Human Diet & Digestion (Cambridge (CIE) IGCSE Biology)

True.

Vitamins A is needed for the production of pigments in the retina. Sources of vitamin A include meat, dairy, eggs and leafy greens.

Dietary fibre provides bulk in the intestines, aiding the movement of solid waste and preventing constipation.

True.

Water is the main component of the blood, where it is essential for carrying nutrients and waste products, and regulating body temperature. Water is also the main component of cell cytoplasm.

Carbohydrates can be obtained from:

• Pasta

• Rice

• Potatoes

• Cereals

• Bread

• Sugary foods, e.g. fruit juice, chocolate, biscuits

Iron is essential for production of haemoglobin, which carries oxygen in the blood.

Vitamin D aids absorption of calcium, so is essential for strong bones and teeth. Deficiency in vitamin D can lead to rickets.

Scurvy is caused by a lack of vitamin C and leads to anaemia, exhaustion, bleeding, pain in the limbs, swelling, tooth loss.

The function of the digestive system is to break down large, insoluble food molecules into small, soluble molecules that can be absorbed.

The organs of the alimentary canal through which food passes are:

• Mouth

• Oesophagus

• Stomach

• Small intestine (duodenum and ileum)

• Large intestine

• Rectum

Other organs, e.g. the pancreas, are not in this list because food does not directly pass through them.

True.

Teeth grind food in the mouth; this is mechanical digestion.

Saliva contains amylase enzymes that begin the chemical breakdown of starch into sugars. Saliva also moistens food to aid in swallowing.

The oesophagus is the tube through which food passes between the mouth and the stomach.

True.

Muscular contractions of the stomach wall play a role in mechanical digestion, while protease enzymes start to chemically break down the proteins in food.

The role of the large intestine is to allow absorption of water from solid waste before it is egested; the remaining solid waste makes up the faeces.

False.

Accessory organs, such as the pancreas, are not part of the tube through which food passes. Their role is to produce substances, such as enzymes, needed for digestion.

Three organs of the digestive system that release enzymes include:

• Salivary glands

• Stomach

• Small intestine

• Pancreas

Bile is released from the liver.

True.

Physical digestion is sometimes described as mechanical digestion

Physical digestion increases the surface area of food for the action of enzymes in chemical digestion.

Physical digestion includes chewing food in the mouth, churning food in the stomach and emulsification of fats in the intestine.

Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecule.

Tooth number 3 is an incisor which is shaped specially to facilitate biting and cutting.

Number 1 is a premolar which is designed for chewing and grinding food up.

Human teeth include:

• Canines

• Incisors

• Premolars

• Molars

False.

Teeth are part of physical digestion, although they are used to increase the surface area which aids chemical digestion.

Teeth are made up of enamel, dentine, pulp, nerves, blood vessels and cement, they are embedded in bone and the gums.

An organ is a collection of tissues working together to perform one function.

The stomach has three roles:

• To mechanically digest food through the churning of food

• To produce the enzyme protease

• To produce hydrochloric acid (stomach acid)

The stomach is part of the digestive system.

The role of mucus-producing cells in the stomach is to protect the stomach lining from hydrochloric acid (stomach acid).

Two other organs of the digestive system:

• Mouth/tongue/salivary glands

• Oesophagus

• Liver

• Gall bladder

• Pancreas

• Small intestine

• Large intestine

• Rectum

• Anus

Bile's main roles are neutralising stomach acid and emulsifying fats.

Emulsification is the process of breaking apart large fat droplets into smaller ones, increasing the available surface area for enzyme action.

Emulsification increases the surface area of fat droplets, increasing the efficiency of fat digestion by lipase enzymes in the small intestine.

False.

Emulsification breaks large fat droplets into smaller ones but does not involve the breaking of any chemical bonds within fat molecules. Chemical breakdown requires the breaking of bonds.

Bile is produced by cells in the liver.

Bile is stored in the gall bladder before it is released into the small intestine.

False.

Food does not pass directly through the liver and the gall bladder, so they are accessory organs and do not form part of the alimentary canal.

The role of chemical digestion is to break down large insoluble molecules into small soluble molecules which can be absorbed.

True.

Insoluble carbohydrates are broken down into glucose which can be absorbed in the small intestine.

Enzymes are biological catalysts that speed up chemical reactions without being consumed or changed in the process.

The three main types of digestive enzymes are:

• Amylase (carbohydrase)

• Protease

• Lipase

Carbohydrase enzymes break down s down starch into simple reducing sugars, e.g. glucose.

Amylase enzymes are produced in the:

• Salivary glands

• Pancreas

• Small intestine

False.

Protease enzymes break down proteins into amino acids. Fatty acids are a product of lipid digestion.

Lipase enzymes carry out lipid digestion.

Lipids (fats) are broken down into glycerol and fatty acids by lipase enzymes.

The pancreas produces the following digestive enzymes:

• Lipase

• Amylase

• Protease

The functions of stomach acid include

• killing harmful microorganisms in food

• providing an acidic pH for optimum enzyme activity

Gastric juices contain hydrochloric acid.

False.

Stomach acid does not break down molecules into smaller molecules. Enzymes are responsible for breaking down the large molecules.

False.

Amylase enzyme works best at pH 7 which is the pH in the mouth and small intestines.

Hydrochloric acids provide the right environment for some types of protease enzymes for protein digestion.

Stomach acid found in the gastric juice kills pathogens that are ingested by an individual, therefore protecting against infection;

False.

The pH of the environment in the stomach is around pH 2. It is acidic due to the hydrochloric acid found in the gastric juices, this provides the optimum environment for enzyme activity.

True.

Amylase breaks down starch into maltose, and then maltase breaks down maltose into glucose.

Starch is digested by amylase and maltose. These enzymes are denatured by stomach acid which means that starch digestion halts when the food reaches the stomach.

The enzymes required in starch digestion require an optimum pH of around pH 7.

False.

Maltase breaks down maltose into glucose. This is the second part of starch digestion and occurs after amylase has first broken down starch into maltose.

Maltase enzyme is found in the small intestine, embedded into the lining of the epithelium.

False.

Trypsin is a protease that is released into the small intestine where it digests proteins.

Pepsin is the enzyme that breaks down protein in the acidic conditions of the stomach.

The protease enzyme found in the gastric juices of the stomach is pepsin.

Trypsin works best in alkaline conditions of the small intestine, at a temperature of around 37 °C (body temperature).

Two protease enzymes found in the human digestive system are pepsin and trypsin.

The alkaline conditions will lead to the denaturing of pepsin so it would be unable to digest proteins as the active site will no longer fit the substrate.

True.

Bile is alkaline so works to neutralise hydrochloric acid from the stomach. This creates a suitable pH for enzyme activity in the small intestine.

An alkaline pH is needed in the small intestine because this is the optimum pH for the enzymes (amylase, trypsin, lipase) that function in this part of the digestive system.

False.

The enzymes of the small intestine work best at a slightly alkaline pH, hence the importance of bile neutralising the stomach acid as it enters the small intestine.

False.

Water is absorbed mostly in the small intestine with some also being absorbed in the colon.

The following nutrients are absorbed in the small intestine:

• glucose

• amino acids

• fatty acids

• glycerol

False.

Proteins are too large to be absorbed, they must be broken down into amino acids before they can be absorbed.

The majority of digested food is absorbed in the small intestine.

Absorption is the process of moving small, digested food molecules from the digestive system into the blood.

Features of the small intestine that increase its surface area are:

• It is very long

• It has villi

• The cells of the villi have microvilli

Features of villi which aid absorption are:

• large surface area

• short diffusion distance

• well supplied with blood capillaries

True.

A good blood supply aids absorption as it:

• shortens the diffusion distance between the intestine and the blood stream

• maintains concentration gradients as the blood flow removes molecules as soon as they are absorbed

Microvilli further increase the surface area of villi, increasing the rate at which nutrients are absorbed into the bloodstream.

False.

Villi are surrounded by a single layer of cells; this keeps the diffusion distance between the intestine and the blood as short as possible.

The lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph.