Introduction to plant physiology; plant organ; leaves; Its anatomy, tissues and functions, plant growth Hormones; their functions. Plant Physiology BS |

Leaves:

• leaves are known as the photosynthetic factories of the plant
• role of the leaves is tp perform photosynthesis, to provide food to whole plant body.
• structure of the leaves consist of the blade that is the flat expended area of the leaf. 
• leaves consist of petiole that is the stalk which connect leave blade with the stem , and provide food water.

Anatomy of the leaf:

• anatomy of the leaves is correlated to the process of photosynthesis.
• in photosynthesis carbon dioxide combine with the the water in the presence of sun light and result in the synthesis  sugar and oxygen.

Leaf epidermis:

• the epidermis layer of the leaf is transparent so that sun light can easily pass through it. 
• waxy cuticle layer that is present on the epidermis layer prevent the leaves from being drying out by water loss
• lower epidermis of the leaf has stomata and the guard cell that perform the function of exchange of the gasses. for example water and CO2 into the leaf and oxygen out of the leaf

Leaf vascular tissue:

• vascular tissues of the leaf is veins.
• composition of veins consist of the xylem( for water transport), phloem( for food transport) and consist of bundle sheath which are the cells that are surround the xylem and phloem tissues to provide them strength and support.

Leaf mesophyll:

• it is the basically middle of the leaf.
• its composition consist of the photosynthetic ground cells.
• Palisade parenchyma: this is the long column shape cells bellow the epidermis. it has many chloroplast that are for the process of photosynthesis and called chlorenchyma.
• below it lies the spongy parenchyma  that are the spherical cells. having air spaces among the cells and around cells that allow air exchange.

Plant hormones:

• plant hormones are basically chemical compounds. that are produced by the plants.
• these compounds are effective at even low concentration.
• five major groups of plant hormones are:
• Cytokinin, Gibberellin, Abscisic acid, Ethylene and Auxin.

Auxin:

• the function of the auxin hormone is to control growth of the cell.
• auxin promotes gravitropism and phototropism. 
• auxin control the development of the fruit.

Gibberellin:

• it causes the stem to elongate.

Cytokinin:

• it increases the division of the cell 
• it causes the differentiation of the organ.

Abscisic acid:

• stomata closing is occurred by this hormone.
• function of abscisic acid is to increase seed dormancy.

Ethylene:

• ethylene involve in the gaseous exchange.
• it causes the ripening of the fruits.