Water Balance

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Why is water balance a critical component of homeostasis?

• Solute concentration is constant so that reactions can occur

• Cell volume and shape is constant (ex: wilting plants)

• Circulatory systems move liquids (ex: blood)

• Evaporative cooling (ex: sweat)

What are the pros and cons of having a large surface area to volume ratio (in plants' leaves)?

Pros: Large surface areas are beneficial to gain the most light and CO2

Cons: Water will leave plants at a greater rate

What are some examples of plants having a large surface area to volume ratio?

• flat leaves

• roots

How do plants minimize water loss in but take in adequate amount of light and CO2?

• succulent stem (holds water)

• waxy (hydrophobic) cuticles

• spines/needle-like leaves

• leaf hairs (keep air out of leaf)

• thick epidermis (more layers)

• stomatal crypts (stores moist air)

stomata

small pores on the bottom of leaves that can open or close to let in/out O2, CO2, and water

guard cells

cells that flank the stomatal pore and regulate the opening and closing of the pore

CAM photysynthesis

• Stomata stay closed during the day, dramatically reducing water loss through transpiration

• Stomata open at night and carbon fixation occurs

C4 photosynthesis

• co2 gets trapped in bundle sheath cells where photosynthesis happens internally

• since stomata stay open for shorter, water loss is decreased

How do organisms limit integumentary (surface) water loss?

• waxy cuticles (ex: insects)

• multiple layers of skin (ex: vertebrates)

How do organisms limit respiratory water loss?

• invaginated (inside the body) respiratory systems (ex: lungs)

• trachea that close (ex: spiracles)

carbon fixation

The addition of carbon atoms from inorganic carbon dioxide to an organic compound

Rubisco

enzyme that converts inorganic carbon dioxide molecules into organic molecules during the final step of the Calvin cycle

How do organisms limit urinary water loss?

they convert ammonia to uric acid or urea

osmosis

the movement of water across a membrane

Which way does water flow though osmosis?

From the side of lower osmolarity—that is, lower solute concentration—to the side of higher osmolarity—higher solute concentration

Osmotic stress

when the concentration of dissolved substances in a cell or tissue is abnormal

osmoregulation

the process by which organisms control the concentrations of water and solutes in their bodies

water potential

the potential energy of a volume of water, expressed as a pressure

water goes from high water potential to low water potential

solute potential

the tendency of water to move by osmosis

pressure potential

the tendency of water to move by pressure

isotonic

water moves

hypotonic

the surrounding solution has a lower solute concentration than a cell

hypertonic

the surrounding solution has a higher solute concentration than a cell

turgor pressure

the pressure of the fluid in the cell