Topic 4 - Biodiversity and natural resources

Structure of plant cells

cells wall, chloroplasts amyloplasts, vacuole, tonoplast, plasmodesmata, pits, middle lamella

Cell wall

Structure:

• made of cellulose macrofibrils embedded with pectin

Function:

• provides support

Chloroplasts

Structure:

• Contain stacks of thylakoid membranes called grana containing chlorophyll.

• The grana are connected by extensions of thylakoid membranes called lamellae.

• Grana are surrounded by a colourless fluid called stroma which contains enzymes needed for photosynthesis

Function:

• site of photosynthesis

Amyloplasts

Structure:

• Organelles surrounded by a double membrane

Function:

• contain amylopectin (starch)

Vacuole

Structure:

• contains cell sap and is surrounded by a tonoplast (single membrane)

Function:

• provides strength and support

Tonoplast

Structure:

• a single membrane

Function:

• Membrane that separates the vacuole from the surrounding cytoplasm and helps maintain turgor pressure

Plasmodesmata

Junction where the cytoplasm of one cell is connected to the cytoplasm of another cell through gaps in the cell wall.

Pits

Gaps in the cell wall where lignification was not completed and allows water to pass between cells/vessels.

Middle lamella

pectin layer that cements two adjoining cells together

Structure + function of starch - amylose

Source - plant

Subunit - a-glucose

Bonds - 1,4

Branches - no

Function - energy storage

Structure + function of starch - amylopectin

Source- plant

Subunit - a-glucose

bonds - 1,4 +1,6

Branches - yes (- per 20 subunits)

Function - energy storage

Structure + function of cellulose

Source - plant

Subunit - B-glucose

Bonds - 1,4 + 1,6

Branches - no

Function - structural

Molecular structure of cellulose

Molecular structure of starch

How is cellulose organised into microfibrils

Cellulose Microfibrils

• Formation: Long cellulose chains align and bond via hydrogen bonds.

• Structure: Multiple chains bundle into microfibrils (10-30 nm diameter).

• Function: Provides strength and structural support in plant cell walls.