Plants Flashcards
What are the 3 principles all plants use to build tall structures?
they produce strong cell walls out of cellulose (polymer made from sugar molecules), build columns and tubes from specialised cells, stiffen some of these special cells with another polymer called lignin
what is cellulose?
a polysaccharide, made up of beta glucose, a condensation reaction between the -OH groups on the 1st and 4th carbons (which are adjacent), tends to contain 1000 to 10000 glucose units
What is a microfibril?
hydrogen bonds form between the the -OH groups in neighbouring cellulose chains, forming bundles. Individually the H bonds are weak compared to glycosidic bonds, but due to their numbers they are able to form a strong structure. They are held together by a “glue” that is composed of polysaccharides called hemicellulose and pectins
Why is cellulose used by plants?
cellulose has a slow decomposition rate, is the most abundant organic molecule on Earth, and is mechanically strong
What do plants use for transport?
xylem vessels transports water and minerals and their stiffened walls help support the plant, sclerenchyma fibres form columns of stiffened cells to provide support, and phloem sieve tube cells are long tubes that transport organic solutes such as sugars & amino acids but provide no structural support
How does xylem become specialised for its job?
the xylem starts as cells with thick walls, which become waterproof with lignin that impregnates cellulose, breaking down tonoplast. Autolysis (self-digestion) of the cell contents by enzymes occurs, leaving the cell dead, hollow, and with pits to allow movement between tubes
how does the xylem’s structure relate to its function?
Contain lignin, which waterproofs the cell, preventing water loss lower down the plant lignin also strengthens the xylem, preventing them collapsing when under low pressure (in the leaves) or under high pressure (in the roots)
Pits in the lignin allow water to move between vessels and out to surrounding tissue
Hollow tubes made from dead cells allow continuous water flow
The end walls of each cell are lost or highly perforated to allow continuous water flow
how does water move through plants?
Water evaporates through the stomata, diffusing down the water concentration gradient (transpiration)
Water is drawn out of the xylem in the leaves to replace the lost water, reducing the hydrostatic pressure in the xylem
The pressure in the roots is higher, because water has entered the root cells by osmosis (due to high mineral content), so water travels up to the leaves to even out the pressure
Water is drawn up because the water molecules hydrogen bond to the cellulose in the cell walls (adhesion)
Water travels in a continuous column up and out of the xylem because each water molecule is hydrogen bonded to other water molecules (cohesion) and therefore pulls other water molecules along
How is the Phloem formed?
the nucleus and other organelles breakdown, leaving the cell mostly empty so that organic molecules can flow through (translocation)
What do companion cells do?
they perform the metabolic functions of the sieve cells
what do transport cells do?
they help to actively transport/load sugars, amino acids and other organic substances into the sieve tubes
What is parenchyma?
parenchyma is a type of plant tissue found throughout the plant. these cells fill spaces between more specialised tissues. they are sometimes used in different places, such as the roots where they may have a storage role, and in leaves they may contain chloroplasts
What does the xylem and sclerenchyma have in common?
they are both lignified
What are plant fibres used for?
they are used in clothes, rope, and some parts of houses
