Cell structure

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Cell structure

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Nuclear envelope

  • Double membrane surrounding the nucleus
  • Outer membrane has ribosomes on the surface
  • Controls the entry and exit of materials in and out of the nucleus

Nuclear pores

  • Allows the passage of molecules out of the nucleus


  • Jelly-like material that makes up most of the nucleus


  • It manufactures ribosomes

Functions of the nucleus

  • Controls activities of the cell
  • Collects the genetic material
  • Makes ribosomes
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Double membrane

  • The inner membrane folds to form extensions called cristae


  • Provides a large surface area for the attachment of enzymes and other proteins


  • Contains proteins, lipids, ribosomes and DNA that allows mitochondria to produce its own proteins
  • Many enzymes involved in respiration are found in the matrix

Functions of mitochondria

  • To produce ATP- an energy carrier molecule from respiratory substrates
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Chloroplast envelope

  • Double plasma membrane that surrounds the chloroplast
  • It's very selective in what it allows in and out of the chloroplast

The granum

  • Stacks of disc-like structures called thylakoids
  • It's where the first stage of photosynthesis occurs (light absorption)

The stroma

  • Fluid-filled matrix where the second stage of photosynthesis occurs (synthesis of sugars)

The chloroplasts adaptations for photosynthesis

  • The double membrane provides a large surface area for the attachment of chlorophyll, electron carriers and enzymes
  • The fluid in the stroma has the enzymes needed to make sugars for the second stage of photosynthesis
  • They contain DNA and ribosomes so they can make proteins needed for photosynthesis
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Endoplasmic reticulum

Rough endoplasmic reticulum (RER)

  • Has ribosomes on the surface
  • Provides a large surface area for protein synthesis
  • Provides a pathway for transport of materials
  • The double membrane folds to form sacs called cisternae

Smooth endoplasmic reticulum (SER)

  • Hasn't got ribosomes on the surface
  • More tubular in appearance
  • It synthesises, stores and transports lipids and carbohydrates
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Golgi apparatus


  • Has small rounded, hollow structures called vesicles

Proteins and lipids

  • The endoplasmic reticulum produces them and then they're transported to the golgi apparatus
  • The golgi apparatus modifies the proteins by adding non-protein components (eg: carbohydrates)
  • It labels the proteins so that they can be sent to the right destinations
  • They're then sent to the golgi vesicles, then the cell surface where they fuse with the membrane and release the contents

Functions of the golgi apparatus

  • To add carbohydrates to proteins to form glycoproteins
  • To produce secretory enzymes
  • To secrete carbohydrates
  • To transport, modify and store lipids
  • Form lysosomes
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-Formed from the golgi apparatus

  • Has lysozymes which is an enzyme that hydolyses the cell walls of certain bacteria

Functions of lysosomes

  • To hydrolyse materials ingested by phagocytic cells (eg: white blood cells)
  • Release enzymes to destroy material around the cell
  • Digest worn out organelles so that useful chemicals can be re-used
  • Breaks down cells after they have died
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70s ribosomes

  • They're slightly smaller
  • Found in prokaryotic cells, mitochondria and chloroplasts

80s ribosomes

  • Found in eukaryotic cells

Function of ribosomes

  • Protein synthesis
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Cell wall

  • Consists of microfibrils of cellulose that are embedded in a matrix
  • Microfibrils have good strength, so it strengthens the cell wall

The middle lamella

  • Thin layer
  • Marks the boundary between adjacent cell walls and brings them together

Cell walls of fungi

  • Doesn't contain cellulose
  • Has a mixture of chitin, glycan and glycoproteins

Cell walls of algae

  • Made of cellulose or glycoproteins or both

Functions of cell walls

  • Provide strength to prevent osmotic lysis
  • To allow water to pass through
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  • It's a fluid-filled sac bounded by a single membrane- The single membrane is called the tonoplast

Plant vacuole

  • Contains a solution of mineral salts, sugars and amino acids


  • Sugars and amino acids can act as temporary food
  • The pigments can colour petals to attract pollinating insects
  • They support herbaceous plants by making them turgid
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Prokaryotic cells

  • They're smaller and they have no nucleus
  • Instead of a nucleus, they have circular DNA and they may have smaller strands called plasmids
  • Has no membrane-bounded organelles
  • Has 70s ribosomes
  • The cell wall is made of murein
  • May have an outer mucilaginous layer called a capsule
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