Homeostasis

Question 1

Define homeostasis

Answer 1

Homeostasis is the maintenance of constant internal environment, allowing them to function normally despite internal or external changes such as changes in temperature pH in water potential

Question 2

Organisms that control the environment and more independent of their environment
What does this lead to?

Answer 2

Greater geographical range, so can colonise more habitats and ecosystems
Greater chance of finding food, shelter and mates

Question 3

Basic control mechanism

Answer 3

The set point- optimum or Norm at which the system operates at for example body temperature
A receptor - detects changes from the set points and informs the controller for example, baroreceptors
Controller - coordinates information from various receptors and sends instructions to an appropriate effect
For example, the brain
The effector- brings about the changes needed to return the system to the set point
For example, a grand
Feedback loop - informs the Receptor of the changes to the system brought about by the effector

Question 4

Define negative feedback

Answer 4

When there is an increase or decrease from the set point, the opposite effect is instigated producing a response that returns the value to norm

Question 5

Define positive feedback

Answer 5

When a deviation from an optimum causes even greater deviation from the normal

Question 6

Explain how insulin reduces the blood glucose concentration

Answer 6

More insulin binds to receptors
Simulates uptake of glucose by channel proteins
Activate enzymes which converts glucose to glycogen

Question 7

Explain the action of glucagon

Answer 7

Attaches to receptors on target cells and activates enzymes
Glycogen to glucose
Gluconeogenesis

Question 8

Explain the effect of sweating or panting on temperature control

Answer 8

Evaporation of water from lining of mouth or skin
Heat transferred from blood

Question 9

Describe how a change in blood PH of blood pressure can cause a change in heart rate.

Answer 9

Carbon dioxide detected by chemoreceptors or pressure detected by baroreceptors
Cardiac centre
More impulses to the Sino atrial node along the sympathetic nerve

Decrease PH detected my chemo receptors in carotid artery
Send more impulses to the medulla
More nerve impulses sent by the sympathetic nervous system to sinoatrial node

Question 10

Less carbon dioxide in blood leads to a reduction in heart rate
Explain how

Answer 10

Less carbon dioxide in blood detected by chemoreceptors
Chemoreceptors located in aorta or carotid artery
Fewer impulses to the cardiac centre
Less impulses along the sympathetic nerve
To Sino atrial node

Question 11

Describe the secondary messenger model

Answer 11

Second messenger produced
Activate enzymes in c cell
So Glyco neogenesis occurs

Question 12

Describe the role of glycogen information and its role in lowering the blood glucose levels

Answer 12

Glucose concentration in cells fall
Below that in blood
Maintains glucose concentration
Glucose into cells by facilitated diffusion using carrier channel proteins

Question 13

Describe how blood glucose levels can be increased using hormones

Answer 13

Release of glucagon
Leads to formation of glucose in the liver
From non carbohydrates

Question 14

Describe how ultrafiltration occurs in glomerulus

Answer 14

High blood pressure
Water and glucose pass out
Through gaps in endothelium
Through capillaries basement membrane

Question 15

Explain why a thicker medulla leads to more concentrated urine

Answer 15

Thicker Medela means longer loop of Henle
Increase in sodium ion concentration, so sodium ion gradient maintained for longer
So water potential gradient maintained so more water reabsorbed by osmosis

Question 16

Describe the action of ADH in the kidney

Answer 16

Permeability of membrane is increased
More water absorbed from collecting duct
Smaller volume of urine
Urine becomes more concentrated

Question 17

Explain why glucose is found in the urine of a person with untreated diabetes

Answer 17

High concentration of glucose in the blood
Not all glucose is reabsorbed at the proximal convoluted tubule
Co transport proteins and carrier proteins are working at maximum rate

Question 18

Control of high blood glucose concentration

Answer 18

Insulin is synthesised and secreted by beta cells in the pancreas
Insulin binds to complimentary receptors on the cell surface membrane of target cells
This controls the uptake of glucose by regulating the inclusion of glucose carrier proteins in the surface membrane of target cells
Insulin also activates enzymes that stimulate the conversion of glucose to glycogen- glycogenesis
Decreasing blood glucose

Question 19

Control of low, blood glucose concentration

Answer 19

Glucagon is synthesised and secreted by alpha cells in the pancreas
Glucagon binds to receptors on the cell surface membrane of target cells
Activating enzymes involved in the hydrolysis of glucagon to glucose- glycogenolysis
Activating enzymes involved in the conversion of glycerol and amino acids into glucose -glyconeogenesis

Question 20

Which cells in the pancreas secrete hormones

Answer 20

Islets of Langerhans

Question 21

Control of blood glucose after a meal

Answer 21

Glucose is absorbed from the ileum into the hepatic portal vein
Blood glucose concentration increases which is detected by the pancreas
Pancreas secretes insulin from beta cells
Insulin causes, gout, close to be taken up by the liver and converted into glycogen
This reduces blood glucose, which is detected by pancreas which stops secreting insulin
If glucose levels fall too far, this is detected by the pancreas
Pancreas secretes glucagon from his alpha cells
Glucagon causes deliver to hydrolyse some of its glycogen store to glucose
Diffuses into the blood down a concentration gradient by facilitated diffusion
Increases blood glucose, which causes Pancras to stop secretin glucagon
Negative feedback loop

Question 22

Second messenger model of hormone action- adrenaline and glucagon

Answer 22

1. Adrenaline and glucagon both bind to specifiic receptor on the surface of target cell= first messenger
2. Hormone- receptor complex causes a change in receptor protein change tertiary structure
3. Also activates adenylate cyclase resulting in the conversion of atp into cyclic AMP= secondary messenger
4. Secondary messenger causes series of chemical changes that produce the required rapid response
5. CAMP is secondary messenger and activates kinase enzymes which produce a cascade of chain reactions that catalyse the glycogen to glucose

Question 23

Glucagon

Answer 23

Hormone

Question 24

Glycogen

Answer 24

Energy store

Question 25

Glycogenesis

Answer 25

Glucose to glycogen

Question 26

Glycogenolysis

Answer 26

Glycogen to glucose

Question 27

Gluconeogenesis

Answer 27

Glucose from amino acids and glycerol

Question 28

Diabetes
Type one

Answer 28

Insulin dependent
Severe insulin deficiency due to autoimmune killing beta cells or faulty gene

Question 29

Diabetes
Type two

Answer 29

Non insulin dependent
Insulin produced but insulin receptors in target cells are unresponsive so insulin has no effect

Question 30

How diabetes occurs

Answer 30

Very high blood glucose concentration after a meal
Active transport pumps into proximal convoluted tubule of the kidney which can’t re absorb it all from kidney filtrate
So glucose excreted into urine

Question 31

Symptoms of diabetes

Answer 31

High thirst due to osmosis of water from cells to blood which had low water potential
Large volumes of urine production due to excess water in the blood
Poor vision due to osmotic loss of water from eye lens
Tiredness due to loss of glucose in urine and poor uptake of glucose by liver and muscle cells

Question 32

Treatment diabetes

Answer 32

Insulin injections
Managed diet