Edexcel International A Level Biology

Revision Notes

4.1 Plant Cell Structure

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Plant Cell Structure & Ultrastructure

  • The structure of plant cells is made up of a complex system of organelles and ultrastructures
  • Plant cells contain many of the organelles found in animal cells, along with a few other organelles that are only found in plant cells

Cell wall

  • Cell walls are formed outside of the cell membrane and offer structural support to the cell
    • This structural support is provided by the polysaccharide cellulose
  • Cell walls are freely permeable, and will allow most substances to enter the plant cell

Middle lamella

  • This forms the outermost layer of the plant cell and acts like glue to stick adjacent plant cells together
  • It is mainly composed of a polysaccharide called pectin

Cell components_Cell wallA diagram to show the cell wall and middle lamella of one plant cell


  • Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
  • This interconnected system of cytoplasm between plant cells is known as the symplast


  • These are very thin regions of the cell wall
  • The pits in adjacent plant cells are lined up in pairs
  • They are formed due to the absence of secondary thickening in the cell walls in the areas where plasmodesmata are present


Detailed structure of plant cell wall


  • Chloroplasts are larger than mitochondria
  • Surrounded by a double-membrane
  • Within the chloroplast there are membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana (singular = granum)
  • Grana are joined together by lamellae (thin and flat thylakoid membranes)
  • Chloroplasts also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis

Cell components_ChloroplastChloroplasts are found in the green parts of plants - the green colour is due to the presence of the pigment chlorophyll


  • Small, membrane bound organelle containing starch granules
  • Large numbers are found in plant storage organs, such as potato tubers


Structure of an amyloplast

Vacuole and tonoplast

  • The vacuole is a sac in plant cells surrounded by the tonoplast (selectively permeable membrane)
  • They are large, permanent structures in a plant cell
  • Contains cell sap, which is a mixture of different substances such as water, minerals, waste and enzymes
  • The concentration of the cell sap enables water to enter the vacuole by osmosis

Cell components_VacuoleThe structure of the vacuole

Plant Cell Structure & Ultrastructure: Function

  • The ultrastructures and organelles listed above each perform a specific function in a plant cell

Cell wall

  • The cellulose component of cell walls provides structural support to the cell
  • Due to its rigid nature, it is responsible for the regular shape of a plant cell

Middle lamella

  • It provides stability to the plant by ensuring that adjacent plant cells are adhered together


  • The cytoplasmic strands connect the contents of adjacent plant cells
  • This allows substances to be transported between cells and facilitates cell to cell communication


  • Since the cell wall is very thin in these regions, it allows for the transport of substances between cells
  • This is particularly useful in xylem vessels, where it allows for the lateral flow of water and mineral ions between adjacent vessels


  • Due to the presence of chlorophyll and thylakoids, chloroplasts are the site of photosynthesis
    • Certain parts of the process occur in thylakoid membranes, while other parts happen in the stroma


  • They are responsible for storing starch in plants and converting it back to glucose when the plant needs it

Vacuole and tonoplast

  • Vacuoles have several functions in plant cells:
    • They keep cells turgid, which stops the plant from wilting
    • Store various substances, such as pigments and waste products
    • Break down and isolate unwanted chemicals in plant cells
    • The tonoplast controls what can enter and leave

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Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.