Plant cell organisation

Plant cells have similar cells to form tissues, different types of tissues to make organs and then multiple organs to make organ system
The leaf is an organ
Leaves, stems and roots are transport substances
leaves are the site of photosynthesis, they require a lot of carbon dioxide and water in order to make sugars
The water comes from the soil and goes through the roots and transported to the leaf by the xylem
Carbon dioxide diffuses directly into the leaf from the outside through little holes called stomata. Each leaves have thousands of stomata. They are scattered through the lower epidermis
Once the carbon dioxide diffuses, it moves up the leaf and enters the spongy mesophyll which has lots of air gaps. This is so the gas can easily diffuse through the next layer (palisade mesophyll)
The palisade mesophyll is where most photosynthesis happens, they are packed with chloroplasts
The layer above is the upper epidermis, which is almost transparent, this is because they allow sunlight through

Once photosynthesis has produced a sugar molecule, they are carried to the rest of the plant by a green tube called the phloem
The main problem leaves face is water loss.The xylem continously brings water from the roots for the palisade cells to use in photosynthesis but that water can be lost from the top and bottom of the leaf
The waxy cuticle is a thin waterproof layer of lipids, which is used to prevent water loss at the top
At the bottom of the leaf, the main issue is the stomata. The water will diffuse out of any gaps really easy. However, the gaps are needed for carbon dioxide.
To prevent this, the stomata opens for as short as possibl, this is so they can maximise carbon dioxide concentration and minimise water loss
Each stoma (singular stomata) is formed from the gap between two guard cells

When a leaf has lots of water, so they don’t need to conserve water, the guard cells would be well hydrated. This is called turgid. This makes them have a larger gap and so more carbon dioxide can go through

When the plant is short of water, the guard cells lose water due to osmosis and will become flaccid. This closes the stomata, thereofre the plant doesn’t take in carbon dioxide. despite this, it will conserve water vapour

Another adaption is that guard cells are sensitive to light, they close at night. Most of the stomata are on the underside of the leaf because it is more shaded and cooler, meaning less water will evaporate

The meristem tissue are found at the growing tips of the roots and shoots They can also diffeerentiate into different cells. This is so the plant can grow