BIOLOGY TEST, MONDAY OCTOBER 21ST: REVISION SHEET AND PRACTICE QUESTIONS

This test will be based on Chapters 3 and 4 of your IGCSE book (Pages 20 – 38).Note that you will also be asked on the additional material that we covered in the class presentations.

You must know the key definitions, which relate to: Diffusion (p. 21) and Facilitated diffusion (you should also

know the differences and smiliarities between diffusion and facilitated diffusion)

Osmosis (p. 23) Active transport (protein pumps and endocytosis/exocytosis) (p.

29)

You must know the key ideas featured on Page 30 and Page 89

You should revise for this test using the Revision Questions on Page 30 and Page 38.

You should be familiar with the principles and definitions used in your potato osmosis lab.

BASIC BIOCHEMISTRY

1  State that the most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen

The approximate proportions of the four main elements in living things are:• Carbon (19%)                        • Hydrogen (10%)                        • Oxygen (65%)                        • Nitrogen (3%)

2. Be able to draw and label a diagram showing the structure of water molecules to show their polarity and hydrogen bond formation

Structure of a Water Molecule:

▪ Water (H2O) is made up of two hydrogen atoms polar-covalently bound to an oxygen atom

▪ While this bonding involves the sharing of electrons, they are not shared equally 

▪ The oxygen atom, having more protons (+ve), attract the electrons (-ve) more strongly (i.e. the oxygen has a higher electronegativity)

▪ Thus the oxygen atom becomes slightly negative and the hydrogen atoms become slightly positive

Hydrogen Bonding between Water Molecules▪ Covalently bonded molecules that have a slight potential charge

are said to be polar▪ The slightly charged regions of the water molecule can attract

other polar or charged compounds▪ Water molecules can associate via weak hydrogen bonds (F/O/N

bonding with H)

Structure and Bonding of Water Molecules

3. Outline the thermal, cohesive and solvent properties of water

Thermal Properties▪ Water has a high specific heat capacity (the measure of energy

required to raise the temperature of 1 g of substance by 1°C)▪ Water has a high heat of vaporisation (amount of energy absorbed

per gram as it changes from a liquid to a gas / vapour)▪ Water has a high heat of fusion (amount of energy required to be

lost to change 1 g of liquid to 1 g of solid at 0°C)▪ These properties occur as a result of the extensive hydrogen

bonding between water molecules - this allows water to absorb considerable amounts of energy with little change in form (H-bonds need to be broken first)

Cohesive Properties▪ Water molecules are strongly cohesive (they tend to stick to one

another)▪ Water molecules will also tend to stick to other molecules that are

charged or polar (adhesion) ▪ These properties occur as a result of the polarity of a water

molecule and its ability to form hydrogen bonds with appropriate molecules

Solvent Properties▪ Water can dissolve many organic and inorganic substances ▪ This occurs because the polar attraction of large quantities of

water molecules can sufficiently weaken intra-molecular forces (such as ionic bonds) and result in the dissociation of the atoms

Other Properties▪ Water expands when frozen, becoming less dense / lighter

(important for life on earth - oceans don't freeze)

3.1.6  Explain the relationship between the properties of water and its use in living organisms as a coolant, medium for metabolic reactions and transport medium

Coolant▪ Both plants and animals use the evaporation of water from the

surfaces of their bodies to facilitate cooling (sweating and panting in animals, transpiration from leaves in plants)

Medium for Metabolic Reactions▪ Water can dissolve many organic and inorganic substances to

facilitate chemical reactions▪ (Water can also absorb thermal energy released as a by-product

of many chemical reactions)

Transport Medium▪ The forces of attraction between water molecules help facilitate

the transport of water up the xylem of plants▪ Water is an effective transport medium for dissolved substances

(in plants, minerals from the soil and sugars from the leaves can be transported in water through the xylem and phloem respectively; while in animals, water in the blood is used to transport oxygen, glucose and urea)

Surface Tension▪ The force of attraction between water molecules makes water

sufficiently dense for some smaller organisms to move along its surface

CARBOHYDRATESCarbohydrates are organic compounds consisting of one or more simple sugars that as monomers follow the general basic formula of (CH2O)x

Note:  Exceptions to this basic formula and the inclusion of other atoms (e.g. N) can occur

1. Identify glucose from diagrams showing ITS structure

            Glucose (C6H12O6)                                                                       

2. List examples of monosaccharides, disaccharides and polysaccharides

Monosaccharides:  Glucose, galactose, fructoseDisaccharides:  Lactose, maltose, sucrosePolysaccharides:  Cellulose, glycogen, starch

3. State one function of glucose, lactose and glycogen in animals and of fructose, sucrose and cellulose in plants

AnimalsGlucose:  A source of energy which can be broken down to form ATP via cellular respirationLactose:  A sugar found in the milk of mammals, providing energy for suckling infantsGlycogen:  Used by animals for short term energy storage (between meals) in the liver

Plants

Fructose:  Found in honey and onions, it is very sweet and a good source of energySucrose:  Used primarily as a transportable energy form (e.g. sugar beets and sugar cane)Cellulose:  Used by plant cells as a strengthening component of the cell wall

4. Outline the role of condensation and hydrolysis in the relationship between monosaccharides, disaccharides and polysaccharides

▪ Condensation reactions occur when molecules are covalently joined together and water is formed as a by-product

▪ The opposite of a condensation reaction is a hydrolysis reaction, which requires a water molecule to break a covalent bond between two subunits

▪ Monosaccharides are single monomers that are joined to form disaccharides, while sugars containing multiple subunits (more than 10) are called polysaccharides

A Condensation Reaction between Two Monosaccharides

LIPIDSLipids are a group of organic molecules that are insoluble in water but soluble in non-polar organic solventsCommon lipids include triglycerides (fats and oils), phospholipids and steroids

1. Identify fatty acids from diagrams showing their structure

  General Structure       Saturated (no double bonds)                  Unsaturated (double bonds)

2. State three functions of lipids

Structure:  Phospholipids are a main component of cell membranesHormonal signalling:  Steroids are involved in hormonal signalling (e.g. estrogen, progesterone, testosterone)Insulation:  Fats in animals can serve as heat insulators while sphingolipids in the myelin sheath (of neurons) can serve as electrical insulators Protection:  Triglycerides may form a tissue layer around many key internal organs and provide protection against physical injuryStorage of energy:  Triglycerides can be used as a long-term energy storage source

3. Compare the use of carbohydrates and lipids in energy storage

Similarities:▪ Complex carbohydrates (e.g. polysaccharides) and lipids both

contain a lot of chemical energy and can be used for energy storage

▪ Complex carbohydrates and lipids are both insoluble in water - they are not easily transported

Differences:▪ Lipid molecules contain more energy per gram than carbohydrates

(about twice as much)▪ Carbohydrates are more readily digested than lipids and release

their energy more rapidly▪ Monosaccharides and disaccharides are water soluble and easier

to transport to and from storage sites than lipids▪ Animals tend to use carbohydrates primarily for short-term energy

storage, while lipids are used more for long-term energy storage

▪ Carbohydrates are stored as glycogen in animals while lipids are stored as fats (in plants carbohydrates are stored as cellulose and lipids as oils)

PROTEINSProteins are large organic compounds made of amino acids arranged in a linear chainThe sequence of amino acids in a protein is defined by a gene and encoded in the genetic code

1. Identify amino acids from diagrams showing their structure

Generalised Structure of an Amino Acid

2. Outline the role of condensation and hydrolysis in the relationship between amino acids and polypeptides

▪ A condensation reaction occurs between the amino group (NH2) of one amino acid and the carboxylic acid group (COOH) of another amino acid

▪ This reaction forms a dipeptide (plus a molecule of water) that is held together by a peptide bond

▪ Multiple amino acids can be joined together to form a polypeptide chain

▪ In the presence of water, polypeptides can be broken down into individual amino acids via hydrolysis reactions

Formation of a Dipeptide

Functions of proteinsStructure:  Support for body tissue (e.g. collagen, elastin, keratin)Hormones:  Regulation of blood glucose (e.g. insulin, glucagon)Immunity:  Bind antigens (e.g. antibodies / immunoglobulins)Transport:  Oxygen transport (e.g. haemoglobin, myoglobin)Movement:  Muscle contraction (e.g. actin / myosin, troponin / tropomyosin)Enzymes:  Speeding up metabolic reactions (e.g. catalase, lipase, pepsin) 

FOOD TESTSYou must know how to test for the presence of simple (reducing) sugars, starch, protein and fat in different food stuffs.

To revise, you can use this link:http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/food_detective/activity/

A Food Test is a chemical test which determines the presence of biological molecules commonly found in food. These biological molecules include sugars - reducing and non-reducing,  starch, protein and lipids.

Food tests use reagents which react predictably with the biological molecules  to give observable color changes. More than one test - involving the use of different reagents, or with an extended procedure - exists for the same biological.

Common Biological Molecules and their Tsts

BiochemicalReducing Sugar

Non-Reducing Sugar

Starch

Protein

Lipid

Food TestBenedict's Test for Reducing Sugar

Benedict's Test for Non-reducing Sugar

Iodine Test for Starch

Biuret Test

Ethanol Emulsion Test

Practice Questions from past IGCSE papers

Practice Questions on Cell membrane and transport mechanisms