practice errors made (component three) Flashcards
explain what is meant by homeostasis
it is the maintenance of a constant internal environment in the body, to counteract a stimulus and provide the optimal condition for reactions in the body
why does a person not feel thirsty after an increase in the solute potential of the blood but only after a certain threshold
Because, straight after the solute potential increases, the ADH released into the bloodstream by the posterior pituitary gland can achieve sufficient water reabsorption through the collecting ducts
after reaching a certain threshold, the solute potential becomes too high and the person has to drink water to avoid dehydration, hence they become thirsty.
name three conditions that stimulate to ADH secretion
severe diarrhea
vomiting
blood loss
explain how the nephron and it’s blood supply are adapted for ultrafiltration
the glomerulus has a high hydrostatic blood pressure which forces small molecules like glucose out of the capillaries
the capillaries have fenestrae through which the molecules leave into the PCT
podocytes and pedicels in the basement membrane increase the filtration rate
the basement membrane is permeable to water and glucose but not large molecules like protein and starch
the efferent arteriole is narrower that the afferent arteriole and that increases the pressure in the glomerulus
explain how chloride ions are selectively reabsorbed
they diffuse through the phospholipid membrane of the cells of the PCT by facilitated diffusion, through channel proteins, down their concentration gradient
explain how water is selectively reabsorbed
water moves through the partially permeable membranes of the cells of the PCT by osmosis, down it’s water potential gradient
explain how sodium ions are selectively reabsorbed
they have actively transported out the cells of the PCT, using energy from ATP against their concentration gradient, through a sodium-potassium pump.
there are more sodium ions in the filtrate than in the PCT cells, so a concentration gradient is generated
the sodium ions diffuse down their concentration gradient into the PCT cells, through channel proteins, which only allow the sodium ions to diffuse through if coupled with glucose
a parasite
an organism that lives in a host and obtains nourishment at the expense of the host, by doing harm to it
autotroph
organism that uses inorganic molecules to synthesise organic compounds
saprobionts
organisms that secrete enzymes on food outside the body, thereby feeding by extracellular digestion, and then absorbing the products by diffusion
three features of the gut parasite that are characteristics to their parasitic way of life
they produce a large number of eggs
they have hooks and suckers for attachment to the host’s gut
they are thin, to provide a large surface area for absorbing pre-digested food by the host
they have no digestive system, as they feed on pre-digested food by the host
how is the mode of nutrition of parasites similar to that of carnivores
they both feed by doing harm to other organisms
how is the parasitic mode of nutrition different from that of a carnivore
carnivores digest their own diet, while parasites feed on a pre-digested diet by their host
carnivores have a digestive system while parasites do not
parasites absorb food externally, while carnivores absorb food internally
how is a tapeworm adapted to resist peristalsis in the human intestine
it has hooks and suckers to attach to the intestinal walls
why does a tapeworm not need a mouth for feeding
because it absorbs it’s nutrients through it’s body surface, so there is no need for a mouth
functions of cuticles on the body of a tapeworm
it protects the worm from the effects of enzymes and acids in the gut
functions of muscles in the body wall of tapeworms
it allows the tapeworm to increase contact with the digested food
how does a low-protein diet lead to fluid retention in the tissues
presence of proteins reduces water potential of the blood
so less protein means a higher water potential of the blood
so there is little water potential gradient between the blood and the fluid
so less water is reabsorbed into the blood(more water remains in the tissue fluid)
why are log scales used on the axes of graphs
it makes it easy to compare values that cover a large range
apart from the exchange of gases and nutrients, state three other roles of the placenta
provides a barrier between the maternal and foetal blood
protects the foetus from the mother’s immune system
protects the foetus from differences between the mother’s and the foetal’s blood
advantage of a 25 percent increase of red blood cells in the blood of a pregnant woman
can carry more oxygen to the developing foetus
advantage of a parasite not secreting digestive enzymes
does not have to waste it’s own resources in synthesizing it’s own digestive system
advantages of capillaries being narrow
friction in blood vessel increases, so blood flow is slower
therefore there is more time for exchange of substances to occur
features of water that enable it to travel up the xylem
hydrogen bonds formed between partially positive hydrogens and partially negative oxygen of adjacent water molecules provide cohesion
this creates a transpiration stream up the xylem as water leaves the leaves during transpiration
Adhesion is also provided to the walls of the xylem vessel
