Organisms Respond To Changes In Their Environment: - Control Of Heart Rate.

- Control Of Heart Rate -

The Autonomic Nervous system

It has two subdivisions:

1. Sympathetic nervous system - stimulates effectors so speeds up any activity. Acts rather like an emergency controller // allows us to cope with stressful situations heightening our awareness and prepare us for the activity. 
2. Parasympathetic nervous system -  inhibits effectors so it slows down any activity. It controls activities to a normal resting conditions // conserves the energy and the body's reserves are replenished. 

The system oppose each other - antagonistic. If one contracts a muscle the other relaxes a muscle. Each doing the opposing job 

- Control Of Heart Rate -

Cardiac muscle = myogenic // able to contract without receiving signals.

1. Sinoatrial node (SAN) is in the wall of the right atrium, recieves an electrical activity which spreads across both atria casuing them to contract. SAN is like a pacemaker, setting the rhythm of the heart. 
2. Layer of non-conductive collagen tissue // atrioventricular septum // stops waves of electrical activity from being passed directly to the ventricles. 
3. The waves are then passed to/enters the atrioventricular nodes (AVN) This is in between the atria 
4. There is a slight delay when the AVN passes the electrical activity to the bundle of His // a series of muscle fibres (Purkyne tissue) which collectively make up the bundle of His // the atria would have had to emptied before the AVN reacts. 
5. Bundle of His grouped of muscle fibres responsible for conducting the waves of electrical activity between ventricles to apex. // bottom of the heart. 
6. Purkyne tissue carries the waves of electrical activity into a muscular walls of both ventricles, both contracting at the same time // from the bottom up. 

- Modifying the resting heart rate - 

Adult human hearts has a resting heart beat of 70BPM // important to be able to change this heart rate in order to meet the varying demands for oxygen.
During exercise the heart rate is likely to increase to double the original resting heart rate.

Medulla Oblongata = controls the changes to the heart rate in the a region of the brain // sub-divided into two centres:

1. Centre that increases heart rate - linked to sinoatrial node - sympathetic nervous system (SNS)
2. Centre that decreases heart rate - linked to sinoatrial node - parasympathetic nervous system (PNS) 

- Control by chemoreceptors -

Pressure receptors = baroreceptors in the aorta & carotid arteries // stimulated by high & low blood pressure. 

Chemical receptors = chemoreceptors in the aorta, carotid arteries, and medulla // monitor oxygen levels in the blood and carbon dioxide and pH - both indicators of O2 levels. 

This works by: 

1. Blood has a higher than normal concentration of carbon dioxide // pH is lowered. 
2. Chemorecpetors in walls of carotid arteries // aorta detect & increases the frequency of nerve impulses to the centre in medulla oblongata - increases heart rate. 
3. This centre increases the frequency of impulses via SNS to SAN increasing the rate of production of electrical waves by SAN thus increasing the heart rate
4. Increased blood flow that causes leads to lungs removing the carbon dioxide, CO2 concentration return to normal in the blood. 
5. pH of the blood rises to normal // the chemoreceptors in the walls of the carotid arteries & aorta reduce frequency of nerve impulse to the medulla oblongata 
6. Medulla oblongata reduces frequency of impulses to SAN, leads to a reduction in the heart rate. 

- Control by pressure receptors - 

The pressure receptors = occurs within heart walls // carotids arteries & aorta // sequence of that follows changes in activity levels:

• When blood pressure is higher than normal = receptors transmits more nervous impulses to the centre in medulla oblongata = decreases heart rate. Impulses sent via PNS (Parasympathetic) to SAN from centre. 
• When blood pressure is lower than normal = receptors transmit more nerve impulses to centre in medulla oblongata = increases heart rate. Impulses sent via SNS (Sympathetic) to SAN from centre. 

Organisms Respond To Changes In Their Environment: - Receptors

- Receptors - 

A Pacinian corpuscle is a sensory neruone :

1. Specific to single type of stimulus - responds to mechanical pressure 
2. Produces a generator potential, acting as a transducer which converts the change in form of energy by stimulus into nerve impulses, that can be understood. Nerve Impulse = energy 

Receptors in nervous system convert energy of the stimulus into a nervous impulse = generator potential. 

- What does the structure of the Pacinian corpuscle look like? -

The sensory neurone ending at the centre of the Pacinian corpuscle has special sodium channel in the plasma membrane = stretch-mediated sodium channel. 

The permebility to sodium changes when it is deformed = i.e. stretching the pacinican corpuscle. 

- What is the function of the Pacinian corpuscle? -

1. Pacinian corpuscle contain the end of the sensory neurone - wrapped in many layers of connective tissue = lamellae
2. When it is stimulated the lamallae is deformed and presses on the sensory nerve endings. 
3. This causes the sensory neruone's cell membrane to stretch, defroming the stretch-mediated sodium ion channels. // channels open and sodium ions diffuse into the cell 
4. Influx of the sodium ions changes the potential of the membrane - becomes depolarised - a generator potential is created. 
5. If the generator potential reaches the threshold an action potential is triggered. 

- Differences between Rods and Cones -

Rods = sensitive // firing action potential in dim light. Many rods join to only one neurone, this means that a weak generator potential needed, as well as, a weak threshold to trigger the action potential. 

Rods have low visual acuity // many rods attached to one neurone 

Cones = less sensitive // enables to cones to differentiate whether an image is of two objects or one object. 

Cones have high visual acuity // one cone is attached to one neurone 

when the light hits two cones from two points two action potentials are produced and go to the brain. 

In other words, this enables the two points that were close together as two separate points. 

Organisms Respond To Changes In Their Environment: - A Reflex Arc

- Reflex Arc -

The nervous system has two main devisions:

1. Central Nervous System = made up of the spinal cord and the brain ~ (CNS)
2. Peripheral Nervous System = made up nerves branching from either the brain or the spinal cord. ~ (PNS) 

Peripheral System the divides into subdivisions: 

1. Sensory neurons = carries electrical impulses AWAY from receptors TO CNS 
2. Motor neurons = carries nerve impulses AWAY from CNS TO effectors 

Motor neurons are sub-divided into:

1. Voluntary nervous system = carries nerve impulses to body muscle // conscious control = voluntary 
2. Autonomic nervous system = carries nerve impulses to glands // smooth muscle & cardiac muscle under subconscious control = involuntary. 

This is a summary of the nervous organisation. ↑

Spinal Cord

This is summarised in the picture // no need for additional information the spinal cord for the specification is pretty simple. 

Reflex Arc 

Involuntary response to a sensory stimulus = Reflex Arc.

For example, withdrawal reflex // a spinal reflex 

Spinal reflex has 7 main stages:

Stimulus > Receptor > Sensory Neurone > Coordinator > Motor Neurone > Effector > Response  

An example of this would be if you was to touch a hot surface -

Stimulus = heat from the surface

Receptor = temperature receptors on the skin generates a nerve impulse in sensory neurone

Sensory Neurone = passes impulse to spinal cord

Coordinator // Intermediate neruone = links sensory to motor neruone in spinal cord

Motor Neurone = carries the impulse from spinal cord to the muscle in the upper arm

Effector = muscle in the upper arm is stimulated to move

Response = pulling your hand away from the hot surface 

Organisms Respond To Changes In Their Environment:- Plant Growth Factors

- Plant Growth Factors -

Plants respond to many different things, a number of factors they do respond to would include:

1. Light 
2. Gravity 
3. Water 

Control of tropism by IAA.

IAA = Indoleacetic acid // an important auxin produced in the tips of the shoots.
IAA is moved around the plant to control of tropism - moving by:
short distance = diffusion or active transport
long distance = via the phloem

Different parts of the plants would have different concentrations of IAA.
Uneven distribution of IAA means there is uneven growth of the plant.

- How is Indoleacetic acid (IAA) involved in phototropism? - 

Light is detected by photorecpetors, which set off a chain of reactions leading to the redistribution of the auxin IAA. More IAA moves to the shaded side of the stem.

IAA causes the cells to elongate by loosening the structure of the cell wall. The mechanism, for this process is unknown, but is thought to involve hydrogen ions (H+).

Because the cells on the shaded slide have a higher concentration of IAA they stretch more than the cells in the light. This causes the shoot to bend towards the light. // = Positive phototropism.

Populations In Ecosystem: - Conservation Of Habitats

- Conservation Of Habitats - 

 

So what is conservation?

Conservation is the protection and management of species and habitats in a sustainable way.



 

 

What are the main reasons for conservations?

 

 

1. Personal - maintaining our planet // supporting our life support system.
2. Ethical - other species should be able to co-exist with us since they have been here for a much longer time than we have.
3. Economics - long term productivity is greater if ecosystems are maintained in their natural (balanced) states. These organisms have a vast genetic pool of genes which have a capacity to make millions of substances // substances = valuable future sources.
4. Culture and Aesthetic - Habitats provide variety to the environment and everyday life, for example, inspiring many writers or providing entertainment.

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Remember -

 

PEECA

 

Like PieCaChu - from Pokémon

 

P - Personal

E - Ethical

E - Economics

C - Culture

A - Aesthetics

 

 

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- So how are we able to conserve habitats by managing succession -

 

 

Species that had existed in the earlier stages no longer exist in the present due to the climax community. Their habitats have been destroyed as a result of succession or other species have out-competed the pioneering species, another would be due to human activities.

 

By conserving the habitats you would be able to prevent a change to the next stage so the species do not exist when it could have been prevented.

 

If the factors effecting further development of succession is removed then the ecosystem would develop in to a climax community naturally // = secondary succession.

 

 

What are the problems with conservation of habitats? 

 

 

There are conflicts with human needs and conservations, farming and habitats have always been a problem.  

With farming, the grass is needed for the cattle, however the cattle grazing using the grass would reduce the habitats for other species. Therefore a balance would need to be found between the two and to also maintain the sustainability of natural resources.

 

 

 

Populations In Ecosystems - Succession

- Succession - 

Succession occurs over a number of steps: 

At each of these new stages the species colonies and alter the environment at each stage. This could go either one of two ways:

1. The environment is made less suitable for the existing species. Which means that the new species may out compete the existing species as they may have adapted to the environment // would have a given advantage. 
2. The environment is made more suitable for different species that have different adaptations. This species may be out competed by the better adapted new species. 

Stages of succession 

1. Single organisms rapidly multiple through asexual reproduction // to build the population. 
2. A vast quantity of wind-dispersed seeds/spores produced // reach isolated areas 
3. Rapid germination of seeds // do not require a period of dormancy
4. The ability to photosynthesise // light = available, other sources of food = not available 
5. Soil has few or no nutrients // able to fix nitrogen from the air 
6. tolerance/adaptations to the extreme conditions. 

There would need to be a stable state to find a balance in the equilibrium of species with few, if any, new species replacing those have become established. In this state there are many species that flourish // increase in biodiversity = climax community. 

The climax community is determined by the limiting abiotic factors. 

For examples - trees are unlikely to grow on mountains as the conditions are too cold and there is little soil for the roots to bury itself in to collect the required nutrients for the tree - especially at the start of succession. 

During succession there are a number of common features that occur 

• Non-living (Abiotic) environment becomes less hostile - soil forms // retains water & nutrients. 

• A greater number and variety of habitats and niches - this produces 

• Increased biodiversity - different species occupy these habitats // reaches peak in mid-succession // decreases as climax community is reached - in other words the dominant species out compete the pioneer species. 

• More complex food webs 

• Increase in biomass // during mid-succession. 

Secondary succession = when land has already sustained life however due to land clearance for agriculture for example, forest fire, the ecosystem returns to it's climax community // occurs more rapidly. Land has been changed/altered in a way that results in the climax community being different. 

This is an example of an ecological succession : ↓

Populations In Ecosystems: - Investigating Populations

- Investigating Populations - 

Investigating population:

There are a number of sampling techniques

- random sampling using frame quadrats or point quadrats

- systematic sampling along a belt transect  

Quadrats:

There are two types of quadrats that are frequently used.

Point quadrat consisting of horizontal bar supported by two legs. The intervals are set along the horizontal bar are ten holes each of which are long pins may be dropped. Each species that is touched by the pin is recorded.

Frame quadrat is a square frame divided by string or wire into equally sized subdivisions it's designed to make it more compact, so it's easy to store and transport. It can be placed in the areas being studied.

Point Quadrat Frame Quadrat

There are three factors to consider when using quadrats:

1 )The size of the quadrats to use = this depends on the size of the animal or organism being counted and how they are distributed within the area. Larger species require larger quadrats. In an area which the species are not largely distributed a large number of small quadrats would give a more representative result than a small number of large ones.

2)The number of sample quadrats to record within the study area = larger the number of sample quadrats the more reliable the results will be. As the recording the species within a quadrats

3)The position of each quadrat within the study area = produce a statistically significant results a technique - random sampling must be used

Sampling at random

To obtain a true random sample is to:

> Lay out two long tape measures at right angles, along two sides of the study area.

> Obtain a series of coordinates by using random numbers taken from a table or generated by a computer.

> Place a quadrat at the intersection of each pair of coordinates and record the species within it.

Systematic sampling along belt transects

- Species would need to be measure in a systematic system rather than a random manner. This is important to measure gradual change in the communities of plants and animals to take place.

An example of this would be distribution of organisms along a line of succession. Stages of succession is shown using transects. A belt transect can be made by stretching a string or tape across the ground in a straight line. Frame quadrat is then laid down alongside the line and the species within it recorded. It is then moved along it's own length along a line and the process is then repeated - a record of species in a continuous belt.

Measuring abundance

Random sampling with quadrats and counting along transect used to obtain measures of abundance.

Abundance - number of individuals of a species within a given area for species that don't move around. This is measured in several ways:

• Frequency = likelihood of a particular species occurring in a quadrat.
• Percentage cover = an estimate of the area within a quadrat than a particular plant species covers. This is useful where a species is difficult to count, data could be collected rapidly and individual plants do not need to be covered. Not useful when organisms occur in several overlapping layers.

It's necessary to ensure that the species sample is large, the larger the sample the more representative the data is.

Mark release recapture techniques

Estimated population size  = total no. of individuals in 1st sample X total no. 2nd sample     

                             No. of marked individuals recaptured

The technique requires a no. of assumptions:

1. Proportion of marked to unmarked individual in 2nd sample is the same as the proportion of marked to unmarked individuals in the population as a whole.
2. Marked individuals released from 1st sample distribute themselves evenly amongst the remainder of the population have sufficient time to do so.
3. Population has a boundary = no immigration into or emigration out of the population.
4. Few death and births within the population.
5. Method marking not toxic to the individual nor does it make the individual more conspicuous therefore more liable to predation.
6. Mark or label is not lost or rubbed off during the investigation.

Populations In Ecosystems: - Predation

- Predation - 

Predation

A predator is an organism that feeds on another organism known as their prey.

Predation

→ Occurs when one organism is consumed by another. Evidence of predation and prey in the laboratory does not reflect what happens in the wild. At the same time the it's difficult to obtain reliable data on natural populations as it's not possible to count all of the individuals in the population. Size can only be estimated.

Effect of predator-prey relationship on population size:

The relationship between predators & their prey, it's effects on the population is shown in steps as followed:

→ Predator eat their prey, prey population decreases.

→ Fewer prey available predators in greater competition with each other for the other prey.

→ Predator population then decreases as some are unable to obtain enough prey either survival or for them to reproduce.

→ The prey population increases as they are not being hunted for.

→ More prey available for food.

→ Predator population in turn increases.

These periodic population crashes are important in evolution as there is a selection pressure // means that those individuals who are able to escape predators or withstand diseases or adverse climate change are more likely to survive and reproduce.


An example of this would be: the Canadian lynx and the snowshoe hare:

There has been long observation of the population of snowshoe hare, and it is shown that there is fluctuations in cycles. It can be said that various factors caused the fluctuations i.e the predator Canadian lynx also plays a part in this as well as the availability of food and other sources.

Populations In Ecosystems: - Competition

- Competition - 

Intraspecific competition  

→ Occurs when individuals of the SAME species compete with one another for resources such as food, water, breeding sites. It is the availability of the resources that determines the size of the population.

Example of this would be the squirrels in the picture → 

Interspecific competition  

→ Occurs when individuals of DIFFERENT species compete for resources such as food, light, water. When a population of the two species are in competition one will normally have a competitive advantage over the other.

As a result this species would increase in size gradually whereas the other would begin to diminish. This is if the conditions remain the same ⇒ competitive exclusion principle.

An example of this would be shown in this picture →

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To remember the difference between interspecific and intraspecific competition remember that:

INTRASPECIFIC = has RA in the word and SAME has an A within the word.

INTERSPECIFC = has ER in the word and DIFFERENT has an ER within the word.

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This graph shows the effects of interspecific competition on population size. 

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