Water Properties and Functions

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Questions and Answers

What property of water helps minimize temperature fluctuations in living organisms?

Low density

Incompressibility

High surface tension

High heat specific capacity (correct)

What is the consequence of the polarity of water molecules?

Water molecules have a uniform charge distribution

Water molecules exhibit strong cohesion (correct)

Water cannot dissolve ionic compounds

Water has a high latent heat of vaporization

How does ice contribute to the survival of organisms in water bodies?

Ice vaporizes quickly, reducing water temperature

Ice creates an insulating layer, preventing water below from freezing (correct)

Ice dissolves easily in water, increasing oxygen levels

Ice is denser than water, allowing it to sink

What occurs during a condensation reaction?

Monomers are joined and a water molecule is eliminated Signup and view all the answers

Why is water described as a good solvent for metabolic reactions?

It is a polar molecule that can dissolve many ionic and polar substances Signup and view all the answers

What are monomers in the context of biological molecules?

Small, simple units that combine to form larger molecules Signup and view all the answers

What property of water enables it to provide good support for organisms?

Incompressibility Signup and view all the answers

What defines carbohydrates in terms of their elemental composition?

Carbon, hydrogen, and oxygen Signup and view all the answers

What type of protein is haemoglobin and what does it do?

A water-soluble globular protein that carries oxygen Signup and view all the answers

What color change indicates the presence of a reducing sugar during a Benedict's test?

Blue to red precipitate Signup and view all the answers

Which reagent is used to test for proteins, and what color indicates a positive result?

Copper (II) sulfate giving a lilac color Signup and view all the answers

In the emulsion test, what does a cloudy solution indicate?

Presence of lipids Signup and view all the answers

How does potassium iodide solution indicate the presence of starch?

It turns yellow to black/blue in the presence of starch Signup and view all the answers

What type of bond forms between monosaccharides during the condensation reaction?

Glycosidic bonds Signup and view all the answers

Which disaccharide is formed from glucose and fructose?

Sucrose Signup and view all the answers

What is the primary storage form of energy in animals?

Glycogen Signup and view all the answers

Which type of glucose is used to form cellulose?

Beta glucose Signup and view all the answers

What structure does amylose have that allows it to store energy compactly?

Coiled structure Signup and view all the answers

How are the glucose molecules in starch primarily joined?

1, 4 and 1, 6 glycosidic bonds Signup and view all the answers

What characteristic of glycogen allows for quick energy release?

High number of side branches Signup and view all the answers

Which of the following is NOT a polysaccharide?

Maltose Signup and view all the answers

What role do hydrogen ions play in biological systems?

They determine the pH of substances. Signup and view all the answers

Which of the following best describes a dipeptide?

A chain formed by two joined amino acids. Signup and view all the answers

What structural feature distinguishes fibrous proteins from globular proteins?

Fibrous proteins tend to be long and provide structural support. Signup and view all the answers

What is the primary structure of a protein?

The sequence and number of amino acids in the chain. Signup and view all the answers

Which ions are critical for the transport of glucose and amino acids in cells?

Sodium ions. Signup and view all the answers

What is the secondary structure of proteins primarily determined by?

Hydrogen bonding within the amino acid chain. Signup and view all the answers

What is the role of phosphate ions in living organisms?

They are essential components of DNA and ATP. Signup and view all the answers

Which of the following statements about collagen is correct?

Collagen is a fibrous protein that contributes to the strength of bone and cartilage. Signup and view all the answers

What is the characteristic structure of saturated lipids?

They do not contain carbon-carbon double bonds. Signup and view all the answers

Which of the following statements is true about unsaturated lipids?

They contain carbon-carbon double bonds. Signup and view all the answers

What is the primary function of triglycerides in cells?

To serve as energy reserves. Signup and view all the answers

What happens to the melting point of lipids as the number of unsaturated bonds increases?

The melting point decreases. Signup and view all the answers

How do phospholipids behave in water?

They form micelles with hydrophobic tails inward. Signup and view all the answers

Which of the following best describes the composition of a triglyceride?

One molecule of glycerol and three fatty acids. Signup and view all the answers

What role do inorganic ions play in organisms?

They occur in solution in varying concentrations. Signup and view all the answers

Which statement correctly compares saturated and unsaturated fats?

Unsaturated fats contain carbon-carbon double bonds, while saturated fats do not. Signup and view all the answers

Study Notes

Water

Water is a polar molecule due to the uneven distribution of charge, the oxygen atom attracts electrons more strongly than the hydrogen atoms. This gives a slightly negative charge near the oxygen atom and slight positive charges near the hydrogen atoms.
Water is a metabolite in condensation and hydrolysis reactions where chemical bonds are formed and broken, respectively.
Water is a solvent, allowing many metabolic reactions to occur.
Water has a high specific heat capacity, therefore a lot of energy is needed to raise its temperature, minimizing temperature fluctuations in living things.
Water's relatively large latent heat of vaporisation means that evaporation provides a cooling effect with little water loss.
Strong cohesion between water molecules enables effective transport of water in transport cells, providing support and allowing for high surface tension at the water-air boundary.
Water's maximum density is at 4 degrees Celsius meaning ice is less dense and floats, providing insulation for organisms in large bodies of water, preventing them from freezing.
Water is incompressible, making it good support.

Monomers and Polymers

Monomers are small units that form larger molecules, examples include monosaccharides, amino acids, and nucleotides.
Polymers are molecules made from monomers joined together.
Condensation reactions join monomers by chemical bonds, eliminating a water molecule.
Hydrolysis is the opposite of condensation, adding water to break a bond between two molecules.

Carbohydrates

Carbohydrates are molecules consisting of carbon, hydrogen, and oxygen, made of long chains of sugar units called saccharides.
There are three types of saccharides: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides can join to form disaccharides and polysaccharides through glycosidic bonds formed via condensation reactions.

Monosaccharides

Glucose is a monosaccharide with six carbon atoms, and it is the main substrate for respiration.
Alpha and beta glucose are isomers of glucose with different structures.

Disaccharides

Maltose is formed via condensation of two glucose molecules.
Sucrose is formed via condensation of glucose and fructose.
Lactose is formed via condensation of glucose and galactose.

Polysaccharides

Polysaccharides are formed from many glucose units joined together. Some examples include:
- Glycogen, formed from alpha glucose, is the main energy storage molecule in animals. It has many side branches for quick glucose and energy release and is a compact molecule maximizing energy storage.
- Starch stores energy in plants and is made up of two polysaccharides: amylose and amylopectin.
  - Amylose is an unbranched chain of glucose molecules joined by 1,4 glycosidic bonds, making it coiled and compact for efficient energy storage.
  - Amylopectin is branched with 1,4 and 1,6 glycosidic bonds, making it rapidly digestible with fast energy release due to the presence of many side branches.
Cellulose, a component of plant cell walls, is made up of long, unbranched chains of beta glucose joined by glycosidic bonds.
Microfibrils are strong threads formed by long cellulose molecules joined together by hydrogen bonds, providing structural support in plant cells.

Lipids

Lipids are biological molecules only soluble in organic solvents like alcohols.
Two types of lipids: saturated and unsaturated.
- Saturated lipids, such as those found in animal fats, contain no carbon-carbon double bonds.
- Unsaturated lipids, found in plants, contain carbon-carbon double bonds and melt at lower temperatures than saturated fats.
The greater the number of unsaturated bonds, the weaker the intermolecular bonds, resulting in lower melting points.
Saturated fats are solid at room temperature, while unsaturated fats are liquid.
Triglycerides are lipids consisting of one glycerol molecule and three fatty acids joined by ester bonds formed in condensation reactions.
Fatty acids differ in chain length, the presence and number of double bonds, and some triglycerides contain a mix of different fatty acids.
Triglycerides are used as energy reserves in plant and animal cells.
In phospholipids, one of the fatty acids in a triglyceride is replaced by a phosphate-containing group.
Phosphate heads are hydrophilic, while the tails are hydrophobic, leading to phospholipids forming micelles in water with the heads facing outwards and the tails inwards.

Inorganic Ions

Inorganic ions are found in solution in the cytoplasm and body fluid of organisms, some in high concentrations and others in low concentrations.
Some essential ions:
- Hydrogen ions determine the pH of substances like blood; higher concentrations lead to lower pH.
- Iron ions are components of haemoglobin, an oxygen-carrying molecule in red blood cells.
- Sodium ions are involved in co-transport of glucose and amino acids.
- Phosphate ions are components of DNA and ATP.

Proteins

Proteins are made from amino acids as monomers.
Amino acids contain an amino group, a carboxylic acid group, and a variable R group (carbon-containing chain).
There are 20 different amino acids with different R groups.
Amino acids are joined by peptide bonds formed through condensation reactions.
Dipeptides contain two amino acids, while polypeptides contain three or more.
Protein structure is determined by the order and number of amino acids, bonding present, and the shape of the protein.
- Primary structure: order and number of amino acids in a protein chain.
- Secondary structure: shape of the amino acid chain, either alpha helix or beta pleated sheet, determined by hydrogen bonding.
- Tertiary structure: 3D shape of the protein, which can be globular or fibrous.
  - Globular proteins like enzymes are compact.
  - Fibrous proteins like keratin are long and form fibers.
Collagen is a fibrous protein with great strength due to the presence of hydrogen and covalent bonds, forming strong collagen fibers for structural support in bones, cartilage, connective tissue, and tendons.

Haemoglobin

Haemoglobin is a water-soluble globular protein consisting of two alpha and two beta polypeptide chains, each containing a haem group.
It carries oxygen in the blood as oxygen binds to the haem (Fe2+) group and is released when needed.

Tests

Benedict’s Test

This test is used to detect reducing and non-reducing sugars.
All monosaccharides and some disaccharides are reducing sugars, meaning they can donate electrons.
An alkaline solution of blue copper (II) sulfate is added to the sugar and heated.
In the presence of a reducing sugar, a red precipitate of copper (I) oxide forms.
The Benedict’s reagent does not change color in the absence of reducing sugar.

Biuret Test

This test is used to detect proteins.
Add equal amounts of a sample solution and NaOH to a test tube.
Add a few drops of dilute copper (II) sulfate solution and gently mix.
If protein is present, the solution turns lilac due to the presence of peptide bonds.
The solution remains blue in the absence of protein.

Emulsion Test

This test is used to detect lipids.
Add 2ml of the sample to 5ml of ethanol and mix thoroughly to dissolve the lipids.
Add 5ml of water and mix, a cloudy solution indicates the presence of lipid due to the formation of an emulsion where light is refracted between oil and water droplets.

Iodine Test

This test is used to detect starch.
The color of potassium iodide solution changes from yellow to black/blue in the presence of starch.

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Description

This quiz explores the unique properties of water and its crucial roles in biological systems. Topics include its molecular structure, specific heat capacity, and functions as a solvent. Test your understanding of why water is essential for life.