Flash cards for igcse biology

02/05/15 10:28 amFlashcards Table on IGCSE Biology All Topics

of 34http://www.proprofs.com/flashcards/cardshowall.php?title=igcse-biology-all-topics

Home (/flashcards/) Create Flashcards (/flashcards/create-flashcards.php)

Browse (/flashcards/browse/) Tour (/flashcards/tour/) Pricing (/flashcards/signup/business/)

Text Size: S | M |L

(855) 776-7763

IGCSE Biology All TopicsTotal Flash Cards » 38

Cells

All animals and plants aremade up of cells. Most cells

have:A nucleus – controlling theactivity of the cell. All cellshave these at one point.

Cytoplasm – wherechemical reactions occur.Inside the cytoplasm areenzymes which speed up

these reactions. Cytoplasmalso contains mitochondriawhich is where energy is

released.A cell membrane – to

Login (/flashcards/login.php?return=/flashcards/)

Sign Up Free (/flashcards/register.php)

Search Flashcards

http://www.proprofs.com/flashcards/

http://www.proprofs.com/flashcards/create-flashcards.php

http://www.proprofs.com/flashcards/browse/

http://www.proprofs.com/flashcards/tour/

http://www.proprofs.com/flashcards/signup/business/

http://www.proprofs.com/flashcards/login.php?return=/flashcards/

http://www.proprofs.com/flashcards/register.php



control the passage ofsubstances in and out of

the cell.

Plants also haveCell walls – to strengthen

the cell.Chloroplasts – to absorbsunlight energy to makefood by photosynthesis.Vacuole –full of cell sap.

Cells, tissues and organs

Cells act together to formtissues. For instance, the cellson the surface of a leaf form"pallisade tissue". A group ofcells with similar structuresand a particular function arecalled a tissue. Tissues aregrouped together to form an

organ. A leaf is an organ.Organs are grouped togetherto form an organism such as a

whole plant or animal. Cells ----> Tissue ----> Organ -

---> Organism Tissues are usually formedfrom specialised cells. The

cells in the pallisade tissue arespecialised to perform

photosynthesis and containmany chloroplasts. Some

other specialised cells are:Guard cellsEgg cells

Sperm cellsRed blood cells



Diffusion

Diffusion is the net movementof particles from an area of

high concentration to an areaof a lower concentration. The

steeper the concentrationgradient, the more rapid the

rate of diffusion. 2 examples of diffusion are:

Oxygen (required forrespiration) passes through

cell membranes and gasexchange surfaces (e.g.

alveoli in lungs) by diffusionCarbon dioxide entersleaves and leaf cells by

diffusion

Osmosis

Osmosis is the movement ofwater from an area of highwater concentration (moredilute) to an area of a low

water concentration (stronger)through a partially permeable

membrane. A partially permeable

membrane allows watermolecules to pass through (as

they are smaller) but notsolute molecules (they are too

big). It acts like a sieve.Visking tubing is a partiallypermeable membrane. It isused in dialysis machines.Diffusion and osmosis can



Active Transport

only work if the concentrationgradient is right. Sometimes

an organism needs totransport something against aconcentration gradient. Theonly way this can be done is

through active transport, usingenergy produced by

respiration. In Active transport,the particles move across a

cell membrane from a lower toa higher concentration.

Examples of active transport In plants: Plants need mineralsalts (e.g. nitrates) for makingproteins and growth. Nitratesare at a higher concentrationinside the root cells than they

are when dissolved in thewater around the soil particles.If the plant relied on diffusionalone, the vital nitrate saltswould drain out of the cellsinto the soil. So energy isdeployed by the cells to

actively transport nitratesacross the cell membrane into

the root cells, against theconcentration gradient. Inhumans Active transport

takes place during digestion offood in the small intestine.

After food has been absorbedby the villi for some time, the

concentration of food



molecules inside the villiincreases, making it

impossible for more food todiffuse into the villi. So simplesugars, amino acids, minerals

and vitamins are activelyabsorbed into the villi, from an

area of lower to an area ofhigher concentration

Shareen Saqlain

The Cell Cycle happens in cells

Prophase

The first and longest phase ofmitosis, prophase, can take asmuch as 50-60 percent of thetotal time to complete mitosis.

During prophase, thechromosomes become visible.

The centrioles, two tinystructures located in the

cytoplasm near the nuclearenvelope, separate and take

up positions on opposite sidesof the nucleus. The centriols

lie in a region called thecentrosome that helps to

organise the spindle, a fanliekmicrotubule structure that helpseparate the chromosomes.

During prophase, thecondensed chromosomes

become attached to fibers in



the spindle at a point near thecentromere of each chromatid.

Metaphase

The second phase of mitosis,metaphase, often only lasts a

few minutes. Duringmetaphase, the chromosomes

line up across the center ofthe cell. Microtubules connect

the centromere of eachchromosome to the poles of

the spindle.

Anaphase

Anaphase is the third phase ofmitosis. During anaphase, the

centromeres that join thesister chromatids separate,

allowing the sister chromatidsto separate and become

individual chromosomes. Thechromosomes continue to

move until they haveseparated into two groups

near the poles of the spindle.Anaphase ends when the

chromosomes stop moving.

Telophase

Following anaphase istelophase, the fourth and finalphase of mitosis. In telophase,the chromosomes, which weredistinct and condensed, begin

to disperse into a tangle ofdense material. A nuclearenvelope re-forms around

each cluster of chromosomes.The spindle begins to break



apart, and a nucleolusbecomes bisible in each

daughter nucleus. Mitosis iscomplete

Plant structure

Plants are divided into flowers,stems, leaves and roots with

root hairs. A generalised plantis shown in the illustration.

The stem provides support forthe leaves and flowers. It alsoallows water and food to travelboth up and down the plant. The leaves make the food for

the plant. Photosynthesistakes place in the leaves.



The roots anchor the plant inthe soil and take up water andsalts (mineral ions) from the

soil. The root hairs provide alarge surface area for water

and salt uptake. The flowersare reproductive organs. Theyattract insects that carry pollenfrom one plant to another. Thisprocess of transferring pollen

from plant to plant is known aspollination.

The structure of the leaf

Leaves produce the food forthe plant. The structure of theleaf is shown in the illustration.The leaf has prominent veins

that contain two types oftubes, the xylem tubes andthe phloem tubes. The leafhas the following parts (from

top to bottom):Waxy cuticle

Upper EpidermisPallisade layerSpongy layer

VeinsLower epidermis



Guard cells that formstomata

Leaves are green becausethey contain the green

pigment called chlorophyll.Chlorophyll is used in

photosynthesis.

The structure of flowers

lowers are composed of:Sepals - these are arrangedunderneath the flower and

are typically green.Petals - often brightly

coloured to attract insects.Stamens - stalk-like

filaments that have anthersat the top which produce

pollen. Pollen contains themale gametes.

Pistil - contains one orseveral carpels that containthe ovaries with ovules, the

female gametes.Sometimes the carpels aremerged. A stalk called thestyle leads upwards from

each pistil and is topped bya sticky stigma thatreceives the pollen.

The pistil is the bottle shaped



structure. A pistil can becomposed of one or many

carpels and a flower can haveseveral pistils.

Plant growth

Plant growth requires glucoseproduced by photosynthesis

and energy produced byrespiration. It also requiresminerals obtained from the

soil. Plant growth is controlledby plant hormones calledauxins. Auxins Mineralsneeded for plant growth

There are three minerals thatare essential for plant growth:

phosphates, nitrates andpotassium. Small quantitiesof iron and magnesium are

also needed, especially for theproduction of chlorophyll.

Phosphates: used inphotosynthesis and

respiration. Phosphatedeficiency: purple leaves and

small roots. Nitrates: used in the

production of aminno acids.Amino acids are combined to

make proteins.

Nitrate deficiency: yellowingof leaves and poor, stunted

growth.



Potassium: maintainselectrical potentials and helps

enzyme action.Potassium deficiency:

leaves become yellow withspotty, brown, dead areas.

Photosynthesis

Like all living things, plantsneed food to live. This food isused for energy and to makenew materials when plants

grow. Plants are able to taketwo inorganic chemicals,

carbon dioxide gas and water,to make an organic chemical,glucose. This simple food canbe used as an energy sourceor converted into other useful

organic molecules. The process requires an inputof energy. Plants have found a

way to capture the energyfrom sunlight using a pigmentcalled chlorophyll. Once this

light energy has beencaptured it can be used to

create glucose, converting thelight energy into chemical

energy. Oxygen gas isreleased as a waste chemical.

As light energy is used tocreate organic materials the



process is namedPhotosynthesis. The formula for

photosynthesis is:

Respiration in plants

Respiration is the productionof energy from glucose andoxygen with the release of

carbon dioxide and water aswaste products. This is theopposite of photosynthesiswhich is the production of

glucose and oxygen from theenergy in sunlight, carbon

dioxide and water. Respiration: C H O + 6O→ 6CO + 6H O + Energy

released Glucose + Oxygen→ Carbon dioxide + water +

Energy released Photosynthesis: 6CO +

6H O + Energy → C H O +6O Carbon dioxide + water +Energy → Glucose + Oxygen

Plants use the energy fromrespiration to power the

processes involved in growth.

The energy obtained fromrespiration is used to turnglucose into many other

substances. Typical uses ofglucose are:

Storage products

6 12 6 22 2

22 6 12 62



Uses of glucose

- glucose is used to makestarch which can be

converted back to glucose asrequired. Potatoes and rice

are examples of parts ofplants that contain starch.-glucose is converted into

lipids, especially in seeds.Sunflower oil and rapeseed

oil, which are used in cooking,come from sunflower and

oilseed rape seeds.Structural products

- glucose is converted tocellulose to make cell walls.

Other products- glucose and nitrates are

used to make amino acidswhich are used to make

proteins.- glucose is also abasic raw material for making

chlorophyll.

The Human Digestive System Yummy in my TUMMY

The Mouth

Digestion begins inside themouth, where chewing does 2things - makes the food easierto swallow and increases the

surface area (this helps tospeed up digestion). Also

inside the mouth, amylase (fordigesting starch) can be



found, produced by thesalivary glands. The gulletthen carries food from the

mouth to the stomach by itsmuscular squeezing action

called peristalsis.

Stomach

The stomach does a numberof things, including:

pummels and churns thefood

produces proteaseenzymes to digest proteinproduces hydrochloric acid

which kills bacteria andgives the ideal pH for

protease to work.

Liver

The liver produces bile whichemulsifies fats i.e. breaks

them down into small dropletsfor a larger surface area. Thiswill increase the rate at whichthe fat is digested by lipase.Bile also neutralizes the acidproduced by the stomach to

provide ideal alkalineconditions for enzymes in the

small intestine. The gallbladder stores the bile madeby the liver until it is needed.The small intestine produces

amylase, lipase and protease.The pancreas, a pistol shapedorgan, produces the enzymesamylase, lipase and protease



Small Intestine

and releases them into thesmall intestine when needed.The enzymes are used to fullydigest the food molecules, sothat they are small enough todiffuse into the bloodstream.Food molecules diffuse in thesmall intestine, which is idealfor this purpose. The small

intestine walls are very thin sothat there is a short diffusionpathway. It is long and foldedwith villi to increase surfacearea. There is a rich bloodsupply to maintain a steepconcentration gradient for

diffusion.

Large Intestine & Anus

When all the useful productshave diffused into the blood,the remaining waste reachesthe large intestine where the

majority of the remainingwater is absorbed into theblood stream. Finally the

waste products leave the bodyin the form of faeces through

the anus.

Breathing and Respiration The Basics



Breathing

The zone of the bodybetween the neck and the

bottom of the ribs is knownas the thorax. The major

organs in the thorax are theheart and lungs. The lungs

and associated airwaysallow us to breathe.

In the head the airwaysconsist of the mouth and nasalpassages. Air and food has a

common passage in thethroat.

Larynx or voicebox. This iswhere there is speech and

sound generation.Trachea or windpipe.

Two tubes that are each



known as a bronchus,plural bronchi.

Bronchioles which aresubdivisions of each

bronchus.Alveoli which are sacks atthe end of the airways thatallow oxygenation of the

blood.Pleural cavity"

pleural membrane.

The key features of breathingare that when we breathe in

the intercostal musclesbetween the ribs and thediaphragm both contract;

when we breathe out both ofthese muscles relax. When we

breathe in the contraction ofthe intercostals pulls the

sternum up and away from thebody and the descent of the

diaphragm increases thevolume of the thoracic cavity.Notice that in the resting state(breathing out) the diaphragmbulges up under the lungs, thelungs themselves are slightlyelastic and pull the diaphragm

back to this position



Oxygenation of the blood

The two main functions of thelungs are to oxygenate theblood and to remove waste

carbon dioxide. The blood is oxygenated in the

alveoli. The alveoli are thinwalled and surrounded by

capillaries. The blood entersthe capillary network around

the alveoli from thepulmonary artery and leavesthe capillary network via the

pulmonary vein.Oxygen diffuses into the blood

through the alveolar andcapillary walls and carbondioxide diffuses out of theblood. The alveoli have asurface area of about 70

square metres to make thisgas exchange as fast as

possible. Carbon dioxide dissolves inwater and can easily and



reversibly form compoundssuch as carbonic acid and

bicarbonates. Oxygen does not dissolve

much in water, to overcomethis problem the oxygen in theblood is stored in red blood

cells. These containhaemoglobin which can

combine with oxygen to formoxyhaemoglobin. The red

blood cells contain the oxygenin the blood. The blood

transports oxygen from thelungs to the rest of the body. Oxy-haemoglobin is bright redand haemoglobin is dark red,

this is why veins look dark andwhy all the diagrams showveins in blue and arteries in

red. The exception is thepulmonary artery which carriesdark red, de-oxygenated blood

to the lungs and thepulmonary vein which carriesbright red oxygenated blood

away from the lungs.Thespecial adaptions of the alveoli

for gas exchange are:Thin walls

Huge surface areaCovered in capillaries to

provide bloodA wet lining to dissolve

gases



Aerobic respiration

Respiration is the process inwhich the chemical bonds of

energy-rich molecules such asglucose are converted into

energy usable for lifeprocesses. Aerobic

respiration uses oxygen tooxidise glucose and produceenergy. The equation for the

oxidation of glucose is:C H O + 6O → 6CO +6H O + Energy released

Glucose + Oxygen → Carbondioxide + water + Energy

released In a fire there is a massive

uncontrolled release of energyas light and heat. Respiration

is a similar process but itoccurs in gradual steps.

Most animals and plants useaerobic respiration as a

primary source of energy. glucose + oxygen = carbondioxide + water = energy

When a person is doing veryheavy exercise and the bloodcannot supply enough oxygen

another sort of respirationoccurs. This converts glucoseinto energy without the needfor oxygen and is known asanaerobic respiration. The

reaction is: Glucose → Energy

6 12 6 2 22



Anaerobic respiration

released + lactic acid Anaerobic respiration releases

less energy than aerobicrespiration. Unfortunately theinsufficient blood supply that

leads to anaerobic respirationalso means that the lactic acidbuilds up in the muscles. Highlactic acid concentrations are

painful and felt as cramp.When exercise stops, the

blood supply is able to provideenough oxygen to convert thelactic acid to carbon dioxideand water but this takes time

and the muscle pain maycontinue after exercise until

the lactic acid has beenconverted.

The delay in the removal oflactic acid is known as the

oxygen debt. Carbon dioxideand lactic acid both causeincreases in breathing rateand heart rate to allow thebody to repay the oxygen

debt. The oxygen debt is thereason why we continue to be

out of breath even afterexercise. If athletes are very fit

their circulation can provideextra oxygen more rapidly andtheir recovery time, the time

required to restore normalbreathing and pulse, will be



shorter than in people who arenot fit.

Yeasts and anaerobicrespiration

The direct conversion ofglucose to energy without theuse of oxygen occurs in manyyeasts and fungi. The ethanolthat is used in alcoholic drinks

is a result of anaerobicrespiration in yeast, the

reaction is: Glucose → Energyreleased + ethanol + carbon

dioxide Brewers use various types of

brewers yeast to producealcohol. In fizzy alcoholic

drinks such as champagne thebottles are tightly stoppered to

prevent the carbon dioxidefrom escaping.

The Heart a Muscle

The blood transports food,proteins, blood cells, gases,water, minerals and wasteproducts around the body.

Blood contains:Plasma - a straw colouredliquid in which the bloodcells are suspended and

the other components of theblood are dissolved.



Blood

Red blood cells - these arered and doughnut shapedfor a large surface area.

They carry oxygen from thelungs to the tissues as oxy-

haemoglobin (theoxygenated form of

haemoglobin). They do nothave a cell nucleus.

White blood cells - theseare colourless cells with alarge cell nucleus. Theydefend the body against

disease by engulfing micro-organisms (bacteria andviruses) and producing

antitoxins and antibodies.Platelets - these are

fragments of cells and verysmall. They do not have a

cell nucleus. They formblood clots at the site ofinjuries. Clots protect the

body from further infectionand blood loss.



How the heart works

Due the continuous cardiaccycle which takes an

approximate second, the heartis the fastest and the strongest

muscle in the body. Thestrongest external muscle is

the tongue, however the heartis much stronger.

The heart works in threestages:

1. Blood flows into the atria.2. Both atria contract at the

same time, forcing bloodinto the ventricles.

3. Both ventricles contract atthe same time, forcing

blood through thepulmonary artery and aorta.

The heart valves ensure thatthe blood goes in the correctdirection, they stop backflow.When the atria contract the

valves between the atria andthe ventricles open passivelyand the high pressure in the

arteries keeps the valvesbetween the ventricles and the

arteries closed. When theventricles contract the valves

between the ventricles and theatria shut and the valves

between the ventricles and thearteries open.



The net effect of the action ofthe heart is as follows.

Deoxygenated blood from thebody enters the right atrium

and flows into the rightventricle where it is pumped

through the lungs. In the lungsthe blood is oxygenated. It

then flows into the left atriumand on into the left ventriclewhere it is pumped out at

sufficient pressure to reachevery part of the body. Theatria have thin walls and actas reservoirs, the ventricles

have thick, muscular walls andact as pumps. The valves inthe heart prevent backflow.

You need to know thefollowing names of arteries

and veins:Aorta - the big artery that

comes out of the leftventricle.

Pulmonary artery - the bigartery that comes out of the

right ventricle.Vena cava - this refers to

the big vein that connects tothe right atrium. It has two

sections the "superior" venacava that drains blood fromthe top part of the body andthe "inferior" vena cava thatdrains blood from the bodybelow the heart. To make

the sections clear it is oftensaid that there are two



"vena cavae", the superiorvena cava and the inferiorvena cava. Either learn thenames of the two sections

or, when you draw the heartput the arrow to the venacava as close to the heart

as possible.Pulmonary vein - the veinthat is directly attached to

the left atrium.

The menstrual cycle is acycle of events that occurs in

the womb (uterus) andovaries of female mammals. It

is associated with theproduction of eggs and

preparing the uterus for theimplantation of fertilised eggs.

The menstrual cycle occursover a period of about 28

days. The changes during thecycle are due to four

hormones, progesterone,oestrogen, FSH (follicle

stimulating hormone) and LH(luteinising hormone).

Progesterone and oestrogenhave wide ranging effects onthe body but in the context of

the menstrual cycleprogesterone is mainly

involved in maintaining thelining of the uterus and

oestrogen is mainly concernedwith building up the lining of



The menstrual cycle

the uterus. FSH stimulates theproduction of eggs and LH

stimulates the release of theegg. FSH and LH are

produced by the pituitarygland in the brain.

There are four stages in themenstrual cycle.

Stage 1. Days 1-4.Menstruation (bleeding)occurs. The lining of the

uterus disintegrates and isshed. This is due to low levels

of progesterone. Stage 2. Days 4-14. The

uterine lining grows back. Thisis due to high levels of

oestrogen. Stage 3. Day 14. The egg

(called an ovum) is released.This is due to LH.

Stage 4. Days 14-28. Thelining of the uterus is

maintained in case the eggbecomes fertilised andimplanted in the uterus.

Maintenance of the lining isdue to high levels of

progesterone. The four hormones interact

with each other. FSH causesOestrogen release and

oestrogen inhibits FSH. LHstimulates both oestrogen and

progesterone production.



Before ovulation LH release isstimulated by oestrogen but

after ovulation it is inhibited byboth oestrogen and

progesterone. In summary, the hormoneshave the following effects:

Oestrogen: causes growth ofthe uterine lining. Inhibits FSH.Stimulates release of LH and

hence release of the egg.Inhibits LH after ovulation.

Progesterone: maintains theuterine lining. Inhibits LH afterovulation. LH: Stimulates the

release of the egg (calledovulation). Stimulates

oestrogen and progesteroneproduction. FSH: Stimulates

egg development and therelease of oestrogen.

Birth control tablets containhigh levels of progesterone

and oestrogen. The oestrogeninhibits FSH production so that

eggs cease to develop. FSH is used to treat infertility

because it stimulates theproduction of eggs.

The nervous system consistsof the brain, spinal cord and

relay neurones (Centralnervous system) and

peripheral nervous system



The Nervous System (sensory neurones and motorneurones). The nervous

system lets the organism reactto the environment and

surroundings and coordinatetheir behaviour.

The senses

Sense organs containreceptors that are sensitive to

stimuli. Typical stimuli aredue to changes in chemical

composition, mechanicaleffects, heat, sound and light.Stimuli are the changes that

are detected. Receptorsdetect the change.

There are five sense organsthat are studied at this stage,the nose, tongue, eyes, ears

and skin. The nose has smell receptors

that are sensitive to a widerange of chemical stimuli.

Much of what is called 'taste'is actually smell; the range offlavours in food is very limited

if the nose is blocked. The tongue has taste

receptors that are sensitive tochemical stimuli. There arefour basic tastes: bitter, salt,

sweet and sour. The eyes have receptors thatare sensitive to light, the ears

have receptors that are



sensitive to sound and theskin has receptors that aresensitive to temperature,

touch, pressure and stretch.

Light from the surroundingsenters the eye through thepupil. It is focussed by thecornea and lens so that it

forms an image on the retina.The cornea performs crude

focussing and the lensperforms active, fine

focussing. The eye is filledwith transparent liquid (the

humours). The iris controls the size of

the pupil and so controls howmuch light gets into the eye. In

bright light the circularmuscles in the iris contract,this makes the pupil smallerand allows less light into theeye. In dim light the radial



The eye

muscles contract, this makesthe pupil larger and allows

more light into the eye. The lens changes shape toallow the eye to focus on

things at various distances.The shape of the lens is

changed by the action of theciliary muscles. The ciliarymuscles form a circle that isattached to the lens by thesuspensory ligaments. Tofocus on distant objects theciliary muscles relax which

pulls the suspensoryligaments tight and makes the

lens thinner. To focus onnearby objects the ciliary

muscles contract which allowsthe suspensory ligaments torelax so that the lens forms a

more spherical shape. The retina contains cells thatare sensitive to light. These

cells are called rods andcones.

The rods are more sensitivethan the cones but do not

provide any colourinformation. In dim light ourview of the world is largely

provided by rods and appearsas a black and white image. There are three types of coneand these are each sensitive



to different colours of light.The cones are especially

densely packed in the part ofthe retina called the fovea;

this dense packing means thatthe fovea is most sensitive to

fine detail in the image. The part of the eye where theoptic nerve enters is called

the blind spot. The blind spotdoes not contain any light

receptors (it has no rods orcones).

Neurones

Neurones are cells that arespecialised to transmit

electrical impulses aroundthe body. They consist of three

principle components: thedendrites, the cell body andthe axon. Each neurone has

its own nucleus. (The USspelling of neurone is

"neuron").

There are three types ofneurone: sensory neurones,relay neurones and motor

neurones. Neurones connect to other

neurones by means ofsynapses. Nerve impulsestravel down the axon to one

side of the synapse where the



electrical signal causeschemicals to be released.These chemicals diffuse

across the gap and generatean electrical impulse in the

neurone on the other side ofthe synapse.

Reflex arcs

The nervous system has manyreflexes. These are automatic

responses to stimuli. Veryquick responses are managed

by Reflex arcs. A reflex arcconsists of the following

components:StimulusReceptor

Sensory neuroneRelay neuroneMotor neurone

EffectorResponse

Pain reflex: a painful stimuluscauses a muscle to contract

automatically



A typical reflex arc called the"pain reflex" is illustrated.

In the pain reflex the stimulusis mechanical damage, the

receptor is a "pain receptor",the pain receptor generates anelectrical impulse in a sensory

neurone which creates anelectrical impulse in a relay

neurone, which in turn createsan electrical impulse in a

motor neurone. The impulse inthe motor neurone stimulatesa muscle, which is an effector,

and this creates movementaway from the painful stimulus

as a response. Another reflex is the "patellar"or "knee jerk reflex" where ablow beneath the knee-cap

makes the leg straighten. Thecontraction of the pupil in

response to bright light is yetanother reflex.

Flash cards for igcse biology

Education

Transcript of Flash cards for igcse biology