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
A 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
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
Chloroplasts 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
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
The structure of the vacuole