LESSON 8

• Both plants and animals have complex systems that regulate and control various physiological processes
• In animals, this control is primarily achieved through the endocrine system, which consists of glands that secrete hormones into the bloodstream
• Plants, on the other hand, lack a circulatory system but have a similar mechanism called the plant endocrine system.
• Hormones - Plants produce hormones that regulate growth, development, and responses to environmental stimuli
• hormones are chemical messengers that are synthesized in one part of the plant and transported to target cells in another part.
• Auxins: Promote cell elongation, root development, and apical dominance.
• Gibberellins: Stimulate stem elongation, seed germination, and flowering.
• Cytokinins: Promote cell division, delay senescence, and regulate nutrient distribution.
• Abscisic Acid: Inhibits growth, promotes seed dormancy, and regulates stomatal closure.
• Ethylene: Regulates fruit ripening, leaf senescence, and abscission.
• Mode of Transport - Unlike animals, plants lack a circulatory system to transport hormones. Instead, plant hormones are transported through the vascular tissues, such as xylem and phloem.
• Xylem carries hormones upwards from the roots to the shoots, while phloem transports hormones in both
• Target Cells- Plant hormones can act on cells in close proximity or at a distance from their site of synthesis.
• Target cells also act on the same cells that produce them (autocrine) or on neighboring cells (paracrine)
• The target cells of plant hormones have specific receptors that bind to the hormones and initiate a response.
• Hormones - the animal endocrine system consists of various glands, such as the pituitary gland, thyroid gland, adrenal glands, and reproductive glands, that secrete hormones into the bloodstream.
• hormones (animal)-,regulate growth, metabolism, reproduction, and other physiological processes.
• Insulin: Regulates blood sugar levels by promoting glucose uptake by cells.
• Thyroxine: Controls metabolism and growth.
• Adrenaline: Triggers the "fight or flight" response in stressful situations.
• Estrogen and Testosterone: Regulate reproductive functions and secondary sexual characteristics
• Mode of Transport- Animal hormones are transported through the bloodstream to reach their target cells.
• hormones - are released by endocrine glands into the bloodstream and then carried to specific tissues or organs where they exert their effects.
• Target Cells- Animal hormones act on specific target cells that have receptors for the hormones
• receptors are usually located on the surface or inside the target cells.
• When a hormone binds to its receptor, it triggers a series of biochemical reactions that lead to a physiological response.
• Hormones - act as chemical messengers that coordinate and integrate various functions within the organism
• hormones produced in response to internal or external stimuli and can have long-lasting effects on the target cells.
• Nervous Control - animals have a welldeveloped nervous system that allows for rapid and precise control of physiological processes
• Nervous control involves the transmission of electrical signals, called nerve impulses, through specialized cells called neurons
• the nervous system is responsible for immediate responses.