Organisms Response To The Environment - Homeostasis

Question 1

What is the definition of homeostasis?

Answer 1

The maintenance of a constant internal environmemt via physiological control systems to survive a greater range of habitats

Question 2

Why is temperature controlled by homeostais?

Answer 2

Too high: enzymes will denature as their tertiary structure will become distored due to the breaking of r group interactions

Too low: kinetic energy of the substrates decreases and so less emzyme substrate complexes are formed

Question 3

Why is blood glucose concentration controlled by homeostasis?

Answer 3

Too high: water potential of blood plasma decreases so water leaves cells by osmosis
Too low: glucose is a respiratory substrate so the ATP cycle decreases which if stops could cause cell death

Question 4

Why is water potential controlled by homeostasis?

Answer 4

Too high: the cell swells which could cause it to burst
Too low: the solute concentration increases distrorting r group interactions in proteins such as transport proteins and enzymes altering their tertiary structure so much less escs are formed

Question 5

How do organisms know when to trigger a response to a change in their internal environment?

Answer 5

• greater deviation from set point
• stronger error signal from the hypothalamus
• effectors have to work more to counteract the deviation
• deviation from set point decreases
• error signal decreases
• effectors reduce their response

Question 6

What is positive feedback? Give an example

Answer 6

When a deviation from the optimum causes changes that result in even greater deviation from the normal e.g. in the neurones where a stimulus causes a small influx of sodium ions which increases the permeablity of the neurone membrane to sodium ions so more enter

Question 7

Give the negative feedback loop for the increase in temperature (include all the effectors)

Answer 7

1. Stimulus = the increase in temperature as the input stimulus
2. Receptors = thermoreceptors in the hypothalamus
3. Output signal triggers autonomic nervous system or hormones
4. Effectors:
   - vasodilation in the arterioles so blood runs closer to the skim surface for faster heat loos
   - erector muscles relax so body hair is lowered
   - sweat glands release water by evaporation
5. Response = cooling effects reducing the input signal so the output signal is reduced as negative feedback

Question 8

What is negative feedback?

Answer 8

When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off

Question 9

What hormone is released at hyperglycaemia?

Answer 9

Blood glucose concentration too high from set point so insulin released

Question 10

What hormones are released at hypoglycaemia?

Answer 10

Blood glucose comcentration is too low from set point so glucagon and adrenaline are released

Question 11

What chemical processes occur during hyperglycemia?

Answer 11

• glycogenisis = the conversion of glucose to glycogen
• conversion of glucose to lipid
• increased metabolism so increased respiration to reduce blood glcuose levels

Question 12

What chemical processes occur during hypoglycaemia

Answer 12

• glycogenolysis = breakdown of glycogen to glucose

- gluconeogenisis = production of glucose from non carbohydrate sources e.g amino acides to glucose

Question 13

How is the increase in blood glucose regulated?

Answer 13

1. Stimulus of the increased blood glucose concentration is detected as the input signal by the receptors being beta cells in the pancreas
2. The output signal triggers insulin release which is a polypeptide hormone so a chemical messenger
3. Effectors = liver/ muscle tissue
4. Insulin binds to the protein receptor in the cell surface membrane of liver / muscle cells.
5. Tertiary protein structure changes shape and the cells insert carrier proteins through which the glucose can enter the cell via facilitated diffusion
6. Glucose is polymerised into glycogen
7. Response is triggered of blood glucose concentration being lowered
8. Negative feedback

Question 14

How is a decrease in blood glucose concentration regulated?

Answer 14

1. Stimulus of the decreased blood glucose concentration is detected as the input signal by the receptors being alpha cells in the pancreas
2. The output signal triggers glucagon release which is a polypeptide hormone so a chemical messenger
3. Effectors = liver
4. Glucagon binds to the protein receptor in the cell surface membrane of liver cells.
5. Tertiary protein structure changes shape and the cells insert carrier proteins
6. Glycogen glycosidic bonds are hyrolysed to release alpha glucose which moves out if tge carrier proteins by facilitated diffusion
7. Response is triggered of blood glucose concentration being increased
8. Negative feedback

Question 15

What three factors influence blood glucose concentration?

Answer 15

• glucose from hydrolysis of consumed carbohydrates such as starch
• glycogenolysis
• gluconeogenisis

Question 16

What is the mechanism by which adrenaline in regulates blood glucose?

Answer 16

1. Adrenaline binds to the transmembrane protein receptor in the cell surface membrane of the liver cell
2. Tertiary structure of protein receptor changes shape activating adenyl cyclase enzyme inside the membrane
3. Convertes ATP to cAMP (cyclic AMP) whihc acts as a second messenger
4. cAMP changes the tertiary protein structure shape and activates kinase enzyme
5. Active kinase catalyses conversion of glycogen to glucose

Question 17

Describe the two forms of diabetes

Answer 17

Type I - insulin dependent

Type II - insulin resistant

Question 18

How are the two types of diabetes controlled?

Answer 18

Type I - Insulin injections that cant be taken by mouth as insulin is a protein and would be digested by the alimentary canal. Blood glucose concentration is monitored using biosensors to ensure corect insulin dose

Type II - controlled by regulating carbohydrate intake in diet based on level of exercise. Drugs can stimulate insulin production or slow down rate of glucose absorption by the intestine

Question 19

What are the three things to know about hormones in general?

Answer 19

• Produced in glands which secrete the hormone directly into the blood
• carried in blood plasma to target cells which have specific receptors on their cell surface membranes which are complementary to a specific hormone
• effective in very low concentration and have widespread long lasting effects

Question 20

What does the kidney’s structure consist of?

Answer 20

• fibrous capsule: outer protective membrane
• cortex: lighter coloured region made of bowmans capsules, convuluted tubes and blood vesseles
• medulla: darker coloured region (kind of heart shaped) made of loops of henle, collecting ducts and blood vessels
• renal pelvis: the funnel shaped cavity that collects urine into the ureter
• ureter: carries urine into bladder
• renal vein: returns blood back to heart
• renal aretry: supplies kidney with oxygenated blood from the aorta

Question 21

What do the afferent and efferent arteriole do?

Answer 21

• Afferent arteriole is a tiny blood vessel that supplies the nephron with blood via the renal capsule
• efferent arteriole is a tiny blood vessel with a diameter smaller than the afferent arteriole causing an increase in blood pressure in the arteriole and carries blood away from the renal capusle

Question 22

Label the structire of the nephron

Answer 22

Check biology folder

Question 23

Give the broad sequence of events in the kidney

Answer 23

1. Ultrafiltration in the glomerulus
2. Selective reabsorption in the proximal convoluted tuble
3. Loop of henle maintains a sodium ion concentration gradient so water can be reabsorbed into the blood comcentrating the urine
4. Water moves out of the distal convuluted tuble and into the collecting duct to return it back to the blood and the collecting duct carries the remaining liquid being urine to the ureter

Question 24

give the steps to ultrafiltration

Answer 24

1. There is a high hydrostatic pressure in the glomerulus
2. This is because the efferent arteriole is narrower than the incoming afferent arteriole so have higher blood presure
3. Water solutes pass out through the tiny endothelial pores
4. Pass through a basement membrane which is a molecular filter
5. Pass through the slits in the podocytes which prevent the capillary bursting as they grip it
6. This forms a filtrate in the renal capsule

Question 25

What part of the blood’s composition is squeezed out of the capillary to make the glomerular filtrate?

Answer 25

The blood plasma except the plasma proteins as they are too large to pass through the selectively permeable membrane. Eveything else thats part of the blood e.g. red blood cells are also too large so dont pass through.

So everything that does pass through is

• glucose
• amino acids
• electrolytes
• urea
• water

Question 26

What in the glomerular filtrate ends up in the urine?

Answer 26

Excess water and salt as well as urea, glucose, amino acids

Question 27

How is urea made and give the steps of the sequence

Answer 27

Through deamination:

1. Red glood cells are broken down into haemoglobin
2. The Hb is hydrolysed into amino acids
3. The amine group is removed from the NH4+ which is very toxic hence turns into urea so it can be excreted

Question 28

What are the structurual features of the proximal convulted tuble that help it carry out its fun tion? What is its function?

Answer 28

• has a large surface area due to many microvilli
• numerous mitochondria to generate ATP which releases energy for active transport

Its function is to carry out selective re absorption

Question 29

Give the steps to selective re absorption

Answer 29

1. Na+ is actively transported out if the proximal convuluted tuble into the blood capillary (pct) by the active transport so ATP driven exchange pump
2. This lowers the na+ conc in the pct so there is a higher concentration of na+ in the glomerular filtrate
   3, the na+ diffuses down the concentration gradient from the filtrate into the pct via co transporter protein bringing in glucose with it
3. Glucose diffuses down the concentration gradient out of the the pct into the blood capillaey via carrier protein in facilitated diffusion
4. Water diffuses down the concentration gradient into the pct and into the blood capillary via osmosis
5. Very dilute urine remains in the glomerular filtrate

Question 30

Why is the salt gradient useful in the medulla of the loop of henle?

Answer 30

Because it means that in any section of the descending limb, there is always a downwards water potential gradient so water can diffuse out by osmosis across the whole length of the decending limb

Question 31

Why is the top of the ascending limb thicker than the rest?

Answer 31

To make space for mitochondria which produce ATP which release energy for the active transport of sodium ions

Question 32

Give the steps of comcentrating urine at the loop of henle

Answer 32

1. The descending limb wall is impermeable to na+ ions and permeable to water while the ascending limb wall is impermeable to water and permeable to na+ions
2. At the top of the ascending limb, active transport forces dilute salt out of the ascending limb
3. The water potential gradient means the water potential is higher in the descending limb than the ascending limb
4. Water diffuses out if the top of the descending limb down the water potential gradient by osmosis
5. In the descending limb, the volume of water decreases and the comecntration of salts increase and the salt becomes increasiningly concentrated further down the descending limb
6. At the bottom of the descending limb going into the ascending limb, salts can now diffuse out

Question 33

Give a sign of diabetes

Answer 33

Sugar in the urine

Question 34

Give the steps of osmoregulation when the water potential is below the set point

Answer 34

1. Stimulus is the water potential of the blood plasma being to low in dehydratiom
2. osmoreceptors in the hypothalamus shrink due to the dehydration triggering the response
3. Response being polypeptide hormone ADH is secreted from the posterior pituitary and directly diffuses into the blood capillary
4. ADH binds to the protien receptors in the plasma membrane lining the collecting duct
5. The tertiary structure of the protein receptors changes shape to activate specific phosphorylase enzyme
6. Phosphorylase enzyme creates vesicles which fuse with the plasma membranes to form aquaporins increasing membrane permeability to water so water diffuses out by osmosis
7. This means more water in the blood is retained so less is lost in urine

Question 35

What are the steps of osmoregulation when water is above the set point?

Answer 35

1. The stimulus is that the water potential of the blood plasma is too high
2. Osmoreceptors in the hypothalamus swell and so trigger the response of the prosterior pituitary secreting less of the polypeptide hormone ADH
3. There is less ADH to bind to the protein receptors in the plasma membrane lining the collecting duct so less phosphorylase enzyme is activated and less vesicles fuse with the membrane so less aquaporins are inserted making the membrane less permeable to water
4. This means the urine has a higher water potential as its more dilute and so more water leaves the body