Water balance in organisms

Kidneys  Eliminate ammonia/urea  Ensure water balance: dilution of urine

Blood pressure  Water level goes up, so does blood pressure  Governed by antidiuretic hormone (ADH or vasopressin)

Vasopressin  Produced in hypothalamus  Dehydration = more vasopressin  Vasopressin stops water moving from blood into urine  Also creates a thirsty sensation to animal

Renin  Hormone secreted in kidneys  Response to low blood pressure  Allows more water into blood, increase blood pressure again

Water balance in organisms OrganismWays to balance water Amoeba-Enters cell by osmosis -Excess water expelled by vacuoles FishSee table 10.4 on pg 328 -generally: salt water fish conserves water, fresh water expels water Sea birds-Must conserve water -Concentrated uric acid (like urine) -Excess salt excreted from salt glands above eyes, runs out nose Reptiles- Aquatic – do not need to conserve water - Terrestrial usually need to conserve water - Deactivation of water excreting part of kidney -Water reabsorbed from cloaca - May have salt secreting glands Amphibians-frogs: continuous uptake of water from surrounds via skin osmosis -Produce a lot of dilute urine

Activities Glossary: renin, vasopressin, diuretic Quick Check pg 330

Water balance in plants  90 – 95% of plant = water

Stomata: pores in leaf  May be covered by cuticle, which is water proof  Stomata open to let water in or out  As water leaves through stomata, more water is pulled up the xylem to replace it

Transpiration  Loss of water vapour through stomata 5/show/transpiration.swf  Transpiration stream is the stream of water from roots to top of plant

Cuticle  Thin cuticle means more transpiration/water loss can occur

Sunken stomata  Stomata sunk into pits  Prevents water loss by creating a barrier between the water in the leaf and the outside air  Fine hairs on leaves may do a similar thing

Rolled up leaves  Reduce surface area, and area for water to be lost

Succulents  Have large vacuoles to store excess water  Dry climates  Thick cuticle  Few stomata

Factors affecting transpiration  Humidity – lots of water in air = less transpiration  Wind – less wind/air movement = less transpiration  Air temperature – low temperature = less transpiration  Stomata close if too much water is lost

Activities Glossary: transpiration stream, stomata, cuticle Quick Check questions pg 335 Biochallenge Chapter review questions: 2, 3, 5, 6, 7, 9, 10, 13, 15