4.4 Making use of Biodiversity Flashcards
What are the three basic principles of plants to build tall structures?
1) They produce strong cell walls out of cellulose
2) They build columns and tubes from specialised cells
3) They stiffen some of these special cells with another polymer called lignin
What is cellulose?
A polysaccharide which is an important component of plant cell walls. A molecule of cellulose consists of a long straight chain of beta-glucose molecules joined by
glycosidic bonds, formed in condensation reactions. Hydrogen bonds form between neighbouring chains. These bonds hold the cellulose molecules together in bundles called microfibrils. In cellulose, the glycosidic bonds are 1,4, so it is a long unbranched molecule.
Where is starch found in plant cells?
Storage vacuoles in the cytoplasm called amyloplasts.
What is parenchyma?
A type of plant tissue found throughout the plant. Cells fill spaces between more specialised tissues and may have specialised functions themselves. Forms the cortex of stems. Can differentiate into chlorenchyma (for photosynthesis).
Thin cell walls. Provides support through turgidity.
What are microfibrils?
60-70 cellulose molecules are arranged in bundles called microfibrils. The arrangement of the microfibrils makes the wall of the cell very strong and helps it to resist the forces acting on it.
Hydrogen bonds form between -OH groups in neighbouring cellulose chains.
What are plasmodesmata?
Narrow, fluid-filled channels that cross the cell walls, making the cytoplasm of one cell continuous with the cytoplasm of the next. Often located in ‘pits’ in the cell walls, aiding the movement of substances between cells.
How are microfibrils arranged and how do they stick together?
They are in a helical arrangement around the cell and they are stuck together with a polysaccharide glue, which is composed of short, branched polysaccharides known as hemicelluloses and pectins. These polysaccharides bind to the surface of the cellulose and to each other.
What is a vascular bundle?
Contains xylem vessels and phloem vessels (vascular tissue). On the outside of the bundle are sclerenchyma fibres.
What are xylem vessels?
Vessels that form tubes for transport of water and minerals up the plant, forming a mass flow system. Their stiffened cell walls (with lignin) help to support the plant.
The cells are dead.
What are sclerenchyma fibres?
Long, thin plant cells which are tapered at both ends. Sclerenchyma fibres help to provide plants with support. They have cell walls which are thickened with lignin.
They do not have living contents.
What are phloem vessels?
Vessels that form long tubes for transport of organic solutes (including the photosynthesis products - sugar and amino acids) up and down the plant, forming a mass flow system. The tubes are divided by sieve plates.
The cells are alive and respire to release energy for active transport. They have cellulose cell walls.
What are sieve tubes/plates?
Thin plates which separate neighbouring phloem cells.
What is lignin?
A polymer found in the cell walls of plants which helps to stiffen the cell walls.
What happens when lignin impregnates the cellulose cell wall?
Cells become lignified, and the entry of water and solutes into them is restricted.
What is the tonoplast?
A membrane that surrounds a vacuole.
