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Transport in plants: 1. Types of plant cells and their organisation into tissues and organs

Doc Brown's Biology exam study revision notes

There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index of biology notes on transport systems in plants

(1) Types of plant cells and their organisation into tissues and organs

Plant cells are organised into tissues and these form plant organs such as leaves, roots and stems.

These organs must function together in such way to work as an organ system - to ensure the plant gets all its needs to survive and grow into a mature plant.

Transportation of e.g. nutrients or waste products is one of the most important function of a plant organ system.

Plant organs are made of tissues

(A summary of those you must know are briefly described below and in more detail later where necessary)

Epidermal tissue

Epidermal tissue covers the whole surface of the plant - its the equivalent of our 'skin'!

Meristem tissue

Meristem cells are found in the growing tips of shoots and roots.

They can differentiate into all the different types of plant cell needed for growth and reproduction.

Palisade mesophyll tissue

Most photosynthesis occurs in the palisade mesophyll tissue, part of the leaves.

Spongy mesophyll tissue

Spongy mesophyll tissue forms part of the leaf and contains lots of air spaces to let gases diffuse in and out of the leaf structure.

Xylem and phloem

Xylem and phloem are tubular cell networks that allow the transportation of mineral ions, food e.g. sugars and water around the plant - the leaves, roots and stems must be all connected together.

Both xylem and phloem tissue networks are held together in vascular bundles which give strength and protection to plant tissues.

Waxy cuticle

The cuticle is a water repellent protective layer covering the epidermal cells of leaves and other parts and limits water loss.

and this is how some of the above fit together in the structure of a leaf ...

More on the tissue structures of a leaf and their functions - adaptations of leaves

These descriptions apply to dicotyledonous plants.

So, starting from the top layers, and all marked on the above diagram ...

The epidermal tissue on the upper side of the leaf are covered with a waxy cuticle layer which is water repellent - this helps water loss by evaporation.

The upper epidermal layer is transparent to visible light, so light can penetrate to the palisade cell layer where it is needed for photosynthesis.

The palisade mesophyll layer is made of the palisade cells which are packed with lots of chloroplasts - the sites of photosynthesis - note that the palisade cells are near the upper surface to receive the most light.

The xylem and phloem are networks of vascular sheathed bundles of cells that are the backbone veins of the plant's transport system .

The details of how all these function is described in detail in Part 2.

The leaf tissues are adapted for efficient gas exchange.

The broad flat green leaves of plants exposed to light, provide a large surface area for the light absorbing sites of photosynthesis - more than the thinner stem.

The leaves are thin so the absorbed carbon dioxide has only a short distance to diffuse to the photosynthesising cells.

Leaves have veins (vascular bundles of xylem and phloem cells) that support the leaf and transport water and minerals to the leaves and glucose away from the leaves.

The lower epidermal tissue is full of tiny holes (stomata, pores) which allow carbon dioxide to diffuse into the leaf for photosynthesis.

Reminder:  carbon dioxide + water == light/chlorophyll  ==> glucose + oxygen

The opening and closing of stomata is controlled by guard cells which respond to changes in environmental (ambient) conditions including the movement of water in and out of leaves.

The spongy mesophyll tissues contain air spaces which increase the rate of diffusion gases in (carbon dioxide) and out (oxygen).

Keywords, phrases and learning objectives for this part on transport systems in plants

Be able to describe the types of plant cells and their organisation into tissues and organs in the context of transferring materials out, in and around a plant.

Know the function of epidermal tissue, meristem tissue, palisade cells, spongy mesophyll tissue, xylem and phloem tubular cell systems, the waxy cuticle, veins and vascular bundles.



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