Homeostasis and Response Flashcards
The brain
Cerebral cortex - responsible for consciousness, intelligence, memory and language
Medulla - controls unconscious activities
Cerebellum- responsible for muscle coordination
The eye
Sclera - tough supporting wall of the eye
Cornea - transparent outer layer at the front of the eye. It refracts light into the eye
Iris - contains muscles that allow it to control the diameter of the pupil and how much light enters the eye
Lens - focuses light onto the retina
Retina - contains receptor cells sensitive to light intensity and colour
The shape of the lens in controlled by the ciliary muscles and suspensory ligaments
Optic nerve - carries impulses from the receptors on retina to the brain
Focusing light on near objects
The ciliary muscles contract , which slackens the suspensory ligaments
The lens becomes fat (more curved)
This increases the amount by which it refracts light
Focusing on distance objects
The ciliary muscles relax , which allows the suspensory ligaments to pull tight
This makes the lens go thin ( less curved )
So it refracts light by a smaller amount
Vision defects (long sighted)
Hyperopia - occurs when the lens is the wrong shape and doesn’t refract light enough or the eyeball is too short
The image of distance objects are brought behind the retina
To correct this glasses with a convex (curves outwards) lens can be worn as they refract the light rays so they focus on the retina
Vision defects (short sighted )
Myopia - Occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long
The images of distance objects are brought in front of the retina
To correct glasses with a concave lens (curves inwards) so that light can focus on the retina
Response to being too hot
Sweat is produced by sweat glands and evaporates from skin transferring energy
Vasodilation so more blood flows closer to the surface transferring more energy to the environment
Response to being too cold
Hairs stand up to trap an insulating layer of air
No sweat produced
Vasoconstriction to reduce skins blood supply
Shivering because your muscles contract automatically
Endocrine system
Pituitary gland - located near brain. Like a master gland.
Thyroid - located in neck. Produces thyroxine which regulates rate of metabolism, heart rate and temperature
Adrenal gland - located near pancreas. Produces adrenaline.
Pancreas - produces insulin which regulates blood glucose level
Ovaries (female only) - produce oestrogen which is involved in the menstrual cycle
Testes (males only) - produce testosterone which controls puberty and sperm production
Hormones vs nerves
Nerves - fast , act for short time , precise area
Hormones - slower , act for a long time , act in a more general way
Negative feedback loop
Receptor detects a stimulus
- level is too high or low
Coordination centre receives and processes information , then organises a response
Effector produces a response which counteracts the change restoring the optimum level - the level increases or decreases
This is an automatic process
Nervous system
Detects and reacts to stimuli
Receptors - detect stimuli in environment
Sensory neurones - carry information as electrical impulses from receptors to CNS
Relay neurones - connect sensory neurones to motor neurones
Motor neurones - Carry impulses from CNS to effectors
Effectors - all muscles and gland that provide a respond to nervous impulses
Synapses
Connect neurones
The nerve signal is transferred by chemicals
Neurotransmitters are released and they diffuse across the synapse binding to the receptors on the next neurone
The presence of a neurotransmitter causes the production of an electrical impulses in the next neurone
Reflex arc
The neurone in reflex arcs go through the spinal cord or through an unconscious part of the brain
This allows faster responses
Stages of menstrual cycle
Day 1 - menstruation starts - uterus lining breaks down for about four days
Day 4-14 - the uterus lining builds up again
Day 14 - ovulation an egg develops and is released
Day 14-28 - the wall is maintained
Menstrual cycle hormones
FSH - ( Follicle-stimulating hormone) - made in pituitary gland causes egg maturity and stimulates ovaries to produce oestrogen
Oestrogen - produced in ovaries , causes lining of uterus to grow. Stimulates the release of LH and inhibits release of FSH
LH - (Luteinising Hormone) - produced by pituitary gland , stimulates release of egg on day 14 (ovulation)
Progesterone - produced in ovaries , maintains the lining of uterus in second half of cycle. When levels fall the lining breaks down. Inhibits the release of LH and FSH
Hormonal methods of controlling fertility
The pill - contains oestrogen and progesterone (very effective at preventing pregnancy but does not protect against STD)
Progesterone only pill - fewer side effects than the pill but just as effective
Contraceptive patch - contains O and P. Patch stuck to skin and lasts 1 week.
Contraceptive implant - inserted under skin of the arm. Releases progesterone continuously. Lasts for 3 years.
Contraceptive injection - contains P. Lasts for 2 to 3 months
IUD - T shaped device inserted into uterus to kill sperm
Barrier methods of contraception
Stop egg and sperm meeting
Condoms
Diaphragm - plastic cup put on cervix and has to be used with spermicide ( a substance to kill sperm)
Spermicide
Other methods of avoiding pregnancy
Sterilisation - permanent procedure. Cutting or tying tubes
Abstinence - not having intercourse
Plant hormones
Auxin - at tips of shoots and roots. Growth
Gibberellin - seed germination , stem growth and flowering
Ethene - stimulates fruit ripening
Uses of plant hormones
Auxin - killing weeds , growing cuttings with rooting powder , growing cells in tissue culture
Gibberellin - controlling dormancy , inducing flowering , growing larger fruit
Ethene - speeding up the ripening of fruit
Light and shoot growth
More Auxin accumulates on the side in the shade
This makes cells grow (elongate) faster on the shaded side so the shoot bends towards the light
Gravity and shoots and roots
Shoots grow away from gravity and roots grow towards gravity
In a root extra auxin inhibits growth. This meanest cells on top elongate faster and the root bends downwards
