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Homeostasis
Homeostasis and hormonal action
| Question | Answer |
|---|---|
| What is homeostasis ? | The maintenance of a constant state in the internal environment of organisms. It is the ability to return to a set point (normal range) so organisms can maintain balanced equilibrium. |
| Set point | the desired level at which the system operates. This is monitored by the receptor. |
| Receptor | detects internal and external stimuli which indicate any deviation from the set point and informs the central control |
| Central control | coordinates information from various sources and sends instructions to a suitable effector |
| Effector | often a muscle or gland that brings about the necessary change needed to return the system to the set point. This return creates a feedback loop. |
| Feedback loop | informs the receptor of the changes to the system brought about by the effector |
| Negative feedback | the response reduces the initial stimulus and decreases the hormone signalling. The signal pathway is 'turned off' and is not continuously active. |
| Positive feedback | the response increases the initial stimulus and increases hormone signalling so that the response becomes more intense. |
| Give 2 examples of positive feedback in biological systems. | 1) Depolarization of neurones 2) Oxytocin causing contractions of the uterus at childbirth 3) Fruit ripening |
| State the 6 main components of typical control system. | Input, receptor, control unit, effector, output and feedback loop |
| Any change to the system is considered an | input |
| This component measures the level of a factor | receptor(sensor) |
| This component stored operational information and coordinates effectors | control unit |
| This component brings about changes to the system in order to return it to the set point | effector |
| The return of the system to the set point is considered to be an | output |
| This component turns off the system | feedback loop (negative feedback in this case) |
| What is a hormone? | A molecule that is secreted into the extracellular fluid that surrounds the cells and enters the bloodstream where it circulates and communicates signals that regulate body functions. |
| A chemical that is produced by one set of cells that affects a different set of cells called target cells is known as a | hormone |
| State 5 functions of hormones in the body. | 1) Growth 2) Reproduction 3) Development of sexual characteristics 4) Regulation of blood glucose levels 5) Production of cells for the immune system etc |
| Name a few conditions which can result from hormone deficiencies or non-responsive target cells. | Dwarfism, cretinism, Addison's disease, Cushing's syndrome, diabetes mellitus etc |
| T or F. Only cells with receptors for a particular hormone are affected by that hormone; no other cells respond to that hormone. | T |
| List the major endocrine glands in the human body. | 1) Hypothalamus and pituitary gland in the brain 2) Thyroid and parathyroid glands in the neck 3) Adrenal glands, pancreas and kidney 4) Ovaries (female) and testes (male) |
| What is an endocrine gland? | A specialized, ductless organ that produces and secretes hormones directly into the bloodstream. |
| What is an exocrine gland? | Gland with ducts which release products e.g. salivary gland which secretes saliva via a duct into the mouth. Exocrine glands do NOT secrete hormones. |
| Which two hormones work together to maintain blood glucose concentration? | Insulin and glucagon |
| From which endocrine gland is insulin and glucagon secreted? | islets of Langerhans of the pancreas glucagon - from the alpha cells insulin - from the beta cells |
| T or F. Insulin is made up of 2 polypeptide chains. | T |
| What is the normal blood glucose range in humans? | 70 - 100 mg per 100 ml |
| What happens when blood glucose level rises above normal? | 1) insulin hormone production is stimulated 2) Pancreas secretes insulin hormone into blood 3) Liver takes up glucose 4) Insulin influences body cells to take up glucose 5) Blood glucose level is reduced to normal |
| What happens when blood glucose level falls below normal? | 1) Glucagon hormone production is stimulated 2) Pancreas secretes glucagon into blood 3) Glycogen is broken down to glucose in the liver 4) Blood glucose level rises to normal |
| What is diabetes mellitus? | A hormonal disease in which body cells do not take up glucose from the bloodstream or do not metabolise glucose. If the blood glucose level rises greatly, glucose and water are excreted in the urine because the kidneys cannot reabsorb all the glucose. |
| Describe a diagnostic test for diabetes mellitus. | Test for sugar in urine |
| If the body is no longer using glucose as fuel, what is used instead? | proteins and fats |
| The metabolism of fats leads to the build up of compounds called ketones. How do these affect blood pH? | The make the blood more acidic (acidosis occurs). |
| Which type of diabetes is called insulin-dependent diabetes? | Type 1 |
| Which type of diabetes is called non-insulin-dependent diabetes? | Type 2 |
| What is the cause of type 1 diabetes? | The body does not produce insulin therefore daily injections of insulin are necessary. |
| What is hypoglycaemia? | Low blood sugar |
| What is the cause of type 2 diabetes? | This occurs when the liver, muscle cells and other other body tissues do not have the receptor proteins to allow insulin to bind. This is often developed due to lifestyle choices. |
| What is hyperglycaemia? | High blood glucose |
| How can type 2 diabetes be prevented/controlled? | 1) Eat a low-fat diet 2) Eat fruits and vegetables 3) Exercise regularly |
| How can type 1 diabetes be controlled? | 1) Take the correct dose of insulin daily 2) Eat regular meals to maintain blood sugar level |
| What is the role of the gaseous plant hormone ethylene (ethene)? | 1) Promotes the ripening of fruits 2) Influences abscission - the controlled loss of leaves, fruit or flowers and senescence- ageing, cell death and recycling 3) Promotes formation of roots and root hairs |
| Why does 'one bad apple spoil the whole bunch'? | Excess ethylene from an overripe apple will spread and the entire load will be overripe in a short period of time. |
| What are climacteric fruits? | Fruits that will continue to ripen even after they have been harvested. They produce more ethylene than non-climacteric fruits which do not continue to ripen after harvesting. |
| What is enthephon? | A synthetic chemical used to supply ethylene for commercial purposes. When it breaks down, it releases ethylene gas. |
| Certain fruits are harvested before they are fully ripe. They are then stored in a container and flushed with CO2. What is the purpose of the CO2? | CO2 inhibits the synthesis of ethylene by the fruit so that the fruit can be preserved and ripened when needed by supplying ethylene at that time. |
| What is the effect of ethylene on respiration in plants? | Ethylene increases respiration in plants. |
| What is one factor which can increases ethylene production in plants? | Wounding of the plant e.g. when fruits are harvested. The stem is wounded and ethylene production is increased. |
| Fruits that show increased respiration during ripening and senescence are called | climacteric |
| Fruits that do not show increased respiration during ripening and senescence are called | non-climacteric |
| State a few conditions which inhibit ethylene production in fruit preservation and storage. | presence of CO2, low temperatures,.. |
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CAPE Biology Unit 2
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