Topic 4 - Lesson 7

Question 1

Xylem

Answer 1

• transport water and mineral ions from the roots to the rest of the plant.
• made up of dead, hollow cells with no end cell walls, forms one continuous tube when. The cells have no organelles or cytoplasm
• The cell walls contain pits which allow water and mineral ions to move into and out of the vessel. The cell wall also contains lignin, which strengthens the xylem vessel and provides structure and support to the plant.

Question 2

Phloem Vessels

Answer 2

• transport dissolved substances, such as sucrose and amino acids from (sources) to (sinks).
• sieve tube elements are living cells and are joined end-to-end to form sieve tubes. The ends of each cell consist of a ‘sieve plate’ which contains lots of holes to allow solutes to move. contain no organelles and very little cytoplasm to create more space
• companion cell, which contains a nucleus and is packed full of mitochondria. provide energy for the active loading of sucrose

Question 3

Sclerenchyma

Answer 3

sclerenchyma fibres are also found within vascular bundles and provide structural support to the plant. They are made up of bundles of long, dead cells. The cells have a hollow lumen and the cell walls are thickened with lignin.

Question 4

Plant Fibres

Answer 4

Plant fibres, such as cotton and hemp, are made up of long tubes of plant cells. Plant fibres are strong which makes them useful for materials such as rope or sacks. Their strength is due to two factors:

The arrangement of cellulose microfibrils in the cell wall

The secondary thickening of cell walls with lignin

Question 5

CPAC - Dissecting Plant Stems

Answer 5

Cut a thin section of the plant stem using a scalpel. Take care when using the sample and remember to cut away from you.

Place the tissue sample into water to prevent it from drying out.

Place the tissue sample into a small dish containing the stain. A common stain that is used to view vascular bundles is toluidine blue O (TBO) which stains lignin blue/green which will enable you to visualise the xylem and sclerenchyma fibres. The phloem cells and remaining tissue will appear a pink/purple colour.

Rinse the tissue samples in water and place each one onto a microscope slide.