Edexcel A (SNAB) AS Biology

Revision Notes

4.2.1 Plant Cell Structure

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Plant Cell Structure

  • Plant cells contain most of the organelles found in animal cells, along with a few extra 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

Middle lamella

  • This forms the outermost layer of the plant cell and acts like glue to stick adjacent plant cells together
  • It provides stability to the plant

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

Plasmodesmata

  • Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
  • This allows substances to be transported between plant cells and facilitates cell to cell communication

Pits

  • These are very thin regions of the cell wall
  • The pits in adjacent plant cells are lined up in pairs
  • This facilitates transport of substances between cells

detailed-structure-of-plant-cell-wall

Detailed structure of plant cell wall

Chloroplasts

  • Larger than mitochondria, also surrounded by a double-membrane
  • 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 are the site of photosynthesis:
  • Certain parts of photosynthesis occur in thylakoid membranes, while other parts happen in the stroma
  • 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

Amyloplasts

  • Small, membrane bound organelle containing starch granules
  • They are responsible for storing starch in plants and converting it back to glucose when the plant needs it

structure-of-an-amyloplast

Structure of an amyloplast

Vacuole and tonoplast

  • The vacuole is a sac in plant cells surrounded by the tonoplast (selectively permeable membrane)
  • Contains cell sap, which is a mixture of different substances such as water, minerals, waste and enzymes
  • Vacuoles have several functions in plant cell:
    • They keep cells turgid, which stops the plant from wilting
    • They can break down and isolate unwanted chemicals in plant cells
    • The tonoplast controls what can enter and leave

Cell components_VacuoleThe structure of the vacuole

Recognising Organelles from Electron Microscope Images

  • It is important to be able to recognise the plant organelles mentioned earlier from electron microscope images

Plant Cell MicrographTEM electron micrograph of a plant cell showing key features

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Marlene

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.