All of Edexcel BIOLOGY Paper 1 in 30 minutes - GCSE Science Revision

00:26:40
https://www.youtube.com/watch?v=ZMTmmifPuR0

Summary

TLDRThis video provides a detailed summary of the key concepts in EDXL GCSE Biology Paper One, focusing on essential topics such as cells, genetics, natural selection, and health. It explains the structure and function of eukaryotic and prokaryotic cells, the role of enzymes in biological reactions, and the processes of diffusion and osmosis. The video also covers the significance of the Human Genome Project, the function of the nervous system, and the use of monoclonal antibodies in medicine. Practical experiments related to these concepts are discussed, along with the implications of genetic modification and the importance of vaccines in disease prevention.

Takeaways

  • ๐Ÿ”ฌ All life consists of cells, visible with light and electron microscopes.
  • ๐Ÿงฌ Eukaryotic cells have a nucleus; prokaryotic cells do not.
  • โš—๏ธ Enzymes are biological catalysts that speed up reactions.
  • ๐Ÿ’ง Osmosis is the diffusion of water across a membrane.
  • ๐Ÿงฌ The Human Genome Project mapped all human genes.
  • ๐Ÿ’‰ Vaccines help the immune system prepare for pathogens.
  • ๐Ÿงช Monoclonal antibodies are used for treatment and diagnosis.
  • ๐Ÿง  The nervous system coordinates responses to stimuli.
  • ๐Ÿ“ˆ Benign tumors are non-spreading; malignant tumors are dangerous.
  • ๐ŸŒฑ Genetic modification can enhance crop yields and nutritional value.

Timeline

  • 00:00:00 - 00:05:00

    The video introduces the main ideas of the EDXL GCSE biology paper one, covering key concepts such as cells, genetics, natural selection, and health. It emphasizes the importance of understanding cell structures, including the differences between eukaryotic and prokaryotic cells, and the role of organelles in cellular functions.

  • 00:05:00 - 00:10:00

    The discussion on enzymes highlights their specificity and the lock-and-key model of enzyme activity. It explains how temperature and pH affect enzyme function, and describes a practical experiment to determine optimum conditions for enzyme activity using amylase and starch.

  • 00:10:00 - 00:15:00

    The video explains diffusion and osmosis, emphasizing the movement of molecules across membranes and the factors that affect these processes. A practical experiment using potato cylinders in sugar solutions is described to illustrate osmosis and its effects on mass change.

  • 00:15:00 - 00:20:00

    Cell division through mitosis and meiosis is covered, detailing the processes involved in growth and reproduction. The importance of stem cells and their potential applications in medicine is also discussed, along with the ethical considerations surrounding cloning and genetic modification.

  • 00:20:00 - 00:26:40

    The final sections address the nervous system, the structure and function of the eye, and the processes of sexual and asexual reproduction. It concludes with a discussion on genetics, evolution, and the impact of genetic engineering on agriculture and medicine, including the use of monoclonal antibodies.

Show more

Mind Map

Video Q&A

  • What are the main topics covered in EDXL GCSE Biology Paper One?

    The main topics include cells and control, genetics, natural selection, genetic modification, and health and disease.

  • What is the difference between eukaryotic and prokaryotic cells?

    Eukaryotic cells have a nucleus containing DNA, while prokaryotic cells do not.

  • What is the role of enzymes in biological processes?

    Enzymes act as biological catalysts that speed up chemical reactions by breaking down larger molecules into smaller ones.

  • How does osmosis differ from diffusion?

    Osmosis specifically refers to the diffusion of water across a semi-permeable membrane, while diffusion is the movement of molecules from high to low concentration.

  • What is the significance of the Human Genome Project?

    It mapped out every gene's function, helping to identify genes responsible for diseases and inherited disorders.

  • What is the purpose of vaccines?

    Vaccines expose the immune system to a harmless version of a pathogen, allowing it to produce antibodies without causing disease.

  • What is the difference between benign and malignant tumors?

    Benign tumors do not spread and are easier to treat, while malignant tumors spread throughout the body and are more dangerous.

  • What is the function of the nervous system?

    The nervous system coordinates responses to stimuli through the central and peripheral nervous systems.

  • What are monoclonal antibodies used for?

    They are used for treating diseases, medical diagnosis, and detecting pathogens in labs.

  • What is the role of DNA in genetics?

    DNA contains the genetic code that determines an organism's traits and characteristics.

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  • 00:00:00
    Let's see how quickly we can cover the
  • 00:00:01
    main ideas found in EDXL GCSE biology
  • 00:00:04
    paper one. This is good for higher end
  • 00:00:06
    foundation tier, double combined or
  • 00:00:08
    triple separate. That's topics one to
  • 00:00:10
    five. Key concepts cells and control
  • 00:00:12
    genetics natural selection and genetic
  • 00:00:14
    modification and health disease and
  • 00:00:16
    medicines. It's a mouthful, isn't it?
  • 00:00:18
    I'll tell you when some of the bigger
  • 00:00:19
    concepts are just for triple but not for
  • 00:00:21
    higher and foundation tier because
  • 00:00:22
    there's not a lot of difference to be
  • 00:00:23
    honest. We're going to be really moving
  • 00:00:25
    here. So, pause the video if you need a
  • 00:00:26
    bit more time to get your head around
  • 00:00:28
    something you see. Let's go. All life
  • 00:00:30
    consists of cells. We can see cells with
  • 00:00:32
    a normal light microscope and maybe the
  • 00:00:34
    nucleus, but the subcellular structures
  • 00:00:36
    won't really be visible. Using an
  • 00:00:38
    electron microscope, however, allows us
  • 00:00:39
    to see far finer details. So, we can see
  • 00:00:42
    an image of the organels. As such, these
  • 00:00:44
    microscopes have a better resolving
  • 00:00:46
    power and a higher resolution. We say we
  • 00:00:49
    can calculate the actual size of a cell
  • 00:00:51
    by knowing the magnification of the
  • 00:00:53
    microscope. Magnification is equal to
  • 00:00:55
    image size divided by object size.
  • 00:00:58
    Therefore, rearranging this, we can
  • 00:00:59
    measure the size of the image, then
  • 00:01:01
    divide by the magnification, and that
  • 00:01:03
    gives us the actual cell size. We put
  • 00:01:05
    them into two main groups. Ukarotic
  • 00:01:08
    cells have a nucleus in which their DNA
  • 00:01:10
    is found. That's your plant and animal
  • 00:01:12
    cells, for example. Proarotic cells
  • 00:01:14
    don't have a nucleus. Both ukarotic and
  • 00:01:16
    proarotic cells contain similar organels
  • 00:01:19
    or subcellular structures. The cell
  • 00:01:21
    membrane keeps everything inside the
  • 00:01:22
    cell, but they're also semi-permeable,
  • 00:01:24
    which means they allow certain
  • 00:01:26
    substances to pass through. Plant cells
  • 00:01:28
    and most bacteria have an extra cell
  • 00:01:30
    wall made of cellulose providing a rigid
  • 00:01:33
    structure for them. Cytoplasm is the
  • 00:01:35
    liquid that makes up the cell in which
  • 00:01:37
    most chemical reactions take place.
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    Mitochondria where respiration takes
  • 00:01:41
    place releasing energy for the cell to
  • 00:01:43
    function. Ribosomes are where proteins
  • 00:01:45
    are assembled or synthesized. Plant
  • 00:01:47
    cells also contain chloroplasts which
  • 00:01:49
    contain chlorophyll where photosynthesis
  • 00:01:52
    takes place. Plant cells also contain a
  • 00:01:54
    permanent vacule in which sap is stored.
  • 00:01:56
    Enzymes are biological catalysts, some
  • 00:01:58
    of which break down larger molecules
  • 00:02:00
    into smaller ones that can then be
  • 00:02:02
    absorbed by the villi in your small
  • 00:02:03
    intestine into the bloodstream to be
  • 00:02:05
    transported to every part of your body.
  • 00:02:07
    For example, amalayise is the enzyme
  • 00:02:09
    that breaks down starch into glucose.
  • 00:02:11
    It's found in your small intestine and
  • 00:02:13
    saliva. Enzymes are specific that is
  • 00:02:15
    they only break down certain molecules.
  • 00:02:17
    For example, carbohydrases break down
  • 00:02:19
    carbohydrates into simple sugars. Ama is
  • 00:02:22
    one of these. Proteases break down
  • 00:02:24
    proteins into amino acids. And lipases
  • 00:02:27
    break down lipids, that's fats, into
  • 00:02:29
    glycerol and fatty acids. They're
  • 00:02:31
    specific because they work in a lock and
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    key principle. The substrate, for
  • 00:02:34
    example, the starch, binds to the
  • 00:02:36
    enzyme's active site. We then call this
  • 00:02:39
    a complex. However, this can only happen
  • 00:02:41
    if the substrate is the right shape in
  • 00:02:43
    order to fit the active site. In
  • 00:02:45
    reality, they're incredibly complex
  • 00:02:46
    shapes. No pun intended. These shapes
  • 00:02:48
    here are just to represent them. Much
  • 00:02:50
    like a lock and key, it only works if
  • 00:02:52
    they're the right shape for each other.
  • 00:02:53
    The rate of enzyme activity increases
  • 00:02:55
    with temperature due to the molecules
  • 00:02:57
    having more energy. That is until the
  • 00:02:59
    active site changes shape and so the
  • 00:03:02
    substrate no longer binds. We say the
  • 00:03:04
    enzyme has denatured. This maximum rate
  • 00:03:06
    occurs at the optimum temperature.
  • 00:03:08
    Optimum meaning best. This is similar
  • 00:03:10
    for pH as well except it can denature at
  • 00:03:13
    too high or too low pH. The practical on
  • 00:03:15
    this involves mixing amalayise with
  • 00:03:17
    starch at different temperatures or with
  • 00:03:19
    different pH buffer solutions. Once
  • 00:03:21
    mixed, we start timing. Then every 10
  • 00:03:23
    seconds, we remove a couple of drops and
  • 00:03:24
    put in a spot in tile dimple with iodine
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    in. To begin with, the iodine will turn
  • 00:03:28
    black due to there still being starch
  • 00:03:30
    present, but eventually will stay orange
  • 00:03:32
    showing that all of the starch has been
  • 00:03:34
    broken down. Calculate the time taken to
  • 00:03:36
    do that. Then plot these times against
  • 00:03:39
    pH or temperature. draw a curved line of
  • 00:03:41
    best fit and the lowest point is where
  • 00:03:43
    the starch would have taken the shortest
  • 00:03:44
    time to be broken down. That's the
  • 00:03:46
    optimum temperature or pH. However, in
  • 00:03:49
    true biology fashion, we're technically
  • 00:03:50
    not allowed to interpolate between
  • 00:03:52
    points for some reason. So, we must only
  • 00:03:54
    say that the optimum pH or temperature
  • 00:03:56
    is between the two lowest points. Shrug.
  • 00:03:59
    Food tests allow us to identify what
  • 00:04:01
    nutrients are in our grub. Iodine turns
  • 00:04:04
    from orange to black in the presence of
  • 00:04:05
    starch, like we just saw. Benedict's
  • 00:04:07
    solution turns from blue to orange in
  • 00:04:09
    the presence of sugars. Bouet's reagent
  • 00:04:12
    turns from blue to purple with proteins.
  • 00:04:14
    Cold ethanol will go cloudy with lipids,
  • 00:04:17
    that is fats. Diffusion is the movement
  • 00:04:20
    of molecules or particles from an area
  • 00:04:22
    of high concentration to an area of low
  • 00:04:24
    concentration. We say they move down the
  • 00:04:26
    concentration gradient. Like a ball just
  • 00:04:28
    rolling down a hill, it'll do it by
  • 00:04:30
    itself. This doesn't require any energy
  • 00:04:32
    input. So, we say it's passive. This
  • 00:04:34
    will happen across a semi-p permeable
  • 00:04:36
    membrane if the holes are large enough
  • 00:04:38
    for the molecules to move through. For
  • 00:04:40
    example, water can pass through, but
  • 00:04:41
    glucose will not, at least not by
  • 00:04:43
    diffusion anyway. Osmosis is the name
  • 00:04:45
    specifically given to the diffusion of
  • 00:04:47
    water across such a membrane. For
  • 00:04:49
    example, if there is a higher
  • 00:04:50
    concentration of glucose outside a cell,
  • 00:04:52
    the glucose cannot diffuse in to balance
  • 00:04:55
    the concentration. So instead, the water
  • 00:04:57
    moves out of the cell resulting in a
  • 00:04:59
    decrease in its mass. The rate of
  • 00:05:01
    diffusion and osmosis can be increased
  • 00:05:03
    by increasing the difference in
  • 00:05:05
    concentrations, increasing the
  • 00:05:06
    temperature or increasing the surface
  • 00:05:08
    area. This is why the villi in your
  • 00:05:10
    small intestine are lumpy as well as
  • 00:05:12
    alvioli in your lungs and root hair
  • 00:05:14
    cells for example too. The practical on
  • 00:05:16
    osmosis goes as follows. Cut equaliz
  • 00:05:19
    cylinders from a potato or other
  • 00:05:20
    vegetable. Weigh them and place in test
  • 00:05:23
    tubes with varying concentration of
  • 00:05:24
    sugar solution. After a day or so, we
  • 00:05:27
    remove them, dab the excess water off
  • 00:05:29
    their surface, and reweigh. We calculate
  • 00:05:31
    percentage change in mass by doing final
  • 00:05:33
    mass take away initial mass divided by
  • 00:05:36
    the initial mass times 100. If it's
  • 00:05:38
    lighter than it was before, this must be
  • 00:05:40
    a negative change in mass. We plot these
  • 00:05:42
    percentages against sugar concentration
  • 00:05:44
    and we draw a line of best fit. Where
  • 00:05:46
    this crosses the x-axis is what
  • 00:05:49
    concentration should result in no change
  • 00:05:51
    in mass. So, no osmosis. So this means
  • 00:05:54
    this must be the same as the
  • 00:05:55
    concentration inside the potato. Glucose
  • 00:05:58
    and other nutrients and minerals can
  • 00:05:59
    move through a membrane by active
  • 00:06:01
    transport where carrier proteins use
  • 00:06:04
    energy to move substances through the
  • 00:06:06
    membrane. As there's energy used, this
  • 00:06:08
    can actually move them against a
  • 00:06:09
    concentration gradient. For example,
  • 00:06:11
    moving mineral ions into plant root hair
  • 00:06:13
    cells. Ukarotic cell nuclei contain DNA
  • 00:06:17
    which is stored in several chromosomes.
  • 00:06:19
    Humans have 23 pairs of these in every
  • 00:06:21
    nucleus. So we call them diploid cells.
  • 00:06:23
    That's not the case for gametes though.
  • 00:06:25
    They have half so just 23 not 23 pairs.
  • 00:06:28
    So therefore we call them hloid cells.
  • 00:06:30
    New cells must constantly be made for
  • 00:06:32
    growth and repair. They do this by
  • 00:06:33
    duplicating by mitosis. Here's the
  • 00:06:36
    process, the mitosis process. The
  • 00:06:38
    genetic material is duplicated and the
  • 00:06:40
    number of ribosomes and mitochondria is
  • 00:06:42
    doubles as well. The nucleus breaks down
  • 00:06:44
    and one set of each chromosome pair is
  • 00:06:46
    pulled to opposite sides of the cell. A
  • 00:06:48
    new nucleus forms in each of these to
  • 00:06:50
    house the copied chromosomes. And we now
  • 00:06:52
    have two identical cells. Cells
  • 00:06:54
    specialize depending on the function
  • 00:06:56
    they need to fulfill. For example,
  • 00:06:58
    nerve, muscle, root hair, xyllem, phm
  • 00:07:00
    cells. Stem cells are those that haven't
  • 00:07:02
    yet specialized. They're found in human
  • 00:07:04
    and animal embryos and the merry stem of
  • 00:07:06
    plants. That's the top of the chute.
  • 00:07:08
    Stem cells are made in your bone marrow
  • 00:07:10
    throughout your life as well, but these
  • 00:07:12
    ones can only specialize into blood
  • 00:07:13
    cells. We can use stem cells to combat
  • 00:07:16
    conditions like diabetes and paralysis.
  • 00:07:18
    In fact, right out of the movie The
  • 00:07:19
    Island, people are now getting clones of
  • 00:07:21
    themselves made, then harvesting the
  • 00:07:23
    stem cells, as these won't be rejected
  • 00:07:25
    by the patient. Personally, I think this
  • 00:07:27
    is a dystopian man-made horror beyond
  • 00:07:29
    comprehension. You have to weigh up the
  • 00:07:31
    ethical arguments for yourself. Cloning
  • 00:07:33
    plants can be used to prevent species
  • 00:07:34
    from becoming extinct or produce crops
  • 00:07:36
    with specific characteristics. Our
  • 00:07:38
    nervous system, it consists of the CNS,
  • 00:07:41
    that's central nervous system, that's
  • 00:07:43
    the brain and spinal cord, and the PNS,
  • 00:07:45
    peripheral nervous system, the nerves
  • 00:07:47
    that go through the rest of the body. A
  • 00:07:49
    receptor, for example, skin, detects a
  • 00:07:51
    change due to a stimulus, like a hot
  • 00:07:53
    hob. An electrical signal travels to the
  • 00:07:56
    spine through sensory and relay neurons,
  • 00:07:58
    nerve cells. The signal travels across
  • 00:08:00
    the gap between these neurons called the
  • 00:08:02
    sinapse by a neurotransmitter chemical.
  • 00:08:05
    Once at the spine, the signal can go to
  • 00:08:07
    the brain where you can make the
  • 00:08:08
    conscious decision to act. The signal
  • 00:08:10
    then goes back to an aector like the
  • 00:08:13
    muscle in your arm via relay and motor
  • 00:08:16
    neurons so that you move your arm. A
  • 00:08:18
    reflex is when the signal bypasses the
  • 00:08:20
    brain and goes straight through the
  • 00:08:21
    spine to the aector. This is a reflex
  • 00:08:24
    arc. This of course is much faster than
  • 00:08:26
    a conscious decision. Glands can also be
  • 00:08:28
    aectors which produce specific chemicals
  • 00:08:30
    your body needs depending on the
  • 00:08:31
    situation. For example, your salivory
  • 00:08:34
    glands in your mouth making saliva when
  • 00:08:36
    you eat food. You can investigate into
  • 00:08:38
    reaction times by holding the bottom of
  • 00:08:39
    a ruler between a person's finger and
  • 00:08:41
    thumb and drop it without warning. Then
  • 00:08:43
    you measure the distance it falls before
  • 00:08:45
    they catch it. Do this multiple times
  • 00:08:46
    and take a mean average. Not too many
  • 00:08:48
    times though, as their nervous systems
  • 00:08:50
    will start to get a bit better at
  • 00:08:52
    reacting to this. You can introduce an
  • 00:08:54
    independent variable like a stimulant
  • 00:08:55
    for example coffee or a sugary drink or
  • 00:08:57
    a depressant which will have the
  • 00:08:58
    opposite effect although I can't think
  • 00:09:00
    of any ones that are legal for you at
  • 00:09:02
    the minute to see how they decrease or
  • 00:09:04
    increase reaction time respectively. You
  • 00:09:07
    could calculate the reaction time from
  • 00:09:08
    the distance using suvat s= 80^ squ but
  • 00:09:12
    you'll never be expected to do that in
  • 00:09:14
    this paper but it's something you could
  • 00:09:15
    mention if you were asked a six marker
  • 00:09:17
    on this. There are three parts of the
  • 00:09:19
    brain you need to know. The cerebral
  • 00:09:21
    cortex is responsible for higher level
  • 00:09:23
    functions like memory, speech, and
  • 00:09:25
    problem solving. The cerebellum is
  • 00:09:27
    responsible for your motor skills,
  • 00:09:28
    movement, balance, and coordination. The
  • 00:09:30
    medulla gata controls unconscious
  • 00:09:33
    actions your body takes. You don't think
  • 00:09:35
    about them, like your heart and
  • 00:09:36
    breathing rates. It's also what controls
  • 00:09:38
    the release of adrenaline. MRI scans,
  • 00:09:41
    magnetic resonance imaging, are a way of
  • 00:09:43
    seeing the activity in your brain
  • 00:09:45
    safely. If something goes wrong with
  • 00:09:46
    your brain, though, it can be very
  • 00:09:48
    difficult or impossible to treat without
  • 00:09:50
    damaging important parts of it. Your
  • 00:09:52
    eyes are the most mind-bogglingly
  • 00:09:54
    designed cameras ever conceived of.
  • 00:09:56
    Accommodation is the eyes ability to
  • 00:09:58
    change the shape of the lens in order to
  • 00:10:00
    focus light that comes from objects that
  • 00:10:02
    are different distances away on the
  • 00:10:04
    retina. To focus light that comes from
  • 00:10:05
    objects that are far away, the siliary
  • 00:10:08
    muscles relax and the suspensory
  • 00:10:10
    ligaments tighten. They're both
  • 00:10:11
    connected to the lens. This results in
  • 00:10:13
    the lens becoming thin and that means
  • 00:10:16
    that light is only refracted a little
  • 00:10:18
    bit and that focuses the light on the
  • 00:10:19
    retina. To focus on near objects, the
  • 00:10:22
    opposite is true. The siliary muscles
  • 00:10:24
    contract. The suspensory ligaments
  • 00:10:26
    slacken and the lens becomes fatter or
  • 00:10:28
    thicker and so that means that it
  • 00:10:30
    becomes more powerful actually. So light
  • 00:10:31
    is refracted more which means that the
  • 00:10:33
    light coming from the object still
  • 00:10:34
    converges meets focuses on the retina.
  • 00:10:38
    So you can see a clear image. The pupil,
  • 00:10:40
    the hole in the iris can change size
  • 00:10:42
    depending on the light intensity hitting
  • 00:10:44
    the eye. The cornea is the transparent
  • 00:10:46
    outer layer where light enters the eye.
  • 00:10:48
    It has a slight lensing effect itself.
  • 00:10:50
    While the white surface that covers the
  • 00:10:52
    rest is called the scara. The light is
  • 00:10:54
    focused then on the retina at the back
  • 00:10:56
    of the eye which consists of rod and
  • 00:10:58
    cone cells which respond to light. Rods
  • 00:11:00
    can only detect light intensity so no
  • 00:11:02
    color while there are three different
  • 00:11:04
    types of cones which detect green, blue
  • 00:11:06
    or red wavelengths of light. a mix of
  • 00:11:09
    which will produce the colors we then
  • 00:11:11
    perceive when the signal reaches our
  • 00:11:13
    brain via the optic nerve. Myopia is the
  • 00:11:15
    medical term for short-sightedness. You
  • 00:11:17
    can't focus on far objects. Hyperopia is
  • 00:11:21
    long-sightedness. Glasses or contact
  • 00:11:23
    lenses are usually used to mitigate this
  • 00:11:25
    by slightly converging or diverging the
  • 00:11:27
    light before it enters the eye. Laser
  • 00:11:29
    eye surgery aims to change the shape of
  • 00:11:30
    the cornea to achieve the same effect.
  • 00:11:33
    In order to reproduce sexually, gametes,
  • 00:11:35
    sex cells, must be made. This happens by
  • 00:11:38
    meiosis. For example, in the testes to
  • 00:11:40
    make sperm. The chromosomes in a diploid
  • 00:11:42
    cell that is 23 pairs for us are copied.
  • 00:11:46
    Similar chromosomes then pair up and the
  • 00:11:48
    genes are swapped between them. The cell
  • 00:11:50
    then divides to make two diploid cells
  • 00:11:52
    which then divide again along with the
  • 00:11:54
    chromosomes themselves to make four
  • 00:11:56
    hloid cells ready to fuse with another
  • 00:11:59
    gamet which in this case would be an
  • 00:12:00
    egg. This is one way that variation
  • 00:12:02
    occurs in offspring. Plants do this with
  • 00:12:04
    pollen and egg cells, but they can also
  • 00:12:06
    reproduce asexually. But as it doesn't
  • 00:12:08
    involve gametes, the daughter cells will
  • 00:12:10
    be genetically identical. So a clone of
  • 00:12:12
    the parent is made by mitosis. An
  • 00:12:15
    advantage of sexual reproduction is that
  • 00:12:16
    variation occurs, which can result in
  • 00:12:18
    organisms becoming better suited to
  • 00:12:20
    their environment. More on this in a
  • 00:12:21
    bit. So more likely to survive. An
  • 00:12:23
    advantage for asexual is that only one
  • 00:12:25
    parent is needed. So for example, a
  • 00:12:27
    plant on its lonesome can still
  • 00:12:28
    reproduce in order for the species to
  • 00:12:30
    survive. Another thing that can do both
  • 00:12:32
    is the parasite that causes malaria.
  • 00:12:35
    Genome is the term given to all the
  • 00:12:37
    genetic material in an organism. This
  • 00:12:39
    code is stored in DNA, of course, which
  • 00:12:41
    is a two stranded polymer in a double
  • 00:12:44
    helix shape. A gene is a section of DNA
  • 00:12:47
    that codes for a specific protein. The
  • 00:12:49
    human genome project completed its
  • 00:12:51
    initial goal in 2003 when scientists
  • 00:12:53
    mapped out what every gene is
  • 00:12:55
    responsible for coding. This is powerful
  • 00:12:57
    because it can help us identify what
  • 00:12:59
    genes cause diseases or inherited
  • 00:13:01
    disorders. Genotype is the term given to
  • 00:13:04
    what code is stored in your DNA
  • 00:13:06
    specifically. While phenotype is how
  • 00:13:09
    that code is expressed in your
  • 00:13:11
    characteristics, what proteins are made.
  • 00:13:14
    It affects your physiology. For triple,
  • 00:13:16
    you need to know that the monomers
  • 00:13:17
    between the two strands are called
  • 00:13:19
    nucleotides, and they're made from a
  • 00:13:21
    sugar and phosphate group, of which
  • 00:13:23
    there are four types, A, T, C, and G.
  • 00:13:26
    You don't need to know what the names
  • 00:13:28
    are, but A and T always match to each
  • 00:13:30
    other in the sequence, as do C, and G.
  • 00:13:34
    Every three of these bases, we can call
  • 00:13:36
    them, are a code for an amino acid. The
  • 00:13:38
    sequence is copied by mRNA. This copy is
  • 00:13:42
    then taken out of the nucleus to a
  • 00:13:43
    ribosome in the cell where amino acids
  • 00:13:46
    are connected in the order needed which
  • 00:13:48
    makes a protein the shape of which
  • 00:13:50
    affects its function. They need to be
  • 00:13:52
    folded as well first. Harmful mutations
  • 00:13:54
    can change a gene so much that it
  • 00:13:56
    results in a protein being synthesized
  • 00:13:58
    that doesn't do the job it's supposed
  • 00:13:59
    to. We now know that some DNA however
  • 00:14:02
    doesn't directly code for proteins, but
  • 00:14:04
    it influences how other genes are
  • 00:14:06
    expressed. This is the realm of
  • 00:14:07
    epigenetics and it's changing the way
  • 00:14:09
    that we view DNA quite drastically. Back
  • 00:14:12
    to double. Some characteristics are
  • 00:14:14
    controlled by just one gene like color
  • 00:14:16
    blindness. These different types of the
  • 00:14:18
    same gene are called alals. Usually
  • 00:14:20
    characteristics are dependent on two or
  • 00:14:22
    more genes though and them interacting.
  • 00:14:25
    Dominant alals are those that result in
  • 00:14:27
    a characteristic being expressed even if
  • 00:14:29
    there is another alil present, a
  • 00:14:31
    recessive al. For example, if you have
  • 00:14:33
    the alals big B, little B for eye color,
  • 00:14:36
    big B being brown, little B being blue,
  • 00:14:38
    you will have brown eyes. It's only when
  • 00:14:41
    there's no dominant alil in this case
  • 00:14:43
    that the recessive alil is expressed. So
  • 00:14:46
    me having blue eyes, I must have the
  • 00:14:48
    gene little B little B. Big B big B or
  • 00:14:51
    little B little B are called homozygous
  • 00:14:54
    as they only have one type of alil.
  • 00:14:55
    Whereas big B little B is what we call
  • 00:14:57
    hetererozygous. We can use a punit
  • 00:14:59
    square to predict the probability of a
  • 00:15:02
    certain phenotype. My parents have brown
  • 00:15:04
    eyes, but they both have hetererozygous
  • 00:15:06
    alals for eye color. There are three
  • 00:15:08
    different outcomes of these combining
  • 00:15:10
    with a 25% chance of making me. That's
  • 00:15:13
    little B, little B. So, I'm not so much
  • 00:15:15
    one in a million, more one in four. My
  • 00:15:17
    sister has brown eyes, but her son has
  • 00:15:20
    blue eyes, so she must be big B, little
  • 00:15:22
    B. Eye color is by the by, but some
  • 00:15:24
    alals can result in disorders being
  • 00:15:26
    inherited. For example, polactylene,
  • 00:15:29
    extra fingers or toes, which is caused
  • 00:15:31
    by a dominant alil, or cystic fibrosis,
  • 00:15:34
    which is caused by a recessive alil.
  • 00:15:36
    Even if two parents don't have cystic
  • 00:15:38
    fibrosis, they could still be carrying
  • 00:15:40
    the recessive alil. So, their child
  • 00:15:42
    could have the disorder. Human DNA is
  • 00:15:45
    contained in 23 pairs of chromosomes,
  • 00:15:46
    but only one pair determines sex. If you
  • 00:15:49
    have XX chromosomes, you are female. XY,
  • 00:15:52
    you're male. The expression of these
  • 00:15:53
    genes affects every cell in your body,
  • 00:15:56
    every aspect of your physiology. We can
  • 00:15:58
    also make a punit square for these. As
  • 00:16:00
    you can see, there's a 50/50 chance of a
  • 00:16:02
    child being male or female. Variation is
  • 00:16:05
    a result of the genes inherited from an
  • 00:16:06
    organism's parents and also
  • 00:16:08
    environmental factors. Charles Darwin's
  • 00:16:10
    theory of evolution states that random
  • 00:16:12
    variation in offspring will result in
  • 00:16:14
    some being better suited to the
  • 00:16:15
    environment than others and so are more
  • 00:16:17
    likely to survive and reproduce. But
  • 00:16:19
    like we've seen, we know that our DNA is
  • 00:16:20
    able to respond to the environment in
  • 00:16:22
    order to turn genes on and off depending
  • 00:16:24
    on whether they're needed or not. For
  • 00:16:26
    example, there were some blind
  • 00:16:27
    translucent skin mackerel that were
  • 00:16:29
    found in a dark cave. When they were
  • 00:16:30
    bred with normal mackerel in sunlight,
  • 00:16:32
    they regained fully working eyes and
  • 00:16:34
    opaque skin within a few generations.
  • 00:16:36
    Jean Baptiste Lamar's theory asserted
  • 00:16:38
    that adaptation of variation is guided
  • 00:16:40
    by DNA in response to a changing
  • 00:16:43
    environment. This was scoffed at, but we
  • 00:16:45
    now know that there is some truth to
  • 00:16:46
    this thanks to the discoveries made in
  • 00:16:48
    epigenetics. Bacterial resistance is
  • 00:16:51
    largely considered to be evidence of
  • 00:16:52
    Darwinian evolution. Bacteria divide,
  • 00:16:55
    mutations occur, and inevitably a
  • 00:16:57
    bacterium with an increased resistance
  • 00:16:58
    to antibiotics will be produced. That's
  • 00:17:01
    why we only want to use them when
  • 00:17:03
    absolutely necessary. It also means you
  • 00:17:04
    have to complete the whole course of
  • 00:17:06
    antibiotics. If you don't, weaker
  • 00:17:08
    bacteria will have been killed off, but
  • 00:17:10
    more resistant ones will still be there,
  • 00:17:12
    and then they'll reproduce and make you
  • 00:17:14
    even more ill. If organisms are able to
  • 00:17:16
    produce fertile offspring, we say
  • 00:17:18
    they're of the same species. Tigers and
  • 00:17:20
    lions have been known to make like
  • 00:17:22
    offspring, but as they're infertile, we
  • 00:17:24
    don't consider tigers and lions to be
  • 00:17:26
    the same species. We can selectively
  • 00:17:28
    breed living things with desired
  • 00:17:30
    characteristics to enhance these. For
  • 00:17:32
    example, breeding dogs to produce breeds
  • 00:17:34
    like Labrador's colleagues. And if
  • 00:17:36
    you're into undesirable characteristics,
  • 00:17:38
    pugs, too. Just for triple, Johan Mendel
  • 00:17:41
    was one of the first people to assert
  • 00:17:42
    their characteristics were determined by
  • 00:17:44
    units that are passed on to offspring.
  • 00:17:47
    Due to the discovery of genes and
  • 00:17:48
    chromosomes, he was proven largely
  • 00:17:50
    correct. Advancements in biology over
  • 00:17:53
    the last few decades mean that we can
  • 00:17:54
    also genetically modify organisms if we
  • 00:17:57
    don't want to wait for selective
  • 00:17:58
    breeding to do the job or when it can't
  • 00:18:00
    actually achieve what we want it to, for
  • 00:18:02
    good or ill. For example, scientists
  • 00:18:04
    have genetically modified bacteria to
  • 00:18:06
    produce insulin, which can be harvested
  • 00:18:08
    and used to treat people with diabetes.
  • 00:18:10
    Genetically modifying crops is one way
  • 00:18:12
    of boosting their yields or nutritional
  • 00:18:15
    value. For example, golden rice has a
  • 00:18:17
    gene inserted into it that produces
  • 00:18:19
    vitamin A. It was developed to combat
  • 00:18:22
    diets in certain areas that were lacking
  • 00:18:23
    in this. Other GM crops have been
  • 00:18:26
    modified to be more resistant to
  • 00:18:27
    diseases, for example. The process of
  • 00:18:30
    genetic engineering goes as follows. A
  • 00:18:32
    gene is chemically cut from the organism
  • 00:18:34
    that has the desired characteristic.
  • 00:18:36
    This is done using enzymes. For example,
  • 00:18:39
    the gene from a jellyfish that causes it
  • 00:18:40
    to glow in the dark. This is then
  • 00:18:42
    inserted into a vector like a bacteria
  • 00:18:45
    plasmid or virus that in turn inserts
  • 00:18:48
    the gene into another organism, say a
  • 00:18:50
    bunny rabbit. But it must be done in the
  • 00:18:52
    early stage of its development. Say just
  • 00:18:54
    after the egg has been fertilized, as
  • 00:18:56
    this is the only way you can be sure
  • 00:18:58
    that the gene will be present in every
  • 00:19:00
    cell of the bunny as it grows. By the
  • 00:19:02
    way, I didn't make up this example. This
  • 00:19:04
    has actually been done. Fossils are the
  • 00:19:06
    remains of organisms that died a very
  • 00:19:08
    long time ago. The classic fossils we
  • 00:19:10
    think about are the bones that we dig
  • 00:19:12
    up, but they're not strictly speaking
  • 00:19:14
    bones anymore. In fact, minerals have
  • 00:19:16
    replaced the organic material to
  • 00:19:18
    effectively leave rock in exactly the
  • 00:19:21
    same shape as the bone. Sometimes there
  • 00:19:23
    can still be organic tissue left behind
  • 00:19:25
    if the conditions for decay are not
  • 00:19:27
    present. Footprints left in mud that
  • 00:19:29
    have hardened over time, for example,
  • 00:19:31
    are also considered fossils, as well as
  • 00:19:34
    any other trace of an organism. It
  • 00:19:36
    doesn't have to be the organism itself.
  • 00:19:38
    CVD, cardiovascular disease, is an
  • 00:19:41
    example of a non-communicable disease as
  • 00:19:43
    the cause of it comes from inside your
  • 00:19:45
    body. Other examples of such diseases
  • 00:19:48
    include autoimmune conditions like
  • 00:19:50
    allergic reactions and cancer. A
  • 00:19:52
    communicable disease must be caused by a
  • 00:19:54
    pathogen that enters your body that will
  • 00:19:56
    cause a viral, bacterial, or fungal
  • 00:19:59
    infection. Again, more on these in a
  • 00:20:01
    bit. Back to non-communicable diseases.
  • 00:20:03
    Obesity and too much sugar can cause
  • 00:20:05
    type 2 diabetes. A bad diet, smoking,
  • 00:20:08
    and lack of exercise can affect the risk
  • 00:20:09
    of heart disease. Alcohol can cause
  • 00:20:12
    liver diseases. Smoking, lung disease,
  • 00:20:14
    or cancer. A carcinogen is the name
  • 00:20:16
    given to anything that increases the
  • 00:20:18
    risk of cancer, for example, ionizing
  • 00:20:20
    radiation. Cancer is a result of damaged
  • 00:20:23
    cells dividing uncontrollably, leading
  • 00:20:25
    to tumors. Benign cancers don't spread
  • 00:20:28
    through the body, and they're relatively
  • 00:20:29
    easy to treat. However, malignant
  • 00:20:31
    cancers are when these cancerous cells
  • 00:20:33
    spread through your body, much worse.
  • 00:20:36
    BMI stands for body mass index. It's an
  • 00:20:39
    indication of whether or not somebody
  • 00:20:41
    has a healthy weight or not relative to
  • 00:20:43
    their height. The equation is this. BMI
  • 00:20:45
    is equal to weight. Well, mass we know,
  • 00:20:47
    don't we? Divided by height squared. And
  • 00:20:50
    whatever number you have will put you
  • 00:20:51
    into certain bands will determine
  • 00:20:53
    whether or not you're a healthy BMI,
  • 00:20:55
    overweight, obese, etc. As mentioned
  • 00:20:58
    just now, communicable diseases are
  • 00:21:00
    caused by pathogens. That can be
  • 00:21:02
    viruses, bacteria, fungi, or protests.
  • 00:21:05
    These are single-sellled parasites. They
  • 00:21:07
    all reproduce in your body and cause
  • 00:21:09
    damage. But viruses can't reproduce by
  • 00:21:11
    themselves. A virus is in fact just a
  • 00:21:13
    protein casing that surrounds genetic
  • 00:21:15
    code that it injects into a cell, which
  • 00:21:18
    causes the cell to produce more copies
  • 00:21:20
    of the virus. The cell explodes, and the
  • 00:21:23
    virus goes on to infect more cells.
  • 00:21:25
    Creepy, isn't it? HIV is an STD or STI,
  • 00:21:28
    sexually transmitted disease or
  • 00:21:30
    infection that compromises your immune
  • 00:21:32
    system. This is also called AIDS for
  • 00:21:34
    short. It can also be spread by people
  • 00:21:36
    sharing needles. Bacteria on the other
  • 00:21:39
    hand release toxins that damage your
  • 00:21:41
    body's cells. Fungi do something similar
  • 00:21:44
    like athletes foot while protest do all
  • 00:21:46
    sorts of different things. For example,
  • 00:21:48
    malaria is caused by a protest that
  • 00:21:49
    burrows into red blood cells to multiply
  • 00:21:51
    then burst out destroying the red blood
  • 00:21:53
    cell in the process. It's spread by
  • 00:21:55
    mosquitoes. So, we say mosquitoes are
  • 00:21:57
    the vector for the disease. Our bodies
  • 00:22:00
    are excellent at protecting us from
  • 00:22:01
    these pathogens, though, thank goodness.
  • 00:22:03
    Skin is the first barrier to them
  • 00:22:05
    entering. And if they do enter your nose
  • 00:22:07
    and trachea, they can be trapped by
  • 00:22:09
    mucus. Acid and enzymes in your
  • 00:22:11
    digestive system will destroy them, too.
  • 00:22:13
    If they still manage to enter the
  • 00:22:15
    bloodstream, though, white blood cells
  • 00:22:16
    are ready to combat them. One type of
  • 00:22:18
    these are called lymphosytes. They
  • 00:22:19
    produce antitoxins to neutralize the
  • 00:22:21
    poisons pathogens produce and also they
  • 00:22:24
    make antibodies which stick to the
  • 00:22:26
    antigen on a pathogen and this stops
  • 00:22:28
    them from being able to infect more
  • 00:22:29
    cells and it makes them clump together.
  • 00:22:32
    Fagasites are then able to ingest them
  • 00:22:34
    and destroy them. An antigen on a
  • 00:22:36
    pathogen will have a specific shape. So
  • 00:22:38
    that means only an antibbody that fits
  • 00:22:40
    it will neutralize it. If pathogens are
  • 00:22:43
    unknown to the immune system,
  • 00:22:44
    lymphosytes will start making all
  • 00:22:46
    different shapes until one fits.
  • 00:22:48
    Miraculously, your immune system will
  • 00:22:50
    then store a copy of this antibbody next
  • 00:22:52
    to a copy of the antigen, so it's ready
  • 00:22:54
    to stop it from causing an infection
  • 00:22:56
    next time you're exposed to it. You now
  • 00:22:58
    have immunity. A vaccine is a dead or
  • 00:23:01
    inert version of a pathogen, usually a
  • 00:23:03
    virus, that exposes your immune system
  • 00:23:05
    to the pathogen so it can produce the
  • 00:23:07
    antibbody without it infecting you. For
  • 00:23:09
    example, the flu vaccine, you're
  • 00:23:10
    injected with the virus that has been
  • 00:23:12
    irdiated, so the DNA has been damaged
  • 00:23:15
    inside, so it can't do the job.
  • 00:23:17
    Incidentally, the co jab, however, was
  • 00:23:19
    intended to work differently. Instead,
  • 00:23:20
    you're injected with the DNA,
  • 00:23:22
    technically mRNA, needed to trick your
  • 00:23:25
    cells into synthesizing part of the
  • 00:23:27
    virus, including the antigen. It was the
  • 00:23:29
    first widely used jab that used this
  • 00:23:31
    mRNA technology. Just for triple,
  • 00:23:34
    bacteria multiply by binary fision. So,
  • 00:23:37
    the number doubles every, say, 10
  • 00:23:39
    minutes. So, if we started with one
  • 00:23:40
    bacterium, after an hour, we'd have 2 ^
  • 00:23:43
    of 6, that's 64. After 6 hours that's 36
  • 00:23:47
    lots of 10 minutes. So in theory we'd
  • 00:23:49
    have 2 ^ of 36. That's in standard form
  • 00:23:52
    6.87 * 10. We can do a practical on this
  • 00:23:56
    by producing a culture on agar in a
  • 00:23:58
    petra dish using aseptic technique. That
  • 00:24:00
    is making sure nothing else contaminates
  • 00:24:02
    the culture. We lift the lid of the dish
  • 00:24:04
    towards a flame which causes other
  • 00:24:06
    microbes in the air to move away and
  • 00:24:07
    upwards from the dish and it destroys
  • 00:24:09
    them too. Using sterilized equipment, we
  • 00:24:11
    can either put a drop of bacteria
  • 00:24:13
    culture in the middle or spread it all
  • 00:24:14
    around and put spots of different
  • 00:24:16
    antibiotics on top instead. We put a few
  • 00:24:18
    bits of tape around the dish to hold the
  • 00:24:20
    lid on, but not all the way around,
  • 00:24:22
    otherwise air will not get in and the
  • 00:24:24
    bacteria will respire anorobically. We
  • 00:24:26
    then incubate it at 25ยฐ. Once the
  • 00:24:28
    culture has grown, we can either
  • 00:24:30
    calculate the size of the culture from
  • 00:24:31
    an initial drop or the area in which
  • 00:24:33
    bacteria did not grow or were killed by
  • 00:24:35
    an antibiotic to then compare with
  • 00:24:37
    others. In both cases, we use p r^
  • 00:24:39
    squ or p d^2 over 4 to calculate
  • 00:24:42
    the area of the circles. Antibiotics
  • 00:24:44
    kill bacteria. They don't kill viruses.
  • 00:24:47
    Penicellin was the first one. There are
  • 00:24:49
    good bacteria in our bodies. So,
  • 00:24:51
    antibiotics are designed to be as
  • 00:24:53
    specific as possible because you don't
  • 00:24:54
    want to damage those or your body cells
  • 00:24:56
    either. Problem is, as bacteria mutate,
  • 00:24:59
    they can become resistant to them. So,
  • 00:25:01
    the more you use them, the less
  • 00:25:02
    effective they become. Drugs used to be
  • 00:25:04
    extracted from plants and other
  • 00:25:06
    organisms. For example, aspirin comes
  • 00:25:08
    from willow trees, penicellin from a
  • 00:25:10
    mold. Now synthesizing drugs is one of
  • 00:25:12
    the biggest industries on the planet.
  • 00:25:14
    They have to be trial to see how
  • 00:25:15
    effective they are and to check for side
  • 00:25:17
    effects. First, we do lab trials on cell
  • 00:25:20
    tissue, then trials on animals. Next,
  • 00:25:22
    human trials. We give the drug to a
  • 00:25:24
    group of people, but we also give a
  • 00:25:26
    placebo to a control group without
  • 00:25:28
    telling them. Say a pill that's just
  • 00:25:30
    sugar, not the actual drug. This is what
  • 00:25:32
    we call a blind trial because the test
  • 00:25:35
    subjects don't know what they're taking.
  • 00:25:37
    A double blind trial is when even those
  • 00:25:39
    analyzing the results from the tests
  • 00:25:42
    aren't aware of which group is which.
  • 00:25:44
    And that's to eliminate any bias. Just
  • 00:25:46
    for triple, this is a crazy one.
  • 00:25:48
    Monocclonal antibodies. They're made
  • 00:25:50
    from clones of a cell which is able to
  • 00:25:52
    produce a specific antibbody to combat a
  • 00:25:55
    disease. This is achieved by combining
  • 00:25:57
    lymphosytes from mice to tumor cells and
  • 00:25:59
    this makes a hybrid cell. This is then
  • 00:26:02
    cloned to produce a lot of antibodies
  • 00:26:04
    ready to treat a patient. These
  • 00:26:06
    monoconal antibodies can also be used
  • 00:26:07
    for medical diagnosis, pathogen
  • 00:26:10
    detection in a lab, or even just
  • 00:26:11
    identifying molecules in tissue by
  • 00:26:14
    binding them to a dye so they glow when
  • 00:26:17
    grouped together because they'll be
  • 00:26:19
    designed to bind to a specific molecule.
  • 00:26:21
    The downside to these is that the side
  • 00:26:22
    effects are turning out to be worse than
  • 00:26:24
    scientists expected. So, I hope you
  • 00:26:26
    found that helpful. Leave a like if you
  • 00:26:28
    did and pop any questions or comments
  • 00:26:30
    below. And hey, after you've done the
  • 00:26:31
    exam, come back here and tell us all how
  • 00:26:33
    you found it. We'd love to know. Click
  • 00:26:34
    on the card to go to the playlist for
  • 00:26:36
    all six papers, and I'll see you in the
  • 00:26:38
    next video.
Tags
  • Biology
  • Cells
  • Genetics
  • Natural Selection
  • Health
  • Enzymes
  • Osmosis
  • Vaccines
  • Monoclonal Antibodies
  • Human Genome Project