Biology last CAT- teacher A Flashcards
Where does ultrafiltration take place?
The glomerulus.
Describe ultrafiltration:
- the high pressure in the efferent arteriole forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule.
- The liquid and small molecules pass through 3 layers to get into the Bowman’s capsule and enter the nephron tubule (the capillary wall, the basement membrane and the epithelium of the Bowman’s capsule)
- larger molecules like proteins and blood cells can’t pass through so stay in the blood. The substances that enter the Bowman’s capsule are known as the glomerular filtrate.
- The glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way.
- Finally the filtrate flows through the collecting duct and passes out the kidney along the ureter.
What is the efferent arteriole?
- the arteriole that takes blood away from the glomerulus.
- smaller in diameter, making blood under a higher pressure.
What is the afferent arteriole?
-the arteriole that takes blood into each glomerulus
Describe selective reabsorption:
- selective reabsorption takes place as the glomerulus filtrate flows along the proximal convoluted tubule, through the loop of Henle and along the distal convoluted tubule.
- Useful substances leave the tubules of the nephrons and enter the capillary network that wrapped around them.
- the epithelium of the wall of the PCT has microvilli to provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood.
- Useful solutes like glucose are reabsorbed along the PCT by active transport and facilitated diffusio.
- Water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate.
- Water is reabsorbed from the PCT, loop of Henle, DCT and collecting duct.
- The filtrate that remains is urine, which passes along the ureter to the bladder.
What is urine usually made up of?
- Water
- Urea
- Other substances such as hormones and excess vitamins.
What doesn’t urine usually contain?
- Proteins and blood cells- they’re too big to be filtered out pot the blood.
- Glucose- recuasse its actively reabsorbed back into the blood.
Where does most of the regulation of water potential take place?
loop of Henle, DCT and collecting duct.
Describe how the loop of Henle maintains a sodium ion gradient:
1) Near the top of the ascending limb, Na+ ions are pumped out into the medulla using active transport.The ascending limb is impermeable to water, so the water stays inside the tubule.This creates a low water potential in the medulla, because there is a high concentration of ions.
2) because there’s a lower water potential in the medulla than in the descending limb (which is permeable to water), water moves out of the descending limb into the medulla by osmosis.This makes the filtrate more concentrated (the ions cannot move out).The water in the medulla is reabsorbed into the blood through the capillary network.
3) Near the bottom of the ascending limb Na+ ions diffuse out into the medulla, further lowering the water potential in the medulla. The ascending limb is impermeable to water, so stays in the tubule.
4) Water moves out of the distal convoluted tubule by osmosis and is reabsorbed into the blood.
5) The first three stages omassively increase the ion concentration in the medulla which lowers the water potential.This causes water to move out of the collecting duct via osmosis.As before, the water in the medulla is reabsorbed through the capillary network.
How is ADH released?
1) the water potential of the blood is monitored by osmoreceptor cells in the hypothalamus.
2) When the water potential of the blood decreases, water will move out of the of the cells by osmosis making the cells decrease in volume.This sends a signal to other cells in the hypothalamus, which send a signal to the posterior pituitary gland, this causes it to release ADH.
How does ADH work?
1) makes the walls of the DCT and collecting duct more permeable to water
2) This means more water is reabsorbed from these tubules into the blood by osmosis.A small amount of concentrated urine is produced meaning less water is lost fro. the body.
How does water move up a plant?
1) Water evaporates from the leaves at the top of the xylem.
2) This creates tension which pulls water into the leaf.
3) Water molecules are cohesive (they stick together) so when some are pulled into the leaf others follow.This means the whole column of water in the xylem, from the leaves down to the roots, moves upwards.
4) Water enters the stem through the roots.
What is transpiration?
the loss of water from a plants surface:
- water evaporates from the moist cell walls and accumulates in between the spaces between the cells in the leaf.
- when the stomata open, it moves out of the leaf down the concentration gradient.
What are the four main factors that affect transpiration rate?
- light- lighter the faster transpiration- the tomato opens when it is light to let co2 in for photosynthesis.
- temperature- the higher the temp the faster the rate
- humidity- the dryer the air the quicker rate as there is a higher concentration gradient.
- wind- windier the quicker the rate, lots of air movement moves water molecules away from tomato so maintains a higher concentration gradient.
What are examples of xerophytic adaptations?
- stomata sunk in pits that trap moist air reducing, the concentration gradient of water between the leaf and the air, this reduces the amount of water diffusing out of the plant.
- A layer of hairs on the epidermis to trap moist air
- curled leaves with stomata inside protecting them from wind.
- a reduced number of stomata
- waxy waterproof leaves to reduce evaporation.
