Homeostasis

Question 1

How can organisms limit the external changes to cells?

Answer 1

By maintaining a relatively constant internal environment for their cells.

Question 2

HOMEOSTASIS

Answer 2

The maintenance of a constant internal environment in organisms.

Question 3

What is the internal environment made up of?

Answer 3

Tissue fluids that bathe each cell, supplying nutrients and removing wastes.
Maintaining the features of this fluid at the optimum levels protects the cells from changes in the external environment, thereby giving the organism a degree of independence.

Question 4

What does homeostasis involve and ensure?

Answer 4

Involves maintaining the chemical makeup, volume and other features of the blood and tissue fluid within restricted limits.

Ensures that the cells of the body are in an environment that meets their needs and allows them to function normally despite external changes.

Question 5

Why is homeostasis essential for the proper functioning of organisms?

Answer 5

• The enzymes that control the biochemical reactions within cells, and other proteins, such as channel proteins, are sensitive to changes in pH. Any changes to these factors reduces the efficiency of enzymes or may even prevent them working altogether, eg denaturing them. Even the smallest fluctuations in temperature or pH can impair the ability of enzymes to carry out their roles effectively.
• Changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand as a result of water leaving or entering by osmosis. In both instances the cells cannot operate normally. The maintenance of constant blood glucose conc. is essential in ensuring a constant water potential. A constant blood glucose conc. also ensures a reliable source for resp. by cells.
• Organisms with the ability to maintain a constant internal environment are more independent of the external environment. Have wider geographical range and therefore greater chance of finding food, shelter, etc.

Question 6

What does maintaining a constant internal environment mean?

Answer 6

Reactions take place at a constant and predictable rate.

Question 7

What are the series of stages of control of a self regulating system?

Answer 7

THE SET POINT: which is desired level at which system operates.
RECEPTOR: which detects any deviation from the set point and informs the…
CONTROLLER: which coordinates information from various receptors and sends instructions to an appropriate…
EFFECTOR: which brings about the changes needed to return the system to the set point. This return to normality creates a…
FEEDBACK LOOP: which informs the receptor of the changes to the system brought about by the effector.

Question 8

How are control mechanisms coordinated?

Answer 8

Systems normally have many receptors and effectors. It is important to ensure that the information provided by receptors is analysed by the control centre before action is taken. Receiving information from a number of sources allows a better degree of control.

Question 9

Example of how control mechanisms are coordinated?

Answer 9

Temperature receptors in the skin may signal that the skin itself is cold and that the body temperature should be raised. However, information from the temperature centre in the brain may indicate that blood temperature is already above normal.

This situation could arise during strenuous exercise when the blood temperature rises but sweat cools the skin.

By analysing info from all detectors, the brain can decide the best course of action.

Question 10

What else must the control centre do?

Answer 10

Coordinate action of the effectors so that they operate harmoniously.
E.g. sweating would be less effective in cooling the body if it were not accompanied by vasodilation.

Question 11

Why must body temperature be regulated?

Answer 11

If too low- rate at which enzyme controlled reactions take place may be too slow for the organism to function properly.
If too high- Enzymes may be denatured and the organism may cease to function altogether.

Question 12

What are two methods of gaining heat?

Answer 12

• Production of heat by the metabolism of food during respiration.
• Gain of heat from the environment by conduction (e.g. from ground), convection (e.g. from surrounding air or water) and radiation.

Question 13

What are two methods of losing heat?

Answer 13

• Evaporation of water (e.g. during sweating)
• Loss of heat to the environment by conduction (e.g. to the ground), convection (e.g. to the surrounding air or water) and radiation.

Question 14

CONDUCTION

Answer 14

Occurs mainly in solids and is the transfer of energy through matter from particle to particle. Heat causes the particles to vibrate and gain kinetic energy. These particles cause adjacent particles to vibrate and so the kinetic energy is transferred through the material.

Question 15

CONVECTION

Answer 15

Occurs in fluids (gases and liquids) and is the transfer of heat as a result of the movement of the warmed matter itself. The heat causes the fluid to expand and move, carrying with it the heat that it has absorbed.

Question 16

RADIATION

Answer 16

Energy transferred by electromagnetic waves. When these waves hit an object they normally heat up.

Question 17

ECTOTHERMS

Answer 17

Gain most of their heat from the environment, so their body temperature fluctuates with that of the environment.

Question 18

How do ectotherms control their body temperature?

Answer 18

By adapting their behaviour to changes in the external temperature.

Question 19

Give an example of an ectotherm and explain why it cannot warm up by exercising.

Answer 19

Reptiles- e.g. lizards cannot warm up by exercising because, if their body temperature is low, they cannot respire fast enough to provide the energy for rapid movement.

Question 20

What methods can ectotherms use to control their body temperature?

Answer 20

• EXPOSING THEMSELVES TO THE SUN. In order to gain heat lizards orientate themselves so that the maximum surface area of their body is exposed to the warming rays of the sun.
• TAKING SHELTER. Lizards will shelter in the shade to prevent over-heating when the Sun’s radiation is at its peak. At night they retreat into burrows in order to reduce heat loss when the external temperature is low.
• GAINING HEAT FROM THE GROUND. Lizards will press their bodies against areas of hot ground to warm themselves up. When the required temperature is reached, they raise themselves off the ground on their legs.
• GENERATING METABOLIC HEAT. Although not the main source of heat, respiration still provides a proportion of a lizard’s body heat.
• COLOUR VARIATIONS. Darker colours absorb more heat while lighter colours reflect more heat. Lizards in colder environments are generally darker in colour that those in warmer areas.

Question 21

How do endotherms regulate their temperature?

Answer 21

Gain most of their heat from internal metabolic activities. Their body temperature remains relatively constant despite fluctuations in the external temperature.

Use behaviour to maintain a constant body temperature.
Shelter from cold wind or hot sunshine.
Curl up when its cold and spread out more when it is hot.

Also use a wide range of physiological mechanisms to regulate temperature.

Question 22

What is the core body temperature of endotherms?

Answer 22

35-44C
This range is a compromise between having a temperature at which enzymes work more rapidly and the amount of energy needed to maintain that higher temperature.

Question 23

What are the short term adaptations that mammals and birds in cold climates have evolved to have in order to survive?

Answer 23

-Body with a small surface area to volume ratio.
Within volume that heat is produced and from surface area that heat is lost.
Small SA:vol means the easier it is to maintain a high body temperature.

Mammals in cold climates are therefore relatively large, they also have smaller extremities, such as ears, and thick fur or fat layers for insulation.

Some of these features can be varied over a period of time, e.g. more fat in winter.

Question 24

How do mammals make rapid changes to body temperature? (6)

Answer 24

VASOCONSTRICTION: The diameter of arterioles near the surface of the skin made smaller. This reduces the volume of blood reaching the skin surface through capillaries. Most of the blood entering the skin therefore passes beneath the insulating layer of fat and so loses little heat to environment.

SHIVERING: The muscles of the body undergo involuntary rhythmic contractions that produce metabolic heat.

RAISING OF HEAT: The hair erector muscles in the skin contract, thus raising the hairs on the body. This enables a thicker layer of still air, which is a good insulator, to be trapped next to the skin, thus improving insulation and conserving heat in mammals with thick fur.

INCREASED METABOLIC RATE: In cold conditions more of the hormones that increase metabolic rate are produced. As a result metabolic activity, including respiration, is increased and so more heat is generated.

DECREASE IN SWEATING: Sweating is reduced, or ceases altogether in cold conditions.

BEHAVIOURAL MECHANISMS: Sheltering from the wind, basking in the sun and huddling together all help animals to maintain their core body temperature.

Question 25

What are long term adaptations to life in a warm climate?

Answer 25

Large SA:volume ratio (large extremities, such as ears) Lighter coloured fur to reflect heat.

Question 26

What are the rapid responses that enable heat to be lost when environmental temperature is high?

Answer 26

VASODILATION: The diameter of the arterioles near the surface of the skin becomes larger. This allows warm blood to pass close to the skin surface through the capillaries. The heat from this blood is then radiated away from the body. INCREASED SWEATING: To evaporate water from the skin surface requires energy in the form of heat. In relatively hairless mammals, such as humans, sweating is highly effective means of losing heat. In mammals with fur, cooling is achieved by the evaporation of water from the mouth and tongue, which occurs when air is rapidly passed over these surfaces during panting. LOWERING BODY HAIR: The hair erector muscles in the skin relax and the elasticity of the skin causes them to flatten against the body. This reduces the thickness of the insulating layer and allows more heat to be lost to the environment when the internal temperature is higher than the external temperature. BEHAVIOURAL MECHANISMS: Avoiding the heat of the day by sheltering in burrows and seeking out shade help to prevent the body temperature from rising.

Question 27

What are the two parts of the thermoregulatory centre in the hypothalamus?

Answer 27

- Heat gain centre- which is activated by a fall in blood temperature. This controls the mechanisms that increase body temperature. - Heat loss centre- which is activated by a rise in blood temperature. This controls the mechanisms that decrease body temperature.

Question 28

How is temperature regulation an example of homeostasis? (steps)

Answer 28

STIMULUS: a change in body temperature Detected by RECEPTORS: Thermoreceptors which pass the information to a COORDINATOR: Hypothalamus in the brain, which then causes an EFFECTOR: the skin to produce the appropraiate RESPONSE: increase or decrease in core temperature.

Question 29

HYPOTHALAMUS

Answer 29

Region of the brain adjoining the pituitary gland that acts as a control centre for the autonomic nervous system and regulates body temperature and fluid balance.

Question 30

Describe the regulation of body temperature.

Answer 30

The hypothalamus monitors the temperature of the blood passing through it. In addition the thermoreceptors in the skin measure skin temperature. These thermoreceptors send impulses along the autonomic nervous system to the hypothalamus. They provide information on the environmental temperature and so give advanced warning of potential changes in the core body temperature. The animal can therefore take measure to conserve or lose heat as appropriate, before core temperature is affected. The two sets of thermoreceptors (in the hypothalamus and the skin) interact to control temperature. Of the two it is the core temperature, as measured in the blood passing through the hypothalamus, which is most important.

Question 31

How does problems with the thyroid cause inability to regulate body temperature?

Answer 31

An overactive thyroid can cause a person to become too hot whereas an under active thyroid can cause people to become too cold. The thyroid produces hormones that are able to influence how much blood vessels dilate, which in turn affects how much heat can escape from the body.

Question 32

What is the regulation of blood glucose an example of?

Answer 32

How different hormones interact in achieving homeostasis.

Question 33

What characteristics do hormones have in common?

Answer 33

- produced by glands, which secrete the hormone directly into the blood (endocrine glands). - Carried in the blood plasma to the cells on which they act- known as target cells- which have receptors on their cell-surface membranes that are complementary to the hormone. - are effective in very small quantities, but often have widespread and long-lasting effects.

Question 34

How does the second messenger model of hormone action work?

Answer 34

- The hormone is the first messenger. It binds to specific receptors on the cell-surface membrane of target cells to form a hormone-receptor complex. - The hormone-receptor complex thus produced activates an enzyme inside the cell that results in the production of a chemical that acts as a second messenger. - The second messenger causes a series of chemical changes that produce the required response. In the case of adrenaline, this response is the conversion of glycogen to glucose.

Question 35

PANCREAS

Answer 35

Large, pale coloured gland that is situated in the upper abdomen, behind the stomach.

Question 36

What does the pancreas produce?

Answer 36

Enzymes (protease- breaks down protein, amylase- starch and lipase- fats) for digestion and hormones (insulin and glucagon) for regulating blood glucose.

Question 37

What is the pancreas largely made up of?

Answer 37

When examined microscopically, the pancreas is made up largely of the cells that produce its digestive enzymes. Scattered throughout these cells are groups of hormone producing cells known as islets of LAngerhans.

Question 38

What are the two types of cells of the islets of Langerhans?

Answer 38

- alpha cells, which are the larger and produce the hormone glucagon. - beta cells, which are smaller and produce the hormone insulin.

Question 39

What is the main substrate for respiration?

Answer 39

Glucose- provides the source of energy for almost all organisms.

Question 40

Why is it essential that the blood of mammals contains a relatively constant level of glucose?

Answer 40

For respiration- Glucose broken down during glycolysis and, if oxygen is present, the Kreb's cycle and electron transport chain, to provide ATP (the energy currency of cells).

Question 41

What happens if levels of glucose fall too low?

Answer 41

Cells will be deprived of energy and die- brain cells are especially sensitive in this respect because they can only respire glucose.

Question 42

What happens if glucose levels rise too high?

Answer 42

Lowers water potential of the blood and creates osmotic problems that can cause dehydration and be equally dangerous.

Question 43

What is the normal level of glucose?

Answer 43

90mg in each 100cm3 of blood.

Question 44

Where does blood glucose come from?

Answer 44

- DIRECTLY FROM THE DIET. In the form of glucose resulting from the breakdown of other carbohydrate. - FROM THE BREAKDOWN OF GLYCOGEN (GLYCOGENOLYSIS) stored in the liver and muscle cells. A normal liver contains 75-100g of glycogen, produced by converting excess glucose from the diet in a process called glycogenesis. - FROM GLUCONEOGENESIS, which is the production of new glucose (from a source other than carbohydrate). The liver, for example, can make glucose from glycerol and amino acids.

Question 45

Why does level of glucose fluctuate in animals?

Answer 45

Do not eat continuously and diet varies. | Also glucose is used up at different rates depending on the level of mental and physical activity.

Question 46

What do the beta cells of the islets of Langerhans in the pancreas do when they detect a rise in blood glucose level?

Answer 46

Respond by secreting the hormone insulin directly into the blood plasma.

Question 47

INSULIN

Answer 47

A globular protein made up of 51 amino acids.

Question 48

What do almost all body cells have that bind with insulin molecules?

Answer 48

GLYCOPROTEIN RECEPTORS on their cell surface membrane.

Question 49

What does insulin bring about when it combines with glycoprotein receptors?

Answer 49

- A change in the tertiary structure of the glucose transport protein channels, causing them to change shape and open, allowing more glucose into the cells. - An increase in the number of carrier molecules in the cell-surface membrane. - Activation of the enzymes that convert glucose to glycogen and fat.

Question 50

How is blood glucose lowered by the binding of insulin to glycoprotein receptors?

Answer 50

- By increasing the rate of absorption of glucose into the cells, especially in muscle cells. - By increasing the respiratory rate of cells, which therefore use up more glucose, thus increasing their uptake of glucose from the blood. - By increasing the rate of conversion of glucose into glycogen (glycogenesis) in the cells of the liver and muscles. - by increasing the rate of conversion of glucose to fat.

Question 51

What is the effect of the processes brought about by insulin binding to glycoprotein receptors?

Answer 51

To remove glucose from the blood and so return its level to normal. This lowering of blood glucose level cause the beta cells to reduce their secretion of insulin (=negative feedback)

Question 52

What do the alpha cells in the islets of Langerhans do?

Answer 52

Detect a fall in blood glucose and respond by secreting the hormone glucagon directly into the blood plasma.

Question 53

Where are the receptors that bind to glucagon?

Answer 53

Only the cells of the liver have receptors that bind to glucagon, so only liver cells respond.

Question 54

What do liver cells do once glucagon has been bound to their receptors?

Answer 54

- Activate an enzyme that converts glycogen to glucose. | - Increasing the conversion of amino acids and glycerol into glucose (gluconeogenesis).

Question 55

What is the overall affect of glucagon binding to receptors on liver cells?

Answer 55

Increase the amount of glucose in the blood and return it to its normal level. The raising of blood glucose causes the alpha cells to reduce glucagon secretion (=negative feedback).

Question 56

When is adrenaline produced?

Answer 56

At times of excitement or stress.

Question 57

Where is adrenaline produced?

Answer 57

By the adrenal glands that lie above the kidneys.

Question 58

How do adrenaline raise glucose levels?

Answer 58

- It activates glycogenolysis (glycogen to glucose) - It inhibits glycogenesis (glycogen from glucose) - Activates glucagon secretion and inhibits insulin secretion.

Question 59

When is glucagon produced?

Answer 59

Released overnight and between meals.

Question 60

What does it mean that insulin and glucagon act antagonistically?

Answer 60

They act in opposite directions, insulin lowers blood glucose level and glucagon increases it.

Question 61

How is the insulin/ glucagon system self regulating?

Answer 61

It is the level of glucose in the blood that determines the quantity of insulin and glucagon produced. This allows highly sensitive control of blood glucose level.

Question 62

What does glucose level fluctuate around?

Answer 62

The set point- negative feedback.

Question 63

Describe how blood glucose level is controlled by negative feedback.

Answer 63

Only when blood glucose level falls below a set point is the insulin secretion reduced, leading to rise in blood glucose. In the same way, only when the level exceed the set point is glucagon secretion reduced, causing a all in the glucose level.

Question 64

What is diabetes?

Answer 64

A chronic disease in which a person is unable to metabolise carbohydrate, especially glucose, properly. Metabolic disorder caused by the inability to control blood glucose levels due to lack of insulin or loss of responsiveness to insulin.

Question 65

Which form of diabetes is more common?

Answer 65

Diabetes mellitus (sugar diabetes).

Question 66

What is Type 1 (insulin dependent) diabetes caused by?

Answer 66

The body being unable to produce insulin.

Question 67

When does Type 1 diabetes usually begin?

Answer 67

Childhood.

Question 68

What could Type 1 diabetes the result of?

Answer 68

An autoimmune response whereby the body's immune system attacks its own cells, in this case the B-cells of the islets of Langerhans. After eating, the blood glucose level rises and stays high- hyperglycaemia. The kidneys can't reabsorb all the glucose, so some is excreted in urine.

Question 69

How does Type 1 diabetes develop?

Answer 69

Quickly, over a few weeks, and symptoms are normally obvious.

Question 70

What are the symptoms of diabetes?

Answer 70

- High blood glucose level. - Presence of glucose in urine. - Increased thirst or hunger. - Need to urinate excessively. - Genital itching or regular episodes of thrush. - Tiredness. - Weight loss. - Blurred vision.

Question 71

What is Type 2 diabetes usually due to?

Answer 71

The glycoprotein receptors on the body cells losing their responsiveness to insulin. However, it may also be due to an inadequate supply of insulin from the pancreas.

Question 72

When does Type 2 diabetes usually develop?

Answer 72

In people over the age of 40. | However, an increasing number of cases of obesity and poor diet leading to Type 2 diabetes in adolescents.

Question 73

How does Type 2 diabetes develop?

Answer 73

Slowly and symptoms are usually less severe and may go unnoticed.

Question 74

How is type 1 diabetes controlled?

Answer 74

By injection of insulin, typically either two or four times a day. The dose of insulin must be matched exactly to the glucose intake as glucose levels may drop dangerously low (hypoglycaemia).

Question 75

What percentage of those with diabetes have type 2?

Answer 75

75%

Question 76

Why can't insulin be taken orally?

Answer 76

Being a protein, it would be digested in the alimentary canal.

Question 77

What happens if a diabetic takes too much insulin?

Answer 77

They will experience a low blood glucose level that can result in unconsciousness.

Question 78

How is the correct does of insulin ensured?

Answer 78

Blood glucose levels are monitored using biosensors.

Question 79

How is type 2 diabetes controlled?

Answer 79

By regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken. In some cases this may be supplemented by injections of insulin or by the use of drugs that stimulate insulin production. Other drugs slow down the rate at which the body absorbs glucose from the intestine.

Question 80

What is gestational diabetes?

Answer 80

Diabetes that arises in pregnant women. Usually goes away once baby is born.

Question 81

What causes gestational diabetes?

Answer 81

It is the hormonal changes (hormones made by the placenta that resist insulin) in the second and third trimesters of pregnancy, along with the growth demands of the foetus, that increase a pregnant woman's insulin needs by two to three times that of normal. If your body cannot make this amount of insulin, sugar from the foods you eat will stay in your blood stream and cause high blood sugars.

Question 82

How is gestational diabetes usually managed?

Answer 82

diet and exercise. | rarely need insulin injections

Question 83

What is Type 3 diabetes?

Answer 83

Title that has been proposed for Alzheimer's disease which is results from insulin resistance in the brain.

Question 84

What is double diabetes?

Answer 84

When someone with type 1 diabetes develops insulin resistance, a key feature of Type 2 diabetes.

Question 85

What is the most common reason for developing double diabetes?

Answer 85

Obesity

Question 86

What is secondary diabetes?

Answer 86

``` Diabetes that results from a medical condition: Cystic fibrosis Hemochromatosis Chronic pancreatitis Polycystic ovary syndrome (PCOS) Cushing's syndrome Pancreatic cancer Glucagonoma Pancreatectomy ```

Question 87

How is a blood clot rapidly activated after injury?

Answer 87

- Platelets become activated and release a chemical- this triggers more platelets to be activated. - Platelets very quickly form a blood clot at the injury site. - The process ends with negative feedback, when the body detects the blood clot has been formed.

Question 88

How do both adrenaline and glucagon activate glycogenolysis inside a cell even though they bind to receptors on outside of cell? (Second messenger model)

Answer 88

- Adrenaline and glucagon bind to their specific receptors and activate an enzyme called adenylate cyclase. - Activated adenylate cyclase converts ATP into a chemical signal called a "second messenger". - The second messenger is called cyclic AMP. - cAMP activates a cascade that breaks down glycogen into glucose.