C3.1 Integration of body systems [done]

Question 1

System integration

Answer 1

1. necessary process in living systems
2. coordination is needed for component parts of a system to collectively perform an overall function
   - all organisms use multiple systems to perform the various functions of life & within these systems there are interdependent subsystems that work to perform an overall function –> at every level in the functioning of an organism, there must be coordination btw & within systems [achieved by system integration]

*system integration depends on effective communication between components so they can interact [interactions: positive/ negative feedback OR can be complex & multifactorial w many loops and branches]

Question 2

Hierarchy of subsystems integrated in a multicellular living organism: cells, tissues, organs, body systems

Answer 2

This integration is responsible for emergent properties [eg a cheetah becomes an effective predator by integration of its body systems]
In order for complex organisms to evolve to survive in their environments, it was necessary for cells to become specialised for certain functions

Groups of specialised cells –> specialised tissues
Groups of specialised tissues –> organs
Some organs evolved to work collectively to accomplish certain functions; Some organs –> body systems

Body systems are specialised for functions: obtaining nutrients, obtaining waste, reproduction. All of the body systems working in unison represent the entire organism

Question 3

Emergent properties

Answer 3

Emergent properties are those that exist when the sum of all the parts creates features that do not exist within the individual components
- advantage of an organism level of complexity
- organism level of organisation results in a combination that is said to be greater than the sum of its parts

Question 4

Nervous system VS endocrine system

Answer 4

Similarities:
1. both used for communication btw cells
2. both cause a response (stimulate/ inhibit processes) in target cells
3. hormones & neurotransmitters are both chemicals that bind to receptors
4. both can work over long distances in the body
5. both under overall control of the brain as the brain has a role in sending hormones and nerve impulses
6. both use negative feedback

Differences
1. hormones are chemical messengers while nerve impulses are electrical signals
2. hormones are transported in blood while nerve impulses are transported by neurons
3. hormones take a longer time to travel while nerve impulses travel faster
4. Hormones are carried throughout the body while nerve impulses are carried to a single/ specific cell/ muscle fibre
5. in the endocrine system, all/ a wide range of tissues/ organs are affected while in the nervous system, only muscles/ glands receive signals
6. Reponses in the endocrine system are USUALLY longterm/ persistent while the responses in nervous system are short-lived/ short duration

Question 5

Role of blood system in transporting materials between organs

Answer 5

Most multicellular organisms have become so large that it is impossible for nutrients & waste products to be efficiently and directly moved from cell to cell

Examples of role of blood system (MUST KNOW)
1. transport vessels & aqueous fluids have evolved to serve that purpose
2. humans & many other animals use blood circulating in arteries & veins to transport a variety of substances throughout the body tissues
3. the oxygen needed by leg muscles will be supplied by blood that has received that oxygen from lung tissues a short time before it is used
4. urea produced as a by-product of protein metabolism in the liver will be transported by blood to the kidneys to be filtered out & become part of urine

Question 6

Brain is the central information integration organ

Answer 6

The brain is the central integrating organ of our body
- it receives info –> processes it –> stores some of it & sends instructions to all parts of the body to coordinate life processes
- the info received by the brain comes from sensory receptors, both in specialised sense organs [eg eye] & from receptor cells in other organs [eg pressure receptors in blood vessels]

The brain can store information for the short-term/ longer term & sometimes for the rest of life
- Memory: capacity to store information [essential for learning]
- processing of info leads to decision making by the brain –> result in signals being sent to muscles or glands which cause these organs to carry out a response

Question 7

Difference between unconscious VS conscious processes

Answer 7

1. performed when awake/ asleep VS performed only when awake
2. performed involuntarily [we do not have to think about the actions and cannot normally prevent them through thought] VS performed voluntarily [we can think about the action & decide whether or not to carry it out]
3. secretion by glands & contractions of smooth muscle [not attached to bones] are unconscious & therefore involuntary VS contraction of striated muscle (attached to bones) can be done consciously & therefore voluntary
4. coordinated by brain & spinal cord VS coordinated only by the cerebral hemisphere of the brain
5. eg swallowing food once it has entered the oesophagus & vomiting when stomach contents are regurgitated VS eg initiation of swallowing when food is pushed from the mouth cavity into the pharynx

Question 8

Central nervous system (CNS) & Peripheral nervous system (PNS)

Answer 8

The nervous system is made up of the CNS and PNS that connect the CNS to all other organs of the body
Two organs in the CNS: brain & spinal cord
PNS: cranial nerves, spinal nerves, ganglia outside CNS

Nervous System:
- CNS
- PNS –> somatic nervous system
–> autonomic nervous system
= sympathetic nervous system
= parasympathetic nervous system

*do not confuse effectors & receptors
- receptors: detect stimuli
- effectors: respond to stimuli
Sensory neurons pass impulses from receptor to CNS, motor neurons stimulate effectors (muscles/ glands)

Question 9

Spinal cord is the integrating centre for unconscious processes

Answer 9

The spinal cord is located inside the vertebral column (backbone)
- pairs of spinal nerves branch off to the left & right between the vertebrae

Spinal cord has 2 main tissues:
1. White matter - containing myelinated (layer of fat/insulation that make the signals go faster) axons & other nerve fibres which convey signals from sensory receptors to the brain & from the brain to the organs of the body
2. Grey matter - containing cell bodies of motor neurons & interneurons with many synapses between these neurons

Synapses in the grey matter: used to process information & for decision-making so the spinal cord is also an integrating centre

The spinal cord only coordinates unconscious processes, esp reflexes; in some cases, it can do this more quickly than if signals were conveyed to and fro form the the brain

Question 10

Sensory receptors

Answer 10

Sensory receptors:
- changes in the external environment can act as stimuli to the nervous system, if perceived by sensory receptors
- located in the skin & sense organs
- nerve endings of some sensory neurons act as receptors for touch & heat
- other stimuli are perceived by specialised receptor cells that pass impulses to sensory neurons [eg light-sensitive rod & cone cells in retina of eye]

There are also receptors inside the body that monitor internal conditions
- stretch receptors in striated muscle sense the state of contraction, allowing the brain to deduce the position of the body
- stretch receptors in the walls of arteries give a measure of blood pressure
- chemoreceptors in the walls of blood vessels detect whether concentrations of oxygen, carbon dioxide & glucose are low/ high

Question 11

Sensory neurons convey messages from receptor cells to the CNS

Answer 11

Signals from all receptor cells & from nerve endings that perceive stimuli directly, are conveyed to the CNS by sensory neurons
- signals are in form of nerve impulses carried along the axons of sensory neurons
- these axons vary in length depending on the distance btw receptor cell & brain/ spinal cord

Brain receives all signals from the main sense organs located in the head: eyes, ears, nose & tongue
Spinal cord receives signals from other organs of the body including skin and muscles

Sensory inputs to the brain are received by specialised areas in the cerebral hemispheres
- the axons of sensory neurons enter either the spinal cord through one of the 31 pairs of spinal nerves, or the brain by one of the 12 pairs of cranial nerves

Question 12

Motor neurons convey output from cerebral hemisphere to muscles

Answer 12

The cerebral hemispheres of the brain have a major role in the control of striated muscles & certain glands
- in particular, the primary motor cortex sends signals via motor neurons to each striated muscle in the body

Striated muscle is attached to the bone
- it is used for locomotion & controlling posture and it can be controlled consciously
- eg to stand up from a sitting position, signals are sent from parts of the motor cortex via motor neurons to muscles in the legs

The signals in motor neurons are nerve impulses

Question 13

Structure of neurons

Answer 13

Grey matter of cerebral hemispheres contain: the cell body & dendrites of many motor neurons
- typically there are many dendrites, receiving signals from diff relay neurons & transmitting them to the cell body

One axon leads from the cell body out of the brain & down the spinal cord –> there it forms a synapse with a second motor neuron, whose axon leads to one specific striated muscle [the axons of these two motor neurons may in total extend to a metre or more, depending on the location of the muscle]

The axons of motor neurons are bundled up in nerves, often tgt with the axons of sensory neurons
- when a nerve impulse reaches the end of the axon, it stimulates the muscle fibres to contract & gland cells to secrete

Question 14

Structure of nerves
*see slide 22 for reference

Answer 14

Nerves are bundles of nerve fibres of both sensory & motor neurons
- protective sheath, myelinated & unmyelinated nerve fibres
- nerves consist of the axons of multiple nerve cells

A neuron is an individual cell of the nervous system, whereas a nerve is a collection of neurons surrounded by a protective sheath
Neurons may be:
1. sensory neurons - carry action potentials from receptors to the CNS
2. motor neurons - carry action potentials from the CNS to a muscle
3. interneurons - located between sensory & motor neurons and are only found within the CNS

Neurons can be myelinated/ unmyelinated
- myelinated neurons have cells called SCHWANN CELLS wrapped around their axon & intervening areas where there are no Schwann cells [schwann cells produces myelin sheath]
* the areas btw Schwann cells are called NODES OF RANVIER
- the action potentials of myelinated axons are able to skip from one node of ranvier to the next, making transmission of the action potential much faster compared to unmyelinated axons
- groupings of myelinated & unmyelinated axons are surrounded by protective sheaths

*axon hillock decides whether or not the signal is fixed

Question 15

Pain reflex arcs with a single interneuron in the grey matter of the spinal cord & a free sensory nerve ending in a sensory neuron as a pain receptor in the hand & skeletal muscle as the effector

Answer 15

A pain reflex arc is an example of an involuntary response & involves only 3 neurons
1. first of the neurons is a receptor neuron known as a nocireceptor/ pain receptor
eg if you accidentally hold a finger too close to an open flame –> results in nocireceptors located in skin of finger initiating afferent (sensory) action potentials –> action potentials travel through your hand & eventually join one of the spinal nerves

2. after entering the spinal cord, the afferent neuron synapses with a short interneuron (also called relay neuron) located entirely within the grey matter of the spinal cord
   - the interneuron synapses with a motor neuron & the resulting action potentials go directly to arm muscles (effector), which moves quickly to pull your finger away from the flame

The action of pulling your finger away from the source of pain occurs much faster than truly sensing the pain
- the reason for this is that the sensation of pain must travel to your cerebrum to be integrated by many neural synapses before a sensation is felt & a motor response formulated

The pain reflex arc has evolved to limit damage to body tissue by generating a quick reaction involving only 3 neurons
- the unusual aspect of this is that the reflex arc uses skeletal muscle as the effector, tissue that is normally innervated by the frontal lobe of the cerebrum

Question 16

Role of cerebellum in coordinating skeletal muscle contraction & balance [overall control of movements of the body]

Answer 16

Although cerebellum is a v impt part of the brain associated with body movements, it does not initiate those movements.
The initiation of muscle contractions & thus body movements is accomplished by the MOTOR CORTEX of the cerebrum
- as soon as a movement begins, the cerebellum receives feedback impulses from the area of the body that is moving & many sense organs
- the cerebellum then sends out impulses to coordinate the movement –> results in smooth & balanced muscular activity, leading to coordinated movements
- cerebellum coordinates posture, balance, walking, hand & finger movements, eye movements, speech & much more

“Muscle memory” is more to do with training coordinated movements by the cerebellum than actually training muscle

Question 17

Modulation of sleep patterns by melatonin secretion as a part of circadian rhythms [diurnal pattern of melatonin secretion by pineal gland & how it helps to establish a cycle of sleeping & waking]

Answer 17

A circadian rhythm is any pattern of behaviour/ physiology that is based on a 24-hour cycle
- the most obvious pattern of a circadian rhythm is our wake & sleep cycle
- many other organisms follow a circadian rhythm for sleep

Some animals like us are diurnal –> more active in daylight ours while other animals are nocturnal –> more active at night

Evidence suggests that the circadian rhythm is largely controlled/ modulated by a small endocrine gland: PINEAL GLAND
- located near the centre of brain between cerebrum & brainstem
- function is to produce a hormone: MELATONIN –> it regulates the sleep schedule

Studies have shown that melatonin levels are night during the night for diurnal animals & high during the day for nocturnal animals
Other studies have shown that light striking the retina of the eye inhibits melatonin production

Over a prolonged period of time our body become naturally regulated to a circadian rhythm that is only interrupted by atypical events
- eg travelling through several time zones in a short period of time –> jet lag
- eg extended viewing of television, mobile phones & computer screens in the evening –> alter natural circadian rhythm

Question 18

Epinephrine (adrenaline) secretion by adrenal glands

Answer 18

When humans encounter a stressful situation, a hormone called EPINEPHRINE is released from ADRENAL GLANDS located on the upper/ superior side of each kidney
- epinephrine is released into the bloodstream –> resulting in numerous responses by the body

Epinephrine prepares us for fight-or-flight response [called this bc the body’s resources are called upon for immediate action in response to a threat/ other stimuli that require a vigorous & immediate response]
- intense muscle contractions & vigorous activity are facilitated by epinephrine release
- increased heart rate, blood glucose, breathing rate [fight-or-flight response]

Question 19

Wide spread effects of epinephrine

Answer 19

1. increasing heart rate & blood pressure
2. increasing diameter of air passages –> more air received by lungs
3. dilation of pupils of eyes –> see clearer
4. increasing blood sugar levels by stimulating glycogen conversion to glucose in liver
5. increasing blood supply to muscles

Question 20

Hypothalamus

Answer 20

Area of the brain that acts as a link between nervous system & endocrine system
- contains receptors associated with autonomic nervous system functions –> receives action potentials from other areas of the body that also contain this type of receptor
- composed of both neurons & glandular cells
- glandular cells of hypothalamus produce hormones that either stimulate hormone release by the pituitary glands/ inhibit their release

Question 21

Pituitary gland

Answer 21

Pituitary gland is referred often to as a singular gland, but it consists of two glands that exist as different “lobes”: Anterior & Posterior pituitary
- anterior & posterior lobes of the pituitary communicate with the hypothalamus in diff ways
- each secretes its own hormones

Majority of these hormones are chemical signals released into the bloodstream that regulate the homeostasis of various physiological factors (eg metabolic rate, reproductive cell formation, water balance)

Question 22

Example: ADH

Answer 22

Antidiuretic hormones (ADH) produced by the hypothalamus is sent to the posterior pituitary & when needed is secreted by the posterior pituitary
- ADH controls homeostatic levels of water in body

Hypothalamus has specialised receptors: OSMORECEPTORS
- capable of sensing the water content of blood as it passes through the hypothalamus
- nerve impulses sent along the axons of neusecretory cells, causing secretion of ADH into bloodstream

If the water content is relatively low, the hypothalamus will send action potentials to the cells in posterior pituitary –> then the posterior pituitary secretes ADH into the blood stream

Target tissue of ADH is the collecting tubules of nephrons in the kidneys
- when the collecting tubules detect ADH, they reabsorb water that would have been released as part of urine

Many hormones (like ADH) work using a mechanism called negative feedback –> goal is to maintain homeostasis
- ADH & kidney function maintain a homeostatic level of water in the body
- if water in the body rises above homeostatic level, more urine is produced
- if water becomes too low, ADH is produced & water is reabsorbed before becoming part of urine

When ADH reaches the kidneys, ADH binds to membrane receptors –> leads to temporary increase in number of aquaporin molecules in the plasma membrane of distal tubules & collecting duct cells. More reabsorption of water gives rise to hyper osmotic urine, restoring blood plasma conc to normal
- alcohol is diuretic as it inhibits the release of ADH

Question 23

Feedback control of heart rate

Answer 23

Changes to ventilation rate, body temperature & heart rate are brought back to set points by feedback control mechanisms

Eg when the body is “at rest”, the heart rate is under the control of the natural pacemaker within the heart –> sinoatrial (SA) node
- when u are active, muscle tissue requires additional oxygen & releases additional carbon dioxide as a result of increased rate of cell resp
- an increase in heart rate & stroke volume is required to carry the additional respiratory gases to and from the lungs
*Stroke volume = volume of blood pumped out of the heart w each ventricular contraction

Receptors known as baroreceptors & chemoreceptors can detect changes in the blood vessels & contents of the blood associated with an increase in the rate of cell respiration

Question 24

Baroreceptors

Answer 24

Baroreceptors are sensitive to pressure changes in arterial blood vessels

When blood pressure increases, the wall of an artery is distended/ stretched outwards –> distention results in an increase in rate of action potentials sent to the medulla
- Medulla responds by sending impulses to the SA node (in the heart) to decrease the heart rate & force of contraction, leading to lower stroke volume
- when blood pressure falls below normal, a decrease in action potentials sent to the medulla will lead to an increase in heart rate & stroke volume

One location for BARORECEPTORS is on the arch of the aorta [largest artery in body is aorta & it forms an arch shape as it exits the left ventricle of the heart –> almost immediately, other major arteries begin to branch from the aortic arch]
- 2 of those major branches are the carotid arteries [carry oxygenated blood to head & brain] –> just before these 2 carotid arteries branch, they form an enlargement called a SINUS –> both carotid sinuses have baroreceptors on the walls of the blood vessels

Question 25

Chemoreceptors

Answer 25

Chemoreceptors are sensitive to levels of 3 diff factors in the bloodstream that change as a result of an increase in cell respiration rate: 1. oxygen levels, decrease bc oxygen is a reactant of cell respiration 2. carbon dioxide levels, increase bc carbon dioxide is a product of cell respiration 3. pH, lowers bc most carbon dioxide entering blood combines w water to form carbonic acid Each of these 3 chemical changes has its own chemoreceptors that send an increased rate of action potentials to the medulla when there is an increase in the rate of cell respiration - an increase in heart rate & stroke volume from action potentials sent from the medulla to the SA node - the same chemoreceptors can sense the opposite physiological effects when excercise ceases, & action potentials will be sent to the heart to slow the heart rate & lower the stroke volume Chemoreceptors are located in tissue near where the baroreceptors are located, but they r outside the blood vessels - each of the major arteries has small arteries that extend from the vessel & immediately branch into capillaries - chemoreceptors monitor oxygen, carbon dioxide & pH levels in capillaries - chemoreceptor cells are capable of releasing a neurotransmitter that initiates action potentials that are carried to the medulla

Question 26

Feedback control of ventilation rate

Answer 26

When resting, ventilation rate of the lungs is controlled by groups of cells: respiratory centres, located in medulla - when at rest, spontaneous action potentials are released by these cells which travel to diaphragm & intercostal muscles to maintain breathing at a relatively slow & controlled pace Chemoreceptors located in the medulla allow feedback control of the ventilation rate during & after exercise - many chemoreceptors monitor the levels of carbon dioxide & pH in the blood passing through the medulla The pH of blood typically falls within the range of 7.35-7.45 --> slightly alkaline - the response to exercise serves to keep the blood pH in slightly alkaline range Body activity increases the rate of cell respiration & thus leads to an increase in carbon dioxide production & a large number of hydrogen ions produced - chemoreceptors in medulla sense this increase in hydrogen ions --> send action potentials at higher rate proportional to the number of hydrogen ions All muscles associated with lung ventilation [esp diaphragm & intercostal muscles] respond to these action potentials - rate of ventilation increase, volume of air moving in and out [stroke volume] increases - when exercise decreases, hydrogen ion concentrations also decrease & action potentials sent from the respiratory centres will decrease

Question 27

Control of breathing (FYI)

Answer 27

1. Co2 increases, pH drop 2. chemoreceptors in carotid artery & aorta 3. medulla oblongata 4. phrenic nerves --> diaphragm ; intercostal nerves --> rib muscles 5. inhalation 6. lungs/ chest expand 7. stretch receptors in the walls of chest & lungs 8. medulla oblongata 9. stops sending signals to respiratory muscles 10. inhalation stops/ exhalation occurs

Question 28

Initiation of swallowing food & egestion of faeces --> voluntary control by central nervous system (CNS)

Answer 28

Swallowing food is a voluntary action & is controlled by the CNS; many hours later, after nutrients have been removed from the food, faeces are digested & this is under control of CNS

Question 29

Peristalsis between these points --> involuntary control by enteric nervous system (ENS)

Answer 29

ENS is a separate nervous system that keeps the food (at various stages of digestion) moving along the alimentary canal --> movement of food is called peristalsis under involuntary control - ENS is a web of sensory neurons, motor neurons & relay neurons embedded in the tissues of the alimentary canal; stretches from the lower portion of the oesophagus all the way to the rectum Peristaltic reflex: a series of smooth muscle contractions occurring along the entire length of the alimentary canal to keep food moving - most smooth muscle in the body is controlled by areas of the brainstem - when food moves through alimentary canal, it forms into rounded masses: bolus - bolus initiates peristaltic reflex - wherever a bolus is located in the tube of alimentary canal, that area of tube becomes distended, stimulating stretch receptors in ENS 1. Contraction of circular muscles behind food mass 2. Contraction of longitudinal muscles ahead of food mass 3. Contraction of circular muscle layer forces food mass forward Sensory stretch receptors then synapse with nearby relay neurons --> which then synapse with 2 diff types of motor neurons: 1. One type of motor neuron releases an Excitatory neurotransmitter to an area of smooth muscle "behind" the bolus of food --> smooth muscle contracts, pushing bolus along 2. Another type of motor neuron releases an Inhibitory neurotransmitter "ahead" of the bolus --> smooth muscle ahead of bolus relaxes in response & opens lumen (central space of tube) for bolus to slide through This reflex occurs many times along the gut, ensuring movement of food material moves forward in coordinated manner

Question 30

Observations of tropic response in seedlings (AHL)

Answer 30

Plants often compete for light - as immobile (sessile) organisms, plants tend to live out their lives wherever a seed takes root - as seedling shoot begins to grow, it is often in an area where the greatest light availability is in one direction only - root system may not be able to move location but plants have evolved a mechanism that enables directional growth towards light This phenomenon of growing towards a light source is: PHOTOTROPISM - categorised as positive tropic response bc plant growth is towards light stimulus - a tropism is any directional growth response to an external stimulus Positive phototropism as a directional growth response to lateral light in plant shoots 1. When sunlight is overhead, the IAA molecules produced by the apical meristem are distributed evenly in shoot 2. Once sunlight shines on shoot at an angle, the IAA molecules move to the far side & induce the elongation of cells on that side 3. cell elongation results in the bending of the shoot towards the light *IAA is a form of auxin

Question 31

Phototropism in plants

Answer 31

1. shoot grows towards brightest light 2. auxin moved from lighter to shadier side of stem apex by auxin efflux pumps 3. auxin promotes cell growth & there is more growth on shady side of stem due to auxin conc gradient 4. auxin binds to auxin receptors in target cells & promote expression of genes for growth

Question 32

Nature of Science

Answer 32

all measuring tools have a degree of uncertainty which is based on smallest increments for which the tool is marked [written in the heading of a data table] Precision: all measurements within a single grouping are close to each other Accuracy: data comes close to an accepted value Reliability: same/ very similar results consistently by using same methods under same circumstances In biological expt, it is not always possible to determine accuracy bc an accepted value may not be available - if data sets show poor precision, you may have to reconsider procedure and/ or measuring tools & begin again Always report precision of measurement tools & discuss precision, accuracy & reliability of data sets as part of lab report, including possible importance to any conclusions drawn.

Question 33

Phytohormones as signalling chemicals

Answer 33

Auxin: plant cell elongation Cytokinin: increase rate of cell division Ethylene: promote fruit ripening Gibberellin: control stem elongation, seed germination, flowering & dormancy Plants do not have a nervous system but they can repond to environmental cues by producing hormones - hormones by plants = phytohormones Phytohormones are used as signalling molecules to control growth & development of flowers, fruit & seeds & to help plant respond to environmental stimuli

Question 34

Phytohormones (plant growth regulators) vs Animal hormones

Answer 34

1. produced in a region of plant structure (eg stem/ root tips/ in unspecialised cells) VS produced in specific glands in specialised cells (eg islets of Langerhans in the pancreas) 2. not necessarily transported widely, or at all, and some are active at sites of production VS transported to all parts of the body by the bloodstream 3. not particularly specific, tend to influence different

Question 35

Auxin efflux carriers maintain concentration gradients of phytohormones

Answer 35

Auxin is a phytohormone produced in growing regions of plants [esp in tips of shoots & roots & growth buds] - under certain environmental influences, auxin is evenly concentrated in an area of growth & cell elongation is uniform in that area - auxin can enter phloem tissue & be moved throughout the plant within phloem sap - auxin can diffuse freely INTO plant cells but not OUT of them Auxin efflux carriers can be positioned in a cell membrane on one side of the cell - if all cells coordinate to concentrate these carriers on the same side, auxin is actively transported (ATP) from cell to cell through the plant tissue & becomes concentrated in part of the plant Auxin can be concentrated in certain areas of a plant/ on one side of growing tissue --> leads to differential growth Auxin easily enters into cells by diffusion but requires membrane proteins = auxin efflux carriers to exit a cell - if needed, a plant can distribute efflux carriers predominantly on one side of a series of adjoining cells to encourage a one-way movement of auxin through that series of cells --> cell-to-cell movement is a type of active transport bc it requires ATP

Question 36

Promotion of cell growth by auxin

Answer 36

Cell elongation in plants necessitates an increase in length of plant cell walls --> can only occur if the cross-linking fibres of cellulose are first loosened Auxin is the phytohormone that promotes this loosening - when auxin enters a cell, it promotes the synthesis of hydrogen ion (proton) pumps - auxin also binds to the proteins making up the hydrogen pumps & stimulates their insertion into the plasma membrane of the cell - using ATP as energy source, the pumps move hydrogen ions from the interior of the cell through the plasma membrane --> this concentrates the hydrogen ions in an area called the apoplast Apoplast = any area of adjoining plant cells outside the plasma membranes [includes cell wall & any intercellular spaces between cell walls] Hydrogen ions activate a protein: expansin, which is already found within cell wall - expansin loosens hydrogen bonds that cross-link cellulose fibres, allowing fibres to move past each other into new positions Absorption of water creates high internal turgor pressure, creating the force necessary for the fibres to slide past each other - fibres of cellulose make new hydrogen bonds in new positions --> resulting in longer cell walls & elongated cells Auxin makes cells grow by alternating gene expression to promote cell growth

Question 37

Growth in plant apex

Answer 37

1. growth in shoots is unlimited 2. plant apex produces stem & leaves 3. growth is controlled by hormones (eg auxin, IAA) 4. new cells produced by mitosis as apex is a meristem 5. phototropism occurs as plant grows towards light 6. auxin moved away from sunny side to shady side of shoot apex as auxin efflux pumps set up concentration gradients

Question 38

Auxin & Cytokinin regulate shoot & root growth

Answer 38

Root tips produce cytokinin [transported to shoots] Shoot tips produce auxin [transported to roots] --> interactions btw these 2 phytohormones ensure root & shoot growth are integrated Both hormones must be transported to affect a region of growth where they are not produced - cytokinin is transported in xylem fluid, bc direction of fluid id from root to shoot - auxin is transported in sap within phloem tissue from shoot to root At certain concentrations, these 2 hormones work synergistically w each other --> best plant growth is when the growing tips of shoots & roots have access to both cytokinin (for cell division) & auxin (for cell elongation)

Question 39

Positive feedback in fruit ripening & ethylene production

Answer 39

Ethylene (IUPAC: ethene) stimulates the changes in fruits that occur during ripening & ripening stimulates increased production of ethylene During ripening, fruits produce a has called ethylene - bc it is a gas, when one fruit begins to ripen & produce ethylene, any adjacent fruit is exposed to the has & all the fruit ripen quickly and at the same time --> example of positive feedback mechanism bc the release of ethylene is a self-perpetuating event = release of ethylene leads to higher release of ethylene This positive feedback mechanism ensures fruit ripening is rapid & synchronised

Question 40

Why have plant species evolved to have all their fruit ripen at the same time?

Answer 40

A fruit is an ovary with one/ more seeds contained within Most fruits are green when they start their development & become bright & less camouflaged as they ripen, they also become sweeter - this is to attract herbivores that eat the fruit & disperse the seeds when they deposit faeces - the display of bright fruit is to be a colourful & tasty advertisement to attract helpful animals

Question 41

Role of nerves & hormones in integration of body systems

Answer 41

1. coordination & communication is necessary btw cells, tissues & organs for them to work as an entire organism 2. the nervous system & endocrine system are both impt for info integration within many animals 3. brain is a central information integration organ in animals 4. sensory information is carried to the brain & spinal cord through sensory neurons 5. motor information is carried away from brain & spinal cord to muscles through motor neurons 6. the cerebellum coordinates impulses going to muscles to make movements smooth & efficient 7. hypothalamus & pituitary glands control many hormones secreted from endocrine glands 8. plants use phytohormones to control many processes like directional growth & fruit ripening

Question 42

Role of feedback mechanisms in regulation of body systems

Answer 42

1. melatonin secretion by pineal gland helps regulate circadian rhythm of sleep/ wake cycle 2. epinephrine secretion by adrenal glands prepares body for immediate rigourous activity 3. baroreceptors & chemoreceptors send info to the medulla in order to regulate contraction rate & stroke volume of the heart 4. the brainstem uses chemoreceptors to send info to regulate ventilation rate 5. peristalsis is controlled by neurons within alimentary canal that form the enteric nervous system 6. most hormones help maintain homeostasis within the body & use negative feedback control to maintain a physiological variable within a narrow range 7. fruit ripening is controlled by a positive feedback mechanism where ethylene production is enhanced by previous ethylene production