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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. Its

made mainly of the carbohydrate cellulose

Supports plant cells.

Middle lamella The outermost layer of the cell. This layer acts as an adhesive, stickingadjacent 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. Theyre 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. Its 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 arelinked 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. Theyre 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. Theyre 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 noend walls.

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 theres no lignin7. 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 support2. Like xylem, theyre also made up of bundles of dead cells that run vertically up the stem3. 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. Theyre 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. The angles of the glycosidic bonds give it a coiled

structure, almost like a cylinder. This makes it compact, so its really good for storage because you can fit

more in to a small space.Amylopectin a long, branched chain of -glucose. Its side branches allow the enzymes that break down the

molecule to get at the glycosidic bonds easily. This means that glucose can be released quickly.

Starch is insoluble in water, so it doesnt cause water to enter the cells by osmosis and therefore doesnt make the

cells swell. This also makes it good for storage.

Cellulose the major component of cell walls in plants:

Cellulose is made of long, unbranched chains of beta-glucose, joined by glycosidic bonds.

The glycosidic bonds are straight, so the cellulose chains are straight.

Between 50 and 80 cellulose chains are linked together by a larger number of hydrogen bonds to form strong

threads called microfibrils. The strong threads mean cellulose provides structural support for cells (e.g. they

strengthen the plant cell walls)

I can explain the importance of water and inorganic ions (nitrate, calcium ions and magnesium ions) to plants:1. Water - is needed for photosynthesis, to maintain structural rigidity, transportation of minerals and regulate

temperature

2. Magnesium ions needed for the production of chlorophyll the pigment needed for photosynthesis3. Nitrate ions are needed for the production of DNA, proteins (including enzymes) and chlorophyll. Theyre

required for plant growth, fruit production and seed production.

4. Calcium ions are important components in plant cell walls. Theyre required for plant growth.Investigating plant mineral deficiencies:

1. Take 30 seedlings of the same plant (same age, height) and plant them in separate pots2. Make up 3 nutrient broths containing all the essential minerals, but vary the concentration of calcium ions.

Make up one broth with a high concentration, one with a medium concentration and one with a low

concentration3. Split the plants into three groups. Each should be given only one of the three broths4. Record the heights of the plants after seven weeks. Calculating average height of each group of plants5. Keep all other variables the same

Results:

1. The greater the concentration of calcium, the more the plants grew, average heights of 12, 18 and 23cmwere reached for plants given low, medium and high concentrations respectively.

2. This shows that when calcium is deficient, plant growth is inhibited.