C3.1 Integration of body systems Flashcards
Why do organisms systems?
All organisms use multiple systems to perform various functions of life. Within these systems, there are interdependent subsystems that work together to perform an overall function. At every level in functioning of an organism, there must be coordination between and within systems. This is achieved by system integration.
Different systems in an organism need to effectively communicate with each other & interact in order to be functional. Negative & positive feedback between components supports this, but more commonly they are complex & multifactorial, with many loops & branches which allow connections between complex processes.
What is the importance of integration of body systems for cheetah being a predator?
Thus, integration of body systems & complex social interactions result in qualities that make cheetahs incredible predators & provide an example of an emergent property.
- Small, aerodynamic head to reduce wind resistance
- Black tear marks protect from glare & help them see long distances
- Semi-retractable claws that provide traction while running
- Large heart & lungs
- Flexible spine that acts as a spring while running and increases stride length
- Undercoat with solid black spots helps in camouflage
- Lean body with long legs
- Longer & heavier hind limb bones enable longer strides
- Long muscular tail acts as a stabiliser while running at high speeds
- Black rings at tip of bushy tail help in camouflage
- Grooves on claw pads help in traction
What is the hierarchy of subsystems in a multicellular living organism?
Cells, tissues, organs and body systems as a hierarchy of subsystems that are integrated in a multicellular living organism.
What are emergent properties?
Emergent properties are those that exist when sum of all parts creates features that do not exist within individual components. This is advantage of an organism level of complexity. “The whole is greater than sum of its parts”(Aristotle).
What is an example of emergent properties?
- Tissues: Cells within multicellular organisms are specialised to perform specific functions. Their structure is adapted to their function. One cell by itself cannot usually carry out its function on a large enough scale to meet needs of organism. Instead, organisms use groups of cells of same type to carry out a function. These groups of cells are called tissues. Large organisms tend to have more cells in each tissue, rather than larger cells (because of SA:vol issues). Tissues may contain two or more cell types, which specialise for diff aspects of the function of tissue. E.g. epithelium that forms wall of alveoli in lungs has two cell types: AT1 (alveolar type 1) cells make up 95% of respiratory surface. They are extensive but very thin, allowing diffusion of gases. AT2 cells are cuboidal with dense cytoplasm. They secrete a surfactant that prevents collapse of alveoli.
Cells in a tissue adhere (stick) to each other. Plant cells do this with a middle lamella between the cell walls that is rich is gluey pectin. Animal cells use transmembrane proteins that form strong links between neighbouring cells. If blood is regarded as a tissue, it is unusual because blood cells do not stick together. Cells within a tissue communicate with each other.
E.g. plant tissues may use efflux pumps to transfer auxin, to coordinate growth, &
heart muscle tissue transmits electrical impulses which trigger contraction. Cells within tissues also communicate with cells elsewhere in an organism.
Why is organs an example of emergent properties?
- Organs: An organ is a group of tissues in an animal or plant that work together to carry out a specific function of life. E.g. the kidney is an organ of excretion & leaf is an organ of photosynthesis. Tissues within an organ are interdependent. E.g. within a leaf: Spongy mesophyll is adapted for gas exchange; it depends on conc gradients of carbon dioxide & oxygen, created by photosynthesis in palisade mesophyll. Palisade mesophyll is adapted for photosynthesis; it depends on spongy mesophyll for a supply of carbon dioxide & for removal of oxygen.
How is organ systems an example of emergent properties?
- Organ systems: Groups of organs interact with each other to perform an overall function of life. These groups are known as organ systems.
- Circulatory
- Digestive
- Endocrine
- Gas exchange
- Integumentary
- Lymphatic
- Muscular
- Nervous
- Reproductive
- Skeletal
- Urinary
How is organism an example of emergent properties?
- Organism: An organism is a living individual made up of interconnected parts – organ systems, composed of organs, made up of tissues with constituent cells. These parts are interdependent so failure of a single group of cells in a tissue can cause an organism to die.
Parts of an organism interact, & integration of body systems results in emergent properties. E.g. a cheetah is a successful predator. However, this may be difficult to predict if each component is studied separately. To understand emergent properties of organisms, you must consider systems as a whole.
How is the endocrine and nervous enable integration?
Nervous system & endocrine system are used for internal communication. Both send messages that enable integration of organs in animal bodies.
What is the nervous system?
In nervous system electrical impulses are used to send messages by cells called neurons which transmit & receive impulses. Responses occur quickly but are short lived.
What is the endocrine system?
Endocrine system: Hormones are chemical substances that are produced & secreted from cells of ductless or endocrine glands. In effect, hormones carry messages about body – but in a totally diff way from nervous system – they travel in bloodstream.
Compare the characteristics of the nervous and endocrine system. (Main components, types of signal, medium for the transmission of signal, destination of signal, effectors, type of response, speed of response, duration of response)
What does size of multicellular organism impede?
Most multicellular organisms have become so large that it is impossible for nutrients to be transported from cell to cell. Transport system including blood vessels & lymph have evolved to serve that purpose.
What substances are moved around by the transport system?
- Transporting nutrients around body (e.g. glucose, fatty acids, amino acids, vitamins)
- Transporting inorganic ions to all cells
- Transporting waste to kidneys and liver (e.g. urea, toxins, …)
- Transporting gases (oxygen & carbon dioxide)
- Circulating antibodies
- Distribution of heat (temp regulation)
- Absorption & supply of water (hydration)
- Distribution of hormones for development and communication (from endocrine glands to target organs) or osmotic balance
What is the blood composition?
- plasma
- red blood cells (erythrocytes)
- white cells (leucocytes)
- platelets
What role does brain play in body system?
Brain acts as a central info integration organ with capacity to store info for long period of time. System relies on a sensory input which integrates info to effectuate a response.
Describe the three components of the central information organ.
- Sensory input: Info received by brain comes from sensory receptors (in specialised sense organs e.g. photoreceptor in retina of eye or in receptor cells in other organs e.g. pressure receptors in blood vessels).
- Integration: Info is processed (leads to decision-making), stored (in short or long term memory which is essential for learning), & instructions are sent out.
- Motor output: Signals are then sent out along motor neurons to muscles or glands, which execute instructions.
Where is learning and memory formed? And how is information processed?
Learning and memory are formed in the cerebrum - large folded part of brain. Info that is processed by brain is usually conscious – it happens at an awake state of mind.
What are the three main regions of the brain?
The brain is divided into three main regions: the cerebrum, cerebellum and the brain stem.
What is the cerebrum?
Cerebrumis largest part of brain & controls multiple functions like vision, hearing, touch & other senses, speech, thinking & so on. It also initiates and coordinates movement. Cerebrum is divided into two halves, cerebral hemispheres. Each of cerebral hemispheres consists of four lobes: frontal lobe, parietal lobe, occipital lobe & temporal lobe. These lobes control specific functions.
What is the cerebellum?
Cerebellum is located at back of head. Cerebellum plays an important role in voluntary muscular movements, balance & coordination. Like cerebrum, cerebellum is composed of two hemispheres.
What is the brainstem?
Brainstem consists ofmidbrain, pons &medulla oblongata. Pons connect midbrain to medulla. Medulla regulates involuntary activities like heartbeat, breathing rate, blood flow as well as activities like vomiting, swallowing, sneezing & coughing. Medulla continues downward as spinal cord.
Annotate brain diagram.
What does the nervous system consist of?
Where is the spinal cord located and what does it make up?
- Spinal cord is located inside vertebral column (backbone), with pairs of spinal nerves branching off to left & right between vertebrae.
- In humans there are 31 pairs of spinal nerves, each serving a different region of body.
- Together with brain spinal cord makes up central nervous system (CNS).
- It is widest at its junction with brain & tapers going downwards towards pelvis.
What is the role of the spinal cord in unconscious processes?
Spinal cord only coordinates unconscious processes, especially reflexes. Brain is not involved in that pathway.
What is the types of matter which make up the spinal cord ?
White and grey matter
What is white matter?
White matter: myelinated axons & other nerve fibres, which convey signals from sensory receptors to brain, & from brain to organs of body.
What is grey matter?
Grey matter: Contains cell bodies of motor neurons & interneurons, with many synapses between these neurons. These synapses are used for processing info & for decision-making so spinal cord is also an integrating centre.
What is the difference between conscious and unconscious process?
What are two exception, that are both conscious and unconscious?
Many of our actions are non-binary – we may consciously choose to carry them out but the processing then used is unconscious. Striated muscle can be controlled consciously or unconsciously e.g. we consciously choose to stand up & use striated muscles for this action, but unconscious postural reflexes that keep us standing use same muscles. When asleep in bed, we might turn over unconsciously; we use striated muscle to do this. Anus is a sphincter composed of smooth muscle cells, but early in our lives we achieve conscious control of it so we no longer have to wear diapers/nappies.
What are the different types of neurons?
- motor neurons
- interneuron/ relay neuron/ intermediate
- sensory neuron
What is a motor neuron?
Motor neurons have many fine dendrites, which bring impulses towards cell body & a single long axon that carries impulses away from cell body. Function: impulses are carried from CNS to a muscle or gland (effector).
What is a interneuron?
Interneurons, intermediate or relay neurons have numerous short fibres. Each fibre is a thread-like extension of a nerve cell. Relay neurons occur in CNS & connect sensory and motor neurons.
What is a sensory neuron?
Sensory neurons have a cytoplasmic fibre running to cell body (dendron), which is part way along neuron. Exon runs away from cell body.
What is the passage of of impulse of neuron?
Dendrites: collect electrical signal
Cell body: integrates incoming signals & generates outgoing signals to axon
Axon: passes electrical signals to dendrites of another cell or to an effector cell
What are sensory receptors?
Sensory receptors (e.g. light-sensitive rod & cone cells in retina of eye) or free nerve endings (of some sensory neurons act as receptors for touch & heat) are located in the skin & sense organs perceive changes in the environment.
Where does the stimulus pass after being detected by sensory receptor?
Stimulus is passed on to sensory neurons which convey it to CNS in form of nerve impulses carried along axons fibres.
What is appearance of sensory neuron?
Sensory neurons can appear in many different shapes & forms with axon fibres varying in length (they can be more than 1m long – if receptor cell is at end of a toe). There are many diff types of sensory receptors throughout the human body. They are adapted to perception of diff types of stimuli.
What is the location and function of the photoreceptors in the retina of the eye?
Rod & cone cells in retina of eye receive light in form of electromagnetic waves as a stimulus. Signal is transmitted to visual cortex in cerebral hemisphere of brain.
What is the location and function of the Auditory receptors in the ear?
Tiny hair cells imbedded within a fluid in cochlea of ear act as mechanoreceptors responding to soundwaves which are transported through fluid. Processing of sound occurs in auditory cortex of brain.
What is the location and function of the touch, pressure and temperature receptors in the skin?
A number of diff touch receptors in skin respond to diff stimuli such as pressure, pain or temperature & transmit their signal to spinal cord.
What is the location and function of the olfactory receptors in the nose?
These chemoreceptors in form of free nerve endings receive airborne chemicals as a stimulus & transmit their signals to brain.
What is the location and function of the taste receptors in the mouth?
Taste receptors embedded within tissue of tongue act as chemoreceptor, binding to food chemicals as a stimulus. Info is passed to brain.
How is the brain connected to the spinal cord?
Axons of sensory neurons enter either through spinal cord through one of 31 pairs of spinal nerves, or brain by one of 12 pairs of cranial nerves.
How are sensory inputs received by the brain?
Sensory inputs to brain are received by specialised areas in cerebral hemisphere.
What does the left and right side of the brain received?
Left cerebral hemisphere receives sensory input from sensory receptors in right side of body & right side of visual field in both eyes & vice versa for right hemisphere.
What is the cerebral hemisphere responsible for?
Cerebral hemispheres of brain are responsible for control of striated muscles & glands. Striated muscle is attached to bone & used for locomotion. It can be controlled consciously.
How does signal get from brain to target cells?
Nerve impulses from primary motor cortex in cerebral hemispheres move along motor neurons to each striated muscle in body. Cell body a& dendrites of motor neurons are in grey matter of brain. One axon leads out from brain into spinal cord.
What is the role of the primary motor cortex?
Primary motor cortex is main region responsible for control of voluntary (muscle) actions. Several overlapping areas control muscles throughout body, from mouth at one end to the toes at other end.
What is a nerve bundle?
A nerve is a bundle of nerve fibres enclosed by a protective sheet. They vary in size depending on number of fibres, & depending on proportion of them that are myelinated. Widest is sciatic nerve, which is approx. 20mm across. Optic nerve is estimated to contain between 770,000 and 1.7 million nerve fibres. Small nerves may contain fewer than a hundred fibres.
Most nerves contain nerve fibres of both sensory & motor neurons. However, some contain only sensory neurons (e.g. optic nerve) & some contain only motor neurons (e.g. oculomotor nerve). All organs of body are served by one or more nerves.
What is a reflex?
A reflex action is a rapid, autonomic or involuntary response to a specific stimulus. If a response happens without conscious thought, it is called involuntary response. Reflexes are simplest type of coordination by nervous system, as signals pass through smallest number of neurons. This helps to speed up reflexes, which is an advantage if response prevents harm to body.
When are reflexes developed? Which are developed in new-born babies?
Reflexes help identify normal brain & nerve activity. Some reflexes occur only in specific periods of development. Following are some of normal reflexes seen in new-born babies:
- Tonic neck reflex
- Grasp reflex
- Step reflex
- Crawl reflex
What can reflex actions be coordinated?
Some reflex actions are coordinated by spinal cord, such as pain reflex when we lift our foot after treading on a sharp object. Other reflexes are coordinated by brain e.g. constriction of pupil in eye in response to bright light.
What a reflex? What is a stimulus? What is a response?
Reflex: A rapid & unconscious response, e.g. response to pain.
Stimulus: A change in external or internal environment that is detected by a receptor & elicits a response.
Response: A change in behaviour in reaction to a stimulus.
What is a monosynaptic reflex arc?
Monosynaptic reflex arcs consist of a stimulus, receptor, sensory neurons, (interneurons), motor neurons and an effector (muscle or gland) which result in a response.
What is the function of receptors in monosynaptic reflex arc?
- Sense a change in conditions, known as a stimulus.
- Each receptor cell detects only one type of stimulus.
- Nerve endings of some sensory neurons can perceive a stimulus directly, so there is no need for a separate receptor cell.
- Pain & heat are detected in this way by nerve endings in skin.
What is the function of sensory neurons in monosynaptic reflex arc?
- Receive signals, either from receptor cells or from their own sensory nerve endings, & pass them to neurons in CNS.
- To do this they have long axons that carry nerve impulses from receptor to spinal cord or brain.
- These axons end at synapses with interneurons in grey matter of spinal cord or brain.
- Grey matter is tissue containing many cell bodies of interneurons & motor neurons.
What is the function of Interneurons in monosynaptic reflex arc?
- These cells are located inside CNS.
- They typically have many branched fibres called dendrites, along which nerve impulses travel.
- They process signals brought by sensory neurons & make decisions about appropriate responses.
- They do this by combining impulses from multiple inputs & passing impulses to specific other neurons.
- Decision-making process that results in a reflex action is very simple because there may be one interneuron connecting a specific sensory neuron to motor neuron that can cause an appropriate response.
What is the function of motor neuron in monosynaptic reflex arc?
- They receive signals via synapses with interneurons.
- If a threshold potential is achieved in a motor neuron, an impulse is passed along axon which leads out of CNS to an effector.
- Axon does not change its position or connections, so impulse always travels to same effector cell or small group of effector cells.
What is the function of effectors in monosynaptic reflex arc?
- These carry out response to a stimulus when they receive signal from a motor neuron.
- There are 2 types of effector:
Muscles respond by contracting e.g. muscles in leg contract to lift the foot off a sharp object
Glands responds by secreting e.g. smell of food may cause glands in head to secrete saliva.
What is role of cerebellum?
Cerebellum controls balance & muscle contraction. It does not make decisions about which muscles will contract but it fine-tunes & coordinates timing of contractions. Cerebellum helps us to keep balance, maintain posture, but also is involved in formation of muscle memory.
What is the circadian rhythms?
Circadian rhythms are controlled by a ‘biological clock’ within brain. This rhythm is a 24-hour cycle & continues even if a person is placed experimentally in continuous light or darkness as they are controlled by an internal system. This rhythm is controlled by melatonin.
What time does melatonin secretion start and stop?
Start: 21:00
Stop: 7:30
What is the role of the suprachiasmatic nuclei?
Suprachiasmatic nuclei set & follow a daily rhythm (even when grown in vitro with no external clues).
What is the role of melatonin?
SNC control secretion of hormone melatonin by pineal gland. When retina is stimulated through expose to light, release of melatonin is inhibited.
How is melatonin removed from the body?
Melatonin is rapidly removed from blood by liver so blood concentrations rise & fall rapidly in response to these changes.
What is the effect of melatonin?
Most obvious effect of melatonin is sleep-wake cycle. High levels of melatonin secretion cause drowsiness & promote sleep during night. Falling levels induce wakening at end of night. Melatonin also contributes to night time drops in body temp. Melatonin receptors have been discovered in kidney, suggesting that decreased urine output at night may be another effect.
What happens when there is no light, to the circadian rhythm?
When humans are placed experimentally in an artificial environment with no light cues to indicate time of day, SCN & pineal gland usually maintain a rhythm of slightly longer than 24 hours. This shows that timing of rhythm is normally adjusted by a few minutes or so each day so that it is synchronised with diurnal cycle. A special type of ganglion in brain detects light of wavelength 460-480nm & passes impulses to cells in SCN. This signals to SCN timings of dawn & dusk & allows it to adjust melatonin secretion so it corresponds with day-night cycle.
What is the other effects of melatonin?
Release of melatonin has also a knock-on effect on several other metabolic or homeostatic functions in body by stimulating body temp, hunger & acetylcholine production.
What effect of epinephrine (adrenaline) ?
- Epinephrine (adrenaline) has effects on most tissues. In particular when preparing the body for vigorous activity, epinephrine plays an important role.
- It is secreted by adrenal glands.
- Secretion is controlled by brain.
- When it reaches tissues where it has an effect, it binds to adrenergic receptors in plasma membrane of target cells. This triggers responses inside these cells.
What is the effect of epinephrine (adrenaline) on muscle cells during vigorous exercise?
Muscle cells break down glycogen into glucose, which can be used in respiration. Skeletal muscles used during vigorous activity receive a greater volume of blood per minute & this blood carries more glucose & oxygen.
What is the effect of epinephrine (adrenaline) on liver cells during vigorous exercise?
Liver cells also break down glycogen into glucose, which is released into the blood stream.
What is the effect of epinephrine (adrenaline) on Bronchi and bronchioles in lungs, during vigorous exercise?
Bronchi & bronchioles dilate due to relaxation of smooth muscle cells, so airways become wider & ventilation is easier. Ventilation rate increases so a larger total volume of air is breathed in & out per minute.
What is the effect of epinephrine (adrenaline) on heart and sinoatrial node during vigorous exercise?
Sinoatrial node speeds up heart rate, so cardiac output increases.
Arterioles that carry blood to muscles & to liver widen due to relaxation of smooth muscle cells (vasodilation) so more blood flows to them. Arterioles that carry blood to gut, kidneys, skin & extremities become narrower due to contraction of smooth muscle cells (vasoconstriction) so less blood flows to them.
What is the hypothalamus and where is it located?
Hypothalamus is a small region in brain that has major roles in integration of body systems, linking nervous system to endocrine system via the pituitary gland. It directs release of hormones into blood. It consists of a thin wall of tissue located on left & right sides of 3rd ventricle & below it.
What is the role of specialised areas in hypothalamus?
Specialised areas in hypothalamus (called nuclei) can act as sensors for blood temperature, blood glucose concentration, osmolarity and concentration of various hormones. Many nuclei receive signals from sense organs, either directly or indirectly via the cerebral hemispheres. There are also inputs from other parts of the brain, such as the medulla oblongata, hippocampus and amygdala.
What is the relationship between hypothalamus and pituitary gland?
There are close relationships between hypothalamus & pituitary gland, which is located directly below it & connected to it via a narrow stalk. Pituitary gland responds to directives from hypothalamus, releasing a range of diff hormones. Pituitary gland has 2 distinct parts; anterior lobe & posterior lobe. These 2 lobes operate in diff ways, but both of them secrete hormones into blood capillaries under direction of nuclei in hypothalamus.
What hormones are produced by anterior pituitary glans?
- HGH (human growth hormone)
- TSH (thyroid stimulating hormone)
- LH (luteinising hormone)
- FSH (follicle stimulating hormone)
- prolactin
What hormones are produced by posterior pituitary gland?
- ADH (Antidiuretic hormone)
- Oxytocin
How is osmoregulation and puberty based on system integration by the hypothalamus and pituitary gland?
- Osmoreceptors in hypothalamus constantly monitor solute conc of blood. This & other inputs influence how much ADH is produced by neurosecretory cells in hypothalamus. Axons of neurosecretory cells transport ADH to pituitary gland, where it is secreted into blood capillaries.
- Hypothalamus initiates puberty by secreting GnRH, a neurohormone that stimulates secretion of LH & FSH by pituitary gland. These hormones in turn stimulate secretion of testosterone in males & oestradiol in females, leading to changes associated with puberty.
What is sinoatrial node (SAN)?
SAN is a special group of cardiac muscle cells in the wall of the right atrium. It acts as a pacemaker for heartbeat. Pacemaker receives signals from cardiovascular centre, in medulla oblongata of brain via 2 nerves.
What two nerves affect the pace of the heart?
- Sympathetic cardiac nerve carries signals from medulla oblongata to pacemaker to speed up beating of heart (increase in frequency).
- Vagus nerve carries messages from brain to pacemaker to slow down beating of heart.
What is the role of chemoreceptors and baroreceptors?
Chemoreceptors & baroreceptors detect changes in blood pressure. Both types of receptors adjust base rhythm of sinoatrial node according to demands. Through stress, emotions or physical exercises (CO2, O2) heart rate can be modified which in turn affects BP.
Where is the chemoreceptor located?
Chemoreceptors in aorta & carotid arteries monitor blood oxygen conc & others monitor pH.
What is the response of the chemoreceptor when there is high and low oxygen concentration?
- High oxygen conc & high pH activate vagus nerve resulting in a decrease of heart rate.
- Low oxygen conc & low pH (due to increase of CO2) during physical exercise result in an activation of cardiac nerve by releasing epinephrine from adrenal glands increasing heart rate.
Where is the baroreceptor located?
Nerves supplying cardiovascular centre bring impulses from stretch receptors (baroreceptors) located in walls of aorta, in carotid arteries, & in wall of right atrium, when change in blood pressure at these positions is detected.
What is the response of the baroreceptor when there is high and low blood pressure?
- When blood pressure is high in arteries, rate of heartbeat is lowered by impulses from cardiovascular centre, via vagus nerve.
- When blood pressure is low, rate of heartbeat is increased via cardiac nerve.
What does the sinoatrial node respond to?
- SAN also responds to epinephrine in blood, increasing heart rate.
- This happens when amygdala sends distress signals to hypothalamus, which sends signals directly via nerve fibres to cells in adrenal gland that secrete epinephrine.
- Epinephrine can override normal feedback control mechanisms while the body responds to a threat (often a vigorous physical activity).
What is the role of chemoreceptors in arteries?
Chemoreceptors in arteries monitor blood pH, determined by CO2 conc in blood & communicate with brainstem (medulla and pons). If blood pH is low, breathing becomes deeper & more frequent.
What regulates ventilation rate?
Ventilation rate is number of times air is inhaled per minute. It is regulated by negative feedback mechanism.
What causes the pH to become low and what is the consequence?
Carbon dioxide conc must not be allowed to rise too high, bc this causes a decrease in pH known as acidosis, with harmful consequences. Normal range for blood pH is 7.35-7.45. Levels below 6.8 can be life-threatening.
What is the gut?
Gut is a long tube extending from mouth to anus. As food passes along gut, secretions are added to it from gland cells in stomach and from pancreas into small intestine. Enzymes in these secretions hydrolyse molecules so that they can pass through epithelium cells that line gut.
What is the first phase of swallowing?
1st phase of swallowing, in which food is passed from mouth cavity by the tongue (striated muscle) to pharynx (where it touches touch receptors which pass to brainstem which stimulates contractions that push food down the pharynx) & egestion of faeces (defecation – ring of muscle in anus = smooth muscle – a sphincter), is voluntary (CNS, cerebral cortex).
How does the food pass from the pharynx to the stomach?
When food passes from pharynx to stomach via oesophagus via peristalsis, involuntary phase is coordinated by the enteric nervous system.
What is peristalsis and how does it work?
Peristalsis moves food along small intestine. Bolus of food is mixed with enzymes from pancreas under action of muscles. Mass of food is moved along digestive tract under the subsequent contraction of circular (cells arranged in rings) & longitudinal (cells orientated along the axis of gut) muscles (smooth) in wall of small intestine.
How do plants control the direction of growth of both roots and shoots?
Plants control direction of growth of their roots & shoots as a response to an external stimulus such as gravity or sunlight. Process of differential growth to directional stimuli are called tropism or tropic responses.
What is the difference between a positive tropism and negative tropism?
Positive tropism = growth towards stimulus
Negative tropism = growth away from stimulus
What happens if there is a difference in speed of growth of the roots to the shoots?
If one side of root or shoot grows more quickly than other side, root or shoot will become curved.
Root or shoot tip will then be pointing in a new direction.
Most roots are positively gravitropic (geotropic) which means they grow downwards, in same direction as gravity.
Most shoots are positively phototropic & negatively gravitropic which means they grow towards source of light, &, in darkness, they grow upwards in opposite direction to gravity.
How is flowering plant growth regulated?
In flowering plants, differential growth is regulated by plant growth hormones. One of main ones is auxin (Indole 3 acetic acid, IAA), which has effects on growth & development by direct action on components of growing cells, including walls, & on gene expression mechanisms operating in nucleus.
What direction do shoots grow towards?
Shoots usually grow towards highest light intensity in their environment. If a shoot tip detects that it is not growing towards brightest light, it responds by differential growth.
What happens to the side facing the light?
Side of shoot facing brighter light is stimulated to grow at a slower rate than shadier side causing the shoot to curve towards light. This is due to the auxin which collects on the shady side.
Annotate diagram to explain positive phototropism?
What is Auxin?
Auxins (Indole 3 acetic acid, IAA) promote growth by elongating cells. Auxins are produced i coleoptile, a protective sheath around emerging roots or shoots. Under normal conditions, auxin is distributed evenly along shoot, causing even (vertical) growth.
What happens if phototropism receptors detect light?
If phototropism receptors in coleoptile detect a light stimulus from one direction, auxin is transported to other/opposite side of growing shoot using specialized transport proteins (PIN3), where it causes changes in elasticity of coleoptile/cellulose cell wall.
What does the uneven distribution of auxin lead to?
Uneven distribution of auxin leads to increased growth on one side – & plant grows towards direction of the light. This is positive phototropism.
What are plant hormones?
A hormone = chemical message that is produced & released in one part of an organism to have an effect in another part of organism. Plants & animals produce, transport & use hormones in diff ways, so plant hormones = phytohormones.
Phytohormones are signalling chemicals that control all aspects of plant growth & development.
What are examples of plant hormones?
- Abscisic acid
- Cytokinin
- Gibberellin
- Auxin
- Ethylene
What is the difference between phytohormone and hormone in animals?
Phytohormones occur in very low conc, making it difficult to determine their precise role.
They can diffuse from cell to cell or be carried in phloem or xylem. Contrary to hormones in animals phytohormones are: often not transported widely & some are only active at sites of production not particularly specific & often have multiple effects in contrasting ways. They are also produced in a region of plant structure (e.g. stem or root tips, in unspecialised cells)
What is the function of Gibberellin?
Growth - Phytohormones can either promote or inhibit growth, by affecting rates of cell division & cell enlargement. E.g. Gibberellin promotes stem growth.
What is the function of Ethylene?
Development - Phytohormones can promote or inhibit aspects of development such as whether a bud starts to grow to produce a side shoot, or whether apex of a stem produces more leaves or changes to produce flowers. E.g. Ethylene promotes ripening in fruits & other aspects of development.
What is the function of Jasmonic acid?
Response to stimuli - Tropic responses are controlled by phytohormones. Tendrils of climbing plants respond to touch stimuli by coiling around a potential support. Communication using electrical signals is used for rapid responses e.g. capture of an insect by a Venus fly trap plant. However, a phytohormone called jasmonic acid triggers subsequent secretion of enzymes to digest fly.
What is the function of Auxin?
- Root & shoot growth*
- Fruit development
- Leaf development
- Wound response
Whenever auxin affects cell growth, it does so by changing pattern of gene expression.
What does auxin directly affect?
Auxin directly affect components of growing cells, including cell walls, & gene expression mechanisms operating in nucleus.
How do auxins change the pattern of gene expression?
When auxin binds to a plant auxin receptor upon stimulation of an environmental stimulus (e.g. light) it promotes transcription of specific genes coding for glycoproteins (PIN3 proteins) which act as auxin efflux carriers. These proteins are found in plasma membrane of cells that facilitate polar transport of auxin (efflux!).
What is the name of the specialized proteins, which facilitates the transport of auxin from cell to cell? And where is it located?
PIN3 proteins
Plasma membrane of stem.
What is the transport of auxin?
Auxin transport across cells is polar, with its entry into cell being passive (by diffusion) & its efflux being active (ATP-driven)
How is auxin transported into and out of the parenchyma cell of a plant?
- Auxin (IAA) is produced in apical shoot meristem. It can freely diffuse into cell, but not out of them.
- It then enters plant cells (via passive transport) as IAA- or IAAH, which is protonated form).
Auxin can enter cells by passive diffusion as long as its carboxyl group (COOH) remains undissociated. Cytoplasm of plant cells is slightly alkaline, so once auxin has entered a plant cell carboxyl group dissociates by losing a proton. This leaves it with a negative charge (COO-), so auxin is trapped inside plant cell. - Once inside cell auxin cannot leave except through membrane proteins called auxin efflux pumps (PIN3 carrier proteins) via active transport. These proteins can pump auxin in its charged state across plasma membrane into surrounding cell wall. Cell wall is slightly acidic, so auxin reverts to its uncharged state.
- For auxin to leave a conc gradient must be set up, so auxin is transported to one side of cell. It can then diffuse into adjacent cell.
Where are the efflux carriers located?
Plant cells can control distribution of auxin efflux carriers. To transport auxin across a tissue & generate a conc gradient, carriers are moved to same side of each cell. Auxin is therefore pumped out on that side & tends to enter cell by diffusion on other side.
What happens to cell wall during plant growth?
Cell wall allows high turgor pressures to develop inside plant cells without them bursting. Turgidity helps shoots resist forces of gravity & wind. It gives roots strength to push through soil. When plant tissue has finished growing, cell walls can be thickened to provide extra strength & resilience. Until then, they must remain thin enough to allow cells to increase in size. Cell walls are constructed using bundles of cellulose molecules, called microfibrils. When wall needs to be thickened, extra microfibrils are made & passed out through the plasma membrane. Cellulose molecules are inelastic, so a microfibril cannot stretch or extend in length. Therefore, extension of cell walls involves microfibrils moving further apart or sliding past each other. Therefore, extension of cell walls involves microfibrils moving further apart or sliding past each other.
Cellulose microfibrils are crosslinked by a variety of other carbohydrates, including pectin.
Strength of these crosslinks is influenced by pH. Decreases in pH weaken links, allowing wall to extend. Auxin promotes synthesis of proton pumps, which are inserted into plasma membrane. These pumps transport H+ ions from inside the cell (protoplast) to cell wall outside apoplast), acidifying apoplast. This allows wall to expand so cell can elongate. Conc gradients of auxin cause gradients of apoplastic pH, leading to differential cell wall extensions & growth – as in phototropism.
What are the step to auxin activating proton (H^+) pumps?
- Auxin stimulates proton pumps in plasma membrane.
- Proton pumps lower pH in cell wall – it becomes acidic.
- Acidity activates expansin enzymes that loosen wall`s fabric.
- Cell wall loosening enzymes cut cross linking polysaccharides.
- With cellulose in cell wall loosened, cell can elongate under turgor pressure.
How does the promotion of hydrogen secretion, by auxin, elongate cells?
Auxin promotes hydrogen secretion into cell walls & spaces between cells, acidifying the cell wall. Low pH causes proteins called expansion to alter pattern of hydrogen bonding between polysaccharides in cell wall, loosening cross-links between cellulose molecules to facilitate cell elongation.
What is gravitropism?
Gravitropism in roots is also auxin dependent. Upward growth of shoots & downward growth of roots is in response to gravity.
Auxin has opposite effect in tissue of root cells & inhibits cell growth.
What are the steps of gravitropism?
- Specialized cells called statoliths accumulate on lower side of cells due to gravity.
- Consequently, PIN3 transporter proteins that direct auxin transport to bottom of cells, redistribute.
- Here, high auxin concentrations inhibit cell elongation.
What is the relationship between auxin and auxiliary buds?
Auxin promotes elongation of cells in shoot apex – & enhances stem elongation at low conc. It also inhibits growth & development of lateral buds that occur immediately below terminal growing point (apical dominance). When apical bud is intact, axillary buds are inhibited to grow by auxin while stem continues to elongate. When apical bud is removed, axillary buds grow into lateral branches. When auxin is added to decapitated stem, it again inhibits growth of axillary bud .
What is hte relationship between cytokinins and auxin?
Cytokinins (another type of phytohormone) are antagonistic to auxin – they pass from root apex (tips) e.g. back up stem in xylem attracted by auxin & promote lateral bud growth.
What determines whether auxiliary bud is formed?
Relative ratio of cytokinins & auxins determine whether axillary bud will develop.
Together they balance root & shoot growth.
What does pruning allow for?
Manipulating a natural response to damage (known as principle of apical dominance, i.e. control of lateral growth by auxin & suppressor hormones) by processes such as pruning allows horticulturist to determine shape, size & productivity of many fruiting trees & bushes.
How does nutrients and water availability affect the concentration of auxin and cytokinins?
If nutrient & water is available, cytokinin is produced in roots and from there transported to shoot where it stimulates growth. Proportional concentrations of auxin & cytokinin determine inhibitory effect.
What happens if plants has shoot eaten or roots eaten?
Roots eaten = Auxin high and cytokinin low
Shoot eaten = Auxin low and cytokinin high
What is the process of ripening fruits?
Process of fruit ripening happens over a relatively short time & it involves colour changes from green, changes to fruit flesh (softening by partial digestion of cell walls), conversion of acids & starch to sugar & development of scent (volatile chemical).
What is the biological purpose of the positive feedback loop of ripens fruits?
In many plant species, these changes are stimulated by ethylene using a positive feedback mechanism.
Once seeds are ready for dispersal, ethylene stimulates ripening & ripening fruits produce ethylene. Ethylene is volatile & release of it by one fruit will cause others to ripen. This helps to synchronise ripening of fruits on a plant such as a peach tree. It is useful for fruit farmers but in wild plants, it encourages animals that disperse seeds to visit a plant by ensuring that plenty of ripe fruit is available at same time.
