Digestion

The diagram shows the alimentary canal of a rabbit with some parts labelled.

The table lists descriptions of some parts of the alimentary canal. Complete the table by giving the correct part from the diagram to match each description. One has been done for you.

Explain how the liver helps digestion in the alimentary canal.

Rabbits eat grass. The diagram shows the cell wall of a leaf cell from a grass plant. Complete the diagram by drawing and labelling other structures in this leaf cell.

Grass cell walls are made of cellulose. Rabbits cannot digest cellulose. Bacteria living in the large intestine of rabbits can digest cellulose into glucose. Rabbits eat their own faeces to obtain this glucose.

Give two differences between the structure of bacterial cells and the structure of plant cells.

Describe a test to show that rabbit faeces contain glucose.

Many people in the UK eat fish and chips. The drawing shows a plate of fish and chips.

Describe what happens to fish protein in the stomach.

The chips are made from potatoes. Potatoes are the underground carbohydrate storage organs of the potato plant. The diagram shows a cell from potato tissue, as seen through a microscope.

Name the parts labelled A, B and C.

Chips are cooked by frying them in lipid (oil). Some of this lipid is left on the surface of the chips after cooking. The diagram shows three different shaped chips from the same potato. Each chip has the same mass.

The table shows the surface area, the volume and the surface area to volume ratio for chips A and B. Use the diagram to complete the table for chip C, which is a cube.

Eating too much lipid is harmful to health. Explain which shape of chip, A, B or C, is the most healthy to eat.

All living cells contain enzymes.

Describe the role of enzymes in cells.

The table lists some enzymes, where they are produced and their function. Complete the table by giving the missing information.

Explain how changes in temperature affect the activity of an enzyme.

A student uses this method to investigate the effect of temperature on the digestion of lipid. Step 1 Add five drops of an indicator to a test tube. Step 2 Add 5 cm³ of milk to the test tube. Step 3 Then add 7 cm³ of sodium carbonate solution to the test tube. Step 4 Place a thermometer in the test tube, put the test tube in a water bath and leave it until the contents reach a temperature of 20 °C. Step 5 Add 1 cm³ of lipase solution to the test tube and start a timer. Step 6 Stir the contents of the test tube. Step 7 Record the time it takes for the indicator to change colour. The student then repeats these steps using water baths at five higher temperatures, increasing the temperature by 10 °C each time.

Name the independent variable in the student’s investigation.

Identify two variables that the student controls in his investigation.

Give the reason for including step 6.

Sodium carbonate solution is an alkali that turns the indicator pink in step 3. Explain why the indicator changes colour in step 7.

Sketch a graph on the axes to show the results you would expect the student to obtain.

Explain the effect of temperature on the time taken for the indicator to change colour.

Describe the role of bile in the digestion of lipid.

A student investigates the movement of substances from the gut into the blood using a model. The Visking tubing bag represents the gut and water represents the blood. Visking tubing is permeable to small molecules.

The student puts different solutions of various substances into the bag. After 20 minutes he carries out food tests on the water.

Complete the table to show the results obtained by the student. One has been done for you.

Explain how the volume of the bag would change when it only contains starch solution.

Describe the test the student should use to find out if glucose is present in the water.

Explain how you could use this apparatus to investigate the effect of bile on the digestion of lipid.

The diagram shows the digestive system of a human with parts labelled A, B, C and D.

The table lists these four parts of the digestive system and three types of food. For each part, complete the table by putting a tick () in the box if the food is digested, or a cross () if it is not digested. Some have been done for you.

Coeliac disease results in part C containing fewer villi.

Draw a labelled diagram of a villus.

Suggest why coeliac disease may affect the growth of a child.

Name the producer in this food web.

Gazelles try to avoid being caught by lions by running away quickly. They can run at a top speed of 96 km per hour.

Calculate the distance in metres a gazelle runs in one minute at a speed of 96 km per hour. Show your working.

distance =_........ metres

Gazelles cannot maintain their top speed for a long time because a change in the type of respiration takes place in their muscle cells. Explain how this change in respiration stops gazelles from running at a top speed for a long time.

Zebras also try to avoid being caught by lions. It was thought that the striped coat of zebras helps to camouflage them. A new theory suggests the striped coat evolved because it reduces the number of biting flies that feed on zebra blood. Use your knowledge of natural selection to explain how a striped coat that reduces the number of flies feeding on zebra blood may have evolved.

Lions’ eyes are adapted to help them see in dim light.

Their eyes have a layer of cells behind the retina that reflects light which has passed through the retina. Suggest how this would help a lion see in low light intensities.

Suggest one other adaptation in the structure of a lion’s eye that helps the lion to see in low light intensities.

When a lion catches its prey it tears the meat into smaller pieces in its mouth before swallowing.

Suggest why the saliva released into the lion’s mouth does not contain amylase.

Explain how tearing the meat into smaller pieces helps digestion in the stomach.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Glucose control Many years ago some scientists wanted to find out more about the role of the pancreas in digestion. They used surgery to remove the pancreas from dogs to see what would happen. During this investigation a laboratory assistant noticed that flies collected around the dogs’ urine. This urine was later found to contain large amounts of glucose. Urine from dogs with a pancreas does not contain glucose. Another scientist used string to tie a knot around the pancreatic duct of rabbits, which closed the duct. This meant that no pancreatic enzymes could reach the small intestine. It was noticed that when this was done, the cells in the pancreas that made enzymes died, but no glucose appeared in the rabbit urine. Other scientists made pancreas extract by crushing up a pancreas in water. They injected this extract into dogs that had their pancreas removed. They found that the blood glucose level in these dogs was much reduced. These investigations and observations suggest that the pancreas has two different functions. Some of the cells produce enzymes needed for digestion. Other parts of the pancreas are not involved in digestion but are important in controlling blood glucose levels. We now know that pancreas extract contains two hormones involved with the regulation of blood glucose levels – insulin and glucagon. High blood glucose levels are detected by the pancreas. This stimulates the pancreas to release insulin. The role of insulin is to lower blood glucose levels. The insulin is released from specialised cells directly into the blood. The insulin travels in the blood to target cells that are in the liver and in large muscles. Insulin causes these cells to absorb glucose and use it to make an insoluble storage carbohydrate called glycogen. The second hormone called glucagon is released by different cells in the pancreas when the blood glucose level falls too low. Glucagon causes liver and muscle cells to change glycogen into soluble glucose.

Explain what is meant by the term digestion (line 2).

Explain why dogs that had their pancreas removed produced urine that contained glucose (lines 4 and 5).

Name two enzymes produced by cells in the pancreas (lines 8 and 9).

Suggest why rabbits that have had their pancreatic duct tied can still regulate their blood glucose levels (lines 10 and 11).

The scientists who injected pancreas extract into dogs should have carried out a control experiment (line 13). Explain the control experiment they should have carried out.

Name the blood vessel that transports hormones into the liver (line 24).

Suggest one advantage of storing glycogen in cells rather than storing glucose in cells (lines 25 and 26).

A number of different substances and structures are involved in the control of blood glucose.

Describe the stimulus.

Name the structure that acts as a receptor.

Name a structure that acts as an effector.

Describe the response.

The diagram shows a section through a rat. Some of the rat’s organs have been labelled.

What is meant by the term organ ?

Name the organ labelled in the diagram that is part of the circulation system.

Name three other systems shown in the diagram.

Name a system that is not shown in the diagram.

The table lists several processes that take place in the organs of a rat. Complete the table by naming the correct organ for each process.

An investigation was carried out to find out the effect of a growth hormone on milk production. Groups of cows were given different masses of a growth hormone. The volume of milk the cows produced was then measured. The graph shows the results.

mass of growth hormone given per day

How much growth hormone should have been given to the control group?

Describe the effect of growth hormone on milk production.

Farmers want to make reliable comparisons about the effect of different doses of growth hormone.

What was done in this investigation to make the results reliable?

Many variables that affect milk production need to be kept the same for each group of cows. This allows a valid comparison to be made between each group. Give two variables that need to be kept the same.

Growth hormone is a protein. It might be present in the milk produced by the cows and then be consumed by humans. Some people are worried that this may harm humans. Other people say that this is not a problem for two reasons. Firstly, the milk is pasteurised (heated to high temperatures). Secondly, the growth hormone is destroyed in the human stomach.

Suggest what happens to the growth hormone when milk is pasteurised.

Describe how the growth hormone could be destroyed in the stomach.

The growth hormone used in this investigation was obtained from genetically modified bacteria. Describe how bacteria can be genetically modified and used to produce growth hormone.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Conditioned Reflexes Humans respond to stimuli such as sound, sight, smell and taste. Sometimes the response is a simple reflex. If we get a puff of air onto our eye, we blink. If we touch a hot object with our fingertips, we pull our hand away. Another type of reflex is a conditioned reflex. These were first described around the beginning of the 20^th century by the Russian physiologist Ivan Pavlov. Pavlov was studying digestive processes in dogs when he discovered that the dogs began to produce saliva before they received their food. In fact, after several occasions of the lab assistants bringing the food, the dogs started to produce saliva at the sight of the lab assistants. Pavlov called this ‘psychic secretion’. He noted that dogs responded to a biological need (hunger) and also to a need developed by learning.

To experiment on conditioned reflexes, Pavlov used a tuning fork that produced a note of constant frequency. He hit the tuning fork and then gave the dog food. In the beginning the dog produced saliva only when given the food. After the combination of sound and then food were repeated, the dog produced saliva at the sound of the tuning fork. Even when Pavlov took away the food, the dog continued to produce saliva at the sound of the tuning fork alone. The dog had learned to associate one stimulus with another. The dog learned that the first stimulus is to be followed by the second stimulus. In Pavlov’s experiments, the sound of the tuning fork informed the dogs that food was coming. The production of saliva was a conditioned reflex. Pavlov then used a different tuning fork to produce a note of a different frequency. He measured the size of the dog’s response to this note. He could then compare this response to the dog’s response to the original tuning fork. Many examples of conditioned reflexes exist in humans. Some psychologists believe that phobias, such as the fear of spiders, may develop by associating a neutral stimulus with a fearful one.

Humans produce saliva when food is in their mouth. Describe the function of saliva in humans.

Complete the table by giving two sense organs that the dogs use to detect the arrival of food and the stimulus that each sense organ detects.

Explain how reflex responses, such as blinking (line 2), differ from other nerve responses, such as picking up a pencil.

Pavlov originally conditioned the dogs with a tuning fork of note B. The dogs would then produce saliva when the tuning fork was hit. Different tuning forks produce notes of different frequencies as shown in the box.

E G B D F

Suggest why notes G and D produce a greater response in the dogs than notes E and F.

Suggest how Pavlov might have measured the size of the conditioned response.

Scientists make conclusions about humans from studying animal behaviour. Suggest two reasons why these conclusions may not be valid.

Simple reflexes are responses to stimuli. Explain the structure and functioning of a simple reflex arc, using the example of the withdrawal of a finger from a hot object.

A student is given a Petri dish containing starch mixed with agar jelly. The student makes five wells each of diameter 10 mm in the agar. She fills the wells with solutions of amylase, each with a different pH. After 24 hours she pours iodine solution on to the agar jelly. The iodine solution turns the starch in the agar jelly a dark blue colour. The diagram shows the appearance of the Petri dish.

The student measures the clear area around each well using a ruler. Two have been done for you. Complete the remainder of the table.

Explain why there is a clear zone around some of the wells containing amylase.

Explain why the clear zones have a range of different diameters. The diameters of the wells do not change during the experiment.

Name the independent variable in this investigation.

The student keeps the Petri dish at 20 °C to control the temperature in order to make a valid comparison between each pH. Name three other variables that the student needs to control.

The student repeats the experiment, keeping the Petri dish at 37 °C on this occasion. On the diagram, draw the results you would expect to see.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Maggots and Wound Healing The photograph shows maggots eating dead tissue at a human wound.

At the beginning of the 20^th century maggots were widely used to treat wounds. When penicillin started to be used in the 1940s, the use of maggots to treat infections by killing bacteria declined. However, the recent increase in infections caused by antibiotic resistant bacteria such as MRSA (methicillin resistant Staphylococcus aureus) is creating renewed interest in maggots. The maggots used in hospitals to treat wounds are bred in a sterile environment. Green blowfly maggots are used as this species only digests dead tissue and does not burrow down into live flesh. It is not fully understood how the maggots work but there are several theories. The first theory is that they produce an antibiotic in their gut called mirabilicide, which kills the bacteria they eat. A second theory is that the maggots secrete enzymes to break down dead tissue, and digest bacteria in the process. A third theory is that the maggots secrete ammonia as a waste product which changes the pH of the wound, making it unfavourable for bacteria to reproduce. Using maggots to treat a wound also helps to speed up the production of new tissue. One hypothesis is that the wriggling movement of maggots acts as the stimulus, but there is little evidence to support this view. A more likely explanation is that the maggots, or their products, stimulate the body’s immune system to kill bacteria in the wound and allow the healing process to occur. Doctors have developed a ‘maggot bag’, for applying the maggots to wounds. The bags take longer to work than if the maggots are free to move in the wound, so are less useful if the wound needs to be treated quickly. It is expensive to use maggot bags because they cost much more than a typical wound dressing.

State what is meant by the term antibiotic (line 5).

Name two of the antibiotics mentioned in the passage.

Suggest why maggots are bred in a sterile environment (line 7).

Why are green blowfly maggots chosen to treat wounds (line 8)?

Suggest the name of an enzyme used by maggots to digest bacteria (line 13).

Describe how the body’s immune system kills bacteria (lines 19 and 20).

Give a disadvantage of using maggot bags to treat wounds (lines 22 to 24).

Use your knowledge of natural selection to explain why there has been an increase in the number of MRSA bacteria (line 5).

The graph shows the units of energy in the plants and primary consumers in a food chain.

Not all the energy in the plants is transferred to the primary consumers.

Calculate the percentage of energy in plants that is transferred to the primary consumers. Show your working.

One reason why energy is not transferred is because certain molecules in plants cannot be digested. Give two other reasons why energy is not transferred.

Primary consumers can digest the starch from plants. Describe how starch is digested in humans.

The photograph shows a bird called a parakeet.

Parakeets eat seeds. Parakeets can be eaten by birds of prey called raptors. Use this information to draw a food chain.

Many seeds contain starch. Suggest what happens to starch in the gut of a parakeet.

The graph shows the volume of oxygen used by a resting parakeet compared to a flying parakeet.

Calculate the extra volume of oxygen used in litres per gram per hour when flying compared to the volume used at rest. Show your working.

_........ litres per gram per hour

Like humans, parakeets need to keep their body temperature constant. Suggest how the volume of oxygen used by a parakeet at rest would change if it was moved to a colder environment.