B11.20ThenucleusofthecellB21.1ComponentsofabacterialcellB21.2FunctionofthecomponentsofaplantcellB21.3FunctionofthecomponentsofananimalcellB21.4HowplantandanimalcellscanbestudiedwithalightmicroscopeB21.5Simplemagnificationcalculations

Thislessonwewill cover…

Allorganismsarecomposedofcells,life’sbasicunits.Cellswerediscoveredby

RobertHookeinEnglandin1665.Hookewasusingoneofthefirstmicroscopes.

CellTheory:OrganizationofLife

Anton van Leeuwenhoekused microscopes capableof magnifying 500 times,and discovered anamazing world of single-celled life in a drop ofpond water.

CellTheory:OrganizationofLife

summarisedalargenumberofobservations

bythemselvesandothers,concludedthatalllivingorganismsconsistofcells.Theirconclusionformsthebasisofwhathascometobeknownasthe

celltheory.

In1839,twoGermanbiologists…MatthiasSchleiden andTheodor Schwann

Usingamicroscope:http://www.udel.edu/biology/ketcham/

microscope/scope.html

Magnificationandresolution:Of all the techniques used in biology microscopy isprobably the most important. The vast majority ofliving organisms are too small to be seen in anydetail with the human eye, and cells and theirorganelles can only be seen with the aid of amicroscope.

size of the image

size of the objectMagnification =

size of the image

MagnificationSize of Object =

Resolution: Is the ability to distinguishbetween two points on an image i.e. the amountof detail or clarity. The resolving power of aparticular microscope depends on thewavelength or form of radiation used.

ThediagramshowsanEscherichiacolibacteriumatamagnificationofx20000.WhatistheactuallengthofthebacteriumfromAtoBinmicrometers(µm)?Showyourworking.

0.0075x1000=7.5µm(micrometers)

1.MeasurethedistancefromAà Binmm

150mm

(I)150/(M)20000=(A)0.0075mm

3.Convertmillimeters(mm)tomicrometers(µm)

The ElectronMicroscopeIn the 1930s a differenttype of microscope wasmade that used a beam ofelectrons instead of lightThe electron microscope(EM). By using a beam ofelectrons, instead of light,higher resolution powerscan be achieved due toelectrons having a smallerwavelength than light.

Transmission electron microscope (TEM)A TEM transmits a beam of electrons (from an electron gun) througha thin section of the specimen.

Parts of the specimenabsorb electrons andappear dark on theimage. Other parts donot absorb electronsand appear light.

The resolving power ofa TEM is around 0.1nm(very good) but oftenthis cannot be achieveddue to problems withspecimen preparations.

Electron gun

Specimen holder

Projection chamber

Much Smaller that eukaryotic cells (0.5 - 10 µm)DO NOT have a nucleus – their DNA floats free in the

cytoplasm.It is circular DNA present as one long coiled-up strand.

Have Fewer Organelles (e.g. they don’t have mitochondria)

Have smaller Ribosomes.

Draw and label a

Prokaryote!

Cells: Structure and function

Ribosomes

Cell Wall

Mitochondria

Nucleus

Chloroplast

Cytoplasm

Cell Membrane

Eukaryotic cells are more complex than prokaryotic cells, and include all animal and Plant cells.

Different Organelles, e.g. True nucleus, Larger ribosomes, mitochondria,

The nucleus contains the genetic information of the cell in multiple strands of DNA and protein (chromosomes).

Eukaryotespossess a well defined

Nucleus,

Eukaryotes have membrane bound organelles, where important cellular functions take place.

The

NucleusThe nucleus contains genes that control the eukaryotic cell…

The nucleus: contains DNA. Key functions are –replication, cell Division, & protein synthesis. In a eukaryotic cell DNA is linear & attached to proteins (Histones)

Q.Chromosomes consist of long coiled molecules of DNA.a. State the 2 types of Human cells that do not have 23 pairs of chromosomes.

Sperm and Egg.

b. Explain why these cells only have 23 chromosomes.

They are Haploid cells (contain 23 chromosomes) which, via fertilisationcombine to form a cell (zygote) resorting the diploid number ofchromosomes. (46, 23 pairs).

Ribosomes (site of protein synthesis).

Small & dense structure, NO membrane!

Mitochondria are found in almost alleukaryotic cells, are responsible for generatingmost of the ATP(energy)

Thesespecialisedcellsareveryactiveandrequirelotsofenergy.Assuchtheyhavemanymitochondriatoprovidetheenergy(ATP)generatedfromcellularrespiration.

Ok, so lets Draw and label an

animal cell

Draw and label a

Plant cell

Chloroplasts are the sites of photosynthesis and are found only in the cells of plants and green algae.They have chloroplasts – where photosynthesis occurs, and they contain a green substance called chlorophyll.

Plant cells:

The cell wall a tough, flexible, (sometimes fairly rigid) layer, located external to the cell membrane.

Inside the plant cell is a permanent vacuole containing cell sap – a weak solution of sugars and salts.

1. Name 4 plant cell structures thatyou would see with a lightmicroscope.

Electron microscope.

Cell wall, nucleus, mitochondria, vacuole

2. Name another type of microscope.

Light microscopes rely on refraction of light to magnify imageswhereas electron microscopes rely on focused beams of electrons.Electrons have a shorter wavelength than light, as such electronmicroscopes are more powerful.

3. State the difference between the way light microscopes andelectron microscopeswork. Identify which is most powerful.

Question time!

4. The Flagellum of the bacterium Escherichia coli is0.001mm long. You observe the flagellum at 400 xmagnification. Calculate how long the magnifiedimage will be.Imagesize=ActuallengthofflagellumxMagnification.Imagesize=0.001mmx400=0.4mm

TrueNucleus,Largepermeantvacuole,MitochondriaandChloroplasts.

5.Name4featuresofaplantcellthatisnotseeninbacterialcells.

Question time!