biology c9

what is homeostasis?

the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

• maintains optimum conditions for enzyme action and all cell functions

what does homeostasis control?

• blood glucose concentration

• body temperature

• water

• ion levels

how does homeostasis control ion levels? give examples

makes sure too much water does not go in and out of cells controlled by sweating, passing urine

water levels may change by sweating, food, drink

how does homeostasis control blood glucose concentration? give examples

if too low, the cells will not have enough to use for respiration, if too high glucose may pass out through urine controlled by hormones called insulin and glycagon

e.g consuming good, drink, exercise, starvation

how does body temperature control homeostasis?

enzymes won't work at optimum temperature controlled by respiration, control temperature of blood flow, sweating, shivering

e.g exercise, hot climate, cold climate

how does water levels control homeostasis?

needed for osmosis and chemical reaction, maintains cell structure, too little flaccid, too much turgid controlled by kidneys, reabsorb more or less water

e.g drinking, sweating , dehydration, high salt levels

what is an automatic control system?

automatic control systems- detect changes and respond to them

give an example of a automatic control system (2)

• nervous response

• chemical response (hormones)

what do all control systems involve?

receptors, coordination centres and effectors

what is a stimulus?

a change in the environment of an organism

what is a receptor?

cells which detect stimuli, detect changes in the environment

what is the coordination centre (CNS)?

brain and spinal cord, receive and process information from receptors

what is an effector?

muscles or glands that bring about a response which restore optimum levels

what is a response?

a reaction to a stimulus

what is the peripheral nervous system? (PNS)

sends information to the central nervous system (CNS) from the outside world, and transmits messages from the CNS to muscles and glands in the body

how are eyes a sense receptors?

detect changes in light intensity and colout

how is skin sense receptor?

detect changes in temperature and pressure

how is the tongue a sense receptor?

detect changes in chemicals within food

how is the nose a sense receptor?

detect changes within chemical in air

how are ears sense receptors?

detect changes in sound waves

what is the normal human body temperature and why is it useful?

37°C, gives optimum temperature for enzymes to work

what does the thermoregulatory system do?

• monitors and controls body temperature

• has receptors that monitor the temperature of the blood flowing through the brain

• recieves information (impulses) from temperature receptors in the skin

where is the thermoregulatory system located?

hypothalamus

what is vasolidation?

blood temperature too high causing blood vessels to widen, directing more blood to the surface of the skin

what does vasodilation do?

• more sweat is produced from the sweat glands and evaporates

• both these mechanisms cause a transfer of energy from the skin to the environment

what happens in vasoconstriction?

blood vessels narrow, directing blood away from the surface of the skin

what happens in vasolidation?

• sweating stops

• skeletal muscles uncontrollably contract (shiver) and relaxing quickly, causing more heat to the blood

what does the CNS do?

brain and spinal cord, coordinates the response of effectors which may be contracting muscles or secreting hormones

what is a reflex?

actions that are rapid and automatic biological control systems that link a stimulus in response don't use conscious part of brain

where do reflexes occur?

spinal cord as CNS sends electrical impulses to muscles before the brain can process message

what are conditional reflexes?

an automatic response that has been learned through repetition e.g sneezing

what does the nervous system do?

enables humans to react to their surroundings and coordinate their behaviour

what does the sensory neurone do?

carries nerve impulses towards CNS

what does the relay neurone do?

relays the electrical impulse from the sensory neurone to the appropriate motor neurone, found in spinal cord

what does the motor neurone do?

carries electrical impulses from CNS to effectors

how do neurones communicate?

via synapses (gaps between neurones)

what does myelin sheath do?

insulates the axon and increases the speed of impulse conduction

what does the axon do?

carries impulses away from the cell body, allows electrical impulses to carry through

what do dendrites do?

receive messages from other cells, extends from the cell

what does the brain control?

complex behaviour, made up of billions of interconnected neurones

what is a conscious action?

where the brain makes a considered response, not automatic

what is an involuntary action?

an action completed without conscious thought in response to a stimulus

what is a neurone transmitter?

electrical impulses travel through axon triggering nerve ending of neurone to release a neurone transmitter

what do neurone transmitters do?

diffuse across the synapse until it reaches second neurone, neurotransmitters bind to receptor molecules stimulating thr second neurone to transmit the electrical impulses does the second neurone

what are the regions of the brain?

cerebral cortex, cerebellum, medulla, hypothalamus, pituitary gland

what does the cerebral cortex do?

highly folded, two folded

controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory

what does the cerebellum do?

coordinates movement and balance

what does the medulla do?

controls automatic actions e.g heartbeat and breathing

how can you investigate brain functions?

• studying patient with brain damage

• electrically stimulating different parts of the brain

• using MRI scanning techniques

why is the investigation and treatment of the brain difficult?

• the brain is complex and delicate

• the brain is easily damaged and destroyed

• certain membranes prevent drugs from reaching the brain

• the exact function of each part of the brain is not known

what does the retina do?

contains receptors that are sensitive to brightness and colour of light

what does the optic nerve do?

carries impulses from the retina to the brain

what does the sclera do?

forms a tough outer layer

what does the cornea do?

allows light to enter the eye

what does the iris do?

controls the amount of light entering the pupil by using its muscles to control the diameter of the pupil

what do ciliary muscles and suspensory ligaments do?

change the shape of the lens to focus light onto the retina

what happens when the eye focuses on a near object?

Ciliary muscles contract

• suspensory ligaments loosen

• lens is thicker and more curved

• refracts light rays more strongly, light enters at wider angle

what happens when the eye when it focuses on a distant object?

• ciliary muscles relax

• suspensory muscles are pulled tight

• lens is pulled thin and only slightly refracts light rays, light enters in a parallel line

what happens to the eye in bright light?

the pupil constrics, the circular muscles in the iris contract and the radial muscles relax

what happens to the eye in dim lights?

the pupil dialates, the circular muscles in the iris relax and the radial muscles contract

what is myopia and how is it caused?

short-sightedness, light focuses in front of the retina so images thay land on the retina are blurred and out of focus

• result that the lense is too curved or long eyeball

how can you treat myopia?

use concave lens- spreads out light from distant object before it reaches the eye, lens is thicker and can bring focus to retina

what is hyperopia?

long-sightedness, light focuses behind retina causing light to not be refracted enough

• result that the lens is less curved than normal or short eyeball

how can you treat hyperopia?

convex lens- brings light0 rays together before they reach the eye itself, thinner lens can bring rays of light into perfect focus on the retina

what are new technologies to treat eye problems?

• hard and soft contact lenses

• laser eye surgery to change shape of cornea

• replacement lens in the eye

what is the eye?

a sense organ containing receptors sensitive to light intensity and colour

what is a sense organ?

an organ that contains receptor cells

what is the endocrine system?

composed of glands which secrete hormones directly into the bloodstream

• blood carries hormones to target organ where it produces an effect

what is a hormone?

chemical messengers thay are carried in the blood to target organ where they produce an effect

how does the endocrine system differ to the nervous system?

• produces chemicals which transport in bloodstream compared to nervous system uses neurones to transport electrical signals to effector

• widespread response however nervous system has a localised response only effecting effector