The nervous system

The body controls its internal environment. One example of this is control of the concentration of the blood.

Give the name for controlling the internal environment.

Give the name for controlling the concentration of the blood.

A person entering a warm environment may become dehydrated as the concentration of the blood changes. Explain how the concentration of their blood is restored.

A person’s response to a changing environment involves communication by nerves and by hormones. State three differences between communication by nerves and communication by hormones.

The diagram shows a cell from the human nervous system.

Name the structure labelled A.

Name the structure labelled B.

Draw an arrow on the diagram to show the direction of a nerve impulse.

Describe the role of this neurone in a simple reflex arc.

Nervous communication differs from hormonal communication. State three ways that nervous communication differs from hormonal communication.

The diagram shows a food web from a forest.

Use information from the food web to complete the table. The first one has been done for you.

Plant cell walls are made of cellulose. Cellulose is an insoluble molecule made from the same simple sugar as starch. The rabbit’s intestine contains bacteria that can digest cellulose. Suggest why this is an advantage for the rabbit.

The deer runs away when it sees the wolf.

Name the effector in this response.

The deer releases a hormone when it sees the wolf. Explain how this hormone helps the deer to run away.

The owl uses its eyes to find prey. The diagram shows a section through the owl’s eye.

Name the parts labelled A and B.

Describe the function of part A.

Describe the function of part B.

7 (a) A person touches a sharp pin.

Name the parts labelled A, B, C and D.

Explain how this reflex arc protects the body.

Reflexes in animals and phototropism in plants are both responses to stimuli.

Give two similarities between the mechanisms involved in each response.

Give two differences between the mechanisms involved in each response.

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.