What is unique about Earth?

Biological Molecules

Nutrients: Why do we need food?

Nutrients: Why do we need food?

Food is a source of energy & raw materials for organisms.

Food is required to:1. Provide energy for vital body activities2. Synthesize new protoplasm for cell

growth, repair, cell division3. Stay healthy

The longest time that anyone has ever lived without food or water is

18 days. An 18-year-old man in Austria was put into a police cell on 1st April 1979 and forgotten. When he was discovered on 18th April, he

was very close to death…

What was the longest time someone survived without food/water?

Learning objectives

By the end of this chapter, you will learn to: State roles of water in organisms. List chemical elements that make up

carbohydrates, proteins, fats State that large molecules are made

from smaller basic units Describe & carry out tests for starch,

reducing sugars, proteins and fats

Overview of topic

Water & Living Organisms Carbohydrates, Fats & Proteins Enzymes

Learning objectives: Water

By the end of the lesson, you should be able to:

State the roles of water in living organisms

Water

Water is essential to life. It can be found:

Within organisms Outside organisms

In ponds, lakes, seas, oceans

In cytoplasm of cells

In bloodIn intercellular spaces/

interstitial fluid

In vacuoles of cells

Water: Regulates temperature Regulates temperature in organisms

1. Cooling by evaporation of: sweat in animals water from leaves by transpiration Removal of latent heat of vaporization

from organism

2. Water in intercellular spaces, cytoplasm & blood absorbs heat produced by metabolic activities

Water has high heat capacity Temperature changes within water are

minimised Constant external

environment for cells & organisms

Water: Good solvent Good solvent for:

1. Metabolic waste, e.g. urea2. Gases, e.g. carbon dioxide & oxygen3. Nutrients from digestive tract, e.g. glucose4. Part of digestive juices, e.g. enzymes5. Part of protoplasm

Acts as a medium in which chemical reactions occur

Acts as a transport medium in: blood, lymphatic and excretory systems,

alimentary canal, xylem & phloem

Water: Provides support

Supports structures & organisms1. Maintains turgor pressure in plant cells

& keeps their shape2. Provides support (buoyancy) to

aquatic organisms

Turgor in plant cells

Recap: Water enters plant cells by osmosis, causing them to be firm and turgid.

Turgor pressure is important to keep plants upright

Water enters by osmosis

Water leaves by osmosis

Importance of turgor pressure in plants

Usually, for most substances…

Which state is denser, solid or liquid?

But, look at this beaker of ice & water.

Ice is less dense than water.

But, for water…

Ice is less dense than water. Ice forms insulating layer over water Prevents lakes from freezing upwards Ensures survival of aquatic organisms

in winter

Densityice<Densitywater: Ensures survival of aquatic organisms

Water: Lubrication

Helps in lubrication, e.g.

1. Mucus aids movement of food along digestive tract

2. Synovial fluid facilitates movement in joints

3. Pericardial fluid facilitates movement in heart

Water: Photosynthesis

Substrate for photosynthesis in plants

Water: Hydrolytic reactions

Substrate for certain reactions in animals, e.g. hydrolysis in digestion

+

C6H12O6 glucose (monosaccharide)

C6H12O6 glucose (monosaccharide)

H2O water

+

C12H22O11 maltose (disaccharide)

Water: Helps in fruit dispersal

Helps in dispersal of: certain fruits, e.g. coconut, nipah

Water: High surface tension & cohesion

Surface tension: Force of attraction between molecules on surface of liquid Allow many small organisms to settle

on water or skate over its surface

Cohesion: Force which causes molecules to stick together Important in transporting water

upwards in plant

Water Requirements Water is lost daily from the body:

during breathing (in expired air) in urine in faeces through sweating

Average amount required to replace that lost daily - 3 litres / 8 glasses

More water needed by: active people people with diseases, e.g. diabetes Those living in hot and dry climates

Summary: Roles of water in organisms

Role of water in organisms

Regulates temperature

Good solvent

Provides supportLubrication

Photosynthesis

Fruit dispersal

Survival of aquatic organisms in winter

Sweat Transpiration

In animals In plants Nutrients

Gases

Metabolic waste

Digestive juices

Protoplasm

Buoyancy Turgor pressure

Mucus in digestive tract

Synovial fluid in joints

In animals In plants

Pericardial fluid in heart

Learning objectives (achieved)

By now, you should be able to: State the roles of water in living

organisms

Overview of topic

Water & Living Organisms Carbohydrates, Fats & Proteins Enzymes

Learning objectives: Carbohydrates

By the end of the lesson, you should be able to:

List elements that make up carbohydrates

State that large molecules (glycogen) are synthesised from smaller basic units (glucose)

Describe and carry out tests for: starch (iodine solution) reducing sugars (Benedict’s solution)

Types of biological molecules

Carbohydrates

Proteins Fats Nuclei acids

Contain carbon, hydrogen & oxygen Hydrogen:Oxygen = 2:1 Chemical formula: Cn(H2O)m

Carbohydrates: Functions

Substrate for respiration Provide energy for cell activities

Form supporting structures E.g. plant cell walls

Form nuclei acids, e.g. DNA, RNA Synthesize lubricants

E.g. mucus: glycoprotein Synthesize nectar in some flowers

The world of carbohydrates

Carbohydrates

Polysaccharides (complex carbohydrates)

Disaccharides (double sugars)

Monosaccharides(single sugars)

Examples:1. Glucose2. Fructose

3. Galactose

Examples:1. Maltose 2. Lactose 3. Sucrose

Examples:1. Starch

2. Glycogen 3. Cellulose

Carbohydrates: Monosaccharides

Are carbohydrates that cannot be broken down into simpler forms

Common examples: Glucose

Found in all animals Fructose

Common in plants (e.g. fruits), but rare in animals

GalactoseFound in milk in mammals

C6H12O6 glucoseC6H12O6 fructose

Carbohydrates: Disaccharides Created when 2 monosaccharides

become linked through a condensation reaction

Examples: Glucose + glucose = Maltose (Germinating

seeds)

Glucose + galactose = Lactose (Milk) Glucose + fructose = Sucrose (Table sugar)

+

C6H12O6 glucose (monosaccharide)

C6H12O6 glucose (monosaccharide)

H2O water

+

C12H22O11 maltose (disaccharide)

Carbohydrates: Polysaccharides

Are long chains/polymers of monosaccharides

Most common carbohydrates in nature Examples:

Glycogen (Found in animals & fungi) Starch (Found in plants) Cellulose (Found in plants)

Carbohydrates: Polysaccharides: Starch

Polymer of glucose Energy reserve in plants Stored as starch granules in cytoplasm

Carbohydrates: Polysaccharides: Glycogen Polymer of glucose Primary store of carbohydrates in

animals Stored in liver & skeletal muscles of

vertebrate animals

Why are glycogen & starch used as storage materials?

Insoluble in water Osmotically inactive i.e. does not change

water potential in cells Large molecules

Cannot diffuse across cell membranes Easily hydrolysed to glucose when

needed for respiration Have compact shapes

Occupy less space than sum of individual molecules

Carbohydrates: Polysaccharides: Cellulose

Forms cell walls in plant cells to provide support

Cannot be digested in humans But is a valuable source of fibre

The purpose of food tests…

Given an unknown sample X, how do you find out what nutrient is present?

?

Different food tests that can be done:

Test for:

REDUCING SUGARS PROTEINS

FATS

Benedict’s test

Biuret test

Ethanol emulsion

test

STARCH

Iodine test

Carbohydrates: Polysaccharides: Iodine test for starch

Add a few drops of iodine solution to food sample

If iodine solution turns blue-black: Starch is present

If iodine solution remains yellowish-brown: Starch is absent

Different food tests that can be done:

Test for:

REDUCING SUGARS PROTEINS

FATS

Benedict’s test

Biuret test

Ethanol emulsion

test

STARCH

Iodine test

Test for carbohydrates: Reducing sugars

What are reducing sugars? Sugars with a free aldehyde or ketone group

that can reduce other substances e.g. all monosaccharides & some disaccharides

Carbohydrates

Polysaccharides (complex carbohydrates)

Disaccharides (double sugars)

Monosaccharides(single sugars)

e.g. glucose, fructose, galactose

e.g. maltose, sucrose, lactose

e.g. starch, glycogen, cellulose

Test for carbohydrates: Reducing sugars

To test for reducing sugars, carry out the Benedict’s test.1. Add 2 cm3 of Benedict’s solution to 2

cm3 of test solution.2. Shake well.3. Heat contents in boiling water bath for

5 min.

Test for carbohydrates (3): Reducing sugars

Results:

If Benedict’s solution remains clear blue, and no precipitate is formed, reducing sugar is absent

Benedict’s solution turns green OR Formation of a precipitate from yellow and orange to brick red Reducing sugar is present

Colour when there is a lot of reducing sugars

present

Colour when there is no

reducing sugar

Test for carbohydrates (2): Reducing sugars Which tube has the most reducing

sugars? Which tube has no reducing sugars?

Learning objectives: Carbohydrates

By now, you should be able to: List elements that make up

carbohydrates State that large molecules (glycogen)

are synthesised from smaller basic units (glucose)

Describe and carry out tests for: starch (iodine solution) reducing sugars (Benedict’s solution)

Biological Molecules

Proteins

Overview of topic

Water & Living Organisms Carbohydrates, proteins & fats Enzymes

Lesson objectives

By the end of this lesson, you should be able to:

State that proteins & polypeptides are synthesized from amino acids

State the test for proteins

Types of biological molecules

Carbohydrates

Proteins Fats Nuclei acids

Contain carbon, hydrogen, oxygen, nitrogen, phosphorus & sulphur

Roles of proteins in our bodies

Functions of proteins

Synthesis of new protoplasm, for growth & repair of worn-out body cells

Synthesis of enzymes and peptide hormones

Formation of antibodies to fight diseases

Structure of proteins Proteins are polymers of amino acids Amino acids are aligned in genetically

determined sequence Amount, type & arrangement of amino acids

affects protein properties

Amino acids ProteinPolypeptide

Denaturation of proteins

Under certain conditions, e.g. heat or change in pH, unique 3D shape of proteins can be changed Protein loses ability to function Protein is denatured

Heat or acids/alkalis

Different food tests that can be done:

Test for:

REDUCING SUGARS PROTEINS

FATS

Benedict’s test

Biuret test

Ethanol emulsion

test

STARCH

Iodine test

Test for proteins: Biuret test To test for proteins:

1. Add 2 cm3 of sodium hydroxide to 2 cm3 of sample in a test tube. Shake well.

2. Add copper(II) sulphate solution dropwise. Shake after each drop.

Step 1: 2cm3 of sodium hydroxide

2cm3 of sample

Step 2:Copper sulphate solution added dropwise

Blue solution turns violet Protein is present

Solution remains blue Protein is absent

Test for proteins: Biuret test

Copper ions react with peptide bonds in protein to give a violet coloration.

Blue solution Protein is absent

Violet coloration Protein is present

Lesson objectives

By now, you should be able to: State that proteins & polypeptides are

synthesized from amino acids State the test for proteins

Biological Molecules

Fats

Overview of topic

Water & Living Organisms Carbohydrates, Proteins & Fats Enzymes

Learning objectives

By the end of the lesson, you should be able to:

State that fats are made from glycerol and fatty acids

Describe and carry out test for fats (ethanol emulsion test)

Types of biological molecules

Contain carbon, hydrogen & oxygen Compared to carbohydrates, fats have

less O relative to H No fixed ratio for elements in fats

All fats are insoluble in water Can be animal fats or plant fats

Carbohydrates

Proteins Fats Nuclei acids

Glycerol Fatty acids waterFat

+ +

Fats

Fats are commonly used as a store of energy, especially by animals

Fats are made from fatty acids & glycerol in a condensation reaction

Functions of fats

Source & store of energy Insulating material Solvent for fat-soluble vitamins &

certain hormones Essential part of protoplasm (esp.

cell membranes) Sebum helps reduce water loss from

skin surface

Different food tests that can be done:

Test for:

REDUCING SUGARS

PROTEINS

FATS

Benedict’s test

Biuret test

Ethanol emulsion

test

STARCH

Iodine test

Test for fats: Ethanol emulsion test

To 2 cm3 of ethanol in a test tube, add 5 drops of test sample.

Shake well. Then add 2 cm3 of water. Shake well. If fats are present, a white emulsion

is seen. If fats are absent, no white emulsion

is seen.

Learning objectives (achieved)

By now, you should be able to: State roles of water in living organisms. List the chemical elements that make up:

Carbohydrates Proteins Fats

Learning objectives (achieved)

By now, you should be able to: Describe and carry out tests for:

1. Starch (Iodine solution)2. Reducing sugars (Benedict’s solution)3. Protein (Biuret test)4. Fats (Ethanol emulsion test)

State that large molecules are synthesised from smaller basic units:1. Glycogen is made from glucose2. Proteins are made from amino acids3. Fats are made from fatty acids & glycerol