What do plants look like inside? Part 1, leaves.

David Beeson

August 2020.

A section through the mid-rib of an Acer plant.

A section through the mid-rib of an Acer plant.

The mid-rib is the central support of a leaf and has both structural support and the transport (vascular) tissues.

The cells are visible as they have firm cellulose walls which hold their shape (provided they are water-filled).

You will notice the cells vary in design with smaller cells on the surface (epidermal cells) and some larger ones inside.

The central core of the mid-rib contains the main veins, with xylem (water transport) and phloem (organic transport – sugars, amino acids and hormones).

Those cells that appear to have thicker walls are some of the support tissues, holding the leaf in a position to enable effective light capture.

On either side are the flat parts of the leaf – the leaf lamina.

Part of a leaf lamina. This shows a small leaf vein and the lower epidermis.

The big red-coloured (they are stained and not naturally this colour) cells are xylem. They have their cellulose cell walls filled with water-proofing lignin. Beneath the two large xylems is a patch of green-coloured cells (also stained). These small cells, with cellulose walls, are the phloem.

Green-stained cells containing red dots are the main photosynthetic cells – chlorenchyma. The red dots are chloroplasts, the organelles that carry out the light capture and production of glucose.

You know the formula!

6CO2 + 6H2O + light energy = C6H12O6 + 6O2 + some waste heat.

Carbon dioxide combines with water, if suitably activated by energy, to form carbohydrates with the release of oxygen.

Here you can see from the upper epidermis down to the lower epidermis. Between are the chlorenchyma cells – long thin ones at the surface and more irregular one below. The irregular shaped ones allowing gases to move (diffuse) between them.

Upper epidermal cells usually have thicker walls and a surface layer of wax (lipid or fats) to reduce water loss.

Epidermal cells contain the leaf’s toxins.

A single stoma (plural, stomata) with a hole in the middle of variable width and two guard cells containing chloroplasts. These mainly occur on the lower surface and allow gas exchange into and out of the lamina. They can open and close to control flow.

Above, vertical section through a leaf with stomata visible with their guard cells.

The red structure is a leaf hair. These are mostly used for protection against water loss in that they reduce the diffusion of water vapour to the environment. They are especially common on the leaves of plants living in dry locations.

A section through a heather leaf. This is living in dry conditions, so has thicker epidermal cells with (look carefully) a thick waxy surface. Small leaves are an adaptation to reduce water loss.

A section through a growing shoot. You should notice the young leaves developing and dense areas of rapid cell division. The small dots are nuclei.

Chromosomes! Can you see the darkly staining nuclei in the cells and some are dividing, showing the chromosomes.

Hope you liked that! Feed back appreciated!!!!!

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