Homeostasis Revision Flashcards
What is homeostasis?
The condition of a relatively stable internal environment, maintained within narrow limits. When deviations (increases or decreases) occur in the internal environment of a healthy organism, mechanisms act to restore values to the normal (optimum) state.
What are the components of the steady state control model (SRMERF)?
Stimulus- change in internal environment
Receptor- detects the change
Modulator- control centre (processes info from receptors, compares info to optimum, sends message to effector)
Effector- carries out the response (muscle or gland)
Response- counteracts the stimulus
Feedback- original stimulus changed
What is negative feedback?
An increase in one thing leads to a decrease in another.
What characteristics of an organism’s internal environment need to be maintained within tolerance limits? (8)
- Carbon dioxide
- Oxygen
- Wastes
- Temp
- Salts
- Water
- pH
- Glucose
Explain how animals maintain body fluid homeostasis:
Water gets into your body through food, drink and metabolism. Water is lost from the body through lungs, skin, kidneys and faeces. Fluid balance is water gain = water loss. Long loop of henle = more water reabsorbed. Factors that affect water gain/loss are the environment (availability of water and temperature), structure (SA:Vol, skin, scales and gills) and physiology (kidneys (loop of henle) and large intestine).
List adaptations terrestrial animals have to maintain body fluid and salt levels: (6)
Camels:
* Sweating only at high temps (40oC)
* Concentrated syrupy urine
* Dry faeces
* Metabolism of fat produces water
* Can withstand large water loss- oval shaped blood cells
Kangaroo rats:
* Water from metabolism of food (90%)
* Respiratory moisture condenses in nasal passage
* Long Loop of Henle produces concentrated urine
* Dry faeces - long large intestine
* Burrow during heat of day
Kangaroos
* Metabolic water
* Elongated large intestine- dry faeces
* Concentrated urine
* Efficient locomotion-stretchy tendons= less heat produced
* Feed dawn and dusk- cooler, plants contain more water
Reptiles:
* Scaly skin impervious to water- ↓ evaporation
* N excreted as uric acid paste- low in water
* Nocturnal or shade during day- cooler, ↓ evaporation
Amphibians:
* Near water or humid environments
* Some secrete waxy covering- ↓ evaporation
* Some live underground during dry weather- cooler, humid microclimate
Invertebrates:
* Waxy cuticle- impervious to water
* Uric acid paste- low in water
* Seek shade- ↓ evaporation
* Absorb water from air
Explain the difference between osmoregulators and osmoconformers:
Osmoconformers: maintain ion and water levels to be isotonic with surroundings
Osmoregulators: maintain ion and water levels at an optimum level which is either hypertonic or hypotonic to their surroundings
List adaptations freshwater animals have to maintain body fluid and salt levels: (6)
- large amounts of dilute urine/ high filtration rate in kidneys
- reabsorption of salts/ions in kidneys by active transport
- active uptake of salts through the gills of fish
- cells can actively pump salts into the cells
- preventing water entering the cells so the water only enters the blood and is then excreted
- scales/mucus layer prevents water entering body
List adaptations marine animals have to maintain body fluid and salt levels: (6)
Fish
* drink sea water
* secretory cells in the gut actively absorb salts and transfer them to the blood
* salts actively excreted by secretory glands in the gills
* small amounts of highly concentrated urine
* retaining high levels of urea (cartilaginous fish)
Mammals
* survive on metabolic water by highly efficient reabsorption of water from the rectum (mammals).
Compare nitrogenous wastes in terms of toxicity, solubility and energy expenditure:
Ammonia: extremely toxic, very soluble, energy inexpensive
Urea: mildly toxic, moderately soluble, energy expensive
Uric Acid: Virtually non-toxic, very low solubility, energy expensive
Describe adaptations organisms have to remove nitrogenous wastes and limit water loss:
Ammonia: needs to be excreted in a very dilute urine, excreted directly into surroundings. only fish and larval amphibians which have a large water supply. Produce soft shelled eggs in water so the ammonia produced by the embryo can diffuse into the environment.
Urea: Mammals and Amphibians - animals with access to water. Allows internal development, as foetal urea can be passed across the placenta.
Uric Acid: excreted without loss of H2O, allowing birds and reptiles to live in very dry areas. low toxicity and insolubility means it can be stored in hard shelled, dry eggs during development. Allows birds to fly because they don’t have to carry heavy water with their nitrogenous wastes
Briefly describe the three ways heat moves from one area to another:
- Radiation- 65% of body heat lost this way (no physical contact, waves of energy, the sun)
- Conduction- 2% of body heat lost this way in air (contact, passes from one molecule to another)
- Convection- Approx 15% of body heat lost this way in air (Cool air that comes into contact with a warm body is heated, expands, becomes less dense, so rises)
Explain how SA:Vol affects an organisms ability to lose or gain heat:
Heat is lost at a set rate per unit of area regardless of the volume. Therefore organisms with a higher sa:vol will lose a greater proportion of their heat (or faster) than an organism with a smaller sa:vol. The smaller the organism, the greater the sa:vol therefore the greater the heat loss to the environment and the greater the metabolism required to maintain homeostasis.
Discuss counter current blood flow as an adaptation to a cold environment: (8)
- in paws/extremities
- potentially high rate of heat loss from extremities (lack fur/in contact with ground)
- warm arterial blood (moving from heart to paws)
- passes close to cold venous blood (moving from paws to heart)
- heat is transferred from warm blood to cold blood
- heat transfer is by conduction or conduction and radiation
- blood is already cooled by the time it moves into extremities
- (therefore) less heat loss through extremities
Explain the difference between endotherms and ectotherms:
Ectotherm:
* Gain heat from external environment
(sun/warm rocks/water)
* Body temp fluctuates
* May regulate temp through behaviour
* Most invertebrates, reptiles, amphibians and fish
Endotherm
* Body heat from metabolic activity (internal)
* High metabolism
* Relatively constant temp
* Birds, mammals, some fast fish (tuna), some insects (bumble bees)
