2.1 Cell Theory Objectives 8/25/10 8:28 PM

Topic 2 - Cells2.1 Cell theory

Orange book: pg. 7-21Green book: pg. 9-15

2.1.1 Outline the cell theory (pg. 7-9, 9-10)

2.1.2 Discuss the evidence for cell theory (pg. 7-11, 9-10)

2.1.3 State that unicellular organisms carry out all the functions of life (pg. 10, 10)

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit (pg. 12-13, 10)

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification (practical).

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size (pg. 14-15, 12)

2.1.7 State that multicellular organisms show emergent properties (pg. 16&21, 12-13)

2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others (pg. 16, 13)

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways (pg. 17, 14-15)

2.1.10 Outline one therapeutic use of stem cells (pg. 18-20, 14-15)

Cell Theory 8/25/10 8:28 PM

2.1.1 Outline the cell theory

Orange book: pg. 7-9Green book: pg. 9-10

To do:1 Check out further information on ‘Cell Theory’ on Wikipedia2 Discuss your findings 3 Add notes 4 Summary in Green book

The idea behind cell theory is that all living things are made of cells, and cells are the smallest units that can be alive. There are thousands of different kinds of cells, but the biggest division is between cells of the prokaryote kingdom (the bacteria) and those of the other four kingdoms (animals, plants, fungi and protoctista), which are all eukaryotic cells.

Development of this theory progressed during the mid 1600s due to development of the microscope.

The theory states that new cells are formed from other existing cells.

Evidence for Cell Theory 8/25/10 8:28 PM

2.1.2 Discuss the evidence for cell theory

Orange book: pg. 7-11Green book: pg. 9-10

To do:1 Read the relevant sections in the text books2 Discuss your findings 3 Add notes 4 Summary in Green book

Life Processes 8/25/10 8:28 PM

2.1.3 State that unicellular organisms carry out all the functions of life

Orange book: pg. 10Green book: pg. 10

To do:1 List the seven processes carried out by all living things? 2 Summary in Green book

Cell Size 8/25/10 8:28 PM

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.

Orange book: pg. 12-13Green book: pg. 10

SI UnitsMetres (m)Centimetres (cm)Millimetres (mm)Micrometres (m)Nanometres (nm)

Conversions1mm = 1,000m = 1,000,000nm0.1mm = 100m = 100,000nm

If you get stuck the following website will help you to convert:http://www.cleavebooks.co.uk/scol/ccleng.htm

MoleculesDNA

2nm wide – width kept constant due to specific base pairing.70,000,000nm (70mm) long

Phospholipid5nm long

Water Molecule0.385nm

The general rule would be to say molecules are usually nm in size.Cells and cell organelles are composed of molecules and so molecules are the smallest.Proteins can be very large molecules but remember they are found INSIDE cells or are synthesized inside cells and secreted so they are smaller than cells.

Cell Membrane10nm wide

This is calculated from the length of 2 phospholids (each which are 5nm).We now have evidence to support this in the form of electron micrographs.

VirusesLargest 100nm (think the book is being abit conservative here – the smallpox virus is 300nm)

HIV – 100nmPolio Virus – 30nm

Remember that viruses can infect cells and so they have to be smaller than cells, including bacteria. (Bacteriophages are viruses that infect bacterial cells).

BacteriaUsually within range of 1 to 10m

OrganellesNucleus Human cheek cell - 5m (5000nm)

CellsAnimalUsually within range of 10 to 30mRed Blood Cell 7.5mHuman Cheek Cell 60mAmoeba Cell 300m

Plant Usually within range of 10 to 100m

To do:1 Visit the following website: http://www.cellsalive.com/howbig.htm2 Summary in Green book

Microscope 8/25/10 8:28 PM

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification (practical).

Orange book: pg.Green book: pg. 11-12

To do:1 Practical “Viewing Animal Cells”2 Summary in Green book (you only need to show the equations for magnification.

Conversions1mm = 1000µmIf you get stuck the following website will help you to converthttp://www.cleavebooks.co.uk/scol/ccleng.htm

MethodYou have been provided with a compound light microscope with low (x4), medium (x10) and high (x40) objective lenses and an eyepiece lens (x10).

Turn the objectives lenses so that you are using the lowest objective lens (x4).

Place your slide on the stage. Hold it in place with the metal clips.

Arrange the mirror so that light shines up through the hole in the stage.

BEFORE you look down the microscope, move the lens nearest the slide down until it is just above the slide.

*Warning*With some microscopes it is possible to move the objective lens so far down that it will break the slide.

Look down the eyepiece and slowly turn the coarse focusing knob so the lens moves AWAY from the slide.Once a blurred image is seen, use the fine focusing knob to obtain a clear view.

To increase magnification, ALWAYS focus on low power first. Once a clear image is obtained on low power, turn the objective lenses round to medium power and use the FINE focusing knob to focus.

Only once you have obtained a focused image at medium power should you move onto high power. From medium power, turn the objective lenses round to high power and use the FINE focusing knob to focus the image.

Microscopic Observation of cells and tissues.This practical focuses on microscope technique and making and recording observations in the form of biological drawings.

Background InformationDrawings should be done with a sharp HB pencil making clear single lines. Examiners do not give credit for sketchy lined drawings. A soft rubber can be used to correct errors.

Always draw what you see and not what you expect to see from memory or textbook diagrams.

Candidates often draw diagrams too small but rarely draw them too large. Ensure that your drawing is large enough to show all the detail.

All parts of the drawing should be kept in correct proportions.

Biological drawings can be both high-power and low-power.

Low and medium power drawings are usually plan drawings that do not contain cellular detail but do show the distribution of various tissues.

Look at the following two sets of drawings of a red and white blood cell, made by different students and how marks would be allocated by an examiner.

Student A would be awarded 1 mark.

Student B would be awarded 6 marks.

Marking – Low, Medium and High Power Plan DiagramsGood quality of drawing i.e. clear single lines in pencilIn tissues – no individual cells, for cells – unshaded organellesAccurate and informative title Magnification slide was observed at Some accurate labels Large drawing (magnify what you see) with correct proportions Scale bar/ Magnification of drawing indicated

Marking - High power drawing – Detailed DrawingGood quality of drawing i.e. clear single line

In tissues – several cells for each cell type, for cells – unshaded organellesAccurate and informative title Magnification slide was observed at Some accurate labels Large drawing (magnify what you see) with correct proportions

Scale bar/ Magnification of drawing indicated

Making Observations – Human Cheek Cells Scrape some cells from the inside of you cheek (inside the mouth), using either a clean fingernail or a cotton bud.

Rub some of the cells obtained onto a clean side.

Add one drop of methyl blue stain.

Gently lower a cover slip onto the cells – trying to prevent air bubbles.

View the cells under low power to start and work up to high power.

Make a high power detailed drawing of what you observe.

Calculating Linear Magnification of your Drawing

Magnification is calculated from the Image (your drawing) and the object that you viewed.

If you calculated the size of your image to be 45mm (45000m) and you were told the object was 90m then you work out the magnification as follows:

Magnification = ImageObject

=4500090

=¿500

Magnification = Image Object

Based on the following information you should be able to calculate the linear magnification of your drawing.Human cheek cell diameter - 60m

Draw a straight line across the diameter of the cell you have drawn.

Measure the diameter of the cell along the line (remember to convert it into m).

Divide the Image (the measurement you have taken) by the Object (60m). This is the magnification of your drawing.

Write the magnification of your drawing in the bottom left hand corner of your drawing.

Another way to show magnification is to draw a scale bar.

If 45mm (your image) = 90m (the object) then 10mm = 10×9045

=20m

A scale bar of 10mm with 20m could be drawn on the bottom right hand corner of your drawing.

20mYou can also recheck the magnification of your drawing from this: 1000020

=¿500

Surface area : Volume 8/25/10 8:28 PM

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size.

Orange book: pg. 14-15Green book: pg. 12

To do:1 Highlight key words in above text2 Read the relevant sections in the text books3 Discuss your findings 4 Summary in Green book

IntroductionSmall organisms don’t have a bloodstream, but instead rely on the simple diffusion of materials for transport around their cells. This is OK for single cells, but it would take days for molecules to diffuse through a large animal, so most animals have a circulatory system with a pump to transport materials quickly around their bodies. This is an example of a mass flow system, which means the transport of substances in the flow of a fluid (as opposed to diffusion, which is the random motion of molecules in a stationary fluid). The transport of materials in the xylem and phloem of plants is another example of mass flow. Mass flow systems work together with the specialised exchange systems (such as lungs, gills and leaves).

From Cells to OrganismsDiffusion and the Problem of SizeAll organisms need to exchange substances such as food, waste, gases and heat with their surroundings. These substances must diffuse between the organism and the surroundings. The rate at which a substance can diffuse is given by Fick's law:

The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. The requirements for materials depends on the mass or volume of the organism, so the ability to meet the requirements depends on

which is known as the surface area : volume ratio. As organisms get bigger their volume and surface area both get bigger, but not by the same amount.

As organisms get bigger their surface area/volume ratio gets smaller. A bacterium is all surface with not much inside, while a whale is all insides with not much surface. This means that as organisms become bigger it becomes more difficult for them to exchange materials with their surroundings. In fact this problem sets a limit on the maximum size for a single cell of about 100 µm. In anything larger than this materials simply cannot diffuse fast enough to support the reactions needed for life.

Organisms also need to exchange heat with their surroundings, and here large animals have an advantage in having a small surface area/volume ratio: they lose less heat than small animals. Large mammals keep warm quite easily and don't need much insulation or heat generation. Small mammals and birds lose their heat very readily, so need a high metabolic rate in order to keep generating heat, as well as thick insulation. So large mammals can feed once every few days, while small mammals must feed continuously. Human babies also loose heat more quickly than adults, which is why they need woolly hats.

So how do organisms larger than 100 µm exists? All organisms larger than 100 µm are multicellular, which means that their bodies are composed of many small cells, rather than one big cell. Each cell in a multicellular organism is no bigger than about 30µm, and so can exchange materials quickly and independently.

Emergent Properties 8/25/10 8:28 PM

2.1.7 State that multicellular organisms show emergent properties.

Orange book: pg. 16 & 21Green book: pg. 12 & 13

To do:1 Read the relevant sections in the text books2 Discuss your findings 3 Add notes 4 Summary in Green book

Differentiation 8/25/10 8:28 PM

2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.

Orange book: pg. 16Green book: pg. 13

To do:1 Read the relevant sections in the text books2 Find and insert an image for each of the cells in the table3 Complete the table by listing some adaptations of each cell and relate this to function 4 Summary in Green book (only need an explanation of why cells are different)

Animal Cell Differentiation

Cell Adaptation FunctionRed Blood CellNerve CellPalisade Cell of PlantWhite Blood Cells

All cells within an individual organism contain EXACTLY the same DNA (except gametes, and RBCs – after they lose their nucleus).

Cells differential into specialized cells depending on which GENES are EXPRESSED.

Genes code for PROTEINS and proteins control the FUNCTIONING of the cell.

E.g. every cell contains the gene for INSULIN but only the PANCREAS expresses it.

Stem Cells 8/25/10 8:28 PM

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways.

Orange book: pg. 17Green book: pg. 14-15

To do:1 Visit each of the websites2 Discuss your findings.3 Jot down some main points.4 Summary in Green book

http://stemcells.nih.gov/ Go to the pink box called “Frequently Asked Questions” (top left).1. Introduction

2. What are the unique properties of stem cells (first two paragraphs only)

3. What are embryonic stem cells (first couple of lines only)

4. What are adult stem cells (first paragraph only).

5. Similarities and Differences in Adult and Embryonic Stem cells

Adult Embryonic

http://www.tellmeaboutstemcells.org/You only need to read through the section on “Stem Cell Basics”.Stem Cell Basics

Are there Different Types of Stem Cells?

Why Does the Difference Matter?

http://www.dnalc.org/stemcells.html

Therapeutic Stem Cells 8/25/10 8:28 PM

2.1.10 Outline one therapeutic use of stem cells.

Orange book: pg. 18Green book: pg. 14-15

To do:1 Read the relevant sections in the textbooks.2 Visit the following website and jot down some main points.http://stemcells.nih.gov/Go to the pink box called “Frequently Asked Questions” (top left).Can they cure disease?3 Discuss your findings4 Summary in Green book