Biology Flashcards
what’s an organelle?
tiny structures within cells
what does the nucleus do?
it contains the genetic material that controls the cell’s activities
give two examples of flowering plants.
cereals: maize and herbaceous legumes: peas and beans
what do plants store carbohydrates as?
sucrose or starch
are plants multicellular of single-celled?
multicellular
what is nervous coordination?
being able to respond rapidly to changes in the environment
what do animals store carbohydrates as?
glycogen
are fungi multicellular or single-celled?
some are single-celled and others have a body called a MYCELIUM which is made up of HYPHAE(thread-like structures)
what do the hyphae in fungi contain lots of?
nuclei
what are fungi cell walls made up of?
chitin
what is saprotrophic nutrition?
they secret extracellular enzymes into the area outside their body to dissolve their food, so they can then absorb the nutrients
what do fungi store carbohydrate as?
glycogen
give an example of a single-celled fungus and a multicellular fungus with mycelium and hyphae.
yeast (s.c) and mucor (m.c)
give two examples of protoctists, one plant-cell-like and one animal-cell-like.
chlorella (p.c.l) and amoeba (a.c.l)
how do bacteria feed?
off other organisms, living or dead
what bacteria is used to make yoghurt and how?
LACTOBACILLUS BULGARICUS- turns milk sour which turns into yoghurt. It’s rod-shaped
what’s an example of a spherical-shaped bacteria?
Pneumococcus
what are viruses?
they are particles and can only reproduce inside living cells so they are parasites as they depend on other organisms to live. They infect all types of living organisms. They either have DNA or RNA and they have a protein coat.
give 3 examples of viruses and explain one of them
influenza virus
HIV
tobacco mosaic virus- this makes the leaves of the tobacco plants discoloured by stopping them from producing chloroplasts.
what are pathogens?
organisms that cause disease
give examples of pathogens
protoctist: Plasmodium, which causes malaria
bacterium: Pneumococcus, which causes pneumonia
viruses: Influenza virus, which causes flu and HIV which causes AIDS
What is a catalyst?
a substance which increases the speed of the reaction, without being changed or used up itself in the reaction
what are metabolic reactions?
the useful chemical reactions
enzymes are what and made up of what?
proteins and made up of chains of amino acids
what is a substrate?
a molecule that is changed in the reaction
what is active transport?
the movement of particles against a concentration gradient, from an area of low conc to an area of higher conc, using energy released during respiration.
what do carbohydrates contain elements of?
carbon, hydrogen and oxygen
what do proteins contain atoms of?
carbon, hydrogen, oxygen and nitrogen
what do lipids contain atoms of?
carbon, hydrogen and oxygen
where is vitamin A found and what is its function?
found in liver. helps improve vision and keep your skin and hair healthy
where is vitamin C found and what is its function?
Found in oranges. needed to prevent scurvy
where is vitamin D found and what is its function?
found in eggs, needed for calcium absorption
where is the mineral ion calcium found and what is its function?
found in milk, cheese. needed to make bones and teeth
where is the mineral ion iron found and what is its function?
found in red meat. needed to make haemoglobin for healthy blood.
what enzyme converts starch to maltose?
amylase
what is converted into glucose and by what enzyme?
maltase converts maltose into glucose
what converts proteins into amino acids?
proteases
what does lipase convert lipids into?
glycerol and fatty acids
what does bile do and why?
it neutralises the stomach acid as it is alkaline because enzymes in the small intestine work best in these alkaline conditions; the stomach has hydrochloric acid in. it also emulsifies fats into tiny droplets. this gives a much bigger surface area of fat for the enzyme lipase to work on-which makes its digestion faster.
where is bile produced and stored?
produced in the liver and stored in the gall bladder
why is hydrochloric acid produced in the stomach?
to kill bacteria and to give the right pH for the protease enzyme, pepsin, to work- pH 2
how is food moved through the gut?
by peristalsis. There’s muscular tissue all the way down the alimentary canal which squeezes balls of food (boluses) through the gut otherwise it would get clogged up. This squeezing action is called peristalsis which is waves of circular muscle contractions.
what is digestion?
the break-down of large, insoluble molecules into small, soluble ones
what is absorption?
the moving of molecules through the walls of the intestines into the blood.
what is assimilation?
once digested molecules have been absorbed, they’re moved into body cells which then becomes part of the cells- assimilation. e.g. amino acids are assimilated to make cellular proteins in cells
how is the small intestine adapted to help with absorption of food? (4 things)
1) it’s very long, so there’s time to break down and absorb all the food
2) there’s a big surface area for absorption- the walls are covered in millions of little projections called villi
3) each cell on the surace of a villus has its own microvilli to increase the S.A even more
4) villi have a single permeable layer of surface cells and a very good blood supply for quick absorption
how are leaves adapted for photosynthesis?
1) broad- large surface area exposed to light
2) most chloroplasts are found in the palisade layer so near the top of the leaf where it can get most light
3) the upper epidermis is transparent so that light can pass though it to the palisade layer
4) vasuclar bundles- transport vessels xylem and phloem which deliver nutrients to every part of the leaf and take away excess glucose produced by photosynthesis
5) the waxy cuticle helps to reduce water loss by evaporation
6) lots of little holes called stomata on the lower surface to let CO2 diffuse directly into the leaf
what does chlorophyll do?
it absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. oxygen is always produced
what are the word and symbol equations for photosynthesis?
carbon dioxide + water—> glucose +oxygen
6CO2 + 6H2O—-> C6H1206 + 602
Why is photosynthesis an important process?
it converts light energy to chemical energy, which is stored in the glucose. This chemical energy is released when glucose is broken down during respiration
what is the limiting factor?
something that stops photosynthesis from happening any faster e.g. light intensity, co2 concentration and temperature
how can you show the effect of light intensity on the rate of photosynthesis?
- canadian pondweed
- a source of white light is placed a specific distance from the pondweed
- the pondweed is left to photosynthesise for a set amount of time whilst oxygen will be collected in the delivery tube
- at the end of the experiment, the syringe is used to draw the gas bubble in the tube up along side a ruler and the length of the gas bubble is measured. this is proportional to the volume of O2 produced.
- keep any variables controlled
- repeat the experiment with the light source placed at different distances from the pondweed
how do nitrates help plant growth?
contain nitrogen for making amino acids and proteins which are needed for cell growth. if a plant can’t get enough nitrates it will be stunted and have yellow older leaves
how do phosphates help plant growth?
contain phosphorus for making DNA and cell membranes and they’re needed for respiration and growth. Plants without enough phosphate have poor root growth and purple older leaves
how does potassium help plant growth?
it helps the enzymes needed for photosynthesis and respiration. if not enough, plants have poor flower and fruit growth and discoloured leaves
why is magnesium needed in small amounts to help plant growth?
it is required for making chlorophyll which is needed for photosynthesis. Plants without enough magnesium have yellow leaves
what are a plants 2 main transport systems and what do they transport?
1) XYLEM- transports water and minerals, carries from the roots up the shoot to the leaves in the transpiration stream
2) PHLOEM- transport food e.g. sugars like sucrose and amino acids from where they’re made in the leaves to other parts of the plant
- this movement of food substances around the plant is known as TRANSLOCATION
What are root hair cells and what do they do?
they are microscopic hairs on each branch of a root which stick out into the soil. This gives the plant a big surface area for absorbing water from the soil. Water is taken in by osmosis- there’s usually a higher concentration of water in the soil than there is inside the plant, so the water is drawn into the root hair cell by osmosis.
what is transpiration caused by?
the evaporation and diffusion of water from a plant’s surface. Most transpiration happens at the leaves.
why is water drawn up through the xylem vessels?
to replace the water lost by evaporation from the leaves
what is a transpiration stream?
when water is drawn up at the roots and water is lost through the leaves at a constant rate so there’s a constant transpiration stream of water through the plant
what 4 things affect the transpiration rate
1) LIGHT INTENSITY
2) TEMPERATURE
3) HUMIDITY
4) WIND SPEED
what is respiration?
it’s the process of releasing energy from glucose, which happens constantly in every living cell
what is released by respiration?
chemical energy and heat. Chemical energy is used to create large molecules from smaller ones and contract muscles. The heat energy helps to maintain a steady body temperature.
write the word and symbol equation from aerobic respiration
glucose + oxygen –> carbon dioxide + water
C6H1206 + 602 –> 6CO2 + 6H20
What is anaerobic respiration?
respiration without enough oxygen
when does anaerobic respiration happen in humans?
when you do really vigorous exercise your body can’t supply enough oxygen to your muscles for aerobic respiration- even though your heart rate and breathing rate increase as much as possible. Your muscles have to start respiring anaerobically.
why isn’t anaerobic respiration the best way to convert glucose into energy?
because it releases much less energy than aerobic respiration and the glucose is only partially broken down and lactic acid is produced.
what are the word equations for anaerobic respiration for animals and plants?
ANIMALS
glucose—> Lactic acid (+energy)
PLANTS
glucose—> Ethanol + carbon dioxide (+energy)
how are leaves adapted for efficient gas exchange?
1) leaves are broad so there’s a large surface area for diffusion
2) they’re thin, which means gases only have to travel a short distance to reach the cells where they’re needed
3) there are air spaces inside the leaf that lets gases like co2 and oxygen move easily between cells and increases the surface area for gas exchange
4) the lower surface has stomata where gases like co2 and o2 and diffuse in and out, it also allowed water to escape which is known as transpiration
5) stomata begin to close when it gets dark, photosynthesis can’t happen in the dark so don’t need to be open to let co2 in. water can’t escape stopping the plant drying out
6) stomata also close when supplies of water from the roots start to dry up. this stops the plant from photosynthesising but if they didn’t close they would dry out and die
7) the opening and closing of stomata is controlled by the cells that surround them - guard cells
what is the thorax?
the top part of your body
what are the lungs surrounded by?
the ribcage and the pleural membranes
what happens when you breath in?
1) intercostal muscles and diaphragm contract
2) thorax volume increases
3) this decreases the pressure, drawing air in
what happens when you breath out?
1) intercostal muscles and diaphragm relax
2) thorax volume decreases
3) this increases the pressure, forcing air out
how do alveoli carry out gas exchange in the body?
the blood passing next to the alveoli has just returned to the lungs from rest of body so contains lots of co2 and little o2. o2 diffuses out of the alveolus into blood. co2 diffuses out of the blood into the alveolus to be breathed out
what happens when blood reaches body cells?
oxygen is released from the red blood cells and diffuses into the body cells and co2 diffuses out of the body cells into the blood. It’s then carried back to the lungs
how are alveoli specialised for gas exchange?(5 things)
1) lots of them so enormous surface area for diffusion
2) there’s a moist lining for gases to dissolve in
3) they have very thin walls- one cell thick so the gas doesn’t have far to diffuse
4) they have great blood supply to maintain a high concentration gradient
5) the walls are permeable- so gases can diffuse across easily
why can smoking tobacco cause problems?
1) damages the walls inside the alveoli, reducing the surface area for gas exchange and leading to diseases like EMPHYSEMA
2) the TAR damages the CILIA in your lungs and trachea. These hairs, along with mucus, catch dust and bacteria before they reach the lungs. The cilia also help to keep the trachea clear by sweeping mucus back towards the mouth. When the cilia are damaged, CHEST INFECTIONS are more likely.
3) tar irritates the bronchi and bronchioles, encouraging mucus to be produced which can’t be cleared very well by damaged cilia- causes SMOKER’S COUGH AND CHRONIC BRONCHITIS
4) The carbon monoxide reduces the amount of o2 the blood can carry. To make up for this the heart rate increases- which leads to an increase in blood pressure. High blood pressure damages the artery walls, making the formation of blood clots more likely- increasing the risk of CORONARY HEART DISEASE
5) tobacco smoke contains CARCINOGENS- chemicals that can lead to CANCER
What are the four main components of the blood?
Plasma, platelets, red blood cells and white blood cells
What part is plasma in the blood and what does it carry?
It’s the liquid part of the blood- it’s a pale yellow colour.
It carries:
- red and white blood cells and platelets
- digested food products from gut to body cells
- carbon dioxide from liver to the kidneys
- hormones
- heat energy
What do red blood cells carry?
Oxygen from the lungs to all the cells in the body
How is a red blood cell adapted to it’s function?
1) small and have a biconcave shape to give a large sura e area for absorbing and releasing oxygen
2) they contain haemoglobin, which gives blood it’s colour- it contains a lot of iron. In the lungs haemoglobin reacts with oxygen to become oxyhemoglobin. The reverse reaction happens to release oxygen to the cells
3) they don’t have a nucleus- frees up space for more haemoglobin so can carry more oxygen
What are the two types of white blood cells?
Phagocytes and lymphocytes
How do phagocytes work?
They detect things that are ‘foreign’ to the body (pathogens) then they engulf them and digest them
They are non-specific- they attack anything that’s not meant to be there
How do lymphocytes work?
They produce antibodies.
1) every pathogen has unique molecules on it’s surface called ANTIGENS
2) when lymphocytes come across a foreign antigen, they start to produce proteins called ANTIBODIES- these lock onto the invading pathogens and mark them out for destruction by other white blood cells
3) the antibodies produced are specific to that type of antigen and won’t lock onto any others
4) antibodies are produced rapidly to flow around the body to mark similar pathogens
5) some stay around as memory cells so they can reproduce very fast when the same antigen enters the body a second time- immunity
What are the 3 blood vessels Nd what are their function?
1) arteries- carry blood away from the heart
2) veins- carry blood to the heart
3) capillaries- involved in the exchange of materials at the tissues
How are arteries adapted for their function?
- walls are strong and elastic as heart pumps blood out at high pressure
- the walks are thick compared to the size of the lumen- they contain thick layers of muscle to make them strong
- LARGEST ARTERY IS THE AORTA
How are capillaries adapted for their function?
- they are really tiny so can carry blood really close to every cell in the body to exchange substances with them
- they have permeable walls so substances can diffuse in and out
- their walls are only one cell thick which increases the rate if diffusion by decreasing the distance over which it happens
What do capillaries carry?
They supple food and oxygen and take away wastes like carbon dioxide
How are veins adapted to their function?
- walls are thin as blood is at lower pressure than in arteries
- they have a big lumen to help blood flow despite the lower pressure
- they have valves to keep the blood flowing in the right direction
THE LARGEST VEIN IS THE VENA CAVA
How does exercise increase heart rate?
When you exercise, your muscles need more energy so you respite more
You need more oxygen into the cells to remove the carbon dioxide. Blood has to flow faster so heart rate increases
- exercise increases the amount of co2 in the blood
- high levels of blood co2 are detected by RECEPTORS in the AORTA and CAROTID ARTERY
- these receptors SEND SIGNALS to the BRAIN
- the brain Sends signals to the heart causing it to contract more frequently and with more force
How does the hormonal system help control heart rate?
1) when an organism is threatened the adrenal glands release adrenaline
2) adrenaline binds to specific receptors in the heart. This causes the cardiac muscle to contract more frequently and with force, so heart rate increases and the heart pumps more blood.
3) this increases oxygen supply to the tissues, getting the body ready for action
What is pulmonary to do with?
The lungs
What’s hepatic to do with?
The liver
What’s renal to do with?
The kidneys
What are the 3 main roles if the kidneys?
1) removal if urea from the blood. Urea is produced in the liver from excess amino acids
2) adjustment of salt water levels in the blood
3) adjustment of water content of the blood
How does ultrafiltration work?
1) blood from the renal artery flows through the glomerulus
2) a high pressure is built up which squeezes water, urea, salts and glucose out of the blood and into the BOWMAN’s CAPSULE
3) the membranes between the blood vessels in the glomerulus and the BOWMAN’s capsule act like filters, so big molecules like PROTEINS and BLOOD CELLS are not squeezed out. They stay in the blood.
What is a glomerulus?
A bundle of capillaries at the start of the nephron
What is the filtered liquid in the BOWMAN’s capsule known as?
The glomerular filtrate
How does reabsorption work?
The filtrate flows along the nephron and useful substances are selectively reabsorbed back into the blood:
1) all the glucose is reabsorbed from the PROXIMAL CONVOLUTED TUBULE. This involves active transport against the concentration gradient
2) SUFFICIENT SALT is reabsorbed. Excess alt isn’t
3) SUFFICIENT WATER is reabsorbed from the COLLECTING DUCT into the blood stream
What is osmoregulation?
Constantly balancing the water coming in against the water going out of the body
How does ADH help control water content?
ADH makes the nephrons more permeable so water is reabsorbed back into the blood
2- the brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed
3- the whole process of osmoregulation is controlled by negative feedback so if water content gets too high or too low a mechanism will be triggered that brings it back to normal
What happens when brain detects water loss?
Pituitary gland releases more ADH which makes kidney reabsorb more water
What happens when the brain detects water gain?
Pituitary gland releases less ADH which means kidney reabsorbs less water
How do animals increase their chances of survival?
By responding to changes in their external environment
What do receptors do?
Detect stimuli- the receptors in SENSE ORGANS are groups of cells that detect external stimuli
Give two examples or receptors in the eye
Rod and cone cells that detect changes in light
What do effectors do?
They are cells that bring about a response to stimuli they include muscle cells and cells in glands
What two ways do effectors respond?
muscle cells contract
Glands secrete hormones
How do receptors communicate?
Via the nervous system and the hormonal system
How does the central nervous system coordinate information?
Consists if the brain and spinal chord only
1- when receptors in a sense organ detect a stimulus, they send electrical impulses along sensory neurones to the CNS
2- the CNS then sends electrical impulses to an effector along a motor neurone. The effector then responds accordingly
What’s the job of the CNS?
To coordinate a response- which always need a stimulus, a receptor and an effector
Why are the responses in the CNS very rapid?
Because the neurones transmit information using high speed electrical impulses
What are reflexes?
Automatic responses to certain stimuli
How does a reflex work?
1) when a stimulus is detected by receptors, and impulse is sent along a sensory neurone to the CNS
2) in the CNS the sensory neurone passes on the message to a relay neurone. The gap between the neurones is called a synapse. Messages are passed across synapses using chemicals
3) relay neurones relay the impulse to a motor neurone
4) the impulse then travels long the motor neurone to the effector
5) the effector contracts or releases a hormone
What are the 7 parts of a reflex?
1- stimulus 2- receptor 3- sensory neurone 4- relay neurone 5- motor neurone 6- effector 7- response
What does the conjunctiva do?
It lubricates and protects the surface of the eye
What does the cornea do?
It refracts light into the eye. The cornea is transparent and has no blood vessels to supply it with oxygen, so oxygen diffuses in from the outer surface
What does the iris do?
It controls the diameter of the pupil and therefore how much light enters the eye
What does the lens do?
It focuses the light onto the retina
What is the retina?
The light- sensitive part which is covered in light receptors called rods and cones
What are rods sensitive to?
More sensitive in dim light but can’t sense colour
What are cones sensitive to?
Colours but aren’t so good in dim light. They are found all over the retina but most at the FOVEA
What does the optic nerve do?
Is carries impulses from the receptors to the brain
What are hormones?
Chemicals released directly into the blood- chemical messengers. They’re carries bj the blood plasma to other parts of the body, but only affect particular cells called target cells in particular places. They control things in organs and cells that need constant adjustment.
Where is ADH made and what is it’s role?
Pituitary gland and controls water content
What are the effects of ADH?
Increases the permeability of the kidney tubules
Where is adrenaline produced and what’s it’s role?
Adrenal glands on top of the kidneys and it readies the body for a ‘fight or flight’ response
What are the effects of adrenaline?
Increases heart rate, blood flow to muscles and blood sugar level
Where is insulin produced and what’s it’s role?
Pancreas and helps control the blood sugar level
What are the effects or insulin?
Stimulates the liver to turn glucose into glycogen for storage
Where is testosterone produced, what’s it’s role and effects?
Testes, main male sex hormone, promotes males secondary sexual characteristics
Where is progesterone produced, role and effects?
Ovaries, supports pregnancy, maintains the lining of the uterus
Where is oestrogen produced, role, and effects?
Ovaries, main female sex hormone and controls menstrual cycle and promotes secondary sexual characteristics- widening if the hips
What are the differences between nerves and hormones?
Nerves are fast messages and hormones are slower
Nerves act for short time and hormones act for a long time
Nerves act on a very precise area and hormones act in a more general way
What’s homeostasis?
The maintenance of a constant internal environment
How is water lost from the body?
1/ through the skin as sweat
2- via the lungs in breath
3- via the kidneys as urine
How do smaller organisms cool down?
They have bigger surface area to volume ratios so gain or lose heat faster because more area for the heat to transfer across. Small organisms can lose heat in hot climates and reduces the chance if them overheating.
Why do smaller surface area to volume ratios gain heat or lose heat more slowly?
Because less area for the heat to transfer across
how do plants maximise light absorption for photosynthesis?
they sense the direction of light and grow towards it
how do plant’s roots grow in the right direction?
they sense gravity
how do climbing plants reach the sunlight?
they have a sense of touch so find things to climb towards the sunlight
what does white clover produce to stop cattle eating it?
produces toxins
what do carrots produce at low temperatures?
antifreeze proteins that bind to ice crystals and lower the temperature that water freezes at, stopping more ice crystals from growing
what are auxins?
plant hormones which control growth at the tips of shoots and roots. they move through the plant in solution
where are auxins produced?
in the tips and diffuse backwards to stimulate the cell elongation process which occurs in the cells just behind the tips
what does auxins do to the shoot and root?
promotes growth in the shoot and inhibits growth in the root
what are response to light called?
phototropism
what are responses to gravity called?
geotropism
what’s negative tropism?
growing away from the stimulus
what’s positive tropism?
growing towards the stimulus
what happens when a shoot tip is exposed to light?
positively phototropic, so it accumulates more auxin on the side that’s in the shade which makes the cells grow faster on the shaded side so the shoot bends towards the light
what are negatively geotropic?
shoots- when growing sideways, gravity produces unequal distribution of auxin in the tip, with more on lower side so it grows fast, bending towards the light
what are roots in tropism?
positively geotropic- root the grows sideways will have more auxin on its lower side as auxin inhibits growth in roots so the cells on top elongate faster so the root bends downwards
how does pH affect enzymes?
if it’s too high or too low, the p\h interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme
what is the optimum temp for enzymes?
often neutral- pH 7 but not always:
pepsin an enzyme that breaks down proteins in the stomach works best at pH 2 so well-suited to the acidic conditions there
when is a plant said to be turgid?
when a plant is well watered, all its cells will draw water in by osmosis and become plump and swollen
what’s turgor pressure?
when the contents of the cell push against the cell wall which helps support the plant tissues
when is a plant said to be flaccid?
when there’s no water in the soil, a plant starts to wilt because the cells start to lose water and so lose their turgor pressure
-the plant doesn’t totally lose its shape though, because the inelastic cell wall keeps things in position
what are the 6 essential nutrients you need for a balanced diet?
1- carbohydrates 2- proteins 3- lipids 4- vitamins 5- minerals 6- water
how do energy requirements vary in different people?
activity level- active people need more energy than those who don’t do any exercise
age- children and teenagers need more energy than older people- they need energy to grow and they’re generally more active
pregnancy- pregnant women need more energy than other women as they’ve got to provide the energy their babies need to develop
what are phloem tubes used for?
transporting sugars like sucrose and amino acids from where they’re made in the leaves to other parts of the plant
this movement of food substances around the plant is known as translocation
what does the net exchange of gases depend on?
light intensity
how does net gas exchange work?
1- photosynthesis only happens during the day when there’s light available.but plants respire all the time to get the energy they need to live
2- during the day when light intensity is high- plants make more oxygen by photosynthesis than they use in respiration. So in daylight, they release oxygen. They also use up more CO2 than they produce, so they take in CO2
3- at night though plants only respire- there’s not enough ligh for photosynthesis. This means they take in oxygen and release CO2
what are platelets?
small fragments of cells that help blood clot
how do platelets work?
1) when you damage a blood vessel, platelets clump together to ‘plug’ the damaged area
2) this is known as blood clotting. Blood clots stop you losing too much blood and prevent microorganisms from entering the wound
3) in a clot, platelets are held together by a mesh of a protein called fibrin- this process also needs other proteins called clotting factors to work properly
How do vaccinations work?
1) when you’re infected with a new pathogen it can take your lymphocytes a while to produce the antibodies to deal with it, in that time you can get very ill or die
2) to avoid this you can be vaccinated against some diseases like polio or measles
3) vaccination involves injecting dead or inactive pathogens into the body. These carry antigens, so even though they’re harmless they still trigger an immune response- your lymphocytes produce antibodies to attack them
4) some of these lymphocytes will remain in the blood as memory cells so of live pathogens of the same type ever appear, the antibodies to kill them will be produced much faster and on greater numbers
Why is there an iris reflex?
Because very bright light can damage the retina- so you have a reflex to protect it
In bright light how does the iris adjust?
bright light triggers a reflex that makes the pupil smaller, allowing less light in. Light receptors detect the bright light and send a message along a sensory neurone to the brain. The message then travels along a relay neurone to a motor neurone, which tells the CIRCULAR MUSCLES to contract, making the pupil smaller
In dim light, how does the iris adjust?
Light receptors detect the dim light and send a message along a sensory neurone to the brain. The message then travels along a relay neurone to a motor neurone, which tells RADIAL MUSCLES to contract, which makes the pupil bigger
What is accommodation?
The eye focuses light by changing the shape of the lens
How does the lens focus on distant objects?
1- the ciliary muscles relax, which allows the suspensory ligaments to pull tight
2- this makes the lens go thin( less curved)
How do you focus On Near objects?
1) the ciliary muscle contract, which slackens the suspensory ligaments
2) the lens becomes fat (more curved)
What happens to the lens as you get older?
It loses flexibility so it can’t easily spring back to a round shape. This means light can’t be focused well for near viewing, so old pekoe often have reading glasses
How do long sighted people see?
Long-sighted people are unable to focus on near objects. This occurs when the cornea or lens doesn’t bend the light enough or the eyeball is too short. The images of near objects are brought into focus behind the retina
How do short-sighted people see?
Short-sighted people are unable to focus on distant objects. This occurs when the cornea or lens bends the light too much or the eyeball is too long. The images if distant objects are brought into focus in front of the retina
How does your body maintain a constant temperature when you’re too hot?
1) lots of sweat is produced- when it evaporates it transfers heat from you to the environment, cooling you down
2) blood vessels close to the surface of the skin widen- this is called VASODILATION. It allows more blood to flow near the surface, so it can radiate more heat into the surroundings
3) hairs lie flat
How does your body maintain a constant temperature when you’re too cold?
1) very little sweat is produced
2) blood vessels near the surface constrict - VASOCONSTRICTION so that less heat can be transferred from the blood to the surroundings
3) you shiver, and the movement generates heat in the muscles. Exercise does the same
4) hairs stand on end to trap an insulating layer of air which helps keep you warm
