Plant Anotology

Internal Structure Of A Plant

PLANT CELL STRUCTURE

Plant cells are classed as eukaryotes organisms, because they have a membrane enclosed nuclei and organelles.

Here is a diagram of a plant cell;

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Cytoplasm

Most chemical reactions take place here. It helps the cell maintain it’s shape.

Nucleus

The nucleus has two main roles. Firstly it contains all the cells genetic information. Secondly it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).

Chloroplasts

Contain a green pigment known as chlorophyll which absorbs light energy (needed in the plants food making process of photosynthesis.) It does this by converting the water and carbon dioxide, found in the cell, into sugars and carbohydrates. Therefore the chloroplasts covert light energy into chemical energy.

Permanent vacuole

Large liquid filled (cell sap) storage containers help to support the cell. The vacuole can store anything from waste, to nutrients, even water. These can be quite big, allowing a cell to grow without having to produce new cytoplasm.

Cell wall

Made from a compound of cellulose, the cell wall protects the cell and strengthens the cell.

Cell membrane

Controls the chemical movement in and out of the cell. It is crucial to the cells survival as an internal balance of chemicals needs to be maintained. As the membrane is semi-permeable this allows some substances to pass through freely, but others cannot. Here the process of diffusion takes place.

Diffusion

Substances dissolved in water move naturally from areas where there are large amounts to scarce areas. An example could be that of carbon dioxide (co2.) Carbon dioxide will distribute itself from inside the cell through the membrane to water outside the cell until a balanced level is reached.

PLANT TISSUES

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(Britannia,2008)

Parenchyma cells

Parenchyma tissue is composed of cells (parenchyma cells) that are thin-walled, more or less isodiametric, and alive at maturity. Parenchyma cells function in the manufacture of food for the plant (most of the chloroplast-containing cells of the leaf are parenchyma cells) and in the storage of materials within the plant body.

Collenchyma cells

Collenchyma tissue is composed of cells that are slightly more specialized than those of parenchyma tissue. Collenchyma cells tend to be elongate and have unevenly thickened walls and function in providing support for the plant body. Like parenchyma cells, the cells of collenchyma are alive at maturity.

Sclerenchyma cells

Sclerenchyma tissue is composed of cells (sclerenchyma cells) that have extremely hard, thick walls. In fact, the cell walls of sclerenchyma cells are so thick that, at maturity, the cell is completely cut off from the extracellular environment and dies. Two general types of sclerenchyma cells are recognized: sclereids, which may be more or less isodiametric or may be branched, and fibers, which are greatly elongate cells.

The gritty texture of pears is caused by groups of sclereids (often called "stone cells") that are embedded in the parenchyma tissue of the fruit's flesh. The appearance of typical stone cells from a pear is illustrated below:

THE STEM

Here is a simple cross section diagram of a stem;

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(GHS,2008)

Xylem and Phloem

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The xylem and phloem vessels of a plant play a major role in carrying food and water to different areas. The xylem has the function of transporting water and soluble mineral salts up the stem from the roots to the leaves through the process of osmosis. The phloem takes the sugary food solution (produced in the leaves) known as sap down to the rest of the plant, thus providing nutrients to storage organs and growing regions.

Osmosis

Osmosis is the diffusion of water from a high concentration to a low concentration area, through a partially permeable membrane. Note that high concentrations of water molecules are found in hypotonic solutions, where there are few dissolved substances. They then diffuse into solutions where water molecules are few but there are many dissolved substances, called solutes.

So as water is lost through transpiration in leaves, it is replaced by water that is taken in at the roots.

THE LEAF

Here is a cross section of a leaf;

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(Science of biology,2008)

Epidermis

Every leaf has a single layer of cells that form the epidermis. The underside of a leaf is also completed by a lower epidermis. On top of the epidermis is a waxy coat, known as a cuticle. This protects the leaves in hot, dry, windy conditions by preventing too much water from evaporating from the leaf.

Palisade mesophyll cell

Beneath the epidermis the palisade cell contains several layers of parenchyma