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Cell Reactions in Metabolic and Aerobic Changes

Obligate anaerobes are organism that cannot live with the presence of oxygen, meaning they live without oxygen and cannot survive with the presence of oxygen. If to compare with obligate aerobes on the other hand, obligate aerobes only can live with the presence of oxygen. According to the question, facultative anaerobes can live in both condition, which is with or without the presence of oxygen. An example of obligate anaerobe is clostridium tetani (tetanus). An example of facultative anaerobe is vibrio cholerae (cholera). (source- nelson’s biology page 92)
Clostridium species include bacteria that produce serious infections in humans.
(a) Are Clostridium species obligate aerobes, obligate anaerobes, or facultative anaerobes? Explain.
Clostridium species are obligate anaerobes. This means that they cannot live with the presence of oxygen. (source –
(b) What waste products of energy metabolism do Clostridium species excrete?
Waste products of energy metabolism that Clostridium species excrete is toxins. (source –
(c) Describe three infections in humans caused by Clostridium species.
The three infections in humans that is caused by Clostridium species are clostridium perfringens, clostridium clostridioforme, and clostridium tertrium. Clostridium perfringens is related to gastrointestinal disease. Clostridium clostridioforme is related to liver abscess. Clostridium tertrium is related to brain abscess.

How do ADP and ATP differ in structure? In free energy content?
The structure of ATP or also known as Adenosine Tri-Phosphate has 5 carbon ribose sugar. It is a small molecule. It is also nitrogenous based. Based on it’s name which is obvious, it has 3 phosphates. As for the structure for ADP or also known as adenosine diphosphate. The difference is that adesonice diphosphate has 2 phosphate compared to ATP which has 3 phosphates. From my understanding, these molecules release energy when everytime a phosphate is removed from the structure. For an example when the outer most phosphate atom is released from the tri-phosphate structure, free energy is released. From this process also, the molecule becomes adenosine diphosphate or ADP. If another phosphate is released from ADP, free energy will be released again. When this happens, the molecule structure will only have one phosphate, so it will be named adenosine monophosphate or AMP. The rate of energy released when ATP is converted to ADP from the process of removal of the phosphate is about 30.5KJ/mol. In the human body, the total amount of ATP ADP will always be at constant rate because it is converted from ADP to ATP or vice versa constantly.

Arrange the following types of cells in order of increasing number of mitochondria in the cytoplasm: nerve cell, skin cell, fat cell, heart muscle cell. Provide a rationale for your sequence.
According to my opinion, the least most number of mitochondria in the cytoplasm is the fat cell. This is because there is no significance movement of the body, and the function of the fat cells is just to store fat. Therefore, not much of energy is needed for this process. The second most number of mitochondria in the cytoplasm is the skin cell. Again, the skin cells do not require much energy. The third most number of mitochondria in the cytoplasm is the nerve cell. The nerve cells require a significant amount of energy because it transfers nerve impulse throughout the body along the spinal chord and periphery system at very fast rate. It requires information to be transferred at the synapse from the brain to the rest of the body and vice versa. The most number of mitochondria in the cytoplasm has got to be the heart muscle cell. The heart is the primary or the most important muscle in all our system. Without the function of the heart, a person cannot live. This is because the hearts role to pump the oxygenated and deoxygenated blood through our body at very high pressure. In order to pump the blood throughout the body, the heart muscle needs great amount of constant energy source, which in this case is the mitochondria. (no source)
(a) Why is every reaction of cellular respiration catalyzed by a specific enzyme?
Enzyme is a protein catalyst and is found throughout the human body. Enzyme plays an important role to make sure that every process is carried out. Basically, if there are no enzymes, no process will take place. Each enzyme is specific to its reactants and its process. For an example, enzyme related to cellular respiration do not catalyze reactants for reproduction processes, cardiovascular enzymes do not react or bind with hormonal production enzyme, and so forth. So, each enzyme has its own role and do not mixup with each other. This can be described by the term ‘lock and key’. The enzymes ensures that each cellular respiration process happens on time, and also in order. (source-
(b) What would happen to an organism that lacked the gene for hexokinase, the enzyme that catalyzes the first reaction in glycolysis?
The first step in glycolysis is already the phosphorylation of of glucose by the enzyme called hexokinase. This is the first step, hence it plays the most important role. So, if an organism lacks the gene for hexokinase, my opinion is that the cellular respiration would not likely to happen. (source –
10. Describe the function of NAD and FAD in cellular respiration.
NAD and FAD has important role in the process of glycolysis, pyruvate oxidation and the Krebs Cycle as it co-relates with each other. NAD which also is known as nicotinamide adenine dinucleotide and FAD which is also known as flavin adenine dinucleotide. NAD functions in oxidative phosphorylation by removing two hydrogen atoms which consists of two protons and electrons. NAD is used to shuttle the electrons to the first component. So when two hydrogen atoms is removed, two electrons and a proton is then attached to NAD and then it becomes NADH. NADH is already oxidized, meaning the oxygen atoms are removed. FAD also function almost the same like NAD. Like NAD, FAD also remove two hydrogen atoms and becomes FADH. This process happens in the Krebs cycle. When NAD and FAD is reduced to become NADH and FADH, it actually releases energy which is transferred to the ATP molecules. Below is a diagram of the Krebs cycle. (source – nelson’s biology page 96-105) (image source – googleimages)
Why is aerobic respiration a more efficient energy-extracting process than glycolysis alone?
Well, first of all, if we see in numbers, aerobic respiration produces about 36ATP meanwhile glycolysis produce only 2 ATP. From these numbers, in can be concluded that aerobic respiration is more efficient energy-extracting process than glycolysis. This is because during glycolysis, only about 2% of the energy is being harnessed. As for aerobic respiration, the energy harnessing process is more thorough and complete. In fact, by the end of the krebs cycle, the whole glucose structure is broken down and all the energy is harnessed into ATP’s. (source –
(a) Distinguish between metabolic rate and basal metabolic rate.
According to Nelson’s biology, the metabolic rate is defined as the amount of energy consumed by an organism at a particular time. Basal metabolic rate or BMR is defined as the minimum energy that is required by an organism to survive. (source- nelson’s biology page 110 and 111)
(b) Explain how and why metabolic rate changes as we grow older.
Metabolism is often associated with one’s weight or rate of weight gaining. This is also correct. Metabolism is actually very wide and is often defined as the rate of chemical process in our body. Different individuals have different metabolic rate. When we are young, our body is in our prime state. Our muscles are strong. Our bones are tough, we carry out daily activities which consumes alot of energy. Actually, metabolic rate fluctuates regularly depending on the person’s daily physical activity. If a person’s daily activity is rigid and requires alot of energy, the metabolic rate will be higher. This means that the rate of chemical process that occur in the body will be of greater speed. All the production of hormones and other processes will be faster. Now back to the question, as we grow older, our metabolic rate is actually becoming lower. The term for this is declining in efficiency. This will normally lead to death of the time once the body has completely been broken down, meaning the bodily functions becoming absolutely zero. The main source of energy is in the form of ATP. As we know, ATP requires oxygen. As we age, our respiration rate becomes slower. When our respiration rate becomes slower, hence, the production of ATP’s will decrease. This will lead to energy insufficiency. Another source of energy is from carbohydrates and other nutrients. As we grow older, our digestion function tends to become less optimum. This will result in poor digestion of the nutrients to supply energy. When the energy is less, the metabolic rate will become less as well. Basically, all of these points that I have given relates to the changes of the metabolic rate as we grow older. (source

Food Processing Strategies for Quality

Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry. Food processing typically takes clean, harvested crops or butchered animal products and uses these to produce attractive, marketable and often long shelf-life food products. Similar processes are used to produce animal feed.
Food processing encompasses all the steps that food goes through from the time it is harvested to the time it arrives on consumer’s plate. According to Food and Agriculture Organization (FAO), processed foods can be classified into three types (1) Primary (2) Secondary and (3) Tertiary. The primary processing includes basic cleaning, grading and packaging as in case of fruits and vegetables. Secondary processing includes alteration of the basic product to a stage just before the final preparation as in case of milling of paddy to rice. Tertiary processing leads to a high value-added ready-to eat food like bakery products, instant foods, health drinks, etc.
Traditional food processing had two functions: to make food more digestible and to preserve food during times of scarcity. Most crops are seasonal. There are times of the year when either glut can result in high levels of wastage or shortages can arise if adequate measures are not taken to preserve and store the foods. This is particularly important in areas that have a dry season or winter period when crops cannot be grown and animals are slaughtered because of a lack of fodder. In these situations stored dry grains or root crops provide energy; dried, salted or smoked meats, or cheeses provide a source of protein, vitamins and minerals; and processed fruits and vegetables such as pickles, chutneys or dried fruits or leaves provide vitamins and minerals. A few crops, including cassava and some types of beans also contain poisons or anti-nutritional components, which must be removed by processing to make the food safe to eat. Hence, Food processing enables to maintain the health of the human beings throughout the year by increasing its food security.
By processing food, it can be customized to suit the nutritional requirements of groups such as the elderly, pregnant women, infants, young children and athletes. Such foods are characterized by a balanced composition of energy suppliers in the form of fats, carbohydrates and proteins, and by a cocktail of vitamins and minerals composed according to the current state of scientific knowledge. Food processing is a route to creating sustainable livelihoods and economic development for rural communities.
Sophisticated technologies define modern food production. They include many areas. Agricultural machinery, led by the tractor, has reduced the human labor in many areas of production. Biotechnology is driving much change, in areas as diverse as agrochemicals, plant breeding and food processing. Many other areas of technology are also involved, to the point where it is hard to find an area that does not have a direct impact on the food industry. Computer technology is also a central force, with computer networks and specialized software providing the support infrastructure to allow global movement of the myriad components involved.
Modern food processing has three major aims: To make food safe (microbiologically, chemically)
To provide products of the highest quality (flavour, colour, texture)
To make food into forms that is convenient (ease of use)
The following table summarizes the item to be controlled in food processing and comments on the major approaches involved in this control.
To be Controlled
Active water
Prevents growth
Reduces growth rate
Preservatives retard growth
Do not grow below Aw of 0.6
Reduces numbers
Destroyed by heat activity
Decrease reaction rate
Modify activity
Alters rate of enzyme activity
increase ES complex formation
Chemical Reactions
Increases chemical rate, browning, oxidation
Reduces reaction rate
May inhibit or activate
Can alter rate of reaction, like oxidation
Not applicable
Physical Structure
Increases effects
Decreases effects
May modify structure
High. Aw may cause caking
Can destroy structures
The significant benefits for different stakeholders involved in food processing are:
Farmer – higher yield, better farm realization, lower risk
Consumer – greater variety, lower prices, new products
Companies – new business opportunities, demand growth
Economy/Government – Employment generation, reduced rural migration
The emerging opportunities in food processing are interesting and challenging as well.
NEED FOR FOOD PROCESSING Once food is harvested, it begins to deteriorate immediately due to the following factors:
micro-organisms (yeast, mould, bacteria);
intrinsic enzymes;
moisture; and
Insects and vermin
Because of the risk of spoilage, much of our food is processed in some way to increase its availability. A food is considered preserved once it is stabilized with respect to safety and quality.
Nearly every food preparation process reduces the amount of nutrients in food. In particular, processes that expose foods to high levels of heat, light, and/or oxygen cause the greatest nutrient loss. Nutrients can also be “washed out” of foods by fluids that are introduced during a cooking process. For example, boiling a potato can cause much of the potato’s B and C vitamins to migrate to the boiling water. We can still benefit from these nutrients if we consume the liquid (i.e. if the potato and water are being turned into potato soup), but not if we throw away the liquid. Similar losses also occur when we broil, roast, or fry in oil, and then drain off the drippings.
It’s important to note that no type of food processing can transform poor quality raw materials into good ones. It can only increase the product’s shelf life. To ensure that product meets high standards:
use the highest quality raw ingredients;
establish good processing techniques-and follow them; and
Maintain an appropriate product environment after processing.
Not all processing methods are applied to foods to achieve preservation. Some are also used to change or stabilize food texturally.
Microorganisms require water, nutrient, oxygen and a suitable temperature for optimal growth and reproduction.
Microorganism can only survive in condition with optimum pH and solute concentration as these will not destroy them. Food can be preserved by destroying the microorganism present in the food or by stopping the activities of these microorganisms
FOOD PROCESSING METHODS USED FOR FOOD PRESERVATION Methods of processing food can be divided into two main categories-chemical and physical.
Chemical Processing Methods The following techniques use the chemical approach in processing food.
Intermediate Moisture Foods (IMF) Binding the water that is present preserves intermediate moisture foods-for example, cookies, cake and bread. This reduces the availability of the water for deteriorative reactions.
Water is immobilized by adding permissible humectant additives such as glycerol, glycols, sorbitol, sugars and salts.
Generally, IMFs possess water activities that range from 0.6 to 0.85. This enables the food to be stable at room temperature, because the growth of most micro-organisms is inhibited at these levels.
Water Activity (aw) Water is the most important factor in controlling the rate of deterioration of a food. However, knowledge of the moisture content of a food is not sufficient to predict its stability. It is the availability of water for microbial, enzymatic, or chemical activity that determines the shelf life of foods. This water availability is measured as water activity (aw).
Water activity is measured on a scale of 0 to 1, where 0 indicates no water and 1 indicates all water. Food spoilage micro-organisms, in general, are inhibited in food where the water activity is below 0.6. However, if the pH of the food is less than 4.6, micro-organisms are inhibited when the water activity is below 0.85.
Addition of Chemicals The addition of some chemicals inhibits microbial growth in foods. These chemicals include not only those classified as preservatives. Salt, sugars, wood smoke and some spices also inhibit the growth of micro-organisms.
PH Control Almost every food, with the exception of egg whites and soda crackers, has a pH value of less than 7. Foods can be broadly categorized on the basis of their pH as high acid, acid, medium acid or low acid. Examples of each category include:
high acid (3.7) : apples, lemons, raspberries
acid (3.7 to 4.6) : oranges, olives, tomatoes (some)
medium acid (4.6 to 5.3) : bread, cheese, carrots
low acid (over 5.3) : meat, fish, most vegetables
Most micro-organisms grow best in the pH range of 6.5 to 7.5. Yeasts and moulds are capable of growing over a much broader pH range than bacteria. Few pathogens will grow below pH 4.0. This information is important, because it will help us in determining food stability with respect to microbial spoilage.
Physical Processing Methods A number of physical methods are available to you for processing foods.
Sterilization (Retorting) A pathogen is any microorganism that causes illness. Food pathogens cause food-borne illnesses such as food poisoning or food intoxication.
Sterilization destroys all pathogenic and spoilage micro-organisms in foods and inactivates enzymes by heating. All canned foods are sterilized in a retort (a large pressure cooker). This process enables food to have a shelf life of more than two years.
Foods that have a pH of more than 4.6, such as meat and most vegetables must undergo severe heating conditions to destroy all pathogens. These foods are heated under pressure to 121°C for varying times.
Severe conditions are applied to ensure that Clostridium botulinum spores are destroyed during processing. These spores produce the deadly botulinum toxin under anaerobic conditions (that is, where there’s no oxygen). The spores are destroyed by heat or are inhibited at pH values of less than 4.6. Therefore, a food with a pH of less than 4.6 that is packaged anaerobically, such as spaghetti sauce, doesn’t need to undergo such a severe heat treatment.
Pasteurization Pasteurization is the process of heating a food-usually a liquid-to or below its boiling point for a defined period of time. The purpose is to destroy all pathogens, reduce the number of bacteria, inactivate enzymes and extend the shelf life of a food product.
Foods with a pH of less than 4.6, such as milk and spaghetti sauce, can be pasteurized.
Permanent stability-that is, shelf life of about two years-is obtained with foods that can withstand prolonged heating, such as bottled juices.
There is a greater loss of flavour from foods that are exposed to a longer time-temperature relationship. Therefore, temporary stability (that is, limited shelf life) is only obtained with some foods where prolonged heating would destroy its quality. These foods, such as milk, usually require subsequent refrigeration.
“High temperature short time” (HTST) and “ultra high temperature” (UHT) processes have been developed to retain a food’s texture and flavour quality parameters.
Blanching Blanching is a slight heat treatment, using hot water or steam that is applied mostly to vegetables before canning or freezing.
Blanching is used before freezing to inactivate enzymes present that cause deteriorative reactions to foods during frozen storage. These reactions include colour and texture changes, off-flavours and a decrease in nutritional value.
Blanching is used before canning for different reasons, because enzymes will inevitably be destroyed during canning. Blanching induces a vacuum in canned goods, and it’s also used to control the fill into containers (for example, spinach).
Microwaving Microwave ovens are rarely used for processing large quantities of food. They are mainly of interest if you cater to the convenience food market.
Microwave ovens use electromagnetic radiation to excite water molecules in food. The actual waves penetrate only about 10 inches from the source of the radiation. Within the food, the waves only penetrate 3.4 to 1 inch on all sides. As a result, the actual ovens must be limited in size. Heat is produced within the food by the friction of water molecules, which spreads to the centre of the food by conduction.
Small portions are cooked rapidly in microwave ovens. As the quantity of food increases, however, the efficiency is lost.
Frying Frying differs from other methods of heat processing in that the cooking medium is hot oil. Because of the big difference between the temperature of the oil and the food, as well as the small size of the food pieces, cooking is completed in a relatively short time-anywhere from 20 seconds to six minutes.
Fried foods are known for their characteristic crispy outer surface as well as their high fat content. The fat that is absorbed by the food product varies from 10 percent to 40 percent, depending on the time the food is immersed in the oil. Continuous fryers are often used in the food industry.
Refrigeration Refrigerators should be set to below 4°C to control the growth of micro-organisms in foods. This lowered temperature also reduces the respiration rate of fruits and vegetables, which retards reactions that promote spoilage.
Refrigeration is generally used to:
reduce spoilage during distribution of perishable foods;
increase the holding period between harvesting and processing
Extend the storage life of commercially processed foods.
Not all foods benefit from cold temperatures. For example, bananas turn black and bread goes stale when refrigerated.
Freezing While many home freezers are held at -10°C, commercial freezers are under -18°C. At this temperature, the growth of micro-organisms is almost stopped. Deteriorative microbial reactions will still occur, but over a much longer time.
In addition, deteriorative enzymatic reactions will still take place during frozen storage. Uncooked fruits and vegetables must be blanched before freezing to prevent these reactions.
During freezing, the water in food forms ice crystals. The rate of this phenomenon has a big impact on the quality of frozen foods:
Slow freezing (e.g. home freezer)
Large ice crystals formed, which puncture cell walls
Cellular fluid released
Results in shrunken appearance of thawed food
Rapid freezing (e.g. blast freezer)
small, numerous ice crystals formed
no change to cell structure
The shelf life of frozen foods is largely dependent on storage conditions. Under ideal conditions, frozen foods can have a shelf life of one year.
However, if foods are continuously exposed to warmer temperatures, such as the opening and closing of freezer doors, then heat shock occurs. Heat shock is when ice melts and re-forms into larger ice crystals. The best example is ice cream, which has a gritty texture if large ice crystals have developed.
Irradiation Irradiation is the controversial process of applying low doses of gamma radiation to food products. Research have shown that the process exhibits no safety hazard. As a result, irradiation is permitted in some countries to:
Prevent sprouting in potatoes and onions
Control insect infestation of wheat flour; and
Reduce the microbial load of ground spices
If irradiation becomes more widespread among various other food products, it is expected to replace fumigation, ensure hygienic quality and reduce the dependence on refrigeration.
Batch vs. Continuous Processing Food is processed in either discrete batches or a continuous system. Although there are advantages and disadvantages to each method, choice in the matter is restricted only to those replacing or setting up a new processing line. Generally, batch systems are used to produce small quantities of food, whereas larger volumes are required for continuous systems.
Advantages of Batch Processing Advantages of Continuous Processing Greater flexibility to change product
formulation and rates
Lower operation and labour costs
Lower equipment costs
Less floor space required
Easier operation and control
Greater product uniformity
Evaporation Evaporation is the partial removal of water from liquid foods by boiling. When the operation is done under vacuum, boiling is avoided and the food’s flavour qualities are retained.
Some of the foods that have undergone evaporation are evaporated milk, tomato paste and juice concentrates.
This process is carried out for three main reasons:
To reduce the weight and, therefore, reduce storage and transport costs
To preserve foods by decreasing the water activity and increasing the solids content
To provide consumers with convenient foods
Dehydration Dehydration-or drying-is the nearly complete removal of water from solid foods. One of the oldest methods of food preservation, it was traditionally carried out by the sun.
This application is used for the same reasons that liquid foods undergo evaporation-preservation, convenience and cost savings. Dried soup mixes, dried fruit, powdered milk and spices are just a few examples of dehydrated foods.
Spray drying and freeze drying are two drying methods used widely today. Spray drying is when a liquid food is atomized into a fine, dry powder. Examples include natural and artificial flavours and milk powders. Freeze drying involves first freezing the food and then driving off the ice, leaving a high quality, porous dried food such as instant coffee.
Emulsions An emulsion is a system containing two liquid phases that don’t mix, where one phase (dispersed phase) is distributed throughout the other phase (continuous phase) in the form of very small droplets. Generally there are two types of emulsions:
oil in water (O/W)
water in oil (W/O)
An example of an O/W emulsion is salad dressing, and an example of a W/O emulsion is butter.
Homogenization Homogenization is used to stabilize an emulsion. More specifically, it is the reduction in size and the increase in number of droplets of the dispersed phase by the application of intense shearing forces.
Generally, homogenization is applied to change the functional properties or improve the texture of emulsions. For example, most fluid milk sold at the retail level is homogenized to improve its stability, and most caramel fillings are homogenized to increase their smoothness.
Extrusion Extrusion is the process in which a food is compressed and worked to form a semi-solid mass. This mass is then forced through a restricted opening, or die, to create a desired texture or shape. The purpose of this application is simply to provide a greater variety of textured foods to consumers.
Food may also be cooked while extruded. This is referred to as extrusion cooking, or hot extrusion.
Some extruded food products are licorice, puffed wheat and cornflakes.
Hurdle or Combination Processing Hurdle technology is a concept that was developed to address the consumer demand for more natural, fresh-like foods. It is a way for food processors to employ only mild preservation techniques to their food products.
The idea is to use deliberate low-level combinations of existing and novel preservation techniques (“hurdles”) to eliminate the growth of micro-organisms. Lower-intensity individual methods can be used because of the collective effect of the combined methods. Some of the more common hurdles include:
water activity (aw)
freezing; modified atmosphere packaging (MAP)
Some micro-organisms present will be able to survive the individual treatments applied. However, no microorganism will be able to overcome all of the combined hurdles. Thus the food is stable and safe.
The only way to ensure that the correct combination of hurdle technologies is used is to make sure that a qualified resource conducts quality and safety shelf-life studies. For a list of product development laboratories that can do these studies, see the Resources section of this guide.
Examples of hurdle processing can be found in traditional and recently developed foods, such as yogurt and pre-packaged fresh salads. The hurdles employed in yogurt manufacture include low temperatures, high acid and competitive microbial flora. Those used to prepare pre-packaged fresh salads include low temperatures and modified atmospheres.
GLOBAL FOOD PROCESSING INDUSTRY The global processed food industry is estimated to be valued around EUR 2.5 trillion and accounts for three-fourth of the global food sales. The global food industry is ever changing and evolving. However, health, convenience and value continue to be the key value propositions in this industry.
Despite the large size of the industry, only 6 percent of processed foods are traded across borders compared to 16 percent of major bulk agricultural commodities. The United States and European Union together account for over 60 percent of total retail processed food sales in the world.
Trade liberalization policies through multi-lateral and regional trade agreements have led to a rapid growth in food processing. In the Asian region, Japan is the largest food processing market, but India and China are likely to grow at a faster rate in the next decade. The processed food industry is strong in Japan and South Korea, as they are the leading meat importing countries in the world and consumption of meat is high in these countries. The Australian processed food industry is one of the most technically advanced in the world and it produces products of international standards at comparatively lower prices for the world market. The U.S. continues to live up to its reputation as the “breadbasket to the world”. Countries in the Sub-Sahara African region, Latin America and parts of Asia continue to be on the lower-end of technology prowess in food items and are inclined to their staple diets, whereas, those in Europe, North America, and Japan are on the higher-end of technology, with a sharper shift towards convenience and diet foods.
Apart from the current large size of the processed foods, the growth trends reported are very encouraging. According to a study done by AC Nielsen, “What’s Hot around the globe in F