Biology, 4c.

• Stem is for support, and transport. (Water travels up the stem).
• Leaf is for photosynthesis.
• Flower is for reproduction. 
• Roots are for water and mineral uptake, and anchorage.

Phloem Tubes.

They are used for translocation, which is the movement of food substances, such as sugars, made in the leaves,  up and down the stem, to growing and storage tissues. The columns are made of living cells. They have, perforated, end plates, to allow stuff to flow through.

Xylem Tubes.

They are used for transpiration. This means they move water, and minerals, from the roots, to the shoots, to the leaves. They are made of dead cells. They have a hollow lumen, (hole), they also have a thick cellulose cell wall, for support. 

Both tubes form a continuous system, in leaves, roots, and stems. 

Vascular bundles are groups of cells, that together make the, transport system of a plant. 

Root cross section. 

Roots have to prevent being crushed, as they push through the soil. The Xylem is in the centre to give it strength. 

Stem cross section.

Stems need to resist bending. The xylem forms a sort of scaffolding, the phloem is always around the outside of the stem. 

Leaf cross section. 

Xylem and phloem form a network of veins, to support the leaves. 

A dicotyledron is the majority of plant species. It has 2 seed leaves in its embryo. 

Transpiration rate is increased by:

Increase in light intesity. Stomata close when it gets darker. Photosynthesis can't happen in the dark, so they don't need to be open to let CO2 out. 

Increase in temperature. Particles have more energy to evaporate and diffuse out.

Increase in air movement. If air movement is high, water vapour surounding the plant is swept away. The concentration of water vapour is low on the outside, therefore diffusion happens quickly.

Decrease in humidity. If the air around the leaf is dry, diffusion happens more quickly.