Evolution Notes

IB Biology SL Options: Evolution + Neurobiology and Behaviour

Cram Packet -2009-

David Glover

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Four processes were needed in order for life to be spontaneously formed on Earth: – The synthesis of organic molecules; – The synthesis of polymers from organic molecules; – Mechanisms for the self-replication of organic molecules; – The packaging of these molecules inside of membranes; Miller and Urey experimentally reproduced organic molecules from the atmospheric components thought to have existed on pre-biotic Earth. Conditions conducive to the formation of organic molecules may have existed along intertidal zones, deep-sea hydrothermal vents or volcanic areas on Earth. Organic molecules may have existed in space and been delivered to Earth by comets. RNA may have been the first molecule capable of passing on hereditary information Protobionts are structures that may have preceded the first living cells. Early photosynthetic prokaryotic organisms started to generate an oxygen-rich atmosphere by expelling oxygen gas as a waste product. The endosymbiotic theory states that the first eukaryotic cells were formed when larger prokaryotic cells ingested, bit did not digest, smaller prokaryotic cells.

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The sum total of all alleles and their frequencies within a population constitutes the gene pool of a population of organisms. Evolution is a change in the frequency of alleles in a population when measured over many generations. The concept of a species cannot be appreciated in a simple definition. Speciation is the formation of new species and is initiated when a single gene pool is separated by various kinds of barrier. The barriers are: – geographic isolation, e.g. formation of a new mountain range; – hybrid infertility, i.e. offspring of the mating of two closely related species are most often physiologically incapable of reproduction; – temporal isolation, e.g. development of timing patterns for migration, hibernation, etc. lead to organisms no longer mating and sharing the same gene pool; – behavioural isolation, i.e. development of behaviours which are not favourable to mating chances and thus a gene pool is no longer shared. Allopatric speciation happens when two or more subsets of a population are geographically separated. Sympatric speciation happens in the same geographical area. Adaptive radiation is a term that describes the development of many species, all from a single common ancestor. Divergent evolution happens when one or more species with dissimilar traits emerge from a single species. Convergent evolution occurs when two or more organisms undergo similar natural selection pressures and thus evolve to become

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more and more similar to each other. Convergent evolution will never lead to two or more species becoming one. Two main theories have been developed to describe the relative pace of evolution: – gradualism, i.e. evolutionary changes are small, continuous and slow; – punctuated equilibrium, i.e. evolutionary changes are relatively quick and are then followed by long periods of little or no change. Transient polymorphism is a term that describes a population of organisms that has two or more forms and that change their 'fitness, depending on the environmental selective pressures at work at a given time. Sickle cell anaemia is an example of balanced polymorphism: different forms of haemoglobin are selected for because of the different positive advantages of each haemoglobin form. Each form of haemoglobin has some positive advantages and some negative aspects and thus each allele type stays relatively 'balanced' in frequency.

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The age of rocks and fossils can be quantified with some degree of accuracy by using radioisotopes. Two common radioisotopes are 14C and 40K. The half-life is the time it takes for half of a radioactive isotope to decay. An object that contains a radioactive isotope will give off half of its original level of radioactivity after one half-life has passed. Humans are primates because we are mammals with: – opposable thumbs, and hands with fingers capable of great dexterity; – a shoulder socket capable of complete circular motion; – forward-facing eyes which give us stereoscopic vision. The ancestor species which preceded modern humans may have been only one hominid lineage and more than one ancestral line may have been alive on Earth at certain points in time. The fossil record of human evolution is very incomplete and new discoveries are sure to change our thinking of our fossilized ancestors. The change in diet from primarily vegetarian to a partial carnivore may have coevolved with an increase in brain size during hominid evolution. Humans have undergone both genetic and cultural evolution. Genetic evolution is by way of Darwinian mechanisms due to natural selection. Cultural evolution is due to acquired knowledge which is passed on by social mechanisms within a social group. Currently, the pace of cultural evolution has far surpassed the pace of genetic evolution for our species.

David Glover IB Biology Option E Review Sheet 1. What is animal behavior?

Behavior - the aggregate of the responses or reactions or movements made by an organism in any situation 2. Define the terms stimulus, response and reflex in the context of animal behavior.

Stimulus - Anything that elicits or evokes action in a person or creates a response in a muscle, nerve, gland or other excitable tissue or organ of the body. Response - a bodily process occurring due to the effect of some antecedent stimulus or agent Reflex - an automatic instinctive unlearned reaction to a stimulus 3. What is a sensory neuron, a relay neuron (interneuron) and a motor neuron and how

are they related? Sensory Neuron- Nuerons activated by sensory input that send projections to the nervous system. Theyre activated from light, sound, temperature, and chemical stimulation Relay Neuron- A multipolar neuron which connects afferent neurons and efferent neurons in neural pathways. Motor Neuron- that project their axons outside the Central nervous system and directly or indirectly control muscles. All three of the neurons are related because they are parts that are used in the reflex arc. Sensory neurons pick up the initial information from one of the senses, and then transmits the signal to a relay neuron, which transfers the signal to the brain or spinal cord. from here it is processed, and once the appropriate answer is chosen, it is sent back through more relay neurons to a motor neuron, which preform the required action. 4. Explain the role of receptors, sensory neurons, relay neurons, motor neurons,

synapses and effectors in the response of animal to stimuli Animal response to stimuli is a long processes that incorporates many cells, and cellular structures to create a stimuli-response pathway. Receptors are made up of Sensory neurons, and are essentially organs or cells that pick up the initial information. This signal is transferred to another neuron in order to make its way to the brain and/or spinal cord, to do this it transmits the signal across the synapse, which is the space between two neurons, where the signal passes through neurotransmitters. The signals is transmitted to a relay neuron to the brain or spinal cord. The brain and/or spinal cord process the information, and send a response signal again through relay neurons. This time, instead of going to a sensory neuron, it travels to a motor neuron, which stimulates a muscle or gland. This muscle or gland is called an effector, and is what creates the 'response'. 5. Draw and label a diagram of a reflex arc for pain withdrawal reflex, including the

spinal cord, and its spinal nerves, the receptor cell, sensory neuron, relay neuron,

motor neuron and effector.

6. Explain how animal responses can be affected by natural selection, using two

examples Natural selection can lead to different animal responses depending on what has been changed through the generations. An example of this is seen in dogs, some dog breeds are noted for certain traits and thusly through natural (and sexual) selection they are carried on; As a response to the scent of another animal, pointer dogs will stop and raise their paw and straighten their tail, while other dogs such as Labradors, will go and investigate, without straightening its tail, or raising its paw. Bears developed hibernation as a response to the cold weather, other members in the bear family that do not hibernate do so because they were in a different climate range, or different setting, so they did not have the need passed down through natural selection. 7. Outline the diversity of stimuli that can be detected by human sensory receptors.

Photoreceptors: The visual sense of light may be detected by the eyes. Mechanoreceptors: A mechanical pressure or distortion. Thermoreceptors: An absolute and relative changes in temperature Chemoreceptors: The smell of chemical odours. Nocicreceptors: Sense of pain 8. Draw, label and annotate a diagram of the human eye

Cornea- Transparent outter coating of the eye which protects it from injury. Pupil- Sphere shape in center of the eye which controls amount of light entering. Iris- Pigmented tissue which connects parts to dilate the pupil. Aqueous Humor- Thick watery substance that is between the lens and the cornea. Suspensory Ligament- Strands connecting the ciliary body and lens of the eye.

Conjunctiva- Clear membrane which lines the inside of eyelids. Ciliary Muscle- A muscle in the eye that controls the eye's accommodation for viewing objects at varying distances. Retina- They receive light and transform it into image-forming signals which are transmitted through the optic nerve to the brain. Choroid- Layer of the eye which provides nutrients and oxygen to retina. Sclera- Fibrous, protective, outer layer of the eye which is white. Retinal Artery- Supplies nerves close to eye and all nerve fibers. Lens- Refracts light to be focused on the retina. Hyaloid Canal- Artery which leads from front of the eye to the back. Optic Nerve- The nerve that transmits visual information from the retina to the brain. Retinal Vein- Drains blood from the capillaries of the retina into the larger veins. Fovea- Responsible for sharp central vision. 9. Annotate the diagram of the retina (below) noting the different cell types and the

direction the light moves [LIGHT MOVEMENT IS OPPOSITE TO THIS ARROW!]

I. Ganglion Cells - Are cells that release of epinephrine and norepinephrine into the blood stream. II. Rod and Cone cells - Cells in the retina used to observe and see from light absorbtion III. Bipolar cells - Sensory pathways for smell, sight, taste, hearing. 10.Compare rod and cone cells Rod Cells - One of two types of light receptor cells in the retina; rods see in dim light and provide side vision; more sensitive to movement Cone Cells - These are cells in the retina of the eye which only function in relatively bright light. 11.Explain how visual stimuli are processesed including edge enhancement and

contralateral processing.

Visual receptors such as rods and cones, synapse in the retina with several types of interneurons, e.g. bipolar cells. These, in turn synapse with ganglion cells ---> the axons of ganglion cells make up the optic nerve and thus conduct impulses to the brain. Contralateral processing is defined by how images are analyzed according to their position in relation to visual hemisphere, either left or right (of sight). Images are processed using the opposing hemisphere of the brain; it is important to understand that images are not analyzed by eye, but rather entire visual field. Edge enhancement is, in short, a creation of contrast (in lines) to create a seemingly "enhanced" image. 12.Draw and label a diagram of the human ear including the pinna, eardrum, malleus,

incas and stapes, oval window, round window, semicircular canals, auditory nerve and cochlea.

13.Explain how sound is perceived by the ear.

First the sound is taken in by the ear drum, which picks up the vibrations of the sound. Then it is through the hammer, anvil, then stirrup. The stirrup sends the sound to the cochlea which is filled with thousands of cilia. The auditory nerve then translates these and sends them to the brain. Your brain then translates all that and tells you what you are hearing. 14.Distinguish between innate and learned behavior. Give at least three examples of

each. Innate behaviors are those an organism already knows when they're born (genetically, etc.). Learned behaviors must be taught to or observed by the organism for it to be learned. Innate- Breathing, reflexes, sound (communication), chewing. Learned- Flight, Birdsongs, Fighting

15.Define kinesis and taxis and give an example of each

Kinesis- A non-directional movement or activity of a cell or an organism in response to a stimulus. Example: Woodlice changing environment to find one more moist. Taxis- An activity or movement of a call or organism in response to a stimulus with a direction. Example: Protozoans often move towards light. 16.Discuss how the process of learning can improve an animal's chance of survival.

The actions or responses an animal may learn can help its chances of surviving in its environment. If something were to change in the environment, and the animal does not learn how to adapt to the new condition, it may cause the animal to suffer. If an organism also doesnt learn something when it needs to, it will have a disadvantage as it goes on through life. Learned behaviors give said animal a greater set of solutions to unspecific problems that could result in death, thus the animal is more likely to survive if said animal knows how to handle the stimuli with which it is faced. 17.Outline Pavlov's experiments in conditioning dogs including all of the pertinent

vocabulary. Ivan Pavlov developed the basic principies of classical conditioning. Classical conditioning centers around the ¡dea that through experience, a stimulus.that had no previous relation to a specific reflex could come to trigger that reflex. A reflex is simply an unleamed, automatic response that is elicited by a specific stimulus. Pavlov made this discovery while he was studying the salivation reflex of dogs in response to food. If food powder, for example, is placed into dogs' mouths, they reflexively salivate. The dogs don't leam this; it is reflexive. Food ¡s the specific type of stimulus that is required for salivation to occur. Pavlov found that if the food powder was repeatedly paired with a neutral stimulus like a bell ring, eventually, the dogs would leam to salivate in response to the ringing of a bell. In Pavlov's inital trials, the bell ring was paired with the meat powder; there, the bell did not trigger any response whatsoever. Through repeated triáis, however, the originally insignificant stimulus, the bell ring, became significant for the dogs. They carne to realize that once they heard the bell ring, the food would soon be placed in their mouths. Technically, we can say that the bell ring became paired, or associated, with the meat powder that was placed in the dogs' mouths. Once this association was made, the dogs began to salivate when they heard the bell ring. In other words, the dogs had become conditioned to salivate in response to the bell ring. Eventually a bell ring would trigger salivation without the présense of the meat powder. In this example, the meat powder was the unconditioned stimulus (UCS), which, when placed in the mouth, resulted in the unconditioned response (UCR) of salivation. This ¡s called unconditioned because the animáis' salivation is the natural response to the stimulus and didn't need to be learned (conditioned). After conditioning, the new, initially neutral stimulus (the bell in this example) that elicits the response is called the conditioned stimulus (CS); the animals’ response to the conditioned stimulus (salivation) is called the conditioned response (CR). They are both called conditioned because the animal had to leam to salivate to the bell. 18.Describe the basic structure of a birdsong

The appropriate song repertoire is acquired in a series of distinct stages. Young

birds, during an early Sensory Phase, listen to a conspecific tutor and thereby obtain information about the characteristics of its own song. Only a very specific subset of surrounding songs is actually accepted as suitable, suggesting the presence of an in-built song template. Following this sensory phase, young birds actively begin to vocalize themselves. Their Subsong is an atonal, noisy, meaningless repetition of sounds, which lacks recognizable syllables. Akin to human Babbling birds practice coordinated movements of the respiratory system, sound producing organs, and related structures (e.g., tongue). During Sensory-motor Phase, young birds spontaneously produce Plastic Song, consisting of vocalizations with distinct syllables and recognizable elements. Such "work in progress" will include elements from the song of tutors and elaborate them into a variety of syllables and phrases that even exceed what eventually will be used in its adult song. The ability to hear its own vocalizations are critical for normal development. In transition to the Mature phase, birds adopt a Crystallized Song with syllables and syntax structure that is characteristic of its species. Once established, these song patterns remain fixed in many species, are no more disrupted by deafening, and are presented intact during each subsequent breeding season. In contrast open-ended learners (e.g. starlings and canaries) retain the capacity to adjust or alter their song throughout life. 19.Outline the role of inheritance and learning in the development of birdsong in the

young birds. Birds can learn their song in two ways, with a crude template or opened ended. With crude template the young bird inherits its parents basic understanding of the song, but the bird must then hear its song and practice it to finally learn it. With the inheritance from the parents, the bird is able to be born with a outline of their song, which they then must master. 20.State how presynaptic neurons can

affect postsynaptic neurons. Chemical synapses pass information directionally from a presynaptic cell to a postsynaptic cell and are therefore asymmetric in structure and function. The proteins are then involved in anchoring and trafficking neurotransmitter receptors and modulating the activity of these receptors. 21.Draw and label a typical motor neuron

including the dendrites, cell body, axon, axon hillock, myelin sheath, nodes of Ranvier, nucleus and axon terminals 22.What is a synapse? Describe what

happens in a synapse? Synapse are specialized junctions through which neurons signal to each other and to non-neuronal cells like

muscles. Actionpotenital travels down the membrane of the presynaptic cell --- channel opens --- calcium concentration increases --- neurotransmitter chemical activated --neurotransmitter content goes into synaptic cleft --- receptor is then activated --molecules break off 23.Neurons communicate through both electrical signals and chemical signals. Explain

both mechanisms and give examples of each. The neuron will send a electric signal from one to the other by reaching its minimum voltage called the action potential. (Pain reflex) Chemically, theyare packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and released into the synaptic cleft. (seratonin) 24.What four things can happen to a neurotransmitter once it is released into the

synaptic cleft? It may bind to the receptors in the adjacent nerve cell, send the message on, leave the receptor. It may bind to the first cell's autoreceptors, which tell that cell not to release any more of the neurotransmitter molecules, then leave the autoreceptor. It may be rendered inactive by an enzyme. It may never make its way to the adjacent nerve cell, and not trigger it to fire. 25.Explain the decision-making process in the CNS.

A neuron is on the receiving end of many excitatory and inhibitory stimuli. The neurone sums up the signals. If the sum of the signals is inhibitory then the axon does not fire. If the sum of the signals is excitatory, then the axon fires. This is the interaction that takes place between the activities of the excitatory and inhibitory neurones at the synapses. The summation of the messages is the way that decisions are made by the CNS. 26.Explain how psychoactive drugs affect the brain and personality.

Psychoactive drugs affect many different parts of our brains. They cause our brains to produce a degree of chemicals differing from the normal amount. Things like dopamine are produced much more than usual, making the brain change its thoughts and personality. Our personality can be affected by the chemicals changing in the brain, making it act in a completely different way. 27.List three excitatory and three examples of inhibitory psychoactive drugs.

Excitatory- methylphenidate, amphetamine, cocaine Inhibitory- Barbituratures, ethanol, anti depressants 28.Explain the effects of THC and cocaine in terms of their action at the synapses in

the brain. Cocaine will bind to dopamine transporters, which causes a flood of dopamine to the brain. THC will mimic anandamide, which then opens the flow of dopamine, releasing it to bind to the synaptic cleft.

29.Discuss the causes of addiction including the role of dopamine secretion.

Physical addiction occurs when the body stops producing neurotransmitting chemicals and starts relying on outside sources to initiate responses. Dopamine is one of the naturally occuring chemicals in the body that act as pain-killers and mood enhancers. Some psychoactive drugs act directly with dopamine secretion, varying moods and physical effects. The bodys need to secret dopamine at different times while lacking the neurotransmitter to begin the process, mess with natural working order of the CNS. This often occurs due to addiction. 30.Explain what threshold means for an action potential.

The threshold is the line that the total voltage must cross so the action potential may fire. If the total voltage does not cross this threshold, then no action potential will fire.