Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
My Basket
Basal Nuclei and Diseases of Basal nuclei£7.50
Woman Repoduction£2.00
Total£9.50
Or: Edit My Basket
Title: IGCSE Biology Complete Notes
Description: All Topic Summary IGCSE Biology book summary
Description: All Topic Summary IGCSE Biology book summary
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
Complete Revision Notes IGCSE Biology Book
Teacher
Romana Bano IGCSE Bio
Characteristics and classification of living organisms
•
•
•
•
•
•
•
•
•
•
•
•
•
o
o
o
o
o
o
o
movement as an action by an organism or part of an organism causing a change of
position or place
...
growth as a permanent increase in size and dry mass by an increase in cell number or cell
size or both
...
excretion as removal of the waste products of metabolism (chemical reactions in cells
including respiration), toxic materials, and substances in excess of requirements
...
species as a group of organisms that can reproduce to produce fertile offspring
...
tissue as a group of cells with similar structures, working together to perform a shared
function
...
organ system as a group of organs with related functions, working together to perform
body functions
...
cell wall: supports the cell and prevents it from bursting
...
cytoplasm: contains nutrients such as sugars and proteins and contains all the cell
organelles; site for metabolic reactions
...
ribosome: on the membrane of rough endoplasmic reticulum; site for protein synthesis
...
2] Movement in and out of cells
•
diffusion as the net movement of particles from a region of their higher concentration to
a region of their lower concentration down a concentration gradient, as a result of their
random movement
...
•
osmosis as the net movement of water molecules from a region of higher water potential
(dilute solution) to a region of lower water potential (concentrated solution), along
the water potential gradient, through a partially permeable membrane
...
protein molecules move particles across a membrane during active transport
by changing shape and allowing them to be transported
...
They are located on the cell membrane
...
Uses:
used for energy: 1 molecule releases 17 kJ of energy
...
3 fatty acids and 1 glycerol
...
insulation in the form of adipose tissue
...
protection from mechanical damage
...
Made up of long chains of amino acids
...
Water:
Required for metabolic reactions in cells
...
Required to dissolve nutrients in order for enzymes to act on them in the alimentary
canal
...
each strand contains chemicals called bases
...
the bases always pair up in the same way: A with T, and C with G (full names
are not required)
...
Add benedict’s solution
...
If present: mixture turns from blue to green to yellow to orange to brick red
...
Test for starch:
Crush and grind to make extract
...
If present: mixture will turn blue-black
...
Add ethanol to extract
...
If present: solution turns milky white
...
Crush and grind to make extract
...
If present: turns purple/mauve/lilac
...
add DCPIP drop by drop using a pipette/burette
...
if vitamin C is present:
turns from blue to colourless
...
4] Enzymes
•
catalyst as a substance that increases the rate of a chemical reaction and is not changed
by the reaction
...
Importance of enzymes:
•
Without enzymes, processes occur too slowly
...
Reactions can take place at lower temperatures
...
Enzyme has a ‘dent’ known as the active site
...
Enzyme and substrate bind at the active site to form a temporary structure known as
enzyme-substrate complex
...
This product is no longer complimentary to shape of the active site, and so it is released
...
•
•
•
•
•
•
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
Factors affecting enzyme activity:
Temperature:
At 0 degrees, enzyme activity is zero because molecules have very less kinetic energy
...
Velocity of molecules increases
...
Frequency of successful collisions
More enzyme-substrate complexes formed
...
At optimum temperature, enzyme activity is at the highest and enzyme functions
fastest
...
Shape of active site nolonger complimentary to shape of substrate
...
pH:
Every enzyme has an optimum pH
...
Enzyme and substrate concentrations
...
•
•
•
6CO2 + 6H2O → C6H12O6 + 6O2
Hydrogencarbonate indicator: used to measure carbon dioxide concentration in water
...
•
o
o
o
o
▪
▪
o
▪
▪
▪
o
▪
▪
▪
▪
o
o
▪
▪
▪
Nitrate ions
Magnesium ions
Required for amino acid synthesis
...
· Reduced/stunted growth
· Yellowing between veins of leaves
...
· Lower leaves turn green
· Lower leaves turn yellow
· Upper leaves turn yellow
...
If present: turns blue-black
...
Perform starch test
...
Proving light is needed for photosynthesis:
Destarch the plant [leave in a dark cupboard for 24-48 hours; ensuring that all starch
produced is only during the investigation]
Cover one leaf [to prevent light from entering]
Keep the plant in an environment where all factors of photosynthesis are present, for 6
hours
...
Control: an experimental setup that is given all the variables, including the independent
variable, for comparison of results
...
Carbon Dioxide
Light Intensity
Temperature
6] Human Nutrition
•
•
o
•
Balanced diet as a diet containing all seven nutrients in correct amounts and proportions
...
If enough is not supplied, it
can cause a deficiency disease
...
Iron
Red meat; egg
yolk; dark green
vegetables
...
Vitamins:organic substances required in small amounts
...
Vitamin
Contained
in:
Required for:
Deficiency effects
Vitamin C
Citrus fruits
Making stretchy proteincollagen
...
Vitamin
D
Butter; egg
yolk
Helps calcium get
absorbed; for making
bones and teeth
· Rickets: bones become soft and
deformed;
· Muscle cramps
· Stunted growth
· Fatigue
· Reduced ability to absorb
calcium ions
...
cannot be digested
...
prevents (colon) cancer
...
removal of bacteria,
Prevents muscles from becoming weak and prevents constipation
...
Cholesterol can get deposited on the walls of
coronary arteries and can lead to Found in red meat and dairy products
...
Symptoms:
underweight
bloated stomach
...
Symptoms:
lack of growth
diarrhoea / vomiting
fatigue
(more) prone to, infections / disease
ingestion as the taking of substances, e
...
food and drink, into the body through the
mouth
...
This increases the surface area and increases enzyme
activity
...
absorption as the movement of small food molecules and ions through the wall of the
intestine into the blood
...
assimilation as the movement of digested food molecules into the cells of the
body where they are used, becoming part of the cells
...
diarrhoea as the loss of watery faeces
...
stimulates the cells in the wall of the small intestine to release chloride ions
...
osmoticmovementofwater into the gut, causing diarrhoea and dehydration
...
water must be sterilised
...
1
...
o teeth crush and grind to increase surface area[mechanical digestion]
...
▪ Prevention:
▪ regular, brushing / mouthwash / flossing / wash / clean, teeth
▪ avoid sugary foods / diet described
▪ dental check-ups
▪ saliva contains salivary amylase which breaks down starch to maltose[chemical
digestion]
2
...
Stomach:
o sphincter muscles are present at both the entrance and the exit to prevent acid reflux
and keep the food in the stomach
...
4
...
Functions:
neutralises the acidic chyme from the stomach to give suitable pH for enzyme action
...
[mechanical digestion]
Also contains bile pigments made of old RBCs
...
Also denatures enzymes from the stomach such as
villi: secrete enzymes for digestion of food
...
lacteals in close proximity: to allow for faster diffusion and active transport, to absorb
and carry fats and cholesterol
...
villi wall is one cell thick: faster diffusion
...
goblet cells present: secrete mucus to protect the villus from:
enzymes such as proteases and lipases
...
acid from the stomach
...
5
...
•
1
...
3
...
5
...
7
...
Role of the liver:
all nutrients are transported to the liver via the hepatic portal vein
...
excess amino acids are
amino group is converted to urea and sent to kidney
...
haemoglobin removed from dead RBCs, and the remaining part is converted to glycogen
and stored
...
2
...
4
...
2
...
4
...
6
...
Xylem
Phloem
Made up of many dead cells joined end
to end, where the end walls are
dissolved
...
They have perforations
...
Translocate sucrose and amino acids
...
No nucleus [cytoplasm is present]
Lignin present
...
Unidirectional movement
...
Adaptations of Xylem:
Lignin present: lignin is waterproof and prevents any loss of water from the xylem
...
End walls dissolved: to allow a free, smooth passage of water
...
Transpiration stream:
water moves from root cells to xylem by cell-to-cell osmosis
...
evaporation/transpiration of water in the leaves at the top of the xylem, followed
by diffusion of water vapour though stomatareduces the pressure at the top
...
water moves up in a continuous column
...
adhesion causes water molecules to stick to lignin, allowing a continuous column of
water
...
Process of transpiration:
1
...
2
...
3
...
4
...
This is known as
• Factors affecting transpiration:
1
...
Humidity
3
...
Keeps water moving up the xylem vessel due to transpirational pull that is created
...
Evaporation helps cool the leaves
...
This causes loss
of water through cell-to-cell osmosis, causing plant cells to become flaccid, and the plant
starts to wilt
...
• Adaptations of plants to take up water:
o root hair cells have very large surface area for active transport and diffusion
...
o xylem vessels are hollow and narrow to provide an easy pathway for water
...
o stomata being open allows vapour to diffuse easily out of the leaf
...
New shoots
Storage organs
contain starch which is
used for respiration and
energy for the shoot
...
Plumule/radicle
Leaves have not yet
developed to
photosynthesise so energy
is needed for the growth of
the plumule and
radicle
...
8] Transport in animals
•
•
o
•
o
o
o
▪
▪
consists of blood vessels, with a pump known as the
Single circulation:
blood passes through the heart once in one complete circuit around the body
...
one loop through the lungs and one loop through the rest of the body
...
prevents mixing of oxygenated and deoxygenated blood
...
2
...
4
...
2
...
4
...
6
...
allows different blood pressure in each loop
...
Consists of:
pulmonary circulation
systemic circulation
Pulmonary circulation
Systemic circulation
Between heart and lungs
Between heart and rest of the body
Involves pulmonary artery[deoxygenated blood] and
pulmonary vein[oxygenated
blood]
Involves vena cava[de-oxygenated
blood] and aorta[oxygenated blood]
Faster, because it involves
a smaller circuit
...
Low pressure circulation: because
of thinner walls of right ventricle
High pressure circulation: due to
thicker walls of left ventricle
...
left ventricle pumps blood further
...
left ventricle pumps blood at higher pressure
...
atrial systole: atriums
atrioventricular valvesopen and blood is pushed down to ventricles
...
blood flows to the aorta and pulmonary artery
...
semi-lunar valves close to prevent blood from flowing back
...
prevent backflow of blood
...
ensure that blood flows in one direction only
...
to prevent mixing of oxygenated and de-oxygenated blood
...
ECG[Electro Cardiogram]
...
pulse rate
...
one ‘lub-dup’; the sound of valves opening and closing
...
Process:
deposition of fat on walls of coronary arteries
...
thrombosis may occur[complete blockage]
...
increases blood pressure
...
less/no aerobic
muscle cells in heart die as no nutrients supplied
...
cardiac arrest/heart attack
...
high cholesterol diet
...
Prevention:
exercise (regularly)
...
reduce (animal / saturated) fat / cholesterol in diet
...
reduce salt intake
...
avoid stress situations
...
control diabetes
...
How does exercise help?
prevents blocked arteries / prevents thrombus formation
...
lowers cholesterol / lowers fats / reduces risk of atheroma
...
lowersstress
...
•
o
o
o
CHD treatment:
drug treatment
...
aspirin:
to, reduce risk of / prevent, blood clotting
...
attached to carry blood around the blocked artery
...
balloon inflated to widen artery
...
opens / supports, (narrow / weak) artery
...
Effect of physical activity on heart rate:
muscles need energy, thus requiring oxygen and glucose
...
heart also needs to remove carbon dioxide and lactic acid as they affect enzyme action,
and so to remove them it needs pump blood faster
...
Blood vessels:
▪
o
▪
▪
o
▪
▪
o
▪
▪
▪
o
1
...
3
...
o
1
...
Adaptations:
thick muscular wall: withstands high pressure of blood
...
fibrous tissue: maintains the shape of the artery and prevents it from bursting
...
folded/crinkly endothelium: allows artery to stretch, allowing a larger volume of
blood to flow
...
Veins:
o carry de-oxygenated blood from the tissue/muscle to the heart[except for the
pulmonary artery]
...
o Adaptations:
▪ valves: prevent backflow of blood
...
▪
thin wall: allows contraction of muscles outside the veinto be felt inside the lumen,
which allows blood to flow
...
Capillaries:
o exchange of substances between the blood and tissue/cells by diffusion occurs in
capillaries
...
allows filtration/movement of small molecules and nutrients between blood to tissue
...
allows WBCs to squeeze
▪ one-cell thick:faster
▪ very narrow:
1
...
2
...
▪ large number of capillaries/capillary bed: to increase surface area for faster
•
Components of blood:
Component
Function
Red blood cells
Transporting oxygen
...
White blood cells
Phagocytosis and antibody
production
...
Plasma
Transport of blood cells, ions, soluble
nutrients, hormones, proteins and
carbon dioxide
...
platelets stimulate clotting
...
platelets bump into rough edges of the wound and react, releasing clotting
factors[thrombin]
...
these clotting factors cause fibrinogen in blood to convert to fibrin
...
this creates a mesh around the wound
...
red blood cells get trapped in this mesh and it forms a scab
...
prevents loss of blood
...
prevents entry of pathogen
...
Consist of lymphatic capillaries
...
2
...
3
...
4
...
• Tissue fluid:
o Capillaries empty nutrients into the tissue fluid, from which the nutrients diffuse into
each cell
...
▪ keep environment constant: for optimum temperature for enzymes in cells
...
2
...
4
...
6
...
8
...
•
1
...
transmissible disease as a disease in which the pathogen can be passed from one host to
another
...
Therefore, only
specific antibodies can fit the specific shapes, and those antibodies are needed
...
antibodies lock on to antigens
...
antibodies / antigens, are specific
...
antibodies destroy pathogens (directly)
...
antibodies mark pathogens for destruction by phagocytes by phagocytosis
...
Pathogens can enter the body by:
Direct Contact:
through blood
...
2
...
▪ from animals
...
Vectors
• The body has the following defences:
1
...
▪ skin has a layer of dead cells that prevent it from getting penetrated
...
2
...
o HCL produced by the stomach kills any bacteria present in the food
...
o WBCs can be enhanced by vaccines
...
How vaccination works/how vaccination helps control spread of diseases:
1
...
2
...
3
...
4
...
5
...
6
...
7
...
8
...
9
...
10
...
• Hygiene:
1
...
▪ keep animals away from food
...
▪ keep raw meat away from other food
...
Personal hygiene:
▪ keep your body clean
...
3
...
4
...
Otherwise, it could affect
aquatic life
...
passive immunity is short-term defence against a pathogen by antibodies acquired
from another individual, e
...
mother to infant
...
Antibodies produced and
acquired from another individual
...
Memory cells not produced
...
Short-lived immunity
...
Response in subsequent infection
is slower
...
Type 1 Diabetes:
WBCs attack and destroy beta cells in the pancreas, that produce the hormone insulin
...
Leads to:
weight loss
...
C6H12O6 + 6O2 → 6CO2 + 6H2O
anaerobic respiration as the chemical reactions in cells that break down nutrient
molecules to release energy without using oxygen
...
C6H12O6 → 2C2H5OH + 2CO2
In humans, anaerobic respiration produces lactic acid only
...
Absence of oxygen
...
Less energy released
...
Incomplete breakdown of glucose
...
In human muscle cells:lactic
acid produced
...
All living cells
...
]
Breathing
Respiration
Mechanical process
...
Inhaling and exhaling
...
Involves lungs, diaphragm, and ribcage
muscles
...
•
Uses of energy in the body:
o
muscle contraction
...
cell division
...
growth
...
maintenance of a constant body temperature
...
2
...
o
▪
1
...
▪
Trachea:
Contains cartilage:
keeps, airways / trachea / bronchi, open
...
allows flexibility / can breathe even when, bent / swallowing
...
capillaries: form large network
...
Thin walls:
1
...
▪ reduces diffusion distancefor oxygen and carbon dioxide
...
alveoli: high concentration of oxygen flowing in from bronchi
...
capillaries:high concentration of carbon dioxide by continuous flow of blood
...
•
Moist surface:
1
...
dissolves oxygen before diffusion
...
•
Process of breathing:
Inhalation:
1
...
internal intercostal muscles
•
o
3
...
5
...
7
...
9
...
2
...
4
...
6
...
8
...
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
lifts ribs upwards and
diaphragm contracts and flattens and drops
...
down the pressure gradient
...
Exhalation:
internal intercostal muscles contract
...
lifts ribs downwards and inwards
...
volume of thorax/lungs/chest
pressure in thorax/lungs/chest
air flows out
...
lungs
Effect of exercise on breathing rate:
increase in muscle contraction
...
increase in aerobic respiration
...
increase in carbon dioxide concentration
...
detected by the, brain/chemoreceptors
...
brain stimulates an increase in depth of breathing
...
Muscles switch to anaerobic respiration
...
extra oxygen required by the muscles after exercise to break down the lactic acid
...
Breathing rate remains high after exercise:
to supply muscles with oxygen to break down lactic acid
...
to remove lactic acid from muscle cells and move it to the liver
...
2
...
4
...
o
0
...
2
...
4
...
6
...
8
...
Excretion
Egestion
The removal of toxic materials, waste
products of metabolism and excess
materials
...
Excreted through the lungs, skin,
kidneys and liver
...
Excretory organs:
Lungs:
carbon dioxide
...
Kidney:
excess salts and water
...
spent hormones
...
Process of deamination:
nitrogen-containing part of excess amino acids is converted to ammonia, in the liver
...
it is converted to urea and taken to the heart via the hepatic vein
...
remaining part of amino acids is converted to glycogen and stored in the liver
...
synthesises plasma proteins such as fibrinogen from amino acids
...
neutralises toxins
...
breaks down old RBCs, storing iron and excreting remaining part as bile pigments
...
stores potassium
...
Kidney has three main parts:
Leading from the pelvis is a tube to the urinary bladder, known as the ureter
...
o The role of kidney tubules:
0
...
▪ the blood goes through the afferent arteriole[which is wide], into the glomerulus
...
▪ the difference in pressure between the afferent and efferent arteriole causes high
pressure in the capillaries in the glomerulus and causes nutrients to move out of the
glomerulus
...
▪ plasma proteinsdo not come out as they are too big
...
Reabsorption:
o takes place in all parts of the kidney tubule except for the renal capsule
...
o they move into the capillaries which join up to form the renal vein
...
▪ excess water
...
o this flows into the collecting duct and goes to the ureter
...
De-oxygenated blood
...
No urea
...
Less water
...
Less salts
...
•
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
No toxins
...
veins are easy to find
...
blood flows from body into the dialysis machine
...
the tube is surrounded by dialysis fluid, containing:
glucose, salts and water[according to blood concentrations and osmotic potential]
no
the tube separates the person’s blood from the dialysis fluid
...
excess water and saltsmove out by diffusion and osmosis and enter the dialysis fluid
...
dialysis fluid is constantly refreshed to maintain the concentration gradient
...
blood returns back to the vein
...
restricted
quality of life affected
...
noneed to go for hospital
...
nolong term pain/discomfort
...
Disadvantages:
rejection of kidney
...
riskassociated with operation
...
12] Coordination & Response
nerve impulse: an electrical signal that travels along nerve cells known as neurones
...
central nervous system:
▪ spinal cord
...
peripheral nervous system:
•
•
•
1
...
3
...
5
...
7
...
Impulse is picked up by a
This impulse travels along sensory neurones
...
It processes the impulse
...
To the appropriate
Response to stimulus occurs
...
Voluntary action
Involuntary action
Not a rapid response
...
Requires conscious thought
...
Requires learning/not present from
birth
...
Not protective in nature
...
Myelin sheath:
layer of fat and protein that wraps around a neurone
...
prevents leakage of impulses
...
A synapse consists of:
1
...
2
...
3
...
• Process:
1
...
2
...
3
...
4
...
5
...
6
...
7
...
• Advantage of a synapse: ensures that impulses travel in one direction only
...
• sense organs as groups of receptor cells responding to specific stimuli: light, sound, touch,
temperature and chemicals
...
2
...
4
...
cornea:refracts light
...
lens:focuses light onto the retina
...
optic nerve:carries impulses from the eye to the brain
...
In bright light:
•
•
•
•
•
circular muscles contract
...
pupil constricts
...
to prevent damage to photoreceptors
...
radial muscles contract
...
allows more light to enter in order to activate more receptors for clearer vision
...
When the object is near:
•
•
•
•
•
ciliary muscles contract
...
muscle tension low
...
increased refraction of light
...
suspensory ligaments stretched/tense
...
lens shape:thin/narrow
...
Rods
Cones
Sensitive to dim light
...
[R, G, B]
Distributed throughout the
retina
...
]
Concentrated mainly in the fovea
...
Responsible
for colouredvision and sharpimages
...
•
o
o
Adrenaline:
secreted by the adrenal gland
...
Effect
Reason
Target organs
Increases breathing and
pulse rate
...
Lungs and heart
...
More light enters the eye,
leading to clearer vision
...
Liver
...
Artery and arteriole
muscles
...
Blood vessels in leg
muscles dilate
...
controls the glucose concentration in blood
...
cause development of secondary sexual characteristics in females, and helps in
the control of the menstrual cycle
...
cause development of secondary sexual characteristics in males
...
Made of secretory cells and hormones
...
Chemicals carried dissolved in plasma
...
Information carried in chemicals called
hormones
...
Hormones travel more slowly
...
Effect of a hormone lasts long
...
phototropism as a response in which parts of a plant grow towards or away from the
direction of light
...
they are broken down by light, so they move away from light by diffusion
...
this results in a difference in concentrations in the shaded side and the side facing light
...
this causes unequal growth in the shaded region and non-shaded region, leading to
the shoot tip bending toward light
...
leading to more light absorbed
...
flowers are morelikely to attract pollinators
...
Auxins and positive gravitropism in roots
...
they diffuse towards gravity
...
this causes unequal concentrations in the lower side and the upper side
...
this causes unequal growth in the lower side and the upper side, leading to the root tip
bending towards gravity
...
absorb more minerals ions and water
...
auxins are distributed evenly around the shoot tip and shoot grows rapidly upwards[in
search of light]
chlorophyll synthesisreduced
...
condition is reversed when grown in light
...
shoot[leaves and stem] are stimulated to grow rapidly
...
roots cannot absorb enough water and minerals to support the rapid growth of the
shoot
...
13] Homeostasis
•
•
o
▪
▪
▪
o
▪
▪
homeostasis as the maintenance of a constant internal environment
...
Contains melanin
...
layer of fatty tissue[adipose tissue]
...
It evaporates from the surface of the skin
and produces a cooling effect
...
Less air is trapped, so less insulation
...
This leads
to more heat loss due to radiation/conduction/convection
...
erector muscles contract: hair stands up, traps more air, leading to more insulation
...
Shunt vessels dilate to
allow more blood to flow through them, and less amount of blood flows through
capillaries near the skin’s surface
...
Coordination of temperature regulation:
temperature receptors pick up change in temperature/stimulus
...
to the hypothalamus in the brain
...
hair erector muscles
...
arteriole muscles
...
Negative feedback:
body temperature needs to remain constant
...
by the hypothalamus
...
hair erector muscles
...
arteriole muscles
...
response occurs
...
response is switched off
...
Glucose metabolism:
Response to concentration of glucose higher than normal:
beta cells in pancreas secrete insulin
...
reduces concentration of glucose in blood
...
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
•
o
o
o
o
o
stimulates the liver cells to break down glycogen to give glucose
...
Negative feedback:
blood glucose concentration needs to be kept constant
...
by hypothalamus in the brain
...
this increases/decreases blood glucose concentration
...
response is switched off
...
Diabetes:
Blood glucose concentration goes up and remains up as no insulin produced
...
weight loss
...
wounds heal slowly
...
blurred vision
...
more glucose concentration in urine
...
high blood, glucose/sugar
...
regular blood sugar tests
...
exercise
...
14] Drugs
•
•
o
o
▪
▪
o
drug as any substance taken into the body that modifies or affects chemical reactions in
the body
...
They kill bacteria by:
targeting bacterial enzymes: responsible for mitosis and cell division
...
However they are ineffective against viruses, because:
▪
▪
o
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
•
o
o
o
o
o
•
o
o
o
o
o
o
o
o
viruses do not have cell walls
...
Antibiotic resistance Is increasing due to:
over usage of drugs, even when not needed
...
frequent prescriptions of antibiotics, leading to more antibiotic resistant bacteria
...
highly
depressant:slows down transmission of nerve impulses, increasing reaction
time
...
increases
people lose control and become violent
...
effects of alcohol addiction:
cirrhosis of the liver/liver failure
...
brain damage
...
oral cancer/throat cancer
...
heart failure/stroke/heart attack
...
depressant: slows down functions of the brain, lengthens reaction time
...
vomiting,
withdrawal symptoms:
intense carving for heroin
...
nausea and vomiting
...
extreme pain in joints
...
heroin diffuses into synapse
...
heroin is complementary to receptor
...
stimulates
reducespain
...
o
•
o
o
o
o
•
•
also desensitizes the receptors, so after some time more is required to feel the same
sensation
...
often resort to crime to get money for drugs
...
use of non-sterile needles to inject heroin can lead to HIV
...
carbon monoxide:
o poisonous/toxic gas
...
o puts strain on the heart, leading to exhaustion and tiredness
...
nicotine:
o stimulant: leads to hypertension and makes the user feel more alert by narrowing
arterioles and increasing heart rate
...
o decreases appetite
...
tar:
o contains chemicals called carcinogens
...
o it can cause irritation in the airways, leading to more mucus being produced by goblet
cells
...
Leading to reduced surface for
gas exchange
...
smoke particles:
o get trapped in the lungs
...
o leads to COPD and emphysema
...
smoker’s cough: may burst weakened alveoli
...
oxygenation of blood decreases
...
lung cancer:
caused by carcinogens
...
excess production of mucus
...
inflammation of bronchial lining: bronchitis
...
smoking and heart disease:
nicotine and CO increase the tendency of blood to clot
...
blockage of coronary arteries due to clots/fat deposits
...
heart failure
...
these hormones stimulate anabolic reactions that build up large molecules from small
ones
...
increase in protein synthesis that can lead to increased recovery from muscle damage
...
growthof limb bones and increasein lung capacity
...
they are banned due to:
an unfair advantage
...
they can damage immune system and
15] Reproduction in plants:
•
asexual reproduction as a process resulting in the production of genetically identical
offspring from one parent
...
in bacteria, it is known as binary fission
...
faster adaptation: if parent plant is well adapted offspring will be well adapted also
...
Disadvantages of asexual reproduction to plants:
absence of genetic variation: offspring more susceptible to same disease
...
overcrowding leads to competition for resources
...
fertilisation as the fusion of gamete nuclei
...
more chances of evolution
...
more energy required:flowers need to attractive and nectaries need to be present to
attract pollinators
...
petal:brightly coloured/conspicuous, used to attract insects
...
stigma:receives pollen grain, which germinates in it
...
Part
Insect pollinated flower
Wind pollinated flower
Petal
...
Inconspicuous and dull
...
Have strong, attractive
scent
...
Nectaries
...
Absent
...
Sticky, have ridges and
grooves
...
Quantity of pollen
...
Anther
...
Hanging out/pendulous
...
Inside flower; sticky
...
•
pollination as the transfer of pollen grains from the anther to the stigma
...
cross-pollination as transfer of pollen grains from the anther of a flower to the stigma of
a flower on a different plant of the same species
...
No
...
Capacity to respond to
changes to environment
...
However, if
parent plant is well
adapted, offspring will
adapt well also
...
Reliance of pollinators
...
Requires pollinators
...
•
1
...
3
...
5
...
•
1
...
3
...
5
...
•
1
...
•
•
1
...
pollen tube grows and secretes enzymes to digest a pathway through the style
...
pollen nucleus travels down the pollen tube and enters at the micropyle
...
After fertilisation:
diploid zygote à embryo plant[through mitosis]
...
ovary à
ovary wall à fruit skin
...
Embryo:
plumule: forms shoot
...
Testa: prevents embryo from damage and prevents bacteria and fungi from entering the
seed
...
16] Reproduction in humans
▪
▪
Parts of the male reproductive system:
testes:
produce
make the hormone testosterone[stimulates changes during puberty]
...
epididymis:
small tubules outside testes that store sperm for maturation
...
have a sphincter muscle to prevent urine loss during sex
...
prostate gland secretes mucus and others secrete sugarsfor respiration for sperm cells
...
main function is to deliver sperm to vagina for fertilisation
...
▪
▪
2
...
▪
4
...
▪
▪
6
...
ovaries:
▪ produce one egg cell every month
...
2
...
▪ cilia are present for peristalsis for movement of egg cell
...
▪ site for fertilisation
...
uterus:
▪ foetus develops in uterus
...
4
...
▪ separates vagina from uterus
...
vagina:
▪ muscular tube
...
▪ receives male penis during sexual intercourse
...
Sperm
Egg cell
Smaller
...
Motile, uses tale for movement
...
500,000 produced
...
Less amount of food store
...
Sperm are produced in high numbers because:
to increase chances of fertilisation, as they are:
1
...
2
...
•
o
o
▪
▪
▪
▪
o
▪
▪
▪
o
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
▪
1
...
3
...
5
...
7
...
Adaptations of sperm:
lots of mitochondria: required for energy for movement to egg cell
...
haploid
acrosome: contains hydrolytic enzymes that dissolve the membrane of the egg cell and
allow sperm to penetrate
...
cytoplasm: contains lots of food store and nutrients to provide nourishment to zygote,
for energy for mitosis and development
...
takes place in oviducts
...
forms a ball of cells/blastula
...
reaches the uterus and implantation occurs,
...
some of the cells form the placenta
...
It is now called a
Placenta:
disk like structure formed from cells of the embryo
...
at the junction between the placenta and the endometrium, blood vessels of both sides
are close to each other, allowing for diffusion of nutrients and waste between the blood
of the mother and the blood of the foetus
...
provides protection against pathogens that may have affected the mother
...
allows excretory products to diffuse out of the foetus’s blood and into the mother’s
blood
...
prevents harmful substances from entering foetal blood
...
also secretes oestrogen and progesteroneduring pregnancy
...
2
...
4
...
6
...
8
...
2
...
4
...
2
...
▪
▪
1
...
3
...
5
...
7
...
▪
1
...
3
...
however, some substances such as nicotine and rubella virus can pass through the
placenta and affect the foetus
...
Arteries carry oxygen and nutrients from mother’s blood
to foetal blood whereas veins carry excretory products from foetal blood to mother’s
blood
...
Functions of amniotic fluid:
prevents entry of pathogens
...
protects against sudden change in temperature
...
needed for bone/muscle growth
...
collectsfoetal urine
...
Antenatal care of pregnant women:
Diet:
vitamin D: for absorption of calcium, growthof foetal bones
...
iron: for blood to be formed
...
gentle exercise is also required as it plays an active part when giving birth
...
drugs: like heroin can give baby
cigarettes: nicotine and CO result in premature and underweight
Breastfeeding:
Advantages of breastfeeding:
antibodies provided[passive immunity]
...
protects the mother against breast cancer
...
contraceptive effect
...
at body temperature
...
Disadvantages of breastfeeding:
viruses such as HIV can be transmitted to baby
...
drugs/alcohol can be passed on to the baby
...
▪
▪
▪
▪
▪
▪
▪
▪
▪
•
o
o
1
...
3
...
o
1
...
3
...
5
...
hormones released by the foetus and the increase in pressure in the uterus stimulate
hormonal changes in the mother
...
the contraction become stronger and more frequent and the opening of the cervix
stretches/dilates and the amnion breaks to release the amniotic fluid
...
the contractions are even stronger now, pushing the baby towards the cervix
...
the umbilical is cut and tied just above where it attaches to the baby
...
Males[testosterone]:
enlargement of testes and penis
...
rapid increase in growth
...
growth of
widening of
growthofhairin pubic region and armpits
...
Hormones in the menstrual cycle:
Hormone
Function
Follicle stimulating hormone[FSH]
Stimulates the maturing of eggs in the
ovary and the production of oestrogen by
ovaries
...
•
1
...
3
...
5
...
Stimulates pituitary gland to produce
LH
...
Prevents menstruation
...
Menstrual cycle:
FSH produced by pituitary gland stimulates an ovary to produce and mature an egg
cell [0-5 days]:
the ovary also makes a follicle
...
follicles also produces oestrogen, and allows the egg cell to grow,
oestrogen stimulates the thickening of the uterus wall
...
LH stimulates the release of the egg from one of the ovaries, which is ovulation [Day
14]:
the follicle ruptures and the egg cell is released
...
the egg cell travels through the oviduct
...
the progesterone released stimulates and maintains the thickening of the uterus
wall [14-28 days]
...
this does not produce any hormones
...
uterus wall sheds, along with the unfertilised egg cell and the corpus albicans
...
extra-thickened uterus wall sheds, along with the unfertilised egg and blood
...
endometrium wall thickening is rebuilt by oestrogen from ovary[5-14 days]
3
...
[14-28 days]
•
•
o
Birth control:
Natural Methods:
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
Abstinence:
couple avoids sexual intercourse
...
[increases during ovulation]
state of cervical mucus
...
Artificial methods:
Barrier/mechanical methods:
Condom:
a rubbersheath placed on an erectpenis before sexual intercourse, which prevents
sperm from reaching the uterus by trapping it
...
Femidom:
sheath or a pouch, made of rubber and inserted in the vagina
...
reduces risk of STI transmission
...
used with spermicides
...
Chemical methods:
IUD:
T-shaped plastic and copper
inserted by a doctor or nurse
...
does not protect against STIs
...
when mixed in suitable proportions, these hormones prevent ovulation and prevent
conception/fertilisation
...
needs to be taken for 21 days daily during menstrual periods
...
Spermicides:
chemicals that immobilise or killsperm
...
prevents sperm from reaching the egg cell, therefore preventing fertilisation
...
semen does not contain any sperm
...
•
o
▪
▪
Fertility and conception treatments:
Artificial insemination:
sperm is harvested from a donor and stored in low temperatures
...
around the time of ovulation
...
stimulates the production of FSH & LH
...
makes sure that FSH concentration is high enough
...
more eggs are released
...
many egg cells increase the chances of fertilisation
...
stated problem with multiple births
...
issues with elderly parent(s)
...
any reference to cost of the treatment
...
can be used to increase populations / any positive effect of population increase
...
sperm duct damaged
...
low sperm count
...
Treatment:
artificial insemination
...
Woman is
given fertilitydrugs that stimulate her ovaries to produce multiple eggs
...
Initial zygote is developed in the lab and
later injected into the uterus
...
follicles do not
damages
uterus wall does not
low concentration of progesterone
...
tablets that make pituitary gland insensitive to oestrogen
...
an example is HIV, which causes AIDS
...
in semen
...
blood transfusion
...
at birth, when the two blood streams come in close contact
...
Methods of prevention:
free needle exchange schemes
...
condoms and femidoms
...
Process:
HIV attacks T-lymphocytes, which stimulate other lymphocytes to produce antibodies
...
so, there are fewerantibodies every time an infection occurs
...
symptoms:
swollen glands
...
weight loss
...
17] Inheritance
•
•
•
•
•
•
•
•
o
inheritance as the transmission of genetic information from generation to generation
...
gene as a length of DNA that codes for a protein
...
haploid nucleus as a nucleus containing a single set of unpaired chromosomes, e
...
in
gametes
...
g
...
mitosis as nuclear division giving rise to genetically identical cells
...
it is when a diploid cell divides to form two daughter cells
...
replacement of tissue/cells
...
stem cells:
unspecialisedcells that divide by mitosis to produce daughtercells that
become specialised for specificfunctions
...
bone marrow, skin, liver
...
•
o
o
Meiosis:
exactduplication of maternal and paternal chromosomes occurs before meiosis
...
during meiosis, chromosomes are separated and chromosome number is
halved from diploid to haploid
...
o
o
•
o
o
•
o
o
o
o
o
o
o
•
•
•
•
importance of meiosis:
production of gametes
...
Genes and protein synthesis:
each gene codes for a specific protein, and the sequence of bases in a gene is the genetic
code for putting together amino acids in the correct order to make the specific protein
...
mRNA molecules carry a copy of the gene from the nucleus to the cytoplasm
...
ribosomes assemble the amino acids in the correctorder and convert it into protein
molecules
...
all body cells in an organism contain the same genes, but many genes in a particular
cell are not expressed because the cell only makes the specific proteins it needs
...
phenotype as the observable features of an organism
...
heterozygous as having two different alleles of a particular gene
...
recessive as an allele that is only expressed when there is no dominant allele of the gene
present
...
examples: red-green colour blindness, haemophilia
...
this phenotype is an intermediate of the two phenotypes
...
example: ABO blood groups in humans
...
Continuous variation
Discontinuous variation
Results in a range of phenotypes between
two extremes
...
Caused by genes and environment
...
[genotypic
variation]
o
Causes of variation:
Meiosis:
during meiosis, maternal and paternal chromosomes crossover and exchange genes
before separating
...
maternal and paternal chromosomes separate during meiosis, which also causes
variation
...
This leads to many combinations
of genes in the zygote, leading to variation
...
•
o
▪
▪
o
▪
•
•
•
•
o
•
o
▪
▪
▪
▪
▪
▪
o
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
o
▪
genemutationas a change in the base sequence of DNA
...
they are the only source of new characteristics in a gene pool
...
mutations are caused by:
ionising radiation
...
mRNA code changes from GAA à
amino acid sequence changes from GLUTAMATE à
people can inherit the allele for sickle cell anaemia, which is either in homozygous
recessive combination [HbS HbS] or heterozygous combination
...
red blood cells have sickle shape
...
symptoms:
red blood cells become sickle shaped
...
fewer normal RBCs
...
fatigue, pain, exhaustion, due to:
capillaries being blocked
...
can lead to sickle cell crisis, which leads to:
damage to certain organs
...
slow
reduced life span
...
shortness of breath
...
brittle
poor
Malaria and sickle cell anaemia:
malaria acts as an agent for natural selection for individuals who have the heterozygous
genotype[codominant] of sickle cell anaemia
...
The malarial
parasite passes a few stages of its life
cycle in RBCs, so it is a breeding ground
...
HbA HbA [heterozygous: 50% RBCs are
sickle shaped]
These individuals are less likely to suffer
from a fatal attack of malaria and are
resistant, and are not seriously affected
by sickle cell anaemia
...
They are able
to survive and pass on this allele to the
next generation
...
•
fitness as the probability of an organism surviving and reproducing in the environment in
which it is found
...
shedding of leaves, fewer leaves
...
hairs to absorb more water
...
Adaptations of hydrophytes
...
floating leaves: in order to absorbsunlight and allowdiffusion of oxygen/carbon dioxide
...
little/no roots:no need for roots to absorb mineral ions/water
...
o
o
o
o
o
•
o
o
o
o
o
o
o
o
o
•
o
▪
▪
▪
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
•
o
o
o
aerial roots: to allow roots to absorboxygen
...
little xylem/lignin: as the waterprovidessupport
...
Natural selection:
Process:
variation within population
...
competition for resources
...
reproduction by individuals that are better adapted to their environment than others
...
Evolution of anti-biotic resistant bacteria:
arisen due to mutation
...
some variants produce an enzyme that breaks down the antibiotic
...
therefore, the antibiotic acts an agent for natural selection
...
increased use of antibiotics results in the creation of selective pressure, which favours
the development of resistant forms of bacteria
...
process of adaptation as the process, resulting from natural selection, by which
populations become more suited to their environment over many generations
...
of individuals with desiredfeatures
...
by:
manual pollination
...
embryo implantation
...
done over many generations
...
animals:
cows: milk [quantity and quality], mass/muscle [quantity and quality]
...
techniques:
▪
▪
o
▪
▪
▪
▪
▪
▪
•
o
o
o
artificial insemination
...
plants:
size of crop
...
disease/frost/drought resistance
...
technique:
manual pollination
...
Organisms are selected by humans
...
Results are predicted and planned
...
Species are more useful to humans
...
This can reduce the fitness of the
variety
...
at a future date, when the new combinations of genes are needed, some potentially
useful genes may no longer be available
...
food chain as showing the transfer of energy from one organism to the next, beginning
with a producer
...
food web as a network of interconnected food chains
...
consumer as an organism that gets its energy by feeding on other organisms
...
carnivore as an animal that gets its energy by eating other animals
...
Energy transfer:
energy is transferred between organisms by ingestion
...
Why are only a few top predators present in a food chain:
only 10% of energy is passed on to the next organism
...
top consumers have bigger body/volume
...
therefore, large numbers cannot be sustained by the environment
...
energy loss between food chains due to movement, heat, respiration and excretion
...
leads to 90% being lost and only 10% passed on to humans
...
one organism can feed at multiple trophic levels
...
gives a better idea of the actual quantity of the plant/animal material that is being
consumed at each trophic level
...
Nitrification: ammonium compounds are converted to nitrates by nitrifying bacteria
...
These
oxides dissolve in rain and are washed into the soil, where they form
nitrogen-fixing bacteria taken nitrogen from the air and convert it into nitrates and store
them in root nodules of legumes
...
nitrogen is absorbed by plants for amino acid synthesis in the form of nitrates by active
transport
...
•
•
•
•
o
▪
▪
o
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
•
o
o
o
▪
▪
▪
o
•
o
o
o
o
o
•
o
o
o
•
o
▪
▪
population as a group of organisms of one species, living in the same area, at the same
time
...
ecosystem as a unit containing the community of organisms and their
environment,interacting together
...
time need to adjust to new habitat or attain reproductive maturity
...
birth rate > death rate
...
stationary phase:
birth rate = death rate
...
increase in limiting factors:
less
less
less
death phase:
resources severely limited
...
severe limiting factors:
no
no
no
build-up of waste that is toxic
...
competition with other types of predators
...
habitat destruction
...
Predator-prey populations:
population of a predator depends on the population of the prey
...
increases and decreases in predator populations always lag
behind corresponding increases/decreases in prey population
...
▪
▪
▪
▪
▪
▪
▪
hygiene: better sanitation, sewage treatment, garbage removal, increase in awareness
and information on importance of hygiene
...
medicinal facilities: greater access to hospitals
...
moreefficientfoodproduction due to fertilisers/pesticides
...
20] Biotechnology
•
o
o
o
o
o
o
•
o
▪
▪
▪
▪
•
o
o
•
o
o
o
•
o
o
o
o
o
•
o
Bacteria are used in biotechnology because:
they are small and easy to grow in labs
...
they can form complex molecules
...
the genetic code is universal and can be shared with other organisms
...
Yeast and biofuels:
Process:
maize can be used as a crop in the process to make ethanol
...
then, yeast is added, and allowed to respire the glucose in anaerobic respiration
...
Advantages:
uses renewable and sustainableresources[plants] to make ethanol
...
Disadvantages:
does not contain as much energy per litre, so it is mixed with gasoline, to make fuel for
vehicle engines
...
using large quantities of maize and other crops puts up their price, making
them expensive to other people
...
amylase enzymes are also added to break down starch to glucose
...
the bubbles of carbon dioxide get trapped in the dough
...
Biological washing powders:
contain less chemicals, which is good for sensitive skin
...
detergents help remove grease and dirt by mixing them with water, so they can be
washed away
...
these smallermoleculesdissolveinwater and are washed away
...
these enzymes are packed in microscopic capsules, that dissolve when water is added,
which prevents them from harming the user’s skin
...
This is also beneficial as other components of
washing powders such as detergent, work well at high temperatures
...
pectin is a substance that helps plant cells stick together
...
pectinase is used to break down pectin, so it is much easier to squeeze the juice from
the fruit
...
Lactose-free milk:
Production:
lactase is obtained from yeast or bacteria
...
milk is passed repeatedly over the beads
...
the immobilised enzyme[lactase] remains to be used again and does not affect
the quality of lactose-free milk
...
increases the sweetness of milk, so no requirement of artificial sweeteners
...
as a way of reducing production time for yoghurts or cheese [as bacteria ferment
glucose and galactose more readily than lactose]
...
nitrogen source [ammonia and ammonium compounds]
...
when the fungus respires and releases heat, temperature inside the fermenter increases,
which could kill the fungi, so no penicillin would be produced
...
▪
o
▪
o
▪
▪
o
▪
▪
▪
▪
o
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
A change in pH will affect enzyme activity and reduce the rate of the reaction
...
stirrers/paddles present to:
keep the bacteria/fungus supplied with nutrients
...
downstream processing:
filtration:
solid [microbe] and liquid [culture medium] are separated
...
purification of product
...
does not contaminate
...
genetic engineering as changing the genetic material of an organism by removing,
changing or inserting individual genes
...
insertion of genes into crop plants to make them herbicide/pesticide resistant
...
Using bacteria to produce human insulin:
human cell usually taken from the skin
...
cutting of bacterial plasmid DNA with the same restriction enzymes,
forming complementary sticky ends
...
insertion of plasmid into bacteria
...
Advantages of GM crops:
produces crop that is disease/drought/salt/frost/pest/herbicide resistant
...
crops have higher yield
...
Helps
crops that are drought/salt/frost resistant allow food production in extreme
environments, which helps reduce food shortages
...
▪
▪
▪
▪
Disadvantages of GM crops:
GM seeds are
risk of creation of
crops containing toxins may affect human health
Title: IGCSE Biology Complete Notes
Description: All Topic Summary IGCSE Biology book summary
Description: All Topic Summary IGCSE Biology book summary