[Digestion] 7.How is the food digested in the cow's stomach?

As we know, the cow has four stomachs as compared to the human being who has only one .Thus it is very interesting to find out how the food is actually digested efficiently in the four stomachs.

THE FOUR STOMACHS

Reticulum and rumen

The reticulum and the rumen are the first two stomachs of ruminants. The contents of the reticulum is mixed with that of the rumen almost continuously (once everyminute). Both stomachs, often referred to as the reticulo-rumen, share a dense population of micro-organisms (bacteria,protozoa, and fungi).The rumen is a large fermentation vessel that can contain as much as 100 to 120 kg of digesting material. Fiber particles remain in the rumen from 20 to 48 hours because bacterial fermentation of fiber is a slow process. However, particles that digest faster tend to stay in the rumen for a shorter period of time.The reticulum is the "crossroad" where particles entering or leaving the rumen are sorted. Only particles that are small in sizes may move on to the third stomach.

Omasum

The third stomach or omasum is round and has a capacity of about 10liters. The omasum is a small organ with great absorption capacity. It allows there cycling of water and minerals such as sodium and phosphorus which return to the rumen through the saliva. Since the modes of digestion in the rumen and the abomasum differ drastically, the omasum acts as an organ of transition between these two organs.

Abomasum

The fourth stomach is the abomasum. This stomach is like the stomach of nonruminants.It secretes a strong acid and many digestive enzymes. In nonruminants,ingested foods are first digested in the abomasum. However, the material entering the abomasum of a ruminant is made up primarily of unfermented food particles, some end-products of microbial fermentation and microbes which grew in the rumen.

[Digestion] 6.How is the digestive process controlled?

Digestive process is regulated by homone and nerve regulators.

Hormone Regulators

A fascinating feature of the digestive system is that it contains its own regulators. The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine. These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system, where they stimulate digestive juices and cause organ movement.

The hormones that control digestion are gastrin, secretin, and cholecystokinin (CCK):

Gastrin causes the stomach to produce an acid for dissolving and digesting some foods. It is also necessary for the normal growth of the lining of the stomach, small intestine, and colon.

Secretin causes the pancreas to send out a digestive juice that is rich in bicarbonate. It stimulates the stomach to produce pepsin, an enzyme that digests protein, and it also stimulates the liver to produce bile.

CCK causes the pancreas to grow and to produce the enzymes of pancreatic juice, and it causes the gallbladder to empty.

Additional hormones in the digestive system regulate appetite:

Ghrelin is produced in the stomach and upper intestine in the absence of food in the digestive system and stimulates appetite.

Peptide YY is produced in the GI tract in response to a meal in the system and inhibits appetite.

Both of these hormones work on the brain to help regulate the intake of food for energy.

Nerve Regulators

Two types of nerves help to control the action of the digestive system. Extrinsic (outside) nerves come to the digestive organs from the unconscious part of the brain or from the spinal cord. They release a chemical called acetylcholine and another called adrenaline. Acetylcholine causes the muscle of the digestive organs to squeeze with more force and increase the "push" of food and juice through the digestive tract. Acetylcholine also causes the stomach and pancreas to produce more digestive juice. Adrenaline relaxes the muscle of the stomach and intestine and decreases the flow of blood to these organs.

Even more important, though, are the intrinsic (inside) nerves, which make up a very dense network embedded in the walls of the esophagus, stomach, small intestine, and colon. The intrinsic nerves are triggered to act when the walls of the hollow organs are stretched by food. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs.

[Digestion] 5.How is the nutrients absorbed and transported within the digestive system ?

Digested molecules of food, as well as water and minerals from the diet, are absorbed from the cavity of the upper small intestine. Most absorbed materials cross the mucosa into the blood and are carried off in the bloodstream to other parts of the body for storage or further chemical change. As already noted, this part of the process varies with different types of nutrients.

Carbohydrates. It is recommended that about 55 to 60 percent of total daily calories be from carbohydrates. Some of our most common foods contain mostly carbohydrates. Examples are bread, potatoes, legumes, rice, spaghetti, fruits, and vegetables. Many of these foods contain both starch and fiber.

The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps: First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose; then an enzyme in the lining of the small intestine (maltase) splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.

Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorbable molecules by an enzyme called lactase, also found in the intestinal lining.

Protein. Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein. Further digestion of the protein is completed in the small intestine. Here, several enzymes from the pancreatic juice and the lining of the intestine carry out the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed from the hollow of the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.

Fats. Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestinal cavity. The bile acids produced by the liver act as natural detergents to dissolve fat in water and allow the enzymes to break the large fat molecules into smaller molecules, some of which are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules to move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, most of which pass into vessels (called lymphatics) near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.

Vitamins. Another vital part of our food that is absorbed from the small intestine is the class of chemicals we call vitamins. The two different types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, and K).

Water and salt. Most of the material absorbed from the cavity of the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid we swallow and the juices secreted by the many digestive glands.

[Digestive] 4.How is food digested ?

The food that we ate is broken down into smaller pieces through mechanical manipulation such as chewing. The rest of the process of digestion is largely dependent on enzymatic reaction in the digestive juices.

The glands that act first are in the mouth—the salivary glands. Saliva produced by these glands contains an enzyme that begins to digest the starch from food into smaller molecules.

The next set of digestive glands is in the stomach lining. They produce stomach acid and an enzyme that digests protein. One of the unsolved puzzles of the digestive system is why the acid juice of the stomach does not dissolve the tissue of the stomach itself. In most people, the stomach mucosa is able to resist the juice, although food and other tissues of the body cannot. The churning action of the stomach muscle gives a good mix between the food and the digestive juices hence and enhancing the rate of digestion.

After the stomach empties the food and juice mixture into the small intestine, the juices of two other digestive organs mix with the food to continue the process of digestion. One of these organs is the pancreas. It produces a juice that contains a wide array of enzymes to break down the carbohydrate, fat, and protein in food. Other enzymes that are active in the process come from glands in the wall of the intestine or even a part of that wall.

The liver produces yet another digestive juice—bile. The bile is stored between meals in the gallbladder. At mealtime, it is squeezed out of the gallbladder into the bile ducts to reach the intestine and mix with the fat in our food. The bile acids dissolve the fat into the watery contents of the intestine, much like detergents that dissolve grease from a frying pan. After the fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine.

[Digestion] 3.Where it begin and where it ends ?

Digestion begins in the mouth, when we chew and swallow, and is completed in the large intestine.

The chemical process varies somewhat for different kinds of food. The large, hollow organs of the digestive system contain muscle that enables their walls to move. The movement of organ walls can propel food and liquid and also can mix the contents within each organ. Typical movement of the esophagus, stomach, and intestine is called peristalsis. The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.

The first major muscle movement occurs when food or liquid is swallowed. Although we are able to start swallowing by choice, once the swallow begins, it becomes involuntary and proceeds under the control of the nerves.

The esophagus is the organ into which the swallowed food is pushed. It connects the throat above with the stomach below. At the junction of the esophagus and stomach, there is a ringlike valve closing the passage between the two organs. However, as the food approaches the closed ring, the surrounding muscles relax and allow the food to pass.

The food then enters the stomach, which has three mechanical tasks to do. First, the stomach must store the swallowed food and liquid. This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine.

Several factors affect emptying of the stomach, including the nature of the food (mainly its fat and protein content) and the degree of muscle action of the emptying stomach and the next organ to receive the stomach contents (the small intestine). As the food is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine, the contents of the intestine are mixed and pushed forward to allow further digestion.

Finally, all of the digested nutrients are absorbed through the intestinal walls. The waste products of this process include undigested parts of the food, known as fiber, and older cells that have been shed from the mucosa. These materials are propelled into the colon, where they remain, usually for a day or two, until the feces are expelled by a bowel movement.

[Digestion] 2.What is digestive system ?

The digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. There are also two solid digestive organs, the liver and the pancreas, which produce juices that reach the intestine through small tubes. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system.

The main organ in our body which is actively involved in digestion are shown in the figure on the left namely Mouth,Esophagus,Liver,Stomach,Gall Bladder, Pancreas, Small intestine ,Large intestine and Rectum .

[Digestion] 1.What is digestion ?

When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nutrients. Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.

Digestion occurs at the multicellular, cellular, and sub-cellular levels, usually in animals. This process takes place in the digestive system known as alimentary canal.

Digestion is usually divided into mechanical manipulation and chemical action. In most vertebrates, digestion is a multi-stage process in the digestive system, following ingestion of the raw materials, most often other organisms. The process of ingestion usually involves some type of mechanical manipulation.

Digestion is separated into four separate processes:
Ingestion: Placing food into the mouth,
Mechanical digestion & Chemical digestion: Mastication, the use of teeth to tear and crush food, and churning of the stomach. Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures,
Absorption: Movement of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion,
Egestion: Removal of undigested materials from the digestive tract through defecation.
Underlying the process is muscle movement throughout the system, deglutition and peristalsis.

[Photosynthesis] 6.How will stomata closure affect photosynthesis?

Plants can regulate the movements of water vapor, O2 and CO2 through the leaf surface. This is accomplished by opening and closing pores, called stomata, usually found on the bottom side of the leaf. Opening and closing of stomata is controlled by specialized cells called guard cells.

The figure below shows a section of the bottom of a typical leaf as seen through a microscope. The stomate exists as the small opening between the pairs of guard cells.

Guard cells can respond to a variety of environmental and physiological stimuli by opening and closing the stomate. For example, under hot, dry conditions stomata of many plants close to help conserve water. Stomata of most plants also close in the dark.

CO2 used during photosynthesis first must pass through stomata into internal spaces within the leaf. It then diffuses into mesophyll cells where it becomes available for photosynthesis.

When the stomata close, CO2 levels drop rapidly within the leaf, inhibiting the light-independent reactions. This then causes photosynthesis to stop.

Stomata closure limit the intake of carbon dioxide which is important for photosynthesis to take place.This factor is more significant in the day where there is sunlight.

[Photosynthesis] 5.How does leaf position on a tree affect photosynthesis?

Plants we see out in the wild display evolutionary adaptions to growth in bright sunshine or shade. Leaves of tree often show developmental adaptions to different conditions. Leaves on the exterior of the canopy are refered to as 'Sun' leaves, and they develop under conditions of direct sunlight. Leaves within the crown of the tree are adapted to the shade created by surrounding leaves thus refering them as 'Shade' leaves. These adaptions include differences in leaf anatomy, metabolism (such as photosynthesis) and shape.

Plants are usually adapted to growth in direct sunlight or shaded conditions. Similar differences are observed among the leaves of large trees; those leaves that develop under the shade of other leaves are anatomically and metabolically different from those that grow on exposed canopy surfaces.

Shade-type leaves typically are thinner, have more surface area, and contain more chlorophyll than those of sun leaves. As a result, shade-leaves (curve B) often are more efficient in harvesting sunlight at low light levels; remember, the slope of the line observed under low light conditions is a measure of photosynthetic efficiency. However, sun-leaves (curve A) display a higher light saturation point and maximum rate of photosynthesis.

[Photosynthesis] 4.How does the light intensity affects the rate of photosynthesis ?

Light is the layman's term for visible radiant energy in the 400 to 700 nm wavelength region of the spectrum. In other words, it is the form of radiant energy (i.e. radiation) that animals can see. It is also the wavelengths of radiant energy that plants use in photosynthesis and for most other reactions that require light.

The rate of photosynthsis in a plant depends on the supply of carbon dioxide, supply of light, supply of water, temperature and various other factors like the amount of chlorophyll.In this blog,we will be setting the supply of light and its intensity as a more prominent factor affecting the rate of photosynthesis .

If the plant is in dim light, but has plenty of CO2, H2O and is warm enough, then it will be light which is limiting the rate of the whole process. If this is the case, then increasing the light will increase the rate of photosynthesis.

Measurement of light intensity
1) photometer or common light meter (cheapest) - measures amount of luminance
Expressed as: a) foot-candle (ft-c) - 1 lumen per square foot b) lux - 1 lumen per square meter
1 foot-candle = 10.76 lux

fig 1 : The relation between carbon dioxide exchange and
light intensity

Fig 1 shows the relation beween carbon dioxide exchange and light intensity.The rate of photosynthesis is show by the carbon dioxide exchange in the graph affected by the light intensity. As we can see , the higher the light intensity , the higher the rate of photosynthesis. However, the rate of photosynthesis will level off at the tip of the curve due to the limited amount of chlorophyll on the leave as well as the limited quantity of light that can be absorbed by the plant for photosynthesis.

[Photosynthesis] 3.What is the process of plants consuming the food ? How is it consumed ?

All living things comsume food . Plants do not move,how do they consume their food?

The process of using food and oxygen to get energy is called respiration. Plants must use the energy they trap in the food to stay alive. That's where respiration comes in. At night, plants take in oxygen and use it to get energy from the food they stored. This is a chemical reaction. This is the same reaction that takes place in animals that eat the plants.

Respiration is essential to provide metabolic energy and carbon skeletons for growth and maintenance. As such, respiration is an essential component of a plant€s carbon budget.

[Photosynthesis] 2.Do all plants use carbon dioxide to make food ?

According to Dr. Galapagos answer ,not all plants use carbon dioxide to make food.

1)Plants that Use Carbon Dioxide (CO2):

Autotrophic Plants

Green plants are completely autotrophic. Autotrophic plants require only solar energy, carbon dioxide, water, and a few minerals to make all the organic compounds necessary to keep themselves going and growing. So all autotrophic plants use carbon dioxide. Carbon dioxide, water, and minerals are all inorganic compounds. Autotrophic plants, then, can get everything they need from inorganic compounds.

Semiparasitic Plants

Some plants can't quite do it all from just water, CO2, and sunlight (and a few other nutrients like nitrogen). Semiparasitic plants have some green parts and can take carbon dioxide from the air, but they can't quite do it all by themselves, so they have to take some nutrients from an autotrophic host plant. In other words, these types of plants actually connect themselves to another plant and take some of the food they need from the host plant.

Insectivorous Plants

Another type of plant that uses carbon dioxide for photosynthesis, but still needs a little something extra, are the insectivorous plants. Examples of these are the venus fly trap and pitcher plants. They catch and slowly digest insects and other unfortunate little animals that fall into their traps. Insectivorous plants can live without catching animals but they are a lot healthier if they can catch an occasional bug .

2) Plants that don't Use Carbon Dioxide

Holoparasitic Plants

Holoparasitic plants are parasites like the semiparasitic plants which means they have to be directly connected to an autotrophic host plant. But these plants have no green parts and can't do any photosynthesis. They have to get all their nutrients, energy, water, and carbon from the host plant they are attached to. So holoparasitic plants don't use carbon dioxide and don't release oxygen into the air.

The Plants Formerly Known as Saprophytes

The other type of plants that don't use CO2 are the parasitic plants we use to call saprophytes. These plants are now called myco-heterophytes. They have a fascinating connection to the trees that feed them. A fungus, called a mycorrhizal fungus, connects the myco-heterophytes to the tree and transfers the nutrients from the host plant to the parasitic plant. The host plant does all the photosynthesis work to make food, then "shares" some of it, unwillingly no doubt, with the parasitic plant. The fungus feeds the parasite. I assume the fungus feeds itself also.

Now , i know that not all plants make food using carbon dioxide

[Photosynthesis] 1.What is photosynthesis ?

Humans and plants are living things .All living things need food in order to survive.Humans buy or cook their own food but plants can neither move nor cook so where do they get their food from ?

They photosynthesis .Photosynthesis is the process by which plants, some bacteria, and some protistans use the energy from sunlight carbon dioxide and water to produce glucose.During the day , plants give out oxygen,as a waste product,it is arguably the most important biochemical pathway known; nearly all life depends on it. Chlorophyll in the green leaves help the plant to make food .Plants respire both during the day and at night.They only photosynthesis during the day or in the presence of light .

Photosynthesis occurs in two stages. In the first phase light-dependent reactions or photosynthetic reactions capture the energy of light and use it to make high-energy molecules. During the second phase, the light-independent reactions use the high-energy molecules to capture carbon dioxide (CO2) and make the precursors of glucose.

carbon dioxide + water + light energy → glucose + oxygen + water