B5 Flashcards
Define homeostasis
The regulations of the internal conditions of an organism to maintain a stable internal environment, in response to internal and external changes
What does homeostasis control (in humans)?
- blood glucose concentration
- body temperature
- water levels
What are the two types of responses that may be involved in automatic control systems?
- nervous responses
- chemical responses
What are the three main components that make all automatic control systems? Give their functions.
- receptors- detect stimuli
- coordination centres(e.g. brain, spinal cord, pancreas)- receive and process information from receptors and organise a response
- effectors(muscles or glands)- bring about responses which counteract the change and restore the optimum level
What is a stimulus?
a change in the environment
What’s a negative feedback cycle?
Where a change is detected and a response is produced to counteract the change and maintain optimum conditions
What is the endocrine system?
It relies on hormones which travel through the entire body via the bloodstream.
It’s typically slower, longer-lasting and more generalised than the nervous system
What does the nervous system allow humans to do?
The nervous system allows humans to react to their surroundings and coordinate their behaviour
How does the nervous system work?
Sends very fast and precise electrical impulses via nerves which allows fast responses
What are the different parts that make up the nervous system?
- Central Nervous System (CNS)- vertebrates=brain and spinal cord, mammals= connected to the body by sensory neurones and motor neurones
- Sensory neurones- the neurones that carry information as electrical impulses from the receptors to the CNS
- Motor neurones- the neurons that carry electrical impulses from the CNS to the effectors.
- Effectors- all the muscles and glands, which respond to nervous impulses
Give examples of some receptors in the human body(e.g. taste, sight, hearing…)
• taste - receptors on the tongue
• sound - receptors in the ears (small hairs on the cochlea)
• sight - the retina (of the eye) is covered in light receptor cells
How do muscles and glands respond in different ways?
• muscles - contract in response to a nervous impulse
• glands - secrete hormones
What is the CNS?
the Central Nervous System is a coordination centre that receives information from the receptors and then coordinates a response, which is carried out by effectors
What is a synapse?
the connection between two neurones
What are neurotransmitters?
the chemicals which diffuse across the synapse and bind to the receptor of the next neurone
What are reflexes?
Reflexes are rapid, automatic responses to certain stimuli; they do not involve the conscious part of the brain
What happens to your eyes when a bright light is shone in them?
your pupils automatically get smaller so that less light gets into the eye- this stops it getting damaged
What happens if you get a shock?
Your body releases the hormones adrenaline automatically
Define the term reflex arc
the passage of information in a reflex (from receptor to effector)
What is the eye?
A sense organ containing receptors sensitive to light intensity and colour
What is the function of the cornea?
The transparent region of the sclera which refracts light as it enters the eye
What is the function of the sclera?
the tough white outer layer of the eye which provides protection
What is the function of the iris?
It has sets of muscles to control the size of the pupil and how much light is able to enter
What is the function of the lens?
Further refracts light to focus it onto the retina
What does the retina contain?
contains the light sensitive receptor cells
What is the function of the optic nerve?
carries impulses from the retina to the brain
Explain the role of the ciliary muscles and suspensory ligaments
Control the shape of the lens to focus light on the retina
What is accommodation?
The process of changing the shape of the lens to focus on near or distant objects
What happens when we focus on a near object?
• the ciliary muscles contract
• the suspensory ligaments loosen
• the lens is then thicker and able to refract light rays strongly
What happens when we focus on a distant object?
• the ciliary muscles relax
• the suspensory ligaments are pulled tight
• the lens is pulled thin and only refracts light rays slightly
Explain the condition myopia
(short-sighted)
• the image is formed in front of the retina because the eye is longer than normal
• to correct this a concave lens ensures the light reaches the focus point on the retina (fovea)
Explain the condition hyperopia
(long-sighted)
• the image is formed behind the retina because the eye is shorter than normal
• A convex lens ensures the light is focused on the focal point on the retina (fovea)
What are the two different types of cells in the retina?
Cones and Rods
What are cones sensitive to?
colour
What are rods sensitive to?
low intensity light (only in black and white)
(they allow us to see in dim light)
What two muscles are in the iris?
• circular
• radial
Explains what happens in dim light (pupil reflex)
- the radial muscles contract
- the circular muscles relax
- the pupil becomes dilated
Explain what happens in bright light (pupil reflex)
- the circular muscles contract
- the radial muscles relax
- the pupil is contracted
What is the brain?
Billions of interconnected neurones that has different regions that carry out different functions
What is the function of the cerebral cortex?
The cerebral cortex is responsible for consciousness, intelligence, memory, language and other high-level functions
What is the function of the cerebellum?
The cerebellum controls balance and muscle co-ordination
What is the function of the medulla?
The medulla controls unconscious activities such as breathing and heart rate
How have neuroscientists been able to map the regions of brain to particular functions?
• studying patients with brain damage
• electrically stimulating different parts of the brain
• scans:
- MRI - uses strong magnetic fields and radio waves to produce detailed images of the brain and spinal cord
- CT - uses x-rays and a computer to create detailed images of the body in order to diagnose damage to tissues, strokes and cancer
- EEG - small sensors [electrodes] are attached all over the scalp to detect electrical signals
Give examples of procedures for brain and nervous system damage
- brain surgery
- brain implant
- chemotherapy or radiotherapy
- monoclonal antibodies
- stem cell therapies
What is body temperature monitored and controlled by?
The thermoregulatory centre (in the brain)
What does the thermoregulatory centre contain?
receptors which are sensitive to the temperature of the blood
What does the skin contain and do?
temperature receptors and sends nervous impulses to the thermoregulatory centre
Describe what happens when body temperature is too high
• blood vessels (capillaries on the surface of the skin) dilate- vasodilation- and this allows heat loss
• sweat is produced from the sweat glands
• Hairs lay flat to the surface of the skin
• These enables the body to lose heat energy to the surroundings more easily
Describe what happens when body temperature is too low
• Blood vessels (capillaries at the skin surface) constrict- vasoconstriction- to reduce blood flow
• hair erector muscles contract which causes the hairs on the skin’s surface to stand and sweating stops
• muscles are activated to contract rapidly (shivering)
What is the ‘master gland’?
The pituitary gland (in the brain) which secretes several hormones into the blood in response to body conditions
What organ monitors and controls blood glucose concentration?
the pancreas
What happens when blood glucose concentration is too high?
the pancreas produces insulin that causes glucose to move from the blood into liver and muscle cells where the excess glucose is converted to glycogen for storage
What happens when blood glucose concentration is too low?
the pancreas produces glucagon which causes the glycogen to be converted back into glucose and released into the blood
What is the difference between type 1 and type 2 diabetes?
- Type 1 diabetes is a disorder in which the pancreas fails to produce enough insulin
- Type 2 diabetes is a disorder where the body no longer responds to the insulin produced by the pancreas; obesity is a risk factor
What is removed via the kidneys in the urine?
excess water, ions and urea
What does the digestion of proteins result in?
excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia, which is toxic and therefore it is immediately converted to urea
How do osmotic changes in the body occur?
- water leaves the body via the lungs during exhalation
- water ions and urea are lost from the skin in sweat
How do the kidneys produce urine?
By filtration of the blood and selective reabsorption of useful substances e.g. glucose, some ions and water
Explain the role of ADH
ADH affects the permeability of the kidney tubules.
- It is released by the pituitary gland when blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules
- this is controlled by negative feedback
What is the main female reproductive hormone?
Oestrogen
What is the main male reproductive hormone?
Testosterone
what is the role of plant hormones?
to coordinate and control growth and responses to light and gravity
What do auxins do in the shoots?
stimulate growth
What do auxins do in the roots?
inhibit growth
What is phototropism?
a response to light
What is geotropism?
A response to gravity
Where do auxins always accumulate after diffusing?
- on a shaded side(e.g. shoots)
- on a lower side(roots)
Explain a shoot’s response to gravity and light
- positive phototropic- grow towards the light
- negatively geotropic- grow away from the ground
Explain a root’s response to gravity and light
- negatively phototropic- grow away from the light
- positively geotropic- grow towards the ground
What are gibberellins important for?
• initiating seed germination/ controlling dormancy - allows multiple crops per year to start growing at the same time
• inducing flowering of fruits - can induce flowering on demand
• growing larger fruits - particularly useful for seedless fruits to ensure they grow as well as their seeded counterparts
What is dormancy?
when the seeds are inactive and do not grow or develop
What does ethene control?
cell division and ripening of fruits
How can ethene be used in the transportation of food?
- Fruit are picked and transported before they are ripe
- they are then exposed to ethene, which allows the fruit to ripen
What are uses of auxin?
- rooting powder
- weed killers
- tissue culture
How are auxins used as weed killers?
Adding auxins to the weed could be used to overstimulate growth, as it disrupts a plant’s growth pattern and causes it to die
How is auxin used as rooting powder?
The auxin in the rooting powder causes replication of natural growth conditions in plants, and encourage roots to form so they can be cut
