1. Discuss how an action potential is propagated along an axon, including all re
ID: 47567 • Letter: 1
Question
1. Discuss how an action potential is propagated along an axon, including all relevant molecules and
processes. Be sure to discuss how resting membrane potential is restored. How is the signal transmitted to
the next neuron?
2. Explain the process of contraction in a skeletal muscle, starting with how the signal enters a muscle cell at
the neuromuscular junction. Include all relevant ions, structures, and processes in your explanation.
3. Using your knowledge of both animal behavior and evolution, define and explain altruistic behavior. Under
what sorts of circumstances would we expect to see altruistic behavior, and why? Under what sorts of
circumstances would we expect natural selection to favor alleles associated with behaving altruistically?
4. Use your understanding of population ecology to describe and explain the global human population over
the last one or two thousand years. What can you predict for the future of the global human population, and
why? (Your predictions should be based on population ecology!) What policy changes, if any, do you think
are advisable given the predictions you have made?
5. Define symbiosis and explain the major categories of symbiotic interactions, including how each type of
interaction may be shaped by natural selection. To support your explanation, give at least two examples of
type of symbiosis, explaining how each species is affected (e.g., helped, harmed, or unaffected) and why.
6. Describe the flow of energy in an ecosystem. Where does the energy initially come from? Why isn
Explanation / Answer
1.
Action potential is a small change in memebrane potential which is conducted by axons . As the signal moves down the axon gated ion channels open in response to change in memebrane potential in which the voltage becomes less negative which is Depolarization which achieves a threshold value.It further causes the opening of more voltage-gated sodium channels in those regions. The sodium channel activation moves like a wave and the action potential is propagated down the length of the neuron, from its input source at the dendrites, to the cell body, and then down the axon to the synaptic terminals from which it is passed to Dendrites of other neurons and simillar process occurs.The resting potential is restored by Na+K+ATPase pump.
2.
An impulse is created by stimulation of motor nerves and muscle fibres .When an impulse reaches the muscle fibres of a motor unit, it stimulates a reaction in each sarcomere between the actin and myosin filaments. This reaction results in the start of a contraction .The reaction, created from the arrival of an impulse stimulates the myosin filament to reach forward, attach to the actin filament and pull actin towards the centre of the sarcomere.When the muscle is stimulated to contract by the nerve impulse, calcium channels open in the sarcoplasmic reticulumn and release calcium into the sarcoplasm . Some of this calcium attaches to troponin which causes a change in the muscle cell that produce muscle contraction.
3.
Altruistic behaviour is the type of behaviour which benefits other organisms but at a cost to itself. e.g In birds a breeding pair takes help from other birds to raise their young ones whereas they protect the nest from foreign attack.
Altruistic behaviour is observed in animal kingdom which live in groups and are ready to give up their selfish interests in order to help the other members of the group..Darwin proposed the theory of Group Selection over Natural Selection which leads to this Altruistic behaviour. Kin selection theory predicts that animals are more likely to behave altruistically towards their relatives than towards unrelated members of their species. Moreover, it predicts that the degree of altruism will be greater when the relationship is closer.
4.
The global human population over the last one or two thousand years has increased manifold. Around 200 years ago our population was less than 1 billion But during 1900 and 2000 the population has increased three times just due to better medical facilities , uncontrolled reproduction leading to high birth rates , low death rates.
At this rate the population is going to increase at a faster rate then by which it has increased in the past.If the population increases at the current rate then a time will come when there is no land left to be inhabited by humans .
Some of the policy changes to control over population are:
(i) Proper sex education to be provided to each and every individual because education is one way we can control this mass increase in population.
(ii) Economic policy reforms
5.
Symbiosis is a close relationship between two or more different species . The major categories of symbiotic interactions are:
(i) Commensalism is the relationship in which one species obtain food and shelter from other species and it does not harm or help the other one.e.g Titan triggerfish provides food oppurtunities for smaller fish. Another example is when Lion finishes eating then the left over food is eaten by Vultures and lion does not attack vultures.
(ii) Mutualism in which both species benefit from the relationship. e.g - Pollination caused by Hummingbirds for plants like Dianthus and consumes food from the flowers of the plant. Another e.g is Relationship between Ungulates and bacteria in which the ungulates benefit from the cellulase produced by the bacteria by facilitating digestion and the bacteria benefit from having a supply of nutrients in the host environment
(iii) Parasitism is the relationship in which one species (parasite) nourishes itself to the disadvantage of the other species (host). It has two types (a) Obligate parasite which depends on the host to compleete it's life cycle and (b) Facultative parasite which does not depend on the host to complete it's life cycle. e.g - Tapeworms attach themselves to the insides of the intestines of animals such as cows, pigs, and humans where they get food by eating the host's partly digested food and depriving the host of nutrients. Another e.g - Aphids are insects that eat the sap from the plants on which they live.
6.
Flow of energy takes place in the following . Producers such as green plants absorb the sunlight for the process of photosynthesis . Now , the herbivores feed upon these green plants hence energy flows from plants to the herbivores which may or may not be fed upon by Carnivores . So the energy flows in one direction from plants to herbivores to carnivores and other feeders.
The energy initially comes from sunlight which is used by green plants to produce energy.
The energy that flows from one trophic level to another trophic level is 10% that is if 1000 J of energy is passed from sunlight to plants after then 10% i.e 100 J is passed from plants to herbivores , similarly 10% of 100 J i.e 10 J is passed to carnivores and the process goes on. Only 10% of energy is passed because rest is released in the form of heat as metabolism , respiration, faeces etc.
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