Monday February 22 – Viruses (17-1) Thursday February 25 – Kingdom Monera Part 1 (17-2) Friday February 26 – Microscopes
Week 2
Monday February 29 – Kingdom Monera Part 2 (17-2) Tuesday March 1 – Kingdom Protista Introduction (18-1) Wednesday March 2 – Kingdom Protista cont’d (18-2; 18-3) Thursday March 3 – Kingdom Protista – Animal-like Protists (18-2) Friday March 4 – Kingdom Protista – Animal-like Protists (cont’d) VIRUS/BACTERIA/PROTIST QUIZ
Week 3
Monday March 7 – Kingdom Protista – Plant-like Protists (18-3) Tuesday March 8 – Kingdom Protista – Fungi-like Protists (18-3) Wednesday March 9 – Study day Thursday March 10 – Unit Test Friday March 11 – Gallery Walk
Explain how structure, function, environment and cost-benefit are related (Game)
Explain the current theory on how Protists evolved from Monerans
Identify and Label the generic Protist structure
Identify the structure and functions of Paramecium parts
Describe reproduction of Paramecium
Compare and contrast the Protist Phyla
Provide examples of Protist Phyla
Kingdom Protista is a group created by exclusion. Historically, taxonomists and biologists alike had much trouble classifying these organisms. The reason for this difficulty is that members of Kingdom Protista have characteristics not unlike Animalia, Plantae or Fungi. Unlike the other four kingdoms (Animalia, Plantae, Fungi and Monera), which are relatively clear cut, members in Kingdom Protista are very diverse and share little in common. Lynn Mangulis, the scientist who came up with the endosymbiont hypothesis, wrote that the Kingdom Protista
“is defined by exclusion: its members are neither animals…, plants…, fungi …, nor prokaryotes.”
Perhaps a more scientifically sound definition: “unicellular (single-celled) organisms that are eukaryotic”. As you will recall from our taxonomy unit, Prokaryotes are organisms without a nucleus or membrane-bound organelles, and Eukaryotes are organisms with a nucleus and membrane bound organelles. (Ribosomes are organelles, but are not membrane-bound)
Therefore, a protist is simply a unicellular organism with:
Nucleus containing DNA
Membrane bound organelles
Which about sums up all that these organisms have in common.
But where did these organisms come from? Where did they evolve from?
Several observations seemed to provide some clues as to how it happened.
Mitochondria and Chloroplasts, organelles that exist in eukaryotic cells, have their own DNA. The DNA is completely separate from the DNA of the eukaryotic cell itself.
Some Protists have organelles that can be removed, without ill effect on the Protist. Some of these organelles can even grow on their own!
Some of the Eukaryotic cell’s organelles are structurally, very similar to Prokaryotes
Noticing these characteristics, Lynn Margulis proposed the Endosymbiont Hypothesis. The hypothesis states that organelles are actually descended from prokaryotes that lived inside another prokaryote in a symbiotic relationship. Each benefited the other. For example, a blue-green bacteria that lived in a bigger moneran had shelter, while the bacteria provided the host cell with sugars and nutrients. At some point, the blue-green bacteria may have lost their independence, and became the precursors to the organelles we see today.
A creative way of explaining Endosymbiosis.
Paramecium sp.(Phyla: Ciliophora)
Paramecium is a model organism for protists. Like most model organisms, it has been studied extensively and is easily cultivated (grown). However, a model organism is not necessarily representative of the group it comes from. Just as a lab rat is not necessarily representative of all mammals, or even all rodents, so we should not assume that Paramecium is a perfect representation of Protists.
Movement |Paramecium sp. is classed in Phylum Ciliophora, a protist phylum characterized by cilia.
Feeding | Paramecium sp. feeds on small organisms, such as bacteria. The cilia first sweep the food toward the oral groove, a small opening where food is trapped. The oral groove leads to the gullet, which produces food vacuoles, a small sac where food is stored. the food vacuole then contacts lysosomes, organelles containing digestive enzymes. These digestive enzymes then break down the food, and the wastes are expelled from the anal pore.
Water Balance | Paramecium sp. live in freshwater environments. Because the Paramecium sp. has a higher solute concentration than the freshwater around it, water tends to move inside the cell. Therefore, excess water must be expelled from the Paramecium sp. from the cytoplasm to the contractile vacuole.
Reproduction | Paramecium sp. is able to reproduce via binary fission (asexual reproduction). The micronuclei are duplicated, and the macronucleus is split apart. The split occurs lengthwise, like pulling silly putty apart. During conjugation, however, two paramecium arrange side by side and exchange genetic information.
No new daughter cells result from conjugation, therefore it is not a form of reproduction. However, the exchange in genetic information does lead to an increase in genetic diversity amongst the population. An increase in genetic diversity leads to more diverse traits, and having more traits means there’s a greater chance that at least a few of the cells may have the correct traits to survive, even thrive, in the environment.
Therefore, asexual reproduction occurs more often in stable, unchanging environments. Under these conditions, because Paramecium sp. are likely to survive and thrive, energy is better invested in increasing population numbers. However, all offspring will be genetically identical. Conjugation occurs more often in unstable, changing environments that are stressful. Even if Paramecium sp. numbers increase, because the genetic diversity is low, there is less likely to be individuals that have the gene combination to help them survive in the environment. therefore, it is much more beneficial for Paramecium sp. to invest their energy in conjugation, where gene combinations are reshuffled.
(Binary Fission)
(Conjugation)
Kingdom Protista Phyla
We cover nine Protist phyla in this course: 4 animal like, 3 plant like and 2 fungi like.
Animal-like Protists (Heterotrophic)
Plant-like Protists (Autotrophic)
Fungi-like Protists (Heterotrophic)
Ciliophora
Zoomastigina
Sporozoa
Sarcodina
Euglenophyta
Pyrrophyta
Chrysophyta
Acrasiomycota
Myxomycota
Phyla
Picture
Distinguishing Characteristics
Examples
Ciliophora
“Ciliates”
(“Cilia-bearer”)
Animal like protist with cilia
Paramecium sp.
Stentor sp.
Vorticella sp.
Zoomastigina
“Zooflagellates”
Animal like protist with flagella
Trypanosoma
Trichonympha
Sporozoa
Non-motile, spore producing animal like protist
Plasmodium
Sarcodina
Pseudopods
Some produce silicon shells (SiO2)
Ameba
Heliozoans
Foraminifers
Radiolarians
Euglenophyta
Flagellum
Chloroplasts and red eyespot
Structurally similar to zoomastiginan
Phototrophic Heterotrophs
Euglena sp.
Pyrrophyta
Dinoflagellates
(“fire-plant”)
2 flagellum, one wrapped around like a belt.
Thick plates, armored appearance
Named for bioluminescence in some members of this phyla.
Gonyaulax polyhedron (Red tide)
Chrysophyta
(“golden plant)
Beautiful silicon shells
Cell walls made out of pectin
Stores food as oil rather than starch to stay afloat.
Diatoms
Acrasiomycota
Cellular Slime Molds
Lives part of life as amoeba
Individuals aggregate (group together) into one mass and migrate when food runs low.
Produces fruiting bodies that spread spores.
Myxomycota
Acellular slime molds
Life part of life as amoeba.
Produces plasmodiums, a large single celled, multinucleate mass that may stretch a few centimeters.
Compound microscopes are a basic tool of biology. They are standard for a number of fields, including health care, research, toxicology, and many many more.
They are also just really cool in general.
Parts of a Microscope
Ocular Lens – has a power of 10x
Objective Lens(es) – a set of lenses with three or four different powers
Low power (4 x)
Med power (10 x)
High power (40 x)
Stage – where the slides are placed
Diaphragm – a dial that can be turned to control the amount of light coming through
Coarse focus knob – shifts the height of the stage to help focus. As the name suggests, the coarse adjustment knob shifts the stage faster and should be handled with caution
Fine focus knob – shifts the height of the stage to help focus, but very very slightly.
Light
Total Power
The total magnifying power of a microscope is calculated like this:
Ocular Lens Power x Objective Lens Power = Total Lens Power
In the case of our microscopes, the magnifying power of the ocular lens is 10x. The magnifying power of the objective lens vary (4 x, 10 x, 40 x).
Therefore, the total magnifying power at all levels is:
Low 10 x 4 = 40 x
Med 10 x 10 = 100 x
High 10 x 40 = 400 x
Creating a Wet Mount
Obtain a clean slide and coverslip (be very careful when handling these as both are glass)
Put your specimen flat onto the slide.
Put a drop of water onto your specimen
Put the coverslip on. Make sure to put it down at a 45 degree angle. This pushes out the air to reduce air bubble formation
If there is too much water on your slide, gently dab away with a paper towel.
Calculating size of specimen based on the field of view
Suppose you saw this flea under your microscope. How could you figure out how large it really is? One critical piece of information is just how wide is the field of view?
When we are looking at low power, the field of view will be wider than if we are looking at high power, since we are now focused on a smaller area.
At Low Power, the field of view is about 4.2 mm, or 4200 um (1 mm = 1000 um)
At Med Power, the field of view is about 4.2 mm, or 1680 um (1 mm = 1000 um)
At High Power, the field of view is about 4.2 mm, or 420 um (1 mm = 1000 um)
So how do we calculate the field of view? Suppose we were looking at the cells above at medium power and I was trying to figure out how big the cell is.
I know that the diameter of the field of view is 1680 um. And I estimate that about 6 cells fit across the diameter.
Therefore
1680 um / 6 = 280 um
This means that the cells are about 280 um across.
Identify and label structures of a generic Moneran
Identify and Describe the four criteria through which Moneran are classified
Describe the ways in which Moneran obtain/metabolize energy
Describe the three ways Moneran reproduce
Kingdom Monera is a large, diverse and wholly under-appreciated group of organisms. They perform many critical functions in the ecosystem, such as detritivores. They are used in the food industry for production of foods, such as milk or cheese. They are also responsible for many human diseases, such as the black plague that destroyed a third of the European population in the 14th century.
Members of this kingdom are also called bacteria.
Generally, bacteria all share some common features.
Structure of generic Monera
All Monera are unicellular and prokaryotic
No nucleus. DNA or RNA and ribosomes floating in cytoplasm.
Cell membrane made of lipids
Cell wall made of peptidoglycan to protect cell
Flagellum (plural: flagella) to move
Ways to classify a Moneran
Because of their small size, bacteria are very hard to observe under the microscope. Even when their individual shape or form can be seen, many look far too alike to definitively classify. Thankfully, we do have ways to classify Monera.
Shape – Almost all Monera fit into one of three shapes: round and spherical (cocci), long and rod shaped (bacilli) and spiral shaped (spirilla). Cells can also be classified based on their clustering behavior. Some cluster into colonies and strings, while others are primarily solitary.
Gram stains – because bacteria are for the most part, transparent to the naked eye, they must be stained to be properly observed under the microscope. When Hans Christian Gram, a Danish bacteriologist was staining bacteria with crystal violet, he realized that some bacteria retained the stains and became purple, while some did not and became pink. As it turns out, this has to do with the thickness and structure of the peptidoglycan cell wall. Generally, a thicker cell wall will retain more of the crystal violet, while thin ones will not.
Bacteria movement – some bacteria have flagella, whip like projections, that allow them to move. Some bacteria secrete slime to move along like a slug. Still others don’t move at all.
DNA/RNA Sequencing – the most specific way to identify a bacteria is probably through DNA/RNA sequencing. We do so by identifying the genes of the bacteria, which is probably fairly specific to each species. This method has become more common in recent years as the cost of genome sequencing decreases.
Ways Moneran get their energy
It should be noted that the following terms describe where organisms (any organism, not just bacteria) get their energy from.
Phototrophic Autotroph: organisms that derive their energy from the sun
Chemotrophic Autotroph: organisms that derive their energy from inorganic chemicals (chemicals that are not derived from living things)
Chemotrophic Heterotroph: (aka heterotrophs) are organisms that derive their energy from organic chemicals (chemicals that are derived from living things)
Phototrophic Heterotroph: are organisms that derive their energy from organic chemicals or the sun, depending on which source is available
————- (End of Thursday, February 25) ——————-
Ways Monerans Metabolize their energy
Depending on whether the Moneran uses one or both of the following
1. Cellular Respiration – a series of chemical reactions that uses sugars and oxygen to produce energy.
2. Fermentation – a series of chemical reactions that converts sugars to acids, gases or alcohol, and produces energy. It occurs without oxygen.
we classify monerans as follows.
Obligate Aerobes: Monerans that need oxygen in order to produce energy (aerobic respiration). These Monerans mainly use cellular respiration.
Obligate Anaerobes: Monerans that will die in the presence of oxygen, as oxygen is toxic to these monerans. These Monerans mainly use fermentation.
Facultative Anaerobe: Monerans that can produce energy in oxygen (cellular respiration), but switch to fermentation if there is no oxygen.
Ways Monerans Reproduce
Binary fission – where the cell replicates its DNA, and splits into two daughter cells, where each daughter cell gets one set of DNA
Conjugation – the bacterial form of sexual reproduction. Involves the exchange of genetic information.
Spore Formation – strictly speaking, not a form of reproduction. Occurs when a bacterium produces a hard covering (spore) and becomes metabolically inactive to preserve itself in adverse environments.
https://www.youtube.com/watch?v=EtxkcSGU698
Bacteria Research Mini-Project – One page fact sheet on an assigned bacterium – DUE TUESDAY FEBRUARY 1st
Identify the structures of bacteriophages and retroviruses
Describe the life cycle of (1) Lytic and (2) Lysogenic viruses
Describe the body’s defence mechanisms against a viral/bacterial infection
What are Viruses?
Viruses are defined as “noncellular particles made up of genetic material and protein that can invade living cells”. They do not belong to any of the five kingdoms of organisms. It isn’t even clear whether viruses are living or non-living. While they do evolve in so much as only successful viruses can propagate their genetic information, they do not have cells, do not grow or reproduce, and do not use energy the way living things do. They also cannot live independently of cells, as they depend on cells to replicate.
Nevertheless, viruses are fascinating tiny machines of nature that have been used and studied for a variety of purposes, such as in genetic engineering, combatting cancer, and to destroy harmful bacteria in foods. Some viruses are also responsible for some of the most debilitating diseases known to man, including HIV (Human immunodeficiency virus) leading to AIDS, mono, shingles, herpes and chickenpox.
Identifying Viruses
Viruses come in many shapes, sizes and life cycles. There are two specific groups of viruses we will focus on here.
Bacteriophages
Retroviruses
Bacteriophages have a distinct shape and structure.
There are two distinct parts: a head and a tail. The head is composed of a protein capsid or coat. It contains the DNA information. The tail and fibers at the base are used to attach the virus to bacteria, where it can then inject its genetic information into the cell.
Retroviruses are named for their ability to insert their genetic material into the existing genetic information of the host cell.
Normally DNA is “transcripted” to RNA (nucleic acid made of a single chain of nucleotides, in contrast to two strands in DNA). However, the genetic information in retroviruses are made up of RNA.
When the RNA enters the host cell, enzymes attach the piece of RNA to the DNA of the cell. Complementary nucleotides then attach to the RNA, making it double stranded and indistinguishable from host cell genome.
Just like the head of bacteriophages, made of a protein capsid coat with genetic information inside, retroviruses a protein capsid with RNA. However, they are also surrounded by a lipid membrane (membrane envelope) and often antigens.
Antigens are structures on the outside of the virus, toxins or proteins. The antigens act like the face of a virus, which can be recognized by the body and targeted by the body.
DNA Replication
DNA do not techninically reproduce the way living organisms do. However, they do invade host cells, causing them to create more copies of viruses. There are two ways that this happens.
Lytic Cycle
Lysogenic Cycle
Virus attaches to host cell
DNA information is injected into the cell
Cell reads the virus’s genetic information (it cannot tell the difference between its own DNA and viral DNA)
Cell replicates viruses inside itself
Viruses become very numerous until the cell eventually bursts releases the viruses
NOTE: Bacteriophages can also replicate through the lysogenic cycle. Retroviruses almost always replicate through the lysozenic cyccle.
1, Virus attaches itself to host cell
2. DNA/RNA information is injected into the cell |
3. Virus Genetic information is incorporated into the host cell’s genetic information, where it remain dormant for many years.
4. As the cell goes through cellular respiration, each daughter cell will also contain virus genetic information
5. At some point, the viral genes are activated, and replication begins.
6. Again, the viruses become very numerous until the cell bursts.
Thankfully, the human body also has some ways of protecting ourselves against viruses, at different levels of specificity.
Primary Line of Defense:
These forms of defense are non-specific, as in, it is to protect against any form of pathogen, virus, bacterial, protist, etc.
– Skin
– Oil and Sweat
– Hairs and cilia in mouth and nose
– Stomach (acids)
– Saliva, sweat and tears (lysozyme)
Secondary Line of Defense:
These forms of defense are also non-specific, but are generally activated only when pathogens have invaded.
– Inflammatory response: white blood cells
– Fever
Tertiary Line of Defense
The most specific form of defense. These forms of defense are activated specifically to target the pathogen.
This is usually done through antibodies that are produced based on the antigens on the surface of the pathogen. The antibodies can then target the pathogens.
–Interferons : produced by cells to interfere with virus replication
– Antibody production: white blood cells produce antibodies
Describe the process of ecological succession
Define pioneer species and climax community Define primary and secondary succession
Describe the characteristic of species during early and late succession
Ecological Succession is the gradual process by which ecosystems change and develop over time.
Ecological succession can be described something like a story of an ecosystem. Lets start from the beginning.
Once upon a time, there was an ecosystem. Everything was well, until catastrophe struck (DISTURBANCE)! A volcanic eruption had wiped away all life, and even the soil had been covered and burned (PRIMARY SUCCESSION). There was nothing left but bare rock. There was not a trace of soil to be found. It didn’t look like life was ever going to return.
Yet, there is hope.
Only a few months after the volcanic eruption, life was beginning to come back. Lichens and other hardy species, took root. They produced acids that broke down the rock, producing a thin layer of soil. Other organisms which need soil, such as weeds. Moss grasses then began to grow. As they died, they were broken down by microbes into soil and nutrients. The soil thickened. eventually shrubs and other longer lived, plants were able to grow. Animals that fed on these shrubs returned as well. Eventually, mature oaks, fir trees and other long lived trees came back. They outcompeted and shaded out the weeds and grasses that were there before. Eventually, the community stabilized (CLIMAX COMMUNITY).
Although the process of ecological succession itself may seem random, there are actually some predictable changes that occur.
Disturbance: the disturbance can be in many forms, from the fall of a log to an asteroid destroying 90% of all life on earth.
Primary succession: when the disturbance destroys or leaves no soil. Succession begins with bare rock. e.g. lava flow, a newly formed island and an asteroid
Secondary succession: when the disturbance destroys most of the life, but leaves the soil intact. Succession happens much more rapidly, since some seeds and life may still remain in the soil.
If it is primary succession, lichens are the first to colonize. We call these species that colonize first pioneer species. Pioneer species are the first to colonize an area that has suffered disturbance.
If it is secondary succession, because seeds and most underground life still remains, the speed of succession will be much higher.
The process of succession will continue, usually in the order of
Weedy species (e.g. dandelions)
Small shrubs
Shade intolerant plants (e.g. Red Alder)
Shade tolerant plants (e.g. Western Hemlock and Douglas Fir conifers)
Until a climax community is reached. A climax community is a community which remains relatively stable over a long period of time. Unlike earlier stages of succession, which may be as short as decades or centuries at the longest depending on local conditions, Climax communities may remain stable for thousands of years… until another disturbance resets the community.
Organisms in the early and late stages of succession have very different characteristics, since very different characteristics are needed for organisms to survive and thrive in early and late stages of succession.
Ability to Disperse: since organisms in early succession are in an environment with lots of spaces and little competition, a species that is able to disperse their offspring far and wide is most likely to proliferate and be successful.
Shade tolerance: species in the early stages of succession are in an area with few species. Tall trees that would shade the ground have not yet established. Therefore, species in the early stages of succession tend to be shade intolerant (need lots of sunlight). In the later stages of succession, because tall trees begin to shade the ground, species which can tolerate this shade are more likely to grow.
Lifespan: organisms in early stages of succession tend to be short lived. As the environment is constantly changing, having a shorter lifespan would mean that natural selection can happen at a faster rate (since each generation is short lived, and reproduction rates are high). This would mean the population as a whole will be able to adapt better to these changes.
Competitors: since not many species would have established in the early stages of succession species that establish in early stages would not benefit from being very good competitors, whereas species in later stages of succession need to compete with many other established species for space and resources.
Hardiness: the ability of an organism to be “hardy” (to live in an environment with extreme conditions such as low nutrients or blaring sunlight) is much more important in the early stages of succession than in the later stages.
Explain an exponential growth curve and a logistic growth curve
Describe how Density dependent and density independent factors impact population growth
Interpret a population vs. time graph
Identify and define carrying capacity and steady state
Evaluate what happens when species are removed from their natural habitats
Imagine you had an infinite amount of food and comfort. Everything that you ever want, all the food you could eat, all the space you need, all the luxury you can think of. It’s no wonder that you might think, “What a great world, time to reproduce!”
And so you do. But you don’t just have one child, why stop there when there’s so much space and room for all? Why not have two? Three? Five?
Later on, your children have many children and their children have many children and it keeps going on and on.
Notice that for every generation, you’re getting more and more individuals being born than in the last generation. If we were to graph this growth in individuals, it would look something like this:
Exponential Growth Curve
If nothing stops the population from growing, the population would just keep expanding and expanding faster and faster. If we were to graph this, we would produce an exponential growth curve.
Its calculated that if eastern cottontail rabbits were allowed to reproduce to their fullest capacity (20 kits a year/pair), in seven years, we’d have 184, 597, 433, 860 rabbits!
Thankfully, our world is not yet flooded with rabbits and will likely not be. Realistically, a population cannot keep growing unchecked. Something will come along and beat the population down, as it grows too large. We call these factors density- dependent limiting factors.
Density-Dependent Limiting Factors
Density dependent limiting factors are factors that control population size more strongly on large populations than on smaller ones.
Competition: when populations become crowded both plants and animals compete, or struggle, with one another for food, water, space, sunlight, and other essentials of life. The more individuals the less space and resources per individual.
Predation: As predators become more numerous, they eat more prey than are born and the population of prey decreases. As the population of prey decreases, there is less food for the predators, and their numbers decrease. This predator-prey relationship keeps both species in check. We call this relationship cyclic growth.
Parasitism: Parasites are much like predators, but instead of killing them; they live off of them and weaken them. When the population is very large and crowded, parasites are able to travel from one individual to the other faster and the population would decrease. Parasites are detrimental to their prey, but often not deadly. Why? If the prey were to die the parasite would die too.
Crowding and Stress: Crowding creates stress and could lead to lowered health that would be detrimental to the population. Some fishes, birds and mammals are also extremely territorial. When population numbers increase, the amount of fighting for space will likewise increase and so will stress.
Thanks to the above four density-dependent limiting factors, organisms do not normally exhibit exponential growth. The growth curve looks more like this:
Logistc Growth
Parts A and B still look like the exponential growth curve above. This is where there is still lots of space and resource for everyone and crowding has not become a problem. Birth rate >> death rate.
Part C the growth curve begins to level as less births and death of individuals due to predation, parasitism and competition increases. There is still growth though, so birth rate > death rate.
Part D at this population size, the population birth rate = death rate. For every one individual born, one dies. Which means, the population is not growing. Therefore, this part of the graph is called the steady state.
Since in the environment it is in, the population does not generally increase past this number, the number of individuals at the steady state is called the carrying capacity. It is, theoretically, the MAXIMUM number of individuals that can be held.
Density Independent Factors
Not all organisms have their numbers limited by density dependent factors though. Some are limited by factors that have nothing to do with their numbers.
Boom and bust populations: locusts and algae for example, grow in great numbers when conditions are right, but die in huge numbers suddenly (population crash).
Natural disasters: natural disasters such as floods, rainstorms etc. The population can essentially be wiped out. It doesn’t matter how large the population is at that point.
Apply your knowledge to a new situation
In any one environment, organisms that have evolved in relation to each other have evolved to deal with each other’s strengths and weaknesses. For example, the lynx and hare each evolves over time to compete with each other, the hare evolving traits to run from the lynx and the lynx evolving traits that allow them to hunt hare down. Similarly in an environment where organisms have evolved together (co-evolved) for a long time, they help to keep each other in check.
However, when organisms are torn away from their environments, the checks and balances are also taken away and in some cases, the population has exploded past control.
We see this in invasive species, such as the scotch broom, European starling and House sparrow. These species, which were introduced from the British Isles, have since become pests that compete with and threaten native species.
Identify the abiotic and biotic components of an ecosystem
Describe the roles of photosynthesis and cellular respiration within a pyramid of energy
Compare photosynthesis and cellular respiration in terms of the reactants, products and chemical equations
Explain the roles of producers, consumers and decomposers in ecosystems
Explain the process of a trophic cascade
Explain the process of bioaccumulation
Understanding Ecosystems
Ecology is the study of interactions of organisms with one another and their physical surroundings.
Why is it important for us to study ecology? In order to properly care for, protect and be stewards to the planet, we must first understand how the living world operates. Just like it is not possible to care for a person without a proper understanding of how the human body operates, we must understand how the planet operates. Just as people are a single living organism, so the earth also operates as a single living species.
To understand and appreciate the ecology of the earth, we must take a holistic approach. Instead of considering the components of the ecosystem and biosphere as being independent, like the parts of a puzzle, we are better able to appreciate the interconnectedness of the earth by considering each component in relation to other parts. For example, a deer is an organism, that does not live independent of the grass and plants it eats, that does not live independent of the air it breathes, that does not live independently of the soil it contributes to through defecation, that does not live independently of the wolves that feed on it… A deer is not only a deer; it is a critical link in the ecosystem it exists.
It is very difficult to study systems with a holistic approach. Therefore, in studying ecology, we often artificially separate these components into smaller parts called ecosystems (division of the biosphere including abiotic and biotic factors affecting organisms and their way of life). We also consider the different parts of the ecosystem, called the abiotic and biotic systems.
Abiotic
Biotic
The non-living portions of the ecosystem, or the parts of nature that are derived from living organisms.
· Soil
· Air
· Atmosphere
· Temperature
· Sunlight
· Water (rain/ponds/etc.)
The living portions of the ecosystem, or the parts that are derived from living organisms.
· Plants
· Birds, small mammals, insects
· Microorganisms
· Fungi/decomposers
· Humans (yes, we are a part of the living world too)
It is important to recognize that even as we artificially separate the components of the ecosystem, that they do not exist in isolation from each other. For example, the trees and plants will fundamentally change the atmosphere of the ecosystem it exists; animals that defecate or die will contribute to the soil structure, etc. The physical environment will in turn impact the biotic organisms and their way of life.
Energy Flow in the Ecosystem
All life on earth depends on energy in order to function. Energy, unlike nutrients, cannot be recycled. Once it is used, it cannot be used again. For example, plants use about half the energy it obtains from photosynthesis almost immediately. Therefore, energy is described in terms of energy flow. Unlike nutrients, which can be broken down and reused by other organisms when organisms die, energy that is used cannot be recovered.
Therefore, energy must be replenished. In most ecosystems, the ultimate source of energy comes from the sun. Autotrophic organisms (plants, and photosynthetic protists and monerans) capture the energy of the sun through a process called photosynthesis.
6CO2 + 6H2O + (sunlight) — > C6H12O6 + 6O2
The energy from sunlight is captured in the above process and stored in the C6H12O6 that is produced, otherwise known as glucose, a sugar and energy source. Since autotrophic organisms are able to get energy from this non-living source (sunlight), they are known as producers.
Consumers (heterotrophs) feed on other living things in order to survive, they cannot obtain their own food. Since producers are the only ones, which can obtain energy, all consumers obtain energy from the sun directly or indirectly. They take up this energy in a process called cellular respiration.
C6H12O6 + 6O2 –> 6CO2 + 6H2O + Energy
However, half of the sugar produced by the producers is used up in the daily processes and functions of the organism, like a car engine using up fuel as it runs. Therefore, there is theoretically only half the energy left for consumers to obtain. But since consumers cannot possibly consume all the producers on this planet, the amount of energy that is obtained in the next level is even less than half.
Trophic levels
All organisms on this earth are tied together in networks of feeding relationships (Miller and Levine). We can represent this relationship in terms of a food pyramid. Producers, which obtain energy from the sun, make up the, largest, broadest part of the food pyramid. But remember!
For every level, a large part of the energy is used up immediately.
Some of the energy is used to produce structures, such as wood, which are not edible to most organisms.
Not all of the organisms at each level are consumed. Some die without being consumed.
For all these reasons, for each level of the trophic pyramid, the pyramid becomes smaller and smaller. This represents two things: (1) a smaller biomass (2) less energy in the trophic level. As a rule of thumb only about 10% of the energy from each trophic level is retained.
The trophic level which feeds on producers is called the primary consumers, the trophic level that feeds on the primary consumers are called secondary consumers and the trophic level which feeds on tertiary consumers are tertiary consumers and so on.
There is still one very important component missing in the picture though! Plants, animals and microbes alike that die without being consumed, are broken down by the decomposers. Decomposers come in the form of microbes and fungi alike. They are essentially the recyclers and cleaner-uppers of the natural world!
Decomposers feed on all trophic levels.
This is a very simple construct of the natural world. However, it is important to note that this is oversimplified. In the natural world for example, hawks do not only feed on snakes, they may feed on mice as well. Snakes do not only feed on mice, they may feed on other organisms. The feeding relationships of the natural world is better represented as a web than a pyramid:
Trophic Cascade
Trophic cascades happen when predators in a food web suppress or somehow alter the behaviour of their prey, releasing the next trophic level from predation. See trophic cascades in action in the video below!
An example of this is the wolves of yellowstone national park, which were re-introduced for the first time in 70 years in 1995. Wolves preyed on the deer, which lowered in abundance, and avoided valleys and gorges because of the threat of wolves. This allowed vegetation to increase in abundance, benefiting many other species.
Bioaccumulation
Around the 1940’s and 50’s, DDT, an insecticide, was used to kill various crop pests. At around the same time, bald eagles, peregrine falcons and many other birds of prey started to decline significantly. It was soon discovered (though not soon enough) that these two events were linked. The birds of prey had significantly declined, because their eggshells had thinned so much it was unable to protect the chicks inside, and would even break as the parents sat on the egg to warm it. In the bodies of these birds, high concentrations of DDT was found.
As it turns out, the DDT had somehow made it up the food chain to the top predators. And not only that, the concentration of DDT in their bodies was much higher than for example, in the fish they ate. This is the process known as bioaccumulation: accumulation of substances, such as pesticides or other chemicals in an organism.
Why does the concentration of DDT get higher and higher? Suppose there was a little bit of DDT in every insect. The fish would eat many many of these insects, and accumulate the DDT in their bodies. The larger fish would eat many many of these smaller fish and accumulate the DDT in their bodies, and hawks would eat many many of these larger fish and accumulate more and more into its one body. By the time it reaches the top predators, the amount of DDT that has been “bioaccumulated” is extremely high.
