial (it means ‘two name’) naming system, the first word is the genus (Homo) and the second word is the species.
The name of the species always includes the genus. Otherwise we would not know whether we were talking about Eucalyptus drummondii (a tree) or Lomandra drummondii (a sedge).
Why such a complicated naming system? Couldn’t we just use common names?
We need to use the scientific names as:
many organisms don’t have common names,
often the common name refers to a suite of species
(i.e. wiregrass refers to about 70 odd species of grass!), and
the same common name may be used for different species in different regions. For example, Rosewood refers to Acacia rhodoxylon in central Queensland; however in central Australia it refers to Heterodendrum oleaefolium.
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Type specimens
When a biologist names a new species, it must be described using strict rules and specimens must be lodged at particular places so that other biologists can verify exactly what the author of the species meant by that species name.
So, the specimens that were collected on Captain Cook’s voyage to Australia are located at the Natural History Museum in London, where they are available for examination by biologists.
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The species concept
The species is the basic natural unit of classification of organisms. It is the lowest rank in the Linnaean hierarchy to which an organism must be described.
It is also generally the level at which organisms typically interbreed. Thus although a Great Dane and a Poodle look fairly different they will interbreed fairly readily and so they are both considered to be of the same species - Canis familiaris L..
Two organisms may be of different species if they cannot mate. This may be due to physical differences or there may be differences in behavior, geographic location or reproductive timing that prevent the two species from mating under natural conditions. If the mating does not produce fertile offspring, the parents are of different species.
For example, horses can breed with other horses, producing fertile offspring. Donkeys can breed with other donkeys, producing fertile offspring. But, if horses breed with donkeys, the products are mules, and these are sterile. Thus, horses and donkeys belong to different species. (The same applies to ligers and tigrons!).
The concept of ‘species’ that is defined on the basis of reproductive isolation is described as the biological species concept.
Some difficulties that arise with the use of the biological species concept in practice include the following:
Species are usually named and identified on the basis of physical features, rather than reproductive isolation as reproductive characterisation is time consuming and expensive to achieve.
Genetic studies can indicate isolation between groups of individuals which appear physically similar and if they can not be morphologically distinguished then they are generally not described as separate species.
The concept of ‘reproductive isolation’ is difficult to apply when dealing with species evolving through geological time. As reproductive isolation gradually increases, at what point do two groups of individuals become separate species?
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An aside about authority
Canis familiaris L. is the domestic dog. Note that I have written the species as Canis familiaris L.. What is the ‘L.’?
The full species name includes the authority, that is the name (often abbreviated) of the person who published the description of the species. Thus the ‘L.’ is a recognised abbreviation of Linnaeus, the name of the authority or person to whom the description of a dog is credited.
The full name of the Darwin Stringybark is Eucalyptus tetradonta F. Muell., the F. Muell. being an abbreviation for Ferdinand Mueller. Ferdinand Mueller published a description of the Darwin Stringybark while he was the Victorian Government Botanist between 1853 and 1896.
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Phylogenetic classification
Biological classifications now generally attempt to group organisms phylogenetically.
A phylogenetic classification attempts to group those organisms that evolved from a common ancestor rather than just on the basis of similarity.
This is based on the Darwinian theory of evolution by natural selection – although there has been substantial development of the theory since it was proposed by Charles Darwin in 1859.
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Whereas the species is the lowest rank in which an organism is substantially distinct, the largest groupings of organisms are the superkingdom (= domain) and the kingdom.
Bacteria differ markedly in cell structure from animals, plants and fungi. Another group of ancient bacteria-like organisms, the Archaea, also lack many of the features of animal, plant and fungal cells.
Because of major and fundamental differences in basic cell structure Bacteria, Archaea and Eukarya (organisms with eukaryotic cells including plants, animals and fungi) are recognised as separate domains.
Within the domain of Eukarya, four Kingdoms are recognised, Protista, Fungi, Plantae and Animalia.
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Note: in the phylogenetic tree, organisms that are most similar and have evolved from a common ancestor branch from points that are close to each other.
Three kingdoms, the Fungi, Plantae and Animalia, have evolved from the Protista.
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Bacteria and Archaea differ markedly from the cells of animal, plant and fungal cells.
Recognizing these differences, cells of the Bacteria and Archaea are described as ‘prokaryotic’ whereas cells of protists, fungi, plants and animals are termed ‘eukaryotic’.
Cells of Bacteria and Archaea are much smaller and simpler than cells of eukaryotes but there are many other differences: the table below compares the characteristics of the two cell types.
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What are the traits of prokaryotes?
table in unit 2
What are the traits of eukaryotes?
table in unit 2
The development of microscopes revealed a fantastic new world of life. Bacteria appear as rods, spheres, spirals and filaments. They grow as colonies and singularly in soil, water, on plants and animals and within other organisms.
Bacteria are prokaryotes and differ in many structural aspects to eukaryotic cells. However there are many basic similarities in the biochemical pathways and in the basic make up of the genetic blueprint. This suggests that cellular life on earth shared a common origin.
Bacteria can occur at very high densities. Up to 100 000 per square centimetre on skin and up to 100,000,000,000 per gram in the lower intestine (Knox et al. 2001). They are abundant in some foods and in moist nutrient rich environments. This would include damp rotting vegetation or foods!
Some bacteria, the cyanobacteria, can carry out photosynthesis.
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Economic and environmental importance
Bacteria play a major role in human affairs. They cause disease but benign bacteria are important for inhibiting pathogens. They are used in some industrial and agricultural processes. Bacteria are critical for nutrient recycling and transformations, including the replenishment of nitrogen for plant growth.
Bacteria cause disease in humans, animals and plants. Antibiotics are substances that are toxic to metabolic processes in bacteria but due to differences in the metabolism of eukaryotes, antibiotics aren’t as toxic in humans or animals.
Cyanobacteria are responsible for blue-green algal blooms (though they aren’t really algae) which can produce toxins that poison fish in water ways. They are also an important component of the soil biota and some species convert atmospheric nitrogen gas into nitrogen compounds that can be taken up by plants.
However bacteria also break down and recycle nutrients in waste organic matter. They can break down most organic substances in nature. They transform nutrients in soil and thus allow the nutrients to be taken up by plant roots. Some types allow roots of some plants to fix nitrogen and others allow termites to digest wood. They are used in the production of some foods and vitamins.
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Stromatolites - bacterial colonies one metre in diameter
Cyanobacteria have been able to build large structures up to several metres in diameter and some of the best examples are in Australia. These large structures built by single celled cyanobacteria are called stromatolites.
To form stromatolites sediments are precipitated or trapped and bound by the cyanobacteria to form a laminated structure. These structures range in size from a few centimetres to many metres in diameter.
They were very common 1000 – 2000 million years ago but are now uncommon and tend to survive in very saline waters that limit predation by eukaryotes.
Fossil stromatolites have been found that are 3.46 billion years old.
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Do prescribed reading for unit 2
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Like the Bacteria, the Archaea are also prokaryotes. However they are less diverse than the bacteria and tend to be restricted to extreme habitats, particularly those that are anaerobic, very hot or very saline. They tend to occur in habitats which are not able to be colonised by bacteria or eukaryotic organisms. This includes hot thermal springs, boiling water vents on the ocean floor and saline hot springs.
Another group of Archaea only grow in anaerobic conditions (where oxygen is absent) and produce methane.
Although the Archaea were once thought of as primitive forms of bacteria, genetic and metabolic evidence suggests that they are more similar to the eukaryotes that are the Bacteria.
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PROTISTA
What are they?
Do you recall the Chlamydomonas that we discussed earlier? It is of the Kingdom Protista.
All the Protista are eukaryotes with a nucleus and organelles. Some Protista are autotrophic and carry out photosynthesis with chloroplasts, similarly to plants. An autotrophic organism is an organism that is able to generate its own energy from an inorganic source, such as sunlight.
Other Protista are heterotrophic that is they gain their energy by consuming other organisms, similarly to animals.
Really the Protista is not a natural grouping of organisms, rather is is a convenient grouping of a very diverse range of organisms. However they tend to have the following characteristics.
Protista may occur as single, free-living cells, as groups or colonies of individual cells or as integrated multicellular organisms.
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Most Protista are aquatic but they obtain food and energy by a variety of mechanisms including photosynthesis, predation, parasitism and adsorption.
Most swim using whip-like flagella (usually up to only a few of them) or oar-like cilia (hundreds or thousands of them). Chlamydomonas is an example of a protist with flagella.
Some other Protista have amoeboid movement, as shown in the movie.
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What is the size of a bacterium?
about 1 micrometer
The Kingdom Protista consists of 27 to 45 phyla with at least 100,000 species. Most phyla have 40 to 3,000 species but the Bacillariophyta (diatoms) have 10,000 species while only one species occurs within the Karyoblastea.
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Reproduction and life cycles
In keeping with the wide diversity of disparate organisms in the Protista, they also demonstrate a wide range of modes of reproduction.
Indeed, the Protista demonstrate all of the types of life cycles found in the descendants of the Protista: fungi, plants and animals.
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Origins of the eukaryotes
Eukaryote organisms only appear as fossils in rocks formed about 1.5 billions years ago or less, whereas some prokaryote fossils are older. It appears that eukaryotic organisms developed from prokaryotic organisms as they both share many basic biochemical processes.
It appears that chloroplasts and mitochondria are derived from a internal symbiotic association with bacteria. A symbiotic relationship is when two organisms become closely associated, living together to the benefit of both parties.
Animals and fungi are derived from a large cell with a aerobic bacterial endosymbiont. In plants there has been a further association with a photosynthetic bacterial endosymbiont.
Chloroplasts may be derived from an endosymbiotic relationship with a Cyanobacteria-like organism. The Protista, Glaucocystophyta has chloroplasts which have a cell wall similar to a bacteria, strengthening the support for this hypothesis.
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PHOTOSYNTHETIC PROTISTS
There are many Protista that are photosynthetic. These range from mobile single celled organisms to large multicellular seaweeds.
Recall that photosynthetic organisms capture energy from sunlight producing high energy organic storage compounds that they use to convert carbon dioxide to sugars. They also produce oxygen gas as a bi-product.
Photosynthetic protists were once grouped together as algae. This included the group that was called the ‘blue-green algae’ and is now know as the ‘blue-green bacteria’ or ‘Cyanobacteria’. However the cyanobacteria are very different as they are prokaryotic, very small and only contain chlorophyll a as the compound to carry out photosynthesis.
Photosynthetic protists include pond scums, terrestrial algae, seaweeds, freshwater and marine phytoplankton. Their compounds responsible for photosynthesis includes chlorophyll a plus often either chlorophyll b or chlorophyll c. Chlorophyll a and b are found in plants.
You can see the development of complexity of multicellular organisms in these protists. Single-celled protists group together to form colonies. Cells join in long simple lines to form filamentous forms, or in sheets as in the sea lettuce. Then there are forms in which the cells have been joined in complex shapes to form networks.
In the most advanced algae, cells in different regions have become specialised.
Kelps have tough, binding holdfasts that attach the alga to a rocky substrate. A cylindrical stipe then binds the holdfast to the flattened lamina. Because the lamina is thin, it allows for efficient absorption of nutrients and light capture for photosynthesis.
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HETEROTROPHIC PROTISTS
Many Protista consume other protists or feed on bacteria. Many move through water propelled by long whip like flagella, capturing and engulfing their prey. Some protists remain fixed in place but draw a stream of water to them by the movement of cilia. Some of the species have chloroplasts and can carry out photosynthesis, however when they are in darkness the chloroplasts shrivel and they rely on capturing other protists and bacteria.
The Oomycota resemble fungi in that they produce a network of thin hyphae and absorb nutrients from their food substrate.
The Choanoflagellates use a flagellum to move water towards a filter of tentacles with which they filter out and consume bacteria. They often form colonies of organisms that are attached to each other or a substrate and may be an evolutionary link to the Animalia.
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PARASITIC PROTISTS
Many protists are parasitic and infect and live within plants or animals. In doing so they often cause disease within the host organism. An example is malaria.
Malaria
Malaria kills millions of humans annually and causes illness in hundreds of millions of people. It is caused by a protist of the genus Plasmodium and is borne between human hosts by mosquitoes.
The complexity of the lifecycles of some Protista is illustrated by Plasmodium. It has four different life stages, which are shown in the diagram below.
At the sporozoites stage they are injected by mosquitoes into the blood of humans. Each sporozoite then reproduces asexually to form numerous individuals of the next stage, the merozoites. The merozoites invade red blood cells and develop into trophozoites. These consume the red blood cells and divide asexually to produce more trophozoites. Then the trophozoites develop into gametocytes and are ingested by mosquitoes feeding on infected blood. In the mosquito the gametocytes reproduce sexually and produce sperm and eggs which form an zygote. This zygote then sexually reproduces to produce sporozoites in the mosquito.
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PROTISTA AND ANIMAL EVOLUTION
Some photosynthetic protists or algae, like kelp, are multi-celled organisms with very simple organisation. It is not difficult to see how plants could have evolved from colonies of plant-like protists.
The evolution of multi-celled animals is more problematic and several ‘categories’ of theories have been proposed:
a symbiotic merger of 3 species of protist (because cells with flagella, cilia and amoeboid properties occur in multi-celled animals);
by the subdivision (= ‘cellularisation’), of a ciliate (because ciliates often have several nuclei);
from a colony of co-operating flagellate Protista;
by division of a protist into two layers to form a two-layered organism similar to Trichoplax, which is the least differentiated and has the smallest amount of DNA of any multicellular animal.
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PROTISTS – ECONOMIC AND ENVIRONMENTAL IMPORTANCE
Protists have a range of economic uses and are also of environmental importance.
Rhodophyta or red algae are used to produce agar and carrageenan which are used as food additives, as a microbiological media and in cosmetics. Rhodophyta is used to make sushi in Japanese restaurants while Chlorophyta (green algae) is used in miso soup. Phaeophyta (brown algae) produce alginic acid which is utilised in foods, adhesives, paint and explosives.
Bacillariophyta or diatoms form huge deposits of silca due to their silca cell walls. These deposits of silica are mined as diatomaceous earth for use as a fine abrasive or filtration material. Phytoplankton are also used as food stock for aquaculture.
Some diseases caused by protists include African sleeping sickness, severe dysentery (Giardia) and malaria.
Phytoplankton, including haptophytes, dinoflagellates and diatoms, are the major marine autotrophic food source feeding heterotrophic protists and indirectly giant whales!
In freshwater also, single celled and colonial chrysophytes, diatoms, green algae and dinoflagellates are the source of food for many organisms.
Dinoflagellates and Haptophytes can produce toxic blooms that poison marine organisms over large areas.
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Phytophthora cinnamomi is a serious pathogen of plants and has the capability to eliminate 30% of the flora in infected areas in the south-west of Western Australia. Other species are important pathogens of agricultural crops.
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FUNGI
Fungi include bread moulds, mushrooms, yeasts, bracket fungi, water moulds and rusts on plants.
Fungi:
are eukaryotic,
are heterotrophic with absorptive nutrition: they digest their food externally and excrete enzymes that break down organic substances so that they can absorb the sugars and nutrients,
are dispersed by means of spores,
have cell walls containing chitin.
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What’s the largest organism on Earth?
The tallest tree in the world is the ‘Mendocino Tree’, a gymnosperm of the species, Sequoiadendron sempervirens, that is found in California. It is over 112m tall.
A century ago, the tallest angiosperms exceeded that height. They were mountain ash (Eucalyptus regnans) trees growing in Victoria but those 140m+ giants were cleared during land settlement.
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The blue whale is the largest animal.
The Great Barrier Reef was made by animals and has a surface of animals but that’s a colony.
So what IS the largest single organism? Probably a fungus!
In 2000, scientists found that the mycelium of one giant individual of Armillaria ostoyae in Oregon was 5.5km in diameter and spread through 900 hectares of forest. It was hundreds of tonnes in weight and estimated at over 2,400 years old.
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Nutrition
Fungi have several ways of obtaining carbohydrates and nutrients.
Most fungi are saprobes, organisms that absorb carbohydrates and nutrients from dead organic matter. They excrete enzymes that break down the organic matter so that they can then absorb the resulting small carbohydrate and nutrient substances. They break down some of the carbohydrates to provide energy.
Other fungi are parasites. Many fungi live inside plants and animals and in doing so often cause disease. About 80% of plant diseases are due to parasitic fungi.
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Mycorrhizae
Fungi are also mutualists. That is, they live in mutually beneficial symbioses with other organisms.
Most Australian native plant species form intimate associations with fungi. The plant root provides the fungus with carbohydrate while the fungus assists the plant to obtain nutrients. The thread-like fungal mycelium can explore gaps between soil particles that are too small for plant roots to penetrate.
This association is called a ‘mycorrhiza’, the word coming from ‘myco’ (referring to the ‘fungus’) and ‘rhiza’ (meaning ‘root’).
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Reproduction
The diagram shows the lifecycle of a multicellular fungus.
For much of its life, it occurs as a mass of fine threadlike hyphae that spread though soil or rotting wood.
During warm moist conditions the fungus can form a fruiting body. This is the mushroom-like structure that you may see growing in a lawn, or from a dead log. On the underside there may be pores or gills and it is from these that the fungus produces millions of tiny spores which are dispersed through the air and establish new fungal plants. It is in the mushroom that sexual reproduction occurs. However you need not worry about the details in this group of organisms.
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Economic and environmental importance
Fungi are critical for the maintenance of life. They are the most effective of organisms for breaking down and decomposing organic substances including leaf litter and dead wood. Thus the nutrients within the organic waste are available for recycling, rather than the leaf litter building up and limiting plant growth.
Fungi also could many major plant diseases including botrytis on grape vines, rusts on wheat and smuts in grain. There are about 30,000 species of fungi that are parasitic on plants.
Yeasts that you may consume in bread, beer and wine are all fungi. Of course mushrooms and truffles are fungi, as is the blue veins in blue vein cheese.
Some fungi produce substances that kill bacteria and these are important antibiotics used to treat infections in medicine. This includes penicillin, the first antibiotic discovered, which caused a revolution in medicine. It came from the Penicillium fungus.
You will find fungi referred to in connection with antibiotic drugs: just look for that ‘myc’ part of the word, e.g. streptomycin.
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PLANTS, ANIMALS & VIRUSES
The Plantae and Animalia are the remaining two kingdoms of life we are yet to discuss.
We will devote one of the five themes of the subject to the Plantae and two themes of the subject to the Animalia (Invertebrates and Vertebrates). Their characteristics, diversity and importance will be discussed in those sections.
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Viruses
Viruses are not cellular organisms and therefore do not appear in the kingdoms of life. However they are important causes of disease in all living organisms. Viruses are inert in the absence of a host and are merely genetic material protected by a viral coat.
When they reach a suitable host, however, they are able to manipulate the cellular metabolism of the host organism and cause the host to produce new viral particles. These viral particles can then be dispersed and distributed to new hosts.
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Conclusion
We’ve only really just touched on the huge diversity found in the kingdoms Bacteria, Archaea, Protista and Fungi.
The group of organisms we call the Protista comprises far more diversity than we see in any of the other kingdoms (including the Plants and Animals).
In the next theme of this unit, we will investigate the kingdom Plantae. This kingdom is the basis of the global economy and the survival of humanity!
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What are the learning objectives of unit 3?
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Plants include trees that may be 100m tall, grasses that cover millions of hectares of farmland, ferns and tiny mosses. Mosses, ferns and trees are very different but they share some features and differ in important respects from the algae:
Plants are all eukaryotic: the cells have a nucleus and organelles.
Plants are all multicellular.
The other obvious feature of plants is that they can carry out photosynthesis, that is they generate organic compounds from sunlight. Similarly to the green algae they have chlorophyll types a and b, whereas some algae have other types of chlorophyll molecules.
A feature that separates plants from animals and many algae is that all plant cells have cell walls of cellulose.
There are also several reproductive features of plants that separate them from algae. They are presented here to provide a summary but we will discuss the reproductive features of plants in detail later.
In all plants, a multicellular diploid zygote is produced but it is retained within the haploid female gametophyte.
Plants have multicellular sporangia and the gamete-producing cells are protected by a layer of sterile cells.
Spores of plants contain sporopollenin in the spore wall.
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Go through rest of the resources for all the weeks in 6 hours per day
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