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Reason why multicellular organisms have materials exchange problems Essay

Multicellular organisms have materials-exchange problems because they have a small surface area to volume ratio.  As such they have a small surface area for the exchange of materials between the cells and their surroundings. Materials are not able to reach all parts of the cells quickly since the volume is too large relative to the surface area. Material exchange occurs through diffusion, osmosis and active transport – this is dependent on the size of the surface area. The larger the surface area the higher the rate of material exchange; and the small the surface area the slower the rate of material exchange (Farabee, 2006).

Three functions of the liver

The liver functions as a storage organ storing vitamins, minerals and irons until the body needs them. In addition, it converts glucose into glycogen and stores it until it is required by the body. Another function of the liver is that it makes bile acids which brake-down fat and enhances the absorption of vitamins A, D and E, all of which are found in fat by the body. A third function of the liver is that it functions as a purifying organ; it removes chemicals, alcohol, toxins and medicine from the bloodstream. These materials are sent to the kidney as urea to be excreted as urine or to the intestines to be excreted as faeces (Farabee, 2006).

Functions of the glomerulus

The function of the glomerulus is the ultra–filtration of blood plasma and small molecules contained in the plasma into the Bowman’s capsule (Farabee, 2006).

Functions of the proximal convoluted tubules

Proximal convoluted tubules reabsorb amino acids, glucose and salts from the filtrate that comes from the glomerulus back into the blood capillaries to ensure that they are not lost in the urine (Farabee, 2006).

Functions of loop of henle

The function of the loop of henle is at two levels. In the descending limb of the loop water is reabsorbed through the process of osmosis into the hypertonic medulla of the kidney. The ascending limb of the loop which is impermeable to water, removes salts from the medulla of the kidney. The water and salt balance helps to maintain blood volume (Farabee, 2006).

Functions of the distal convoluted tubule

The function of distal convoluted tubule is tubular secretion a process that involves active transport of material from the blood into the tubule. The secretion of hydrogen and bicarbonate ions, aids in the control of blood pH (Farabee, 2006).

Difference between digestion and assimilation

Digestion is the mechanical and chemical process of breaking down of food into smaller forms and contents that can be absorbed by the body and used to produce energy. Assimilation is the process of using the absorbed food nutrients to build or to be incorporated into cytoplasm of the cell for metabolism. The nutrients are used to form complex compounds of structural components (Farabee, 2006).

How common are vitamin-deficiency diseases in the United States

The lack of certain vitamins in the body results in vitamin-deficiency diseases. The most common vitamin – deficiency diseases in the United States are related to vitamin D deficiency. Out of the entire US population, 40 – 60 % is deficient in vitamin D. vitamin D is critical nutrient responsible for the preventive maintenance of all the body tissues. Vitamin D deficiency results in rickets and it has been linked colorectal cancer, ovarian cancer, breast cancer, kidney cancer, type I and II diabetes, metabolic syndrome, melanoma, cardiovascular diseases such as heart attack, stroke and high blood pressure, periodontal disease, auto immune disorders, pre-eclampsia, difficult birthing, autism and other diseases. People with these diseases have been found to have low serum, blood, levels of vitamin D (Nicholson, 2009).

Recognizing when a person shifts from aerobic to anaerobic exercise

Aerobic exercises require large supplies of oxygen to generate energy while anaerobic exercises involve the production of energy by cellular tissues without relying on oxygen available. Anaerobic exercise is so fast and brief that it doesn’t rely on oxygen. As such when a person shifts from aerobic to anaerobic exercise, his or her body goes into emergency mode. This results in powerful performance on demand such as in brief and high intensity situations. If the body is pushed harder under anaerobic exercise, muscle cramps may develop due to the build-up of lactic acid which is a by-product of anaerobic respiration (Sample, 2007).

Reason why muscles are in antagonistic pairs

Muscles are arranged in antagonistic pairs such as biceps and triceps in order to produce opposite movements. Contraction of one muscle must be accompanied by the relaxation of the other muscle. Bicep causes bending of the muscle while triceps cause muscle to straighten (Farabee, 2006).

How B-cell and T-cell systems work to defend against diseases

B-cells produce a specific antibody into the body’s fluid which helps in killing of a specific disease causing organism. T-cells directly attack cells that have been infected by the microbe by injecting toxic substances into it so that the B-cells can produce antibodies (Farabee, 2006).

Two ways in which the function of the nervous system differ from the endocrine system

 Although both the nervous and endocrine systems maintain homeostasis, this function differs in the method of communication within and among cells, time taken in transmitting the communication, how quickly the response is impacted and how long it continues after the signal is ended. Two main ways that the nervous and endocrine systems differ in their function is therefore time and response. The endocrine is slow and has long term effects while the nervous system is fast and the effects are short lived.

The endocrine system communicates through hormones which are chemical messengers. They are transmitted in the bloodstream to distant part(s) of the body; this mode of transmition is slow but the effects are long term. The nervous system communicates via nerve impulses which are electrical signals which transmit information along nerve fibres; this mode of communication is fast and the effects are short lived (Farabee, 2006).

Definition of sexuality

Sexuality is defined as a concern with sexual activity, health, and intimacy; it is the aspect of one’s need for caring, touch and closeness. It can be categorized into biological sexuality which involves sexual intercourse and sexual contact in all its forms and medical concerns such as psychological aspects of sexual behaviour, sociological sexuality that covers the political, legal and cultural aspects; and philosophical sexuality that include the ethical, moral, spiritual or religious aspects. (Barret , 1999).


Farabee, M.  J. (2006). Online biology book. Retrieved June 13, 2009 from http//:www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html.

Nicholson, L. (2009). Vitamin Deficiency Epidemic in the United States. Retrieved June 11, 2009, from http://ezinearticles.com/?Vitamin-Deficiency-Epidemic-in-the-United-States&id=1903086

Sample, E. (2007). The Difference Between Aerobic and Anaerobic Exercises. Retrieved June 13, 2009, from http://ezinearticles.com/?The-Difference-Between-Aerobic-and-Anaerobic-Exercises&id=441985

Barret , M, (1999). Sexuality and Multiple Sclerosis. University of Tosronto, Canada.

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