Transport in Plants

The two tissues involved are xylem and phloem.

Xylem takes minerals and water up the plant from the roots to the leaves.

Phloem moves organic substances such as sugar both up and down the plant.

Xylem vessles are long, tube like structures made from dead cells which are joined end to end, the xylem vessel is the part of the tissue which actually transports the water and minerals.

Phleom tissues transports solutes (disolved substances) around plants.

Phloem has a tube like structure that is made of sieve tubes and companion cells.

Sieve tube elements are living cells that form the tube for transporting solutes, they have no nucleus and few organelles.

Companion cells are in each sieve tube element, they carry out living functions for the sieve tubes. For example producing energy for the active transport of solutes.

Translocation is the movement of solutes to where they are needed.

It happens in the phloem and it requires energy.

Translocation moves solutes from the source to the sink. The source is where the solute is made and the sink is where the solute is used up.

Enzymes maintain the concenration gradient from the source to the sink by chaning the solutes at the sink.

The concentration gradient is always lower at the sink than the source.

Water evapourates from the moist cell walls and accumulates in the spaces between cells in the leaf.

When the stomata opens, water moves out of the leaf and down the concentration gradient.

Transpiration is a side affect of photosynthesis as the stroma has to open to let carbon dioxide in and whilst opening it lets some water out.

Light - the stomata opens when it is light to let carbon dioxide in, when its dark the stamata closes so their is little transpiration.

Temperature - warm water molecules have more enrgy to evapourate quickly. This increase the concentration gradient between inside and outside the leaf making the water diffuse quickly.

Humidity - Lower humidity the faster the transpiration. The concentration gradient also increases.

Wind - the windier it is the faster the rate of transpiration happens, it also increases the concentration gradient.

Water moves up the plant, against the force of gravity, cohesion and tension allow this to happen.

The water evapourates from the top of the xylem, this creates tension which pulls the water into the leaf.

Water molecules are cohesive so when some are pulled onto the leaf, others follow.

As water enters the plant through the roots it means the water in the coloumn of xylem is moving upwards.