Digestion & the Digestive System in Humans (WJEC GCSE Science (Double Award): Biology): Flashcards

True.

Several organs work together in the digestive system to digest and absorb food.

False.

Glucose is already small and soluble, so it can be absorbed directly without further digestion.

They are absorbed into the bloodstream and delivered to the cells of the body.

Starch is a long chain of many glucose molecules, making it too large to dissolve or be absorbed. Glucose is a single small molecule.

Break up the food using a pestle and mortar.

Transfer it to a test tube and add distilled water, stirring with a glass rod.

Filter the mixture using a funnel and filter paper, and collect the solution.

Iodine solution.

A positive result is a colour change from orange/brown to blue/black.

Add Benedict's reagent to the food solution in a test tube.

Heat in a boiling water bath for about 5 minutes.

A positive result is a colour change from blue to brick red.

Biuret solution.

A positive result is a colour change from blue to violet.

The Benedict's test for glucose. The sample must be heated in a boiling water bath for the colour change to occur.

Iodine solution is used to test for the presence of starch.

A positive Benedict's test changes colour from blue to brick red.

A positive biuret test for protein changes colour from blue to violet.

The iodine solution stays brown, showing no starch is present.

Both reagents stay blue, showing that glucose or protein is not present.

False.

The positive result must be described as blue/black, not blue or black alone.

True.

The examiner expects the term brick red.

Both starch and protein.

The reagents need to reach the food molecules in solution. Grinding and dissolving the food makes the test reliable.

• Iodine solution: brown

• Benedict's reagent: blue

• Biuret solution: blue

• Carbohydrases

• Proteases

• Lipases

An enzyme that breaks down carbohydrates, such as starch, into simple sugars such as glucose.

An enzyme that breaks down proteins into amino acids.

An enzyme that breaks down fats and oils into fatty acids and glycerol.

Proteases are made in the stomach, pancreas and small intestine.

Protein digestion takes place in the stomach and small intestine.

Lipase is produced in the pancreas and secreted into the small intestine, where it acts.

Carbohydrases break down starch into simple sugars such as glucose.

Lipase breaks down fats into fatty acids and glycerol.

Large molecules such as starch and protein are held together by chemical bonds. Enzymes speed up the breaking of these bonds so digestion happens fast enough.

Protease, which breaks proteins down into amino acids.

False.

Enzymes are specific. Each type of enzyme acts on only one type of food molecule.

False.

Enzymes are catalysts, so they are not used up or changed by the reaction.

• Carbohydrase → simple sugars, e.g. glucose

• Protease → amino acids

• Lipase → fatty acids and glycerol

• Mouth

• Oesophagus

• Stomach

• Liver

• Gall bladder

• Bile duct

• Pancreas

• Small intestine

• Large intestine

• Anus

Food is physically broken down into smaller pieces, increasing its surface area.

Carbohydrase begins the breakdown of starch.

The food is moistened and shaped ready for swallowing.

Food is churned and mixed, which physically breaks it up.

Protease enzymes begin the chemical digestion of proteins into amino acids.

It produces all three types of digestive enzyme — carbohydrases, proteases and lipases — and secretes them into the small intestine.

• Digestion is completed by enzymes made there and secreted from the pancreas

• Absorption of the digested food molecules into the bloodstream

Water is absorbed from the remaining waste material.

The solid waste that is left is removed through the anus.

It produces and secretes bile, which emulsifies fats.

The pancreas produces all three types of digestive enzyme and secretes them into the small intestine.

Water is absorbed from the remaining waste material in the large intestine.

False.

Chewing breaks food into smaller pieces, increasing its surface area for enzymes to act on. It does not break any chemical bonds.

False.

The liver and pancreas release substances into the gut, but food does not pass through them.

It gives enzymes a larger area to act on, so chemical digestion happens faster.

Waves of muscle contraction in the walls of the digestive system that move food along.

Fibre gives the muscles bulk to push against as they contract, so food keeps moving along.

Peristalsis is the wave-like muscle contraction that moves food along the digestive system.

Waves of muscle contraction squeeze food along the digestive system.

False.

Food is moved by peristalsis, waves of muscular contraction. This is why you can still swallow while lying down.

True.

Waves of muscular contraction move food along the whole digestive system.

Without enough fibre, the muscles have less bulk to push against, so food moves along the digestive system more slowly.

Muscles in the wall contract rhythmically one section after another.

This creates a wave-like action that squeezes the food mass forwards.

Bile is produced in the liver and stored in the gall bladder.

Through a small tube called the bile duct.

To emulsify fats, breaking large fat droplets into smaller droplets.

This increases their surface area, so lipase can break them down faster.

The breaking apart of large fat droplets into smaller ones, which increases their surface area.

Breaking fat into smaller droplets gives a larger surface area.

This gives lipase enzymes more area to act on, so fats are broken down into fatty acids and glycerol faster.

Bile emulsifies fats, breaking large droplets into smaller ones.

Bile is produced in the liver and stored in the gall bladder.

False.

Bile is not an enzyme. It emulsifies fats physically, but it does not break any chemical bonds.

Lipase, which breaks fats down into fatty acids and glycerol.

Bile could not be stored and released in large amounts when needed.

Fats would be emulsified less effectively, so lipase would work more slowly and fat digestion would be less efficient.

It only breaks large droplets into smaller droplets. No chemical bonds within the fat molecules are broken.

• Liver — produces bile

• Gall bladder — stores bile

• Bile duct — carries bile to the small intestine

• Glucose

• Amino acids

• Fatty acids and glycerol

• A large surface area, from its folded, finger-like lining

• A short diffusion distance, as the wall is one cell thick

• A good blood supply, maintaining a steep concentration gradient

It carries glucose and amino acids away from the small intestine, which maintains a steep concentration gradient for diffusion.

The wall of the small intestine is only one cell thick, giving a short diffusion distance.

Fill a section of Visking tubing with a mixture of starch and carbohydrase solutions.

Suspend the tubing in a beaker of water.

Test the water outside the tubing at intervals for starch using iodine and for glucose using Benedict's reagent.

The carbohydrase digests starch into glucose inside the tubing.

Glucose is small enough to diffuse out through the pores, so its concentration in the surrounding water rises.

Starch stays inside, because its molecules are too large to pass through.

• Similarity: both are partially permeable

• Difference: the small intestine has a much larger surface area, and a blood supply that carries absorbed food away

Distilled water does not flow, so it cannot maintain the concentration gradient the way circulating blood does.

Soluble food substances are absorbed into the blood by the process of diffusion.

False.

Starch molecules are too large. Starch must first be digested into glucose, which is small enough to be absorbed.

More of the food solution is in contact with the absorbing surface at one time, so more molecules can diffuse across per second.

A greater length gives a larger surface area and more time for digested food to be absorbed as it passes through.

It is used in respiration to provide energy, or it is converted to glycogen and stored.

They provide energy.

They are needed to build proteins in the body.

To act as a source of energy. Glucose from carbohydrate digestion is a reactant for respiration.

Growth and repair. Amino acids are used to build new proteins in the body.

• Energy storage, in a more condensed form than carbohydrate

• Insulation

Excess glucose is converted into glycogen and stored in the liver and muscles.

Amino acids from digested proteins are needed to build new proteins in the body.

True.

Excess glucose is converted to glycogen and stored in the liver and muscle cells.

False.

Glucose from carbohydrates is the main energy source. Amino acids are mainly used for growth and repair.

Protein provides the amino acids needed to build new body proteins for growth.

A diet containing all of the food groups in the correct proportions to meet the body's needs.

• Protein

• Carbohydrates

• Fats

• Minerals, e.g. iron

• Vitamins, e.g. vitamin C

• Fibre

• Water

Iron is used to make haemoglobin, which carries oxygen in red blood cells.

Sources include red meat, liver and leafy green vegetables.

Vitamin C forms an essential part of collagen, the protein that makes up skin, hair, gums and bones.

Sources include citrus fruit, strawberries and green vegetables.

Fibre provides bulk (roughage) for the intestine muscles to push against during peristalsis.

Water is needed for the chemical reactions that take place in cells.

They contain different quantities of carbohydrate and fat. Fats in particular contain a high density of energy-storing chemical bonds.

It is stored as fat by the body, under the skin and around the organs. Excess carbohydrate is also stored as glycogen.

When energy from food is taken in excess, it is stored as fat by the body.

These foods contain starch, which breaks down slowly and releases glucose into the blood over a longer time span.

• Type 2 diabetes

• Obesity

• Tooth decay

• Obesity

• Heart disease

• Circulatory disease

Excess salt in the diet is linked to high blood pressure.

The health problems that result from an unbalanced diet, whether from too much or too little of particular nutrients.

False.

Malnutrition results from any unbalanced diet, including eating too much sugar, fat or salt.

Measure 25 cm³ of water into a boiling tube and record its starting temperature.

Weigh the initial mass of the food sample.

Set fire to the food with a Bunsen burner and hold it about 2 cm below the boiling tube until it has completely burned.

Record the final temperature of the water, then repeat with different foods.

Energy stored in the food is transferred into the heat of the flames, which in turn heats the water in the boiling tube.

The food sample contained more stored energy.

A larger rise in water temperature shows the food contained more energy.

So the energy released can be compared fairly between foods.

A larger sample would release more energy whatever type of food it was.

• The food may burn incompletely, so not all its energy is released

• Heat is lost to the surroundings rather than heating the water

Relight the food sample each time it goes out, until it no longer catches light.

As long as the procedure is carried out in exactly the same way each time, especially the distance from the boiling tube, the results can still be used to compare foods.

Burning them can release allergens into the air, risking an allergic reaction or anaphylactic shock.

• Use tongs or a mounted needle to hold the food, keeping hands away from the flame

• Wear safety goggles and point the boiling tube away from you

False.

Heat is lost to the surroundings and burning may be incomplete, so the calculated value is an underestimate. It is still valid for comparison.

False.

A hazard is something that could cause harm. A risk is the harm that could actually occur. A control measure reduces that chance.