Communication and Homeostasis Flashcards
How is communication achieved within a multicellular organism? Please give examples.
Communication between cells is carried out via a process known as cell signalling. Examples of cell signalling are the neuronal and hormonal systems.
What is the importance of communication within a multicellular organism?
Communication is essential for effective coordination of the cells and organs of a multicellular organism in response to changes in the internal and external environment.
Define the term ‘cell signalling’.
Cell signalling is the process by which cells within in a multicellular organism communicates. Cell signalling involves the release of a chemical by one cell which is then detected by another, known as the target cell. This stimulates the desired response from the target cell. The hormone insulin is an example such a chemical transmitter; released by beta cells in the liver.
Define the term ‘negative feedback’.
Negative feedback brings about a reversal of any change in conditions and ensures that the original set of conditions are maintained. Promotes homeostasis.
Define the term ‘positive feedback’.
Positive feedback increases any change detected, promoting variation from the original set of conditions. Usually harmful, for example when the core temperature of an organism drops the enzymes action within organs drop, so less exergonic reactions take place, decreasing temperature further.
Define the term ‘homeostasis’.
The maintenance of a constant internal environment, despite external changes.
How is homeostasis achieved within the body?
Homeostasis is achieved by a process known as negative feedback which involves communication and coordination between many cells and organs within the body. Firstly, a change from normal conditions is detected by a receptor. This receptor then informs the relevant cells of this change via the body’s communication system. These cells are known as the effector and they will act to reverse the change, restoring the internal environment. Homeostasis is achieved.
What is an ectotherm? Give examples.
An ectotherm is an organism that relies on external sources of heat to regulate its body temperature. Examples include bees, locusts and lizards.
What is an endotherm? Give examples.
An endotherm is an organism that can use internal sources of heat, such as the exergonic reactions involved in metabolism within the liver. Examples of endotherms are humans, dogs and birds.
How would an ectotherm maintain its body temperature?
Ectotherms depend heavily on altering their behaviour in order to maintain their body temperature. Often they will bask in the sun on cooler days in order to warm up, which enables more heat to be absorbed. On hot days, lizards will burrow underground which reduces heat absorption by keeping out of the sun. Some ectotherms have physiological adaptations to help exchange heat with the environment. Horned lizards can alter its surface area and hence the amount of heat absorbed by expanding and contracting its rib cage. Locusts increase breathing to allow more evaporation of water.
How do endotherms maintain their body temperature?
Endotherms use their ability to communicate throughout their whole body in order to maintain a fairly constant internal temperature, despite external changes. This is achieved through the peripheral temperature receptors which alert the body to a change in external environment. The hypothalamus within the brain then orchestrates an appropriate response to maintain core body temperature. Examples of these responses include the dilation and constriction of blood capillaries when hot, allowing more blood to flow near the surface and hence more heat being radiated; and when cooler less blood flow to reduce radiation. Other examples include flattening and raising of hairs on skin; sweat glands in skin; rate of metabolism within the liver. Endotherms also alter their behaviour; moving into the shade when too hot; orientating themselves towards the sun when too cold, for example.
What is a sensory receptor? Give examples.
Sensory receptors are specialised cells that can detect changes in our environment. They are energy transducers, converting energy from one form to another. Examples are the rods and cones in our eyes responding to light; olfactory cells in the nose detecting volatile chemicals; tastebuds and the epiglottis detecting soluble chemicals.
Describe the structure and function of sensory neurones.
Sensory neurones carry the action potential from the sensory receptor (e.g rods and cones),to the central nervous system (CNS). It’s structure allows this by having a very long dendron from the sensory receptor to the cell body located just outside of the CNS. A short axon extends the action potential into the CNS. The dendron and axon are encased in a myelin sheath which insulates the cell, concentrating the action potentials and allowing faster transmission. Both sensory and motor neurones have 3Na+/2K+ pumps and gated ion channels which alter the permeability of the plasma membrane, allowing an action potential to be achieved when the appropriate stimulus is sensed.
Describe the structure and function of motor neurones.
Motor neurones carry action potentials from the central nervous system (CNS) out to the effector, usually a muscle or gland. Motor neurones have short dendrites and a large cell body positioned in the CNS. A very long axon extends out of the CNS, carrying the action potential to the effector. The axon is usually insulated by a myelinated sheath to prevent disruption from local electrical activity and focus the action potential. Both sensory and motor neurones have 3Na+/2K+ pumps and gated ion channels which alter the permeability of the plasma membrane, allowing an action potential to be achieved when the appropriate stimulus is sensed.
What is a resting potential and how is it established and maintained?
Neurones are specialised in many ways. One specialisation is the presence of 3Na+/2K+ pumps, which actively transport more sodium ions out of the cell than potassium ions into the cell. Therefore the inside of the cell is more negatively charged with respects to the outside of the cell. A p.d is established across the membrane. The membrane is polarised; a resting potential established.
