Water in Cells and Living Things

Water in the Cells

• All living things are made of one or more cells.
• All cells contain cytoplasm.
• Cytoplasm is comprised of cytosol (a gel-like substance), organelles (e.g., mitochondrion), macromolecules, and ions.
• Cytosol is about 70-80% water and usually colorless.
• Cellular metabolism occurs within the watery content of the cytosol.
• Water is essential for cellular processes like photosynthesis.

Water Around the Cells

• Tissue: a group of cells with similar functions.
• Connective tissue: cellular + non-cellular components.
• Blood: connective tissue comprised of 45% red/white blood cells and 55% blood plasma.
• Blood plasma is 92% water.

Water in Living Things

• Water accounts for 60-70% of the human body.
• Water composes approximately 60-95% of different living things.
• Water is essential for life.
• Brain tissue is 75% water.
• Blood is 83% water.
• The heart is 79% water.
• Bones are 22% water.
• Muscles are 75% water.
• The liver is 86% water.
• The kidneys are 83% water.

Beginning of Life

• Life initially evolved in a marine environment.
• First macromolecules, then organelles, culminated in cells.
• Hydrothermal vents on the deep ocean floor provide abundant water and nutrients in the absence of light.

Water's Polarity

• Hydrogen and oxygen form covalent bonds within a water molecule.
• Hydrogen has a slightly positive charge (H+), while oxygen has a slightly negative charge (O-).
• Each water molecule attracts other water molecules, forming hydrogen bonds due to its polarity, contributing to water's properties of attraction.
• Water attracts or is attracted to other polar molecules and ions.
• Substances that interact with or dissolve in water are hydrophilic (hydro=water, -philic=loving)

Sodium Chloride + Water = Ions + Water

• Salt is made up of sodium chloride (NaCl).
• The positive part of water molecules (hydrogen+) attracts negative chloride ions (Cl-).
• The negative part of water molecules (oxygen-) attracts positive sodium ions (Na+).

Ions Dissolved in Water: Ions Dissolved in the Cytosol

• Ions are important for cell processes, particularly in cellular processes.
• A decrease of chloride ions (Cl-) in the egg's cytosol changes the electronegativity from negative to positive.

Water's States: Gas, Liquid, and Solid

• Liquid water: hydrogen bonds constantly form and break as water molecules slide past each other.
• Gas water: when water boils, the higher energy causes hydrogen bonds to break, releasing water molecules into the air as steam or vapor.
• Solid water: when water temperature reduces, water molecules form a crystal structure via hydrogen bonding.
• Solid water is less dense than liquid water due to hydrogen bonds orienting as the water freezes and pushes the molecules farther apart.
• Ice floats at the surface of liquid water.
• Upon freezing, ice crystals rupture the delicate cell membrane and proteins required for living cells to function
• Adding a solution like glycerol, binds with water’s hydrogen bonds, to make it difficult to crystalize until -37.8C.

Water's High Heat Capacity

• Water's high heat capacity results from hydrogen bonding among water molecules.
• Water has the highest specific heat capacity of any liquid.
• Water is super strong when it comes to heat: A small amount of water can hold a lot of heat without its temperature rising.
• It takes water a long time to heat and a long time to cool.
• Blood plasma is mostly water: this is a great way to disperse and save heat in the body
• Fever is a result of the body's heat capacity.
• The induction of fever in endothermic animals occurs at a high metabolic cost such that a 1°C rise in body temperature requires a 10–12.5% increase in metabolic rate.

Water's Solvent Properties

• Water, a polar molecule with slightly positive and negative charges, can readily dissolve ions and polar molecules, making it a great solvent.
• Ions and polar molecules form hydrogen bonds with water, surrounding the particle with water molecules (sphere of hydration)
• Table salt (NaCl) + water = Na+ + Cl- + water.

Water's Cohesive and Adhesive Properties

• Cohesion allows for surface tension.
• Surface tension is the capacity of a substance to withstand rupturing when placed under tension or stress.
• Water molecules are attracted to each other because of hydrogen bonding.
• A water strider can float on surface water due to its cohesive properties.
• Attraction can be stronger than water's cohesive forces, especially where water is exposed to charged surfaces such as capillary tubes.
• Water “climbs” up the capillary tube.
• Capillary action: water appears higher on the tube's sides than in the middle because water molecules are more attracted to the capillary's charged glass walls than to each other.
• Adhesive forces create a “pull" on the water column.
• Pull results from the tendency of water molecules evaporating on the plant's surface to stay connected to the water molecules below them.

Water is a major component of all living things, from single cells to complex organisms. Cytosol, the gel-like substance inside cells, is 70-80% water, which is essential for cellular metabolism. Water accounts for 60-95% of an organism's mass.