Answers to questions on digestion (continued)
Monacia Williams, Contributor

This week I will continue to answer the questions that were given last week. I was not able to complete the answer to (a) (ii) so I will do so now. Notice that the answer is worth four marks? This means that you should include at least four points with explanations in your answer.

Please note that I have included more than four points in my answer. You should not do this, however, because you will not receive any extra marks for additional points. Also, you would be wasting valuable time that could be used to answer another question.

(a) (ii) (continued)

• Stomach - distensible muscular bag that permits the storage of food. It has gastric pits which secrete digestive juices.
• Associated exocrine glands
• Pancreas - produces pancreatic juice with enzymes, mucus and hydrogen carbonate ions.
• Salivary glands - salivary glands present in the buccal cavity produce saliva that contains water, mucus, chloride ions as well as salivary amylase. The chloride ions activate the enzyme and, along with hydrogen carbonate and hydrogen phosphate, provide the almost neutral pH required for the enzyme to work.
• Liver - produces bile, which emulsifies fats increasing the surface area for the lipase enzymes to work on. It also neutralises the acid of the chyme coming from the stomach.

(b) The liver has many functions which are associated with keeping the body healthy. These functions require that many chemical reactions take place. Some of these are as follows:

• Carbohydrate metabolism - excess glucose is converted to glycogen and stored. Some of this glycogen is reconverted to glucose when the body's sugar level falls.
• Lipid metabolism - excess cholesterol is excreted into bile and removed from the body.
• Protein metabolism - amino acids are broken down to ammonia, which is converted to urea.
• Synthesis of plasma proteins for example prothrombin and fibrinogen.
• Detoxification of poisonous or toxic materials received from the intestines.
• Breakdown of red blood cells to produce iron which may be stored, reused or excreted.
• All the metabolic activity in which the liver is involved produces heat which helps humans to maintain their constant body temperature.

Many questions on heterotrophic nutrition involve the use of figures. Being comfortable with figures is an easy way to score full marks for a question. The following question will provide some help.

Question

The table below gives some information about the nutritional content of a traditional burger and of a similar non-meat burger.

a) i) Which burger had the highest protein content per 100g? (1 mark)

ii) How much protein is present in 120g of beef burger? (1 mark)

iii) In which organ of the body are carbohydrates stored? (1mark)

iv) Name the carbohydrate which is stored in this organ. (1 mark)

b) State two reasons why a person who is anxious to eat a healthy diet might choose the vegetable burger. Give an explanation for the choice in each case. (4 marks)

Try to answer this one by yourself and join me next week to check your answers. Good luck!

George Palmer (left), chemistry teacher at Kingston Technical High School, demonstrates how biodiesel is made to some students attending the Jamaica Public Service Science and Technology Expo 2009 at the Knutsford Court Hotel in St Andrew, recently. - Ian Allen/Staff Photographer