Homeostasis

Question 1

Outline the roles of progesterone

Answer 1

• secreted during the second half of the cycle (from day 14 onwards)
• maintains endometrium
• in preparation for implantation
• inhibits GnRH (development of new follicle)

Question 2

Describe the mechanisms involved in reabsorption in the proximal convoluted tubule and describe how the epithelial cells of the proximal convoluted tubule are adapted to carry out this process.

Answer 2

Mechanisms

• active transport of Na+ out of proximal convoluted tubule cells
• sets up an Na+ ion gradient
• facilitated diffusion using protein carrier
• contra sport of glucose/ AA/ ions from lumen to proximal convoluted tubule cell
• osmosis occurs
• down water potential gradient
• diffusion of x down a concentration gradient

Adaptations

• microvilli
• many mitochondria
• tight junctions
• folded basal membrane
• many transport proteins
• many aquaporins

Question 3

Describe structure of kidney

Answer 3

Outer cortex
Medulla
Pelvis
Renal artery
Renal vein
Nephron
Renal capsule/ PCT/ DCT in cortex 
Loop of Henle/ collecting duct in medulla
Glomerulus 
Afferent and efferent arterioles
Capillary network surrounds tubule/ in medulla

Question 4

Explain why oocytes that have a first polar body are used in the fertilisation process

Answer 4

• indicates that they have undergone meiosis I

- so they are haploid

Question 5

Outline how the loss of potassium ions from guard cells will lead to the closure of a stoma.

Answer 5

Water potential of guard cells increases (becomes less negative)
Water leaves cells by osmosis
Guard cell becomes flaccid

Question 6

Describe how gibberellin brings about fertilisation in seeds

Answer 6

Gibberellin moves from embryo to aleurone layer
Gene switched on/ transcribed/ used to make mRNA
Amylase produced
Amylase hydrolyses starch to maltose
For respiration
For growth in embryo

Question 7

Describe the roles of the hypothalamus and the posterior pituitary in osmoregulation

Answer 7

Hypothalamus detects changes in water potential of the blood
Osmoreceptors shrink when low/less water in blood
ADH produced in hypothalamus
If low water potential, ADH secreted from posterior pituitary
Neurosecretory cells
Aquaporins
ADH increases permeability of distal convoluted tubule
ADH causes more water reabsorption/ smaller volume of urine/ more concentrated urine

Question 8

State precisely the sites of secretion of each oestrogen and progesterone

Answer 8

Oestrogen = follicle
Progesterone = corpus luteum

Question 9

Explain how combined oral contraceptives produce their effects

Answer 9

Oestrogen/ progesterone affect anterior pituitary
Inhibit secretion of FSH/ LH
Follicles do not develop
No ovulation
Negative feedback
Alters cervical mucus to stop sperm
Prevents implantation

Question 10

Describe two social implications of the use of contraceptives

Answer 10

Smaller population so less poverty
Greater care for children that are born
More STD
Population decrease

Question 11

Describe the part played by the proximal convoluted tubules in the functioning of the kidneys

Answer 11

Selective reabsorption
PCT cells have microvilli therefore large SA
PCT cells have many mitochondria 
Na+ leave PCT cells
By active transport 
Na+ concentration falls in PCT cells 
Na+ diffuse from lumen into PCT cells
through transporter proteins 
Co-transport of glucose/ AA/ chloride ions
From PCT cells into intercellular fluid 
Then diffusion into blood
Normally all glucose reabsorbed into blood
Some water reabsorbed into blood
Some urea reabsorbed into blood
(Creatinine secreted into lumen AVP)

Question 12

Explain how the collecting ducts in the kidneys may reduce the loss of water from the body

Answer 12

ADH affects collecting duct
Binds to receptor on membrane and increases membrane permeability to water
Enzyme controlled reactions produces active phosphorylase
Which causes vesicles with aquaporins to fuse with the plasma membrane
More water flows out of the collecting duct
Down/ along water potential gradient
Then into blood
Urine more concentrated/ small volume of urine
Negative feedback
AVP Role of loop of Henle in creating water potential gradient

Question 13

Explain how glomerular filtrate is formed

Answer 13

Endothelium of blood capillaries/ glomerulus
More/ large gaps between endothelial cells
Podocytes
Large gaps between podocytes/ filtration slits
Basement membrane is a selective barrier/ acts as a filter
Prevents large proteins from passing through
No cells pass through
Things that are filtered through = urea/ water/ glucose/ uric acid/ creatinine/ Na+ etc
High blood pressure in glomerulus
Afferent arteriole wider than efferent arteriole
Lower pressure in renal capsule/ Bowman’s capsule
Fluid forced into capsule/ ultrafiltration

Question 14

Explain how the destruction of B cells causes diabetes

Answer 14

B cells detect glucose levels
B cells secrete insulin
When blood glucose conc rises, insulin causes muscle cells to increase uptake of glucose from blood/ increased membrane permeability to glucose
Insulin causes liver cells to increase respiration of glucose
If no B cells, no control of blood glucose levels

Question 15

Outline the effect of ADH on the collecting ducts

Answer 15

Enzyme signalling
Aquaporins 
Vesicles containing aquaporins move fuse with cell membrane 
Increased permeability 
Water leaves lumen into cells by osmosis

Question 16

Describe the main stages of cell signalling in the control of blood glucose concentration by adrenaline

Answer 16

Adrenaline binds to receptors in the cell surface membrane and the receptor changes conformation as a result.
G proteins are activated and so is adenyl cyclase, which catalyses the conversion of ATP to cyclic AMP which is a second messenger
Cyclic AMP acts as a second messenger and activates protein kinase which activates an enzyme cascade. The enzyme cascade leads to the activation of many molecules of glycogen phosphorylase that break down glycogen to glucose. Glucose then diffuses out of the cells into the blood and there is an increase in blood glucose concentration.