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For each of the animal groups you have chosen, describe the structures involved in the biological process you have named. In each case, describe how these structures function, and explain how they allow each group to survive in their habitat.

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Introduction

For each of the animal groups you have chosen, describe the structures involved in the biological process you have named. In each case, describe how these structures function, and explain how they allow each group to survive in their habitat. Insects: Insects have developed an internal gas exchange system. Insects have holes spiracles around the body, these holes are attached to a network of tubes that pass throughout the whole of the body. The tubes get smaller in size and end with a fluid filled tip at the body cells. The circulation system is not required in the transport of gases. The insect has several adaptations to allow an efficient gas exchange rate. The tubes end directly at the body cells which require oxygen and release carbon dioxide. The distance the gases have to travel is therefore small - increasing the rate of diffusion. This also ensures there is a concentration gradient of gases at the gas exchange surface. The gas exchange surface has a large surface area, thus there is a large surface area to volume ratio in an insect. The tips of the tubes are moist - they are fluid filled which increases rate of gas diffusion, fluid from the tube tip is drawn into the body cells further decreasing the distance the gases need to travel. The insect can increase the rate of ventilation at the gas exchange membranes by body movements that draw air in and out through the spiracles. ...read more.

Middle

The air tubes terminate at air sacs called alveoli. There are approximately 300 million alveoli in the lungs. Humans have several adaptations to increase the rate of gas exchange and allow humans to have a high metabolic rate. Millions of alveoli give the lungs a large surface area for gas exchange to occur. Overall this gives a large surface area to volume ratio. The alveoli walls are only one cell thick - this decreases the distance the gases have to travel. The alveoli are surrounded by a network of fine blood capillaries that deliver deoxygenated blood and remove oxygenated blood. The capillaries are thin walled to also reduce the distance gases need to travel. Humans have a circulatory system to transport gases to and from the body cells. Blood contains haemoglobin for the efficient absorption of oxygen. Humans use muscle movements to ventilate the lungs - bringing fresh air in and exhaling used air (breathing) - this maintains the concentration gradient of gases at the exchange membranes thereby increasing the rate of diffusion The surface of the gas alveoli is kept moist and a surface stops the alveoli from collapsing. The trachea has cartilage to keep the airway open. Discuss why diversity exists across your chosen animal groups, in order for them to survive and be successful in their habitats. The three animals chosen all have different gas exchange mechanism and adaptations to increase the efficiency of the rate of gas exchange. ...read more.

Conclusion

Fish, insects and humans can assist the concentration gradient by using muscle/body movements which ventilate the gas exchange membranes. This allows them to control the rate of gas exchange and increase it in times of need. Insects have no way of increasing the rate of diffusion across their skin surface and so can only maintain a low level of activity and metabolic rate. To summarise, insects are terrestrial they do not have an efficient gas exchange mechanism; as a consequence they have a low metabolic rate. They must live in moist conditions. They can not live in aquatic habitats as there is less oxygen available and their gas exchange system is not efficient. Humans are also adapted to a terrestrial environment. They have an internal gas exchange system which is protected from the outside air. Humans can increase the ventilation system allowing a high metabolic rate. Humans can not survive in an aquatic habitat as the gas exchange system is not efficient enough. Fish are extremely well adapted to an aquatic environment and lifestyle. Their fragile gills are supported by the weight of the water - in air they would stick together. Fish have no means of controlling water loss. On land their gills would quickly dry out and gas exchange rates would decrease. They also have no adequate mechanism to ventilate the gills with air. The gas exchange mechanisms of the different animals affect their size, metabolic rate and the habitats in which they can survive and reproduce. ?? ?? ?? ?? Viveca Dourado Yr 12 Biology Ms. O'dwyer 1 ...read more.

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Response to the question

Response to the question is very well done. No introduction which is missing which could be used to make the essay structure flow better rather than just launching straight into the different animal groups and a certain structure. The main ...

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Response to the question

Response to the question is very well done. No introduction which is missing which could be used to make the essay structure flow better rather than just launching straight into the different animal groups and a certain structure. The main body of the text is very well analysed for this level and concise. The conclusion is well done, and brings together how each animal is similar and how each animal is different and how this adapts them to the environment they live in, however the candidate is wrong in the assumption that fish cannot have any method of ventilating their gills with air other than the water (lungfish, respiratory swimbladders, respiratory intestines and corneas).

Level of analysis

The level of analysis for each type of system named for a group of animals is very well done. Concepts which would have only been done in basic detail at A level have been well researched and the research put into clear and concise information, and the structure of each system clearly related to how it enables the animal to survive in their environment. Describes a clear theme of gas exchange and how it differs between three different groups of animals with differ immensely in their mechanisms of gas exchange. Fish could be a lot better explained, as there is more to the structure and how the fish are adapted to gas exchange than the candidate gives, and there is a distinct difference in mechanisms between fresh water and sea water fish and what happens at the gills. Also would have liked to have seen the relevance of ribs and the diaphragm analysed in the human example. The candidate could also have gone on to explain the mechanism of air breathing in reptiles which differs again, and also the fact that different fish can have different respiratory methods such as a swimbladder or that some fish that live on land also have lungs, only primitive fish have the gill, basic heart and tissue capillaries setup.

Quality of writing

Grammar, spelling and punctuation all to a high standard.


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