A1.1 - Water Flashcards
(25 cards)
What makes water a good medium for life?
Water enables molecules to move, collide, and react because it’s a liquid solvent. Life processes like enzyme function occur in water, and the first cells originated in water.
What type of bond holds atoms together by sharing electrons?
A covalent bond, where atoms share one or more pairs of electrons.
What’s the difference between non-polar and polar covalent bonds?
Non-polar covalent bonds share electrons equally. Polar covalent bonds share them unequally, creating partial charges (δ⁺ and δ⁻).
Why is a water molecule polar?
Oxygen attracts electrons more strongly than hydrogen, so the oxygen atom becomes slightly negative and hydrogen slightly positive.
What is a hydrogen bond in water?
It’s a weak attraction between a δ⁺ hydrogen atom and a δ⁻ oxygen atom from another water molecule.
How many hydrogen bonds can each water molecule form?
Up to four hydrogen bonds with neighboring molecules.
What does cohesion mean in the context of water?
Water molecules stick to each other due to hydrogen bonding. This helps with water movement in plants.
How does cohesion help with water transport in xylem?
Cohesion forms a long chain of water molecules pulled up from roots to leaves by transpiration (tension from evaporation at stomata).
What is surface tension in water and why is it important?
Surface tension is caused by cohesion and allows water to resist external force. It creates a “film” at the surface, supporting small organisms.
Why does surface tension occur at the water–air interface?
Molecules at the surface bond more strongly with each other since there are no molecules above, creating a net inward force.
What is adhesion in water and how does it help plants?
Adhesion is the attraction between water and other polar/charged materials. It helps water move against gravity using capillary action.
What is capillary action and how is it useful?
It’s the upward movement of water in narrow spaces, often against gravity. It helps water move through soil and plant vessels.
List four key uses of water in biological systems.
- Temperature buffer – Water’s high specific heat capacity stabilizes temperature.
- Maintains structure – Contributes to cell turgor and shape (e.g. surrounds DNA).
- Solvent – Dissolves and transports ions and molecules.
- Metabolite – Participates in reactions (e.g. photosynthesis, digestion, respiration).
Why is water a good solvent?
Because it’s polar and forms hydrogen bonds with solutes, surrounding them with hydration shells.
What can water dissolve?
Polar molecules (like glucose) and charged ions (like Na⁺ and Cl⁻).
What can’t water dissolve?
Non-polar or uncharged molecules (hydrophobic substances like lipids), which are water-repellent and insoluble.
What is the cytosol and why is water important there?
Cytosol is the fluid in cells (~80% water), essential for dissolving solutes and enabling reactions.
How does water help with molecular transport in plants?
• Xylem: carries dissolved minerals from roots to leaves.
• Phloem: carries sugars from source to sink.
What does blood plasma transport in animals?
Salt ions, amino acids, proteins, glucose, dissolved gases, and waste products.
What is specific heat capacity (SHC)?
The amount of energy needed to raise the temperature of a chemical per unit mass by 1°C.
Why does water have a high SHC?
Because of its many hydrogen bonds, which require a lot of energy to break.
How does water’s SHC affect organisms?
It stabilizes body and environmental temperatures. For example, aquatic habitats heat and cool slowly.
Compare water and air for four physical properties.
Property Water Air
Buoyancy Higher – supports upward force Lower
Viscosity Higher – resists flow Lower – flows easily
Thermal conductivity Higher – transfers heat better Lower – less heat loss
Specific heat capacity Higher – resists temp change Lower – quick temp change
How does water affect the black-throated loon?
• Buoyancy keeps it afloat with little energy.
• In air: low viscosity helps flying, but air has low SHC and thermal conductivity, so temp changes quickly and heat is lost.
