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IGCSE Biology summary notes of various topics
Table of Contents
Characteristics of living organisms
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3
Cell structure
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4
Factors affecting photosynthesis
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5
Experiments affecting photosynthesis
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5
Transport by plants
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7
Water as a solvent
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7
Effects on animal tissues
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7
Energy flow in ecosystems
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8
Carbon cycle
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8
Human influences on the ecosystems
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9
Cons of overuse of fertilizers
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9
Plant nutrition
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10
Glucose
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10
Enzymes
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11
Factors affecting enzymes
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11
Conditions controlled in fermenters
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11
Nutrients
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13
Importance of macronutrients
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14
Difference between bacteria and viruses
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15
What microorganisms need to grow
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15
Fermentation
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16
Nutrition process
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16
Adaptations of small intestines
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18
Structure of villi
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19
Minerals and vitamins
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19
Oral health
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20
Structure of the human teeth
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21
Factors affecting tooth decay
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21
Fluoride
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22
How water travels through the plant
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22
The heart
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23
Coronary heart disease causes
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23
Arteries
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24
Capillaries
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25
Red blood cells
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25
White blood cells
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26
Defences
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27
Parts of the gas exchange system: in lungs
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27
Features of the gaseous exchange in humans
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28
Differences in composition between inspired air and expired air
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28
Effects of tobacco
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29
Anaerobic and aerobic respiration
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29
Lactic acid
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29
Hormones
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30
Tropic responses
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31
Maintenance of a constant body temperature
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31

Control of glucose in the blood
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g
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g
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g
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the rate
will start to decrease

Economics of greenhouses
-

conditions can easily be controlled to provide plants with optimum growing conditions
o artificial light – allows photosynthesis to continue beyond daylight hours, provide higher than
normal light intensity
o artificial heating – allows photosynthesis to continue at an increased rate
o additional carbon dioxide – continue at an increased rate

Experiments affecting photosynthesis
Testing for starch – proves that CO2 and light are important for the production of starch
1
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it is warmed in ethanol until it is colorless – to extract chlorophyll
3
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g
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g
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e
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g
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not the entire organism is digested/consumed
2
...
energy is consumed through transport and movement of the organism

Carbon cycle
-

when we respire and combust fuels, carbon is released into the atmosphere as carbon dioxide
plants first make use of this by making nutrients through photosynthesis
animals eat the plant and consumes the carbon dioxide
a lot of the carbon dioxide is lost through respiration
when the organism dies, they are eaten by decomposers and the carbon they receive is released
back into the atmosphere as C02

Effects of combustion of fossil fuels, cutting down forests on oxygen and C02 concentration
-

combustion of fuel decreases the oxygen concentration – but increase C02 concentration
cutting trees will have less trees consuming C02 and producing oxygen
it will increase C02 concentration, decrease the 02 concentration

Human influences on the ecosystems
Cons of deforestation
- destroys habitat of species: can cause species extinction
- loss of soil: loss fertility
- less C02 consumed through photosynthesis resulting in C02 buildup: cause global
warming
Cons of overuse of fertilizers
- eutrophication
- nitrate concentration in soil and water increases – promotes rapid growth of algae and blocks
-

sunlight reaching the water below
the algae consume oxygen in the water
aquatic creatures begin to die because of the lack of oxygen given to them

Cons of pollution
- water pollution: can cause diseases such as typhoid
- infect and kill crops
- crop harvesting process less efficient
- air pollution: reduce lung functioning
- cancer
- breathing problems
- global warming

Plant nutrition
Photosynthesis: the fundamental process by which plants manufacture carbohydrates from raw
materials using energy from sunlight
Word equation: carbon dioxide + water ---------sun light----------- glucose + oxygen
Formula: 6CO2 + 6H20 --------- C6H1206 + 6O2
Intake of water
1
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3
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5
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Glucose is used for
-

raw materials for growth
to make fats and oils
as energy source
constructing more cells
to make cell walls – cellulose
energy – to turn sugars, nitrates and other nutrients into amino acid – builds up protein
energy stored as sucrose (in fruit)

Enzymes
-

are proteins
biological catalysts (speed up chemical reactions)
specific to one substrate
affected by temperature and pH
obtained from microorganisms – grown in fermenters

‘Lock and key theory’
1
...
the active site brings the substrate molecules closer together
3
...
)

pH

Enzyme uses
-

washing: removes stains using lipase, amylase and protease - breaks down the fats
clothing industry: leather - softened using a protease from bacteria
food production: protease – soften gluten, pectinase – makes fruit juice clear

Conditions controlled in fermenters
-

temperature: so that enzymes can work effectively and they do not denature
sterile conditions: to stop other organisms from growing to avoid competitions and the growth of
harmful organisms - so no contamination
paddle stirrers: to ensure the enzymes are always in contact with nutrients and to control the
temp
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g
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g
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g
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g
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2
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4
...

6
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two types of bacteria are added – they respire anaerobically producing lactic acid
this causes it to solidify and clot
the yogurt is sampled and any food, flavoring or coloring is added
it is then transported for sale – important to keep it refrigerated to avoid it ‘going off’ otherwise
the bacteria will reproduce and make it sour

Lactose ------------- lactic acid + energy
Difference between bacteria and viruses
-

bacteria are bigger
bacteria give off lactic acid in the teeth
viruses don’t have a nucleus, cell membrane or cytoplasm
viruses aren’t considered as living things

Microorganisms
-

are very small living organisms
can be both harmful and useful to humans
they break down substances using aerobic and anaerobic respiration

What microorganisms need to grow
-

food availability
temperature at 36-37 degrees
pH: neutral

Why we used microorganisms
-

because of their rapid growth – they can reproduce within 20 minutes
easy to grow and the substance they produce is easily extracted
use waste products from other industrial processes
production is independent of climate

Fermentation
-

form of anaerobic respiration
some microorganisms that produce useful substances are used in food production
bacteria: used in production of yogurt and cheese
fungi: manufacture of bread, alcohol and mycoprotein

Animal nutrition
Nutrition: taking in of nutrients which are organic substances and mineral ions, then absorbing
and assimilating them
-

nutrition converts food molecules into a form that can be used by organisms
o process takes place in the alimentary canal (gut)
lipids and carbohydrates provide energy through respiration
o lipids have 10x more energy than carbohydrates

Ingestion: taking substances into the body through the mouth
Egestion: the passing out of good substances that has not been digested, as faeces, through the
anus
Absorption: movement of digested food molecules through the wall of the intestine into the
blood
Nutrition process
1
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3
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Ingestion: begins when food and drink enters the body through the mouth
Mechanical digestion: teeth and tongue break the food into small pieces
Chemical digestion: enzymes break down the food into water – soluble molecules
Assimilation: digested food is used by cells for energy, growth and repair – they cross the gut
wall into the blood stream or lymph
5
...
Defecation: indigestible substances are expelled out of the body as faeces

Parts of the alimentary canal
Mouth
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food is converted to a bolus of food
bolus produced by teeth and saliva during mastication (cutting and mixing of food by salvia and
tongue)

Salivary glands
-

three pairs
produce saliva and pour into the mouth through salivary ducts

Epiglottis
-

flap of muscle
closes entrance to trachea during swallowing

Oesophagus
-

muscular tube which helps move food into the stomach by peristalsis
o peristalsis: the contraction of muscles that pushes a bolus of food through the digestive
system

Liver
-

produces bile, which helps to neutralize acidic chyme as it is alkaline and also emulsifies fats
produces insulin: important for regulation of glucose
converts glucose into glycogen
o glucoregulation: the maintenance of glucose in the body
breaks down alcohol and other toxins

Stomach
-

stores the food
mixes food with acidic digestive juices to form the creamy liquid: chyme

Gall bladder
-

stores the bile before pouring it into the duodenum through the bile duct

Pancreas
-

produces pancreatic juices which neutralizes acidic chyme
poured into the small intestine through the pancreatic duct

Ileum
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where digested food is absorbed into the blood and lymphatic system

Large intestine
-

reabsorbs water from gut contents
also absorbs some vitamins and minerals

Small intestines
-

where the digestion and absorption of food takes place

Adaptations of small intestines
-

thin walls: speeds the rate of diffusion of molecules into the blood
rich blood supply: helps carry absorbed molecules away from the small intestines quickly
length: roughly 7m long – increases surface area
contain villi and microvilli to increase SA

Rectum
-

stores faeces

Anus
-

exit for faeces

Components of the villus
Capillaries
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supplies villus with oxygen and carries away absorbed foods
they come together to form the hepatic portal vein that goes directly to the liver for processing

Lacteal
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also a capillary
absorbs and distributes fats in the villi (part of the lymphatic system)

Muscle layers
-

helps mix food in the gut and move it down by peristalsis

Structure of villi
-

each villus is made up of even smaller microvilli
villi increase internal surface area of the intestinal walls
o large surface area needed for absorption: the distance travelled by nutrient molecules is
decreased, allowing for more efficient absorption of nutrients

Nutrients deficiency
Nutrients: raw materials our bodies need for development, growth, tissue repair and for energy
Deficiency: lack of nutrients going into the body
Malnutrition: lack of proper nutrition
-

caused by, having an unbalanced diet, having too little food, eating foods in the wrong
proportions

Minerals and vitamins
Sources/function
fish, cheese and eggs

Deficiency disease or effect
lack of it can lead to blindness

Vitamin C

citrus fruits e
...
limes, lemons,
cherries

Vitamin D

fish
regulates the growth of bones
milk, cheese and other dairy food
helps with bone and muscle growth

scurvy – production of fibers in
the body, bleeding gums and nails
become brittle
rickets – bones become soft and
may bend
weak bones and teeth, poor
clotting of blood, uncontrolled
muscle contraction

Vitamin A

Calcium

Iron

red meat, liver and some veg (spinach)
part of haemoglobin

anaemia – causes weakness as oxygen
needed for respiration cannot be transported
efficiently

Balanced diet: a diet which consists of all nutrients in the food pyramid to suitable proportion
-

diet is determined by age, sex and activity

Dangers of an unbalanced diet
-

high blood pressure: too much salt, can damage blood vessels
tooth decay: diet with high content of acidic sugary foods
coronary heart disease: too much saturated fat and cholesterol can cause blockage to blood
vessels supplying oxygen to heart muscles
constipation: too little fibre means faeces do not pass regularly

Digestion: the breakdown of large insoluble molecules, into small- soluble molecules, using
mechanical and chemical processes

Oral health
Types of teeth
-

incisor: for cutting and biting
canine: for holding and cutting
premolars: for chewing and crushing
molars: chewing and crushing

Structure of the human teeth
-

crown: part of the teeth that shows
root: embedded in the jawbone
enamel: hardest tissue, made of calcium salts, the top of the
teeth
cement: helps to anchor the tooth to the jaw
pulp cavity: contains tooth-producing cells, blood vessels and
nerve endings which detect pain
dentine: very hard, contains series of fine canals which extend
to the pulp cavity
gum: covers the junction between the enamel and cement
membrane: has nerve endings which detect pressure during
chewing and biting

Dental decay: how it develops
1
...
when you consume food and drink high in carbohydrates, the bacteria in the plaque turn the carb
...
the acid begins to break down the surface of your tooth – the enamel
4
...
the cavity can then reach the dentine and may cause severe toothache
6
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Osmosis occurs to move water and inorganic ions from the soil to the root hair cells, down a
concentration gradient
2
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the water and inorganic ions leave the xylem and is absorbed by the cells in the leaves

Transpiration: the evaporation of water at the surface of the mesophyll cells followed by loss of
water vapor from plant leaves, through the stomata
Wilting: occurs if water loss exceeds water uptake – cells become flaccid and tissues become
limp

Transport in humans
Circulatory system: the system in which blood is pumped around the body
-

we need this system to transport oxygen and nutrients to our body cells for respiration

Valves
-

they control the direction of the flow of blood in the body
they ensure blood flows one way
o they do this by opening and closing – prevent back flow

The body contains a ‘double circulatory system’ – one circuit pumps blood to the lungs – blood
becomes oxygenated
-

the oxygenated blood then enters the second circuit, which takes oxygen both to the brain and the
entire body

The heart
Pulmonary veins: transports oxygenated blood from the lungs to the left atrium
Aorta: transports oxygenated blood from the heart to the rest of the body and the brain
Vena cava: transports deoxygenated blood from the body to the heart
Pulmonary artery: transports deoxygenated blood from the heart to the lungs
Hepatic portal vein: transports blood from the alimentary canal to the liver, blood is rich in
nutrients to be produced by the liver
Renal artery: supplies kidney with oxygenated blood

Renal vein: transports blood away from the kidney, into the inferior vena cava
When blood is transported from the heart to the lungs – the pressure is low
Heart to body (second circuit) – high pressure, as blood needs to be pumped all around the entire
blood so greater force is needed
Oxygen rich blood – left side, arteries: blood travelling to the cells, high oxygen content, low
carbon dioxide content
Oxygen poor blood – right side, veins: blood travelling away from body cells, low 02 content,
and high CO2 content

Coronary heart disease
Definition: a heart disease in which certain parts of the ‘coronary artery’ becomes ‘clogged’ with
cholesterol, and substances such as oxygen and nutrients cannot be transported across the body
If not treated:
-

no oxygen or nutrients can be transported around the body
little or no respiration
victim get a heart attack

Coronary heart disease causes
-

lack of exercise
diet high in fat and cholesterol
diabetes
high blood pressure
smoking
stress

Effects of physical activity on pulse rate
-

heart rate increases to supply more oxygen to produce extra energy
the body produces chemical hormones e
...
adrenaline, which can change the heart rate
pulse rate increases to indicate the heart is working hard

Arteries
-

blood is transported at high pressure – very narrow lumen with a small diameter
narrow lumen to increase the speed and flow
deeper in the flesh than veins
thick muscular wall prevents the blood from bursting as under high pressure
thick inner layer of muscle and elastic fibers

Veins
-

low pressure
wide lumen to make it easier for the low pressure in which blood travels at
thin layer of muscles and elastic walls as they do not need high pressure
have valves – to prevent backflow of blood as blood is under low pressure, can only open in one
direction
near the surface of the skin

Capillaries
-

links arteries to veins
one cell thick to allow easy diffusion of blood
leaky
under low pressure
narrow

Blood components
Red blood cells
-

biconcave in shape: larger surface area
no nucleus: to allow more room for haemoglobin
contains haemoglobin which combines with oxygen to form oxyhaemoglobin

Plasma
-

carries waste urea from the liver to the kidneys
carries waste carbon dioxide from the tissues to the lungs
carries dissolved amino acids, fatty acids and glycerol, glucose, antibodies and antitoxins,
hormones, dissolved vitamins and minerals
makes up 55% of the blood and is yellow

White blood cells
-

release antibodies/antitoxins
engulf and digest microorganisms

Platelets: causes scab formation
Kidney: removes waste urea and excess water, reabsorbs glucose and some salts

Immune system
Defences
-

tears and eye lashes: trap microorganisms, tears help to wash them out, high salt content – dries
up
hair on nose: trap particles in mucus
skin: block microorganisms getting in
stomach acid: very corrosive (pH2), destroys cell walls and kills them
trachea: cilia trap microorganisms when enter our bodies in mucus
platelets: stick together to build a clot, stops bacteria getting in

Phagocytosis
-

one type of white blood cells
responsible for killing bacteria by surrounding and ingesting them
they engulf the pathogen and enzymes destroys it

Microbes
-

have antigens on their surface
they allow white blood cells to identify them

Lymphocytes
-

-

produce antibodies and antitoxins
o antibodies are specific to the microbe
o antitoxins neutralize any toxins the bacteria produce but don’t kill the bacteria
they punch hole in the membrane – damaging them
stick the pathogens together making it difficult for them to live
send chemical signals to phagocyte

Gas exchange systems
Parts of the gas exchange system: in lungs
Trachea
-

windpipe
tube that carries air towards the lungs
C-shaped rings of cartilage prevent the trachea from collapsing

Larynx
-

voice box
air passes through here during breathing

Bronchus
-

first branch from the trachea
one bronchus for each lung

Bronchiole
-

final branch
very fine branch leading into the alveolus

Alveoli
-

tiny round spaces filled with air and surrounded by capillaries

Alveolus
-

air sacs
where gas exchange takes place

Pulmonary artery
-

delivers deoxygenated blood at high pressure from the right ventricle of the heart to lungs

Pulmonary vein
-

returns oxygenated blood to the heart

Inside the alveolus
-

deoxygenated blood enters
oxygen diffuses into red blood cells
carbon dioxide diffuses out of the blood plasma
oxygenated blood moves towards the body

Features of the gaseous exchange in humans
-

the walls of the alveoli are one cell thick: allowing for gases to easily diffuse in and out of the
capillaries
alveoli have a moist lining: the oxygen dissolves in the moist lining and enters the blood stream
large surface area: the lungs contain a lot of alveoli, allowing more space for gas exchange

How the trachea is adapted to its function
-

contain rings of cartilage in ’C’ shapes: this expands allowing easy transport of air towards the
lungs, also prevents the trachea from collapsing due to inhalation
contains ciliated epithelial (produce mucus): which help trap microbes travelling down the
trachea

Differences in composition between inspired air and expired air
-

exhaled air (inspired) has high levels of CO2 and water vapor
inhaled air has O2 and very little amount or no water vapor

Effects of physical activity on rate and depth of breathing
-

we breathe faster in order to deliver more oxygen to cells around our body
cells become more active so they need more oxygen in order to perform aerobic respiration to
break down glucose and release energy

Effects of tobacco
Tar
-

causes more mucus to be produced
paralyses our cilia cells meaning that mucus cannot be removed effectively
excess mucus builds up in our airways causing smoker’s cough
also clogs up the alveoli in our lungs: reducing surface area for gas exchange to take place – less
oxygen entering the body
increase risk in cancer and lung cancer

Nicotine
-

makes it difficult to transport oxygen around the body
raises pulse rate
increases blood pressure
additive

Carbon monoxide
-

binds with the haemoglobin, reducing its ability to carry oxygen
puts more strain on our respiratory system
the body favors carbon monoxide more than oxygen it starts using it instead
o carbon monoxide has a higher affinity than oxygen

Breathing system keywords
Diaphragm: the muscle below the lungs, becomes flatter to increase volume in chest making us
breathe in
Intercostal muscle: between the ribs, help move the ribs expanding the chest when we breathe
in
Air sac: at the end of the bronchioles which help increase the surface area for gas exchange

Anaerobic and aerobic respiration
Oxygen + glucose -------- carbon dioxide + water
Anaerobic respiration
-

muscle cells can only do this in human bodies
respiration without the need of oxygen
allows cells to carry on working despite there being shortage of oxygen

Equation = glucose ----- lactic acid
Lactic acid
-

lactic acid is poisonous: it leads muscle cells to become fatigue and causes cramps, eventually the
muscle will stop working
during recovery the lactic acid is transported to the liver via the bloodstream
the liver breaks it down into CO2 and water

Oxygen debt: oxygen that is required to break down lactic acid into CO2 and water in the liver,
causes us to breathe heavily after extreme exercise
Yeast also respire anaerobically – do not produce lactic acid, they make ethanol and CO2
(alcoholic fermentation)
-

used for bread making, fermenting wines, brewing beer

Aerobic respiration
-

releases large amounts of energy through respiration with the use of oxygen

What happens
-

glucose released in our digestive system is absorbed by the bloodstream via diffusion
gas exchange occurring in our alveoli provides the oxygen needed for aerobic respiration
the energy released is then used by the body
carbon dioxide diffuses back into the blood stream and is excreted via gas exchange from our
lungs
some of the water produced is used up anything that is left is excreted by the body
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g
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g
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blood temperature changes with body internal temperature
2
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it sends electrical impulses to the rest of the body so that it can start heating or cooling itself

Control of glucose in the blood
-

-

levels are controlled by the pancreas
levels too high: pancreas secretes the hormone insulin, which decrease glucose levels to normal
o insulin flows in the blood until it reaches the liver
o in the liver, insulin converts the excess glucose into glycogen
o this is stored in the liver cells
levels too low: pancreas secretes glucagon
o when glucagon reaches the liver it makes the liver convert the glycogen into glucose
o this is then secreted back into the bloodstream



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