Homework Assignment Essay

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1. List three abiotic factors in the environment of a fish. The abiotic factors in the aquatic ecosystems include temperature of the water, salinity of the water, presence of dissolve gases such as oxygen and carbon dioxide. 2. Describe two ways that decomposers differ from herbivores. Decomposers are organisms that feed on dead and decaying material including the waste material of other organisms. As they break down complex substances into simpler ones, they provide essential nutrients to other organisms.

The decomposers include several organisms including bacteria, fungi, insects, protozoan, mushrooms, and worms. Decomposers play a vital role in the food chain. Herbivores is an organisms that will not feed on decomposing plants, wastes or animals, but on leaves, roots, barks and other plant products. They include several organisms including parrots, koala, bear, rodents, butterflies, etc. 3. Why must people who live in countries that are not able to produce surplus food eat grains? People living in poor nations eat only food grains for two major reasons.

Firstly, it is very convenient to transport food grains as it does not need any industrial processing, packaging, etc. Secondly, consumption of complex foods including non-vegetarian food requires more energy (as energy may get passed along the food chain) and hence is too costly to afford to people living in poor nations. 4. Why is a food web better than a food chain as a way to describe a community? A food chain usually helps to describe a linear pattern of flow of energy from one level to another.

At different levels, the various animals that are existent would characterize a particular trophic level. In a community the food trophic levels would begin with plants and end with animals. However, a food chain is much more complex than a mere linear chain and would include complex interrelated networks. This would ensure that energy and food material would be disseminated through the entire community. The food wed would include herbivores, carnivores and decomposers. 5.

Describe two situations in which competition may involve combat and two that do not involve combat. An example of a competition non-combat is a situation in a rainforest in which trees would be growing close to each other and the trees that grow the tallest would be the healthiest. It is often found the trees that are short and find it difficult to get sunlight, often struggle and may not survive during the winter months. Another example of competition non-combat is cactus which grows in the desert.

Below the roots of the cactus tends to spread out and so that it is able to use every drop of water that may be present in the soil. An example of the combat competition occurs with big cats that try to exhibit some form of territorialism and would compete with other animals for food, area and mates. Another example for combat within the same species is the direct mating. Often the individuals with of the same sex would be competing with each other to obtain mate and to reproduce. 6. List three introduced species that have become pests, and explain why they became pests.

Introduced species are those species that have been introduced from another ecosystem or environment or would have spread outside their normal environment and threatens the biological diversity of the new environment that they have been introduced into. They are also known as invasive alien species and would include plants, animals, microorganisms, etc. Three alien species being introduced red fire ants (imported into the US from South America in the 1940s); Japanese beetle (introduced first in New Jersey in 1916 from Japan) and the Mediterranean fruit fly (that were introduced and eradicated from Florida and California several times).

7. List four kinds of limiting factors that help set the carrying capacity for a species. The four kinds of limiting factors include competition (ability to fight for food, water, territory, etc), predation (ability to hunt and consume the prey), parasitism (ability of an organism to draw nutrition and other facilities from the host) and crowding (lack of space between the users). 8. Describe four ways in which two populations of the same species can differ.

Two populations of the same species can differ in various aspects including proportion of the genders, phenotypic composition, genetic composition, behavior and variations of behavior, etc. 9. As the human population continues to grow, what should we expect to happen to other species? Often as the human populations tend to grow and increasing, they would be infringing on the other species and threatening their survival to a serious extent. Man depends on plants and animals, and often it is found that human growth would be directly threatening other species.

Any species that seems to be a threat to human would be endangered and many have already become extinct. 10. What forces will ultimately lead to the control of human population growth? There are several factors that could help control the population of human growth including rates of infertility, spread of serious diseases such as HIV/AIDS, limitations of resources that would support growth and development, increase in natural disasters, human conflict leading to wars, etc. References

Do Not Eat US. Org (2009). What Has Eyes, Intelligent People Do Not Eat, Retrieved on June 8, 2009, from Web site: http://www. donoteatus. org/what_has_eyes_s443_layout2. htm Global Change (2006). Population Growth over Human History, Retrieved on June 8, 2009, from Web site: http://www. globalchange. umich. edu/globalchange2/current/lectures/human_pop/human_pop. html Jeffrey, D. W. (1987). Soil-plant relationships, US: Taylor & Francis. http://books. google. co. in/books? id=hTwOAAAAQAAJ

McCluney, R. (2004). How Many People Should the Earth Support? , Retrieved on June 8, 2009, from Web site: http://www. ecofuture. org/pop/rpts/mccluney_maxpop. html Meyer, J. R. (2003). Alien Species, Retrieved on June 8, 2009, from Web site: http://www. cals. ncsu. edu/course/ent425/text18/exotics. html Zunick (2008). Biology Chapters 4 & 5 Notes populations & Communities, Retrieved on June 8, 2009, from Web site: http://zunick. com/BioChapters/BioChapter6_files/BioNotes4-6. pdf.

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