biodiversity

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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 made mainly of the carbohydrate cellulose

Supports plant cells.

MIDDLE LAMELLA

The outermost layer of the cell.

This layer acts as an adhesive, sticking adjacent plant cells together. It gives the plant stability

PLASMODESMATA

Channels in the cell walls that link adjacent cells together

Allow transport of substances and communication between cells.

PITS

Regions of the cell wall where the wall is very thin. They're arranged in pairs - the pit in one cell is lined up with the pit in the adjacent cell

Allow transport of substances between cells.

CHLOROPLAST

A small, flattened structure. It's surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.

The site where photosynthesis takes place. Some parts of photosynthesis happen in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts)

AMYLOPLAST

A small organelle enclosed by a membrane. They contin starch granules.

Storage of starch grains. They also convert starch back to glucose for release when the plant recquires it.

VACUOLE AND TONOPLAST

The vacuole is a compartment surrounded by a membrane called the tonoplast.

The vacuole contains the cell which is made up 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:

The function of xylem vessels is to transport water and mineral ions up the plant, and provide support.

They're very long, tube-like structures formed from dead cells, joined end to end. The tubes are found together in bundles.

The cells are longer than they are wide; they have hollow lumen (they contain no cytoplasm) and have no end walls.

This makes an uninterrupted tube, allowing water and mineral ions to pass up through the middle easily.

Their walls are thickened with a woody substance called lignin, which helps to support the plant.

Water and mineral ions move into and out of the vessels through pits in the walls where there's no lignin

Xylem vessels are found throughout the plant but particularly around the centre of the stem.

Sclerenchyma fibres:

The function of sclerenchyma fibres is to provide support

Like xylem, they're also made up of bundles of dead cells that run vertically up the stem

The cells are longer than they are wide, and also have a hollow lumen and no end walls.

Their cell walls are also thickened with lignin. They have more cellulose than other plant cells.

They're found throughout the stems of plants but particularly around the outer edge.

I can compare the structure and function of the polysaccharide starch and cellulose including the role of hydrogen bonds in β-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 α-glucose. The angles of the glycosidic bonds...
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