BIOLOGY T2 Flashcards
1
Q
Describe the structure of ATP.
A
ATP (or Adenosine triphosphate) is made up of a nucleotide consisting of three phosphate groups, one ribose sugar, and one adenine ring (nitrogenous base).
2
Q
What are the different uses of energy in the human body?
A
Uses of energy:
- muscle contraction
- protein synthesis
- cell division
- active transport
- growth
- the passage of nerve impulses
- maintenance of a constant body temperature
3
Q
Define aerobic respiration.
A
Chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
4
Q
What is the word equation for aerobic respiration?
A
Glucose + Oxygen > Carbon Dioxide + Water + Energy
5
Q
What is the balanced chemical equation for aerobic respiration?
A
C6H12O6 + 6O2 > 6CO2 + 6H2O
6
Q
Define anaerobic respiration.
A
Chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
7
Q
What is the difference between aerobic respiration and anaerobic respiration?
A
Anaerobic breaks down nutrient molecules to release energy without using oxygen. This means that it releases much less energy per glucose molecule compared to aerobic respiration.
8
Q
What is the word equation for anaerobic respiration in yeast?
A
Glucose > Ethanol + Carbon Dioxide
9
Q
What is the balanced chemical equation for anaerobic respiration in yeast?
A
C6H12O6 > 2C2H5OH + 2CO2
10
Q
What is the word equation for anaerobic respiration in humans?
A
Glucose > Lactic Acid + Energy
11
Q
What is the balanced chemical equation for anaerobic respiration in humans?
A
C6H12O6 > 2C3H6O3
12
Q
When and why does anaerobic respiration occur?
A
Anaerobic respiration occurs during strenuous exercise when not enough oxygen can reach your muscle cells and so normal aerobic respiration is replaced by anaerobic respiration because this does not require oxygen to release energy.
13
Q
What is the problem with anaerobic respiration?
A
Lactic acid is produced as a waste product during anaerobic respiration. It builds up in the muscles which causes pain and tiredness and can lead to cramp. Lactic acid is then removed when aerobic respiration recommences.
14
Q
How is lactic acid removed?
A
The lactic acid is transported to the liver through the blood where it is either oxidised into carbon dioxide and water or is converted into glucose and then glycogen.
15
Q
What is oxygen debt?
A
During strenuous exercise, lactic acid builds up due to anaerobic respiration and so after the exercise has stopped, a high level of oxygen consumption is needed to oxidise the excess lactic acid. This is known as oxygen debt and is why a person continues to breathe quickly and deeply for a time after exercise.
16
Q
What is the xylem and its function?
A
The xylem transports water and mineral salts from the roots up to other parts of the plant through a process known as transpiration stream.
17
Q
What is the phloem and its function?
A
The phloem transports sucrose and amino acids from the leaves and other parts of the plant, through the process of translocation.
18
Q
Relate the structure of the xylem to its function.
A
Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels (tubes).
Mature xylem vessels:
- Contain no cytoplasm
- Are impermeable to water
- Have tough walls containing a woody material called lignin.
19
Q
Relate the structure of the phloem to its function.
A
Phloem consists of living cells arranged end to end. Unlike xylem, phloem vessels contain cytoplasm, and this goes through the holes in the sieve plates from one cell to the next.
20
Q
Where are the xylem and phloem located in the root?
A
Xylem is at the center of the plant root or vein whereas phloem are at the outside. Both the xylem and phloem are combined together in the vascular bundle.
21
Q
Describe the process of transpiration.
A
Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by the diffusion of water vapour through the stomata. This creates a water shortage in the leaf (lower water potential than the rest of the plant) which draws up more water from the rest of the plant, which in turn draws more water up from the roots.
Transpiration has two benefits:
- It transports minerals from the soil
- It cools the plant
22
Q
Describe the process of translocation.
A
Translocation is the movement of sucrose and amino acids in the phloem, from regions of production (the ‘source’) to regions of storage or to regions where they are used in respiration or growth (the ‘sink’). Food is made in the leaves by photosynthesis. The soluble products are sugars, amino acids and fatty acids. Phloem may contain up to 25% dissolved solids. These are carried to all parts of the plant in solution in the phloem.
23
Q
Describe the factors which affect transpiration.
A
The rate of transpiration is affected by 4 things:
1. Amount of light
2. Temperature
3. Amount of air movement (wind)
4. Humidity of the surrounding air
So the rate of transpiration is greatest on hot, dry, windy sunny days i.e. weather that dries clothes fast.
This constant stream of water has the advantage of transporting vital minerals from the soil into the roots and all around the plant (nitrates, magnesium etc.)
24
Q
What is diffusion?
A
The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
The steeper the concentration gradient, the faster diffusion occurs.
25
What is osmosis?
The movement of water molecules through a partially permeable membrane, from a solution of high water potential, to a solution of lower water potential.
26
What is the function of a partially permeable membrane?
It allows some substances to pass through but not others.
| It has unequal concentration of ions on both sides of the membrane.
27
What is water potential?
Water potential is the measure of the tendency of water to move from one place to another.
Dilute solution = high water potential
Concentrated solution = low water potential
Same concentration = equal water potential.
Hypotonic - higher water potential
Hypertonic - lower water potential
(both in comparison to eachother).
Isotonic - equal potential.
28
Describe how water is taken up into the plant through the soil.
Water is absorbed by the root hairs which are long and thin. They have a large surface area through which water and minerals can enter.
Water passes into the root hairs by osmosis as the cell sap has lower water potential than the surrounding soil. The water eventually reaches the xylem and is carried up the xylem to the leaves.
29
What is the circulatory system and its function?
It is made up of a pump (heart) and blood vessels with valves so blood only flows one way.
It transports nutrients, oxygen, and waste products.
Different organisms have different types of circulatory system (single and double circulation).
30
Describe single circulation in fish.
It is a very simple circulatory system. The blood only goes through the heart once each loop and it is a low pressure system which makes it inefficient.
31
Describe double circulation in mammals.
The blood passes through the heart twice for each loop. It has higher pressure than a single circulatory system and this higher pressure means higher blood flow rate to the body tissues. It also prevents the mixing of oxygenated and deoxygenated blood.
32
Explain the advantages of a double circulatory system.
There is higher pressure in the double circulatory system and so there is a higher blood flow rate which makes it much more efficient than the low pressure single circulatory system.
33
Describe coronary heart disease.
Over time a fatty substance called atheroma is deposited on the inside of the arteries.
The surface of the atheroma can become rough which causes fibrinogen in the plasma to stick to it and build up.
This can build up to form a thrombus (blood clot) which may get large enough to block the artery and restrict blood flow,
If the blood clot forms in the coronary artery it will starve the heart muscles of oxygenated blood leading to a severe heart attack.
34
Describe the structure and function of the arteries.
Arteries carry oxygenated blood (except the pulmonary artery).
They have thicker, muscular walls with elastic fibres and fibrous tissue to carry blood at high pressure.
They have a narrow lumen (centre) but the elastic capabilities allow it to expand when blood is pumped through it.
They divide into smaller vessels called arterioles.
35
Describe the structure and function of the veins.
Veins carry deoxygenated blood (except the pulmonary vein), this blood is also higher in CO2.
They have thin walls with little or no elastic tissue and predominantly fibrous tissue to carry blood at low/constant pressure.
They have large/wide lumen to reduce resistance to blood flow.
Valves are present to prevent the backflow of blood.
They connect to smaller vessels called venules.
36
Describe the structure and function of the capillaries.
They are the smallest blood vessels.
They are permeable with one cell thick walls to allow diffusion of materials between the capillary and surrounding tissue.
The lumen is one red blood cell wide so the cells pass through slowly to optimise diffusion to and from them.
The blood is still under pressure.
Plasma is able to pass through the walls but not blood cells (partially permeable).
No cell in the body is far from a capillary.
37
Describe the structure of blood vessels.
The blood vessels are made up of layers:
- Tunica externa: The external layer of fibrous connective tissue (collagen) that anchors the blood vessel to nearby structures.
- Tunica media: The middle layer of blood vessels composed of smooth muscle and elastic tissue.
- Tunica intima/Endothelium: The internal layer that lines the blood vessel. Consists of primarily epithelial cells.
38
Describe the movement of blood through the heart.
Blood moves into the right atrium from the vena cava and then into the right ventricle through the tricuspid valve.
Blood moves out of the right ventricle and into the pulmonary artery through the pulmonary valve.
Blood returns from the lungs through the pulmonary vein and enters the left atrium. It then moves through the bicuspid (mitral) valve into the left ventricle.
The blood is then pumped out of the left ventricle through the aortic valve and then moves out to the head and body through the aorta.
39
What are the two types of valve in the heart?
Atrioventricular valves:
Tricuspid valve - between right atrium and ventricle.
Bicuspid valve (or mitral valve) - between left atrium and ventricle.
Semi-lunar valves:
Pulmonary valve - between the right ventricle and the pulmonary artery.
Aortic valve - between the left ventricle and the aorta.
40
What are the different types of blood?
- Red blood cells.
- White blood cells.
- Platelets.
- Plasma.
41
Describe the structure and function of red blood cells.
Red blood cells:
- Are disk shaped (biconcave).
- Have no nucleus.
- Are made in the bone marrow.
- Transport oxygen around the body. Haemoglobin combines with oxygen to form oxyhaemoglobin.
42
What are the different types of white blood cells?
There are several different kinds, all play a different role in the immune system.
The most common are phagocytes and lymphocytes.
Lymphocytes produce antibodies.
Phagocytes engulf and destroy pathogens through phagocytosis.
43
Describe the structure and function of platelets.
Platelets:
- Assist in clotting the blood and stopping bleeding at the site of a wound.
- Are produced in the bone marrow.
44
Describe the structure and function of plasma.
Plasma is the liquid part of the blood.
It contains many dissolved substances such as ions, amino acids, lipids, glucose, hormones etc.
Carbon dioxide, urea and other waste products are also dissolved into the blood plasma.
45
What are the apoplastic and symplastic pathways?
The apoplast and symplast are two separate pathways in plants which transport water and ions.
The apoplastic pathway is where water and minerals flow through the cell walls of the plant cells.
The symplastic pathway is where water moves through the plasmodesmata through the network of cytoplasm between each cell.
46
What is the casparian strip?
The casparian strip is a band of corky, waterproof tissue that is found on the walls of the endodermis in root cells. The strip prevents water from entering the pericycle except through the cytoplasm, just blocking the apoplastic pathway in the cell wall and forcing it into the cytoplasm. This is important in maintaining root pressure.
47
What are arterioles and shunt vessels?
Arterioles are small arteries that have branched off from larger arteries.
They can vasoconstrict and vasodilate to control the distribution of blood around the body.
Shunt vessels are the vessels that blood is diverted through if arterioles are to vasoconstrict.
48
Describe the process of blood clotting.
Clotting is a mechanism to prevent loss of blood and entry of pathogens.
The process begins whenever damage to the endothelium of blood vessels occurs.
Platelets are activated and trigger a number of activation factors to stimulate the conversion of fibrinogen to fibrin.
Fibrinogen is a soluble protein, but fibrin is not. Fibrin forms a mesh around a wound which gathers more platelets and blood cells, causing a clot.
49
What are the activation factors for blood clotting?
Prothrombin.
Vitamin K.
Calcium ions.
50
What is the lymphatic system?
It is a system of vessels that transport plasma fluids around the body and back to the heart.
Fluid comes from body tissues, forced out of capillaries at high pressure.
Fluid also comes from the small intestine, especially the fats and lipids absorbed from digestion.
Lymphatic vessels contain valves that ensure one way travel of fluid.
51
What is the function of the lymphatic system?
Pockets of fluid called lymph nodes are found throughout the lymphatic system.
These contain lymphocytes and other white blood cells.
Bacteria can be carried in the lymph fluid to these nodes where they can be ingested by the white blood cells.
The lymphatic system is therefore an important part of the body's defence system against infection.
52
What is the difference between lymph, tissue fluid and blood?
Lymph fluid is plasma containing fats and lipids with white blood cells.
Blood is plasma with red blood cells, white blood cells, platelets, and many hormones (proteins).
Tissue fluids are not found in vessels and don't have the same concentration of white blood cells as lymph fluid.
53
What is diastole?
The relaxation and filling of heart chambers with blood.
54
What is systole?
The contraction and ejection of blood into the aorta and pulmonary vein.
55
Describe the cardiac cycle.
The cardiac cycle is made up of diastole and systole.
During diastole:
- The atria start filling from blood from the major veins (both valves closed).
- Increased pressure causes the ventricles to also start filling (atrio-ventricular valves open).
During Systole:
- The atria then contract and blood is pumped into the ventricles (atrio-ventricular valves open).
- The ventricles then contract and blood is ejected out through the major arteries (atrio-ventricular valves close, semi-lunar valves open).
56
What controls the cardiac cycle?
The cardiac cycle is controlled by the sinoatrial node.
The sinoatrial node is a group of pacemaker cells in the top right corner of the heart.
A heartbeat is initiated by the sinoatrial node generated by an electrical impulse that is passed throughout the cardiac muscle tissue and causes it to contract.
57
What are some ways of treating coronary heart disease?
A patient who suffers from coronary heart disease can be given a regular dose of aspirin. Aspirin prevents the formation of blood clots in the arteries.
Angioplasty can also be used along with a stent.
And in severe cases, by-pass surgery can be performed.
58
Describe the method of angioplasty in treating coronary heart disease.
Angioplasty involves the insertion of a long thin tube called a catheter into the blocked or narrowed blood vessel. A wire attached to a deflated balloon is then fed through the catheter. Once in place, the balloon is inflated to widen the artery wall which frees the blockage.
59
Describe the method of a stent in treating coronary heart disease.
In some cases, a stent is used along with angioplasty in unblocking an artery. Once angioplasty has been performed, a wire-mesh tube called a stent is applied which can be expanded and left in place. It acts as a scaffolding, keeping the blood vessel open and maintaining the free flow of blood.
Some stents are designed to slowly release chemicals which further prevent the blockage of the artery.
60
Describe the method of by-pass surgery in treating coronary heart disease.
In by-pass surgery, the surgeon removes a section of blood vessel from a different party of the patient's body, such as the leg. The blood vessel is then attached around the blocked region of artery to by-pass it, allowing blood to pass freely. This is a major, invasive operation as it involves open heart surgery.
61
Why are humans well-adapted to gas exchange?
Our gas exchange surface has a large surface area (many alveoli).
Gas exchange surface is very thin (two cells thick), with a high concentration gradient between gases.
Gas exchange surface has a good blood supply of capillaries.
Gas exchange surface has good ventilation with air (alveoli are 'air sacks').
Gas exchange surface is moist to dissolve gases.
62
What is the function of the epiglottis?
It is a flap of skin that closes over the top of the trachea when we swallow to prevent food from travelling down the trachea.
63
What is the function of the larynx?
It is a.k.a the voice box. Contains two vocal cords that vibrate at a range of frequencies when air passes over them to produce sound.
64
What is the function of the trachea?
It is a.k.a the wind pipe. The passage through which the air passes down the throat.
The trachea is lined with rings of cartilage so it doesn't collapse with changing air pressure.
65
What is the function of the bronchus?
The two main branches of the trachea that lead to the left and right lung.
66
What is the function of the bronchiole?
The bronchioles are the smaller branches off the two main bronchi.
67
What is the function of the alveoli?
They are tiny air sacs at the end of the bronchioles where gas exchange occurs.
The alveoli walls are only one cell thick, and they are embedded in a network of capillaries.
68
What is the process when breathing in?
The diaphragm contracts and pulls down.
The external intercostal (rib) muscles contract, pulling the ribs outwards.
The volume of the thoracic cavity increases.
The pressure in the cavity decreases.
Air rushes in to equalise the pressure.
69
What is the process when breathing out?
Usually a passive process where no muscles contract.
The diaphragm relaxes and rises up.
The internal intercostal muscles contract, pulling the ribs downwards and inwards,
The volume of the thoracic cavity decreases.
The pressure in the cavity increases.
Air rushes out to equalise the pressure.
70
What is the process of mucociliary clearance?
The goblet cells secrete mucus to trap foreign particles and pathogens.
Ciliated (hair-like) cells sweep this mucus up the trachea and into the back of the throat so it can be swallowed and destroyed in the stomach.
71
Describe the process of excretion.
Excretion is the removal of toxic materials, the waste products of metabolism (chemical reactions in the cell including respiration), and substances in excess of requirements
- e.g. urea, CO2, salts.
- e.g. urination and gas exchange of CO2 in the lungs
Sweating is an example of secretion, where the substance has a specific task.
NB: Passing of undigested materials is NOT excretion as they are not products of metabolism - this is egestion.
72
What is the function of the kidneys?
Kidneys are important for maintaining the water and ion balance in the body - this is part of maintaining a constant internal environment (homeostasis).
They are part of the excretory system.
They act like filters to "clean" the blood.
The main roles of the kidney:
- Removal of urea from the blood.
- Adjustment of ions (salts) in the blood.
- Adjustment of water in the blood.
73
What is the function of the ureter?
It transports urine from the kidneys to the bladder.
74
What is the function of the urethra?
It facilitates the removal of urine from the body.
75
What is the function of the bladder?
It collects the urine prior to urination.
76
Describe the removal of urea.
Urea is produced in the liver.
Proteins cannot be stored by the body so excess amino acids are broken down by the liver - this is called deamination.
The waste product is urea (the nitrogen containing part) which is passed into the blood to be filtered out by the kidneys. Urea is also lost partly in sweat (the sugar residue is used in respiration to release energy).
Urea is poisonous and must be excreted.
77
Describe how the ion content is adjusted.
Ions such as sodium are taken into the body in food, then absorbed into the blood.
Excess ions are removed by the kidneys.
Some ions are also lost in sweat (which tastes salty).
The important thing to remember is that the balance of ions is maintained by the kidneys.
78
What happens when there is too much water in the body?
1. The hypothalamus detects too much water in the blood.
2. The pituitary gland releases less ADH.
3. Kidneys reduce blood water level.
4. So more water reaches the bladder (the urine is more dilute).
5. Blood water level returns to normal.
79
What happens when there is too little water in the body?
1. The hypothalamus detects too little water in the blood.
2. The pituitary gland releases more ADH.
3. Kidneys maintain blood water level.
4. So less water reaches the bladder (the urine is more concentrated).
5. Blood water level remains the same.
80
Describe the process of ultrafiltration.
The glomerulus is a knot of blood vessels surrounded by the renal capsule.
High blood pressure in the glomerulus forces water, ions, urea, and glucose out of the blood (proteins and red blood cells are too large).
81
Describe the process of selective reabsorption.
In the renal tubule:
- All glucose and sufficient ions/salts are actively reabsorbed.
- Water is also reabsorbed here (depending on effects of ADH). This concentrates the urine, and can get rid of excess ions and water.
82
What is ADH and it's function?
ADH (antidiuretic hormone) is made by the hypothalamus and stored in the pituitary gland. It is released in order to regulate and balance the amount of water in the blood.
83
What is deamination?
The body cannot store excess amino acids and so the amino acids need to be broken down. This process is called deamination and is the removal of the nitrogen-containing part of amino acids to form urea.
84
What is the function of the renal vein?
It transports filtered blood to the inferior vena cava to return to the blood.
85
What is the function of the renal artery?
It transports in unfiltered blood from the aorta.
86
What is the function of the cortex?
Blood is filtered here through selective reabsorption.
87
What is the function of the pelvis?
Urine collects here before passing into the ureter.
88
What is the function of the medulla?
Reabsorption of water to maintain water balance occurs here.
89
What are some causes of kidney failure?
Chronic kidney disease:
- diabetes
- high blood pressure
The kidneys are overworked and become damaged. Proteins may leak into the filtrate, and eventually the kidneys can lose their ability to filter.
Acute kidney injury:
- infection.
- injury causing loss of blood flow to kidneys.
- sudden low blood pressure.
90
What is diabetes?
Diabetics can have much higher blood glucose concentrations. The glucose concentration in the kidney filtrate is too high for active reabsorption of all the glucose.
91
Describe the dialysis treatment.
The dialysis machine artificially regulates the salt and water balance of the blood, and gets rid of toxic wastes such as urea.
Long cellulose tubing coiled up in water bath-large surface area.
Cellulose tubing is a partially permeable membrane so salts and urea can leak out into the water bath. Proteins and red blood cells are too large.
The water bath has a similar composition to blood plasma, but without urea.
Urea and excess salts diffuse out of the blood into the water.
92
Describe the kidney transplant treatment.
One kidney is sufficient for correct function.
A close match (e.g. from a relative) is required to reduce the risk of rejection.
The recipient will need to take immunosupressant drugs.
The kidney may still be rejected.
93
Compare and contrast dialysis treatment in comparison to kidney transplant.
Both are effective treatments.
Dialysis requires regular, lengthy hospital visits (3 times per week) whereas transplant allows a normal lifestyle and no restriction to location.
Transplants require a suitable donor - a relative or dead person that is a close match.
With transplants, there is a greater life expectancy.
Transplants can be rejected - patient will need to use immunosuppressant drugs; whereas these drugs are not required for dialysis.
Transplants are also not accepted in some religions.
94
Describe the human nervous system.
The central nervous system (CNS) is made up from the brain and spinal cord.
Nerves carry electrical impulses from the CNS to effectors in all parts of the body.
Effectors are glands or muscles.
Nerves also carry impulses from receptors back to the CNS.
Receptors are located in the sense organs, eyes, ears, skin etc.
95
What are the different types of nerve impulses?
Nerve impulses that cause an action are motor impulses.
| Nerve impulses that carry information from receptors are called sensory impulses.
96
What are some examples of motor impulses?
The bicep muscle is an effector that flexes the arm when it receives an impulse from the CNS.
The salivary gland is an effector that produces saliva when it receives an impulse from the CNS.
97
What are some examples of sensory impuses?
They eye contains receptors that detect light, that information is sent to the CNS as a sensory impulse.
The skin contains receptors that detect different temperatures, that information is sent to the CNS as a sensory impulse.
98
What are the different types of neurones?
There are three types of neurone:
- Motor neurones: carry impulses from the CNS to effectors.
- Sensory neurones: carry impulses from receptors to the CNS.
- Relay neurones: make connections between other neurones.
99
Describe the structure of neurones.
Each neurone has a cell body containing a nucleus and cytoplasm, most are located in the brain or spinal cord.
The branching fibres from the cell body are called dendrites, they form connections with other neurones.
The long filament surrounded by an insulating myelin sheath is called a nerve fibre, they can only carry impulses in one direction.
100
Describe the reflex arc.
A reflex action is an automatic response to a stimulus.
The nervous pathway for these automatic responses is called a reflex arc.
The impulse never gets to the brain, this makes the response involuntarily.
101
What are some examples of a reflex arc?
Dust touches the eye, causing you to blink.
Someone accidentally touches something hot and pulls their hand back.
Food gets caught in the throat causing a coughing response.
Someone taps the knee and it jerks involuntarily.
102
What are the steps in a reflex arc? (using the knee-jerk response as an example).
1. Stimulus (tapping on kneecap tendon).
2. Receptor detects stimulus (stretch receptor).
3. Impulse travels from the receptor along the sensory neurone.
4. Impulse travels from the sensory neurone, through a relay neurone in the spinal cord, and out through a motor neurone.
5. Impulse travels along the motor neurone until it arrives at the effector (leg extensor muscle).
6. Response occurs (leg kicks forward).
103
Describe a voluntary action.
A voluntary action starts in the brain, the action that results is able to be consciously controlled - it does not happen automatically.
The brain sends motor impulses down the spinal cord and relay neurones carry these impulses out through motor nerve fibres.
The motor nerves are connected to muscles (effectors) and the impulse causes them to move.
104
Describe an involuntary action.
An involuntary action happens automatically, there is no conscious control.
We are aware of some of these (mentioned earlier), like the iris of the eye contracting in bright light.
There are many others we are unaware of that help maintain our bodies (homeostasis).
105
What are some examples of involuntary actions?
An internal pacemaker (the sinoatrial node) regulates our heartbeat.
The wave-like muscular contractions of our oesophagus to push food down to the stomach (peristalsis).
106
What are the steps when an impulse reaches a synapse?
1. An impulse arrives at the synapse.
2. Vesicles in the cytoplasm release neurotransmitter into the synaptic cleft (the gap).
3. The neurotransmitter molecules bind to receptors on the other side of the synaptic cleft.
4. Once enough neurotransmitter is released, an impulse is triggered in the next neurone and the impulse continues down the nerve.
107
What effect does heroin have on the synapses?
Many drugs produce their effects by interacting with receptor molecules at synapses.
Heroin stimulates receptor molecules in the synapses in the brain, causing a release of dopamine (a type of neurotransmitter).
This produces an artificial, short lived 'high'.
This can cause issues with receptor function and lead to addiction issues.
108
What is the function of the cornea?
It is a transparent, curved layer that refracts light entering the eye.
109
What is the function of the iris?
It is a coloured ring of muscle that controls the size of the pupil.
110
What is the function of the pupil?
It is a hole in the centre of the iris.
111
What is the function of the lens?
It is a transparent, convex, jelly-like structure that focuses light on to the retina.
112
What is the function of the retina?
It is a light sensitive layer made up of receptors that detect light intensity and colours.
113
What is the function of the optic nerve?
It is the nerve that carries impulses from the eye to the brain.
114
What happens to the eye in bright light?
- Circular muscles contract.
- Radial muscles relax.
- Pupil constricts or becomes smaller.
- Less light enters the eye and reaches the retina.
115
What happens to the eye in dim light?
- Circular muscles relax.
- Radial muscles contract.
- Pupil dilates or enlarges.
- More light enters the eye and reaches the retina.
116
Describe the pupil reflex.
A change in the size of the pupil caused by exposure to high or low light intensity.
It is an automatic reaction (you cannot control it).
117
What is the function of the rods?
The rods are sensitive to low light levels, and are important for night vision.
118
What is the function of the cones?
The cones enable us to see different colours, there are 3 different kinds for green, red and blue light. The cone cells are concentrated in the central part of the retina called the fovea, it lets us process detailed objects.
119
What is the blind spot?
There are millions of light sensitive cells in the retina, the rods and cones.
There is a blind spot in the eye near the retina, it is the area where the optic nerve leaves the eye. It contains no rods or cones.
120
How does the eye focus?
The eye can produce a focused image for near or distant objects.
It does this by changing the shape of the lens.
- It becomes thinner for distant objects.
- It becomes thicker for closer objects.
The change in shape is caused by the contracting or relaxing of the ciliary muscle
121
How does the ciliary muscle change the shape of the lens?
When the ciliary muscle is relaxed, the suspensory ligaments are pulled taut and the lens is thin.
When the ciliary muscle is contracted, the suspensory ligaments slacken and the lens thicken.
