Biology Notes (Term 1)

8/18/2019 Biology Notes (Term 1)

1/14

Co-ordination and Response

You have previously learned that one of the 7 characteristics of living organism is irritability orsensitivity. And this is the ability to detect a change in the outer environment and respond to it. A

change in the environment is also called a stimulus (plural stimuli). Actions taken by the body inorder to co-operate with a stimuli are called responses. The body detects a stimulus by parts in thebody called receptors and is able to respond to it through other parts called effectors. Two organsystems are continuously working to detect and respond to stimuli these organ system are calledthe nervous system and the endocrine system.

The Nervous System:

The nervous system is a system of organs working together to detect and respond to stimuli. Thenervous system is made up of two systems the Central Nervous System (C.N.S) andthe Peripheral Nervous System (P.N.S) the peripheral nervous system connects the central

nervous system to the other parts of the body.

Central Nervous System (CNS):

The central nervous system is made up of the brain and the spinal cord. The spinal cord isbasically a big bundle of nerve cells running through a tunnel inside the backbone which protectsit while the brain is protected by the skull. The central nervous system is what gives out orders toother parts of the body to perform certain !obs.

The Peripheral Nervous System PNS:

The peripheral nervous system is the other part of the nervous system. The main !ob of the "#$

is to detect stimuli and send impulses to the %#$ according to the stimuli. The "#$ is made ofreceptors and nerves that carry the impulses.

&eceptor cells are ones whose function is to detect something about its environment. There aremany receptors in the body that are able to detect many changes like temperature touch lightsound and chemicals. There are some organs in the body that are there to detect !ust one stimuluslike the eye for e'ample. These are called sensory orans and they can be defined as a group ofreceptor cells responding to specific stimuli.

ffectors are the opposite of receptors. &eceptors are two detect the stimuli while effectors are tworespond to it. ffectors are usually muscles and glands.

Neurons (Nerve Cells):

#eurones are one of the most important structures of the nervous systems. #eurones act as a wirethat transmits electrical impulses all over the body. ike a cable that consists of many wires a bundleof neurones is called a nerve. There are * types of neurones each type is to transmit electricalimpulses from a specific place to another.


2/14

!otor Neurone: This is a neurone that transmits electrical impulses from the %entral nervoussystem to the effectors.

This neurone is made up of three segments+ the cell body which is the start of the motor neuroneand is in the %#$ a'on which stretches out from the cell body all the way to end of the neuron andthe motor plate which is the end of the neurone and is in the effector muscle.#eurones have features that are common between most animal cells like a nucleus cymiddlelasmand cell surface membrane but they also have some e'clusive features like the a"on. The a'on isan e'tended cymiddlelasm thread along which electrical impulses travel. $ome motor neuroneshave a'ons of length , metre. A'ons are coated by a layer of myelin called myelin sheath this is anelectrically insulating layer which is essential for the proper functioning of the nervous system.

Another e'clusive feature of neurones is dendrites these are several short threads of cymiddlelasmcoming out of the cell body. Their function is to pick up electrical impulses from other cells.

The last e'clusive feature of motor neurones only is motor end plate. This is !ust the end of thea'on which is in the muscle. t passes the electrical impulses from the neurone to the muscle fibres.

Sensory Neurones: like other neurones sensory neurones carry electrical impulses from one placeto another. ut sensory neurones carry electrical impulses in the direction different to that of motorneurones from the receptors to the %#$.


3/14

The sensory neurone/s shape is uni0ue. This is because it is made of a cell body with two armse'tending out of it. The first arm is the a'on which/s other end is in the %#$. The second arm isdendrite which/s other end is in the receptor. The dendrite is similar in structure to the a'on e'ceptthat it !oins the receptor with the cell body. The electrical impulses of the sensory neurone flow fromthe receptor through the dendrite to the cell body then from the cell body to the %#$ through thea'on.

Relay Neurone: &elay neurones are located in the %#$. Their !ob is to pass electrical impulsesfrom the sensory neurone onto the motor neurone so it acts like a diversion.

1here neurones meet they are not actually touching each other. nstead there is a gap calledsynapse or !unction bo'. 1hen the electrical impulses reach the end of a neurone the neuronesecretes a chemical transmitter which passes by diffusion to the other neurone causing the impulsesto be carried from the first neurone to the second.


4/14

Refle" #rc (Nervous System in #ction):

f your finger touches a hot surface receptor cells in the skin of your finger detect a stimulus whichis a sudden rise in the temperature. The receptor uses the energy of the stimulus to generateelectrical impulses. These impulses are then carried by the a'ons of the dendrites of the sensoryneurone through cell body to a'on and from the a'on to the %#$. At the %#$ the electrical impulses

travel through the synapse to the relay neurone which passes it onto the motor neurone. The nerveimpulses are transmitted through the a'on of the motor neurone to the targeted muscle whichcontracts when electrical impulses reach it resulting in your finger being pulled away from the hotsurface. This pathway is called the refle" arc and happens in about a fraction of a second.

Reflex Arc: RECEPTOR → Sensory Neurone → CNS → Motor Neurone →

EFFECTOR

$oluntary and %nvoluntary #ctions:

The refle' arc is a refle' action. &efle' means it is automatically done without your choice. This isbecause when the electrical impulses reach the relay neurone in the %#$ from the receptors someimpulses are carried by other neurones to the brain and some impulses are passes onto the motorneurone to the effector muscle and the response takes place. The electrical impulses going to yourbrain are much slower that the ones going to the effector muscle directly. This is why the refle'


5/14

action takes place before you realise it it is uncontrollable. &efle' actions are said to be involuntaryactions. nvoluntary actions start at the sense organ heading to the effector. They are e'tremely0uick. $oluntary actions are the ones that you make the choice to do. ike picking up a bag fromthe floor for e'ample. Your brain sends electrical impulses to the effector muscles ordering them tocontract so you could pick the bag up. 2oluntary actions are slower than involuntary actions and theystart at the brain.

The &uman 'ye:

The human eye is a sensory organ. This means it is an organ of tissues working together to detectand respond to a specific stimulus which is light.

eatures of the &uman 'ye:

• ens: changes shape to focus light on retina

• Ciliary muscles: contracts and rela'es to ad!ust thickness of the lens

• Suspensory liaments: loosens and tightens to ad!ust thickness of lens

•

%ris: widens and narrows to control amount of light entering the eye depending on lightintensity

• Choroid: middle layer surrounding the eye. t contains many blood vessels

• Sclera: outer most tough protective layer of the eye.


6/14

• Retina: inner most layer. t is sensitive to light and it is where the fovea is and it has rods and

cons

• ovea: very light sensitive spot

• *lind spot: 1here the optic nerve touches the eye. #o light sensitive cells in this area.

&o+ ,e See:

1hen the light hits an ob!ect it is reflected in all directions. 1hen a light ray reflected from the ob!ecthits your eye you see that ob!ect. At the back of your eye there is a spot on the retina called thefovea (blind spot). This spot is full of light sensitive cells. 1hen the light ray falls on the fovea thelight sensitive cells generate electrical impulses that travel through the optic nerve to brain. 1henthe electrical impulses reach the brain the brain generates the image you see. This all happens inless than a fraction of a second.

ut this is the general idea only. ight rays enter theeye from every direction. f they are not focused onthe fovea they will most probably not hit it and wewon/t see. 3ere comes the role of the front part ofthe eye. 1hen the light ray hits the eye at an angleit first has to penetrate the cornea which refracts(bends) the light ray inwards. The cornea acts as aconverging (conve') lens. Then the light penetratesthe lens which refracts the ray a little more inwardsfocusing the light ray on the fovea. And thus thelight ray is focused on the retina. 1hen the ray hitsthe retina the closer to the fovea the sharper theimage is.

#ccommodation:

The angle at which the light ray hits the hits the eye depends on the distance of the ob!ect. verylight ray that hits the eye needs a certain amount of refraction in order to be directed to the fovea.This is why the lens has the ability to widen and narrow according to the distant of the ob!ect you/relooking at in order to make the light ray hit the retina at the right spot. This is called accommodation.ight rays refracted from close ob!ects are diverging (spreading out) they need to be refractedinwards to be focused on the fovea. 1hen you look at a close ob!ect it takes some time till the visionbecomes clear. This is because at first the light ray is not correctly refracted so it hits the retinaaway from the fovea. The electrical impulses are generated and sent to the brain which realises thatthe image is not clear. The brain then sends electrical impulses to the ciliary muscles making themcontract. 1hen the ciliary muscles contract the suspensory ligaments become loose this makes the

lens become thicker and rounder for more refraction of the light rays. #ow the light rays are correctlyrefracted and hit the retina at the fovea the image becomes clear.


7/14

4or far visions it is the e'act opposite. The rays reflected from far ob!ects are almost parallel. 2erylittle refraction should be done. The brain sends electrical impulses to ciliary muscles making themrela' the suspensory ligaments now tighten up and pull the lens which become narrow.

5istance %iliary muscles$uspensoryligaments

ens

#ear %ontract oosen 1idens

4ar &ela'es tighten narrows

Rods and Cones:

The retina is full of light sensitive cells called photoreceptors. There are two types photoreceptorsthey are rods and cones. &ods and cones are specialised types of neurons. They look alike but theyare a little different in function.


8/14

&ods are sensitive to dim light. At night or in dark places most light detection electrical impulsestransmission is done by rods. 2itamin A is essential for proper functioning of rods if 2itamin A lacks itcan lead to night blindness. &ods are spread all over the retina.

%ones are sensitive to bright and coloured light. All cones are packed in one area the fovea.

The Pupil:

The pupil of the eye is the dark round area in the centre of it. t is surroundedby a coloured ring structure called the iris. The pupil and the together play abig role in protecting the eye from damage by limiting the amount of lightentering the eye. f too much light fall on the retina the rods and cones getdamaged. The iris and pupil change their si6e to smiddle that happening. Theiris contains two sets of muscles+ Circular and Radial muscles. %ircularmuscles run around the iris and radial muscles run from the centre to theoutside. 1hen circular muscles contract they make the pupil smaller. 1henthe radial muscles contract the stretch the pupil outwards making it wider.

n bright light too much light starts entering the eye which is dangerous for the rods and coneswhich detect the high light intensity. The rods and cones start a refle' arc by sending electricalimpulses to the brain via sensory neurone. The brain responds by sending electrical impulses to themuscles of the iris via motor neurone. These impulses make the circular muscles contract and theradial muscles rela' limiting the amount of light entering the eye thus protecting the rods and conesfrom damage.

f you walk into a dark room the rods and cones sense the little amount of light. They start anotherrefle' arc and send electrical impulses to the brain which responds by sending electrical impulsesthe muscles of the iris. The radial muscles contract and the circular muscles rela' widening the pupilto let more light in.

#ntaonistic !uscles:

You have !ust learned that in order for the pupil to get narrower or wider two muscles worksimultaneously when one contracts the other rela'es. "airs of muscles like that are calledantagonistic muscles.


9/14

The most known antagonistic muscle pair is the biceps and triceps of the arm. The bi and the tri forshort they are what causes the movement of the arm. They work simultaneously to bend orstraighten the arm. The biceps is located in front of the humerus bone of the upper arm. The bicepsis !oined to the radius bone of the lower arm and the triceps is !oined to the ulna bone of the lowerarm. uscles are attached to bones by strong fibres called tendons.

1hen you want to bendyour arm the brain send twoelectrical impulses one tothe bi making it contract andone to the tri telling it torela'. 1hen the bicontracts it becomesshorter pulling the bones towhich it is attached closeand bending the arm. Thiscauses the fibres of the tri

to stretch while they arerela'ed.

To straighten your arm thebrain send electricalimpulses to both musclesmaking the bi rela' in orderto leave the muscle it isattached to free. The tricontracts and becomesshorter pulling the muscle itis attached to into place andstraightening the arm.

The biceps can be called a fle'or because it fle'es (bends) the arm. The triceps can be called ane'tensor because it e'tends (straightens) the arm.

rus:

A drug is a chemical substance that modifies and affects chemical reactions of the body when takenin. any drugs are useful to us like antibiotics painkillers and caffeine.

$ome drugs however are abused by users to feel rela'ed or reach euphoria. uphoria is a state ofmind at which the abuser feels e'tremely happy and rela'ed. These drugs include alcohol andheroin.

#lcohol:

Alcohol is a depressant drug. This means that it reduces the activity of the brain and slows down thenervous system and refle' actions. Alcohol can be e'tremely dangerous when the user is in asituation in which they need fast refle' actions. Alcohol is addictive. The more you drink it the moreyou need it. The user may reach a point where they cannot do without alcohol this is when they


10/14

become alcoholics. Alcohol is broken down into fats by the liver. f the abuser drinks too muchalcohol the cells of the kidney may die shortening their life.

&eroine:

3eroine is a narcotic drug. This means that it relieves pain and induces sleep. 3eroine is e'tracted

from a plant called opium poppy. ost heroine abusers become addicts. 4or the addicts heroinebecome the number one priority in their lives. They would do anything to get the drug even becomecriminals and possess a threat to their society. f not rehabilitated a heroine abuser will end uphomeless or dead. $ome heroine users in!ect the drug in their veins by an unsterili6ed sharedneedle this increases the risk of getting A5832.

The 'ndocrine System:

You have previously learned that messages are delivered aroundbody as electrical impulses by the nervous system. Another waymessages are transported around the body is by chemicals

calledhormones secreted by the endocrine system.

3ormones are chemical substances produced by a gland carried bythe blood which alters the activity of one or more specific targetorgans and is then destroyed by the liver.

3ormones are produced in organs called endocrine lands whichmake up the endocrine system. The following diagram shows theglands of a human body.

9lands are organs made of secretory cells which/s function is toproduce hormones and secret them into the bloodstream. 9lands

have a dense network of blood capillaries in them to secret thehormones in. hormones are carried around the plasma like all othercontent of the blood but certain organs are able to use them theseare taret orans.

9land 3ormone produced 4unction of hormone

Adrenal gland Adrenaline "repares the body for activities that need energy and 0uick refle' actions

"ancreas nsulin akes liver reduce blood glucose level

9lucagon akes liver increase blood glucose level


11/14

Testis Testosterone "roduces male secondary se'ual characteristics

:vary

:estrogen "roduces female secondary se'ual characteristics

"rogesterone 3elps control menstrual cycle and maintain pregnancy

#drenaline:

1hen you get a fright you feel some changes in your body like a sudden increase in heart beat rateblood flowing 0uickly in veins and your breath becomes deeper and faster. This is because the frightyou got caused the brain to send electrical impulses to the adrenal glands making them secreteadrenaline hormone in your bloodstream. Adrenaline is a hormone that is secreted from the adrenalglands to prepare the body for situations that need lots of energy and fast refle' action like fights orrunning away for e'ample. Adrenaline/s main ob!ective is to increase your metabolic rate so that youhave enough energy for fighting or running away etc. This is why adrenaline is called the three 4shormone (4ight fright flight). :ne of adrenaline/s target organs is the heart. 1hen adrenalinereaches the heart it causes the cardiac muscle to contract and rela' much rapider so that o'ygenand glucose reach the muscles of the body faster. Adrenaline also makes the liver convert glycogeninto glucose and secret it in the blood to be used in respiration. 1hen adrenaline reaches the

diaphragm and the intercostals muscles of the ribs they make it contract and rela' faster too toincrease rate of breathing. These changes cause an increase in the respiration rate so that lots ofenergy is being released. 9enerally adrenaline is secreted when you are nervous or an'ious.

se of &ormones in ood %ndustries:

Technologies and science have advanced enough that we can now gut much more money out offarming and animal keeping. 3ormones are now being used in farms to increase milk yields in cowsand growth rate in cattle and fish.

n farms the cows are being in!ected with a hormone called ovine $omatotropin or $T. $T is ahormone that is naturally produced in cows. The function of $T is to produce milk. n!ecting cows

with e'tra $T will boost milk production and bring in more money for the farmers. $ome peoplehowever are against the use of $T and claim it is safer for both the cows and the consumer to keepit natural and keep more cows if we want an increased milk yield.

9rowth hormones are also being mi'ed with the food fed to cattle to increase their growth rate andmake them grow larger. ut again many people are against this and prefer buying meat and fish thatwere naturally grown.


12/14

Comparin Nervous and 'ndocrine Systems:

#ervous $ystem ndocrine $ystem

nformation sent in form of electrical impulses nformation sent in form of chemical hormones

nformation travel neurones nformation travel in bloodstream

nformation travels e'tremely rapidly nformation travels relatively slow

nformation is headed to one target (effector)

nformation may be used by several targeted

organs

lectrical signals have an effect that ends0uickly

3ormones have a longer lasting effect

Coordinates and Responses in Plants:

"lants cannot move themselves to areas of preferable conditions. This is why plants have the abilityto detect a stimulus and respond to it by growing or bending in its direction or away from it. Theseresponses are called tropisms. 4or e'ample a plant tends to grow its stem in the direction of sunlightfor more photosynthesis this is atropism. There are two types of tropism theseare phototropism and eotropism.

• Phototropism: the response in which a plant grows towards or away from the direction from

which light is coming.

• /eotropism: the response in which a plant grows towards or away from gravity.

A tropism can be either positive or negative. f a tropism is in the direction of the stimulus it is

positive. f the tropism is away from the stimulus it is negative.

4or e'ample a plant/s shoot tends to grow in the direction of sunlight this is positive phototropism.ut the plant/s root grows in the opposite direction deeply into the soil this is negative phototropism.3owever positive phototropism can also be described as negative geotropism because it involvesthe plant growing in the direction opposite to gravity. And negative photo tropism can be describedas positive geotropism because it involves the plant growing towards gravity.


13/14

#u"ins:

Tropisms are controlled by a chemical called #u"in. Au'in is a plant hormone. t is produced by cellsat the tip of roots and shoots of plants. At the tip of a shoot there is an area in which cells are beingproduced by dividing so that the shoot grows. :ld cells do not divide but they grow longer instead.The growth of these cells longer is controlled by au'ins. Au'ins is what makes the plant grows this is

why a plant doesn/t grow if you cut it/s tip off.

#u"ins0 Role in Phototropism:

f the sun shines on the right side of a plant/s shoot au'ins will accumulate on the dark opposite leftside. Au'ins accumulating there makes the cells on the left side grow much faster than the cells onthe right side. 1hen the left side of the shoot starts growing faster than the right side the shoot willstart to bend to the right side towards sunlight. This is phototropism.

#u"ins0 Role in /eotropism:

Au'ins tend to settle at the bottom end of the root. 3owever this does not make the sells of the tip of the root grow longer. nstead au'ins prevent the cells at the bottom tip of the root from growingmaking the cells at the middle of the root grow faster. 1hen the cells of the middle of the root growfaster they push the root deeper into the soil and the root gets longer. The root grows in the directionof the gravitational pull. This is geotropism.

&oots show positive geotropism and negative phototropism because they grow towards gravity andaway from sunlight at the same time. $hoots show positive phototropism and negative geotropismbecause they grow towards the sunlight and away from gravity at the same time.

#dvantaes of Positive Phototropism:

• eaves e'posed to more sunlight and are able to do more photosynthesis

• 4lowers can be seen by insects for pollination

• The plant gets higher for better seed dispersal.


14/14

#dvantaes of Positive /eotropism:

• y growing deeply into the soil the root fi'es the plant into the ground firmly

• &oots are able to reach more water

• &oots have a larger surface area for more diffusion and osmosis.

Selective ,eed 1illers:

Au'ins can be used to kill weeds that grow over grass or cereal crops. f weed grows on cropsau'ins are sprayed everywhere. 1eeds absorb au'ins faster than crops or grass. Au'ins accumulatein the weeds making them grow very rapidly. 4ast growth of weed kills it leaving the crops or grassalive. Au'ins are used ass selective weed killers.

Documents

Biology Notes (Term 1)