Flash cards for igcse biology

02/05/15 10:28 amFlashcards Table on IGCSE Biology All Topics
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IGCSE Biology All Topics
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Cells
All animals and plants are
made up of cells. Most cells
have:
A nucleus – controlling the
activity of the cell. All cells
have these at one point.
Cytoplasm – where
chemical reactions occur.
Inside the cytoplasm are
enzymes which speed up
these reactions. Cytoplasm
also contains mitochondria
which is where energy is
released.
A cell membrane – to
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control the passage of
substances in and out of
the cell.
Plants also have
Cell walls – to strengthen
the cell.
Chloroplasts – to absorb
sunlight energy to make
food by photosynthesis.
Vacuole –full of cell sap.
Cells, tissues and organs
Cells act together to form
tissues. For instance, the cells
on the surface of a leaf form
"pallisade tissue". A group of
cells with similar structures
and a particular function are
called a tissue. Tissues are
grouped together to form an
organ. A leaf is an organ.
Organs are grouped together
to form an organism such as a
whole plant or animal.
Cells ----> Tissue ----> Organ -
---> Organism
Tissues are usually formed
from specialised cells. The
cells in the pallisade tissue are
specialised to perform
photosynthesis and contain
many chloroplasts. Some
other specialised cells are:
Guard cells
Egg cells
Sperm cells
Red blood cells

Diffusion
Diffusion is the net movement
of particles from an area of
high concentration to an area
of a lower concentration. The
steeper the concentration
gradient, the more rapid the
rate of diffusion.
2 examples of diffusion are:
Oxygen (required for
respiration) passes through
cell membranes and gas
exchange surfaces (e.g.
alveoli in lungs) by diffusion
Carbon dioxide enters
leaves and leaf cells by
diffusion
Osmosis
Osmosis is the movement of
water from an area of high
water concentration (more
dilute) to an area of a low
water concentration (stronger)
through a partially permeable
membrane.
A partially permeable
membrane allows water
molecules to pass through (as
they are smaller) but not
solute molecules (they are too
big). It acts like a sieve.
Visking tubing is a partially
permeable membrane. It is
used in dialysis machines.
Diffusion and osmosis can

Active Transport
only work if the concentration
gradient is right. Sometimes
an organism needs to
transport something against a
concentration gradient. The
only way this can be done is
through active transport, using
energy produced by
respiration. In Active transport,
the particles move across a
cell membrane from a lower to
a higher concentration.
Examples of active transport
In plants: Plants need mineral
salts (e.g. nitrates) for making
proteins and growth. Nitrates
are at a higher concentration
inside the root cells than they
are when dissolved in the
water around the soil particles.
If the plant relied on diffusion
alone, the vital nitrate salts
would drain out of the cells
into the soil. So energy is
deployed by the cells to
actively transport nitrates
across the cell membrane into
the root cells, against the
concentration gradient. In
humans Active transport
takes place during digestion of
food in the small intestine.
After food has been absorbed
by the villi for some time, the
concentration of food

molecules inside the villi
increases, making it
impossible for more food to
diffuse into the villi. So simple
sugars, amino acids, minerals
and vitamins are actively
absorbed into the villi, from an
area of lower to an area of
higher concentration
Shareen Saqlain
The Cell Cycle happens in cells
Prophase
The first and longest phase of
mitosis, prophase, can take as
much as 50-60 percent of the
total time to complete mitosis.
During prophase, the
chromosomes become visible.
The centrioles, two tiny
structures located in the
cytoplasm near the nuclear
envelope, separate and take
up positions on opposite sides
of the nucleus. The centriols
lie in a region called the
centrosome that helps to
organise the spindle, a fanliek
microtubule structure that help
separate the chromosomes.
During prophase, the
condensed chromosomes
become attached to fibers in

the spindle at a point near the
centromere of each chromatid.
Metaphase
The second phase of mitosis,
metaphase, often only lasts a
few minutes. During
metaphase, the chromosomes
line up across the center of
the cell. Microtubules connect
the centromere of each
chromosome to the poles of
the spindle.
Anaphase
Anaphase is the third phase of
mitosis. During anaphase, the
centromeres that join the
sister chromatids separate,
allowing the sister chromatids
to separate and become
individual chromosomes. The
chromosomes continue to
move until they have
separated into two groups
near the poles of the spindle.
Anaphase ends when the
chromosomes stop moving.
Telophase
Following anaphase is
telophase, the fourth and final
phase of mitosis. In telophase,
the chromosomes, which were
distinct and condensed, begin
to disperse into a tangle of
dense material. A nuclear
envelope re-forms around
each cluster of chromosomes.
The spindle begins to break

apart, and a nucleolus
becomes bisible in each
daughter nucleus. Mitosis is
complete
Plant structure
Plants are divided into flowers,
stems, leaves and roots with
root hairs. A generalised plant
is shown in the illustration.
The stem provides support for
the leaves and flowers. It also
allows water and food to travel
both up and down the plant.
The leaves make the food for
the plant. Photosynthesis
takes place in the leaves.

The roots anchor the plant in
the soil and take up water and
salts (mineral ions) from the
soil. The root hairs provide a
large surface area for water
and salt uptake. The flowers
are reproductive organs. They
attract insects that carry pollen
from one plant to another. This
process of transferring pollen
from plant to plant is known as
pollination.
The structure of the leaf
Leaves produce the food for
the plant. The structure of the
leaf is shown in the illustration.
The leaf has prominent veins
that contain two types of
tubes, the xylem tubes and
the phloem tubes. The leaf
has the following parts (from
top to bottom):
Waxy cuticle
Upper Epidermis
Pallisade layer
Spongy layer
Veins
Lower epidermis

Guard cells that form
stomata
Leaves are green because
they contain the green
pigment called chlorophyll.
Chlorophyll is used in
photosynthesis.
The structure of flowers
lowers are composed of:
Sepals - these are arranged
underneath the flower and
are typically green.
Petals - often brightly
coloured to attract insects.
Stamens - stalk-like
filaments that have anthers
at the top which produce
pollen. Pollen contains the
male gametes.
Pistil - contains one or
several carpels that contain
the ovaries with ovules, the
female gametes.
Sometimes the carpels are
merged. A stalk called the
style leads upwards from
each pistil and is topped by
a sticky stigma that
receives the pollen.
The pistil is the bottle shaped

structure. A pistil can be
composed of one or many
carpels and a flower can have
several pistils.
Plant growth
Plant growth requires glucose
produced by photosynthesis
and energy produced by
respiration. It also requires
minerals obtained from the
soil. Plant growth is controlled
by plant hormones called
auxins. Auxins Minerals
needed for plant growth
There are three minerals that
are essential for plant growth:
phosphates, nitrates and
potassium. Small quantities
of iron and magnesium are
also needed, especially for the
production of chlorophyll.
Phosphates: used in
photosynthesis and
respiration. Phosphate
deficiency: purple leaves and
small roots.
Nitrates: used in the
production of aminno acids.
Amino acids are combined to
make proteins.
Nitrate deficiency: yellowing
of leaves and poor, stunted
growth.

Potassium: maintains
electrical potentials and helps
enzyme action.
Potassium deficiency:
leaves become yellow with
spotty, brown, dead areas.
Photosynthesis
Like all living things, plants
need food to live. This food is
used for energy and to make
new materials when plants
grow. Plants are able to take
two inorganic chemicals,
carbon dioxide gas and water,
to make an organic chemical,
glucose. This simple food can
be used as an energy source
or converted into other useful
organic molecules.
The process requires an input
of energy. Plants have found a
way to capture the energy
from sunlight using a pigment
called chlorophyll. Once this
light energy has been
captured it can be used to
create glucose, converting the
light energy into chemical
energy. Oxygen gas is
released as a waste chemical.
As light energy is used to
create organic materials the

process is named
Photosynthesis.
The formula for
photosynthesis is:
Respiration in plants
Respiration is the production
of energy from glucose and
oxygen with the release of
carbon dioxide and water as
waste products. This is the
opposite of photosynthesis
which is the production of
glucose and oxygen from the
energy 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 from
respiration to power the
processes involved in growth.
The energy obtained from
respiration is used to turn
glucose into many other
substances. Typical uses of
glucose are:
Storage products
6 12 6 2
2 2
2
2 6 12 6
2

Uses of glucose
- glucose is used to make
starch which can be
converted back to glucose as
required. Potatoes and rice
are examples of parts of
plants 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 to
cellulose to make cell walls.
Other products
- glucose and nitrates are
used to make amino acids
which are used to make
proteins.- glucose is also a
basic raw material for making
chlorophyll.
The Human Digestive System Yummy in my TUMMY
The Mouth
Digestion begins inside the
mouth, where chewing does 2
things - makes the food easier
to swallow and increases the
surface area (this helps to
speed up digestion). Also
inside the mouth, amylase (for
digesting starch) can be

found, produced by the
salivary glands. The gullet
then carries food from the
mouth to the stomach by its
muscular squeezing action
called peristalsis.
Stomach
The stomach does a number
of things, including:
pummels and churns the
food
produces protease
enzymes to digest protein
produces hydrochloric acid
which kills bacteria and
gives the ideal pH for
protease to work.
Liver
The liver produces bile which
emulsifies fats i.e. breaks
them down into small droplets
for a larger surface area. This
will increase the rate at which
the fat is digested by lipase.
Bile also neutralizes the acid
produced by the stomach to
provide ideal alkaline
conditions for enzymes in the
small intestine. The gall
bladder stores the bile made
by the liver until it is needed.
The small intestine produces
amylase, lipase and protease.
The pancreas, a pistol shaped
organ, produces the enzymes
amylase, lipase and protease

Small Intestine
and releases them into the
small intestine when needed.
The enzymes are used to fully
digest the food molecules, so
that they are small enough to
diffuse into the bloodstream.
Food molecules diffuse in the
small intestine, which is ideal
for this purpose. The small
intestine walls are very thin so
that there is a short diffusion
pathway. It is long and folded
with villi to increase surface
area. There is a rich blood
supply to maintain a steep
concentration gradient for
diffusion.
Large Intestine & Anus
When all the useful products
have diffused into the blood,
the remaining waste reaches
the large intestine where the
majority of the remaining
water is absorbed into the
blood stream. Finally the
waste products leave the body
in the form of faeces through
the anus.
Breathing and Respiration The Basics

Breathing
The zone of the body
between the neck and the
bottom of the ribs is known
as the thorax. The major
organs in the thorax are the
heart and lungs. The lungs
and associated airways
allow us to breathe.
In the head the airways
consist of the mouth and nasal
passages. Air and food has a
common passage in the
throat.
Larynx or voicebox. This is
where there is speech and
sound generation.
Trachea or windpipe.
Two tubes that are each

known as a bronchus,
plural bronchi.
Bronchioles which are
subdivisions of each
bronchus.
Alveoli which are sacks at
the end of the airways that
allow oxygenation of the
blood.
Pleural cavity"
pleural membrane.
The key features of breathing
are that when we breathe in
the intercostal muscles
between the ribs and the
diaphragm both contract;
when we breathe out both of
these muscles relax. When we
breathe in the contraction of
the intercostals pulls the
sternum up and away from the
body and the descent of the
diaphragm increases the
volume of the thoracic cavity.
Notice that in the resting state
(breathing out) the diaphragm
bulges up under the lungs, the
lungs themselves are slightly
elastic and pull the diaphragm
back to this position

Oxygenation of the blood
The two main functions of the
lungs are to oxygenate the
blood and to remove waste
carbon dioxide.
The blood is oxygenated in the
alveoli. The alveoli are thin
walled and surrounded by
capillaries. The blood enters
the capillary network around
the alveoli from the
pulmonary artery and leaves
the capillary network via the
pulmonary vein.
Oxygen diffuses into the blood
through the alveolar and
capillary walls and carbon
dioxide diffuses out of the
blood. The alveoli have a
surface area of about 70
square metres to make this
gas exchange as fast as
possible.
Carbon dioxide dissolves in
water and can easily and

reversibly form compounds
such as carbonic acid and
bicarbonates.
Oxygen does not dissolve
much in water, to overcome
this problem the oxygen in the
blood is stored in red blood
cells. These contain
haemoglobin which can
combine with oxygen to form
oxyhaemoglobin. The red
blood cells contain the oxygen
in the blood. The blood
transports oxygen from the
lungs to the rest of the body.
Oxy-haemoglobin is bright red
and haemoglobin is dark red,
this is why veins look dark and
why all the diagrams show
veins in blue and arteries in
red. The exception is the
pulmonary artery which carries
dark red, de-oxygenated blood
to the lungs and the
pulmonary vein which carries
bright red oxygenated blood
away from the lungs.The
special adaptions of the alveoli
for gas exchange are:
Thin walls
Huge surface area
Covered in capillaries to
provide blood
A wet lining to dissolve
gases

Aerobic respiration
Respiration is the process in
which the chemical bonds of
energy-rich molecules such as
glucose are converted into
energy usable for life
processes. Aerobic
respiration uses oxygen to
oxidise glucose and produce
energy. The equation for the
oxidation of glucose is:
C H O + 6O → 6CO +
6H O + Energy released
Glucose + Oxygen → Carbon
dioxide + water + Energy
released
In a fire there is a massive
uncontrolled release of energy
as light and heat. Respiration
is a similar process but it
occurs in gradual steps.
Most animals and plants use
aerobic respiration as a
primary source of energy.
glucose + oxygen = carbon
dioxide + water = energy
When a person is doing very
heavy exercise and the blood
cannot supply enough oxygen
another sort of respiration
occurs. This converts glucose
into energy without the need
for oxygen and is known as
anaerobic respiration. The
reaction is: Glucose → Energy
6 12 6 2 2
2

Anaerobic respiration
released + lactic acid
Anaerobic respiration releases
less energy than aerobic
respiration. Unfortunately the
insufficient blood supply that
leads to anaerobic respiration
also means that the lactic acid
builds up in the muscles. High
lactic acid concentrations are
painful and felt as cramp.
When exercise stops, the
blood supply is able to provide
enough oxygen to convert the
lactic acid to carbon dioxide
and water but this takes time
and the muscle pain may
continue after exercise until
the lactic acid has been
converted.
The delay in the removal of
lactic acid is known as the
oxygen debt. Carbon dioxide
and lactic acid both cause
increases in breathing rate
and heart rate to allow the
body to repay the oxygen
debt. The oxygen debt is the
reason why we continue to be
out of breath even after
exercise. If athletes are very fit
their circulation can provide
extra oxygen more rapidly and
their recovery time, the time
required to restore normal
breathing and pulse, will be

shorter than in people who are
not fit.
Yeasts and anaerobic
respiration
The direct conversion of
glucose to energy without the
use of oxygen occurs in many
yeasts and fungi. The ethanol
that is used in alcoholic drinks
is a result of anaerobic
respiration in yeast, the
reaction is: Glucose → Energy
released + ethanol + carbon
dioxide
Brewers use various types of
brewers yeast to produce
alcohol. In fizzy alcoholic
drinks such as champagne the
bottles are tightly stoppered to
prevent the carbon dioxide
from escaping.
The Heart a Muscle
The blood transports food,
proteins, blood cells, gases,
water, minerals and waste
products around the body.
Blood contains:
Plasma - a straw coloured
liquid in which the blood
cells are suspended and
the other components of the
blood are dissolved.

Blood
Red blood cells - these are
red and doughnut shaped
for a large surface area.
They carry oxygen from the
lungs to the tissues as oxy-
haemoglobin (the
oxygenated form of
haemoglobin). They do not
have a cell nucleus.
White blood cells - these
are colourless cells with a
large cell nucleus. They
defend the body against
disease by engulfing micro-
organisms (bacteria and
viruses) and producing
antitoxins and antibodies.
Platelets - these are
fragments of cells and very
small. They do not have a
cell nucleus. They form
blood clots at the site of
injuries. Clots protect the
body from further infection
and blood loss.

How the heart works
Due the continuous cardiac
cycle which takes an
approximate second, the heart
is the fastest and the strongest
muscle in the body. The
strongest external muscle is
the tongue, however the heart
is much stronger.
The heart works in three
stages:
1. Blood flows into the atria.
2. Both atria contract at the
same time, forcing blood
into the ventricles.
3. Both ventricles contract at
the same time, forcing
blood through the
pulmonary artery and aorta.
The heart valves ensure that
the blood goes in the correct
direction, they stop backflow.
When the atria contract the
valves between the atria and
the ventricles open passively
and the high pressure in the
arteries keeps the valves
between the ventricles and the
arteries closed. When the
ventricles contract the valves
atria shut and the valves
arteries open.

The net effect of the action of
the heart is as follows.
Deoxygenated blood from the
body enters the right atrium
and flows into the right
ventricle where it is pumped
through the lungs. In the lungs
the blood is oxygenated. It
then flows into the left atrium
and on into the left ventricle
where it is pumped out at
sufficient pressure to reach
every part of the body. The
atria have thin walls and act
as reservoirs, the ventricles
have thick, muscular walls and
act as pumps. The valves in
the heart prevent backflow.
You need to know the
following names of arteries
and veins:
Aorta - the big artery that
comes out of the left
ventricle.
Pulmonary artery - the big
artery that comes out of the
right ventricle.
Vena cava - this refers to
the big vein that connects to
the right atrium. It has two
sections the "superior" vena
cava that drains blood from
the top part of the body and
the "inferior" vena cava that
drains blood from the body
below the heart. To make
the sections clear it is often
said that there are two

"vena cavae", the superior
vena cava and the inferior
vena cava. Either learn the
names of the two sections
or, when you draw the heart
put the arrow to the vena
cava as close to the heart
as possible.
Pulmonary vein - the vein
that is directly attached to
the left atrium.
The menstrual cycle is a
cycle of events that occurs in
the womb (uterus) and
ovaries of female mammals. It
is associated with the
production of eggs and
preparing the uterus for the
implantation of fertilised eggs.
The menstrual cycle occurs
over a period of about 28
days. The changes during the
cycle are due to four
hormones, progesterone,
oestrogen, FSH (follicle
stimulating hormone) and LH
(luteinising hormone).
Progesterone and oestrogen
have wide ranging effects on
the body but in the context of
the menstrual cycle
progesterone is mainly
involved in maintaining the
lining of the uterus and
oestrogen is mainly concerned
with building up the lining of

The menstrual cycle
the uterus. FSH stimulates the
production of eggs and LH
stimulates the release of the
egg. FSH and LH are
produced by the pituitary
gland in the brain.
There are four stages in the
menstrual cycle.
Stage 1. Days 1-4.
Menstruation (bleeding)
occurs. The lining of the
uterus disintegrates and is
shed. This is due to low levels
of progesterone.
Stage 2. Days 4-14. The
uterine lining grows back. This
is 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. The
lining of the uterus is
maintained in case the egg
becomes fertilised and
implanted in the uterus.
Maintenance of the lining is
due to high levels of
progesterone.
The four hormones interact
with each other. FSH causes
Oestrogen release and
oestrogen inhibits FSH. LH
stimulates both oestrogen and
progesterone production.

Before ovulation LH release is
stimulated by oestrogen but
after ovulation it is inhibited by
both oestrogen and
progesterone.
In summary, the hormones
have the following effects:
Oestrogen: causes growth of
the uterine lining. Inhibits FSH.
Stimulates release of LH and
hence release of the egg.
Inhibits LH after ovulation.
Progesterone: maintains the
uterine lining. Inhibits LH after
ovulation. LH: Stimulates the
release of the egg (called
ovulation). Stimulates
oestrogen and progesterone
production. FSH: Stimulates
egg development and the
release of oestrogen.
Birth control tablets contain
high levels of progesterone
and oestrogen. The oestrogen
inhibits FSH production so that
eggs cease to develop.
FSH is used to treat infertility
because it stimulates the
production of eggs.
The nervous system consists
of the brain, spinal cord and
relay neurones (Central
nervous system) and
peripheral nervous system

The Nervous System (sensory neurones and motor
neurones). The nervous
system lets the organism react
to the environment and
surroundings and coordinate
their behaviour.
The senses
Sense organs contain
receptors that are sensitive to
stimuli. Typical stimuli are
due to changes in chemical
composition, mechanical
effects, heat, sound and light.
Stimuli are the changes that
are detected. Receptors
detect the change.
There are five sense organs
that are studied at this stage,
the nose, tongue, eyes, ears
and skin.
The nose has smell receptors
that are sensitive to a wide
range of chemical stimuli.
Much of what is called 'taste'
is actually smell; the range of
flavours in food is very limited
if the nose is blocked.
The tongue has taste
receptors that are sensitive to
chemical stimuli. There are
four basic tastes: bitter, salt,
sweet and sour.
The eyes have receptors that
are sensitive to light, the ears
have receptors that are

sensitive to sound and the
skin has receptors that are
sensitive to temperature,
touch, pressure and stretch.
Light from the surroundings
enters the eye through the
pupil. It is focussed by the
cornea and lens so that it
forms an image on the retina.
The cornea performs crude
focussing and the lens
performs active, fine
focussing. The eye is filled
with transparent liquid (the
humours).
The iris controls the size of
the pupil and so controls how
much light gets into the eye. In
bright light the circular
muscles in the iris contract,
this makes the pupil smaller
and allows less light into the
eye. In dim light the radial

The eye
muscles contract, this makes
the pupil larger and allows
more light into the eye.
The lens changes shape to
allow the eye to focus on
things at various distances.
The shape of the lens is
changed by the action of the
ciliary muscles. The ciliary
muscles form a circle that is
attached to the lens by the
suspensory ligaments. To
focus on distant objects the
ciliary muscles relax which
pulls the suspensory
ligaments tight and makes the
lens thinner. To focus on
nearby objects the ciliary
muscles contract which allows
the suspensory ligaments to
relax so that the lens forms a
more spherical shape.
The retina contains cells that
are sensitive to light. These
cells are called rods and
cones.
The rods are more sensitive
than the cones but do not
provide any colour
information. In dim light our
view of the world is largely
provided by rods and appears
as a black and white image.
There are three types of cone
and these are each sensitive

to different colours of light.
The cones are especially
densely packed in the part of
the retina called the fovea;
this dense packing means that
the fovea is most sensitive to
fine detail in the image.
The part of the eye where the
optic nerve enters is called
the blind spot. The blind spot
does not contain any light
receptors (it has no rods or
cones).
Neurones
Neurones are cells that are
specialised to transmit
electrical impulses around
the body. They consist of three
principle components: the
dendrites, the cell body and
the axon. Each neurone has
its own nucleus. (The US
spelling of neurone is
"neuron").
There are three types of
neurone: sensory neurones,
relay neurones and motor
neurones.
Neurones connect to other
neurones by means of
synapses. Nerve impulses
travel down the axon to one
side of the synapse where the

electrical signal causes
chemicals to be released.
These chemicals diffuse
across the gap and generate
an electrical impulse in the
neurone on the other side of
the synapse.
Reflex arcs
The nervous system has many
reflexes. These are automatic
responses to stimuli. Very
quick responses are managed
by Reflex arcs. A reflex arc
consists of the following
components:
Stimulus
Receptor
Sensory neurone
Relay neurone
Motor neurone
Effector
Response
Pain reflex: a painful stimulus
causes a muscle to contract
automatically

A typical reflex arc called the
"pain reflex" is illustrated.
In the pain reflex the stimulus
is mechanical damage, the
receptor is a "pain receptor",
the pain receptor generates an
electrical impulse in a sensory
neurone which creates an
electrical impulse in a relay
neurone, which in turn creates
an electrical impulse in a
motor neurone. The impulse in
the motor neurone stimulates
a muscle, which is an effector,
and this creates movement
away from the painful stimulus
as a response.
Another reflex is the "patellar"
or "knee jerk reflex" where a
blow beneath the knee-cap
makes the leg straighten. The
contraction of the pupil in
response to bright light is yet
another reflex.

Flash cards for igcse biology

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Flash cards for igcse biology