Hormonal-Response

Hormonal response and co-ordination in humans Endocrine and exocrine glands Exocrine: Glands whose secretions pass through a series of ducts ultimately to the exterior of the body. Eg: Salivary glands Prostrate gland Sweat glands Portion of Pancreas that secretes bile into the duodenum (Islets of Langerhands are ENDOcrine) Endocrine: Glands whose secretions pass through the blood stream to the target organs. Eg: Islets of Langerhans (in Pancreas) Pituitary gland Hypothalamus Liver Stomach and intestines 481965029654500Adrenaline (An ENDOcrine hormone): Brain senses stress or danger Brain sends electric signals to the adrenal glands Adrenal glands secrete adrenaline into the bloodstream Results of adrenaline: Increase in metabolic activity, releasing more energy to cope with the situation Causes liver to break down glycogen into glucose to provide energy for higher metabolic activity Effects of adrenaline: Faster heart beat Breathing rate increases Pupils dilate Blood diverted from the gut to muscles Chemical co-ordination in Plants Auxins One of five plant growth hormones Made in cells that are dividing (Behind the tip of the root and the shoot) Auxins diffuse into nearby cells: Shoot - Causes growth and elongation Root - Slows down growth and inhibits elongation Tropisms Growth movements made by plants in response to a stimulus Stimuli include: Gravity, light, temperature, water, chemicals, touch 39433509969500Geotropism Positive geotropism (In the root): Growth TOWARDS gravity. Negative geotropism (In the shoot): Growth AWAY FROM gravity. Auxins are responsible for the growth pattern Positive geotropism: Auxins collect at the lower side of the root and inhibits the cell elongation. This causes the downward curve of the root (radicle). Negative geotropism: Auxins collect at the lower side of the shoot and causes growth and elongation. This causes the upward curve of the shoot (plumule). 364807511938000 Phototropism Positive phototropism (In the shoot): Growth TOWARDS the light. Negative phototropism (In the root): Growth AWAY FROM the light. Auxins move away from a source of light and are responsible for the growth pattern: Positive phototropism: Auxins collect in the dimmer side of the shoot and cause those cells to elongate. This causes the curve of the stem (radicle) towards the source of light. Negative phototropism: Auxins collect in the dimmer side of the root and inhibit the cell elongation. This causes the curve of the root (plumule) away from the source light (the soil). Synthetic plant growth substances Definition: Artificial substances which are made to control and regulate plant growth by imitating natural plant growth substances. Several uses: Weedkillers Production of seedless fruits Control of frit ripening Rooting of cuttings Micropropagation of plants Weedkillers Sprayed onto weeds to encourage rapid, uncontrolled growth which eventually cause those plants to die. This type of weedkiller is selective and effects on certain plants. Eg: Broad-leaved plants amongst crops of cereals (narrow-leaved) Weeds on lawns Undergrowth in tree plantations Production of seedless fruits Some fruits develop without fetilization (and therefore without seeds) This development is called parthenocarpy. Synthetic auxins are added to some plants to induce the production of seedless fruits. Gibberellins have a similar effect on other plants. Used to grow seedless grapes and increase their size before harvesting Control of fruit ripening The control of fruit ripening can increase the profitability for farmers and resellers. Auxins are used to prevent potatoes from sprouting buds. Gibberellins are used to slow down the ripening of grapefruit. Ethene gas can stimulate the ripening of fruit.