SIG 3
What is the importance of the plant biomassfor the carbon storage in the atmosphere? What are the second largest contributor?
Plants solely store about 450 Gt of carbon in the atmosphere and is the primary storage contributor in the world. The second largest contributors is bacteria ans it stores about 70 Gt of carbon in the atmosphere.
Describe the general cell wall structure and arrangement of the main components, what are the main components?
The general cell wall consists of cellulose, hemicellulose and pectin. The cellulose places as parallel planes with space in between. This space is filled with hemicellulose and pectin, the hemicellulose connects the cellulose planes and the pectin works as a glue just sitting there chilling.
What are the six functions of the cell wall?
Cell wall protects the protoplast against bursting.
Cell wall protects protoplast against, dehydration, UV radiation and fungal penetration.
Cell walls determines cell size and cell structure.
Cell walls provide means for cell adhesion.
Cell walls provide means of regulated apoplastic transportation of water and ions.
Cell walls may provide safe storage for toxic ions.
Summary: protection, shape, adhesion, transportation of water and ions, storage of toxic ions and signaling.
Where can you find primary and secondary cell walls?
All cells have a primary cell wall, some of them have a secondary cell wall. Secondary cell walls develop inside the primary cell wall, in the xylem and sclerenchyma. The primary wall contains mainly pectin and cellulose, the secondary wall contains mainly cellulose and xanax. The walls can be lignified so that the primary walls have around 70% of lignin and the secondary walls have around 30% lignin.
There are two different cell walls. In what plants can you find them?
There are type 1 that exists mostly in dicots, many monocots and some vascular plants. And there are type 2 that exists in commelinids (grasses, palms and bananas etc.)
Describe the cellulose structure.
First we have the glucan chain that consists of beta 1-4-D-glucopyranose with one non-reducing end and one reducing end and it depends whether the 4th coal is located at the end or if the 1st coal is located at the end. These glucan chains forms sheets. These sheets forms microfibrils, either parallel (cellulose 1) or anti-parallel (cellulose 2) and they are probably twisted. These micro fibrils forms macro fibrils which may look like a coordinate system where the quadrants consists of cellulose microfibrils bundles surrounded by xylan and mannan. The axels are lignin chains.
What is the function of the rosette structures?
To order the structure of cellulose and produces glucose chains, which later bonds together to form microfibrils.
Where are cellulose, pectins and hemicellulose synthesised?
In plants, cellulose is synthesised in plasma membrane by CesA complexes called rosettes. Pectins and hemicellulose is synthesised in Golgi and secreted to wall by exocytosis.
What are the structure, occurrence and function of the hemicellulose xyloglucan?
The hemicellulose xyloglucan is built up by a glucose chain and outsticking pentoses. The functions are polymers of neutral sugars, H-bonding cellulose microfibrils, cross-linkning, provide strength, extractable by alkali and storage walls and signaling.
Describe structure, occurrence and function of pectins homogalacturonan.
The homogalacturonan is galacturonic acid chains with methyl esters sticking out here and there. The functions are polymers of acidic sugars, only limited bonding, cross-linking and regulating porosity, acidity and water content, regulating cellular adhesion, provide strength, regulate properties, extractable with EDTA and signalling.
Mention two lignin “blocks” and where they are made. What are the consequences of lignification for the cell wall?
The consequences are hydrophobic cells, water impermeable, reduced gas exchange, lignified cells are dead at maturity, protective function against stresses, mechanical strengthening, lignin has high energy content it is a big investment for the plants. There are one block called monolignols which are synthesised in the cell wall.
Mention a peculiar trait of lignification of the plant cell wall.
It occurs from the outermost part of the cell wall, and inwards over the secondary cell wall, it only occurs if there happens to be a secondary cell wall. Interestingly enough it can occur after the plant is dead, such as cucumber in the fridge.