Biology B3 Revision by wuyunyi


									Biology B3 Revision
                   What’s in a cell?
                                       Cytoplasm where
                                       many chemical
Cell membrane controls                 reactions happen
the movement of
substances in and out of
the cell

                                             information is
                                             carried on

               Nucleus carries
               genetic information
 • Chemical found inside
   the nucleus.
 • Forms structures
   called chromosomes.
 • Section of a
   chromosome is called
   a gene.
 • Each gene is a code
   for making a protein.
 • Proteins are needed
   for growth and repair.
 • Everyone has their
   own unique DNA code.
• The production of proteins is called protein

• Any time your body needs a particular
  protein, like an enzyme, a new one is
  made using the code on the DNA strand.
            DNA Fingerprinting
• Used to identify people from a fragment of
  DNA in a blood or hair or skin or semen
                              Fragments of DNA are
                              placed on a gel and
                              separated by an
                              electric current.
                              Banding of DNA
                              fragments can be

 So….. Who did it?
           DNA Replication
• Every time a cell divides by mitosis, the
  DNA must replicate itself first.
DNA Replication- Higher
         New bases pair up with their
         complementary base to form two new
         double strands.

         End up with two identical DNA strands.

         Used for mitosis to make genetically
         identical cells for growth and repair.
• Biological catalysts.
• Protein that speeds up a chemical reaction.
• Used in all sorts of reactions:
  – Making cheese                 photosynthesis
  – Respiration
  – Photosynthesis
  – Protein synthesis
                        enzymes are specific
                        because their active site
                        will only fit one type of
• Enzyme –controlled reactions are affected
  – pH (measure the acidity of a solution)
  – temperature
               Lock and Key- Higher

1. The enzyme acts like    2. The substrate fits into   3. Once the substrate
a lock, and the            the active site. The         has broken down, the
substrate fits in like a   substrate gets broken        enzyme releases it.
key                        down.                        The enzyme is not
                                                        changed so can be
                                                        used again.
Denaturing Enzymes- Higher
    • Enzyme is a protein, which is
      made up of a chain of amino
    • At too high temperatures or the
      wrong pH, the structure of the
      enzyme is changed, so the
      substrate no longer fits into the
      active site.
• Diffusion is the movement of a substance
  from a region of high concentration to a
  region of low concentration.

                        Semi-permeable membrane
    Where diffusion occurs in the body

• There is more oxygen in
  the alveoli than in the
  blood, so oxygen moves
  by diffusion into the blood

• There is more carbon
  dioxide in the blood than
  in the alveoli, so it moves
  by diffusion into the
  alveoli and it is breathed
        Digestive system

• After eating there is a high
  concentration of food
  molecules in the small
  intestine compared to the
  blood stream.

• Food molecules move by
  diffusion into the blood.
Diffusion and the placenta
             A foetus growing inside its mother’s
             uterus needs food and oxygen to
             stay alive.

             It also needs to be able to get rid of
             waste products.

             In the placenta the mother’s blood
             and the baby’s blood is separated
             by a semi-permeable membrane.

             Substances are exchanged between
             the two types of blood by diffusion.
           Diffusion and the leaf
• Plants use diffusion to exchange gases
  through the special holes in their leaves
  called stomata.
                                                         Leaf cells

  Xylem vessels
                                    Water enters air
  bring water from                  space by
  roots into leaf cells             evaporation

                          Water diffuses out through stomata
                          to the outside because of the high
                          concentration of water in the air
           Diffusion- Higher

• The rate of diffusion can be increased by:
  – Increasing the surface area
  – Decreasing the diffusion distance
  – Increasing the concentration difference
                                Small Intestine
                                            Increasing the surface area:
Decreasing the diffusion distance:
                                            The surface of the small
Villus is only one cell thick               intestine is covered with villi that
                                            increase its surface area

A greater concentration difference:
A good blood supply means the
digested food is carried away quickly
to maintain the concentration
Increased surface area:
Large number of alveoli
inside the lungs

   Greater concentration difference:
                                       Decreasing the diffusion distance:
   Breathing makes sure there is a
   higher concentration of O2 in the   Alveolus wall is only one cell thick
• It is important to move
  substances across the
  placenta as quickly as

• To speed up this movement,
  the placenta has:
   – A very large surface area
   – A very thin semi-
      permeable membrane so
      substances only have a
      short distance to diffuse
                            The Leaf
To increase the rate of gas exchange, the leaf has a large surface area.
The under-surface of the leaf also has many stomata through which the
gases can diffuse.

                                              Guard cells

  • A synapse is a gap between two neurones
    (nerve cells).
  • To carry a signal from one neurone to the next,
    the synapse releases a transmitter substance.
  • This is a special chemical that can diffuse across
    the gap between the two neurones.
  • When it reaches the other side of the synapse, it
    causes an impulse to travel along the neurone.
Direction of impulse
    Transport around the body
• Blood is made up of 4 things:
  – Plasma- a yellow liquid that transports carbon
    dioxide, nutrients, hormones and other things around
    the body.

  – Red Blood cells- contain a chemical called
    haemoglobin which binds with oxygen and transports
    it around the body.

  – White blood cells- used for fighting diseases.

  – Platelets- fragments of red blood cells used for
    clotting blood.
              Blood Vessels
• Three types:
  – Artery carries blood Away from the heart.
  – Vein carries blood In to the heart.
  – Capillaries join arteries to veins. It is through
    capillary membranes that substances are
    exchanged between the blood and cells.
Blood Vessels- Higher Level
      • Artery- thick muscular and elastic
        wall to help it withstand high blood
        pressure as blood leaves the heart.

      • Vein- large lumen to help blood
        flow at low pressure; valves stop
        blood from flowing the wrong way.

      • Capillaries- thin, permeable wall to
        allow exchange of material with
        body tissue.
The heart pumps blood around the
The right side of the heart pumps
the blood to the lungs to collect
oxygen and drop off carbon dioxide.
The left side of the heart has much
more muscle than on the right side
because it pumps the blood to the
rest of the body.
Valves in the heart prevent the
blood flowing in the wrong direction.
The heart beats faster when you
exercise to supply your muscles
with the oxygen and glucose it
needs for respiration to make
      Double Circulation- Higher
One circuit links the heart and lungs called
the pulmonary circulation.

The other circuit links the heart and the

The left side of the heart has more muscle
so it is able to pump the blood at much
higher pressure to the rest of the body.
                Heart Disease
• Saturated animal fats such as cholesterol can stick to the
  walls of arteries slowing down or blocking the flow of
• If this happens in a main blood vessel it can cause a
  heart attack or a stroke.
• A blockage in a coronary artery (this supplies the heart
  itself with food and oxygen) can cause serious heart
                                     Treating heart disease
                                     Heart transplants- patients
                                     must take drugs to stop their
                                     body rejecting their new
                                     Pacemakers- attached to a
                                     heart to help it beat.
       Cell Division (Mitosis)
• Used for:
  – Growth
  – Repair damaged tissue
  – Replace worn out cells

• A human body cell contains 46
  chromosomes arranged in 23 pairs.
• These cells are called diploid cells,
  because they contain the full amount of
Mitosis- Higher Level
   Eggs and Sperm (Gametes)
• Egg
  – Much larger than a sperm because it contains a food store for
    the growing embryo
• Sperm
  – Much smaller than an egg to help it swim
  – Tail to help it swim
  – Millions are released to increase the chance of one reaching the
  – Head contains an acrosome
    that releases enzymes to help
    digest the egg cell membrane.
  – Contains a large number of
    mitochondria to release energy
    for motion.
• Gametes are made by a special type of cell
  division called meiosis that produces cells with
  half the amount of DNA in it.
• These cells are called haploid.
• When two haploid cells meet, they make a
  diploid cell.
• Meiosis makes every sperm and egg different,
  as they each contain a different combination of
• This is why brothers and sisters look different.
Meiosis- Higher Level
       Animal and Plant Growth
•   Animals grow to a certain size then stop.
•   Plants can continue to grow.
•   Plant cells elongate rather than divide.
•   Plants do cell division at the tips of shoots
    and roots.
                          Stem Cells
• After an egg is fertilised it contains a group
  of cells called stem cells.
• Stem cells are able to grow into any type
  of cell.
• Once the cells have become differentiated
  into skin or bone or blood etc. they cannot
  grow into any other cell.
• In adults, bone marrow contain stem cells
  that turn into different types of blood cells.
   What is a Stem Cell?
               Human Growth
1.   Infancy
2.   Childhood
3.   Adolescence (puberty)
4.   Adulthood (maturity)
5.   Old age

•    Gestation is the length of time form fertilisation
     to birth.
•    Different parts of the foetus and baby grow at
     different rates.
•    The brain and head develop quickly to
     coordinate the complex human structure and
     chemical activity.
Growth problems- Higher Level
Poor weight can indicate problems with
baby’s digestive system.

Larger than normal head size can indicate
fluid collection on the brain or the separate
skull bones not fusing together.
     Controlling Plant Growth
• Special chemicals called hormones control
  different processes in a plant:
  – Growth of shoots towards light (phototropism)
  – Growth of roots downwards in direction of
    gravity (geotropism)
  – Growth of flowers
  – Ripening of fruit
Auxin- Higher Level
             • Plants grow
               towards the sun.
             • Why?
             • Auxin is destroyed
               by sunlight, so is
               found on the side of
               the stem in the
             • It causes only those
               cells in the shade to
             • This tips the stem
               over towards the
    Commercial Uses of Plant Hormones
• Weedkiller- makes weeds grow too fast and
  they die
• Growing roots- taking cuttings from plants to
  clone them
• Seedless fruits- cause fruit to grow even when
  the flowers have not been fertilised
• Transporting fruits- hormones slow down
  ripening of fruit so they do not get as damaged
  during transportation
• Sleeping seeds- hormones can be used to
  force seeds to germinate
• Slowing down growth- so fruit does not fall off
  the tree before the harvest
        Selective Breeding
• Farmers choose the animals and plants
  with the characteristics they want.
• They then breed them together to produce
  the offspring with the desired
   Selective Breeding -Higher
• Often involves breeding animals that are
  closely related.
• This is called inbreeding.
• It reduces the gene pool, so there is not as
  much variation in a species.
• The less variation in a species, the less
  chance that species has of surviving a
  change in the environment or a new
          Mutations- Higher Level
• A mutation is a change in the DNA base sequence.

 original base code               mutation

• Mutation means a different amino acid is coded for, so
  a different protein is made.

• This can cause all sorts of problems for the living

• Mutations can be caused by radiation, chemicals or
       Genetic Engineering
• Scientists can take genes form one
  organism and put them into a different
• These changes are called genetic
  engineering or genetic modification (GM).
     • Genetic engineering involves adding a
       gene to the DNA of an organism.
     • The altered organism is described as
       genetically modified (GM).

Rice does not                         Rice now
contain vitamin                       produces
A                                     vitamin A
                          into rice

Carrots do contain
vitamin A
                     Vitamin A gene
                     extracted from
Advantages and disadvantages
• Developing crops resistant to herbicides, frost and
• Large supplies of insulin can be made using bacteria.
• Rice can have vitamin A added to it using a gene from
  carrots. Vitamin A is needed for night blindness.

• Both methods could cause unexpected problems, for
  example, some people are concerned how our bodies
  will react to GM foods in the future.
• Some people believe that mixing different animal genes
  is like ‘playing God’.
     How Genetic Engineering Works-
             Higher Level
•   Select the characteristic
•   Identify and isolate the gene
•   Insert the gene into the chromosome of a different organisms
•   Replicate (copy) the gene in the organism and produce the

                        DNA in ring                 Insulin added
                                        DNA cut     using ligase
                        shape, enzyme   open                        GM E.coli
     E.Coli bacterium   added                       enzyme
                                                                    starts making

        Chromosome        DNA                     DNA cut open
        from human        extracted               to get insulin
        pancreas cell     from human              gene
   • Cloning produces copies of animals and plants that are
     genetically identical to each other.
   • Cloning involves one parent and is called asexual
   • Natural clones are identical twins.
   • Animals can be cloned by embryo transplantation.
                                                   A cow is artificially
                                                   inseminated with
        Sperm is collected                         the sperm
        form bull
                                              When the fertilised egg
                                              divides into an 8-cell
                                              embryo, it is collected
                                              and split into four 2-cell
Each embryo is then                           embryos
implanted into a
surrogate cow where it
grows into a calf.
        Cloning Sheep- Higher
• Animals can be cloned using a different
  technique called nuclear transfer.

                                                    Cells taken from the
  Egg cell taken                                    udder of sheep B and
  from sheep A                                      the nucleus removed
  and nucleus
                                                Nucleus from sheep B
                                                is put into egg of
                   Egg cell is put into a
                                                sheep A
                   female sheep to
                                            Cell grows into a
                                            clone of sheep B
  Risks and Benefits of Cloning
• Low rate of success with cloning animals
• Cloning humans raises ethical and moral
• Human embryos could be cloned to
  provide stem cells to help cure diseases
• Cloned pigs could be used to help with the
  shortage of organ donors
 Asexual Reproduction in Plants
Plants are able to reproduce sexually (using
flowers) or asexually (cloning themselves).

Asexual reproduction produces a new plant
that is a genetically identical copy to the
original plant- a clone.

Lots of plants use asexual reproduction
    • it produces lots of new plants quickly
    • plants do not need to spend lots of
    energy making flowers and gametes
    • it is guaranteed to produce new offspring
    unlike sexual reproduction
             Taking Cuttings
• To clone a plant artificially we can use the
  technique of taking cuttings.
• First the plant we want to clone is cut into
  smaller sections.
• Then each section is dipped into rooting powder.
• Each cutting is potted into its own container.
• Lastly a plastic bag is placed over each cutting
  to limit water loss.
   Tissue Culture- Higher Level
Small sections of plant tissue can be cloned using tissue culture.
It must be carried out using aseptic technique (sterile conditions).
First plants with the desired characteristics are chosen.
Then a large number of small pieces of tissue are taken from the parent
They are then put into sterile test tubes that contain growth medium.
The tissue pieces are left in suitable conditions to grow into plants.
Advantages and disadvantages of cloning plants
 – All the plants are genetically identical. All the cuttings
   taken from a red rose will grow into red roses.
 – Plants can take a long time to grow from seeds.
   Cloning produces lots of identical plants more quickly.
 – Cloning enables growers to produce plants that are
   difficult to grow from seed such as bananas.

 – The plants are all genetically identical. If the
   environment changes or a new disease breaks out it
   is unlikely that any of the plants will survive.
 – Cloning plants over many years has resulted in little
   genetic variation.
Why can plant cuttings grow into new plants
but cuttings from an animal could not grow
            into a new animal?
• Many plant cells retain the ability to
  differentiate into different cells. Root cells
  used in tissue culture have to change into
  all the different types of cells found in a
• Most animal cells have lost the ability to

To top