PAPER 1 TOPICS 2022 Flashcards
what temperature is the body kept at and why?
37 degrees, as this is the optimum temperature for enzymes in the human body
what happens when you are too hot?
- lots of sweat is produced - when it evaporates it transfers energy from your skin to the environment, cooling you down.
- blood vessels near to the skin widen - vasodilation. it allows more blood to flow near the surface, so it can transfer more energy into the surroundings which cools you down.
- hairs lie flat/erector muscles relax
what happens when you are too cold?
- very little sweat is produced
- blood vessels near the surface of the skin constrict (vasoconstriction). less blood flows near the surface, so less energy is transferred to the surroundings.
- you shiver, which increases your rate of respiration, which transfers more energy to warm the body due to excess heat lost from chemical reactions. exercise does the same
- hairs stand on end to trap an insulating layer of air, which keeps you warm
chromosome
thread like structure in the nucleus of a cell, made of DNA. contains the genetic information (genes)
what is DNA?
- a molecule with a double helix shape, composed of two strands of nucleotides held together by pairs of bases (A&T and C&G).
- carries the genetic information in coded form, for all characteristics of an organism.
homologous pair
- a pair of chromosomes that are the same shape, same size and carry genes for the same characters in the individual
- in the same positions on each chromosome
- one of each pair came from each parent.
haploid
a cell containing one set of chromosomes (one of each pair) (n) e.g. a gamete
diploid
a cell containing two sets of chromosomes (both of each pair) (2n) e.g. body cells
gene
a region along the length of the DNA of a chromosome that contains the information to control a certain characteristic by coding for a specific protein.
allele
an alternative form of a gene- occurs at the same position on the chromosome and controls the same character, but in a different way. recessive or dominant
genotype
the alleles an organism carries for a certain characteristic
phenotype
the appearance of an organism resulting from its genotype
homozygous
genotype with the same alleles of a gene e.g. AA or aa; both dominant or both recessive
heterozygous
genotype with different alleles of a gene e.g. Aa; one dominant one recessive
dominant (allele)
an allele which is always expressed in both homozygous and heterozygous genotypes
recessive (allele)
an allele that is not expressed in the phenotype if a dominant allele of the gene is present. only expressed if homozygous with no dominant alleles.
XX
the two sex chromosomes that are found in female body cells
XY
the two sex chromosomes that are found in male body cells
mitosis
type of cell division that produces two diploid daughter cells that are GENETICALLY IDENTICAL with the same number of chromosomes as the parent cell
meiosis
type of cell division that produces four haploid gametes which are GENETICALLY DIFFERENT to one another and have half the number of chromosomes as the parent cell
gamete
male and female sex cells, formed by meiosis. haploid
zygote
single cell resulting from fertilisation of a female gamete by a male gamete.
what is diffusion?
- the net movement of particles from an area of high concentration to an area of lower concentration.
- passive
- liquids and gases
osmosis
- the net movement of water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane.
- passive
active transport
- the movement of particle from an area of low concentration to an area of high concentration against the concentration gradient using energy from respiration
- active
- e.g. in the digestive system when theres a low conc of nutrients in the gut but a high conc in the blood or in plants to get minerals from the soil
how does surface area to volume ratio affect the movement of substances?
- the rate of diffusion, osmosis and active transport is higher in cells with a larger surface area to volume ratio
how does distance affect the movement of substances?
- if substances only have a short distance to move, then they’ll move in and out of cells faster.
- for example, cell membranes are very thin
how does temperature affect the movement of substances?
- as particles in a substance get warmer they have more kinetic energy, so they move faster
- as temperature increases, substance move in and out of cells faster
how does concentration gradient affect the movement of substances?
- substances move in out of a cell faster if theres a big difference in concentration between the inside and outside of a cell.
- if there are lots more particles on one side, there are more there to move across
- this increases the rate of diffusion and osmosis but conc gradients don’t affect active transport
PRACTICAL: investigate diffusion in a non-living system
- mix agar jelly with phenolphthalein and dilute sodium hydroxide (turns it pink)
- put some dilute hydrochloric acid in a beaker. cut out a few cubes from the jelly and put them in the beaker of acid
- if you leave the cubes for a while they eventually turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide
PRACTICAL: investigate osmosis in a living system
- cut up a potato into identical cylinders and get some beakers with different sugar solutions
- one should be pure water, another very concentrated sugar solution, and a few in between
- measure the length of the cylinders then leave a few un each beaker for about 30 mins
- take them out and measure their lengths again
- if the cylinders have drawn in water by osmosis they’ll be a bit longer.
- if water has been drawn out, they’ll have shrunk.
PRACTICAL: investigate osmosis in a non-living system
- fix some Viking tubing over the end of a thistle funnel. then pour some sugar solution down the glass tube into the thistle funnel
- put the thistle funnel into a beaker of pure water- measure where the sugar solution comes up to on the glass tube.
- leave the apparatus overnight then measure where the solution is in the glass tube. water should be drawn through the Viking tubing by osmosis and this will force the solution up the glass tube.
what is the role of diffusion in gas exchange? (plants)
- when a plant is photosynthesising it uses up lots of CO2, so theres hardly any inside the leaf. luckily, this makes more CO2 move into the leaf by diffusion (from an area of higher concentration to an area of lower concentration)
- at the same time, lots of O2 is being made as a waste product of photosynthesis. some is used in respiration and the rest diffuses out through the stomata (moving from an area of higher concentration to an area of lower concentration)
gas exchange in relation to respiration and photosynthesis
- when plants photosynthesise they use up CO2 from the atmosphere and produce O2 as a waste product.
- when plants respire they use up O2 and produce CO2 as a waste product. these waste products are lost through stomata in the underside of leaves.
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, so gases only have to travel a short distance to reach the cells when they’re needed.
3) there are air spaces inside the leaf. this lets gases like carbon dioxide and oxygen move easily between cells. it also increases the surface area for gas exchange.
4) the lower surface is full of little holes called stomata. they let gases like O2 and CO2 diffuse in and out. they also allow water to escape (transpiration)
5) stomata can open and close and are controlled by guard cells.
what is the role of stomata in gas exchange?
- stomata begin to close as it gets dark. photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in. when the stomata are closed, water can’t escape, which stops the plants drying out.
- 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, the plant might dry up and die :(
how does the net exchange of gases depend on light intensity?
- photosynthesis only happens during the day (when theres light). but plants must respire all the time to get the energy they need to live.
- during the day plants make more oxygen by photosynthesis than they use in respiration. so in daylight they release oxygen. they also use up more carbon dioxide than they produce, so they take in carbon dioxide.
- at night plants only respire - theres not enough light for photosynthesis. this means they take in oxygen and release carbon dioxide.
PRACTICAL: investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator METHOD
- add the same volume of hydrogen-carbonate indicator to 4 boiling tubes
- put similar sized leaved into 3 of the tubes and seal with a rubber bung. keep the fourth tube empty as a control
- completely wrap one tube in aluminium foil and a second tube in gauze.
- place all the tubes in a bright light. this will let plenty of light on to the uncovered leaf and a little light onto the gauze one. the leaf covered in foil will get no light.
- leave the tubes for an hour then check the colour of the indicator.
PRACTICAL: investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator RESULTS.
- no change in the colour of the control tube
- the indicator of the darkened tube should go yellow. respiration will still take place but there’ll be no photosynthesis so the CO2 concentration in the tube will increase
- the indicator in the shaded tube should stay a similar colour (orange). with a little photosynthesis and some respiration taking place, roughly equal amounts of CO2 will be taken up and produced by the leaf, so the CO2 concentration in the tube won’t change very much
- you’d expect the indicator in the well lit tube to go purple. there’ll be some respiration but lots of photosynthesis leading to net uptake of CO2 by the leaf, lowering the concentration in the tube.
what is the structure of the thorax?
- the thorax is the top part of the body
- its separated from the lower part of the body by the diaphragm
- the lungs are like big pink sponges and are surrounded by the pleural membranes
- the lungs are protected by the ribcage. the intercostal muscles run between the ribs
- the air that you breathe in goes through the trachea. this splits into two tubes called bronchi (each one is a bronchus), one going to each lung
- the bronchi split into progressively smaller tubes called bronchioles
- the bronchioles finally end at small bags called alveoli where the gas exchange takes place
what happens when you breathe in?
- intercostal muscles CONTRACT
- rib cage moves UP AND OUT
- diaphragm CONTRACTS
- diaphragm moves DOWN
- diaphragm becomes FLATTER
- volume of thorax INCREASES
- pressure of thorax DECREASES
- air DRAWN IN
what happens when you breathe OUT?
- intercostal muscles RELAX
- rib cage moves DOWN AND IN
- diaphragm RELAXES
- diaphragm moves UP
- diaphragm becomes DOME SHAPED
- volume of thorax DECREASES
- pressure of thorax INCREASES
- air FORCED OUT
how are alveoli adapted for gas exchange?
1) lots of alveoli = very large SA for diffusion
2) thin capillary wall = decreased diffusion distance
3) well ventilated and good blood flow = maintains a steep concentration gradient = increased ROD
4) moist walls = gases can dissolve
PRACTICAL: investigate the effect of exercise on breathing rate
C- intensity of exercise O- human of same respiratory health R- x5 for each intensity M- BR count number of breaths M- per minute S- environmental temperature S- starting from resting BR
how can smoking cause problems?
- it damages the walls inside the alveoli, reducing the surface area for gas exchange and leading to diseases like emphysema
- the tar in cigarettes damages the cilia in your lungs and trachea. these hairs, along with mucus, catch a load of 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.
- tar also irritates the bronchi and bronchioles, encouraging mucus to be produced which can’t be cleared very well by damaged cilia - this causes smokers cough and chronic bronchitis
- the carbon monoxide in smoke reduces the amount of oxygen the blood can carry. to make up for this 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. increases the risk of coronary heart disease
- also contains carcinogens - chemicals that can lead to cancer.
PRACTICAL: investigate the release of carbon dioxide in your breath
- set up two boiling tubes (google diagram?)
- put the same amount of limewater in each
- put your mouth around the mouthpiece and breath nin and out several times.
- as you breathe in, air form the room is drawn in through boiling tube A. the air contains very little carbon dioxide, so the limewater in this boiling tube remains colourless
- when you breathe out, the air you exhale bubbles through the limewater in boiling tube B. this air contains CO2 produced during respiration, so the limewater in this boiling tube turns cloudy.
- since the limewater in boiling tube A remains clear, you can tell that the carbon dioxide in the exhaled air was from respiration - it wasn’t exhaled through boiling tube A. if you’d inhaled the carbon dioxide, the limewater in A would’ve turned cloudy too.
how can simple, unicellular organisms rely on diffusion for movement of substances in and out?
substances like water, minerals and sugars, as well as getting rid of waste substances, can diffuse directly into and out of the cell across the cell membrane. the diffusion rate is quick because of the short distances the substances have to travel.
why do multicellular organisms need a transport system?
direct diffusion from the outer surface would be too slow as substances would have to travel large distances to reach every single cell. transport systems = move substances to and from individual cells quickly.
what is the role of the phloem?
TRANSPORT FOOD:
- the phloem transport sugars, like sucrose, and amino acids from where they’re made in the leaves to the other parts of the plant.
- this movement of food substances around the plant is known as translocation.
what is the role of the xylem?
TRANSPORT WATER AND MINERALS:
- the xylem carry water and mineral salts from the roots up the stem to the leaves in the transpiration stream
how is water taken in by root hair cells?
- the cells on plant roots grow into long “hairs” which stick out into the soil
- each branch of a root will be covered in millions of these microscopic hairs
- this gives the plant a big surface area for absorbing water from the soil.
- water is taken in by osmosis.
what is transpiration?
- the evaporation of water from the surface of a plant.
- this evaporation creates a slight shortage of water in the leaf and so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
- this in turn means more water is drawn up from the roots and so theres a constant transpiration stream of water throughout the plant.
how does LIGHT INTENSITY affect transpiration?
- the brighter the light, the greater the transpiration rate
- stomata begin to close as it gets darker. photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in. when the stomata are closed very little water can escape
how does TEMPERATURE affect transpiration?
- the warmer it is, the faster transpiration happens.
- when its warm the water particles have more energy to evaporate and diffuse out of the stomata.
how does WIND SPEED affect transpiration?
- the higher the wind speed, the greater transpiration rate.
- if wind speed around a leaf is low, the water vapour just surrounds the leaf and doesn’t move away. this means theres a high concentration of water particles aoutide the leaf as well as inside it, so diffusion doesnt happen as quickly
- if its windy, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. diffusion then happens quickly
how does HUMIDITY affect transpiration?
- the drier the air around a leaf, the faster transpiration happens.
- same as wind speed concept
PRACTICAL: measuring transpiration
- using a potometer
VARIABLES: - Independent variable - time.
- Dependent variable - the distance moved by the bubble along the capillary tube.
- Control variables - temperature, air flow or draughts, adequate supply of water.
what are the four main components of blood?
- plasma
- platelets
- RBCs
- WBCs
what is the role of plasma in the blood?
pale yellow liquid that carries:
- red/white blood cells and platelets
- digested food products (like glucose and amino acids) from the gut to all the body cells
- carbon dioxide from the body cells to the lungs
- urea from the liver to the kidneys
- hormones, which act as chemical messengers
- heat energy
how are red blood cells adapted to carry oxygen?
- small and have a biconcave shape to give a large SA for absorbing and releasing oxygen
- they have no nucleus which frees up space for more haemoglobin to carry more oxygen
- they contain haemoglobin. in the lungs, haemoglobin binds with oxygen to form oxyhaemoglobin. in body tissues the reverse reaction happens to release oxygen to the cells.
how are platelets involved in blood clotting?
- when you damage a blood vessel, platelet clump together to “plug” the damaged area.
- this is known as blood clotting. blood clots stop you losing too much blood and prevent micro-organisms from entering the wound.
what are the role of white blood cells in the immune system?
PHAGOCYTES: ingest pathogens. non specific.
LYMPHOCYTES: produce antibodies that are specific to the antigens on the surface of the pathogens. marks the pathogen for destruction by phagocyte.
MEMORY CELLS: produced in response to a foreign antigen. stay in the blood and remember a specific antigen. reproduce very fast if same antigen reenters the body.
how does vaccination protect you from future infections?
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 maybe even die.
2) To avoid this you can be vaccinated against some diseases, e.g. polio or measles.
3) Vaccination usually 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) Memory cells will also be produced and will remain in the blood, so if live pathogens of the same type ever appear, the antibodies to kill them will be produced much faster and in greater numbers.
what are the characteristics and functions of the ARTERY?
CARRIES BLOOD UNDER PRESSURE.
- the heart pumps the blood out at high pressure is the artery walls are strong and elastic.
- the elastic fibres allow arteries to expand.
- the walls are thick compared to the lumen.
- they contain thick layers of muscle to make them strong.
- the largest artery in the body is the aorta.
what are the characteristics and functions of the CAPILLARY?
- arteries branch into capillaries.
- they are really tiny, too small to see
- they carry the 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
- they supply food and oxygen and take away wastes like CO2
- their walls are usually one cell thick. this increases the rate of diffusion by decreasing the distance over which it happens
what are the characteristics and functions of the VEIN?
TAKE BLOOD BACK TO THE HEART
- capillaries eventually join up to form veins
- the blood is at lower pressure in the veins so the walls don’t need to be as thick as arteries.
- they have a bigger lumen than arteries to help the blood flow despite the lower pressure
- they also have valves to help keep the blood flowing in the right direction
- the largest vein in the body is the vena cava.
what is the structure of the heart?
- the right atrium of the heart received deoxygenated blood from the body (through the vena cava)
- the deoxygenated blood moves through to the right ventricle, which pumps it to the lungs (via the pulmonary vein)
- the left atrium receives oxygenated blood from the lungs (through the pulmonary vein)
- the oxygenated blood then moves through to the left ventricle, which pumps it out round the whole body (via the aorta)
- the left ventricle has a much thicker wall than the right ventricle. it needs more muscles because it has to pump blood around the whole body, whereas the right ventricle only has to pump it to the lungs. this also means the blood in the left ventricle is under higher pressure than the blood in the right ventricle
- the valves prevent back flow of blood.
how does heart rate change during exercise?
- when you exercise, your muscles need more energy, so you respire more. you need to get more oxygen into cells and remove more CO2, so blood flows faster = heart rate increases:
- exercise increases the amount of CO2 in the blood
- high levels of blood CO2 are detected by receptors in aorta and carotid artery
- these receptors send signal to the brain
- the brain sends signals to the heart causing it to contract more frequently and with more force.
how does heart rate change under the influence of adrenaline?
- when an organism is threatened the adrenal glands release adrenaline
- adrenaline binds to specific receptors in the heart. this causes the cardiac muscle to contract more frequently and with more force, so the heart rate increases and the heart pumps more blood
- this increases oxygen supply to the tissues, getting the body ready for action.
what factors lead to coronary heart disease?
- coronary heart disease is when the coronary arteries that supply the blood to the muscle of the heart get blocked by layers of fatty material building up.
- this causes the arteries to become narrow so blood flow is restricted and theres a lack of oxygen to the heart muscle - this can lead to a heart attack.
1. fatty diet (saturated fats)
2. age
3. lack of exercise
4. smoking
5. male
6. genetic
structure of the overall circulation system
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2020/01/The-circulatory-system.png
- arteries carry oxygenated blood and veins carry deoxygenated LORD
- the pulmonary artery and pulmonary vein are big exceptions to this rule.
- PULMONARY = LUNGS
- HEPATIC = LIVER
- RENAL = KIDNEY
organisms can respond to…
…changes in their environment
what is homeostasis?
the maintenance of a constant internal environment. temperature and blood water content.
what does a coordinated response require?
- a stimulus
- a receptor
- an effector
why do plants respond to stimuli?
- increase their chances of survival
- respond to the presence of predators
- respond to abiotic stress (anything thats harmful but non living)
what is auxin?
- plant growth hormones
- control growth at tips of roots and shoots
- produced in the tips and diffuses backwards to stimulate the cell elongation process
- promotes growth in the shoot but insist growth in the root
shoots are…
- POSITIVELY PHOTOTROPIC (grow towards light)
- accumulates more auxin on the dark side which makes the cells elongate faster on the shaded side, so the shoot bends towards the light. - NEGATIVELY GEOTROPIC (grow away from gravity)
- when shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
- this causes the lower side to grow faster, bending the shoot upwards
roots are…
- POSITIVELY GEOTROPIC (grow towards gravity)
- a root growing sideways also has more auxin on its lower side
- but in a root the extra auxin inhibits growth. this means the cells on top elongate faster, and the root bends downwards - ROOTS ARE NEGATIVELY PHOTOTROPIC (grow away from light)
- if a root begins to be exposed to some light, more auxin accumulates on the more shaded side.
- the auxin inhibits cell elongation on the shaded side, so the root bends downwards, back to the ground
ROOTS THAT ARE UNDERGROUND AREN’T EXPOSED TO LIGHT. THEY GROW DOWNWARDS DUE TO POSITIVE GEOTROPISM.
what are the differences between nervous and hormonal communication?
NERVES:
- very fast message
- act for a very short time
- act on a very precise area
HORMONES:
- slower message
- act for a long time
- act in a more general way
what is the CNS?
- the brain and spinal
- is linked to sense organs by nerves
how does the CNS coordinate information?
- when receptors in a sense organ detect a stimulus, they send electrical impulses along sensory neurones to the CNS
- the CNS then sends electrical impulses to an effector along a motor neurone. the effector them responds accordingly
- the jobs of the CNS is to coordinate the response. coordinated responses always need a stimulus, a receptor and an effector
- because neurones transit information using high speed electrical impulses, the nervous system is able to bring about very rapid responses
what is the role of neurotransmitters at synapses?
- the connection between two neurones is a synapse
- the nerve signal is transferred by chemicals called neurotransmitters which diffuse across the gap
- these chemicals then set off a new electrical signal in the neurones.
what is a reflex?
automatic responses to stimuli that reduce the chances of being injured
describe a simple reflex arc
- when a stimulus, e.g. touching a hot object is detected by receptor cells, an impulse is sent along a sensory neurone to the CNS
- in the CNS the sensory neurone passes on the message to the relay neurone.
- relay neurones relay the impulse to a motor neurone
- the impulse then travels along the motor neurone to the effector (e.g. a muscle or gland)
- the muscles then contracts and moves your hand away from the hot object.
- because you don’t have to think about the response its very quick.
in what order are the 3 neurones?
- sensory neurone
- relay neurone
- motor neurone
what are the parts of the eye and their functions?
- the CONJUNCTIVA lubricates and protects the surface of the eye
- the SCLERA is the tough outer layer that protects the eye.
- the CORNEA 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
- the IRIS controls the diameter of the PUPIL (the hole in the middle) and therefore how much light enters the eye.
- the LENS focuses the light onto the RETINA (the light-sensitive part - its covered in light receptors called rods and cones). cones are highly concentrated at the FOVEA.
- the OPTIC NERVE carries impulses from the receptors to the brain.
how does the eye adjust to bright (and dim) light
- very bright light can damage the retina, so you have a reflex to protect it
1. circular muscles contract
2. radial muscles relax
3. contracted pupil = less light enters eye - dim light OPPOSITE
how does the eye focus on distant objects?
- the ciliary muscles relax, which allows the suspensory ligaments to pull taut.
- the pulls the lens tall and thin
- so it refracts the light by a smaller amount
how does the eye focus on near objects?
- the ciliary muscles contract, which slackens the suspensory ligaments.
- the lens becomes fat
- which increases the amount by which it refracts light.
what is the source, role and effect of ADRENALINE?
- adrenal glands (on top of kidneys)
- readies the body for a “fight or flight” response
- increases heart rate, blood flow to muscles and blood sugar level
what is the source, role and effect of INSULIN?
- pancreas
- helps control blood sugar level
- stimulates the liver to turn glucose into glycogen for storage
what is the source, role and effect of TESTOSTERONE?
- testes
- main male sex hormones
- promotes male secondary sexual characteristics
what is the source, role and effect of PROGESTERONE?
- ovaries
- supports pregnancy
- maintains the lining of the uterus
what is the source, role and effect of OESTROGEN?
- ovaries
- main female sex hormone
- causes growth of the uterine lining and promotes female secondary characteristics.
what is the source, role and effect of ADH?
- pituitary gland
- controls water content
- increases permeability of kidney tubules to water
what is the source, role and effect of FSH?
- pituitary gland
- female sex hormone
- causes an egg to mature in an ovary. stimulates the ovaries to produce oestrogen
what is the source, role and effect of LH?
- pituitary gland
- female sex hormone
- stimulates the release of an egg from an ovary
what is difference between asexual and sexual reproduction?
- Asexual reproduction generates offspring that are genetically identical to a single parent.
- In sexual reproduction, two parents contribute genetic information to produce unique offspring.
what is fertilisation?
the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo
how are some plants adapted for insect pollination?
- brightly coloured petals
- scented flowers and nectaries to attract insects
- make big, sticky pollen grains - the grains stick to insects as they go from plant to plant
- the stigma is also sticky so that any pollen picked up by insects on other plants will stick to the stigma
how are some plants adapted for wind pollination?
- small, dull petals on the flower
- no nectaries or strong scents
- a lot of pollen grains - they’re small and light so that they can easily be carried by the wind.
- long filaments that hang the anthers outside the flower, so that a lot of the pollen gets blown away by the wind
- a large and feather stigma to catch pollen as its carried past by the wind. the stigma often hands outside the flower too.
how does fertilisation take place in plants?
- a pollen grain lands on the stigma pf a flower, usually with help from insects or wind
- a pollen tube grows out of the pollen grain and down through the style to the ovary and Ito the ovule.
- a nucleus from the male gamete moves down the tube to join with a female gamete in the ovule. fertilisation is when the two nuclei fuse together to make a zygote. this divides by mitosis to form an embryo
- each fertilised female gamete forms a seed. the ovary develops into a fruit around the seed.
what are the male reproductive structures in a plant?
STAMEN:
- consists of the anther and filament
- the ANTHER contains pollen grains, these produce the male gametes.
- the FILAMENT is the stalk that supports the anther.
what are the female reproductive structures in a plant?
CARPEL:
- consists of the ovary, style and stigma
- the stigma is the end bit that pollen grains attach to.
- the style is the rod like section that supports the stigma.
- the ovary contains the female gametes (eggs) inside ovules.
what conditions do seeds need to begin germinating?
- water - to a activate the enzymes that break down the food reserves in the seed
- oxygen - for respiration
- a suitable temperature - for the enzymes inside the seed to work. this depends on the type of seed.
what are the stages of germination?
- the seed takes in water and starts to grow using its store of energy
- the first root starts to grow down into the soil.
- the shoot grows up
- finally, extra roots grow and the first green leaves appear.
PRACTICAL: investigate the conditions need for seed germination METHOD
- set up 4 boiling tubes with ten seeds on top of cotton wool inside with the following conditions:
1. water, oxygen, room temperature (the control)
2. no water, oxygen, room temp
3. water, oxygen, low temp
4. water, no oxygen, room temp. - leave the tubes for a few days and observe.
- its important to control all of the variables during the experiment. you should only be changing one variable at a time so you know which condition has an effect on germination.
PRACTICAL: investigate the conditions need for seed germination OBSERVATIONS
- you should only see germination in tube 1
- this is because ALL the conditions needed for germination are present.
- the seeds in the other boiling tubes won’t germinate - this shows that the seeds need water, oxygen and a suitable temperature to germinate.
how do germinating seeds get energy before they can photosynthesise?
- a developed seed contains an embryo and a store of food reserves, wrapped in a hard seed coat (testa)
- when a seed starts to germinate, it gets glucose for respiration from its own food store. this transfers the energy it needs to grow.
- once the plant has grown enough to produce green leaves, it can get its own food for energy from photosynthesis.
how do plants reproduce asexually using natural methods?
for example: STRAWBERRIES :)
- the parent strawberry plant sends out runners - fast growing stems that grow out sideways, just above the ground.
- the runners take root at various points (a short distance away) and new plants start to grown.
- the new plants are clones of the parent strawberry plant, so there’s no genetic variation between them.
how do plants reproduce asexually using artificial methods?
- gardeners can take cuttings from good parent plants, then plant them to produce genetically identical clones of the parent plant.
- these plants can be produced quickly and cheaply.
what is the role of the placenta?
- once the embryo has implanted, the placenta develops. this lets the blood of the embryo and mother get very close to allow the exchange of food, oxygen and waste.
how is the developing embryo protected?
- the amnion membrane forms.
- this surrounds the embryo and is full of amniotic fluid, which protects the embryo against knocks and bumps,
what is a genome?
the entire DNA of an organism
what is a gene?
- a section of a molecule of DNA that codes for a specific protein.
- it is made up of several thousand base pairs:
> adenine (A) with thymine (T)
> cytosine (C) with guanine (G) - the order in which the base pairs occur varies from gene to gene.
- 3 base pairs code for a particular amino acid in a protein molecule. the DNA code is called the triplet code.
what does a nucleus contain?
contains chromosomes on which genes are located
what are the similarities between DNA and RNA?
- sugar/phosphate backbone
- A, C, G
what are the differences between DNA and RNA?
DNA:
- double stranded
- deoxyribose sugar
- thymine
RNA:
- single stranded
- ribose sugar
- uracil
protein synthesis overview: how are proteins made?
PROTEINS ARE MADE BY READING THE CODE IN DNA.
- proteins are made up of chains of molecules called amino acids. each different protein has it’s own particular number and order of amino acids.
- the amino acid chains fold up to give each protein a different specific shape and ∴ a different function.
- this is why enzymes have active sites with a specific shape and only catalyse specific reactions.
- remember, a section of a molecule of DNA that codes for a specific protein is a GENE. its the ORDER OF BASES IN A GENE THAT DECIDES THE ORDER OF AMINO ACIDS IN A PROTEIN.
- each amino acid is coded for by a sequence of 3 bases in the gene = this is a CODON
- the amino acids are joined together to make proteins following the order of the bases in the gene.
- each gene contains a different sequence of bases which is what allows it to code for a particular protein.
protein synthesis: TRANSCRIPTION
- proteins are made in the cell cytoplasm by subcellular structures called ribosomes. DNA is found in the nucleus and can’t move out of it as its too big. the cell needs to get the information from the DNA to the ribosome.
- this is done using messenger RNA (mRNA)
- RNA polymerase binds to a region of non-coding DNA in front of a gene
- the 2 DNA strands “unzip” and the RNA polymerase moves along one of the strands of the DNA
- it uses the coding DNA in the gene as a template to make the mRNA. base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene.
- once made, the mRNA molecule moves out of the nucleus and joins with a ribosome.
protein synthesis: TRANSLATION
- protein is assembled
- amino acids are brought to the ribosome by transfer RNA (tRNA)
- the order in which the amino acids are brought to the ribosome matches the order of the codons in mRNA
- part of the tRNA’s structure is called an anti-codon - its complementary to the codon for the amino acid. the pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the correct order.
- the amino acids are joined together by the ribosome = PROTEIN.
what are alleles?
there can be different versions of the same gene, which give different versions of a characteristic, like blue or brown eyes. the different versions of the same gene are called alleles.
what is codominance?
some characteristics are caused by codominant alleles. neither allele is recessive, so you show characteristics from both alleles (e.g. not blood group A or B, but blood group AB)
what are most phenotypic features the result of?
polygenic inheritance rather than single genes.
how does mitosis work?
- produced GENETICALLY IDENTICAL CELLS
1. in a cell thats not dividing, the DNA is spread out in long strings.
2. if the cell gets a signal to divide, it needs to duplicate its DNA - so there’s one copy for each new cell. the DNA forms X-shaped chromosomes. each “arm” of the chromosome is an exact duplicate of the other.
3. the chromosomes then line up at the centre of the cell and cell fibres pull them apart. the two arms of each chromosome go to opposite ends of the cell.
3. membranes form around each of the new sets of chromosomes. these become the nuclei the two new cells.
4. lastly, the cytoplasm divides
5. you now have two new cells containing exactly the same DNA - they’re genetically identical
