Past WACE Papers Homeostasis Questions Flashcards
List four different adaptations of plants to a dry environment.
- extensive root system to maximise water absorption
- leaves curl in hot weather to minimise surface area exposed - reduces water loss.
- stomata on the underside of leaves only to minimise water loss
- leaves reudced to spins - photosynthesis takes place on stem - less stomata on stem - minimises water loss
Some desert animals do not need to drink water. explain how they can survive.
some mammals rely on the water produced in the resspiration of carbohydrates
- the water is normally lost mostly in exhaled air
these animsl may not need to drink
they have mechanisms to rettain this water - e.g. cool extensive nasal passages that condese water in exhaled air
i.e. carbohydrate + oxygen -> carbon dioxide + water.
How can diverting blood flow to ears aid in thermoregulation.
reducing the blood flow to the ears by vasoconstriction in cold weather, reduces the rate of heat loss from the animal per g of body weight Increasing the blood flow to the ears (by vasodilation) in hot weather, increasing the rate of heat loss per g or body weight.
Why do tadpoles excrete ammonia while frogs excrete urea?
tadpoles are aquatic animals, have abundant water available to them. this is an energy efficient solution to its N-waste disposal; to dilute toxic ammonia in order to excrete it safely. Adult frogs are mostly terrestrial, they have less water available to use in N-waste disposal. Being less toxic than ammonia, urea does not require much dilution,, it is therefore more water conserving to excrete urea.
Explain the circumstances in which it is an advantage to mammal to excrete uric acid?
animal lives in an environment where water is a scarce resource e.g. desert
animals has enough energy to convert its ammonia into uric acid
uric can be excrete in an undiluted form i.e. as a paste as it is not toxic
water is therefore converved by the animal
Marine bony fish excrete only a small volume of urine explain why?
marine bony fish live in salt water that has a higher osmotic pressure than its internal boy fluids. this fiesh tends to lose water thourgh its gills and digestive tract by osmosis. to conserve water it reabsorbs water from its urine and concentrates its urine. thus volume of urine excreted is reduced.
Outline the role of the effector in homeostasis.
an effector e.g. muscle or gland, respinds to a stimulus
an effector receives a message (e.g. via nerves or hormones) and carriers out a particular response.
Outline the role of the receptor in homeostasis.
a receptor conssits of cells, tissues or organs that detect a stimulus (an external or internal change)
the receptor then conveys a message directly or indirectly to effector/s
State the defining feature of a negative feedback loop.
the response reverses/reduces the stimulus
Is a fishes regulation of salt and water an example of homeostasis?
yes
a marine fish tends to lose express water its external environment by osmosis
the fish will actively excrete salt from its gills and or drink more water, then remove salt by active transport from its gills, in order to maintain a fairly constant internal fluid concentration.
List four features that would assist a plant in water conservation.
- hair-like structures (trichomes) - reduce airflow around the stomates. this reduces water loss by evaporation from the leaves
- recessed stomates create humid pockets of air, increasing the humidity around the stomates which reduces evaporation from the leaves
- a thick waxy cuticle over the upper epidermis reduces water loss from the leaf’s upper surface and reflects heat from the leaf
- the multicellular layers in the upper epidermis provide a thick layer of cells that reduce evaporative water loss.
What are two advantages of surface roots for xerophytes.
roots that grow just below the surface of the soil enable xerophytic plants to exploit any dew that form during cool nights in summer. deeper roots are too removed from this water
light rain may fall during summer, surface roots may capture this water. light showers are unlikely to penetrate far into the soil, the water is likely to evaporate rapidly in summer.
Define homeostasis.
homeostasis means the maintenance of stability within the body of an organism
State the defining feature of a negative feedback mechanism.
if the response in feedback loop reverses the stimulus, it is called a negative feedback
Explain how a greater Bilbys ears could help it to thermoregulate.
the ears are large and highly vasculated, they have a dense network of blook vessels
precapillary sphincters control amount of blood flowing though these blood vessels
when body temp rises, sphincters relax, vasodilation of the blood vessels in ears occurs. more blood flows though them and more head is radiated and conducted from the atmosphere
this vasodilation hekps reduce the bilbys body temperature, reuturning it to normal
Why does the colour of lizards scales change?
pale scales reflect suns radiant heat energy
darker scales abosrb the suns heat energy
therefore, due to change, in warmer months lizard’s body temp will be reduced slightly and during col weather it will be increased slightly
in this way the lizard’s body temp is regulated and kept within broad limits
Why are there few ectotherms in cold environments
warm water provides warm envionrment for ectotherms like sea snakes
they absorb heat energy directly from the water which bathes them
they remain active in the water as it provides the necessary heat energy
How do xerophytes lose water to their environment
- they lose water via transpiration, when stomates are open for photosynthesis
- they lose water through evaporation, through leaf and stem cuticles.
Outline two ways in which animals obtain water in arid environments.
reabsorption of water in exhaled air, nasal structures may have extensive vascular tissue adapted to recapture this moisture
respiratory water, the water that is produced as a by-product of respiration is retained in the animal’s cells. the animal may be adapted to survive on a mainly dry carbohydrate diet.
Outline challenges fish face in water that is hypersaline.
in hypersaline conditions the fish tends to lose body water to envionment though osmosis via its gills and other exposed membranes e.g., lining of digestive system.
To maintain a suitable osmotic pressure within its cells the fish may swallow large amounts of salty water and actively transport salt from its gills while retaining the water.
Outline challenges fish face in water that is hypo-saline.
in hypo saline conditions the fish tends to gain water from the environment by osmosis and lose salts from its gills and digestive tract.
to maintain a suitable osmotic pressure within its cells the fish may not drink any water/ the fish may actively transport salt from its environment via its gills and into its circulating blood.
Outline two main ways in which rodents that live in deserts lose water to the environment.
water is lose in the waste produces. e.g., urine,faeces
urea that is excrete is dissolved in water as urine
faeces contaoin some wate in order to be defaecated
air that is inhaled in dry conditions has a low humidity
when exhaled the water in the humidified air is lost.
Why do animals in deserts need larger kidneys?
desrt animals nedd to reabsorb a greater proportion of water from their urine than animals in other enviornments
they have kidneys in the tubels that reabsorb water from urine filtrate are longer/more numerous - therefore their kidnyes have a greater mass
these tubules will enable a greater proportioion of water, that would be otherwise lost, to be recovered and returned to the blood.
Their urine is, as a result of the reabsorption of water, more concerntrated.
Why does a specialised beak aid in water conservation.
a large beak, which rich supply of blood enables the birds to losee heat at a greater rate than normal.
their blood, which is generally warmer than external environment, would radiate heat to the outside environment and move by conduction to the air and be carrierd away by convection
the amounrt of blood travelling close to the surface in the beak may be adjusted by vasoconstriction and vasodiliationh according to how much heat needs to be lost
host lost from blood will cool the body of the organism and lower its overall body temperature.
Why is a higher body temperature good for desert birds?
objects radiate heat to other objects that have a lower temperautre
the rate at which the heat energy is lost is faster if the temperature difference is greater i.e., if the temperature gradient is greater
the bird’s higher temperature creates a greater temperature gradient between their bodies and the environment
What is brown adipose tissue?
Brown adipose tissue has a high level of mitochondria, so they produce lots of heat by respiration.
This is commonly found in mammalian babies and hibernating animals.
Explain the problems that a bony fish experiences in maintaining water and salt balance in seawater
and explain how the fish solves these problems. (10 marks)
salt concentration in the blood of a bony fish is lower than the seawater concentration. This
creates a concentration gradient, so the water flows from low salt concentration in the fish’s blood
to higher concentration. in the seawater by osmosis. Therefore, maintaining water balance is
difficult as the fish loses water into the sea.
To solve this problem, fish use osmoregulation. This involves drinking seawater to replace lost water.
Excess salt in the seawater is removed through active transport by secretory cells in the gills. The
kidneys have few glomeruli, which facilitates water conservation by producing only. a small volume
of concentrated urine.
What is the main advantage of maintaining a constant body temperature?
enzymes function optimally
