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Revision notes on cells, life processes and living organisms
CHARACTERISTICS OF LIVING ORGANISMS
1.1
recall that living organisms share the following basic characteristics (ch1)
Movement
Muscles in animals, directional growth in plants, flagella in
bacteria
Respiration
Release energy from food
Sensitivity
Responding to changes in the environment
Growth
Increase in size and mass
Reproduction
Producing offspring (more of the same kind of organism)
Excretion
Getting rid of toxic waste
Nutrition
Taking in or producing their own food
Control of internal conditions
Keeping internal conditions constant, e.g body temperature
VARIETY OF LIVING ORGANISMS
1.2
Describe common features shared by organisms within the groups: plants, animals, fungi,
bacteria, protoctists and viruses, and describe examples and their features in each group
(ch2)
Plants
Plants are multicellular organisms
Examples include flowering plants, such as a cereal (for example maize) and a herbaceous legume (for example
peas or beans).
Plants contain chloroplasts and are able to carry out photosynthesis
Plants have cellulose cell walls. The cell wall and the vacuole together give the cell its shape and maintain
turgor (stiffness) to support the plant (see point 2.14)
Plants store carbohydrates as starch or sucrose. Starch is stored in the leaf and the root; sucrose is transported
in the phloem (see point 2.51)
Animals
Animals are multicellular organisms
Examples include mammals (e.g. humans) and insects (e.g. housefly and mosquito).
Mammals keep a constant body temperature and are vertebrates (have a backbone)
Insects are invertebrates
Animals do not contain chloroplasts and are not able to carry out photosynthesis: animals are
heterotrophic – they consume other organisms for their nutrition
Animals usually have nervous coordination and are able to move from one place to another
Animals have no cell walls and they often store carbohydrate as glycogen
Revision notes on cells, life processes and living organisms
Fungi
Fungi are not able to carry out photosynthesis; many are multicellular; some, like yeast, are single-celled.
Their body is usually organised into a mycelium of threadlike structures called hyphae, which contain many nuclei;
the hyphae feed by excreting digestive enzymes onto food
material and absorbing the organic products; this is known
as saprotrophic nutrition
Fungi have cell walls made of chitin; they may store
carbohydrate as glycogen.
Examples include mucor (green-blue mould) which reproduces
using spores, and yeast, used to make bread or beer.
Bacteria
Bacteria are microscopic single-celled organisms with no nucleus
(are prokaryotes).
Examples: Lactobacillus bulgaricus, a rod-shaped
bacterium used to make yoghurt from milk, and
Pneumococcus, a spherical bacterium that causes
pneumonia.
Bacteria have a cell wall, cell membrane, cytoplasm and
plasmids (rings of extra DNA: see points 5.12, 5.13). Bacteria
DNA is in a large loop called the chromosome.
Most bacteria feed off other living or dead organisms (saprotrophic nutrition). A few bacteria can
carry out photosynthesis.
Protoctists
Protoctists are microscopic single-celled organisms. They are complex
cells with a nucleus and other organelles. They are not animals or plants
because each cell is an individual organism, not part of a multicellular
organism.
Some protoctists, like Amoeba, have features like an animal cell.
Others, like Chlorella, have chloroplasts and are more like plants.
A pathogenic protoctist, Plasmodium, is responsible for causing
malaria (see point 1.30)
Viruses
Viruses are small particles, smaller than bacteria; they are parasites and can reproduce only inside living cells;
they infect every type of living organism.

Examples include the tobacco mosaic virus that causes discolouring of the leaves of tobacco
plants by preventing the formation of chloroplasts, the influenza virus that causes ‘flu’ and the
Revision notes on cells, life processes and living organisms
HIV virus that causes AIDS (see point 1.30).
1.3

Viruses have a variety of shapes and sizes; they have no cellular structure but have a protein coat and
contain genetic material - either DNA or RNA.

Apart from reproduction, viruses do not perform any of the life processes (MRSGRENC)
Recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or
viruses.
Pathogen: an organism that causes disease like a virus, fungus or bacterium.
Viruses are responsible for AIDS and 'flu; bacteria can cause pneumonia; malaria is caused by a protoctist;
Athlete's foot (Fusspilz) is a fungal infection (see point 1.2)
NB white blood cells provide defence against pathogens: phagocytes are non-specific,
lymphocytes are specific (see point 2.61)
SECTION 2: STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS
A) LEVELS OF ORGANISATION
2.1
Describe the levels of organisation within organisms: organelles, cells, tissues, organs and
systems. (ch1)
ORGANISM < ORGAN SYSTEM < ORGAN < TISSUE < CELL < ORGANELLE < BIOLOGICAL MOLECULE
Biological molecule – molecule
made by organisms and used in life
processes, e.g. respiration
Examples: DNA, proteins, lipids, starch, glucose,
amino acids, haemoglobin, enzymes
Organelles - structures within a cell
that carry out specific functions
Examples: nucleus, chloroplast, mitochondria (see
point 2.20, 2.30)
Cells - the basic structural and
functional unit from which all
biological organisms are made
Examples of specialized cells include nerve cells,
sperm cells, root hair cells and palisade mesophyll
cells
Tissues - a group of specialized cells,
which are adapted to carry out a
specific function
Examples include muscle tissue, nerve tissue,
palisade mesophyll tissue (in leaves)
Organs - a collection of two or more
tissues, which carries out a specific
function or functions
Examples include the heart, brain, spinal cord,
liver, kidneys, lungs, bladder, small intestine,
pancreas and stomach; in a plant the leaf is an
example of an organ.
Organ Systems - a group of two or
more organs
Examples include the circulatory system, nervous
system, endocrine system and digestive system.
Revision notes on cells, life processes and living organisms
B) CELL STRUCTURE
2.2
Recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall,
chloroplast and vacuole (ch1)
2.3
Describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and
vacuole (ch1)
2.4
Nucleus structure: at the centre of the animal
cell and between the vacuole and cell
membrane in a plant cell. Contains DNA
Nucleus function: Controls cell activities
Cell membrane structure: selectively
permeable boundary of the cell
Cell membrane function: Controls what
substances go in and out of cell
Cytoplasm structure: a jelly-like substance
that fills the cell and contains enzymes
Cytoplasm function: site of most of the
chemical reactions in the cell.
Chloroplast structure: contain a green
pigment called chlorophyll. (Only plant cells)
Chloroplast function: Absorb light
energy to make (food)glucose by
photosynthesis
Cell wall structure: made of cellulose or chitin
which surrounds the cell membrane (Only
plant cells)
Cell wall function: rigid structure that
gives the cell support and strengthens it.
Vacuole structure: largest part of plant cell, in
the centre; contains cell sap, a store of
dissolved sugars and minerals. (Only in plants)
Vacuole function: fills with water and
maintains turgor to support the plant
Describe the differences between plant and animal cells. (ch1)
Both contain a nucleus, cytoplasm and a cell membrane
Animal cells do not have a cell wall, central vacuole or chloroplasts (see point 2.30)
Revision notes on cells, life processes and living organisms
BIOLOGICAL MOLECULES AND ENZYMES
2.5
Recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils)
(ch4)
Carbohydrates and lipids: C,H,O;
Proteins also have nitrogen so their elements are C,H,O,N
2.6
C = carbon, H = hydrogen,
O = oxygen; N = nitrogen
Describe the structure of carbohydrates, proteins and lipids as large molecules made up
from smaller basic units: (ch4)
starch and glycogen from simple sugar (glucose); protein from amino acids; lipid from fatty acids
and glycerol
2.7
Describe the tests for glucose and starch (ch4)
Glucose: Benedict's
solution, heated
Colour of solution changes from blue to yellow/orange with a
brick red precipitate if glucose is present.
Starch: Iodine
solution
Colour change from yellow-brown to blue-black if starch is
present
2.8
Understand the role of enzymes as biological catalysts in metabolic reactions (ch1)
(there is more about specific enzymes in the notes about nutrition and digestion)
2.9
Understand how the functioning of enzymes can be affected by changes in temperature
(ch1)
All enzymes have an optimum temperature where they work fastest
Low temperatures: less kinetic energy means fewer collisions between enzyme and
substrate
High temperature: the enzyme is denatured (changes shape making the enzyme
inactive)
2.10
Understand how the functioning of enzymes can be affected by changes in pH (ch1)
All enzymes have an optimum pH where they work fastest
At high or low pH, the enzyme is denatured so is inactive or less active
2.11
Describe how to carry out simple controlled experiments to illustrate how enzyme activity
can be affected by changes in temperature (ch1)
The experiment in the syllabus is using amylase to break down starch.
Iodine (on a spotting tile) is used to test whether starch is still present (see point2.70), The
amylase / starch mixture is tested at different temperatures, e.g. 20°C, 30°C, 40°C, 50°C
Revision notes on cells, life processes and living organisms
D) MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS
2.12
2.13
recall simple definitions of diffusion, osmosis and active transport (ch1)
understand that movement of substances into and out of cells can be by diffusion, osmosis
and active transport (ch1)
Diffusion: Movement of particles from a region of higher concentration to a region of lower
concentration. It is passive – it does not need energy from respiration as it depends on the
movement energy of the particles themselves (their kinetic energy)
Osmosis: net movement of water molecules from an area of higher water concentration (water
potential) to an area of lower water concentration (or water potential) across a semipermeable membrane
Alternatively, osmosis can be described as the net movement of water molecules from a more
dilute (or hypotonic) solution to a more concentrated (hypertonic) solution across a semipermeable membrane.
Active transport: movement of particles from a region of lower concentration to a region of
higher concentration using energy from respiration
Can also be described as movement against the concentration gradient (whereas passive
diffusion moves substances down their concentration gradient)
2.14
understand the importance in plants of turgid cells as a means of support
The vacuole fills with water and puts pressure on the cytoplasm,
which presses against the cell wall and makes the cell turgid
(stiff)
2.15
understand the factors that affect the rate of movement of
substances into and out of cells
the rate of movement of substances increases when the



surface area to volume ratio is high,
temperature is high, and
concentration gradient is steep (big difference in concentration)
the distance that a substance has to move is also important in root hair cells (see point 2.53), in
the small intestine (see point 2.31), and in gas exchange between the alveoli and capillaries ( 2.46)
2.16
describe simple experiments on diffusion and osmosis using living and non-living systems.
Diffusion: Absorption of coloured substances by cubes of agar gel
(small cubes => fast diffusion as SA:Volume ratio is higher)
Osmosis: Potato stick experiment (increased mass when in distilled
water)
Factors investigated:
SA:Volume ratio, temperature;
concentration gradient
Revision notes on cells, life processes and living organisms
(2.17-2.22 Nutrition, Flowering plants)
2.23
understand that a balanced diet should include appropriate proportions of carbohydrate,
protein, lipid, vitamins, minerals, water and dietary fibre
macronutrients (the main part of the diet) are carbohydrate, protein and lipids;
micronutrients (necessary in small amounts) are vitamins and minerals;
water and fibre are not nutrients but are necessary in the diet
NB diet means all the food and drink you ingest, not special foods or restrictions
2.24
recall sources and describe functions of macronutrients: carbohydrate, protein, lipid (fats
and oils)
carbohydrates are the main form of fuel for respiration so are important for energy
production
in a healthy diet carbohydrate is mainly starch, the storage form of sugar in plants
carbohydrates are digested into single sugars (mainly glucose) by enzymes;
simple sugars are quickly absorbed, so eating them can cause obesity
starch is found in potatoes, rice and cereals;
sugars are found in fruits, desserts and sweets
proteins are made of amino acids, and are found in meat, fish, eggs, milk and beans
We need less protein than carbohydrate. Protein is used for growth and repair.
lipids are fats and oils (oils are liquid at room temperature; fats are usually saturated and are
soft solids at room temperature)
lipids are used to store energy and to make body fat that provides cushioning and heat
insulation. They also build cell membranes.
lipids are very high in energy and so a limited amount should be taken in a calorie-controlled
diet. Saturated fats are generally thought to increase the risk of heart disease.
Recall sources and describe functions of (micronutrients) vitamins A, C and D, and the
mineral ions calcium and iron
Vitamin A is found in leafy vegetables and
in liver
Vitamin A prevents night-blindness
Vitamin C is found in (especially citrus)
fruits
Vitamin C is necessary for wound healing and
sticking cells together
Vitamin D is found in milk products and is
made by the skin exposed to sunlight.
Vitamin D enables us to absorb calcium for
healthy bones and teeth
iron is found in green leafy vegetables and
particularly in red meat
Iron is needed to make haemoglobin that
transport oxygen in red blood cells
Calcium is found in milk and nuts
Calcium is necessary for the growth of healthy
bones and teeth, and prevents rickets
Revision notes on cells, life processes and living organisms
Recall sources and describe functions of water and dietary fibre as components of the diet
Dietary fibre is necessary to prevent constipation and keep the large intestine healthy Fibre is in
wholegrain cereals and in whole fruits and vegetables
Water is involved in all metabolic reactions in the body. It is part of all drinks (yes, really!)
2.26
recognise the structures of the human alimentary canal and describe in outline the functions
of the organs:
mouth
mainly mechanical digestion (teeth bite, grind and chew and saliva moistens)
but also chemical digestion of starch, using salivary amylase
oeesophagus
mechanical digestion: a bolus of food is swallowed and pushed to the stomach
using peristalsis
stomach
mechanical digestion: the stomach
churns the food, increasing its
surface area
chemical digestion: mixing it with a
protease (pepsin) and HCl acid;
chemical digestion: acid kills
bacteria, pepsin begins the digestion
of protein in to peptides
pancreas
Chemical digestion: the pancreas
produces many digestive enzymes
including amylase, proteases and
lipase.
liver
produces bile, which emulsifies lipids and neutralises stomach acid
small
intestine
Most chemical digestion and all absorption takes place here
Reference:
http://bio1151b.nicerweb.net/Locked/media/ch41/41_19HumanDuodenum.jpg
large intestine absorbs water from the undigested food
2.27
understand the processes of ingestion, digestion, absorption, assimilation and egestion
ingestion
taking food into the mouth
digestion
mechanical and chemical processes that break down large insoluble molecules
into small soluble molecules
absorption
small, soluble molecules are absorbed into the bloodstream from the small
intestine (see point2.31)
assimilation
absorbed nutrient molecules are used by cells for respiration or to make new
substances
egestion
undigested food passes out of the body via the anus
Revision notes on cells, life processes and living organisms
2.28
explain how and why food is moved through the gut by peristalsis
Peristalsis: all parts of the digestive tract are surrounded by circular and longitudinal muscle
when the circular muscle contracts, it squeezes the food along
2.29
understand the role of digestive enzymes
amylase
digestion of starch to maltose
maltase
digestion of maltose to glucose
proteases
digestion of proteins to peptides/amino acids
lipases
digestion of lipids to fatty acids and glycerol
2.3
recall that bile is produced by the liver and stored in the gall bladder
understand the role of bile in neutralising stomach acid and emulsifying lipids


2.31
emulsifying: splitting lipids up into droplets to increase the surface area for lipase to act on
neutralising stomach acid to provide optimum pH for digestive enzymes
explain how the structure of a villus helps absorption of the products of digestion in the
small intestine
Remember factors in diffusion: concentration gradient, surface area and short distance
1. large surface area: villi (finger-like shape) with
microvilli on their surface
2. short distance:
- the wall of the villi is one cell thick and
- blood vessels are close to the surface
3. concentration gradient: many blood vessels taking
away absorbed nutrients
4. a lacteal at the centre of a villus transports glycerol
and fatty acids from lipid digestion
2.25
understand that energy requirements vary with activity levels, age and pregnancy
Energy requirements decrease in old age.
Teenagers need quite a high energy intake as fuel for growth and activity.
Athletes or people doing heavy manual work use a lot of energy and need to replace it
In pregnancy, extra energy is required for the foetus to grow
2.32
recall how to carry out a simple experiment to determine the energy content in a food
sample
a calorimeter tests the energy content of food by combusting (burning) a sample and
measuring how much heat energy is released (the heat is absorbed by water)
a simple experiment: burn a food sample (e.g. a nut) on a needle and use it to heat water in a
test tube above it – record mass of nut, temperature increase + volume of water
Revision notes on cells, life processes and living organisms
f) Respiration
2.33
recall that the process of respiration releases energy in living organisms
the energy is stored in the form of a chemical called ATP
energy from respiration is needed for all life processes; in the end, it is all released as heat.
2.34
describe the differences between aerobic and anaerobic respiration
NB. All types use glucose and release some energy. Aerobic is the most efficient.
1. aerobic: uses and needs oxygen;
2. anaerobic: when oxygen is not available – produces lactic acid
3. anaerobic respiration in bacteria / yeast is called fermentation and produces ethanol and
carbon dioxide (how beer is produced)
NB Why we breathe hard after strenuous exercise (the oxygen debt)
1. we can’t get enough oxygen to the muscles for them to get all the energy for hard exercise
just from aerobic respiration, so they use anaerobic respiration
2. anaerobic respiration produces lactic acid
3. this lactic acid can cause cramps and we need to break it down
4. lactic acid is broken down by oxygen, so we need to breathe harder until all the lactic acid
is broken down (the amount of oxygen needed = the oxygen debt)
2.35
2.36
2.37
recall the word equation and the balanced chemical symbol equation for aerobic respiration
in living organisms
Word equation:
glucose plus oxygen => carbon dioxide plus water .
Symbol equation:
C6H12O6 + 6O2 => 6H20 + 6CO2
recall the word equation for anaerobic respiration in plants and in animals
anaerobic respiration in animals:
glucose => lactic acid
fermentation in plants, bacteria and yeast:
glucose => ethanol + carbon dioxide
describe simple controlled experiments to demonstrate the evolution of carbon dioxide and
heat from respiring seeds or other suitable living organisms
Heat from respiration: use peas, for example, in a vacuum flask closed with cotton wool so
that gases can enter and leave. The temperature will rise as the peas respire.
Control: compare with peas that have been boiled and so are dead and cannot respire;
Standardize: sterilise the peas so bacteria cannot grow on their surface; same amount of
peas, same size vacuum flask
Carbon dioxide from respiration: put small organisms into a tube on a wire mesh above some
hydrogencarbonate indicator, and seal the tube (put a bung in). The indicator will change from
orange/red to yellow.
Control: do the same experiment without organisms, or using dead organisms;
Revision notes on cells, life processes and living organisms
Standardize: same size tube, same volumeof hydrogencarbonate indicator, same
temperature
g) Gas exchange
2.38
understand the role of diffusion in gas exchange.
in the tissues, carbon dioxide diffuses from the cells, where it is at a high concentration
because it has been produced by cell respiration, into the capillaries, where it has a lower
concentration.
in the lungs, carbon dioxide diffuses from the blood, where it is at a high concentration, into
the alveoli, where it has a lower concentration and oxygen diffuses from the alveoli, where it is
at a high concentration, into the capillaries where it has a lower concentration
(Remember factors in diffusion: concentration gradient,
surface area and
short distance e.g. the capillaries are very fine so have a large
surface area, and have a thin wall)
2.44
Breathing in humans: describe the structure of the thorax
Structure:
ribs
intercostal muscles
diaphragm
trachea
bronchi
bronchioles
alveoli
pleural membranes
Your notes
Revision notes on cells, life processes and living organisms
2.45
understand the role of the intercostal muscles and the diaphragm, in ventilation
(external)
intercostal muscles
diaphragm
rib cage
volume in the
thorax
pressure in the
thorax
air is forced
2.46
1.
2.
3.
4.
inhalation
contract
exhalation
relax
contracts and flattens
pulled upwards and outwards
increases
relaxes and becomes tent-shaped
moves down and inwards
decreases
decreases
increases
into the lungs
out of the lungs
explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and
blood in capillaries
alveoli have thin walls (short distance for diffusion) and
a large surface area (they are small and there are many of them)
capillaries are close to alveoli (short distance for diffusion) and
the rich blood supply maintains the a steep concentration gradient by bringing CO2 to the lungs
and removing oxygen
Revision notes on cells, life processes and living organisms
2.47 understand the biological consequences of smoking in relation to the lungs and the
circulatory system
tar in cigarette smoke sticks to and irritates bronchioles which fill up with mucus causing lung
infections (bronchitis) and emphysema (enlarged air spaces and less surface area)
tar also contains mutagens (see point 3.34) which cause lung cancer
carbon monoxide in cigarette smoke binds to haemoglobin and prevents it from carrying
oxygen; the heart needs to work harder, leading to heart disease
2.48
describe a simple experiment to investigate the effect of exercise on breathing in humans.
Use a treadmill or steps; stopwatch;
Measure: count the breaths per minute at rest and immediately after exercise.
Standardize: same age, sex, conditions (temperature of surroundings, time of day, size of step,
length of exercise...)
h) Transport
2.49
understand why simple, unicellular organisms can rely on diffusion for movement of
substances in and out of the cell
small organisms have a large surface area to volume ratio so diffusion is fast enough to
support the organism's needs for nutrition and gas exchange for respiration
2.50
understand the need for a transport system in multicellular organisms
large organisms have a lower surface area to volume ratio so diffusion is too slow to support
life processes (nutrition and respiration)
to support respiration the lungs provide a large surface area for gas exchange, and the
circulatory system transports oxygen to the tissues and removes waste carbon dioxide
(2.51-2.56 Transport in flowering plants)
2.57
recall the composition of the blood: red blood cells, white cells, platelets and plasma
2.58
understand the role of plasma in the transport of carbon
dioxide, digested food, urea, hormones and heat energy
2.59
describe the adaptations of red blood cells for the
transport of oxygen, including shape, structure and the
presence of haemoglobin




biconcave shape increases the surface area for faster
diffusion of oxygen into the cell (in the lungs) and out (into
the tissues)
haemoglobin binds to oxygen in the lungs (oxyhaemoglobin)
and releases it in the tissues;
the cell carries more haemoglobin because it has no nucleus.
shape makes it flexible; small size + flexibility help it pass through narrow capillaries
Revision notes on cells, life processes and living organisms
2.60 describe how the immune system responds to disease using white blood cells,
illustrated by phagocytes ingesting pathogens and lymphocytes releasing
antibodies specific to the pathogens.
phagocytes engulf and digest pathogens. (they are non-specific)
lymphocytes produce specific antibodies that
attach to pathogens and destroy them either
directly or make them stick together
2.61
understand that vaccination results in the
manufacture of memory cells, which enables
future antibody production to the pathogen to occur sooner, faster and in greater
quantity
Normally, it takes time for the body to produce
the specific lymphocyte to produce the antibody
that will attach to a new pathogen (1st exposure
to antigen). The pathogen can make you ill before
the immune system responds effectively; Some of
the lymphocytes remain in the blood as memory
cells .
(2nd exposure to antigen)Memory cells make the
immune response fast if a familiar pathogen
enters the body, memory cells produce antibody
SOONER, FASTER and in GREATER QUANTITY.
2.62



2.63
Recall that platelets are involved in blood
clotting, which prevents blood loss and the entry of
microorganisms
When exposed to air or blood vessel damage, Platelets cause:
soluble fibrinogen to be converted to insoluble fibrin threads.
The fibrin threads form a mesh that catches red blood cells to
form a clot.
The clot prevents excessive blood loss and stops pathogens
entering the body.
describe the structure of the heart and how it functions
The heart is a double pump (mammals have a double circulation), so both sides are very
similar, consisting of muscle walls, valves, some nervous tissue and its own blood
vessels, the coronary circulation
The muscle walls on the left side of the heart are thicker to provide enough pressure to
pump the blood through all the arteries of the body; the right side has to pump it
through the lungs only
Revision notes on cells, life processes and living organisms
1. oxygenated blood enters the left atrium from the lungs through the pulmonary
vein
deoxygenated blood enters the right atrium from the body through the vena cava
2. when the atria are full, the atrial muscles contract, increasing the pressure in the atria
3. high pressure in the atria opens the tricuspid and bicuspid valves
4. blood flows through the
valves (tricuspid on the right,
bicuspid on the left) into the
ventricles
5. the ventricles fill with blood
and the ventricle muscle
contracts, increasing the
pressure in the ventricles
6. high pressure in the
ventricles closes the
tricuspid and bicuspid
valves, preventing blood
flowing backwards,
7. high pressure in the
ventricles opens the
semilunar valves
8. blood flows through the semilunar valves into the pulmonary artery and the aorta
9. the pulmonary artery transports deoxygenated blood to the lungs to pick up
oxygen; the aorta transports oxygenated blood to the body
2.64
understand that the heart rate changes during exercise and under the influence of
adrenaline
receptors in the aorta monitor the amount of carbon dioxide in the blood
if the blood has a high level of carbon dioxide (e.g. during exercise), the medulla sends a
signal to the SA node (pacemaker) to increase heart rate.
The SA node is also sensitive to adrenaline, so the heart rate increases when the blood
contains a lot of adrenaline
2.65
describe the structure of arteries, veins and
capillaries and understand their roles
Arteries:
 narrow lumen
 thick wall containing muscle and elastic
fibres
 elastic fibres and muscle in the wall make
the artery flexible so the arteries stretch
and recoil to help push the blood along.

the thick muscular walls of arteries also
maintain the pressure on the blood
Revision notes on cells, life processes and living organisms
Veins:
 wider lumen
 thinner wall than arteries,
o the blood flows more slowly and at lower pressure.
 contain valves
o The valves mean that blood in veins can only flows one way
Capillaries:

2.66
have walls that are just one cell thick, have pores and they are adapted for exchange
between the blood and the tissue fluid by diffusion (oxygen, carbon dioxide, glucose)
recall the general plan of the circulation system to include the blood vessels to and
from the heart, the lungs, the liver and the kidneys
pulmonary artery
aorta
renal artery,
hepatic artery
carries deoxygenated blood from the heart to the lungs,
carries oxygenated blood from the heart to the body
carries oxygenated blood to the kidneys
carries oxygenated blood to the liver
pulmonary vein
carries oxygenated blood from the lungs to the heart to the lungs
vena cava
renal vein
carries deoxygenated blood from the body back to the heart
carries deoxygenated blood from the kidney
hepatic vein
carries deoxygenated blood from the liver
hepatic portal vein carries absorbed nutrients to the liver from the small intestine
(2.67 excretion in flowering plants, 2.68-2.76 excretion in humans, 2.77-279, general coordination,
2.80-2.82- flowering plants)
Humans
2.83 describe how responses can be controlled by nervous or by hormonal
communication and understand the differences between the two systems
endocrine system:
nervous system:

chemical messages travel in the
blood and…

electrical signals* travel along
neurones and …

… have a widespread effect

…communicate directly with other
neurones so have a local effect*

the response is slower and …

nervous responses are usually fast …

…lasts longer than nervous signals

…but only short-lasting.
Revision notes on cells, life processes and living organisms
*Chemicals are released in the synapses, the small gaps
between neurones – a chemical transmitter from the
first neurone diffuses to the membrane of the next
neurone, which starts a new electrical signal
2.84 recall that the central nervous system
(CNS) consists of the brain and spinal
cord and is linked to sense organs by
nerves
The cerebral cortex is responsible for conscious
responses and memory. Coordination happens
in the spine, too. The cells in the CNS are relay
neurons.
2.85 understand that stimulation of receptors in the sense organs sends electrical impulses
along nerves into and out of the central nervous system, resulting in rapid responses
2.86 describe the structure and
functioning of a simple reflex arc
illustrated by the withdrawal of a finger
from a hot object
Automatic responses are known as
reflexes. Examples are blinking, the pupillary
response to bright light, and the knee jerk
(patellar) reflex. They are important for
protecting us from injury.
The pathway of a reflex is called a reflex arc:
the parts of the reflex arc are…
stimulus -> receptor -> sensory neurone
-> relay neurone/s in CNS -> motor neurone -> effector -> response
In the example of withdrawing the finger from a hot object, the stimulus is heat, detected by a
temperature receptor in the finger, and the effector is a muscle in the arm.
There are also reflexes that involve the brain rather than the spinal cord, e.g. the blink reflex or the pupil
reflex.
2.87 describe the structure and function of the eye as a receptor
the cornea
transparent outer layer at front that refracts (bends) light entering the eye
the iris
coloured area around pupil, controls how much light enters eye (see 2.88)
the sclera
protective white outer layer
lens, ciliary muscle and
suspensory ligaments
focuses light rays on the retina (“accommodation”: see point 2.87)
the retina and the optic
nerve
the retina detects light; the signal passes to the brain (the visual cortex) via
the optic nerve
Revision notes on cells, life processes and living organisms
2.88 understand the function of the eye in

focusing near and distant objects

responding to changes in light
intensity
ACCOMMODATION:
the lens refracts the light more when
focusing on a near object - it becomes
fatter because the ciliary muscle
contracts and the suspensory ligaments
become slack
THE PUPILLARY REFLEX:
The iris controls how much light enters the eye.
 In bright conditions, the circular muscle of the iris
contracts and the radial muscle relaxes to constrict
(make smaller) the pupil, so the retina is not damaged
by too much light.

2.90
In dim light the circular muscle relaxes, the radial muscle
contracts and the pupil dilates (gets bigger)
understand the sources, roles and effects of the following
hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen
ADH is released from the pituitary
ADH causes the kidney to reabsorb more water into the
gland- its target organ is the kidney (the
blood when the blood is too concentrated (osmoregulation)
collecting ducts)
(see point2.68 and 2.74)
adrenaline is released from the adrenal
glands in a "fight or flight" response to
situations that cause fear or excitement;
target organs include the heart, lungs,
liver, brain, eye and muscles
the heart pumps more blood, the breathing rate
increases, the liver releases glucose, so more glucose and
oxygen are supplied to the muscles for energy from
respiration; more light enters the eye and mental alertness
increases
insulin is released by the pancreas
when the blood sugar is high; the liver is
the target organ
testosterone is released by the testes,
and oestrogen by the ovaries;
the liver converts glucose to glycogen, lowering the blood
sugar. The glycogen is broken down again when blood
glucose is low
they are responsible for secondary sexual characteristics
in adolescent boys (testosterone) and girls (oestrogen)
Progesterone is produced by the
ovaries, like oestrogen: target organ is
the uterus
Progesterone prepares the lining of the uterus for pregnancy
Revision notes on cells, life processes and living organisms
2.89
(CHAPTER 8) describe the role of the skin in temperature regulation, with reference to
sweating, vasoconstriction and vasodilation
the hypothalamus detects changes in temperature of the blood
when the blood becomes cool:
blood vessels under the skin constrict (vasoconstriction), so less blood flows to the skin,
and less heat is radiated from the skin.
Hairs stand up to trap an insulating layer of air.
when the hypothalamus detects a rise in the temperature of the blood
blood vessels under the skin widen (vasodilation) so more blood flows under the skin and
more heat is radiated by the skin;
and sweat glands produce sweat, which causes the skin to lose heat energy when the
water in the sweat evaporates