Why is water described as a polar molecule?

Water is polar because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges, creating an uneven distribution of charge across the molecule.

How do hydrogen bonds form between water molecules?

Electrostatic attraction occurs between the slightly positive hydrogen atoms of one water molecule and the slightly negative oxygen atom of another water molecule, forming hydrogen bonds.

Explain how water acts as a solvent for ionic compounds.

Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules.

What is a hydration shell?

A layer of water molecules that surrounds an ion due to the attraction between the polar water molecules and the charged ion.

OCR A-Level Biology H420

Cell Structure

Topic overview Microscopy, slide preparation and staining Biological drawings, magnification and resolution Eukaryotic cell ultrastructure The secretory pathway and the cytoskeleton Prokaryotic and eukaryotic cells compared

Biological Molecules

Topic overview The properties of water Monomers, polymers and the elements of life Monosaccharides and disaccharides Polysaccharides and their functions Lipids Amino acids and protein structure Globular and fibrous proteins Inorganic ions The biochemical tests Colorimetry and chromatography

Nucleotides and Nucleic Acids

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Enzymes

Topic overview Enzyme action: lock and key and induced fit Factors affecting enzyme activity Cofactors, coenzymes and enzyme inhibition

Biological Membranes

Topic overview Membrane structure and the fluid mosaic model Factors affecting membrane permeability Diffusion, active transport, endocytosis and exocytosis Osmosis and water potential

Cell Division, Cell Diversity and Cellular Organisation

Topic overview The cell cycle Mitosis and observing it in root tips Meiosis Specialised cells Tissues, organs and organ systems Stem cells and differentiation

Exchange Surfaces

Topic overview Surface area to volume and the features of an exchange surface The mammalian gas exchange system Ventilation and lung volumes Gas exchange in fish and insects Dissecting and examining gas exchange tissue

Transport in Animals

Topic overview Why animals need transport systems Arteries, veins and capillaries Tissue fluid and lymph The structure of the mammalian heart The cardiac cycle and control of the heartbeat The electrocardiogram Transporting oxygen and carbon dioxide Oxygen dissociation curves and the Bohr effect

Transport in Plants

Topic overview Xylem, phloem and vascular tissue Transpiration and the potometer Water uptake and movement up the xylem Xerophytes and hydrophytes Translocation

Communicable Diseases, Disease Prevention and the Immune System

Topic overview Pathogens and how disease is transmitted Plant defences and non-specific animal defences Phagocytes and phagocytosis The specific immune response Antibodies Types of immunity Vaccination Medicines and antibiotic resistance

Biodiversity

Topic overview The three levels of biodiversity Sampling methods and equipment Simpson's Index of Diversity Measuring genetic biodiversity Threats to biodiversity and reasons to maintain it Conservation: in situ and ex situ

Classification and Evolution

Topic overview The taxonomic hierarchy and binomial naming The five kingdoms and the three domains Phylogeny and the evidence for evolution Variation and adaptation Natural selection and resistance

Communication and Homeostasis

Topic overview Cell signalling and communication systems Homeostasis, negative and positive feedback Thermoregulation in endotherms and ectotherms

Excretion as an Example of Homeostatic Control

Topic overview Excretion and nitrogenous waste The liver: structure and function The structure of the kidney The nephron Ultrafiltration Selective reabsorption and the loop of Henle Osmoregulation and ADH Kidney failure, dialysis and transplant Urine testing and monoclonal antibodies

Neuronal Communication

Topic overview Sensory receptors and the Pacinian corpuscle Types of neurone and myelination Resting potential and the action potential Transmission across a cholinergic synapse Summation and inhibitory synapses

Hormonal Communication

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Plant and Animal Responses

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Photosynthesis

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Respiration

Topic overview Respiration, ATP and the mitochondrion Glycolysis The link reaction and the Krebs cycle Oxidative phosphorylation and chemiosmosis Anaerobic respiration Respiratory substrates and the respiratory quotient

Cellular Control

Topic overview Gene mutations and their effects The lac operon Transcription factors and post-transcriptional control Homeobox and Hox genes Mitosis and apoptosis Oncogenes, tumour suppressor genes and cancer

Patterns of Inheritance

Topic overview Genetic and environmental variation Monogenic and dihybrid inheritance, sex linkage and epistasis The chi-squared test Selection, genetic drift and the founder effect The Hardy-Weinberg principle Speciation and isolating mechanisms Artificial selection

Manipulating Genomes

Topic overview DNA sequencing and bioinformatics DNA profiling, PCR and gel electrophoresis Genetic engineering: restriction enzymes and vectors Genetic modification, its ethics, and gene therapy

Cloning and Biotechnology

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Ecosystems

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Populations and Sustainability

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Practical Skills and Mathematical Requirements

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Biological Molecules

The properties of water

1 thing to know
Components 01, 02 and 03

Overview

Why water is polar, the hydrogen bonds that follow from it, and how solvent action, high specific heat capacity, evaporative cooling and floating ice support life.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How do water's properties support living organisms?

Questions from this subtopic

Each one with the model answer underneath.

1
Why is water described as a polar molecule?
Model answer
Water is polar because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges, creating an uneven distribution of charge across the molecule.
2
What charge does the oxygen atom carry in a water molecule?
Model answer
A slight negative charge.
3
What charge do the hydrogen atoms carry in a water molecule?
Model answer
Slight positive charges.
4
How do hydrogen bonds form between water molecules?
Model answer
Electrostatic attraction occurs between the slightly positive hydrogen atoms of one water molecule and the slightly negative oxygen atom of another water molecule, forming hydrogen bonds.
5
Explain how water acts as a solvent for ionic compounds.
Model answer
Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules.
6
What is a hydration shell?
Model answer
A layer of water molecules that surrounds an ion due to the attraction between the polar water molecules and the charged ion.

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AA phospholipid contains one glycerol molecule.

BTwo fatty acids bond to the glycerol molecule.

COne phosphate group replaces the third fatty acid.

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The properties of water

Overview

What you need to know

How do water's properties support living organisms?

Questions from this subtopic

Why is water described as a polar molecule?

What charge does the oxygen atom carry in a water molecule?

What charge do the hydrogen atoms carry in a water molecule?

How do hydrogen bonds form between water molecules?

Explain how water acts as a solvent for ionic compounds.

What is a hydration shell?

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in Biological Molecules, on a schedule.