Assessment Statements 9.1: Plant Structure and Growth
9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.
9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.
Plants grow is restricted to 'embryonic' regions called meristems. Having specific regions for growth and development (restricted to just the meristematic tissue), contrasts with animals in which growth takes place throughout the whole organism.
Apical meristems are found at the tip of the root and the shoot, adding growth to the plant in these regions. The apical meristems are described as indeterminate , this type of growth tends to add length to root and stem in 'module' or 'units' (described below). This tissue remains 'embryonic' for prolonged periods of time and in some cases over 100's of years. Contrast this with the more determinate growth of leaves, petals and flowers in which a very precise growth occurs.
A tropism is a bending-growth movement either toward or away from a directional stimulus.
Phototropism is the bending-growth towards the unilateral source of light.
Auxins are a class of plant growth hormones (growth regulating factor)
Auxins are one of atleast three major classes of plant growth regulators. Unlike animal hormones plant hormones can provide a range of responses from the tissues.
The most common auxin is IAA ( Indolacetic acid). IAA was discovered in 1932 and is believed to be the principle auxin in higher plants.
Auxin is associated with the phenomenon of phototropism.
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9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.
9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.
9.1.3 Explain the relationship between the
distribution of tissues in the leaf and
the functions of these tissues.
Tissues:
(a) Phloem transports the products of photosynthesis (sugars, amino acids).
(b) Xylem transports water and minerals into the leaf tissue from the stem and roots.
(c) Epidermis produces a waxy cuticle for the conservation of water.
(d) Palisade layer which is the main photosynthetic region.
(e) Spongy layer creates the spaces and surfaces for the movement of water and gases.
(f) Lower epidermis contains the stomatal pores which allow gas exchange with the leaf.
The xylem and phloem tissues combine in the vascular tissue to provide support to the leaf.
distribution of tissues in the leaf and
the functions of these tissues.
Tissues:
(a) Phloem transports the products of photosynthesis (sugars, amino acids).
(b) Xylem transports water and minerals into the leaf tissue from the stem and roots.
(c) Epidermis produces a waxy cuticle for the conservation of water.
(d) Palisade layer which is the main photosynthetic region.
(e) Spongy layer creates the spaces and surfaces for the movement of water and gases.
(f) Lower epidermis contains the stomatal pores which allow gas exchange with the leaf.
The xylem and phloem tissues combine in the vascular tissue to provide support to the leaf.
9.1.4 Identify modifications of roots, stems
and leaves for different functions:
bulbs, stem tubers, storage roots and
tendrils.
Stem modification:
Bulbs: Onions & Lilies
Short vertical underground stems.
Many fleshy highly modified leaves for the storage of nutrient.
Can produce new plants by bulb division or the development of one of the many axillary buds.
These should not be confused with the disc-like Corms found in daffodils and tulips.
stem modification:
The horizontal stems called runners spread out from the main body of the plant.
At point the stem touches the ground new roots form.
If the horizontal runner is broken the small plantlet can establish itself independently. (asexual reproduction).
The horizontal stems are often an adaptation to finding water.
Stem modification: e.g. Cacti
Leaves are reduced to spines to prevent water loss in transpiration.
The stem is enlarged for the storage of water.
The stem carries out photosynthesis.
Root tip modification Stem Tuber/ Potato
The potato is an underground modification of the root tip.
The 'eaten potato' contains the carbohydrate and protein stores for the growth.
The 'eyes' are in fact axillary buds.
In effect this diagram show the branching axillary buds or a stem.
Carrot: Tap Root modification
Function: Storage of water.
Carrot plants are often associated with very sandy soils. The enlarged root is familiar to those who have eaten the vegetable.
The root modification allows the storage of water in the cortex and central stele.
The mass of the root stabilizes the plant in the loose sandy soils.
and leaves for different functions:
bulbs, stem tubers, storage roots and
tendrils.
Stem modification:
Bulbs: Onions & Lilies
Short vertical underground stems.
Many fleshy highly modified leaves for the storage of nutrient.
Can produce new plants by bulb division or the development of one of the many axillary buds.
These should not be confused with the disc-like Corms found in daffodils and tulips.
stem modification:
The horizontal stems called runners spread out from the main body of the plant.
At point the stem touches the ground new roots form.
If the horizontal runner is broken the small plantlet can establish itself independently. (asexual reproduction).
The horizontal stems are often an adaptation to finding water.
Stem modification: e.g. Cacti
Leaves are reduced to spines to prevent water loss in transpiration.
The stem is enlarged for the storage of water.
The stem carries out photosynthesis.
Root tip modification Stem Tuber/ Potato
The potato is an underground modification of the root tip.
The 'eaten potato' contains the carbohydrate and protein stores for the growth.
The 'eyes' are in fact axillary buds.
In effect this diagram show the branching axillary buds or a stem.
Carrot: Tap Root modification
Function: Storage of water.
Carrot plants are often associated with very sandy soils. The enlarged root is familiar to those who have eaten the vegetable.
The root modification allows the storage of water in the cortex and central stele.
The mass of the root stabilizes the plant in the loose sandy soils.
9.1.5 State that dicotyledonous plants have
apical and lateral meristems.
apical and lateral meristems.
Plants grow is restricted to 'embryonic' regions called meristems. Having specific regions for growth and development (restricted to just the meristematic tissue), contrasts with animals in which growth takes place throughout the whole organism.
Apical meristems are found at the tip of the root and the shoot, adding growth to the plant in these regions. The apical meristems are described as indeterminate , this type of growth tends to add length to root and stem in 'module' or 'units' (described below). This tissue remains 'embryonic' for prolonged periods of time and in some cases over 100's of years. Contrast this with the more determinate growth of leaves, petals and flowers in which a very precise growth occurs.
9.1.6 Compare growth due to apical and
lateral meristems in dicotyledonous
plants.
lateral meristems in dicotyledonous
plants.
Apical meristem of the apical bud adds new tissue to the stem tip. This addition increases the length of the stem.
Stem growth:
The tissue added includes the units described below:
1. Adds length to the stem and root
2. Added in modules.
3. Each module is added at the meristem and includes leaf (leaves), internode length of stem and axillary buds.
Secondary growth added by the Lateral meristem (cambium) has two types:
1. Vascular cambium that produces secondary xylem and phloem
2. Cork cambium produces some of the bark layer of a stem.
9.1.7 Explain the role of auxin in
phototropism as an example of the
control of plant growth.
Stem growth:
The tissue added includes the units described below:
1. Adds length to the stem and root
2. Added in modules.
3. Each module is added at the meristem and includes leaf (leaves), internode length of stem and axillary buds.
Secondary growth added by the Lateral meristem (cambium) has two types:
1. Vascular cambium that produces secondary xylem and phloem
2. Cork cambium produces some of the bark layer of a stem.
9.1.7 Explain the role of auxin in
phototropism as an example of the
control of plant growth.
A tropism is a bending-growth movement either toward or away from a directional stimulus.
Phototropism is the bending-growth towards the unilateral source of light.
Auxins are a class of plant growth hormones (growth regulating factor)
Auxins are one of atleast three major classes of plant growth regulators. Unlike animal hormones plant hormones can provide a range of responses from the tissues.
The most common auxin is IAA ( Indolacetic acid). IAA was discovered in 1932 and is believed to be the principle auxin in higher plants.
Auxin is associated with the phenomenon of phototropism.
Transport of Auxin:
Auxin is transported through the cell membrane of the adjacent plant cells by protein carriers in the plasma membrane.
These carriers transport the anion of auxin in polar direction, from the top of the cell to the bottom of the cell.
However the stimulus of light would seem to result in the introduction of these carriers into the side of the cell membranes so that the IAA3 can now be laterally transported.
Whilst not part of the examination syllabus for IB Biology look at the many connections that can be made to the various parts of the syllabus including, cell structure; plasma membrane; cell transport.
The role of auxin:
Since IAA3 is a 'hormone' there must be some link between the signal molecule and the sub cellular responses and the cellular responses. It appears that it is the receiving cell that determines the exact cellular response rather than IAA3 having very specific responses across all cells.
As we have noted one of the major functions of auxins is the promotion of growth. Research has shown that in some tissues IAA3 promotes mitosis whilst in other tissue, it promotes cell enlargement.
Auxin is transported through the cell membrane of the adjacent plant cells by protein carriers in the plasma membrane.
These carriers transport the anion of auxin in polar direction, from the top of the cell to the bottom of the cell.
However the stimulus of light would seem to result in the introduction of these carriers into the side of the cell membranes so that the IAA3 can now be laterally transported.
Whilst not part of the examination syllabus for IB Biology look at the many connections that can be made to the various parts of the syllabus including, cell structure; plasma membrane; cell transport.
The role of auxin:
Since IAA3 is a 'hormone' there must be some link between the signal molecule and the sub cellular responses and the cellular responses. It appears that it is the receiving cell that determines the exact cellular response rather than IAA3 having very specific responses across all cells.
As we have noted one of the major functions of auxins is the promotion of growth. Research has shown that in some tissues IAA3 promotes mitosis whilst in other tissue, it promotes cell enlargement.
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