B3 - Specification

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Liver and muscle cells have a high number of mitochondria because they are organs that need alot of energy to function.

  • Some structures in cells, such as ribosomes, are too small to be seen wiht the light microscope
  • ribosomes are in the cyctoplasm and are the site of protein synthesis.
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Structure of the DNA is two strands coiled to form a double helix, each strand contains chemicals called bases, of which there are four different types (A,T,G,C), with cross links between the strands formed by pairs of bases (A-T and G-C).

Chromosomes are long, coiled molecules of DNA, divided in regions called genes.

Each gene:

  • contains a different sequence of bases
  • codes for a particular protein

Proteins are made in the cytoplasm.

A copy of the gene is needed because the gene itself cannot leave the nucleus.

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Protein structure is determined by the DNA base code:

  • the base sequence determines amino acid sequence
  • each amino acid is coded for by a sequence of 3 bases.

The code needed to produce a protein is carried from the DNA to the ribosomes by a molecule called mRNA.

DNA controls cells funtion by controlling the production of proteins , some of which are enzymes

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Watson and Crick

Watson and Crick used data from other scientists to build a model of DNA:

  • x-ray data showing that there were two chains wound in a helix
  • data indicating that the bases occured in pairs.

New discoveries such as Watson and Cricks are not accepted or rewarded immediately. It's important that other scientists can repeat their work and get similar results.

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Proteins are made of long chain of amino acids. Each proteins has it's own number and sequence of amino acids, which results in different shaped molecules, which have different functions.

  • structural - collegen
  • hormones - insulin
  • carrier - haemoglobin
  • enzymes.


  • biological catalysts
  • catalysing chemical reactions occuring in living: respiration, photosynethesis, protein synthesis.
  • having a high specificity for their substrate.
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Proteins 2

Enzymes have a 'lock and key' mechanism. Each enzyme has an active site that the substrate fits into.

Enzyme activity is affected by pH and temperature:

  • lower collision rates at lower temperatures
  • denaturing at extremes of pH and temperatures
  • denaturing is an irreversible reaction changing inhibiting enzyme function
  • denaturing changes the shape of the active site - the substrate doesn't fit.

Q10 -rate at higher temperature (t)/rate at lower temperature (t-10)

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Proteins 3

Genes made lead to the production of different proteins.

Mutations may occur spontaneously but can be made to occur more often by radiation or chemicals.

Mutations are often harmful but may be beneficial or have no effect.

Only some of the full set of genes are used in any one cell; some genes are switched off.

The genes are switched on determine the functions of the cell.

Changes to the genes alter or prevent the production of the protein which is normally made, this is because the base sequence of DNA is changed. This alters the shape and function of the proteins that the gene normally codes for.

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Symbol equation for aerobic equation:

Image result for aerobic respiration equation

Comparing respiration rates:

  • increased oxygen consumption
  • increased carbon dioxide production

Respiratory quotient (RQ)

RQ = carbon dioxide produced/oxygen used

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Respiration 2

Respiration results in the production of ATP and ATP is used as the energy source for many processes in cells.

The rate of oxygen consumption can be used as an estimate of metabolic rate because aerobic respiration requires oxygen.

The rate of respiration is influenced by changes in temperature and pH because the reaction is enzyme controlled so the enzymes denature and extreme temperatures at pHs.

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Respiration 3

Anaerobic respiration takes place during hard exercise in addition to aerobic respiration due to the fact that the muscles are working so hard that the lungs and circulatory system can't deliver enough oxygen to break down the glucose. (Anaerobic produces less energy per glucose molecule to aerobic)

Anaerobic produces lactic acid which accumulates in muscles causing pain and fatigue.

glucose             lactic acid.

Fatigue is the build up of lactic acid, oxygen dept and this is removed during recovery:

  • hard exercise causing of oxygen in cells
  • the incomplete breakdown of glucose
  • continued panting replacing oxygen allowing aerobic respiration
  • increased heart rate ensuring that blood carries lactic acid away from the liver. 
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Advantages of being multicellular:

  • organism can be larger
  • allows cell differentiation
  • allows organism to be more complex

Becoming multicellular requires the development of specialised organ systems:

  • communication between cells
  • supplying the cells with nutrients
  • controlling exhanges with the envionment
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New cells for growth are produced by mitosis. New cells are genetically identical because there are no parents involved and the DNA is copied.

In mammals, body cells are diploid (two copies of each chromosome)

DNA replication must take place before cells divide because the DNA needs to be exactly the same in each cell, so each new cell will have a copy of all the chromosomes.

DNA replication: unzipping to form single strands and new double strands forming by complementary base pairing.

In mitosis the chromosomes:

  • line up along the centre of the cell
  • then the divide
  • the copies move to oppositre poles of the cell.
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Gametes are produced by meiosis. Gametes are haploid (contains chromosome from each pair)

Fertilisation results in genetic variation:

  • gametes combine to form a diploid zygote and genes in the chromosomes combine to control the characteristics of the zygote

The sperm are adapted to their function:many mitochondria to provide energy and an acrosome that releases enzymes to digest the egg membrane.

In meiosis chromosome number is halved and each cell is genetically different:

  • 1 chromosome from each pair seperate to opposite poles of the cell in the 1st division
  • chromosomes divide + copies move to opposite poles of cell in the 2nd division
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A red blood cell is adapted to its function:

  • size - small and flexible to pass through narrow blood vessels
  • shape
  • contains haemoglobin
  • lack of nucleus - packed of haemoglobin

The function of plasma transports several substances around the body including flood like glucose, water, hormones, antibodies and waste products.

The small size and biconcave of red blood cells gives then a large surface are to volume ratio for absorbing oxygen.

haemoglobin + oxygen                          oxyhaemoglobin.

The reverse of this reaction happens the tissus.

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Blood Vessels

Parts of the circulatory system work together to bring abut the transport of substances around the body:

  • arteries transporting blood away from heart
  • veins transporting blood to heart
  • capillaries exhanging materials with tissues
  • thick muscular and elastic wall in arteries (high pressure)
  • large lumen and presence of valves (prevent backflow) in veins
  • permeability of capillaries (exchange of substances between cells and blood)
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The Heart

The Heart:

  • right and left ventricle to pump blood out of the heart
  • left and right atria to receive blood
  • semi-lunar, bicuspid and tricuspid valves to prevent backflow of blood
  • four main blood vessels of the heart.

Left ventricle has a thicker muscle wall because it pumps blood under a higher pressure around the body.

Advantages of having a double circulatory system:

  • higher pressures
  • therefore greater rate of flow to the tissues
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Diagram of the Heart

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Cell Structure

Differences between plant and animal cells:

Both contain:

  • nucleus
  • cell membrane
  • cytoplasm

Plants also contain:

  • chloroplasts
  • cellulose cell wall
  • vacuole
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Cell Structure

Bacterial cells lack:

  • a 'true' nucleus
  • mitochondria
  • chloroplasts

Difference in arrangement of DNA in a bacterial cell and a plant/animal cell:

  • presence/absence of a nucleus
  • single circular strand/chromosomes
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Dry mass is the best measure of growth.

Main phases of growth:

  • gestation
  • infancy
  • childhood
  • adolescence
  • adult hood
  • old age

Two phases of rapid growth, one just after birth and the other in adolescence.

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Growth 2

Advantages and disadvantages of measuring growth:

Length: Advantage - fast and easy. Disadvantage - increase in mass might occur with no increase in length.

Wet Mass: Advantage - not destructive, easy to measure. Disadvantage - water content of living tissue can be very variable and may give a distorted view.

Dry Mass: Advantage - most accurate. Disadvantage - destructive as have to remove water.

The growth rates of parts of an organism may differ from the growth rate of the whole organism for example - a babies head grows rapidly, to coordinate teh complex growth of the rest of the body.

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Stem Cells

Undifferenciated cells called stem cells can develop into different cells, tissues and organs.

Stem cells can be obtained from embryonic tissue and could potientially be used to treat medical conditions.

There are issues from stem cell research on animals - animal cruelty also this is unnatural.Adult stem cells - limited to differenciate into the cell types from their tissues of origin.

Embryonic stem cells - can become any type of body cell, they have a much wider use.

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Plant and Animal Growth

Plant growth differs from animal growth:

  • animals tend to grow to a finite size but many plants can grow continuously
  • plant cell division is mainly restricted to areas called meristems
  • cell enlargement is the main method by which plants gain height
  • many plant cells retain the ability to differenciate but most animal cells lose it at an early stage
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Selective Breeding

A selective breeding programme may lead to inbreeding, which can cause health problems within species.

Selective breeding may reduce the gene pool leading to inbreeding:

  • accumulation of harmful recessive alleles
  • reduction in variation
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Genetic Engineering

Advantages of genetic engineering: organisms with desired features are produced rapidly.

Risks - inserted gene may have some unexpected harmful effects.


  • Taking the genes from a carrot that control beta-carotene production and putting them into rice. Humans can then convert the beta-carotene from the rice into vitimin-A. This happens in parts of the world that rely on rice but have a lack of vitimin A)
  • Production of human insulin by genetically engineered bacteria
  • Transferring resistance to herbicide, frost damage, or disease to crop plants.
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Genetic Engineering 2

Ethical issues with genetic engineering:


  • feed more worlds population (disease resistant crops)
  • feed more areas (crops in dry or poor soil)
  • potientially replacing faulty genes to reduce certain diseases.


  • genetically modified plants may cross-breed with wild plants and release new genes
  • food may not be safe to eat long term
  • designer babies
  • unborn babies with genetic faults could be aborted
  • insurance companies could genetically screen applicants and refuse people who have increased risk of illness
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Genetic Engineering 3

How genetic engineering is completed:

  • selection of desired characteristics
  • isolatino of genes responsible
  • insertion of the gene into other organisms
  • replication of these organisms
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Gene Therapy

Changing a person's genes in attempt to cure diseases is called gene therapy.

Gene therapy can involve body cells or gametes.

Gene therapy involving gametes in controversial because genetic changes don't only affect the individual being treated but also future generations as those genes are passed onto offspring. Future generations dont have a say in the treatment and may affect them.

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Dolly the sheep was produced by the process of nucleur transfer and nucleur transfer involves placing the nucleus of a body cell into an egg cell.

Uses of cloning:

  • mass producing animals with desirable characteristics
  • producing animals that have been genetically engineered to provide human products
  • producing human embryos to supply stem cells for therapy.

Ethical problems:

  • unreliable - animals don't survive
  • animals limited life span
  • effect on humans mental and emotional development not known
  • regious views say that cloning humans is wrong
  • using human embryos and tampering with them is controversial
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Cloning 2

Cloning technique used to produce Dolly:

  • nucleus removed from an egg cell
  • egg cell nucleus replaced with the the nucleus from an udder cell
  • egg cell given an electric shock to make it divide
  • embryo implanted into surrogate mother sheep
  • embryo grows into a clone of the sheep from which the udder cell came.
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Cloning 3

Benefits of cloning:

  • genetically identical cloned animals will have the same characteristics
  • sex of animal and timing of birth can be controlled
  • top-quality bulls and cows can be kept for sperm or egg donation. Others used to give birth to young

Risks of cloning:

  • reduce genetic variation
  • one disease could wipe them all out - genes all the same
  • welfare concerns - cloned may not be as healthy or live as long
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Animal Organ Donation

Animal organ donors could solve the problem of waiting lists for human transplants. Genetically engineer an animal so organs wouldn't be rejected. This animal could then be cloned.


  • concerns that infections might be passed on from animal to human
  • ethical issues concerning animal welfare and rights
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Cloning Plants


  • sure of the characteristics of the plant since all plants will be genetically identical
  • possible to mass produce plants that may be difficult to grow from seed


  • all plants could be affected by one disease or change in environmental condition
  • lack of genetic variation

Cloning plants by tissue culture:

  • selection of plant with desired characteristics
  • obtain large number of small pieces of tissue
  • aseptic technique

Cloning plants is easier than cloning animals because many plant cells retain ability to differenciate or specialise, unlike animal cells which usually lose this ability at an early stage.

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