Human Biology - EDEXCEL IGCSE - Nutrition and Energy

Nutrition and Energy

Balanced Diet: eating foods on a regular basis that provide all the right nutrients (carbs, lipids, protein, minerals, vitamins, water and fibre) in the right amount and proportion for the person to remain healthy.

Your diet will change according to your age, whether you’re pregnant, climate and occupation. Your energy requirement will also change according to your activity, age and whether you’re pregnant. 

Digestive System:

1. Mouth - food is ingested and broken down by the teeth and tongue. Saliva is secreted by the salivary glands which begins the digestion of starch.
2. Oesophagus - helps food move to the stomach through peristalsis.
3. Stomach - a muscular bag where food is mixed with hydrochloric acid and pepsin. The acid is used to sterilise the food and create the optimum pH for pepsin to break down protein.
4. Pancreas - produces pancreatic juices which contains digestive enzymes and hydrogen carbonate which is used to neutralise stomach acids to create the optimum pH for these enzymes to work.
5. Small Intestine - contains the duodenum where food is mixed with bile and pancreatic juices and the ileum where enzymes complete digestion and digested food is absorbed.
6. Large Intestine - contains the colon where water and also some vitamins and minerals is absorbed from undigested food. Also contains the rectum which stores undigested faeces

Bile: produced in the liver, stored in the gall bladder and released into the duodenum. It is used to emulsify/breakdown fats from globules into an emulsion of tiny droplets, giving a larger surface area to volume ratio for lipase to act on. It also neutralises the food.

Peristalsis: a series of muscle contractions that occurs in the gut. When the circular muscle contracts and the longitudinal muscles relaxes the gut narrows. A rhythmic series of narrowing and widening of the gut wall causes the food to be pushed along. Peristalsis needs fibre to work efficiently as this gives the gut something to push against in order to move the food along.

Digestive Enzymes:

Amylase - breaks down starch into maltose. Created in the salivary glands, pancreas and the wall of the gut.

Maltase - breaks down maltose into glucose. Created in the salivary glands, pancreas and the wall of the gut.

Proteases - pepsin and trypsin breaks down proteins into peptides. Peptidases breaks down peptides into amino acids. Both are produced in the stomach wall, pancreas and gut wall.

Lipase - this breaks down lipids into glycerol and fatty acids. Produced in the pancreas.

Experiment to find energy content of food:

1. Clamp test tube with 20ml of water and record the temperature.
2. Set the food alight with a bunsen burner and place the food under the water, relight it if it goes out.
3. When the food cannot be relit, record the new temperature of the water.

energy content = (mass of water * temperature change * 4.2) / mass of food

Experiment with digestive enzymes:

1. Place protein, starch and lipid samples in nine test tubes.
2. Place drops of amylase, lipase and pepsin (with hydrochloric acid) in each sample type.
3. Do iodine, biuret and ethanol test.

Teeth:

Incisors - there are eight in total and are located at the front of the mouth. They are used for cutting and shearing food into chewable chunks.

Canines - there are four in total and are located next to the incisors. They are used to grip and tear food.

Premolars - there are eight in total and located next to the canines. They are used to crush and tear food.

Molars - there are twelve in total and are located nest to the premolars. They are used to chew, crush, and grind food.

Structure:

Factors affecting the growth of teeth:

1. Calcium
2. Vitamin D
3. Genetics
4. Care of teeth

How to care for teeth and gums:

1. Brushing teeth twice a day and correctly.
2. Flossing
3. Not eating too much sugar or acid.
4. Visiting the dentists regularly.
5. Rinsing with mouthwash

Respiration:

Respiration is used to release energy in living organisms.

Anaerobic respiration is respiration without oxygen while aerobic respiration means that oxygen is used.

Aerobic respiration : C₆H₁₂O₆  + 6O₂ —> 6CO₂ + 6H₂O + energy

Experiments to test for carbon dioxide from respiration:

• Collect gas of germinating seeds and bubble through lime water to see if it turns cloudy.
• Bubble air through double bubbler with bicarbonate indicator. If it turns yellow or orange the carbon dioxide is present.

ATP (adenosine triphosphate) is known as the “currency” of energy. It is created during respiration using energy from oxidising glucose. This is then used to provide energy. In the process, a phosphate ion joins with adenosine diphosphate when energy is supplied and it breaks away when energy is needed.

Lactic acid is formed when there is no oxygen present and therefore during anaerobic respiration.

C₆H₁₂O₆ —> 2C₃H₆O₃ + less energy