QUESTION ONE: DIGESTION
Compare and contrast the physical and chemical digestion of proteins, carbohydrates and fats in the digestive system of a mammal such as a human.
In your answer:
• describe the purpose and location of the processes of physical and chemical digestion
• explain how digestion of proteins, carbohydrates, and fats occurs
• discuss why the pH of the different parts of the digestive system is important in the digestion
of food, and how the pH is regulated.
Both physical and mechanical digestion occur in the mouth, where the pH is 7 (regulated by the production of neutral saliva). Mechanical digestion occurs due to mastication, which breaks down the food into smaller particles, meaning there is more surface area available so chemical digestion is more efficient. Salivary amylase is also found in the mouth, and it works most optimally when the pH is 7. Salivary Amylase is an enzyme, that chemically digests carbohydrates, breaking them down into maltose and glucose.
When food enters the stomach of pH 2, (due to the production of HCl) the salivary amylase becomes denatured as the pH is too low. This is where pepsin is found, an enzyme that works optimally at a pH of 2. This enzyme breaks down proteins into polypeptides. Physical digestion also occurs here, due to the churning of the stomach. This again breaks up large particles into smaller particles to increase surface area for chemical digestion.
The food molecules then enter the small intestine. The pH is 7 again, due to the bile from the gall bladder, and bicarbonate salts from the pancreas. The enzyme pepsin denatures here as the pH is too high, however it is ideal for other enzymes to continue chemically breaking down molecules. Amylase breaks down carbohydrates and maltose into simple sugars like glucose. Protease breaks down polypeptides into amino acids, and lipase breaks down lipids into fatty acids and glycerol.
QUESTION TWO: HERBIVORE AND CARNIVORE DIGESTIVE SYSTEMS
Compare and contrast the differences in the digestive system and mouth of a herbivore and a
carnivore.
In your answer:
• describe the diet of a herbivore such as a rabbit, and a carnivore such as a dog
• explain why and how the digestion that occurs in the mouths of a herbivore and a carnivore
are different
• explain the main differences in structures and functions of the herbivore and carnivore gut
• evaluate the effectiveness of the digestive systems of a herbivore and a carnivore
Herbivores such as rabbits eat mainly plant material, while carnivores such as dog mainly eat meat. Due to the differences in these diets, carnivores and herbivores have differences in their digestive systems to most efficiently digest what they eat.
Herbivores such as rabbits have large incisors for cutting plants from the source, while in carnivores they are not as large, and used for cutting food. Carnivores have large and pointed canines for killing prey, and ripping/tearing flesh off animals, while herbivores only have very small (if any) canines for defence. Herbivores often have large diastemas, used to separate cud from fresh food, and allow for free movement of the tongue, while carnivores often do not have diastemas as meat is easier to digest. Herbivores have flat molars which slide together to grind plant material, while carnivores have pointed molars that cut against each other to shear through bones. Herbivores also tend to have jaws which move sideways to grind plants with molars, while carnivore jaws are strong, and open widely to help kill prey. Herbivores also produce salivary amylase to chemically break down carbohydrates into simple sugars, while carnivores do not, as they do not spend long chewing.
Carnivores have a larger stomach than herbivores, as meat has a lot of protein, and this is where protein is digested by enzymes, whereas herbivores do not eat much protein. Herbivores such as rabbits have much longer guts than carnivores however, because plant material is a lot harder to digest, so the plant material needs to be kept in the rabbit for longer. Herbivores also have a large caecum which houses enzyme producing bacteria that digests cellulose.
The digestive systems of both herbivores and carnivores are relatively efficient in digesting the foods specific to the animal.
QUESTION THREE: ABSORPTION, CIRCULATION, ASSIMILATION AND RESPIRATION
Discuss how the processes of absorption, circulation, assimilation, and respiration work together to ensure the products of food digestion are distributed around and used by the body.
In your answer:
• describe the processes of absorption, circulation, assimilation, and respiration, and where
these processes occur
• explain how and why the processes of absorption, circulation, assimilation, and respiration
occur in the body
• discuss how the processes of absorption, circulation, assimilation, and respiration work
together to ensure the healthy functioning of the body.
After food has been digested, it gets absorbed via the villi. These are small threadlike protrusions in the small intestine, which are lined with even smaller threadlike protrusions called microvilli. This increases the surface area of available for absorption, thus increasing the efficiency of the process. Each villus has blood capillaries that absorb glucose and amino acids, as well as lacteals which absorb fatty acids and glycerol.
The blood system then circulates the glucose and amino acids throughout the body, while the fatty acids and glycerol are moved into the lacteals.
Assimilation then occurs, where the blood and lacteals transport the molecules to the hepatic portal vein that take them to the liver, and then are distributed to body cells in need of the specific molecules via diffusion.
Many of the molecules that have been diffused into the cells are used for respiration, where they react with oxygen to produce water, carbon dioxide, and energy. The energy is then used to carry out essential life processes such as feeding and reproduction.