Cell Structure and Organisation

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Organelles

Nucleus

Controls cells activities and holds the chromosomes

  • Double membrane called nuclear envelope
  • Envelope has pores which allows transport of mRNA in and out
  • Nuceloplasm - contains chromatin and coils of DNA bound to histone protein
  • Nucleolus - produces RNA to make ribosomes

(http://www.biology4kids.com/files/art/cell_nucleus1.png)

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Organelles

Mitochondria

  • double membrane - seperated by intermembrane space
  • inner membrane folded inwards to form cristae
  • matrix containing compounds and DNA allowing them to produce own protein

Site of aerobic respiration

Produces ATP

Metabollically active cells contain many mitochondria e.g. muscle cells(http://isite.lps.org/sputnam/Biology/U3Cell/mitochondria_1.png)

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Organelles

Endoplasmic Reticulum (ER)

  • double membrane forming flattened sacs
  • fluid filled spaces between called cisternae
  • interconnected and allows transport of materials throughout cell

Rough ER

  • Ribosomes on outer surface
  • Transports proteins made by ribosomes

Smooth ER

  • Lack of ribosomes
  • Synthesis and transport of lipids
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Organelles

Ribosomes

  • made up of one large and one small sub unit
  • made in nucleolus from rRNA and protein
  • used in protein synthesis

(http://faculty.southwest.tn.edu/rburkett/Cell%20s19.jpg)

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Organelles

Golgi Body

  • Rough ER is pinched off at ends forming vesicles
  • Vesicles fuse to become golgi
  • Proteins transported in vesicles - they are modified and packaged
  • At other end, vesicles are pinched off
  • Products secreted by exocytosis and vesicle fuse with membrane

Functions

  • Produce secretory enzymes
  • Secrete carbohydrates
  • Produce glycoprotein
  • Transport and store lipids
  • Form lysosomes

(http://www.biology4kids.com/files/art/cell_golgi1.png)

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Organelles

Lysosomes

  • small vacuoles formed when portions of golgi body are pinched off
  • contain digestive enzymes
  • remove worn out organelles and dangerous material e.g. bacteria
  • reuse useful components

Centrioles

  • during cell division, they divide and move to opposite poles of cell
  • synthesise microtubules of spindle

located just outside nucleus in cytoplasm (centrosome)

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Organelles

Chloroplasts

  • double membrane
  • stroma - contains ribosomes, lipid, circular DNA, starch grains
  • thylakoids - flattened sacs in stroma
  • granum - many thylakoids
  • chlorophyll found within thylakoids

(http://www.indiastudychannel.com/attachments/Resources/151438-232156-Structure-Chloroplast.png)

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Organelles

Vacuole

  • plant cells have large permanent vacuoles but animal cells have small ones
  • single membrane (tonoplast)
  • contain cell sap (provides osmotic system)
  • water enters cell by osmosis, causing it to swell and it becomes turgid, keeping plants upright

Cellulose Cell Wall

  • contains microfibrils embedded in a polysaccharide matrix
  • permeable to water - strong to resist swelling so it can become turgid
  • microfibirils provide mechanical strength
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Animal and Plant Cells

Plant

  • cell wall and membrane
  • chloroplasts
  • large vacuole
  • no centrioles
  • plasmodesmata

Animal

  • no cell wall, but has membrane
  • no chloroplasts
  • small vacuoles
  • centrioles
  • no plasmodesmata
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Levels of Organisation

Tissues

Group of similar cells, specialised in the same way

  • Cilia epithelial - trachea
  • Columnar epithelial - stomach / intestines
  • Squamous epithelial - alveoli
  • Cuboidal epithelial - kidney tubules

Organs

Aggregation of several tissues that perform a specific function e.g. heart, lungs etc.

Organ System

Aggregation of organs that together perform a specific function e.g. respiratory system, digestive system etc.

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Prokaryote and Eukaryote Cells

Prokaryotes

  • no membrane bound organelles
  • small ribosomes
  • circular DNA free in cytoplasm
  • no membrane
  • cell wall made of peptidoglycan

Eukaroytes

  • membrane bound organelles
  • large ribosomes
  • DNA in chromosomes
  • cell wall made of cellulose (plants)
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Viruses

  • causes diseases
  • no membrane, metabolism or organelles
  • made up of protein coat and nucleic acid
  • invade host cel and take over nucleus and multiply

Bacteriophages (T2 phage)

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