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16 Cards in this Set
- Front
- Back
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Dicotyledonous root- main functions |
•absorbs water and mineral salts from the soil •firmly anchors the plants in the soil •stores foods,mainly carbohydrates |
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External structure of a root |
The root is made up of five regions •root cap- surrounds and protects the growing point •meristematic region: continuously forms new cells •region if elongation: in this region new cells elongate •root hair region: characterised by unicellular ,epidermal outgrowths (the root hairs) that increase the absorption surface of the root. •mature region :where lateral roots develop and branch off, increasing the absorption surface and anchoring the plant more firmly in the soil |
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Internal structure of root |
Consists of: •epidermis •cortex •central cylinder |
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Epidermis of the dicot root |
•it forms the outer later of the stem and consists of a single later of thin-walled,brick shape cells •cuticle is absent • finger- like, unicellular outgrowths,the root hairs ,occur on the root hair region |
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Cortex of the dicot root |
•it is broad band directly under the epidermis that consists of a number of layers of big, thin-walled parenchyma cells with large intercellular spaces •has the endodermis- inner layer of the cortex which is specialised parenchyma which regulates the passage of water •radial and transverse walls of the endodermis contain thickened cork strips which are known as Casparian strips |
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Central cylinder of a dicot root |
•includes all the tissues that are enclosed by the endodermis •directly under the endodermis there are one or more layers of thin-walled cells called pericycle • on the Inside of the pericycle is the vascular tissue that are xylem and phloem • the xylem is arranged in the form of a cross, with the phloem between the arms of the cross •rest of the cylinder has parenchyma cells In a dicot root,a clear endodermis is visible and root hairs are present |
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Functions of the tissue in a dicot root |
Root hair -increase the absorption surface for the uptake of water and mineral salts Epidermis - protects underlying tissues Parenchyma -allows water and mineral salts to pass through to the xylem and it stores starch Endodermis -regulates the passage of water by means of the Casprian strips for from the cortex to the xylem Pericycle -forms lateral roots Xylem -tranports water and minerals salts from the roots to the rest of the plant Phloem -transports manufactured organic subtances |
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External structure |
•stem consists of nodes and internodes •the node is where the leaves and side branches develop •internode is the region between two nodes •the terminal bud occurs at the tip of the stem •terminal bud consists of meristematic tissue which continuously divides and forms new cells and results in primary growth (increase in length) of the plant •auxillary bud occurs in the axils between the petiole and the stem and develop into lateral branches or flowers |
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Internal structure of dicot stem |
•epidemis •cortex •central cylinder |
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Epidermis of a dicot stem |
•forms the outer layer of the stem • consists of a single later of thin-walled,brick shape cells •some epidermal cells are modified to form stoma •outer walls of the epidermis are covered with a waterproof cuticle •multicellular ,hairy outgrowths may occur |
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Cortex of a dicot stem |
•collenchyma - occurs just directly under the epidermis that consists of a few cell layer -thickened at the corners
•parenchyma -made up of a number of layers of big, thin-walled parenchyma cells with large intercellular spaces •Endodermis -single layer of brick -shaped cells that form the inner layer of the cortex -not easily distinguished in the stem - starch is often stored in the endodermis which is a starch sheath |
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Central cylinder of a dicot stem |
•vascular tissue occurs in the vascular bundles •vascular bundles are arranged in a circle •it is arranged like: -xylem on the inside -phloem on the outside -sclerenchyma fibres occur as a cap on the outside of the phloem -consists of dead cells with evenly thickened cell walls. -cambium, a layer of meristematic tissue, occurs between the xylem and the phloem. Cambium makes secondary thickening possible •central region of the stem is the pith and it consists of large thin -walled parenchyma cells with large intercellular air spaces •parenchyma that occurs between the vascular bundles is known as the medullary rays •the medullary rays transport substances between the pith and the cortex
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Functions of the tissue in a dicot stem |
Epidermis -protects underlying tissues Cuticle -prevents moisture loss stomata - allow gaseous exchange Collenchyma -strengthens the stem and acts as a supporting tissue that keeps the stem upright Parenchyma -stores organic substances and the intercellular air spaces allow for gaseous exchange Endodermis -stores starch Sclerenchyma fibres -protects the vascular bundles and strengthen and support the stem Xylem -transports water and mineral salts and provides a pathway from the roots to the rest of the plant Phloem - transports manufactured organic substances from leaves to the rest of the plant. Cambium -makes secondary thickening possible |
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Secondary thickening -formation of the secondary xylem and secondary phloem |
• cambium that occurs in the vascular bundles of dicot stems, between xylem and the phloem is knows fascicular cambium •layers if parenchyma cells in the medullary rays, between the vascular bundles and in line with the fascicular cambium, become meristematic and are known as interfascicular cambium •the fascicular and interfasicular cambium join up with each other to form an unbroken ring of cambium tissue •active cell division (mitosis) takes place in the cambium •new xylem tissue known as secondary xylem is formed towards the Inside •secondary xylem now forms a continuous ring on the inside of the cambium ring and the secondary xylem forms a continuous ring on the outside •each year the cambium forms a new ring of secondary xylem and phloem •as the secondary tissue is formed year after year , the primary xylem and phloem are pushed further away from each other •in some places cambium does not form secondary tissue but parenchyma cells •these parenchyma cells form rays that extend from the middle of the stem and are known as pith rays •pith rays are visible in the secondary xylem and phloem •the formation of the secondary tissue causes the stem's circumference to increase and become thicker
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Annual rings |
•concentric rings are the secondary xylem that consists if xylem vessels and tracheids with thickened walls and are known as annual rings •each annual ring consists of two parts -broad light coloured wood: spring wood -narrow dark coloured part -aumtumn wood •each annual ring (a light and dark band) represents one year •the cambium ring and the primary and secondary phloem are shifted outwards every year •secondary xylem is the youngest and most active lies closet to the cambium,region is called sapwood •inner and older secondary xylem is blocked, appears darker and is known as the heartwood •heartwood provides support and strengthens the trunk of the tree , which bears heavy branches and leaves |
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The formation of cork |
•outer layer of the cortex (collenchyma) becomes meristematic and is known as the cork cambium •cork cambium divides to form cork cells on the outside •cork cells have no living contents and are dead cells taught are surrounded by thickened walls of Suberin •this layer of cork makes the stem |
