How do Trees Grow
How do these large slants grow, nourish themselves and provide oxygen for us?
Trees are oversized plants that become so big that they require a woody stem to support their weight. Not only are they attractive to have in your garden, but they’re also amazing natural air filters, capable of absorbing harmful carbon dioxide and turning it into oxygen. They also clean the soil, provide habitats for wildlife, muffle noise pollution and prevent soil erosion.
Like all plants, trees harness energy from the Sun to convert carbon dioxide and water into glucose and oxygen. Sunlight is the catalyst for photosynthesis, which takes place within the plant’s cells, inside structures called chloroplasts. If you look at a leaf under a microscope it’s possible to see the tiny chloroplasts, which are green due to chlorophyll – this green pigment is vital as it traps the energy which powers photosynthesis.
One of the main differences between flowering plants and trees is the woody stem. You can tell a lot from looking at the cross-section of a tree trunk, including its age and past environmental conditions.
Growth rings – Thick rings indicate excellent growth conditions (eg plenty of water), while thin rings suggest a lack of nutrition. By counting the rings you can calculate the number of seasons (or years) a tree has lived.
Wood ray – This passageway enables nutrients and water to be distributed horizontally though the trunk from pith to phloem.
Heartwood – This darker layer, which surrounds the core of the trunk (the pith), consists of dead sapwood to support the weight of the trunk and branches.
Sapwood – Of ten paler than the rest of the trunk, the sapwood is the living wood inside a trunk. This layer containing structural xylem is capable of transporting raw sap to the leaves.
Phloem – Just below the bark is the phloem, a tissue that transports sap and glucose produced by photosynthesis up and down the tree.
Bark – This fibrous outer layer consists of hardened dead cells that protect the trunk from harmful external forces.
Cambium layer – This tissue layer contains active cells that constantly divide, enabling outward growth that increases the trunk’s diameter The new cells produced form the ring markings, which tell us more about the tree from season to season.
In order to obtain water for photosynthesis, the tree’s root hairs absorb moisture from the soil, entering tubular xylem cells through a process called osmosis. Because water is constantly evaporating from the leaves at the top of the tree (a process called transpiration), negative pressure is created in the xylem, which draws water up into the cells from below. The xylem tissues in the trunk are rigid. A tree’s internal transport system enables water, food and other nutrients to be delivered to all parts of the tree, much like arteries and capillaries in the human body.