Plant structures

Activity In your group list the different structures of a plant

Learning outcomes Describe plant structure: leaves, stem and roots Collect and inspect a range of leaves Analyse and compare a cross section of a leaf Using the microscope examine the areas in the root

Activity In your group explain what is the function of the leaf

Leaf Contains the cells in which photosynthesis takes place, which is the process that produces food for the plant. Release excess water from the plant by the process of transpiration Allow carbon dioxide and oxygen to enter the leave of the plant. These gases are used in the process of photosynthesis and respiration.

External parts

External features Petiole Provides some flexibility in positioning the leaf to gain the maximum light Midrib The main vascular bundle of the leaf that runs along the centre leaf Veins The web of vascular tissue that spreads from the mid rib to all parts of the leaf Tip The distant point of the leaf

Blade Flattened part of the leaf Margin The leaf margin is another tool in plant identification. Stipules Leaf-like appendages at the base of the leaf.

Internal parts

Upper epidermis This is a single layer of cells that covers the surface of the leaf. It provides some protection to the leaf and helps to prevent loss of water from the plant. The protection is increased by a thin waxy layer over the surface of the cells called the cuticle. Palisade mesophyll cell These cells are directly below the epidermis and are specially adapted for the process of photosynthesis by having many chloroplasts in them

Bundle sheath cell Xylem The xylem performs a similar function to the phloem except that it transports water and nutrients absorbed by the roots to all other parts of the plant Phloem The phloem is the part of the plant that transports food from where it is manufactured in the leaves to all other parts of the plant Lower epidermis A thin waxy layer that Protects and helps reduce moisture in the leaf

Cont….. Spongy mesophyll cells These are loosely packed cells which allow gases (carbon Dioxide, oxygen and water vapour) to pass freely between them. Stomata In the epidermis there are pores called stomata. There can be many thousands of stomata within one square centimetre of leaf Guard cells These are the cells either side of the stomata that open and close during photosynthesis. They close at night since no carbon dioxide is needed as no photosynthesis can take place at night

Cuticle Thin waxy layer over the surface of the cells for protection Vein The web of vascular tissue that spreads from the midrib to all parts of the leaf

Activity Using the microscope examine the slides to identify the internal parts of the leaf From the selection of leaves compare and examine the external parts of the leaf

Activity In your group explain what is the function of the stem. Look at the two examples and compare and be able to distinguish between woody and non-woody stems

stem The stem provides the above ground support of the plant to which the leaves and flowers are attached Provide the means of transporting water, nutrients and food around the plant. Stems come in all shapes and sizes. Trunks, branches and shoots are all forms of stem. Newly formed stems are usually green On woody plants the stems usually turn brown as the plant ages

Activity Using the stems and cross sections of timber, identify the named parts of the stem.

Activity In your group discuss What is the function of the root in a plant

root The root holds the plant firmly in the soil, and enable it to take up water and nutrients from the soil. Many roots have a branched structure with a main (or tap) root, with lateral roots branching from it. There are two basic types of roots

There are two basic types of roots TAP ROOT Fibrous root

Tap roots These are comprised of a main root with smaller roots branching from it. Tap roots can extend to a considerable depth, and draw up water from deep in the ground. Most trees and shrubs have tap roots

Tap root

Fibrous roots With a fibrous root there is no main root. All of the roots are multi-branched and originate at the base of the stem. The roots occupy a large area of shallow soil around the base of the plant and are effective in preventing soil erosion. They rely on water draining from the surface of the soil and are therefore the first plants to suffer in periods of drought.

Fibrous root

Roots have four regions: a root cap, a zone of division, a zone of elongation, and a zone of maturation The Root Cap: Is a cup-shaped group of cells at the tip of the root which protects the delicate cells behind the cap, as it pushes through the soil. The root cap gets rid of “mucigel”, a substance that acts as a lubricant to aid in its movement. The root cap also plays a role in a plant's response to gravity. e.g. If a flower pot is placed on its side, the stem would grow upward towards the light, and the root cap would direct the roots to grow downward. The zone of division: Is above the root cap, and above that is the zone of elongation. The zone of division contains growing and dividing cells. As a result, of the combination of both cells, the root tip is literally pushed through the soil.

Cont…….. The zone of Elongation: In this part of the root the newly created cells expand, to push the meristem and root cap through the soil. This involves reshaping the wall, growth of the cell within, and maturation of the organelles in these cells. The zone of maturation: Is just above the zone of elongation in the root tip. It is here that the cells of the root form the various tissues that will make up the mature root. The xylem, phloem, cortex, etc. are the tissues developed here. 

Activity Examine and organise the roots in to perennial, woody perennial and annual. Using the microscope and slides provided identify the named areas of the root

Summary of the lesson http://www.youtube.com/watch?v=pHNc-8GaURU&feature=player_embedded

Group activity Now change groups to question another group member on any part of todays subject. Please remember to be constructive when giving your feed back.