SUMMARY OF UNIT 1 – CELLS
Key Area 1 – Cell Division and its role in growth & repair
All cells have a nucleus, cytoplasm and a cell membrane. Plant cells have three
additional features: a cell wall, a vacuole and chloroplasts.
All new cells are made by existing cells dividing in two. Cell Division is important
because:
a) It produces new cells for growth and repair in multi-cellular organisms
(e.g mending cuts and broken bones)
b) It allows single celled organisms to reproduce (e.g bacteria & fungi)
During cell division, the parent cell divides to produce two identical cells, which
contain the same number of chromosomes in their nuclei as the parent cell.
Cancer is caused by uncontrolled cell division.
Key Area 2 – DNA, genes and chromosomes
Genes are located on chromosomes in the nucleus. Genes are made of DNA
which carries the instructions to make proteins.
DNA exists as two long coiled strands
consisting of a backbone to which bases attach.
The two strands are held together by bonds
between the bases. There are four types of
base which bond as follows: A – T & G – C.
Every group of three bases
along a DNA strand represents a
‘codeword’ for an amino acid.
The amino acids are then linked
together by chemical bonds to
make a chain and finally a protein
molecule.
Key Area 3 – Therapeutic uses of cells
Genetic engineering involves the transfer of one or more genes from one
organism (e.g human) to another organism (e.g bacterium). The diagram below
shows the process of genetic engineering.
Useful products that have been made
by genetic engineering:
-
Insulin (to treat diabetes –
sufferers can’t regulate their
blood sugar)
-
Factor VIII (to treat haemophilia
– sufferers can’t clot their blood
properly)
-
Human Growth Factor (to treat
dwarfism – sufferers don’t grow
properly)
Other therapeutic uses of cells are the use of stem cells. Stem cells are cells
that can make copies of themselves and can differentiate in many different
types of cell. Stem cells are currently being used to grow new skin for burn
victims. In the future they will hopefully be able to help scientists test new
drugs, understand diseases and help find new treatments for diseases.
Key Area 4 – Properties of enzymes and use in industries
Enzymes are not living, they are chemicals made of protein. Enzymes speed up
chemical reactions but are not used up or altered during the reaction so can be
used again and again. Without enzymes, reactions that take place in living
organisms (for e.g photosynthesis) would not occur fast enough to support life.
The substance an enzyme acts upon is called its substrate and what is made as a
result of the enzyme reaction is the product. For e.g
Enzyme
Substrate
Product
Amylase
Starch
Maltose
Catalase
Hydrogen Peroxide
Water & Oxygen
Phosphorylase
Glucose
Starch
Enzymes are very specific, only working on one substrate. They come together
with their substrate like a lock and key.
Uses of enzymes in industry
Enzymes are used in biological washing
powders to help breakdown stains. They
are advantageous because they work
better at lower temperatures saving
energy. Rennet is a substance composed
of lots of enzymes which is used in
cheese making to help the milk curdle
into curds (solids) and whey (liquid).
Key Area 5- Properties of microganisms and use in industries
Micro-organisms (bacteria and yeast) can be very useful in industry as they
grow rapidly, have a wide food source and can make a lot of useful products.
Bacteria Industries
1) Yoghurt. The bacteria feed on the sugar in milk (lactose) and change it
into lactic acid which causes the milk to clot forming yoghurt.
2) Cheese. Cheese making bacteria along with rennet cause milk to curdle
into solid curds making cheese.
3) Treating sewage. Bacteria are used at the sewage works to break down
harmful waste into harmless liquid that can be released back into water
ways.
4) Biofuel. When bacteria feed on sewage in the absence of oxygen,
methane is produced which can be collected and used as a fuel.
Yeast Industries
1) Bread. When yeast feeds on sugar in the absence of oxygen it produces
carbon dioxide. When yeast is added to dough in baking, the carbon
dioxide causes the dough to rise.
2) Brewing. When yeast feeds on sugar in the absence of oxygen it also
produces ethanol. Yeast is therefore used in the brewing industry to
make alcohol.
Key Area 6 – Photosynthesis – limiting factors
Photosynthesis:
Some of the glucose produced during photosynthesis is stored as starch. To
test to see if photosynthesis has taken place in a plant, leaves can be tested for
starch with iodine solution. Photosynthesis cannot work without carbon dioxide,
water, light and a suitable temperature. If any of these is in short supply they
are said to be ‘limiting factors’.
Key Area 7 – Factors affecting Respiration
Respiration is the process by which energy is released from food. There are
two types.
Aerobic respiration in all cells (in the presence of oxygen)
Glucose + Oxygen
Carbon Dioxide + Water + Energy
Anaerobic respiration in animals (in the absence of oxygen)
Glucose
Lactic acid + Energy
Animals would undergo anaerobic respiration during intense exercise when they
cannot get enough oxygen into their bodies to meet their needs. When lactic
acid builds up in muscles it causes fatigue. You may have experienced this as
muscle soreness and lack of strength during intense activity.
Anaerobic respiration in plants & yeast (in the absence of oxygen)
Glucose
Carbon Dioxide + Ethanol + Energy
The products of anaerobic respiration in yeast are utilised in baking and brewing
as described earlier.
Factors affecting respiration
Respiration is controlled by enzymes.
Enzymes are very sensitive to changing
temperature and have an optimum
temperature at which they perform
best. When the enzymes are working at
their best, the rate of respiration will
be at its most efficient.
Key Area 8 – Controversial biological procedures
You need to have knowledge of at least one controversial biological procedure
and the pros and cons of its use. One example is Gene Therapy. Gene therapy
is when defective genes are substituted for normal genes. One advantage of
this technique is that rather than just treating the symptoms of a disease with
drugs, replacing the defective gene provides a cure. One disadvantage is that is
has the potential to be mis-used, for e.g the creation of ‘designer babies’.