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Mattia lau GCSE Biology Rev
Topic 1: key biological concepts
Magnification means how many times larger an image is compared to the actual size
The total magnification of a microscope is worked out by multiplying the magnification of the eyepiece
lens by the magnification of the objective lens
Resolution means the smallest distance between two points that can still be two points
There are many prefixes for units in biology that go before the term meter, you need to understand
these and be able to utilize them in calculations in standard form
Plant cells contain a nucleus, cell membrane, cell wall, chloroplasts, mitochondria, permanent vacuole
and ribosomes
Animal cells contain a nucleus, cell membrane, mitochondria and ribosomes
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A diploid nucleus is one that contains two sets of parental chromosomes and is found in all body cells
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In
humans this means that there are 23 chromosomes
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Enzymes can either breakdown large substrate molecules (polymers) or synthesis (join up) smaller
substrate molecules to create a polymer
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Each enzyme is specific to a certain substrate
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The active site changes shape and Is no longer complementary
to the substrate
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Fluids have continual motion and move in random directions from an area of high concentration to an
are of low concentration, we call this diffusion
Osmosis is the movement of water molecules form an area of high water molecule concentration to an
area of low water molecule concentration across a partially permeable membrane
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This requires the use of energy
...

To use a light microscope, you firs need to prepare the specimen on a glass slide
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Adjust the focusing wheel so that the image is clear, and you can make your observation
To observe with higher magnification and objective lens to a higher magnification and focus again using
the focusing wheel
Electron microscopes have a much greater magnification and resolution than light microscopes
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Not found in animal cells
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Cytoplasm is a watery jelly where cell activity occurs
Nucleus are not found in bacterial cells
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Bacterial cells are much smaller than plant and animal cells
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They are to small to contain cell organelles
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They have a cell membrane and most bacteria have a cell wall
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Multicellular organisms are large plants and animals that are made of large numbers of cells
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Intestinal epithelial cells have a folded membrane of microvilli to increase surface area
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Sperms have a streamlined shape with a flagellum for fast swimming and have an acrosome at the top
of the head containing enzymes to break through the ovum’s jelly coat and lots of mitochondria to
release energy for movement

Mattia lau GCSE Biology Rev
Ciliated epithelial cells are found in oviducts and trachea are adapted with cilia to move from side to side
to move the ovum along the oviduct
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All cells need molecules to stay alive
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Lots of larger molecules in cells are called polymers- large molecules made of repeating subunits called
monomers
...
They are made of amino acid
Carbohydrates are needed for glucose and to make plant cell walls
...
They are made from fatty acids
and glycerine
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Different enzymes include
Amylase which digest starch into glucose and is found in saliva and the small intestine
Catalase breaks down hydrogen peroxide into oxygen and water and is found in most cells
Starch synthase synthesizes starch from glucose and is found is plant cells
DNA polymerase does synthesis of DNA from its monomers and is found in the nucleus of all cells
Enzymes have a specific 3D shape made by a long chain of amino acids folding it on itself
Each enzyme has a specific shaped active site that is complementary to the substrate
...
The substrate is the reactant
One model of how enzymes work is the lock and key model
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– one substrate will fit into the active site and be broken down
into smaller molecules
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After the reaction, the new products leave the active site and the enzyme is
available to react with another substrate
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This is because the molecules have low
kinetic energy so do not collide very frequently
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Enzymes can be damaged by changed in pH and high temperatures
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When this happens, the enzyme becomes denatured and it will no longer fit in the substrate

Mattia lau GCSE Biology Rev
The optimum temperature of pH is the temperature of pH with the highest rate of enzyme activity
...

The stages of mitosis in the correct order are prophase, metaphase, anaphase, telophase and
cytokinesis
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A diploid is a nucleus with two sets of parental chromosomes, in humans this means that all the
cells produced by mitosis has 46 chromosomes
...
This is likely to have occurred because of an error in
DNA replication
Mutations in DNA replication can be due to the deletion, substitution or insertion of different nucleotide
base within the DNA sequence during the process of transcription
...
This results in a clump of abnormal cells, which may cause secondary
jar to the body – a tumour
Asexual reproduction is entirely based upon mitosis
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Some organisms such as the strawberry plant can produce using both asexual and sexual techniques
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Children should ideally be within the 25th to 75th
percentiles
If growth crosses more than one percentile curve on the graph this is a warning sign to medical
professionals and would likely start further investigations
Cell differentiation is the process by which an unspecialised stem cell can change and become
differentiated or specialised cell
...

Modern cell therapies look to utilise this power to create laboratory grown tissues and even organs,
which can be transplanted into patients
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Mattia lau GCSE Biology Rev
There however pockets of adult stem cells, in the skin, brain and bone marrow that can differentiate
into a limited few types of specialised cells
...
They can differentiate into any of their cell types at any time at special
locations behind the tips of roots and shoots called meristems
Plant meristems contain a zone of cell division followed a zone of elongation and then a zone of
differentiation
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A neurone consists of a cell body, dendrites, axon terminals, axon and myelin sheath
The reflex arc is an involuntary response to a potentially dangerous external stimulus
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The sequence of neurones in a voluntary action is stimulus, receptor, sensory neurone, relay neurone,
motor neurone, effector and response
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The gap is between the dendrites of one
neurone and the axon terminal of another
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Instead a neurotransmitter substance is released at
the axon terminals of one neurone when the electrical impulse reaches some vesicles containing the
substance
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Topic 3: Genetics
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They hold 1000s of genes
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Meiosis in humans begins with a parent cell
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Ribonucleic acid also known as RNA is one strand of DNA instead of 2
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Mattia lau GCSE Biology Rev
RNA has a sugar called ribose while DNA has a sugar called deoxyribose
RNA has a base called uracil while DNA has the base thymine
There are two types of RNS messenger RNA or mRNA which rewrites the sequence of bases of a section
of DNA
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That is, it acts as a messenger
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The DNA code is a triplet code
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The alleles are the organisms genotype and its phenotype are what it looks like
Alleles are used in punnet squares
Genetic variation is caused by different alleles inheriting genes during sexual reproduction
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These changes cause changes in the phenotype

Mattia lau GCSE Biology Rev
Environmental variation are characteristics affected by their surroundings
Variation can be grouped into two types
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Most mutations are harmful
Some mutations have no obvious effect, others may lead to variation
A few can be beneficial
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Topic 4: Natural selection and Genetic Modification
The theory of evolution is that different species have developed over time from other life forms
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5 billion years old and there is scientific evidence that life on earth began more than
three billion years ago
...
They point are that
Individuals in a species show a wide range of variation and this variation is because of differences in
their genes
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Those that are poorly adapted to their environment are less likely to survive and reproduce
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Given time, a species will gradually evolve
Both genes and environment can cause variation, nut only genetic variation can be passed onto the next
generation
...
This is an example of
natural selection
In a large population of bacteria, there may be some that are not affected by an antibiotic
...

The number of strains of antibiotic-resistant bacteria has increased, partly due to the misuse of
antibiotics
...

Development of resistance are:
Random mutations occur in the genes of an individual bacterial cell
Some mutations protect the bacterial cell from the effects of the antibiotic

Mattia lau GCSE Biology Rev
Bacteria without the mutation die or cannot reproduce when the antibiotic is present
Resistant bacteria can reproduce with less competition from normal bacterial stains
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Natural selection and selective breeding can cause both changes in animals and plants
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For this reason selective breeding is sometimes called artificial selection
Different varieties of plants and animals with desired characteristics can be developed by selective
breeding
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Genetic modification is the process of altering the DNA in an organism’s genome
This may mean changing one base pair, deleting a whole region of DNA, or introducing an additional
copy of a gene
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Genetic engineering can be applied to any organism, from a virus to a sheep
For example, genetic modification can be used to produce plants that have a higher nutritional value or
can tolerate exposure to herbicides
Examples of genetic modification include the production of insulin
A small piece of plasmid is extracted form the bacteria
A small section is then cut out of the circular plasmid by restriction enzymes, molecular scissors
The gene for human insulin is inserted into the gap in the plasmid
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Mattia lau GCSE Biology Rev
To create large amounts of the cells, the genetically modified bacteria or yeast are grown in large
fermentation vessels that contain all the nutrients they need
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When fermentation is complete, the mixture is filtered to release the insulin
The insulin is then purified and packaged into bottles and insulin pens for distribution
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Communicable diseases are diseases spread through people, animals, water and the air
Non-communicable diseases are hereditary examples include cystic fibrosis
...
But people in developing countries may not get
enough protein in their diet
...
It can lead to a disease called kwashiorkor
which causes a swelling abdomen
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75 x body mass in kg
BMI is a guide to whether someone is underweight, normal weight or overweight
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This is because carbon monoxide and other
harmful chemicals can damage blood vessels and artery’s
...
This can cause a stroke
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Following a stroke, the person can be left disabled or dead
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Bacteria release roxins
and viruses damage our cells
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They can produce
antibodies to destroy pathogens, and anti-toxins to neutralise toxins
In vaccinations pathogens are introduced into the body in a weakened form
...
Some strains of bacteria are resistant
to antibiotics
Pathogens are microorganisms that cause infectious disease
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Bacteria are microscopic organisms that come in many shapes in size
They are living cells and in favourable conditions can multiply rapidly
...
Diseases caused by bacteria include food poisoning, cholera,
typhoid and gonorrhoea
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Eventually the virus fills the host and bursts it open
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Diseases caused by viruses include colds, mumps, chicken pox and aids
White blood cells can ingest pathogens and destroy them
Produce anti-bodies to destroy pathogens
Produce anti-toxins that neutralise the toxins released by pathogens
In a written examination, it is easy to get carried away and waffle on about things such as invaders and
battles
...

Antibodies and antitoxins are not living things – they are specialised proteins
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Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards
pathogens or toxins
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Release an enzyme to destroy them
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Pathogens contain certain chemicals that are foreign to the body and are called antigens
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When a lymphocyte with the appropriate antibody meets an antigen, the lymphocyte reproduces
quickly and makes many copies of the antibody that neutralises the pathogen
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They coat pathogens, clumping them together so that they are easily ingested by phagocytes
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Penicillin was the first antibiotic
One simple way of reducing the risk of infection is to maintain personal hygiene and to keep hospitals
clean
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Chloroplasts contain chlorophyll the green pigment that
makes the leaves green
...
If only green light is shone at
the plant, then no light would not be absorbed
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The plant would soon
use up all its stored sugar compounds for respiration to produce energy
...
Eventually unless other wavelengths of light were
shone at the plant the plant would die
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There is less of the red
and blue parts of the visible spectrum of light available so having green chlorophyll is less of an
advantage
...
The chlorophyll would have reflected these
...
Also,
the presence of stomata on the leaves increase water loss via transpiration
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The nutrients within the leaves are
then replaced into the ground and are available for the roots and to absorb through active transport
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Marram grass is found in beach areas and is a xerophyte
...
It stabilizers sand dunes and leads to the build up of initial
organic matter in dune succession
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Traps column of air inside a
curl of leaf reducing water potential gradient
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This keeps moist air near the leaf and reduces
the water potential gradient
Sunken stomata traps water vapour near the stomata reducing the water potential gradient which
reduces water loss
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The maximum rate of photosynthesis is controlled by the factor in shortest supply
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Mattia lau GCSE Biology Rev
A straight line on a graph shows a linear relationship between two variables
...
This means that if one variable increases, the
other increases by the same percentage
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Secrete means to produce and release
The pituitary gland produces Follicle stimulating hormones and Luteinizing hormones
Luteinizing hormones triggers ovulation
Follicle stimulating hormones stimulate the growth of follicles in preparation for the egg
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Homeostasis is the ability of the body to maintain a constant internal state
The endocrine system is the system of glands that produce hormones to regulate the body and
control bodily activity's
Hormones are seeking target cells after being released by the glands
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The endocrine system is a system of glands that the produce and control hormones and bodily
activity
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The targeted cells send out specific chemicals that brings about a change like
homeostasis
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Adrenaline works by negative feedback,
this is a mechanism that regulates the glands
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Adrenaline is the sense of danger will tell the brain whether it can fight or
flight
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Liver cells turn glycogen into
glucose
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Mattia lau GCSE Biology Rev
To little thyroxine and the metabolic rate is too low which means a lower and weaker heartbeat,
slower rate of breakdown of carbohydrate and protein cells
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Hypothalamus detects the level of thyroxine in the blood
If it’s too low, it secretes TRH and travels to the pituitary gland and the pituitary gland secretes TSH
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Adrenalin causes the liver to convert stored glycogen into glucose causing increased glucose
available to muscles to increase for sudden activity
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It also stimulates the ovaries to produce hormones including estrogen
Estrogen is secreted by the ovaries and inhibits the further production of FSH
A maturing egg releases estrogen which brings a surge of LH on day 14, causing ovulation
It rebuilds the uterus lining after menstruation
Luteinizing hormone stimulates the release of eggs from the ovary
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It maintains the uterus lining to prevent it shedding and inhibits FSH to prevent too many eggs
maturing
It thickens the mucus of the cervix- the entrance to the uterus at the top of the vagina
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FSH and LH increase the chance of Pregnancy while Progesterone and Estrogen inhibit Pregnancy
Oral contraceptives contain hormones estrogen and progesterone to inhibit FSH production and
ovulation, so that no eggs mature
Oral contraceptives containing progesterone also thicken the mucus lining to the uterus stopping
the sperm from reaching the egg
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The fertilized eggs develop into embryos
Embryos need a thickened uterus to embed in
At the stage, the woman is now given progesterone to thicken her uterus lining
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FSH stimulates the maturation of eggs and LH encourages ovulation, when a mature egg leaves the
ovary
Fertilisation takes place outside the woman's body
FSH and LH are given to the woman before IVF to stimulate multiple eggs to mature, ready for
fertilisation
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Once fertilised, any healthy embryos are implanted into her uterus to grow as a normal pregnancy
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More exercise uses more glucose
during respiration
The role of the pancreas is to secrete digestive enzymes and hormone producing cells which release
insulin and glucagon
If blood glucose levels are high the pancreas releases insulin into the blood
Insulin stimulates body cells to absorb glucose
Insulin causes liver and muscle cells to convert glucose to glycogen
There for blood glucose levels fall
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Insulin lowers blood glucose concentration and glucagon, increases it
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This allows highly sensitive control of blood glucose
Type 1 diabetes is when the pancreas produces no insulin
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The pancreas produces some insulin but not enough or target
cells are no longer responding to insulin
The treatment is the change of lifestyle to healthy one with more exercise and low in sugar diet
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Of the egg is fertilised by sperm the embryo will implant into the thick lining
If the egg is not fertilized the lining of the uterus will break down this is the monthly period
FSH controls menstruation
LH controls ovulation
FSH tell the ovaries to produce the hormone estrogen and FSH travels to the ovaries in the blood
stream to start maturing the egg
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Water helps absorb nutrients
Glucose is used as energy in cells
Active transport is movement from low to high concentration (against the concentration gradient)
Osmosis is the movement of water across a partially permeable membrane
Diffusion is the movement the movement from a high to low concentration (down a concentration
gradient)
Fricks law states that the rate of diffusion = surface area x concentration gradient
-------------------------------------------------Diffusion distance
A good exchange surface contains a large surface area, short diffusion distance and a large
concentration gradient
Blood enters the rest of the body with a higher concentration of carbon dioxide and a lower
concentration of oxygen
Alveoli has a cell wall that is one cell thick for a effective diffusion rate
the alveolus has a higher concentration of oxygen and a lower concentration of carbon dioxide than
the blood
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People with emphysema often need to breath air containing a greater concentration of oxygen
because the larger pockets of air create a large space for a higher concentration of oxygen
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This is because the alveoli are joined,
and the diffusion distance is increased
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High concentration of oxygen maintains oxygenated they can’t function normally and are
often exhausted
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Veins have a low blood pressure
Veins are the furthest blood vessel from the heart
65% of blood is found in the veins
Veins have the largest lumens to carry more blood
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90% of plasma is water
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2% is made of insulin,
sugars and electrolytes
There are four blood types: A, B, AB and O
45% of blood are red blood cells
Blood is created in the bone marrow stimulated by EPO
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Oxygen molecules bind to iron in the haemoglobin
Ph lowers causing hydrogen to be produced triggering oxygen to bind to the iron
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Neutrophils consume infections by phagocytosis
They fight infections and pathogens
There are 6 types of white blood cells: monocyte, lymphocyte, neutrophil, macrophage, eosinophil
and basophil
Platelets form initial clots when veins tear
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Arterial clots are artery clots
Venous clots are vein clot
The calculation for calculating cardiac output is: stroke volume x heart rate
Cardiac output is the amount of blood pumped out of the heart
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Increasing stroke volume increases heart size

Mattia lau GCSE Biology Rev
Anaerobic respiration occurs without the presence of oxygen
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Anaerobic respiration equation: glucose  lactic acid + energy
Aerobic respiration equation: glucose + oxygen  carbon dioxide + water
the equation of fermentation: glucose  ethanol + carbon dioxide
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This is
known as interdependence
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Some predators can damage the ecosystem and can be helped with a large diversity of predators
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The aims of surveying an environment include establishing what organisms live in an area, estimating
the number of organisms in an area

Mattia lau GCSE Biology Rev
The two types of data can be gathered using quadrats include ACFOR for giving a general picture of a
species present in the area and stands for abundant, common, frequent, occasional and rare
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You can improve the reliability of a quadrat by taking more samples and
choosing random parts of the grid
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Quadrats
are used for quantitive analysis
Continuous belt transects are used when you want more detail
Kite diagrams show an abundance of a species along a transect and give a great visual representative
of data from a belt transect
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This limits the length of the food chain and guarantees that biomass will decrease as you move up the
food chain
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Benefits of maintaining biodiversity on a global and local scale include protecting human food supplyoverfishing has depleted fish stocks but conservation could secure fish for future generation
Ensuring minimal damage to food chains- if one species in a food chain is wiped out it will have a
knock-on effect on other species in that food chain; conserving one species may protect others as well
Providing future medicines can be a benefit of protecting the rainforest
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Food security means having enough safe and healthy food at all time
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The
predicted population is stated to rise then settle out
Increasing the amount of fish and meat we eat will lead to an increase demand in the future which
could lead to a decrease in food security
Problems with monoculture include rural depopulation which could lead to
A buildup of pests a disease
Soil degradation
This can cause rapid spread of susceptible to pathogens
Could lead to economical failure
The water cycle- rivers flow into lakes and into oceans which get evaporated to form clouds and
condensate back to the rivers and lakes



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