Maintaining Internal Environments (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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Define homeostasis.
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Cards in this collection (49)
Define homeostasis.
The regulation of the internal conditions of a cell or organism, keeping them within narrow limits.
Why must the internal environment be kept constant?
So that metabolic reactions can proceed at the right rate, with enzymes working at their optimum.
Name three internal conditions the body keeps constant.
Body temperature, pH and blood glucose concentration.
Water content and blood pressure are also controlled.
What happens if homeostatic limits are exceeded?
Enzymes and cells stop working properly, and the organism may become ill or die.
Why is homeostasis described as involuntary?
It happens automatically, without conscious thought.
Which two types of response are used in homeostasis?
Nervous responses and chemical (hormonal) responses.
What do receptors do in a homeostatic control system?
They detect the stimulus — a change in the internal or external environment.
What do effectors do in a homeostatic control system?
They bring about the response that restores the condition to its optimum level.
How does the body correct a level that has risen too high?
It responds to make the level fall again, so the condition returns to normal.
Why must the body respond to external changes too?
Changes outside the body, such as a change in temperature, would otherwise disturb the internal conditions.
Why is the level constantly monitored rather than fixed?
Conditions are always being disturbed, so the level is kept within a narrow range by constant small corrections.
Define negative feedback. (Higher Tier Only)
A control mechanism in which a change in a factor triggers a response that reverses it, returning the level to normal.
＿＿＿＿＿＿＿＿ is the regulation of the internal conditions of a cell or organism.
Homeostasis is the regulation of the internal conditions of a cell or organism.
Keeping conditions constant lets ＿＿＿＿＿＿＿＿ work at their optimum rate.
Keeping conditions constant lets enzymes work at their optimum rate.
True or False?
Homeostasis keeps conditions at exactly one fixed value.
False.
Conditions vary slightly and are constantly corrected, so they stay within a narrow range.
True or False?
You have to think consciously to control your blood glucose.
False.
Homeostasis is automatic — it happens without conscious control.
Which organ produces insulin?
The pancreas.
What triggers the release of insulin?
The pancreas detecting that the blood glucose concentration is too high.
How does insulin lower blood glucose concentration?
It stimulates liver and muscle cells to take up glucose from the blood.
The glucose is stored as glycogen.
Define glycogen.
A polymer of glucose used as an insoluble storage molecule in the liver and muscles.
Why is blood glucose stored as glycogen rather than glucose?
Glycogen is insoluble, so it can be stored without affecting the water balance of cells.
Why is a very high blood glucose concentration dangerous?
Cells lose water by osmosis to the concentrated blood, which damages them.
Why is a very low blood glucose concentration dangerous?
The brain does not get enough glucose for respiration, which can lead to a coma or death.
What causes type 1 diabetes?
The pancreas does not produce enough insulin, because the cells that make it have been destroyed.
What causes type 2 diabetes?
The body still makes insulin, but the body cells no longer respond to it — they have become resistant.
How is type 1 diabetes treated?
With insulin injections, replacing the insulin the pancreas cannot make.
How is type 2 diabetes treated?
With a carbohydrate-controlled diet and regular exercise.
Why would insulin injections not help someone with type 2 diabetes?
Their cells are resistant to insulin, so adding more would make little difference.
Name a major risk factor for type 2 diabetes.
Obesity.
What do both types of diabetes have in common?
Both lead to uncontrolled high blood glucose levels.
Insulin causes excess glucose to be stored in the liver and muscles as ＿＿＿＿＿＿＿＿.
Insulin causes excess glucose to be stored in the liver and muscles as glycogen.
In type 1 diabetes the ＿＿＿＿＿＿＿＿ does not produce enough insulin.
In type 1 diabetes the pancreas does not produce enough insulin.
True or False?
People with type 2 diabetes produce no insulin at all.
False.
They still produce insulin, but their cells no longer respond to it. It is type 1 where insulin is not produced.
True or False?
Insulin lowers the concentration of glucose in the blood.
True.
It causes liver and muscle cells to take glucose out of the blood and store it as glycogen.
Which organ produces glucagon? (Higher Tier Only)
The pancreas, acting as an endocrine gland.
What triggers the release of glucagon? (Higher Tier Only)
The pancreas detecting that the blood glucose concentration is too low.
What effect does glucagon have? (Higher Tier Only)
It causes glycogen stored in the liver to be converted back into glucose, which is released into the blood.
How do insulin and glucagon act together? (Higher Tier Only)
Insulin lowers blood glucose by storing it as glycogen.
Glucagon raises it by converting glycogen back to glucose. Together they hold the level steady.
Why are insulin and glucagon described as a negative feedback system? (Higher Tier Only)
A rise in glucose triggers insulin, which lowers it.
A fall triggers glucagon, which raises it. Each change causes a response that reverses it.
Describe what happens when blood glucose falls too low. (Higher Tier Only)
The pancreas detects the fall and secretes glucagon.
Glycogen in the liver is converted to glucose, so the blood glucose level rises back to normal.
What stops glucagon being secreted? (Higher Tier Only)
The blood glucose concentration returning to normal — the pancreas then stops releasing it.
Which organ stores the glycogen that glucagon acts on? (Higher Tier Only)
The liver.
Which hormone would be released after a meal? (Higher Tier Only)
Insulin, because blood glucose rises as the food is absorbed.
Which hormone would be released during a long fast? (Higher Tier Only)
Glucagon, because blood glucose falls as it is used up in respiration.
Which hormone would rise during hard exercise, and why? (Higher Tier Only)
Glucagon — muscles are respiring rapidly, so glucose is used up and must be released from glycogen stores.
Glucagon converts ＿＿＿＿＿＿＿＿ stored in the liver back into glucose. (Higher Tier Only)
Glucagon converts glycogen stored in the liver back into glucose.
Insulin and ＿＿＿＿＿＿＿＿ have opposite effects on blood glucose concentration. (Higher Tier Only)
Insulin and glucagon have opposite effects on blood glucose concentration.
True or False?
Glucagon and glycogen are the same thing. (Higher Tier Only)
False.
Glucagon is a hormone; glycogen is the storage polymer of glucose that the hormone acts on.
True or False?
Both insulin and glucagon are made by the pancreas. (Higher Tier Only)
True.
The pancreas secretes both, releasing whichever is needed to correct the blood glucose level.
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