Biology AS - unit 2 biodiversity and natural resources

1st bit about plants fibres, structure and function etcccc

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Biodiversity and natural resources Chapter 4.1 Plant Structure
The structure of a plant cell ­ I can compare the ultrastructure of plant cells with that of animal cells:
Plant cells have different organelles from animal cells
Organelle Description Function
Cell Wall Arigid structure that surrounds plant cells. It's Supports plant cells.
made mainly of the carbohydrate cellulose
Middle lamella The outermost layer of the cell. This layer acts as an adhesive, sticking
adjacent plant cells together. It gives the plant
Plasmodesmata Channels in the cell walls that link adjacent Allow transport of substances and
cells together communication between cells.
Pits Regions of the cell wall where the wall is very Allow transport of substances between cells.
thin. They're arranged in pairs ­ the pit in one
cell is lined up with the pit in the adjacent cell
Chloroplast A small, flattened structure. It's surrounded by The site where photosynthesis takes place.
a double membrane, and also has membranes Some parts of photosynthesis happen in the
inside called thylakoid membranes. These grana, and other parts happen in the stroma (a
membranes are stacked up in some parts of thick fluid found in chloroplasts)
the chloroplast to form grana. Grana are linked
together by lamellae ­ thin, flat pieces of
thylakoid membrane.
Amyloplast A small organelle enclosed by a membrane. Storage of starch grains. They also convert
They contin starch granules. starch back to glucose for release when the
plant recquires it.
Vacuole and The vacuole is a compartment surrounded by a The vacuole contains the cell which is made up
Tonoplast membrane called the tonoplast. of water, enzymes, minerals and waste
products. Vacuoles keep the cells turgid ­
stops the plant wilting. They're also involved
in the breakdown and isolation of unwanted
chemicals in the cell. The tonoplast controls
what enters and leaves the vacuole.
I can compare the structures, position and function of sclerenchyma fibres (support) and xylem vessels (support and
transport of mineral ions)
Xylem vessels:
1. The function of xylem vessels is to transport water and mineral ions up the plant, and provide support.
2. They're very long, tube-like structures formed from dead cells, joined end to end. The tubes are found
together in bundles.
3. The cells are longer than they are wide; they have hollow lumen (they contain no cytoplasm) and have no end
4. This makes an uninterrupted tube, allowing water and mineral ions to pass up through the middle easily.
5. Their walls are thickened with a woody substance called lignin, which helps to support the plant.
6. Water and mineral ions move into and out of the vessels through pits in the walls where there's no lignin
7. Xylem vessels are found throughout the plant but particularly around the centre of the stem.
Sclerenchyma fibres:
1. The function of sclerenchyma fibres is to provide support
2. Like xylem, they're also made up of bundles of dead cells that run vertically up the stem
3. The cells are longer than they are wide, and also have a hollow lumen and no end walls.
4. Their cell walls are also thickened with lignin. They have more cellulose than other plant cells.
5. They're found throughout the stems of plants but particularly around the outer edge.

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I can compare the structure and function of the polysaccharide starch and cellulose including the role of hydrogen
bonds in -glucose molecules in the formation of cellulose microfibrils:
Starch ­ the main energy storage material in plants:
Cells get energy from glucose. Plants store excess glucose as starch (when a plant needs more glucose for energy, it
breaks down starch to release the glucose).
Starch is a mixture of two polysaccharides of alpha-glucose ­ amylose and amylopectin:
Amylose ­ a long, unbranched chain of -glucose.…read more


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