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Terms in this set (20)
* Define indeterminate growth and totipotent.
Intermediate growth: when cells continue to divide indefinitely and therefore growth is not terminated at a certain stage
Totipotent: the cells in plants which have the ability to generate whole plants
* State that most plants have indeterminate growth and have totipotent cells.
Most plants have indeterminate growth and have totipotent cells.
* Define meristem.
A group of undifferentiated cells which have the ability to continually divide by mitosis.
* Compare apical and lateral meristems.
Apical meristems occur at the apices (tips) of the root. They shoot in flowering plants and cause the plant to increase in length, primary growth.
Lateral meristems are located in the cambium. They cause the plant to increase in girth, secondary growth.
* Outline role of mitosis in the growth of stem and leaves while maintaining a meristem.
Cells in meristems are small and go through the cell cycle repeatedly to produce more cells, by mitosis and cytokinesis. These new cells absorb nutrients and water and so increase in volume and mass.
The root apical meristem is responsible for the growth of the root. The shoot apical meristem is more complex. It throws off the cells that are needed for the growth of the stem and also produces the groups of cells that grow and develop into leaves and flowers. With each division, one cell remains in the meristem while the other increases in size and differentiates as it is pushed away from the meristem region.
* State the generic function of plant hormones.
A hormone is a chemical message that is produced and released in one part of an organism to have an effect in another part of the organism.
* Outline how auxin concentrations regulate plant growth in the root and stem.
in plants, growth involves cell division and cell elongation. Cells elongate due to the pressure caused by water entering the cell by osmosis (turgor pressure). Auxin stimulates cell elongation at the shoot apex by initiating events that cause the loosening of the cell wall fibers. There are two mechanisms which both involve an auxin receptor. Firstly, auxin activates proton pumps in the plasma membrane. These pumps pump protons into the cell wall. A decrease in pH in the cell wall activates cell wall loosening proteins. These disrupt hydrogen bonds between cellulose fibers. Secondly, auxin causes a rapid increase in the expression of genes coding for the proton pump and cell wall loosening proteins.
* Outline the role of auxin in apical dominance.
Auxin has a role in stimulating growth at the shoot apex, inhibiting lateral shoot growth which is apical dominance.
* State two external factors that control the growth of roots and stems.
Light and gravity
* Define tropism, phototropism and gravitropism.
Tropism: a response that is determined by the direction of the stimulus
Phototropism: the growth of shoots towards light (positive tropism)
Gravitropism: the growth of shoots away from gravity (negative tropism)
Outline how PIN-transport proteins can direct direction of auxin flow
The position and type of PIN3 proteins can be varied to transport auxin to where growth is needed.
* Explain how auxin concentrations allow for phototropism in the stem.
Auxin has a role in phototropism, responding to light. Auxin is produced by cells in the apical meristem. The direction of light is detected at the tip of the shoot by pigments called phototropins. Phototropins stimulated by the absorption of light regulate the transport of auxin. Auxin is transported from cell to cell in one direction. Auxin efflux pumps embedded in the plasma membrane transport auxin out of the cell by active transport. The location of auxin efflux pumps determines the direction of transport. When a shoot is exposed to light from above, auxin efflux pumps are located at the base of the cells in the shoot apex. Auxin is transported downwards from the meristem, and has an equal distribution in the cells below the meristem. The cells elongate and the shoot grows straight upwards, symmetric growth. When the shoot is exposed to light from one side, this causes auxin efflux pumps to change location inside the cell. They move to the side of the cell furthest away from the light. This causes auxin to be transported to the shady part of the root, generating a higher concentration of auxin on the shady side than on the side exposed to light. This causes more cells on the shady side to elongate and the shoot bends towards the light, asymetric growth.
* Explain how auxin concentrations allow for gravitropism in the root.
The upward growth of shoots and the downward growth of roots occurs in response to gravity. If a root is placed on its side, gravity causes cellular organelles called statoliths to accumulate on the lower side of cells. This leads to the distribution of PIN3 transporter proteins that direct auxin transport to the bottom of the cells. High concentrations of auxin inhibit root cell elongation so the top cells elongate at a higher rate than the bottom cells causing the root to bend downward.
* State that auxin influences cell growth rates by changing gene expression.
Auxin influences cell growth rates by changing gene expression.
* Define micropropagation.
Micropropagation is the propagation of plants from a very small sample of tissue, generating clones.
* Outline how changing auxin and cytokinin ratios can lead to development of roots or shoots from the same explant tissue.
Micropropagation is carried out in sterile conditions. (1) a small sample tissue is excised from the plant tissue and is sterilised. (2) it is placed onto nutrient agar containing equal concentrations of auxin and cytokinin. This promotes cell division and a mass of undifferentiated cells (callus) is formed. (3) the callus can be split and each part allowed to grow. (4) the callus is then transferred onto nutrient agar containing more cytokinin than auxin to promote shoot development. (5) the shoots are then transferred onto nutrient agar containing more auxin than cytokinin to promote root development. (6) plantlets formed are transferred into soil.
* Outline three roles of micropropagation of plant species.
(1) new plants can be produced in large numbers from small amounts of starting material. Conventials techniques would be slower or very difficult. (2) virus free plants can be produced. The high auxin concentration, high rate of cell division and lack of vascular tissue all have a negative affect on virus presence. (3) orchids and other rare species can be produced in large numbers. Many exotic plants (with a high market value) are available for the horticultural industry.
* Outline role of microarrays in understanding role of plant hormones.
Microarrays allow researchers to detect gene expression. If a gene is being expressed, then when the tissue is tested on the microarray, it will cause fluroscence
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