Biology Topic 8

Question 1

Describe the response to a stimulus?

Answer 1

Stimulus detected by receptors.

Sensory neurones transfer electrical impulses from receptors to central nervous system.

Impulses from CNS transferred to effectors by motor neurones

Effectors carry out response

Question 2

What happens when blood glucose low?

Answer 2

Receptors detect low blood glucose.

Pancreas releases hormone glucagon into blood.

target cells in liver detect glucagon and convert glycogen into glucose

Glucose released into blood, so glucose concentration increases.

Question 3

Differences between hormonal and nervous system?

Answer 3

1. Nervous system used electrical impulses hormonal system uses chemicals.
2. Nervous responses faster than hormonal responses.
3. Nervous responses localised hormonal are widespread.
4. Nervous responses are short-lived hormonal are long-lasting.

Question 4

What happens to rods in the dark?

Answer 4

1. sodium ions pumped out of rod cell by active transport.
2. But sodium ions diffuse back into cell via open sodium channels.
3. This makes the inside of the cell only slightly negative compared to the outside. The cell membrane is depolarised.
4. This triggers the release of neurotransmitters, which inhibit the bipolar neurone- stopping it from firing an action potential. So no information sent to brain.

Question 5

What happens to rod cells in the light?

Answer 5

1. Light energy causes rhodopsin to break apart into retinal and opsin- this process is called bleaching.
2. Bleaching of rhodopsin causes sodium ion channels to close.
3. So sodium ions are actively transported out but cant move back in.
4. So sodium ions build up outside of cell making inside of membrane much more negative than outside, making it hyperpolarised.
5. When a rod cell is hyperpolarised it stops releasing neurotransmitter. So bipolar neurone is not inhibited.
6. Bipolar neurone depolarises and action potential sent to brain via optic nerve if potential difference meets threshold.

Question 6

Describe the resting potential.

Answer 6

1. In a neurone’s resting state, the outside of the membrane is more positive than inside. so is polarised.
2. voltage across membrane at rest is the resting potential, about -70mv.
3. The resting potential is maintained by sodium-potassium pumps and potassium ion channels in the membrane:

3 sodium ions pumped out for for every 2 potassium taken in. This takes ATP.

Sodium potassium pumps move sodium ions out but membrane is impermeable to sodium ions, so they can’t diffuse back in. Potassium also moved in but membrane permeable to potassium so can diffuse back out through potassium ion channels.

Makes outside of cell more positive compared to outside.

Question 7

Describe the action potential

Answer 7

1. Stimulus excites neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the electrochemical gradient. This males inside of the neurone less negative.
2. If potential difference reaches threshold of about -55mv, more sodium ion channels open and more sodium ions diffuse into neurone.
3. At potential difference of about +30mv the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of neurone, starting to bring neurone back to resting potential.
4. Potassium ions slow to close so there slight overshoot where too many potassium ions move out, causing hyperpolarisation where potential difference is more negative than resting potential.
5. Return to resting potential.

Question 8

How does myelination speed up action potentials?

Answer 8

The myelin sheath is an electrical insulator which speeds up electrical impulses.

It is made up of a type of cell called a schwann cell. Between schwann cells there a patches of bare membrane called the nodes of ranvier. Sodium ion channels are concentrated here.

in a myelinated neurone, depolarisation only happens at the nodes of ranvier. The neurones cytoplasm conducts enough electrical charge to depolarise next node. so the impulse jumps from node to node.

This is called saltatory conduction and is much faster than unmyelinated neurones.

Question 9

Explain how neurotransmitters transmit nerve impulses between neurones?

Answer 9

1. Action potential arrives at synaptic knob of presynaptic neurone. The action potential stimulates voltage gated sodium channels to open, causing influx of calcium ions into presynaptic knob.
2. The influx of calcium ions into the synaptic knob force synaptic vesicles to move to the presynaptic membrane. They vesicles then fuse with the presynaptic membrane and release the neurotransmitter into the synpaptic cleft by exocytosis.
3. The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. This causes sodium ion channels in postsynaptic membrane to open. The influx of sodium ions into postsynaptic membrane causes depolarisation. Action potential generated if threshold met.

Question 10

Role of synapses in the nervous system?

Answer 10

1. Synapses allow information to be dispersed or amplified.
   -when one neurone connects to many neurones information can be dispersed to many areas of body. This is synaptic divergence.
   - When many neurones connect to one neurone information can be amplified. This is called synaptic convergence.

Question 11

Phototropism?

Answer 11

Growth of a plant in response to light.

Shoots are positively phototropic and grow towards light.

Roots are negatively phototropic and grow away from light.

Question 12

Geotropism?

Answer 12

Growth of plant in response to gravity.

Shoots are negatively phototropic and grow upward

roots are positively geotropic and grow downwards.

Question 13

How do plants respond to stimuli?

Answer 13

Plants respond to stimuli by growth factors- these are chemicals that speed or slow plant growth.

Produced in growing regions of plants and move to where they are needed. Auxins are growth factors which stimulate shoot growth by cell elongation.

other growth factors:

gibberellins: stimulate flowering and seed germination.

Cytokinins: stimulate cell division and differentiation.

Ethene: stimulates fruit ripening and flowering.

Abscisic acid: involved in leaf fall

Question 14

What is IAA?

Answer 14

Type of auxin that is able to regulate the transcription of genes related to cell elongation and cell growth.

Question 15

Role of IAA in phototropism?

Answer 15

IAA moves to more shaded parts of shoots and roots so there is uneven growth.

Question 16

Role of IAA in geotropism?

Answer 16

IAA moves to underside of shoots and roots to cause uneven growth.

Question 17

Photoreceptors?

Answer 17

Photoreceptors called phytochromes detect light in plants.

Phytochromes are molecules that absorb light. They exist in 2 states- Phytochrome red, which absorbs red light at wavelength of 660nm, and phytochrome for red which absorbs far-red light at wavelength 730nm.

Phytochrome red is quickly converted to phytochrome far red when exposed to red light.

Phytochrome far red quickly converted into phytochrome red when exposed to far red light.

Phytochrome far red slowly converted to phytochrome red in darkness.

Daylight has more red light than far red light so more phytochrome red converted to phy far red than phytochrome far red converted to phytochrome red.

Some

Question 18

Describe the cerebrum

Answer 18

Largest part of brain

Divided into two halves called cerebral hemispheres.

Cerebrum has thin outer layer called cerebral cortex.

Involved in vision, learning, thinking, emotions and movement.

Different parts diff functions e.g. back for vision front for thinking.

Question 19

Describe the hypothalamus

Answer 19

Found just beneath middle of the brain.

Responsible for thermoregulation.

Produces hormones that control the pituitary gland.

Question 20

Describe the medulla oblongata?

Answer 20

At base of brain at top of spinal chord.

Controls heart and breathing rate.

Question 21

Describe the cerebellum

Answer 21

Underneath cerebellum

important for coordinating movement and balance.

Question 22

Describe CT scans

Answer 22

uses x-rays

captures frozen moment

look at structure not function.

Low resolution

Question 23

Describe MRI scans

Answer 23

Uses a magnetic field and radiowaves

When placed in a magnetic field, the nuclei of our atoms line up with magnetic field.

When the radiowaves are turned off, they release the energy which is detected by a computer and an image is formed from this.

different tissues respond differently- common use is to identify tumours, strokes, brain injuries and infections.

good resolution

Question 24

Describe fMRI scans

Answer 24

Used to study the brain in action- looks at uptake of oxygen (deoxyhaemoglobin absorbs radio waves signals whereas oxyhaemoglobin doesnt)

Increased neural activity results in increased blood flow.

assess brain activity in real time

Question 25

Describe PET scans

Answer 25

Detailed images for structure They assess brain activity in real time Uses isotopes with short half lives which become incorporated into glucose and water. These molecules become radiotracers which can be injected into patients Active parts of the brain will have more blood flow and so more radiotracers will show Can only be done few times a year and expensive Useful for diagnosing alzheimers as plaques that form can be seen.

Question 26

Habituation definition

Answer 26

Form of learning where an organism decreases or ceases its responses to a stimulus after repeated or prolonged exposure.

Question 27

Example of investigating habituation with snails?

Answer 27

1. Gently brush something soft, like a blade of grass, across skin near snails tentacles. The snail should withdraw the tentacles into its head. 2. Using a stopwatch, time how long it takes for the snail to full extend its tentacles after touching it. 3. Repeat this at timed intervals and record the time it takes for the tentacles to fully extend. If habituation occurs the time taken for the tentacles the reextend tentacles should get shorter until it eventually stops withdrawing the tentacle.

Question 28

why does habituation happen?

Answer 28

1. Repeated exposure to stimulus decreases the amount of calcium ions that enter presynaptic neurone. 2. Less neurotransmitter released into synaptic cleft, so fewer neurotransmitters bind to receptors on post synaptic membrane. 3. Fewer sodium channels on post synaptic membrane so there is reduced chance of action potential reaching threshold. 4. So fewer signals sent to effector to carry out the response.

Question 29

Animal Experiments?

Answer 29

1. Scientists study the effect of different environments on the brain development of animals of the same species. Differences between brains of same species = morel likely due to nurture than nature. 2. To study the effect of different genes, scientists can genetically engineer mice to lack a particular gene. Mice with and without the gene can then be raised in similar environment. So differences more likely to be nature than nurture.

Question 30

Twin studies?

Answer 30

if identical twins are raised separately theyll have identical genes but different environments. Any differences therefore more likely due to nurture than nature. However separated twins will still share environment of womb, so nature and nurture cannot be completely separated. e..g stuttering more common in identical than non-identical twins

Question 31

Cross cultural studies?

Answer 31

1. Children brought up in different cultures have different environmental influences e.g. beliefs and education. 2. Scientists can study effect of diff upbringing on brain development by comparing large groups of kids same age but in different cultures.

Question 32

Newborn studies?

Answer 32

The brain of a newborn baby hasnt been affected by environment. Scientists study brains of newborns to see what functions are present due to nature or nurture. e.g. can cry but not speak

Question 33

Brain damage studies?

Answer 33

Damage to brain can lead to loss of brain function. Scientists compare a specific function of brain in both children with and without brain damage. If brain damaged kid still develops function more likely nurture than nature. if it doesnt more due to nature than nurture.

Question 34

Describe how low serotonin levels in an individual can affect the transmission of impulses in their brain

Answer 34

serotonin is a neurotransmitter results in fewer depolarisations of post synaptic membranes threshold not achieved / less chance of action potential being produced (in post-synaptic neurone)

Question 35

How does L-dopa work?

Answer 35

1. structure similar to dopamine. 2. L-dopa absorbed into brain and converted into dopamine by enzyme dopa-decarboxylase. 3. more nerve impulses transmitted giving parkinsons sufferers more control over movement.

Question 36

Describe how the use of MDMA could affect the transmission of impulses in the brain.

Answer 36

MDMA stimulates release / prevents re-uptake / increases concentration of serotonin binding to post synaptic receptors more action potentials produced

Question 37

Explain how the use of MDMA could result in the development of depression.

Answer 37

MDMA use results in depletion of serotonin post synaptic membrane becomes less responsive to serotonin lack of serotonin associated with depression

Question 38

Advantages of human genome project?

Answer 38

Disease Prediction & Prevention – Identifying genes linked to diseases allows for early diagnosis and preventive treatment, reducing health risks before symptoms even appear. Personalized Medicine – Treatments and medications can be tailored to an individual's genetic makeup, improving effectiveness and minimizing side effects. Improved Diagnostics – More precise genetic testing enables earlier and more accurate detection of diseases, leading to better treatment outcomes.

Question 39

Disadvantages of human genome project?

Answer 39

1. New drugs for specific genes more expensive- could create a two tier health service. 2. Some could be denied expensive drug is genetics indicate not useful. Even if only drug available. 3. genetics information could be used by employers to discriminate. 4. Revealing drug unlikely to work could psychologically damage patient.

Question 40

How can microorganisms be genetically modified to produce drugs?

Answer 40

1.Gene for protein for the drug isolated using restriction enzymes. 2. Gene copied using PCR. 3. Copies placed into plasmids. 4. Plasmids transferred into microorganisms. 5. Modified microorganisms grown in large containers to produce lots of useful protein. 6. Protein purified and used as a drug.

Question 41

How can plants be genetically modified to produce drugs?

Answer 41

1.Gene for protein for drug placed into bacterium. 2.Bacterium infects plant cell. 3.Bacterium plants gene into plant cell DNA. 4.Plant cell grown into full plant. 5.Drug can be taken by eating the plant.

Question 42

How can animals be genetically modified to produce drugs?

Answer 42

1. The gene for protein (drug) is injected into nucleus of fertilised animal egg cell. 2. The egg cell is then implanted into adult animal- gives birth to animal with copy of this gene in every cell. 3. the protein produced from the gene normally purified from milk of animal.

Question 43

Benefits of GMOs?

Answer 43

1. Crops can be modified to have higher yields and be more nutritious. 2. Crops can be modified to have pest resistance, so less pesticides are needed. 3. Industry uses enzymes. they can be modified to be more effective. 4. Vaccines in plants dont have to refrigerated. 5. genetically modified plants and animals keep producing drugs using conventional farming methods. Cheap so makes drugs cheaper.

Question 44

Risks of genetically modified organisms?

Answer 44

1. Transmission of genetic material. Could create superweeds. 2. Dont know long term effects of GMOs. 3. Some think it is wrong to genetically modify animals just for human benefit.

Question 45

Describe the makeup of the visual cortex

Answer 45

Made of ocular dominance columns. Neurones in visual cortex either get information from left or right eye. Neurones grouped together in ocular dominance columns. They are the same size and in alternating pattern: left,right,left,right across visual cortex.

Question 46

Hubel and Weisel tests?

Answer 46

Young kittens: Stitched shut one eye of each kitten. Kept like this for several months. Stitched eye was blind. Ocular dominance column for stitched up eye much smaller, uncovered eye much larger than normal. Same tried on adult cats but ocular dominance columns stayed same size and adult cats didn't lose eyesight. This highlights a critical period in early life where it is essential to be exposed to visual stimuli for visual cortex to develop. Same tried with cataracts in humans babies with cataracts go blind adults don't. As synapses that don't receive visual stimulation removed.

Question 47

Arguments against animal testing?

Answer 47

1. Animals are different to humans, so drug may have diff effects on humans. 2. Experiments cause pain and distress to animals. 3. There are alternatives to using animals in research e.g. computer models or cultures of human cells. 4. Some think animals have the right to not be experimented on.

Question 48

Arguments for animal testing?

Answer 48

1. Animals similar to humans, so research has led to lots of medical breakthroughs. 2. Animal testing only done when necessary and scientists follow strict rules. 3. currently only way to see how drug affects entire body computer models and human cell cultures don't. 4. Utilitarianism- some believe humans have greater right to life than animals.