2.1 Cell Structure

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  • Created by: ramsha0
  • Created on: 20-12-15 12:18

Eukaryotic Cells & Prokaryotic Cells

Organisms can be prokaryotes or eukaryotes.

Prokaryotic organisms:

  • They are single-celled organisms
  • They are smaller and simpler
  • e.g: bacteria

Eukaryotic organisma:

  • Have membrane-bound organelles
  • More complex
  • E.g: all animal & plant cells

Both contain organelles.

  • Organelle - a part of a cell that has a specific function
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Animal Cells

These contain:

  • plasma membrane (cell surface membrane)
  • rough endoplasmic reticulum
  • nucleus
  • smooth endoplasmic reticulum
  • lysosome
  • ribosome
  • golgi apparatus (golgi body)
  • cytoplasm
  • mitochondrion
  • vesicle
  • cilia
  • flagellum
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Plant Cells

These contain:

  • chloroplast
  • cell wall
  • vacuole
  • plasmodesma
  • plasma membrane (cell surface membrane)
  • rough endoplasmic reticulum
  • nucleus
  • smooth endoplasmic reticulum
  • lysosome
  • ribosome
  • golgi apparatus (golgi body)
  • cytoplasm
  • mitochondrion
  • vesicle
  • cilia
  • flagellum
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  • nuclear envelope
  • nuclear pore
  • nucleolus
  • chromatin


  • large subunit
  • small subunit

Rough Endoplasmic Reticulum:

  • ribosome
  • fluid


  • cell plasma membrane
  • vesicle
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Ultrastructures cont...

Golgi Apparatus:

  • golgi body
  • vesicle


  • outer membrane
  • inner membrane
  • cristae
  • matrix


  • stroma
  • two membranes
  • granum
  • lamella
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Ultrastructures cont...


  • microtubule


  • side
  • cross-section

Cell Wall:

  • cell wall
  • plasma membrane
  • cytoplasm

Plasma membrane:

  • cell surface membrane
  • cytoplasm
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Organelles & Their Functions

Cell membrane - regulates the movement of substances into and out of the cell, it has receptor molecules which respond to chemicals (e.g: hormones)

Nucleolus - makes ribosomes

Nuclear envelope - double membrane

Nuclear pores - allow substances (e.g RNA) to move between the nucleus and the cytoplasm

Mitochondrion - site of aerobic respiration where ATP is produced, found in large number of active cells, require lots of energy

RER - folds and processes proteins that have been at the ribosomes

SER - synthesises and processes lipids

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Organelles & Their Functions cont...

Golgi apparatus - processes and packages new lipids and proteins, also makes lysosomes

Vesicles - transports substances in and out of the cell and between organelles

Lysosome - contains digestive enzymes,kept separate from the cytoplasm by the surrounding membrane and can be used to digest invading cells or to break down worn out components of the cell

Ribosomes - site where proteins are made

Centrioles - involved with the separation of chromosomes during cell division

Chloroplasts - site where photosynthesis takes place

Vacuole - contains cell sap, sugars and solutes


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Organelles & Their Functions cont...

Cell wall - supports plant cell, has channels called plasmodesmata

Cilia - the microtubules allow the cilia to move, this movement is used  by the cell to move substances along the cell structure

Flagellum - for movement, the microtubules contract to make the flagellum move

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Organelles Involved in Protein Production

  • mRNA copy of protein of the gene is made in the nucleus

  • mRNA leaves the nucleus through the nuclear pore

  • mRNA attaches to a ribosome, (could be RER)

  • ribosome reads instructions to assemble the protein

  • protein molecules are ‘pinched off’ in vesicles and travel towards golgi body

  • vesicle fuses with golgi body

  • golgi body ‘processes and packages’ protein molecules ready for release

  • packaged protein molecules are ‘pinched off’ in vesicles from golgi body and move towards plasma membrane

  • vesicles fuses with plasma membrane

  • plasma membrane opens to release protein molecules outside

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Cytoskeleton - Uses & Structure

Cytoskeleton: the network of protein threads


  • provide mechanical strength to cells

  • aiding transport within cells

  • enabling cell movement


  • microtubules - tiny protein cylinders

  • microfilaments - small solid strands


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Cytoskeleton - Functions

Main functions:

  • support cell

  • keep them in position

  • strengthen the cell

  • maintain its shape

  • movement of materials (components) within the cell (e.g: movement of chromosomes during separation of cell division, this depends on microtubules in the spindle)

  • proteins of cytoskeleton can also cause the cell to move (e.g: movement of cilia and flagella is caused by the cytoskeletal protein filaments that run through them)
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Comparison Between Prokaryotes & Eukaryotes

Similarities & Differences:



no true nucleus, naked DNA

nucleus present - genetic material in chromosomes

circular DNA

linear DNA

average size - 0.5-5 um

average size - 10-100 um

ribosomes about 10-20 nm (small)

ribosomes about 22nm (large)

cell wall, not made of cellulose

no cell wall in animals, cellulose cell wall in plants

flagellum in helix

flagellum arranged in a ‘9+2’ formation

not membrane-bound organelles

membrane-bound organelles

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Bacteria Cells

Bacteria cells are prokaryotes:

  • Prokaryotes are roughly a tenth the size of eukaryotic cells
  • This means tge normal microscopes aren't really powerful enough to look at their internal structure.

They have:

  • flaggelum - tail used to propel the cell
  • circular DNA  - bacterial chromosome
  • plasma mebrane
  • cell wall
  • plasmid - ring of DNA
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  • magnification: number of times an image has been enlarged
  • resolution: the ability to distinguish two points as separate points (resolution of human eye is approx. 0.3mm / 3/10th mm
  • organelles: structures within a cell, e.g: nucleus
  • ultrastructure: inner detail organelles within a cell


magnification = image size


                        object size

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Magnification Conversion Units




Conversion factor to the next:



















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Magnification & Resolution of Microscopes

  • magnification: number of times an image has been enlarged

  • resolution: the ability to distinguish two points as separate points

light microscope

transmission electron microscope

scanning electron microscope

max. resolution

0.2 um

0.00002 um

0.002 um

max. magnification




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Light Microscopes

Light Microscopes:

  • use light

  • max. resolution = 0.2 um

  • max. magnification = x1500

  • lower resolution than electron microscopes

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Laser Scanning Confocal Microscopes

Laser Scanning Confocal Microscopes:

  • use intense beams of light (laser beams) to scan a specimen which is usually tagged with a fluorescent dye

  • laser causes the dye to fluoresce (give off light), the light is then focused through a pinhole onto a detector

  • the detector is hooked up to a computer, which generates an image

  • adv: the image can be 3D

  • adv: they have a pinhole which means that any out-of-focus  light is blocked so these microscopes produce a much clearer image (than a light microscope)

  • black and white, with false colour

  • they can be used to look at objects at different depths in thick specimens

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Transmission Electron Microscopes - TEM

Transmission Electron Microscopes - TEM:

  • uses electromagnets to focus a beam of electrons, which is then transmitted through their specimen

  • max. resolution = 0.0002 um

  • max. magnification = x1,000,000

  • images are darker because denser parts of the specimen absorb more electrons

  • black and white, with false colour

  • adv: they provide high resolution images because they can distinguish between the smallest objects so they can be used to look at a range of organelles

  • dis adv: they can only be used on thin specimens

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Scanning Electron Microscope - SEM

Scanning Electron Microscope - SEM:

  • scan a beam of electrons across the specimen, this knocks of electrons from the specimen which are gathered in a cathode ray tube to form an image

  • max. resolution = 0.002 um

  • max. magnification = x500,000

  • black and white, with false colour

  • adv: the image produced shows the surface of the specimen

  • adv: the image produced can be 3D

  • dis adv: they have a lower resolution images than TEM

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Comparison Between Microscopes


Name of microscope



2D or 3D

Black, white or colour

optical/light microscope

x1500 → x2000

0.2 um



laser scanning



transmission electron microscope


50 pm


black + white but adds false colour

scanning electron

x15 → x200,000

50 nm



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