Organisms respond to changes in their internal and external environments Flashcards
Nervous communication
The response to a stimulus is coordinated by the nervous system
Sequence of events for nervous communication
stimulus–+ receptor –+ coordinator –+ effector –+ response
What is simple reflex?
Rapid and involuntary response to a stimulus (not involving the brain) providing a protective effect
Tactic response (taxis)
A simple directional response whose direction is determined by the direction of the stimulus (deliberate)
Positive taxis
Movement towards the stimulus
Negative taxis
Movement away from the stimulus
Kinetic response (kinesis)
A non directional response in which the organism does not move towards or away from a stimulus (random). Instead, it changes the speed at which it moves and the rate at which it changes direction.
Tropism
Response to a part of a plant towards a directional stimulus
Positive tropism
Growth towards stimulus
Negative tropism
Growth away from stimulus
Plant growth factors
- Produced by cells in plants
- May also affect growth of tissues that release them not just distant target organ
- Exert influence by affecting growth
Indoleacetic acid (IAA)
Belongs to a group of substances, auxins
-Controls cell elongation in plants
-Produced in the tips of shoots and roots
Responses for plants
Light, Gravity, Water
Phototropism (shoots)
Initially IAA is evenly distributed throughout regions
- Light intensity changes and auxins move from light side to shaded side of plant
- Causing shaded shoot to elongate
- Shaded shoots bend and grow at a faster rate than lighter side in direction of light
(positive phototropism)
Phototropism (roots)
Initially IAA is evenly distributed throughout regions
- Light intensity changes and auxins move from light side to shaded side of plant
- Causing shaded roots to inhibit cell elongation
- Shaded roots bend and grow at a slower rate than lighter side in direction of light
(negative phototropism)
Geotropism (shoots)
Initially IAA is evenly distributed throughout regions
- Moves to underside of plant causing elongation
- Lower side grows at a faster rate than upper side
- Moves upwards away from gravity
(negative geotropism)
Geotropism (roots)
Initially IAA is evenly distributed throughout regions
- Moves to underside of plant inhibiting elongation
- Lower side grows at a slower rate than upper side
- Moves downwards towards gravity
(positive geotropism)
Hydrotropism (roots)
Positive hydrotropism to direction of water
Hydrotropism (shoots)
Negative hydrotropism away from water
Thigmotropism
Plants able to climb and attach to other things when growing
Positive- move to stimulus
Negative- move away from stimulus
What happens when you remove tips of shoots and roots?
It also removes IAA preventing ability to bend in a direction and grow
What are the principles of coordination?
Two main forms of coordination in animals - the nervous system and the hormonal system
The nervous system
Use of nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting chemicals, known as neurotransmitters, directly on to them. This results in rapid communication between specific parts of an organism. The responses produced are often short-lived and restricted to a localised region of the body
The hormonal system
Produces chemicals (hormones) that are transported in the blood plasma to their target cells. The target cells have specific receptors on their cell-surface membranes and the change in the concentration of hormones stimulates them. This results in a slower, less specific form of communication between parts of an organism. The responses are often long-lasting and widespread.
Neurones
Specialised nerve cells that are responsible for conducting electrical impulses (action potential) around the body
Sensory neurones
Transmits nerve impulses from a receptor to an relay (intermediate) neurone or directly to a motor neurone.
Relay (intermediate) neurones
Transmit impulses between sensory and motor neurones
Motor neurones
Transmits nerve impulses from a relay (intermediate) neurone to an effector, such as a gland/muscle
Structure of neurones
- Dendrons
Extensions of the cell body which subdivide into smaller branched fibres, called dendrites, that can conduct electrical impulses from multiple neurones at the same and carry to cell body
Structure of neurones
- Axons
A single long fibre that carries nerve impulses away from the cell body
Myelinated neurones
Contain a myelin sheath which forms a covering to the axon and is made up of the membranes of the Schwann cells. These membranes are rich in lipids known as myelin
Schwann cells
Surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis (the removal of cell debris) and play a part in nerve regeneration. They wrap themselves around the axon many times, so that layers of their membranes build up around making up myelin sheath
Nodes of Ranvier
Constrictions between adjacent Schwann cells where there is no myelin sheath.
The constrictions are 2- 3 μm long and occur every 1- 3 mm in humans
Cell body
Contains all the usual cell organelles, including a nucleus and large amounts of rough endoplasmic reticulum.
Associated with the production of proteins and neurotransmitters
Reflex
A response to a stimulus that is rapid, short-lived, localised and
totally involuntary.
Reflex arc
The stimulus
A receptor
A coordinator
A motor neurone
An effector
The response
Central nervous system
CNS
- Made up of the brain and spinal cord
Peripheral nervous system
PNS
- Made up of pairs of nerves that originate from either the brain or the spinal cord.
Structure of Pacinian corpuscle
- Occur deep in the skin, most abundant in fingers, soles of feet and external genitalia
- Sensory ending at the end of receptor has a stretch- mediated sodium channel
Function of Pacinian corpuscle
At resting potential, sodium channels are too narrow for sodium ions to pass. When pressure is applied it becomes deformed and membrane around neurone stretches so sodium ions diffuse into it. Influx of sodium ions depolarises membrane producing generator potential.
Receptors of the eye
Sensitive to light and colour
What is the nervous system split into?
- Central nervous system
- Peripheral nervous system
What is the peripheral nervous system split into?
- Somatic nervous system
- Autonomic nervous system
Somatic nervous system
Controls our conscious activity (walking, talking etc)
Autonomic nervous system
Controls our unconscious activity (breathing, digestion etc).
What is the autonomic nervous system split into?
- Sympathetic nervous system
- Parasympathetic nervous system
Sympathetic nervous system
Provides the “fight or flight” response and prepares us for action.
- stimulates effectors and so speeds up any activity
Parasympathetic nervous system
Provides the “rest and digest” response and calms the body down.
- inhibits effectors and so slows down any activity, controlling activities under normal resting conditions. It is concerned with conserving energy and replenishing the body’s reserves.
Spatial summation
A number of different presynaptic neurones together release enough of the neurotransmitter to exceed the threshold value of the postsynaptic neurone. Together they trigger a new action potential.
Temporal summation
A single presynaptic neurone releases the neurotransmitter many times over a very short period. If the concentration of the neurotransmitter exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered.
Neuromuscular junction
Type of cholinergic junction between motor neurone and muscles that uses ACh
Neuromuscular junction characteristics
- Postsynaptic membrane folded to form clefts which store AChE
- Has more ACh receptors
- ACh is always excitatory
Example of an inhibitory neurotransmitter
GABA
Example of an excitatory neurotransmitter
ACh
ACh
Acetylcholine
- an excitatory neurotransmitter, a chemical that carries messages from your brain to your body through nerve cells
AChE
Acetylcholinesterase
- an enzyme
What is a synapse?
The junction between two or more neurones/ neurones and effectors
Synaptic cleft
Gap between neurones
Refractory period purposes
- limits the number of action potentials
- It produces discrete impulses
- It ensures that action potentials are propagated in one direction only
What is homeostasis?
The maintenance of the stable internal environment within restricted limits, regardless of changes to the external environment.
Negative feedback
The change produced by the control system which leads to a change in the stimulus detected by the receptor and turns the system off
Positive feedback
Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal
What are hormones?
Chemical messengers, that are produced in organs called glands. They are released directly in the bloodstream where they are carried around body to target cells.
Characteristics of hormones
- effective in low concentrations
- long lasting and wide spread effects
- produced in glands
- carried in the blood plasma to the cells on which they act known as target cells
Hormones controlling blood glucose concentration
- Glucagon
Produced by cells in pancreas known as islets of Langerhans.
What cells do islets of Langerhans consist of ?
α- cells
β- cells
What do α- cells secrete?
Alpha (α) cells, which are larger, manufacture and secrete the hormone glucagon.
What do β- cells secrete?
Beta (β) cells, which are smaller, manufacture and secrete the hormone insulin.
Role of liver in regulating blood sugar
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
Glycogenesis
The conversion of glucose into glycogen.
- When blood glucose concentration is higher than normal the liver removes glucose from the blood and converts it to glycogen.
Glycogenolysis
The breakdown of glycogen to glucose.
- When blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose concentration.
Gluconeogenesis
The production of glucose from sources other than carbohydrate.
- When its supply of glycogen is exhausted, the liver can product glucose from non-carbohydrate sources such as glycerol and amino acids.
Normal blood glucose concentration
approximately 5 mmol/dm³
What is adrenaline?
A hormone produced in the adrenal glands.
Function of adrenaline in blood glucose concentration
In times of excitement or stress, it increases the blood glucose concentration by binding to specific protein receptors on the cell surface membrane of the target cells, activating enzymes that cause the breakdown of glycogen into glucose in the liver cells.
What is an effector?
Brings about the corrective measures needed to return the system to the optimum point (norm)
What is a receptor?
Detects the stimulus of any deviation from the set point (norm)
What is a coordinator?
Coordinates information from various sources
Feedback mechanism
A receptor detects a stimulus created by the change to the system and the effector brings about the appropriate response
Pancreas and blood glucose regulation
The pancreas is a large, pale-coloured gland situated in the upper abdomen, behind the stomach. It produces enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose concentration.
Location of islets of Langerhans
The pancreas is made up largely of the cells that produce its digestive enzymes. Scattered throughout these cells are groups of hormone-producing cells known as islets of Langerhans
Factors influencing blood glucose regulation
- directly from the diet in the form of glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose, lactose, and sucrose
- from the hydrolysis in the small intestine of glycogen =glycogenolysis stored in the liver and muscle cells
- from gluconeogenesis, which is the production of glucose from sources other than carbohydrate.
β cells function
Have receptors that detect the stimulus of a rise in blood glucose concentration and respond by secreting the hormone insulin directly into the blood plasma.
α cells function
Detect a fall in blood glucose concentration and respond by secreting the hormone glucagon directly into the blood plasma.
Glucagon’s actions after being secreted
- attaching to specific protein receptors on the cell-surface membrane of liver cells
- activating enzymes that convert glycogen to glucose
- activating emymes involved in the conversion of amino acids and glycerol into glucose
Role of adrenaline in regulating the blood glucose level
At times or excitement or stress, adrenaline is produced by the adrenal glands that lie above the kidneys. Adrenaline raises the blood glucose concentration by:
* attaching to protein receptors on the cell-surface membrane of target cells
* activating emymes that causes the breakdown of glycogen to glucose in the liver.
What are Diabetes?
A metabolic disease in which a person is unable to metabolise carbohydrate, especially glucose, properly. There are around 350 million people worldwide with diabetes
- caused by an inability to control blood glucose concentration due to a lack of the hormone insulin or a loss of responsiveness to insulin.
Two forms of diabetes
Type 1 (insulin dependant)
Type 2 (insulin independant)
Type 1 diabetes
The body being unable to produce insulin. lt normally begins in childhood. It may be the result of an autoimmune response whereby - the body’s immune system attacks its own cells, the islets of Langerhans.
They develop quickly, usually over a few weeks, and the signs and symptoms are normally obvious.
Signs of diabetes
- high blood glucose concentration
- presence of glucose in urine
- need to urinate excessively
- genital itching or regular episodes of thrush
- weight loss
- blurred vision
- tiredness
- increased thirst and hunger
Type 2 diabetes
Glycoprotein receptors on body cells being lost or losing their reponsiveness to insulin. However, it may also be due to an inadequate supply of insulin from the pancreas.
Type ll diabetes usually develops in people over the age of 40 years. There is, however, an increasing number of cases of obesity and poor dier leading to type ll diabetes in adolescents. It develops slowly, and the symptoms are normally less severe and may go unnoticed. People who are overweight are particularly likely to develop type ll diaberes
- About 90% of people with diabetes have type II.
Controlling type 1 diabetes
Controlled by injections of insulin. This cannot be taken by mouth because, being a protein, it would be digested in the alimeniary canal.
The dose of insulin must be matched exactly to the glucose intake. If a person with diabetes takes too much insulin they will experience a low blood glucose concentration that can result in unconsciousness.
To ensure the correct dose, blood glucose concentration is monitored using biosensors. By injecting insulin and managing their carbohydrate intake and exercise carefully, people with diabetes can lead normal lives.
Controlling type 2 diabetes
Controlled by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken . In some cases, this may be supplemented by injections of insulin or by the use or drugs that s timulate in sulin production.
Other drugs can slow down the rate at which the body absorbs glucose from the intestine .
Renal pelvis
A funnel-shaped cavity that collects urine into the ureter
Renal artery
Supplies the kidney with blood from the heart via the aorta
Ureter
A tube that carries urine to the bladder
Regulation of the water potential in the blood
The water potential of the blood depends on the concentration of solutes like glucose, proteins, sodium chloride. and other mineral ions as well as the volume of water in the body. A rise in solute concentration lowers its water potential. Caused by:
- too little water being consumed
- much sweating occurring
- large amounts of ions, for example, sodium chloride, being taken in
Structure of muscle fibres in terms of a cell
Sarcolemma- cell surface membrane
Sarcoplasm- cytoplasm
Sarcoplasmic reticulum- ER
What are striated muscles?
Makes up the muscles in the body that are attached to the skeleton
- made up of muscle fibres
What is a muscle fibre?
A muscle fibre is a highly specialised cell-like unit
- organised arrangement of contractile proteins in the sarcoplasm
- surrounded by a sarcolemma
- many nuclei
Sarcolemma of a muscle
Has many deep tube-like projections that fold in from its outer surface known as transverse system tubules or T-tubules which run close to the SR
Sarcoplasmic reticulum of a muscle
Membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR
Sarcoplasm of a muscle
contains mitochondria that
carry out aerobic respiration to generate the ATP required for muscle contraction
contains myofibrils that are bundles of actin and myosin filaments, which slide past each other during muscle contraction
Myofibrils structure
Located in the sarcoplasm, each one is made up of two types of protein filament:
- thick filaments made of myosin
- thin filaments made of actin
Two types of muscle fibres
Fast fibres
Slow fibres
