A1.1 Water

Water

Water

Needed to transport nutrients and product waste, regulating the body temperature and pH balance.

Water

• Is the medium of life

• First cells arose in water

• Is enclosed in a membrane where substances are dissolved and chemical reactions can occur

• Is needed for 

  • transport of nutrients and waste products

  • regulating body temperature 

  • pH balance

  • Respiration & photosynthesis

Solvent

A substance that dissolves other substances.

Hydrogen bonds

Joined by covalent bonding, but due to their electrons of not being shared equally, creating a polar covalent bond.

Hydrogen is the slightly more positive charge and the oxygen is the slightly more negative charge.

Polar Covalent bond

A bond where electrons are unequally distributed between two atoms, causing a charge imbalance.

Cohesion

A water molecule is able to stick to other water molecules via the formation of hydrogen bonds

• Water molecules stick together because of hydrogen bonds, which makes the surface of the water slightly stretchy. This is called surface tension.

• The high surface tension of water makes it sufficiently dense for certain smaller organisms to move along its surface

Xylem

Interconnected tubes in plants that transport water from roots to leaves.

Adhesion

 A water molecule is able to stick to other polar or charged molecules via the formation of polar associations

• Water is attracted to charged or polar surfaces, like cellulose in plant cell walls. This attraction helps water move upward against gravity, a process called capillary action.

• The strength of the capillary action will be dependent on the diameter of the pore through which the water moves (smaller diameter = more action)

Hydrogen Bond

Attraction between water molecules, creating tension.

Capillary action

Capillary action refers to the ability of water to move upward through narrow spaces, such as the tiny tubes (xylem vessels) in plant stems.

Cohesion:

• The attraction between water molecules, which allows them to stick together.

Adhesion

• The attraction of water molecules to the walls of the xylem vessels, which helps water "climb" up the stem

The type of soil will influence the strength of the capillary action, affecting the efficacy of agricultural practices

Adhesion + Cohesion

Hydrophilic ("water-loving,"）

Any Polar molecules and charged ions could dissolve in water.

Water forms around charged molecules to keep them dissolved.  

• Polar: (have regions of partial positive and negative charges due to uneven electron distribution, but they are neutral overall)

  • Salt

  • Sugar

• Charged ion: (atoms or molecules with a full positive or negative charge)

δ

When there is an extremely small particle

Aqueous solution

Water that contains one or more dissolved substance that substances can move and interact

• The cytoplasm in cells is an aqueous solution with a mix of dissolved substances that substances can move in and interact. 

• Enzymes are found in the cytoplasm which help catalyse chemical reactions. All the reactions that occur are known as metabolism.

Metabolism

（新陈代谢）

The sum of reaction in the body that provides energy for each cell within the body with energy.

Transportation of Plant

Use xylem and phloem to move substances in aqueous solutions.

Transportation of Animals

Use blood to transport various substances.

• Soluble: Ionic compounds (e.g., sodium chloride), amino acids, glucose.

• Slightly Soluble: Oxygen, carried by hemoglobin in red blood cells.

• Insoluble: Fats and oils.

Hydrophobic

Substances like fat/water are water hating, and are insoluble in the water. This happens as they are nonpolar or has no charge.

The hydrophobic and insoluble nature of molecules like fats and oils is essential for their function within cells. This characteristic allows them to form cell membranes and store energy efficiently without dissolving in the cell's aqueous environment.

• Lipids can create a barrier that separates the inside of the cell or organelle from the outside environment.

• Steroid hormones are derived from cholesterol. They include hormones like testosterone, estrogen, and cortisol. Their hydrophobic nature allows them to easily cross the hydrophobic lipid bilayer of the cell membrane.

• Fat-soluble vitamins: Vitamins A, D, E, and K are all fat-soluble vitamins that are hydrophobic and insoluble in water. These vitamins are essential for various biological processes, such as vision, bone health, and blood clotting.

Glucose

Polar due to hydroxyl groups (OH groups) Which cause water molecules to form hydrogen bonds with

Amino Acid

If hydrophilic or not depends on the R-group. Some are charged, some polar, some nopolar. Due to the nature of AA forming zwitterions, all are soluble to a certain degree

Cholesterol

The entire structure is nonpolar/without a charge, except on OH group. This provides a small amount of polarity, but not sufficient (in relation to size of the molecule).

Fat & Lipids

Entirely, Absolutely non polar

Oxygen

Entirely non-polar as a molecule, solubility depends on the temperature (cold water - better solubility).

Sodium chloride

Polar molecule due to cations (Nat) & anion (Cl) which are held together by an ionic bond. The ions are surrounded by polar water molecules when dissolved in water.

Sodium chloride is table salt. It is a polar molecule because it is made up of positive sodium ions (Na+) and negative chloride ions (Cl-). When it dissolves in water, these ions are surrounded by water molecules.

Buoyancy

Upwards force of the water that is always floating

Important to all aquatic and semi-aquatic organisms to keep them at or near the water surface.

Viscosity

Thickness of a liquid which determines how easily it can flow.

Water becomes less viscous when  it heats up

Thermal conductivity

Heat can be transferred through water more easily as the temperature increases

Heat can pass through water quicker than in air as the particles collide more easily in water

Specific heat capacity

The amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature.

But Water can absorb a lot of heat before changing state.