Homeostasis & Waste

Question 1

Homeostasis

Answer 1

“The maintenance of a constant internal environment (for cells) by an organism.” It is the ability to return to the set point of ‘norm’. By environment, this tends to mean tissue fluid

Question 2

Tissue fluid

Answer 2

formed from blood plasma, supplies nutrients (e.g. glucose) and removes waste (e.g. urea).

Question 3

Factors that need to be regulated for cells to carry out normally

Answer 3

temp, pH, blood glucose and water potential.

Changes in these factors still take place but they fluctuate around a set point or ‘norm’.

Question 4

Negative feedback meaning

Answer 4

The process of returning to a set point, as a result of an input (change to system). Movement away from the set point is detected and causes movement back towards it.

Question 5

Negative feedback flowchart

Answer 5

INPUT -> RECEPTOR -> CO-ORDINATOR -> EFFECTOR -> RESPONSE

Question 6

What causes the oscillation around the ‘norm’?

Answer 6

Time delays in control systems.

Question 7

Positive feedback

Answer 7

A system in which the effector increases the change - movement away from (not back to) the ‘norm’. Only a few systems in the body operate under positive feedback.

Question 8

Give two examples of positive feedback

Answer 8

Blood clotting - platelets secrete signalling molecules which attract more platelets.
Labour ie giving birth.

Question 9

Target cells

Answer 9

These cells have receptors (like glycoproteins) embedded in the plasma membrane that are complementary shape to the hormones.

Question 10

What does the process of homeostasis achieve?

Answer 10

Helps maintain optimal conditions for cellular reactions. Gives independence from the external environment. The internal environment can maintain conditions throughout different levels of activity.

Question 11

What are hormones?

Answer 11

molecules released by endocrine glands directly into the blood that travel to a target organ to produce an effect.

Question 12

What are endocrine glands?

Answer 12

ductless glands that secrete hormones directly into the blood, e.g. posterior pituitary gland, which secretes anti-diuretic hormone.

Question 13

Excretion

Answer 13

The removal of metabolic waste made by the body. The mammalian body excretes compounds using four excretory organs: kidneys, lungs, skin and liver.

Question 14

Egestion

Answer 14

The removal of undigested food material as faeces.

Question 15

Secretion

Answer 15

The release of useful substances from cells.

Question 16

Exocrine glands

Answer 16

Glands that secrete substances into a duct.

Question 17

Duct

Answer 17

A tube lined with epithelial cells that produces a secretion, e.g. the pancreatic duct.

Question 18

What are the three types of nitrogenous excretory products?

Answer 18

Ammonia, urea and uric acid

Question 19

Describe ammonia

Answer 19

Molecules are small, very toxic and soluble.

Question 20

What animals excrete ammonia and how do they excrete it?

Answer 20

Most aquatic animals excrete ammonia.
SOFT-BODIED INVERTEBRATES - Ammonia diffuses across the whole body surface into the water.
FRESHWATER FISH - Most of the ammonia is lost as ammonium ions (NH4+) across the epithelium of the gills.

Question 21

How do terrestrial animals deal with their ammonia?

Answer 21

Most convert it to urea, to excrete.

Question 22

How is ammonia created?

Answer 22

Excess amino acids (proteins) are deaminated and this leaving to NH3 molecules (ammonia) that need to be dealt with.

Question 23

Why do terrestrial animals convert ammonia to urea?

Answer 23

Because they would have to produce lots of urine to get rid of ammonia, because a compound so toxic could only be transported and excreted in a very dilute solution. Urea can be transported in a much more concentrated form because it is about 100,000 times less toxic than ammonia. It is important to conserve water, living on land.

Question 24

What animals excrete uric acid?

Answer 24

Birds, land snails, insects, some reptiles

Question 25

Uric acid details

Answer 25

1000s of times less soluble in water than either ammonia or urea, and is excreted as a precipitate after nearly all the water has been reabsorbed from the urine. In birds and reptiles, the paste-like urine is eliminated (egested) along with faeces.

Question 26

Describe deamination in humans

Answer 26

Excess amino acids are broken down to ammonia and keto acid by liver cells in this process.

Question 27

What happens to the urea and keto acid after the ornithine cycle and deamniation?

Answer 27

Then urea is carried by the plasma in the blood stream to the kidney. The remaining keto acid can then be respired to release its energy or be converted to carbohydrate or fat for storage.

Question 28

Ornithine cycle

Answer 28

In the ornithine cycle, the potentially toxic ammonia reacts with CO2 to produce less toxic and soluble urea - this is facilitated by liver cells…?

Question 29

What happens to urine once it is produced by the kidney?

Answer 29

Urine passes through the ureters to the bladder, for storage. It is then released out of the body, through the urethra.