biology paper 2 Flashcards
(25 cards)
Describe a reflex arc to show how the stimulus from a hot pan reaches the muscle in the arm
- Receptor in the sensory organ detects a change in a stimulus
- Sensory neurone carries a nerve impulse to the relay neurone
- Relay neurone transfers the nerve impulse from the sensory neurone to the motor neurone
- Motor neurone takes the nerve impulse back to the effector
- The effector is a muscle or a gland
- The effector carries out the response
- The response is the muscle contracting or the gland secreting a hormone
Describe how to do the ruler drop test
Hold a ruler above the hand of a student just between their fingers
Drop the ruler without warning so the other student catches it
Record where the ruler is caught/how far it has dropped
Repeat, discount outliers and calculate a mean
Describe how information is passed between neurones
A synapse is the gap between two neurones so an electrical impulse cannot pass
An impulse triggers release of neurotransmitters from 1 neurone
It crosses by diffusion across the synapse
Neurotransmitter binds with receptors on next neurone which are complementary
Stimulates an electrical impulse to travel down next neurone
Describe how the brain receives information about light entering the eye
Retina detects light
Impulse sent along sensory neuron
To optic nerve which carries to brain
Explain how the eye responds to changes in light
Dim light, pupils dilate as circular muscles relax and radial muscles contract
Bright light pupils contract as circular muscles contract and radial relax
Describe how spectacle lenses can correct long-sightedness
Longsighted means the lens cannot thicken so light rays are focused beyond the retina
Use a convex lens
So light rays are refracted more to focus onto retina
Explain how the person’s eye could adjust to form a clear image of a nearer object
Ciliary muscles contract so have more diameter
Suspensory ligaments loosen causing lens to thicken
Lens is now more convergent so can refract light more to focus light onto retina
Explain how hormones keep the blood glucose concentration constant
After a meal, blood glucose concentration rises and is detected by the pancreas
Pancreas produces insulin which is secreted into the blood
Insulin acts on the liver and muscle cells to absorb more glucose to be used in respiration
Excess glucose is stored as glycogen in the liver
When blood glucose concentration returns to normal insulin is no longer secreted
When blood glucose concentration drops below normal the pancreas secretes glucagon into the blood
Glucagon stimulates the liver to convert stored glycogen back to glucose which is secreted into the blood
When blood glucose concentration returns back to normal glucagon is no longer secreted
Describe the interaction of hormones during the menstrual cycle
FSH released from pituitary gland stimulates the release of oestrogen from the ovaries
FSH also causes an egg to mature
Oestrogen causes the lining of the uterus to thicken
Oestrogen stimulates the release of LH from the pituitary gland and inhibits FSH production
LH stimulates the release of an egg from the ovary
Progesterone produced from the remains of the follicle maintains the thickness of the uterus lining
Progesterone inhibits the production of FSH and LH
Explain how the body regulates the amount of thyroxine that is produced
Pituitary gland produces TSH (thyroid stimulating hormone) which stimulates the thyroid gland to secrete thyroxine
Thyroxine is released into the blood which increases the basal metabolic rate
Chemical reactions such as respiration increase
When the levels of thyroxine in the blood are too high the release of TSH from the pituitary gland is inhibited
This results in less thyroxine being released from the thyroid gland
Compare sexual and asexual reproduction
Sexual involves fertilisation, asexual doesn’t
Sexual is a slower process than asexual
Sexual requires more energy than asexual
Offspring are genetically different in sexual but identical in asexual
Compare meiosis and mitosis processes
Meiosis produces 4 daughter cells, mitosis produces 2 daughter cells
Meiosis has 2 cell divisions, mitosis has 1 cell division
Daughter cells in meiosis are unique, in meiosis they are genetically identical
Meiosis occurs to produce sex cells, mitosis produces cells in the body
Identify the steps in natural selection
There is variation amongst the species
There is competition amongst the species
The better adapted to the environment is able to outcompete others
They are therefore more likely to survive and reproduce
They then pass on gene for favourable feature to offspring
Describe how quadrats should be used to estimate the number of plants in a field
Measure area to be tested
Randomly place quadrats x10
Count plants in each quadrat
Use mean number of plants in quadrats for area of field to estimate population
Total plants found in sample x (total area m2/total area sampled m2)
Describe how a transect can be used to investigate a change in habitat
a transect is a line across a habitat
record the number of organisms of a species at regular intervals along the transect
Explain how human activities are polluting rivers, lakes and seas
Increased human population so more sewage, more food needs to be produced, increased energy demand, more waste products
Sewage causes algae to grow, could block light, causing plants to die and decompose due to lack of oxygen
Increased fertiliser usage to increase crop yield, run into rivers causing algae to grow
Increase use of herbicides/pesticides could run into rivers and build up in food chains
Increase energy demands could lead to toxic chemicals from factories running into rivers and building up in food chains
Build up of waste products – more litter, plastics could be eaten by organisms or get stuck on them, not biodegradable
Increase acid rain formation, oil spills in oceans, radiation leaks form power stations
Describe how an organism has been produced using selective breeding
parents with the desired characteristic are selected
the parents are bred together to produce offspring
offspring with the desired characteristics are selected and bred again
this is repeated over many generations
Describe how carbon from the atmosphere is cycled through living organisms (6)
Plants carry out photosynthesis taking in carbon dioxide
Animals eat plants
Animals and plants respire releasing carbon dioxide back into the atmosphere
Animals and plants die
The carbon stored in animals & plants is broken down by microorganisms
Microorganism respire releasing carbon dioxide back into the atmosphere
Describe the main steps in the process of genetic engineering
Isolate and cut desired gene using enzyme
Using enzymes cut and insert desired gene into vector
Vector reproduces to produce many cells with desired gene
Done at an early stage of development
Describe the advantages and disadvantages of using genetic modification to produce crops
Increases yield, making more money
Produces crops with desired characteristic
But gene could be passed to wild plants and have an effect on food chain
Result in less genetic variation in plants, reduced biodiversity
Describe the steps of adult cell cloning
The nucleus is removed from an unfertilised egg cell
The nucleus from the desired adult cell is removed and placed into the empty egg cell
An electric shock is sued to stimulate the egg to divide to form an embryo
Once embryo is developed into a ball of cells its inserted into womb of surrogate to continue development
Explain why a plant has bent towards the light as its grown
Auxin is released from the tip
The hormone has been unequally distributed on the dark side
stimulating the side in the dark to grow more
So the plant has bent towards the light
Describe how the water content of the blood is controlled
If water content too low, ADH released from pituitary gland into blood
Causing kidneys to reabsorb more water
small volume of concentrated urine
If water content too high, ADH not produced
Less water reabsorbed by kidneys
Large volume of dilute urine
Explain how the skin can help maintain body temperature
If too hot the blood vessels dilate so more blood can flow near surface of skin
So more heat energy can be lost from blood, cooling the body
Sweat glands release sweat using evaporation to cool
Hairs lay flat so not trapping any heat near surface of skin
If too cold the blood vessels constrict so less blood can flow near surface of skin
So less heat energy can be lost from blood
Muscles contract causing shivering releasing heat energy
Hairs stand upright to trap a layer of air next to skin
