AS- Biology Student GuideTopic 1 Biological Molecules- Carbohydrate and Lipids

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Evaluation:Self assessed learning grade ____Comments – (What can I do differently next time I do this?)

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Effective Learning 1-Excellent; 2-Good; 3-Needs to improve; 4-Cause for concern

Independent Learning• Do you work outside of formal learning sessions? • Are you able to demonstrate independent learning?

Questioning • Do you interrogate material/resources • Ask your LT / peers sensible, in depth questions • Question sources of information

Planning • Do you read additional material in preparation for the session • Plan your work in advance • Use assessment criteria to plan your tasks

Review/Amend • Do you look back at notes/tasks and review them regularly • Amend tasks having spoke/discussed with others or read more widely • Amend/review after advice from LTs

Active listening • Listen to understand • Be proactive and contribute in sessions/activities • Listen to other students in the group

Collaboration

• Work effectively with others in the group • Take part in group work to ensure that everyone is involved • Take a range of roles within group work to encourage effective collaboration

Biological moleculesAll life on Earth shares a common chemistry. This provides indirect evidence for evolution.Despite their great variety, the cells of all living organisms contain only a few groups of carbon-based compounds that interact in similar ways.Carbohydrates are commonly used by cells as respiratory substrates. They also form structural components in plasma membranes and cell walls.Lipids have many uses, including the bilayer of plasma membranes, certain hormones and as respiratory substrates.

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3.1.1 Monomers and polymers

The variety of life, both past and present, is extensive, but thebiochemical basis of life is similar for all living things.

Monomers are the smaller units from which larger molecules aremade.

Polymers are molecules made from a large number of monomersjoined together.

Monosaccharides, amino acids and nucleotides are examples ofmonomers.

A condensation reaction joins two molecules together with theformation of a chemical bond and involves the elimination of amolecule of water.

A hydrolysis reaction breaks a chemical bond between two moleculesand involves the use of a water molecule.3.1.2 Carbohydrates

Monosaccharides are the monomers from which larger carbohydrates are made.

Glucose, galactose and fructose arecommon monosaccharides.

A condensation reaction between two monosaccharides forms aglycosidic bond.

Disaccharides are formed by the condensation of twomonosaccharides:•• maltose is a disaccharide formed by condensation of two glucose molecules•• sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule•• lactose is a disaccharide formed by condensation of a glucosemolecule and a galactose molecule.

Glucose has two isomers, α-glucose and β-glucose, with structures:

Polysaccharides are formed by the condensation of many glucose units.•• Glycogen and starch are formed by the condensation of α-glucose.•• Cellulose is formed by the condensation of β-glucose.

The basic structure and functions of glycogen, starch and cellulose.The relationship of structure to function of these substances in animalcells and plant cells.

Biochemical tests using Benedict's solution for reducing sugars andnon-reducing sugars and iodine/potassium iodide for starch.3.1.3 Lipids

Triglycerides and phospholipids are two groups of lipid.

Triglycerides are formed by the condensation of one molecule ofglycerol and three molecules of fatty acid.

A condensation reaction between glycerol and a fatty acid (RCOOH)forms an ester bond.

The R-group of a fatty acid may be saturated or unsaturated.

In phospholipids, one of the fatty acids of a triglyceride is substitutedby a phosphate-containing group.

The different properties of triglycerides and phospholipids related totheir different structures.

The emulsion test for lipids.Students should be able to:

•• recognise, from diagrams, saturated and unsaturated fatty acids•• explain the different properties of triglycerides and phospholipids.

KEY WORDS

keyword definitionMonomer

Polymer

Monosaccharide

Disaccharide

Condensation Reaction

Hydrolysis Reaction

Alpha Glucose

Beta Glucose

Glycosidic bond (1,4 and 1,6)Starch

Cellulose

Hydrogen Bond

Glycogen

Amylose

Amylopectin

Triglycerides

Fatty Acid

Glycerol (glyceride)

Hydrophilic

Hydrophobic

Phospholipid

Polar

Saturated

Mono- and Poly-Unsaturated

Describe Benedicts test

Describe test for Lipids

Define Osmosis using the term water potential

Resources and suggested Reading: find this document on the MLE to be able to click the links.

Copies of Biological Science review can be found in the library : see the MLE for the index of past articles

http://www.biologymad.com/

http://www.mrothery.co.uk/ecology/Mod5Notestrimmed.htm

http://www.freeeschool.blogspot.co.uk/

The awesome Bozeman Biology YouTube site: search for Carbohydrates and Lipids

Practice Questions

Answer these practice questions and self assess them against the markschemes published on www.drharrisbiology.com

Q1.          Cellulose is made from one type of monomer. The monomers are held together by bonds. The diagram shows parts of three cellulose molecules in a cell wall.

(a)     Name the monomer present in cellulose.

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(b)     Name the type of reaction that converts cellulose to its monomers.

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(c)     Cotton is a plant fibre used to make cloth. Explain how cellulose gives cotton its strength.

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(Total 5 marks)

 

 

Q2.          The diagram shows a cell from a potato.

(a)     Give two features which may be found in a prokaryotic cell which would not be found in this cell.

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(b)     (i)      Describe how you could confirm that the granules contained starch.

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(ii)     Name one polysaccharide other than starch that would be found in this cell.

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(c)     Explain one advantage of storing starch rather than glucose in potato cells.

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(Total 6 marks)

Q3.The glycaemic index (GI) is a measure of the increase in blood glucose concentration after eating a given mass of a food compared with eating the same mass of pure glucose. The GI of pure glucose has a value of 100.The GI of a food depends on several factors such as how much starch and sugars it contains. High GI foods include those containing lots of simple sugars or white flour. The carbohydrates in these foods are rapidly digested and absorbed. Low GI foods include wholegrain bread and breakfast cereals that contain a lot of fibre. The carbohydrates in these foods are digested and absorbed more slowly.

The following figure shows changes in blood glucose concentration after eating meals of high GI food and meals of low GI food.

(a)     Complete the table below to give four differences between the effects of high GI and low GI foods on blood glucose concentration.

 

High GI foods Low GI foods

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(b)     White bread and wholegrain bread contain similar proportions of starch. White bread has a higher GI than wholegrain bread.

Suggest one explanation for the difference in GI.

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(Total 6 marks)

Q4.          (a)     Figure 1 shows the structure of a molecule of glycerol and a molecule of fatty acid.

Figure 1

Draw a diagram to show the structure of a triglyceride molecule.

 

 

 

 

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(b)     Explain why triglycerides are not considered to be polymers.

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(c)     Figure 2 shows two types of fat storage cell. Mammals living in cold conditions have more brown fat cells than mammals living in tropical conditions.

Figure 2

Using evidence from Figure 2 to support your answer, suggest how the function of brown fat cells differs from that of white fat cells.

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(Total 6 marks)

 

 

Q5.          (a)     Starch and protein are biologically important polymers.

(i)      Explain what is meant by a polymer.

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(ii)     Give one example of a biologically important polymer other than starch or protein.

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(b)     In an investigation, the enzyme amylase was mixed in a test tube with a buffer solution and a suspension of starch. The amylase broke down the starch to maltose. When all the starch had been broken down, a sample was removed from the test tube and tested with biuret reagent.

(i)      Explain why a buffer solution was added to the amylase-starch mixture.

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(ii)     What colour would you expect the sample to go when tested with biuret reagent?

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(iii)     Give an explanation for your answer to part (ii)

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(Total 7 marks)