biology module 5 communication and homeostasis

what is homeostasis

Maintaining a constant internal environment around an optimum despite external change

what does the nervous system consist of

the central nervous system and the peripheral nervous system

what does the nervous system allow us to do

make sense of our surroundings and respond to them and coordinate and regulate body functions

what is a hormone

a chemical substance produced by an endocrine gland and carried by the blood, they transmit information from one part of the organism to another and bring about a change

what is a gland

a group of cells that produces and released one or more substances

what is the importance of homeostasis

• help organisms keep their internal body conditions including temperature, pH, and blood glucose concentration

• a stable core temperature and blood pH are vital for enzyme activity

stomata

• plants carry out homeostasis as they need to maintain a constant internal environment

• stomata control the diffusion of gases in and out of leaves

• regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion, with the need to minimise water loss by transpiration

environmental stimuli causing stomata to open

• increasing light intensity

• low carbon dioxide concentrations in the air spaces between the leaf

environmental stimuli causing stomata to close

• darkness

• high carbon dioxide concentrations in the air spaces within the leaf

• low humidity

• high temperature

• water stress

advantage of stomata being open during the day

leaves gain carbon dioxide for photosynthesis

advantage of stomata being closed during the day

water is retained inside the leaf

disadvantage of stomata being open during the day

leaves lose large amounts of water by transpiration

disadvantage of stomata being closed during the day

supply of carbon dioxide decreases so the rate of photosynthesis decreases

what do negative feedback control loops involve

a receptor to detect a stimulus that is involved with a condition

a coordination system to transfer information between different parts of the body

an effector to carry out a response

what is the outcome of a negative feedback loop

the stimulus is being continuously monitored

steps of a negative feedback loop

1. receptor detects a stimulus that is involved with the condition

2. receptor sends information through the nervous system to central control in the brain or spinal system

3. central control instructs an effector to carry out an action

4. the stimulus is continuously monitored by receptors so that is fluctuates around a set point or ideal value

what is a positive feedback loop

the original stimulus produces a response that causes the factor to deviate even more from the normal range - they enhance the effect of the original stimulus

what is cell signalling

the process by which cells communicate with each other

why is cell signalling important

it allows multicellular organisms to control and coordinate their bodies and to respond to their environments

what are the basic stages of cell signalling

1. a stimulus is received by a receptor cell

2. the stimulus is converted to a signal that can be passed on (this process is transduction)

3. the signal is transmitted to a target cell

4. an appropriate response is made

why are cell membranes important in cell signalling

• transmission of messages in cell signalling requires crossing barriers such as cell surface membranes

• the membrane controls which molecules can move between the internal and external environments of the cell

what is thermoregulation

the control of internal body temperature

what are the two groups that animals are split into on the basis of their primary thermoregulation mechanism

• ectotherm

• endotherm

what are endotherms

animals that possess the physiological mechanisms for the maintenance of internal body temperature

what are ectotherms

animals that rely on behavioural mechanisms to maintain internal body temperature

thermoregulation in endotherms

• detect external temperature via peripheral receptors which detect heat and cold and send impulses to the hypothalamus

vasodilation

• the muscles in the walls of the arterioles relax, causing dilation and allowing more blood to flow into the skin capillaries

• heat is lost to the environment by radiation

• for high body temperature

sweating in endotherms

• sweat secreted by sweat glands in the skin

• cools the skin by evaporation

• heat energy from the body is used to convert the liquid water into water vapour

• less effective in humid environments as there is a reduced water vapour concentration gradient between the skin and air when humidity is high

• for high body temperature

flattening of hairs

• the hair erector muscles in the skin relax, causing hairs to lie flat

• this stops them from forming an insulating layer of air and allows air to circulate over skin, removing heat lost by radiation

• for high body temperature

vasocontriction

• muscles in arterioles contract, causing the arterioles near the skin to constrict and allows less blood to flow through skin capillaries

• instead, the blood is diverted through shunt vessels, which are deeper in the skin and therefore do not lose heat to the environment

• heat loss by radiation at the skin surface is reduced

• for low body temperature

increased metabolic rate

most of the metabolic reactions in the body are exothermic and this provides warmth to the body

in cold environments, the hormone thyroxine increases the basal metabolic rate, increasing heat production in the body

shivering

• when body temperature is low

• muscles contract and relax repeatedly in quick succession

• the metabolic reactions required to power this muscle contraction releases heat energy to warm the blood and raise the core body temperature

erection of hairs

the hair erector muscles in the skin contract, causing hairs to stand on end

this traps an insulating layer of air over the skin's surface, reducing heat loss by radiation

what would ectotherms do to warm up

• seek out the sun or warmer surfaces and bask in these locations as they warm until their body temperature has been increased sufficiently

• huddle together to retain heat that may have been gained from the sun earlier in the day

what might ectotherms do to cool down

• seek shade

• move their bodies into water