Biology Additional (B2) Parts of a cell DNA Structure A DNA molecule has 2 strands coiled together in a double helix shape. These strands are held together by bases. There are 4 bases: These bases are joined together in the same way (A-T, G-C). This is known as base pairing. These base pairs are joined together by weak hydrogen bonds.
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Biology Additional (B2)
Parts of a cell
DNA Structure A DNA molecule has 2 strands coiled together in a double
helix shape. These strands are held together by bases.
There are 4 bases:
These bases are joined together in the same way (A-T, G-C). This is known as
base pairing. These base pairs are joined together by weak hydrogen bonds.
Discovery of DNA
DNA Extraction
Protein Synthesis Genes are sections of DNA that code for the sequence of amino acids in a
protein. A gene can be broken down into Codons. These are sections of three
basses.
A gene is like a cook book and codons are like the recipe. The gene does not
create the protein, it just provides the information of how to make it. The chef
in this case is a ribosome.
Transcription
1) DNA unzips
2) Each codon codes for the bases on the mRNA
3) Where A would normally code for T, on mRNA it codes for U
Translation
1) mRNA joins the ribosome
2) The anticodons on the tRNA are attracted to the
complementary codons on the mRNA. Specific amino acids are
attached to the tRNA.
3) The amino acids then form peptide bonds
4) The tRNA will then detach from the amino acid and get some
more of the same amino acids
Enzymes Enzymes are biological catalysts. This means they help to speed up biological
processes.
An enzyme has an area called an active site.
This area is complementary to the target
molecule called the substrate. This
active site holds the substrate under
pressure so that it becomes easier for it to be broken down into its
products.
Enzymes are affected by 3 things:
Temperature
PH
Substance Concentration
GMO A GMO is a genetically modified organism. This means a gene has been
removed from one organism and placed into another organism’s genome.
This can be done by:
1) Find the desired gene
2) Use restriction enzymes to cut the DNA out,
ensuring the cut is jagged and therefore leaves
sticky ends
3) Make another cut in the new DNA in order to paste
the new gene using ligase enzyme.
Scientist modify the plasmid as it is less tangled up and therefore can be
modified easier.
Mitosis and Meiosis
Cloning an Animal
1) Remove the diploid body cell from the animal you want to clone.
2) Then remove the nucleus from both cells.
3) Place the diploid nucleus into the haploid cell
4) Give it an electric shock in order to stimulate the division.
5) Then place the cells into a surrogate sheep.
6) The baby born will be an exact clone of the original animal.
Stem Cells The cells in the embryo are all the same and are called embryonic stem cells.
Stem cells can divide into any type of cell. Becoming a specialised cell is called
differentiation. Stem cells could be used to cure diseases. Stem cell research is
banned in many countries.
Aerobic Respiration
Anaerobic respiration
Calculating cardiac output
Diffusion Particles moving from where there is a high
concentration gradient to where there is a low
concentration gradient.
Example
One use of this is when we breathe in oxygen. There is less oxygen in the
capillary this means that will oxygen will diffuse into the capillary in order to
make there be an equal amount in the alveoli and in the capillary. There is also
more carbon dioxide in the capillary than in the alveoli. This causes the carbon
dioxide to diffuse into the alveoli and then into the atmosphere.
Photosynthesis
Leaves have little holes called stomata. This can let gasses in and out. It also
lets water vapour escape. This is called transpiration.
Active Transport When particles move from where there is a low
concentration gradient to where there is a high
concentration gradient. This requires energy.
Example
Root hair cells in plants require minerals
from the soil. To get these minerals
diffusion cannot be used as there is
already a higher concentration in the cell
than in the soil. To get the minerals there
are carrier proteins on the surface of the
root hair cells. Minerals will bond with the
protein. The protein then uses energy to open up and bring the nutrients into
the cell.
Osmosis The movement of water
molecules from a high to low
concentration across a semi-
permeable membrane. A
semi-permeable membrane is
a membrane that has small
gaps in it. This means that
small particles can fit through but larger wans can’t. Pure water has a higher
concentration than water with solutes such as salt in it.
Xylem Carries water and minerals from the roots.
Phloem Carries sugar from leaves to growing tissue and storage tissue.
Looking at the distribution of organisms
Pooters
Pitfall traps
Sweep nets
Pond nets
Quadrat
Evidence for evolution Fossils
Pentadactyl limb
Cell organisation
The Heart and the Circulatory System
Adaptations of the Heart:
Valves prevent backflow of blood
Left ventricle wall is thicker. This is because more muscle is needed to
pump the blood around the whole body
Double pump. Makes sure blood pressure stays high
Septum separates oxygenated blood from deoxygenated blood
The Blood The blood contains:
Red blood cells –
o Adaptations- Dips in the middle. This increases surface area,
allowing for more oxygen to be absorbed.
o Haemoglobin- Contains 4 iron atoms to carry oxygen
o No nucleus. This means there is more space for oxygen
White blood cells-
o Can change shape to engulf pathogens.
o They have a complimentary shape to the pathogens. This means
they can easily fight them with the antibodies and antitoxins they
produce.
Platelets-
o Made up of broken bits of cells. This irregular shape helps to clog
up any wounds in order for them to heal
Plasma-
o Can carry waste materials away from cells such as
Carbon dioxide
UREA
o Can carry useful materials to cells such as
Red blood cells
White blood cells
Platelets
Glucose
Amino Acids
Hormones
Antibodies and Antitoxins
Blood Vessels
Arteries-
Veins-
Capillaries-
Digestive System
Digestive enzymes
Investigating digestive enzymes
1. Visking tubing can be used to represent the gut.
2. A starch and amylase solution can be added. Starch is too big to
leave.
3. The tubing can then be placed in a boiling tube full of water.
This water represents our blood stream.
4. Benedict’s solution tests for the presence
of sugar. Iodine tests for starch. After 0 mins,
the water should not change the colour of the solutions.
After 15 mins, the amylase will have time to break down the
starch. There should be no starch in the water as it’s too big
to fit through. The benedict’s solution should change to brick
red because the starch has been broken down into sugar. This can fit
through the tubing and will therefore be present in the water