4 - Regulation of Systems (copy)

What happens to a plant if the soil is too dry?

The plant will lose too much water to evaporation, causing it to lose water from all of its cells, losing turgor pressure and wilting.

Guard cells

Regulate water loss from stromata. When they are turgid they hold the stomatal pore open, but when flaccid they close it.

Absicisic acid

Plant hormone that regulates the movement of guard cells

Adaptation

Characteristic evolved in an organism (either structural, functional of behavioural)

Abiotic factor

Non-living components of an ecosystem, such as competitors, collaborators, predators, parasites, disease, mates

Biotic factor

Living components of an ecosystem, such as temperature, light intensity, soil pH/texture, water, atmosphere,

wind speed wind direction

Tolerance range

The range of environmental conditions within which an organism can function and reproduce

Optimum range

The range of environmental conditions within the tolerance range over which an organism functions best. Outside this, organisms experience physiological stress or even death

Internal environment

Unicellular organisms - anything inside the plasma membrane

Multicellular organisms - includes within cells, extracellular fluid between cells and blood plasma.

What happens to cells if the internal environment varies to much?

Death can occur, as organisms need to maintain a relatively constant internal state.

Homeostasis

The maintenance of a relatively constant internal environment within narrow tolerance limits despite of changes in the internal or external environment

Conditions which need to regulated include

Temp, 02, glucose, pH, nutrients, waste, water content

Types of receptors

Chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptors, nociceptors and osmoreceptors

Chemoreceptors

Stimulated by molecules of substances e.g. smell, taste and detectors of CO2 and O2 in the blood.

Mechanoreceptors

Detect pressure, touch, tension, sound vibrations, balance. Receptors found in skin.

Photoreceptors

Stimulated by light: eyes and light sensitive cells in the body surfaces of some invertebrates e.g. worms.

Nociceptors

Nerve endings which detect pain.

Osmoreceptors

Detects water levels of the blood, found in hypothalamus

Exteroreceptors

Detect signals from the external environment (e.g pain receptors in skin, taste buds)

Interoreceptors

Detect signals from the internal environment (e.g. CO2 concentration, pH levels)

Which two systems are responsible for homeostasis?

The hormonal and nervous systems are the major ones, but all other systems except for reproductive system play a part.

Negative feedback mechanism

A stimulus-response mechanism in which the response reduces the magnitude of the original stimulus (most homeostatic control) and returns it to an optimum level.

What are the 5 parts of the stimulus response model

- Stimulus: a condition or signal that causes a response

- Receptor: a structure that detects or receives a stimulus or signal

- Co-ordination centre - usually the brain or central nervous system

- Response: any action by an organism to a stimulus

- Effector: muscles or gland which carry out a response

Positive Feedback Mechanism

Increases the intensity of the stimulus to reinforce the condition (not a mechanism of homeostasis)

Human set body temperature

37 degrees

What does high body temperature cause for chemical reactions in the body?

The denaturation (destruction) of enzymes that catalyse (speed up) various reactions.

4 methods of gaining and losing heat from the human body

Conduction, convection, evaporation, radiation

Conduction

Heat will transfer from a hotter object to a cooler object with which it is in contact

Convection

The transfer of heat by means of warmed air or water, rising and being replaced by cooler air or water.

Evaporation

The change from liquid to vapour removes heat off the surface of a body causing cooling. (only one that doesn't work both ways)

Radiation

The transfer of heat from a hot object to a cooler one by means of infrared waves.

Mechanisms for keeping cool

- sweating: evaporative cooling

- vasodilation: arterioles close to skin dilate - increased blood flow results in more heat loss by convection and evaporation

- flattening body hair

- reduced activity

- metabolic rate decreases: lethargic

- behavioural adaptations: remove clothing/seek shade

- increase SA:V

Mechanisms for keeping warm

- sweating ceases

- arrector pili muscles contract raising body hair (goose bumps)

- Vasoconstriction: arterioles close to skin surface constrict reducing blood flow to surface - less heat loss by evaporation/convection

- metabolic rate increases in response to release of adrenaline and thyroxine

- shivering: increased muscle movement generates heat

- behavioural adaptations: put on more clothing/seek warm environments, curling up

Skin responses involved in warming up

1. Piloerection - hair is raised increasing layer of insulation air

2. Sweat reduced

3. Vasoconstriction

Skin responses involved in cooling off

1. Hair lies smooth - does not trap air

2. Sweat produced - cooling by evaporation

3. Vasodilation

Thermoreceptors

Skin receptors detect changes in the temperature of the external environment. The hypothalamus acts as a thermostat for internal temperature with receptors in the bloodstream, and it sends messages to appropriate effectors to regulate temperature.

Masai people

Slender body shape with long arms and legs (larger SA:V), wear few clothes, move out of heat

Inuit people

Stocky bodies with short arms and legs, wear thick fur clothing, diet consists of fatty high calorie foods, huddle when sleeping (reduce SA:V)

Babies and heat loss

Have no behavioural adaptations and can't shiver. High proportion of brown fat and larger SA:V so lose heat more easily.

Brown fat

A type of fat involved in rapid heat production

Glucose

The main source of energy for heterotrophs. Cells require a constant supply that is initially obtained from digestion of food

How is surplus glucose stored?

As glycogen in the liver and muscles or it may be converted to fat.

Normal range of blood glucose

3.0-7.7mmol/L

Which two hormones act to regulate BGL?

Insulin and glucagon

What is the relationship between insulin and glucagon?

They have the opposite effect; they are antagonistic. Both are negative feedback systems

Insulin

Released from Beta cells in the Islets of Langerhans in the pancreas. Targets primarily liver and muscle cells, and decreases BGL by:

- increasing the uptake of glucose from the blood by cells

- converting glucose to glycogen & fat when there is a surplus

- inhibiting the conversion of glycogen to glucose.

Glucagon

Released from Alpha cells in the Islets of Langerhans in the pancreas. Targets liver and pancreas cells, and increases BGL by:

- Causes liver cells to convert glycogen to glucose

- Also acts on Beta cells to inhibit production of insulin.

Diabetes

(Diabetes mellitus) A disease caused by high BGLs (hyperglycaemia). Symptoms include lethargy, large amounts of urine and excessive thirst. Detected by simple blood (BGL > 8mmol/L) or urine test (too much glucose in urine). Can have genetic or lifestile links.

Type I Diabetes Mellitus

- Onset in childhood

- Caused by Beta cell damage leading to a failure of the pancreas to produce insulin

- Prolonged increase in BGLs causes damage to eyes, nerves and kidneys and increases risk of heart disease, stroke, sexual impotence and foot problems.

- If untreated coma and die.

- Can be managed by regularly checking BGLs and using insulin injections.

Type II Diabetes Mellitus

Late onset (>40). Caused by lifestyle factors like being overweight, high sugar diet, lack of exercise or genetic factors. Cells become insulin resistant affecting their ability to take up glucose. Can be controlled by monitoring BGLs, diet, exercise, use of medication.

Osmoregulation

The process by which the osmotic pressure of the blood and tissue fluids is kept relatively constant. It is a homeostatic mechanism under hormonal control.

Where is water found in multicellular organisms?

Cytoplasm, tissue fluid and blood contain solutes dissolved in water. 60-65% of our bodies are water.

What two processes require water?

Metabolism (chemical reactions) and transport of substances (both intracellular and intracellular)

Methods of water gain

Drinking, food, metabolism

Methods of water loss

Evaporation from skin and respiratory surfaces, faeces, urine

Excretion

Removal of metabolic waste chemicals. (Performed by the kidneys in mammals)

Two roles of kidneys

Homeostatic organ

1. Excretion

2. Osmoregulation

Process of removing nitrogenous wastes

Proteins break down to make toxic ammonia, which is converted to urea to be transported with salts to the kidney for excretion through urine.

How is water balanced achieved?

By controlling the amount of water leaving the body in urine. Based on how much water is in the blood.

How many nephrons are in each human kidney?

About 1 million

Nephron reabsorption diagram

ADH

Antidiuretic hormone released when high osmotic pressure is detected (dehydration). Osmoreceptors in hypothalamus detect the change; pituitary releases. Causes kidneys to increase reabsorption of water from the nephron tubules back into the blood. Less is released when you've drunk lots so the kidneys reabsorb less water.

Thyroxines (T3 and T4)

Thyroid hormones secreted by the thyroid gland. Involved in controlling cellular differentiation, growth and metabolic rate. Production and secretion is triggered by TSH.

Maintenance of basal metabolic rate

Thyroxine levels are regulated through negative feedback.

TSH

Thyroid Stimulating Hormone released from anterior pituitary gland. Triggers the production and secretion of thyroxine. Regulated by the amounts of thyroxine (in a negative feedback loop) and TRH in the blood.

TRH

Thyrotropin releasing hormone. Involved in the regulation of TSH. More is released when the hypothalamus detects lower temps, leading to more thyroxine being produced and basal metabolic rate increasing.

Thyroxine feedback loop diagram (- symbolises negative feedback)

Hypothyroidism

Too little production and secretion of thyroxine, resulting in reduced metabolism that impairs development and cretinism in the foetus. In adults, symptoms include fatigue, increased cold sensitivity, weigh gain and slow mental functioning.

Cretinism

Condition that occurs in the foetus due to hypothyroidism in the mother that leads to permanent damage to the developing brain and body

Hypothyroidism treatment

If caused by dietary lack of iodine, iodine can be added to diet through liquids or iodised salt.

If caused by thyroid gland failure, daily synthetic thyroid hormone tablets

Hyperthyroidism

Production and release of too much thyroxine causes exophthalmia, increased metabolic rate leading to weight loss, and faster heart rate