Just like us, plants are multicellular organisms which contain differentiated cells, tissues and organs.
Tissues are vital in the functioning of a plant and provide some really crucial functions to keep the plant alive.
First of all we are going to focus on the phloem and the xylem.
Phloem tissue carries dissolved sugars such as sucrose from the leaves around the plant, whereas xylem tissue carries water and mineral ions. Within phloem there are sieve tube elements, they are a specialised type of elongated cell found on flowering plants.
These cells are unusual because they have no nucleus. The sieve tube element has lots of holes in to allow solute molecules to move through them.
Companion cells within the sieve tube element provides the energy for active transport.
The xylem is used to support a plant. It contains lignin which is a woody substance which helps support the xylem vessels and stops them from collapsing under pressure.
The cells which make up the xylem tube are dead meaning they contain no cytoplasm. Within the xylem vessel there are pits which allow ions to move in and out.
Now we know a bit more about phloem and xylem let’s move on to how water is transported in plants.
Water moves into the roots of plants by osmosis. Osmosis is the movement of water from a region of higher water potential to a region of lower water potential across a partially permeable cell membrane.
Plasmodesmata is used to connect the cytoplasm of neighbouring plant cells. They are used in the symplast pathway of water transport through the roots to the xylem vessel in the stem.
When water reaches the leaves of a plant it moves between cells through the apoplast. This involves water moving through the non-living part of the cell, the cell wall. The cell walls are absorbent, and so water molecules will stick to them and move along the walls.
The colour of a leaf does not affect transpiration. This is the evaporation and loss of water from the surface of a plant.
We know that many animals have hormones to aid certain processes, and plants are no different.
Plant hormones may be produced from any living plant cell and cause tissues to grow. Indoleacetic acid (IAA for short) is a plant hormone that causes cell elongation and can cause them to grow towards a light source – which it does in a pretty clever way.
Light causes IAA to move to the shaded side of a plant shoot causing the cells on the shaded side to elongate and grow faster. This in turn causes the shoot to bend towards the light and away from the shaded side.
IAA also decreases root growth. This enables the roots to grow towards gravity and so grow towards water and mineral ions deeper into the soil.
And that’s everything you need to know about plant tissues and how they work within plants!