Each stoma is bordered by two specialized parenchymal cells, called guard cells. These cells open and close the stoma. When the turgor pressure in the guard cells is high, they bend outward, causing the stomatal pore to open. When the turgor pressure in the guard cells is low, due to a loss of water, the stomatal pore is closed.
The cells in the mesophyll contain numerous chloroplasts , organelles that carry out photosynthesis , converting light, water, and carbon dioxide into sugar the plant can break down to generate energy.
Oxygen is the main byproduct of photosynthesis—which is great for organisms like humans who need oxygen to breathe! In monocot and dicot leaves, vascular bundles are surrounded by one or more layers of parenchyma cells known as bundle sheaths. Both types of vascular tissue have an important role to play in leaves. The xylem brings water and dissolved minerals up from the roots, and the cells in the mesophyll use the water when carrying out photosynthesis.
Excess water is expelled through transpiration , the release of water vapor through the stomata. Download Plant Lab Activities. Monocot leaves differ from dicot leaves in several ways. First, they tend to be more oblong or linear in shape, and their vascular bundles are organized into veins that originate at the base of the leaf and run parallel to one another.
In other words, they have a striate venation pattern. There is usually only one leaf per node growing off of the stem. Monocots and dicots differ in their patterns of venation. Monocots have parallel venation in which the veins run in straight lines across the length of the leaf without converging. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. Ginkgo biloba is an example of a plant with dichotomous venation.
The arrangement of leaves on a stem is known as phyllotaxy. Leaves are classified as either alternate, spiral, opposite, or whorled. Plants that have only one leaf per node have leaves that are said to be either alternate or spiral. Some species belonging to monocots can have characters belonging to dicots, since the two groups have a shared ancestry. Share this comparison:.
If you read this far, you should follow us:. Diffen LLC, n. Under dicots, it says "may bear fruit," but monocots often bear fruit as well ex. Just nitpicking, but it may cause some confusion. Monocot vs. Comparison chart Dicot versus Monocot comparison chart Dicot Monocot Embryo As the name suggests, the dicot embryo has two cotyledons. Monocotyledons have one cotyledon in the embryo. Leaf venation Leaf veins are reticulated branched.
Leaf veins are parallel. Type of leaves Dorsiventral Isobilateral Stomata in leaves Some dicots are epistomatous i. Monocots are amphistomatous i. Bulliform cells Dicot leaves do not have bulliform cells. Many monocots have bulliform cells on their leaves to regulate the loss of water.
Flowers Petals in multiples of four or five. May bear fruit if tree. Petals in multiples of three. Root Pattern Taproot system Fibrous roots Secondary growth Often present Absent Stem and vascular system Bundles of vascular tissue arranged in a ring. The netlike venation in this b linden Tilia cordata leaf distinguishes it as a dicot. The c Ginkgo biloba tree has dichotomous venation. Leaf Arrangement The arrangement of leaves on a stem is known as phyllotaxy.
Leaf Form Leaves may be simple or compound Figure. Leaves may be simple or compound. In simple leaves, the lamina is continuous. The a banana plant Musa sp. In compound leaves, the lamina is separated into leaflets. Compound leaves may be palmate or pinnate. In b palmately compound leaves, such as those of the horse chestnut Aesculus hippocastanum , the leaflets branch from the petiole.
In c pinnately compound leaves, the leaflets branch from the midrib, as on a scrub hickory Carya floridana. The d honey locust has double compound leaves, in which leaflets branch from the veins. Leaf Structure and Function The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. Visualized at x with a scanning electron microscope, several stomata are clearly visible on a the surface of this sumac Rhus glabra leaf.
At 5,x magnification, the guard cells of b a single stoma from lyre-leaved sand cress Arabidopsis lyrata have the appearance of lips that surround the opening. In this c light micrograph cross-section of an A. Wise; part c scale-bar data from Matt Russell. Trichomes give leaves a fuzzy appearance as in this a sundew Drosera sp. Leaf trichomes include b branched trichomes on the leaf of Arabidopsis lyrata and c multibranched trichomes on a mature Quercus marilandica leaf.
Wise; scale-bar data from Matt Russell. In the a leaf drawing, the central mesophyll is sandwiched between an upper and lower epidermis.
The mesophyll has two layers: an upper palisade layer comprised of tightly packed, columnar cells, and a lower spongy layer, comprised of loosely packed, irregularly shaped cells.
Stomata on the leaf underside allow gas exchange. A waxy cuticle covers all aerial surfaces of land plants to minimize water loss. These leaf layers are clearly visible in the b scanning electron micrograph.
The numerous small bumps in the palisade parenchyma cells are chloroplasts. Chloroplasts are also present in the spongy parenchyma, but are not as obvious. The bumps protruding from the lower surface of the leave are glandular trichomes, which differ in structure from the stalked trichomes in Figure.
This scanning electron micrograph shows xylem and phloem in the leaf vascular bundle from the lyre-leaved sand cress Arabidopsis lyrata.
Link to Learning. Evolution Connection. One of the most well known bromeliads is Spanish moss Tillandsia usneoides , seen here in an oak tree. The a Venus flytrap has modified leaves that can capture insects.
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