Control And Coordination

Question 1

Suggest how monoclonal antibodies can be used to obtain purified u-hFSH from urine

Answer 1

Produce monoclonal antibodies that are specific to u-hFSH
Column for attachment/ immobilisation
Urine added/ flows over antibodies
So allowing hormone (hFSH) to bind to monoclonal antibodies
Treatment needed to release hormone from monoclonal antibodies

Question 2

Outline how an action potential arriving at the neuromuscular junction can result in the depolarisation of the sarcolemma

Answer 2

Ca 2+ channels open in pre synaptic membrane
Ca 2+ enter pre synaptic knob
Vesicles containing ACh move towards the pre-synaptic membrane
ACh is released and diffuses across the cleft
ACh binds to receptors on the sarcolemma
Na+ channels open and Na+ enters the sarcoplasm

Question 3

Describe the events occurring during muscle contraction

Answer 3

Sarcolemma is depolarised 
so the transverse t tubules are depolarised 
Ca 2+ ions diffuse out of the sarcoplasmic reticulum 
Ca2+ ions bind to troponin
Troponin changes shape
Tropomyosin moves 
Binding sites on actin are exposed
Myosin heads bind to actin
Myosin heads tilt
Sarcomere shortens

Question 4

Explain the role of abscisic acid in cell elongation in plants

Answer 4

Acid growth hypothesis:
Auxin stimulates proton pumps in the cell surface membrane
H+ is pumped into the cell wall by active transport
PH of cell wall therefore decreases so pH-dependent enzymes are activated
Expansins are proteins which break bonds between cellulose microfibrils
The cell wall therefore loosens so that more water can enter the cell
So cell wall expands

Question 5

Describe the role of abscisic acid in the closure of stomata

Answer 5

At times of water stress, a plant will secrete abscisic acid
Abscisic acid binds to receptors on the cell surface membranes of guard cells and inhibits the proton pump
This means that H+ not pumped out of cell so there is a high H+ conc inside the cell
Abscisic acid stimulates Ca 2+ influx
Ca 2+ acts as the secondary messenger and encourages the efflux of K+ ions
Water potential of the cell increases, so water moves out of the cell by osmosis
Volume of guard cells decreases
Guard cells become flaccid
Response is very fast