biology essay cycles

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Biology library

Course: biology library   >   unit 28, intro to biogeochemical cycles.

• Biogeochemical cycles overview
• The water cycle
• The carbon cycle
• The nitrogen cycle
• The phosphorus cycle
• Phosphorus cycle
• Eutrophication and dead zones
• Biogeochemical cycles
• Energy flows through an ecosystem and is dissipated as heat, but chemical elements are recycled.
• The ways in which an element—or compound such as water—moves between its various living and nonliving forms and locations in the biosphere is called a biogeochemical cycle .
• Biogeochemical cycles important to living organisms include the water, carbon, nitrogen, phosphorus, and sulfur cycles.

Introduction

Energy flows, but matter is recycled., which biogeochemical cycles are key to life.

• Carbon is found in all organic macromolecules and is also a key component of fossil fuels. See the carbon cycle article for more info.
• Nitrogen is needed for our DNA ‍   , RNA ‍   , and proteins and is critical to human agriculture. See the nitrogen cycle article for more info.
• Phosphorus is a key component of DNA ‍   and RNA ‍   and is one of the main ingredients—along with nitrogen—in artificial fertilizers used in agriculture. See phosphorus cycle article for more info.
• Sulfur is key to protein structure and is released to the atmosphere by the burning of fossil fuels.

Attribution

• " Biogeochemical cycles " by Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne, CC BY 4.0 . Download the original article for free at http://cnx.org/contents/[email protected]
• " Biogeochemical cycles " by OpenStax College, Concepts of Biology, CC BY 4.0 . Download the original article for free at http://cnx.org/contents/[email protected]

Works cited

• Brian Kross, "How Many Atoms Are in the Human Body?" Jefferson Lab, accessed June 9, 2016, http://education.jlab.org/qa/mathatom_04.html .

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Free Biology Essay Examples & Writing Tips

Don’t know what to write about in your essay on biology? Looking for good biology essay examples for inspiration? This article has all you need!

A biology essay is a type of academic paper that focuses on a particular topic of biology. It can discuss animal life, cycles in biology, or a botanic subject. You will need to demonstrate your critical thinking skills and provide relevant evidence to support your perspective.

On this page, you will find examples of biology essays. You will also find here tips and topics prepared by our experts . They can assist you in nailing your short or extended essay.

Areas of Research for Biology Essays

If you’ve been assigned to write a biology essay, you probably know which area of research you have to choose. However, it might be beneficial to explore other available scopes. It’s useful for both interdisciplinary study and the cases when you are free to pick your area of research. In this section, let’s figure out what you can study in biology.

Here are biological areas of research you should be familiar with:

• Cancer Biology studies this type of disease to prevent, detect, diagnose and cure it. The ultimate goal of such biologists is to eliminate cancer.
• Cell Biology is a branch that studies the structure, function, and behavior of cells. Here, biologists study healthy and sick cells to produce vaccines, medication, etc.
• Biochemistry is an application of chemistry to the study of biological processes on cell and molecular levels. It is a cross-discipline between chemistry and biology. The focus is on the chemical processes of living organisms.
• Computation Biology is a study of biological data that develops algorithms and models to understand biological systems. Here, scientists either work for institutions or research for private enterprises.
• Genetics is an area that focuses on the study of genes and genetic variations for health benefits. It looks at the way DNA affects certain diseases.
• Human Disease is an area within which scientists study different diseases. The field covers cancer, developmental disorders, disease genes, etc.
• Immunology is a branch of biology that focuses on immunity. Immunologists look at the way the body responds to viruses as a way to protect the organism.
• Microbiology studies all living organisms that are too small for our eye to see. It includes bacteria, viruses, fungi, and other microorganisms.
• Neurobiology is the study of the nervous system. Biologists examine the way the brain works and look into brain illnesses.
• Stem Cell and Developmental Biology seeks to examine how the processes behind stem cell’s ability transform cells. The biologists in this area use the power of stem cells to model human illnesses.

Essay on Biology: Writing Tips

Want to know how to start a biology essay? Wondering about the best way to write your essay on biology? Then check out the following tips.

When you’re writing about biology, pay attention to the following features:

• Introduction . Just as in any other form of academic writing, the first section of your paper introduces the subject. Here, explain why your ideas are relevant to biology as a science.
• Thesis Statement. The final one or two sentences of the first paragraph should include your original hypothesis and experiment. You will be proving them in the main body. You do not have to include the results as the reader will encounter them later. If you’re struggling with this part, try our thesis generator .
• Main Body. In this part, write about all the experiments in detail. Often, teachers require to include visual aid to prove your point. For Zoology, Anatomy, Botany, it is pretty easy to find some photos and illustrations.
• Conclusion. Here, restate your thesis. Reemphasize the most critical aspects described in the main body. You can do it by using our summarizing tool . The goal of this last paragraph is to leave an everlasting impression on the reader.

Thank you for reading our article. We hope you found it helpful. Share it with your class peers who also study biology. Additionally, have a look at the biological essay examples below.

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Timed A-level Biology Essay by A* Student - Cycles in Biology

Subject: Biology

Age range: 16+

Resource type: Unit of work

Last updated

7 February 2023

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A-level biology essay titled “Cycles in biology”.

Written by a year 13 biology student in 2018 who achieved an A* in biology A-level and graduated from Cambridge University with a First in Natural Sciences. Written in 45 minutes without access to notes. Essay is 920 words long .

Featuring the following content: Nitrogen cycle Phosphorus cycle Photosynthetic cycles Predator prey cycles Cardiac cycle Cell cycle

Useful for revision and for gauging the quality of an essay produced under timed conditions by an A* student.

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(Essay question) How are cycles important in biology?

To obtain a top mark in an essay for A-level Biology it is vital that you mention areas covered under all the modules of the course- the questions that are asked are usually very broad and your answer should mirror that! Cycles occur all over biology and this is a good example of a question where you should be able to mention an extensive range of subjects. I would aim to include the following: 1. The cell cycle including G1 (in which some organelles are replicated), S phase (in which DNA is replicated) and G2 then mitosis. This should include detail on the stages of mitosis. 2. The Krebs cycle should also be mentioned as part of respiration which occurs in the mitochondrion. 3. The cardiac cycle is another important one to mention- the control of contraction and relaxation of cardiac muscle by an electrical impulse (Include an account of how the impulse is initiated and propagates through the atria and then the ventricles) 4.   The carbon cycle 5.   The Calvin cycle 6. The menstrual cycle 7.    PCR should be included as a key procedure commonly used in labs. Include a list of all the ‘ingredients’ required and a description of the procedure Top tips for those aiming for an A*: -Get creative in including links between your different subject areas and paragraphs -Ensure that everything you mention is relevant to the question being asked and explain why it is relevant

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Cycles in Biology.

Cycles in Biology

A cycle is an interval during which a recurring sequence of events occurs. Cycles are a hugely relevant component of biology. Practically everything has to be recycled as every resource, to some extent, is a non-renewable resource.  There are cycles in all aspects of biology that can be explored.

Life-materials are the basic particles of Earth, called elements, that all living organisms build their bodies from. They are sometimes called "bio-elements." All living organisms are made primarily of six elements, all in the same proportion: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulphur. Most organisms require small, often tiny, amounts of additional such as iron, copper and iodine. Most plants require a total of twenty-three different nutrients to flourish.

Essential nutrients are limited. We use them for energy to power our bodies (food for metabolism) and as materials to build and renew our bodies. We renew or rebuild our bodies over and over, every day. Nutrients are all recycled so organisms can share them over time. This sharing process is called the Nutrient Cycle. These nutrients have been shared over and over for billions of years. Every organism alive on earth is made of nutrients that have been used and re-used over and over again. Certain human activities may altar the nutrient cycles.  

Living organisms continually release nutrients from their bodies, in the form of wastes, which are really by-products or leftovers from metabolism. Life takes every opportunity to be creative. One organism's wastes become another organism's nutrients. Every animal on Earth releases carbon dioxide as they breathe. It acts as a bi-product, and useless to them; but to every plant on Earth, that carbon dioxide is a necessary nutrient for photosynthesis and continuing life. The plants, in turn, release oxygen into the air, which is necessary for animals. Life on Earth is a balanced process of exchanging each other's leftovers for mutual benefit. Organisms release all their nutrients when they die and are decomposed by fungi and bacteria. Gradually, every part of an organism decomposes and returns to the Nutrient Cycle.

Water is a molecule made of two atoms of Hydrogen (H) and one atom of Oxygen (O). Its chemical formula is H 2 O. Water is reused over and over again. This recycling of Earth's water has been going on for billions of years and is named The Water Cycle. Heat from the sun changes liquid surface water (oceans, lakes, wetlands rivers) into gas water vapour, which rises into the air, known as evaporation. Above the ocean and rain forests, water vapour gathers into clouds. Winds move the clouds of vapour. The clouds release their water in liquid precipitation (rain) or crystal precipitation (snow). The water runs off, or soaks into the ground, and eventually, some of it flows into the ocean, where the cycle is repeated.

Another huge source of water vapour in the air is plants. This is called   transpiration. Transpiration is the evaporation of water from plants. It occurs chiefly at the leaves while their stomata are open for the passage of CO 2  and O 2  during photosynthesis. Air that is not fully saturated with water vapour (100% relative humidity) will dry the surfaces of cells with which it comes in contact, so the photosynthesising leaf loses substantial amount of water by evaporation. This transpired water must be replaced by the transport of more water from the soil to the leaves through the xylem of the roots

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The Carbon Cycle is a complex series of processes through which all of the carbon atoms in existence rotate. All life is based on the element carbon . Carbon is the major chemical constituent of most organic matter, from fossil fuels to the complex molecules (DNA and RNA) that control genetic reproduction in organisms yet carbon is not one of the most abundant elements within the Earth's crust. Carbon is stored on our planet in major sinks. It is stored as organic molecules in living and dead organisms found in the biosphere; as the gas carbon dioxide in the atmosphere; as organic matter in soils; in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk; and in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms.

Ecosystems gain most of their carbon dioxide from the atmosphere. A number of autotrophic organisms have specialized mechanisms that allow for absorption of this element into their cells. These organisms use photosynthesis to chemically convert the carbon dioxide to carbon-based sugar molecules. These molecules can then be chemically modified by these organisms through the metabolic addition of other elements to produce more complex compounds like proteins, cellulose, and amino acids.

Carbon dioxide enters the waters of the ocean by diffusion. Once dissolved in seawater, the carbon dioxide can remain as is or can be converted into carbonate or bicarbonate. Certain forms of sea life produce calcium carbonate. This substance is used to produce shells and other body parts by organisms. When these organisms die, their shells and body parts sink to the ocean floor where they accumulate as carbonate-rich deposits. After long periods of time, these deposits are physically and chemically altered into sedimentary rocks. Ocean deposits are by far the biggest sinks of carbon on the planet.

Carbon is released from ecosystems as carbon dioxide gas by the process of respiration. Respiration takes place in both plants and animals and involves the breakdown of carbon-based organic molecules into carbon dioxide gas and some other compound by products.

Carbon is stored in the lithosphere in both inorganic and organic forms. Inorganic deposits of carbon in the lithosphere include fossil fuels like coal, oil, and natural gas, oil shale, and carbonate based sedimentary deposits like limestone. Organic forms of carbon in the lithosphere include litter, organic matter, and substances found in soils. Some carbon dioxide is released from the interior of the lithosphere by volcanoes.

The nitrogen cycle is the complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere and hydrosphere. The nitrogen cycle represents one of the most important nutrient cycles found in the earths ecosystems and almost all of the nitrogen found in any ecosystem originally came from the atmosphere. Nitrogen is used by living organisms to produce a number of complex organic molecules such as amino acids, proteins, and nucleic acids. The largest store of nitrogen is found in the atmosphere where it exists as a gas. Other major stores of nitrogen include organic matter in soil and the oceans. Despite its abundance in the atmosphere, nitrogen is often the most limiting nutrient for plant growth as they can only take up nitrogen in certain forms. Most plants obtain the nitrogen they need as inorganic nitrate from the soil solution. Animals receive the required nitrogen they need for metabolism, growth, and reproduction by the consumption of living or dead organic matter containing molecules composed partially of nitrogen.

In most ecosystems nitrogen is primarily stored in living and dead organic matter. This organic nitrogen is converted into inorganic forms when it re-enters the biogeochemical cycle via decomposition. Decomposers, found in the upper soil layer, chemically modify the nitrogen found in organic matter.

Eutrophication alters the way in which the nutrient cycles occur. Natural eutrophication is the process by which lakes gradually age and become more productive. It normally takes thousands of years to progress. However, humans, through their various cultural activities, have greatly accelerated this process in thousands of lakes around the globe. Water pollution occurs caused by excessive plant nutrients. Humans add excessive amounts of plant nutrients (primarily phosphorus, nitrogen, and carbon) to streams and lakes in various ways. Runoff from agricultural fields, field lots, urban lawns, and golf courses is one source of these nutrients. Untreated, or partially treated, domestic sewage is another major source. Sewage was a particular source of phosphorus to lakes when detergents contained large amounts of phosphates. The phosphates acted as water softeners to improve the cleaning action, but they also proved to be powerful stimulants to algal growth when they were washed or flushed into lakes.

The excessive growth of algae promoted by these phosphates changed water quality in many lakes. This led to oxygen depletion resulting in the death of many fish. Species resistant to these conditions replaced the native fish. Beaches and shorelines were fouled by masses of rotting, stinking algae. A means to control this problem became a paramount need. Testing concluded that phosphorus was the key nutrient for the control of eutropication.

There are a number of cycles that take place in humans. The menstrual cycle is a cycle that only occurs in females. It involves the preparation of the uterus each month for a fertilised egg. Hormones control the process that occurs and forms a monthly cycle. The hypothalamus is a gland in the brain responsible for regulating the body's thirst, hunger; sleep patterns, libido and endocrine functions. It releases the chemical messenger Follicle Stimulating Hormone Releasing Factor (FSH-RF) to tell the pituitary gland in the brain to secrete Follicle Stimulating Hormone (FSH) and a little Leutenising Hormone (LH) into the bloodstream, which cause the follicles to begin to mature.

The maturing follicles then release another hormone, oestrogen. As the follicles mature over a period of about seven days, they secrete more and more oestrogen into the bloodstream. Oestrogen causes the lining of the uterus to thicken. When the oestrogen level reaches a certain point it causes the hypothalamus to release Leutenising Hormone Releasing Factor (LH-RF) causing the pituitary to release a large amount of Leutenising Hormone (LH). This surge of LH triggers the mature follicle to burst open and release an egg. This is called ovulation.

Inside the Fallopian tube, the egg is carried along by tiny, hair-like projections, called "cilia" toward the uterus. Fertilization occurs if sperm are present as the live egg reaches the uterus.

If fertilisation occurs, the female becomes pregnant and initially the corpus luteum secretes sufficient progesterone to maintain the uterus lining and sustain the developing embryo.  After this, the placenta takes over, where progesterone (and some oestrogen) from the placenta, maintain the uterine lining and inhibit the development of further egg production, so during pregnancy the menstrual cycle stops as the specific hormones are not produced. At the end of pregnancy, progesterone levels fall, and high oestrogen levels trigger the onset of labour. After pregnancy, the menstrual cycle resumes as the correct hormones are being produced for its onset.

The Calvin cycle is a series of biochemical, enzyme-mediated reactions during which atmospheric carbon dioxide is reduced and incorporated into organic molecules, eventually some of this forms sugars . In eukaryotes, this occurs in the stroma of the chloroplast.

Krebs cycle or the citric acid cycle or tricarboxylic acid cycle, occurs in mitochondria, is the common pathway to completely oxidize fuel molecules, which mostly is acetylcholine, the product from the oxidative decarboxylation of pyruvate. It enters the cycle and passes ten steps of reactions that yield energy and CO2

The Krebs cycle is also known as the tricarboxylic acid (TCA) cycle and as the citric acid cycle. The Krebs cycle takes place in the mitochondria and consists of eight steps. The first reaction of the cycle occurs when acetylcholine transfers its two-carbon acetyl group to the four-carbon compound oxaloacetate, forming citrate, a six-carbon compound. The citrate then goes through a series of chemical transformations, losing first one and then a second carboxyl group as carbon dioxide. Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD+, forming NADH. For each acetyl group that enters the Krebs cycle, three molecules of NAD+ are reduced to NADH. In Step 6, electrons are transferred to the electron acceptor FAD rather than to NAD+.

In one turn of the citric acid cycle, two molecules of carbon dioxide and eight hydrogen atoms are removed, forming three NADH and one FADH2. The carbon dioxide produced accounts for the two carbon atoms of the acetyl group that entered the citric acid cycle. These hydrogens come from water molecules that are added during the reactions of the cycle.

Because two acetylcholine molecules are produced from each glucose molecule, the cycle must turn twice to process each glucose. At the end of each turn of the cycle, the four-carbon oxaloacetate is left, and the cycle is ready for another turn. After two turns of the cycle, the original glucose molecule has lost all of its carbons and may be regarded as having been completely consumed. Only one molecule of ATP is produced directly with each turn of the citric acid cycle. The rest of the ATP that is formed during aerobic respiration is produced by the electron transport system.

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• Word Count 2129
• Page Count 4
• Level AS and A Level
• Subject Science

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