Homeostasis Flashcards
Describe how abscisic acid causes the closure of stomata.
ABA binds to receptor on guard cell’s cell surface membrane.
Inhibit proton pump and prevents H+ from leaving the cell.
ABA stimulates Ca2+ ions to enter cytoplasm and act as secondary messenger.
Causes K+ channel protein to open and K+ leaves the cell.
Water leaves cell by osmosis due to high water potential in guard cell.
Flaccid guard cells closes stomata.
Describe the working principles of test strip for glucose.
Strip contains glucose oxidase and peroxidase.
Strip is dipped into urine.
Glucose reacts with glucose oxidase to produce hydrogen peroxidase.
Hydrogen peroxidase reacts with peroxidase to produce colour change.
Colour is matched to a colour chart to give estimate of glucose concentration.
Describe the role of aquaporins in osmoregulation.
Aquaporins are water channel proteins that increases the cell surface membrane permeability to water in the collecting duct. This allows more water to be reabsorbed.
Describe the process that occurs between the Bowman’s capsule and the glomerulus.
It is known as ultrafiltration.
Blood arriving at glomerulus has higher hydrostatic pressure because afferent arteriole is wider than efferent arteriole.
Capillary endothelium has pores so small molecules and blood plasma leaves the capillary.
Basement membrane forms selective barrier.
Describe the process of selective reabsorption.
Na+ actively transported out of cells.
Na+ enters blood.
Na+ concentration decreases in cell.
Na+ enter cells from lumen by facilitated diffusion.
Glucose and amino acids are co-transported with Na+ ions.
Water potential of cell decreases.
Water enter cells from lumen through osmosis.
Glucose and amino acids reabsorbed into blood.
Explain how blood glucose concentration in the body is reduced.
Insulin secreted by liver cells.
Insulin increases uptake of glucose into cells by increasing permeability of cell surface membrane to glucose.
This increases the respiration of glucose in cells.
Insulin also stimulates glycogenesis.
Describe the role of basal membrane in ultrafiltration.
Acts as a selective barrier to prevent molecules more than 69,000 MM such as RBC from passing through.
Describe how the action of antidiuretic hormone (ADH) on the cells of the collecting duct leads to the reabsorption of water in the glomerular filtrate.
ADH binds to receptor on cell surface membrane of collecting duct.
cAMP produced.
Protein kinase activated.
Vesicles of aquoporins activated.
Vesicles move towards the cell surface membrane.
Aquaporins added to cell surface membrane.
This increases the cell surface membrane’s permeability to water.
Water moves out of the collecting duct by osmosis.
