found in the colon bacteria Escherichia coli, recognises the
base sequence GAATTC in DNA duplex and cuts its strands
between G and A as shown below :
5 ′ – G A A T T C – 3′
3 ′ – C T T A A G – 5′.
↓
↑
(b) Plasmids : They are extra-chromosomal, self-replicating,
usually circular and double-stranded DNA molecules that
are found naturally in many bacteria and also in some yeast.
Although plasmids are usually not essential for normal cell
growth and division, yet they often confer some traits on the
host organism, for example, resistance to certain antibiotics
or toxins that can be a selective advantage under certain
conditions. The plasmid molecules may be present as single
copies or in multiple copies (500-700) inside the host
organism. These naturally occurring plasmids have been
modified to serve as vectors in the laboratory. Plasmids
are essential in biotechnological experiment as they help
in transferring a segment of foreign DNA (gene of interest)
into suitable host. Ti plasmid is widely used vector for
cloning genes in plants. The most widely used, versatile,
easily manipulated vector, pBR322 is an ideal plasmid
vector. It was the first artificially cloned vector and is used
widely in gene cloning experiments. The plasmids are cut
and ligated with desired genes and transformed into the
host cell for amplification to obtain the desired products.
Some plasmids have antibiotic resistance genes which can
be used as marker genes to identify recombinant plasmids
from non-recombinant ones.
- Refer to answer 118, page no. 37, MTG CBSE Champion Biology.
- Yes, I agree that all young mothers must breast-feed their
newborn babies to provide best nourishment to them.
Human milk consists of fat, casein (milk protein), lactose
(milk sugar), mineral salts (sodium, calcium, potassium,
phosphorus, etc). and vitamins that are necessary for
development of the child. Mammary glands start producing
milk at the end of pregnancy. The milk produced by the
mammary glands of mother during initial days after child
birth, for 2 to 3 days is called colostrum. It is rich in proteins
(lactalbumin and lactoprotein) and various other nutrients.
It also contains certain antibodies (IgA), which provide
passive immunity to the baby. This milk helps in developing
resistance to disease for newborn babies. It helps the baby
to fight from viruses and bacteria. It is also easily digested
by the baby with no constipation or diarrhoea.
- Refer to answer 38, page no. 62 and 42 page no. 63 MTG CBSE
Champion Biology.
- (a) VNTR stands for Variable Number of Tandem Repeats.
Refer to answer 190(b), page no. 180, MTG CBSE Champion
Biology.
(b) Applications of DNA fingerprinting are as follows:
(i) Paternity or maternity disputes can be solved by DNA
fingerprinting as it can identify the real genetic mother,
father and the offspring.
(ii) This technique is being used to identify genes
connected with hereditary diseases.
(iii) It is useful in detection of crime and legal pursuits.
(iv) It can identify racial groups, their origin, historical
migrations and invasions.
- (a) The major causes of air pollution are:
(i) Combustion of fossil fuels and wood in
automobiles, thermal plants, industries, aircrafts,
etc., that gives out soot, fly ash and gases such as
CO 2 , CO, NO 2 , etc.
(ii) Metallurgical processing adds mineral dust,
fumes rich in fluorides, metallic pollutants like
lead, chromium, nickel, cadmium, etc., to the air.
(iii) Burning of crop residues by farmers in agricultural
lands leaves particulate matter, CO 2 , CO, oxides of
nitrogen, methane, etc. This causes the air quality
index to drop drastically.
(b) Harmful effects of air pollution on plants and humans are :
(i) The soot and smoke particulate matter settles on
leaves and reduces the rate of photosynthesis. In
humans, it penetrates deep into respiratory system and
causes ailments like bronchitis, asthma, cardiovascular
problems, etc.
(ii) Oxides of nitrogen cause lesions, necrosis and
defoliation in plants whereas in humans they cause
decreased gaseous exchange in blood, eye irritation,
lung edema, etc.
(iii) Hydrocarbons, such as methane, lead to premature
leaf fall and fruit drops in plants. In humans, it causes
eye irritation, bronchial constriction, etc. Benzene
and formaldehyde are carcinogenic and may cause
leukemia.
(c) As a captain of my school Eco-club, I would suggest the
programmes to bring awareness among other students are
as follows :
(i) Awareness camps and seminars in the school premises
with volunteers encouraging students to reduce usage
of personal vehicles for pick ups and drops from home
and school. Instead they should use school transports.
Students can encourage their parents at home to use
less of air conditioners, aerosols, etc. Also students can
encourage them to use public transport i.e, buses and
using CNG instead of diesel.
(ii) A tree planting drive can be organised in school with
all students participating and each one planting a tree
sapling around the school or society to improve green
cover. This would bring awareness among students as
to how trees can reduce air pollution.
