Microbes in human welfare Class 12 short Notes: Microbes in Household products

  • A common example is the production of curd from milk. Micro-organisms such as
  • Lactobacillus and others commonly called Lactic Acid Bacteria (LAB) grow in milk and convert it to curd.
  • During growth, the LAB produces acids that coagulate and partially digest the milk proteins.
  • It also improves its nutritional quality by increasing vitaminB12. In our stomachs too, the LAB plays a very beneficial role in checking disease-causing microbes.
  • The dough, which is used for making bread, is fermented by using baker’s yeast (Saccharomyces cerevisiae).
  • “Toddy”, a traditional drink of some parts of southern India is made by fermenting sap from palms.
  • Microbes are also used to ferment fish, soybeans, and bamboo shoots to make
  • foods.
  • Cheese is one of the oldest food items in which microbes were used.
  • The large holes in ‘Swiss cheese’ are due to the production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.
  • The ‘Roquefort cheese’ is ripened by growing a specific fungus on them for a particular flavor.

MICROBES IN HUMAN WELFARE Notes : Microbes in Industrial products


Production on an industrial scale requires growing microbes in very large vessels called

a) Fermented Beverages:

  • The yeast Saccharomyces cerevisiae is used for bread making and commonly called brewer’s yeast is used for fermenting malted cereals and fruit juices to produce ethanol.
  • Wine and beer are produced without distillation whereas whisky, brandy, and rum are produced by distillation of the fermented broth.

b) Antibiotics:

  • Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other disease-causing microbes.
  • Penicillin was the first antibiotic to be discovered and it was a chance discovery.
  • Alexander Fleming while working on Staphylococci bacteria, once observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow.
  • He found out that it was due to a chemical produced by the mould and he named it Penicillin after the mould Penicillium notatum.
  • Later, Ernest Chain and Howard Florey made their full potential effective antibiotic.

c) Chemicals, Enzymes, and other Bioactive Molecules

  • Aspergillus niger (fungus) – Citric acid
  • Acetobacter aceti (bacterium) – Acetic acid
  • Clostridium butylicum (bacterium) – Butyric acid
  • Lactobacillus (bacterium) – Lactic acid
  • Saccharomyces cerevisiae – Ethanol


  • Lipase – used in laundry detergents
  • Pectinase and protease – used in bottled juices
  • Streptokinase (Streptococcus bacterium) – used as clot buster (to remove clots)

Bioactive molecules:

  • Cyclosporin A (Trichoderma polysporum fungi) – used as immunosuppressive agent (for organ transplant patients).
  • Statins (Monascus purpureus yeast) – used as blood cholesterol-lowering agents.

Microbes in human welfare Class 12 short Notes: Microbes in Sewage Treatment

  • Treatment of waste is done by heterotrophic microbes naturally present in the sewage.
  • This treatment is carried out in two stages;

1. Primary treatment / Physical treatment:

  1. It involves the physical removal of particles from the sewage through filtration and sedimentation.
  2. Sequential filtration – to remove floating debris.
  3. Sedimentation – to remove grit (soil and small pebbles).
  4. All solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

2.Secondary treatment / Biological treatment:

  1. The primary effluent is passed into large aeration tanks, this allows vigorous growth of aerobic microbes into flocs.
  2. While growing, these microbes consume the major part of the organic matter in the effluent.
  3. This significantly reduces the BOD (biochemical oxygen demand) of the effluent. BOD is a measure of the organic matter present in the water.
  4. The greater the BOD of wastewater the more is its polluting potential.
  5. Once the BOD of sewage water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.
  6. A small part of this sludge is pumped back into the aeration tank to serve as the inoculum.
  7. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
  8. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas.
  9. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

Microbes In Human Welfare Class 12 short Notes: Microbes in Production of Biogas

  • Biogas is mixture of gases produced by microbial activity and which may be used as fuel. Certain bacteria, which grow anaerobically on cellulosic material, produce a large amount of methane along with CO2 and H2.
  • These bacteria are collectively called Methanogens (Methanobacterium).
  • These bacteria are also present in the rumen of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen.
  • In the rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.
  • Thus, the excreta (dung) of cattle, commonly called Gobar, is rich in these bacteria. Dung can be used for the generation of biogas commonly called gobar gas

Biogas Plant:

  • The technology of biogas production was developed in India mainly due to the efforts of the Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).
  • The biogas plant consists of a concrete tank in which bio-wastes are collected and a slurry of dung is fed.
  • A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity.
  • The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses.
  • The spent slurry is removed through another outlet and may be used as fertilizer.
    The biogas thus produced is used for cooking and lighting.

Microbes In Human Welfare Class 12 short Notes : Microbes as Biocontrol Agent

Biological control of pests and diseases:

  • Ladybird – to control aphids
  • Dragonfly – to control mosquitoes
  • Bacillus thuringiensis (Bt Cotton) – to control wide range of insects
  • Trichoderma (fungi) – protects the root system and controls plant pathogens.
  • Baculoviruses (Nucleopolyhedrovirus) – to attack insects and other arthropods.

Microbes as Biofertilizers:

Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.


  • Symbiosis – Rhizobium with root nodules of leguminous plants
  • Free living (in the soil) – Azotobacter and Azospirillum.


  • Symbiosis – Mycorrhiza with root system of genus Glomus and absorb phosphorus and water from the soil for the plant growth.


  • Symbiosis – Anabaena in Azolla
  • Free living – Nostoc, Oscillatoria and Blue green algae

CBSE Class 12 Chapter 4 Reproductive Health Notes | Reproductive Health ncert Notes

According to World Health Organisation (WHO), Reproductive health is total well-being in all aspects of reproduction i.e., physical, emotional, behavioral & social.


India initiated reproductive health programmes (family planning) in 1951. Now wider reproduction-related areas are in operation under Reproductive & Child Health Care (RCH) programs. Such programs deal with the following:

▪ Give awareness about reproduction-related aspects for creating a reproductively healthy society.

▪ Educate people about birth control, care of pregnant mothers, post-natal care of mother and child, the importance of breastfeeding, equal opportunities for male & female children, etc.

▪ Awareness of problems due to population explosion, social evils like sex abuse and sex-related crimes, etc.

Aims and needs of sex education in schools

▪ To provide the right information about sex-related aspects. It helps to avoid sex-related myths and misconceptions.

▪ To give proper information about reproductive organs, adolescence, and related changes, safe and hygienic sexual practices, sexually transmitted diseases (STD), AIDS, etc.


• In 1900, the world population was about 2 billion. By 2000, it rocketed to about 6 billion and 7.2 billion in 2011.

• In India, the population was nearly 350 million at the time of independence. It reached 1 billion by 2000 and crossed 1.2 billion in May 2011. It means every sixth person in the world is an Indian.

• According to the 2011 census report, our population growth rate was less than 2% (i.e. 20/1000/year), a rate at which our population could increase rapidly.

Reasons for population explosion

  • Increased health facilities and better living conditions.
  • Rapid decline in death rate, maternal mortality rate (MMR) and infant mortality rate (IMR).
  • Increase in number of people in reproducible age.

Control measures

  • Motivate smaller families by using contraceptive methods.
  • Aware people about the slogan Hum Do Hamare Do (we two, our two). Many couples have adopted a ‘one child norm’.
  • Statutory rising of marriageable age of females (18 years) and males (21 years).

Properties of an ideal contraceptive

  • User-friendly, easily available, effective and reversible.
  • No or least side-effects.
  • It should not interfere with sexual drive, desire & sexual act.


  1. Natural/Traditional methods :- Avoid chances of ovum and sperms meeting. It includes
  • Periodic abstinence: Avoid coitus from day 10 to 17 (fertile period) of the menstrual cycle to prevent conception. The fertile period is the period having chances of fertilization.
  • Coitus interruptus (withdrawal): Withdraw penis from the vagina just before ejaculation to avoid insemination.
  • Lactational amenorrhea: It is the absence of menstrual cycle & ovulation due to intense lactation after parturition. Fully breastfeeding increases lactation. This method helps to prevent conception. This is effective up to 6 months following parturition.

Natural methods have no side effects. But chances of failure are high.

  1. Barriers

They prevent the physical meeting of sperm & ovum. E.g.

a. Condoms (E.g. Nirodh):

Made of rubber/latex sheath. Condoms for males: Cover the penis.
Condoms for females: Cover the vagina & cervix. Condoms are used just before coitus. They prevent the entry of semen into the female reproductive tract.
Condoms are very popular because:

male condom
female condom
  • It protects the user from STDs and AIDS.
  • Easily available and disposable.
  • It can be self-inserted and thereby give privacy to users.

b. Diaphragms, cervical caps, and vaults:

  • Made of rubber and are inserted into the female a reproductive tract to cover the cervix during coitus.
  • They block the entry of sperms through the cervix.
  • They are reusable.

c. Spermicidal creams, jellies & foams

Are used along with these barriers to increase contraceptive efficiency.

  1. Intra Uterine Devices (IUDs)

These are inserted by doctors or nurses in the uterus through the vagina. IUDs are the ideal method to delay pregnancy or space children.

Mechanism of functioning of IUDs

▪     It increases phagocytosis of sperms within the uterus

▪     Cu ions released suppress sperm motility and the fertilizing capacity of sperms


Types of IUDs:

  • Non-medicated IUDs: They retard sperm motility. Also have a spermicidal effect.
    E.g. Lippes loop.
  • Copper releasing IUDs: Cu ions suppress motility and fertilizing capacity of sperms.
    E.g. CuT, Cu7, Multiload 375.
  • Hormone releasing IUDs: They make the uterus unsuitable for implantation and the
    cervix hostile to the sperms. E.g. Progestasert, LNG-20.
  1. Oral contraceptives
  • Oral administration of progestogens or progestogen– oestrogen combinations in the form of tablets (pills).


o   Mechanism of action of pills:

  •  Inhibit ovulation and implantation
  •  Alter the quality of cervical mucus to prevent/retard entry of sperms

o   Dosage of pills:

  •    Daily for 21 days of the menstrual cycle.
  •    It should start within the first five days of the menstrual cycle.
  •    Then a gap of 7 days (during menstruation).
  •    This cycle is to be repeated till the time the female wants to prevent conception.

Saheli :

  • Oral contraceptive pill developed by CDRI ( Central Drug Research Institute) Lucknow
  •  Non-steroidal in nature
  •  Low side effect with high contraceptive value
  • Needs to be taken only once a week.

5. Injections or implants under the skin :

  •   Composition: Progestogens alone or in combination with estrogen
  •    Mode of action: Similar to pills
  •    Benefit: effective periods are much longer than pills

Emergency contraceptives

  •    Female can take progesterone or estrogen-progesterone combination preparations.
  •    It must be taken within 72 hours of coitus.
  •    Useful to prevent pregnancy in cases of rape or casual unprotected intercourse.

6.   Surgical method/Sterilisation

  • Terminal method of contraception
  • Non-reversible
  • There will be no more pregnancy

o  Mechanism: Surgical procedure blocks the gamete transport and thereby prevents conception.


  • Sterilisation method in male.
  •  A small portion of the vas deferens is removed or cut and tied.
  • The surgery is performed by making an incision in the scrotum.


  • Sterilisation method in female.
  •  A small portion of the fallopian tube is removed or cut and tied.

 Ill effects of artificial contraceptives

  • Nausea
  • Abdominal pain
  •  Breakthrough bleeding
  •  Irregular menstrual bleeding
  • Breast cancer

Medical Termination of Pregnancy (MTP)

 Also known as induced abortion.Intentional or voluntary termination of pregnancy before full term (complete development of fetus).

Why MTP is required?

  • To get rid of unwanted pregnancies either due to casual unprotected intercourse, failure of the contraceptive used during coitus, rapes
  •  In case the continuation of the pregnancy could be harmful or even fatal either to the mother or to the fetus or both.

When MTPs are performed

Safe in the first trimester (up to 12 weeks of pregnancy) Riskier in the second trimester.

 Misuse of MTPs

Amniocentesis is misused to determine the sex of the unborn child. In case the fetus is found to be female – MTP is performed – female foeticide.

Sexually Transmitted Infections (STIs)

Also known as venereal diseases (VD) or reproductive tract infections (RTI) or sexually transmitted diseases (STDs).

STIs caused by Bacteria:

  • Gonorrhea
  • Syphilis
  • Chlamydiosis

 STIs caused by Protozoa:

  • Trichomoniasis

 STIs caused by viruses:

  • Genital herpes
  • Genital warts
  •  Hepatitis-b
  • Aids

Hepatitis–B and HIV can also be transmitted by sharing of injection needles, surgical instruments, etc., with infected persons, transfusion of blood, or from an infected mother to the foetus too.

Most of these STIs are completely curable except for hepatitis-B, genital herpes, and HIV infections.

Early symptoms of STIs include the following in the genital region: itching, fluid discharge, slight pain, swellings, etc.,

In case proper treatment is done at the early stages of infection it could lead to complications such as:

  • Pelvic inflammatory diseases (PID)
  •  Abortions
  •  Stillbirths
  • Infertility
  •  Even cancer of the reproductive tract

Ectopic pregnancies (pregnancy in which the embryo attaches outside the uterus / extrauterine pregnancy)

 Simple principles to prevent STIs:

  •  Avoid sex with unknown partners/multiple partners.
  •  Always try to use condoms during coitus.
  •  In case of doubt, one should go to a qualified doctor for early detection and get complete treatment if diagnosed with the infection.


Reasons of Infertility:- physical, congenital, diseases, drugs, immunological, or even psychological.

Infertility Clinics: Specialized health care units that could help in diagnosis and corrective treatment of infertility.

Assisted Reproductive Technologies (ART)

Special techniques to help infertile couples to have children.

Method 1: (Test tube baby program)

IVF is followed by ET

 IVF- In vitro fertilization: fertilization outside the body

ET – Embryo Transfer


  • Ovum is collected from wife/donor female
  • Sperm is collected from husband/donor male
  • The collected ova and sperm are then fertilized in the laboratory.
  • The zygote is then placed back in the female by either of the two following techniques:

 ZIFT (zygote intra fallopian transfer)

the zygote or early embryos (with up to 8 blastomeres) transferred to the fallopian tube.

IUT (Intra Uterine Transfer)

  • An embryo with more than 8 blastomeres is transferred to the uterus.
  • Embryos formed by in-vivo fertilization also could be used for such transfer to assist those females who cannot conceive.
  • In-Vivo fertilization – a fusion of gametes within the female

Method 2: GIFT (gamete intrafallopian transfer)

Condition: If a female cannot produce ovum, but can provide a suitable environment for fertilisation


  •  Ovum is collected from a donor.
  • Then it is transferred into the female who cannot produce the ovum.
  • The further development continues as in normal individuals.

Method 3: ICSI (Intracytoplasmic sperm injection)

Sperm is directly injected into the ovum to create the embryo in the laboratory condition.

Method 4: AI (Artificial Insemination)

Condition: If the reason of infertility is due to either one of the following reasons:

  • The inability of the male partners to inseminate
  • Very low sperm count


  • Semen is collected from the husband / healthy donor.
  • It is artificially introduced either in the vagina or into the uterus (IUI – intra-uterine insemination) of the female.

 Possible drawbacks of ART

  • These facilities are presently available only in very few centers in the country.
  •  High cost associated.
  •  Many may not accept these methods due to emotional, religious, and social factors.

Legal adoption is one of the best alternative methods for infertile couples looking for parenthood.

INFERTILITY IN HUMAN: Causes &Consequences :-

Oligospermia: Low sperm countAnovulation: Absence of ovulation.
Azospermia: Absence of sperm.Oligoovulation: Deficient ovulation.
Asthenozoospermia: Low sperm motility.Hyperprolactinemia: Ovum remain trapped
inside the follicle.
Teratozoospermia: Defective sperm
Idiopathic Infertility: Failure or abnormal
Cryptorchidism:Failure of Testes to descend in
the scrotal sac.
Tubal Infertility: Damaged/ligated fallopian


1CHLAMYDIOSISChlamydia trachomatis
2GONORRHOEANeisseria gonorrhea
3TRICHOMONIASISTrichomonas vaginalis
4GENITAL HERPES Herpes simplex virus
5SYPHILISTreponema pallidum 
6GENITAL WARTHuman papilloma virus 
7HEPATITIS-BHepatitis –B

NCERT UNIT 19 – Excretory Products and their Elimination CBSE Class 11 Biology

Excretion is the elimination of metabolic wastes like ammonia, urea, uric acid etc. from the tissues.

Types of excretion

1. Ammonotelism:

Process of excretion of NH3. Ammonotelic animals: Aquatic invertebrates, aquatic insects, bony fishes, aquatic amphibians, etc. NH3 is highly toxic.

So, excretion needs an excess of water.

NH3 is readily soluble in water and is excreted by diffusion through a body surface or gill surfaces (in fishes) as ammonium ions.

Kidneys do not play any significant role in its removal.

2. Ureotelism:

Process of excretion of urea.

Ureotelic animals: Cartilaginous fishes, terrestrial & semi-aquatic amphibians (frogs, toads, etc.), aquatic & semi-aquatic reptiles (alligators, turtles), mammals, etc.

In the liver, NH3 is converted into less toxic urea.

So, it needs only a moderate quantity of water for excretion. Some amount of urea may be retained in the kidney matrix of some animals to maintain the desired osmolarity.

3. Uricotelism:

Process of excretion of uric acid. It is water insoluble & less toxic. So, water is not needed for excretion.

Uricotelic animals: Insects, some land crustaceans, land snails, terrestrial reptiles & birds. Ureotelism & uricotelism are needed for water conservation.

Some excretory organs in animals

Protonephridia (flame cells): In Flatworms, rotifers, some annelids & cephalochordate. Protonephridia are primarily for osmoregulation.

Nephridia: In Annelids. Help in the removal of nitrogenous wastes and osmoregulation.

Malpighian tubules: In Insects. Help in the removal of nitrogenous wastes and osmoregulation.

Antennal or green glands: In Crustaceans (prawn etc.)

Kidneys: In higher animals.


NCERT - Excretory Products and their Elimination CBSE Class 11  Biology human excretory system

It includes kidneys, ureters, urinary bladder & urethra.

Structure of Kidney

– Reddish brown, bean-shaped structures situated between the levels of last thoracic & 3rd lumbar vertebra.

– Length: 10-12 cm, width: 5-7 cm, thickness: 2-3 cm.

Average weight: 120-170 gm. – It is enclosed in a tough, 3-layered fibrous renal capsule.

NCERT - Excretory Products and their Elimination CBSE Class 11  Biology kidney labelled

– On the concave side of the kidney, there is an opening (hilum or hilus) through which blood vessels, nerves, lymphatic ducts, and ureters enter the kidney.

– Hilum leads to funnel shaped cavity called renal pelvis with projections called calyces.

– A kidney has outer cortex & inner medulla.

– Medulla has few conical projections called medullary pyramids (renal pyramids) projecting into the calyces.

– Cortex extends in between the medullary pyramids as renal columns (Columns of Bertini).

– Each kidney has nearly one million tubular nephrons.


– Nephrons are the structural & functional units of kidney.

– Each nephron has 2 parts: Glomerulus & Renal tubule.

NCERT - Excretory Products and their Elimination CBSE Class 11  Biology nephron

o Glomerulus:

A tuft of capillaries formed by afferent arteriole (a fine branch of the renal artery). Blood from the glomerulus is carried away by an efferent arteriole.

o Renal tubule:

It begins with a double-walled cup-like Bowman’s capsule, which encloses the glomerulus.

Glomerulus + Bowman’s capsule = Malpighian body

NCERT - Excretory Products and their Elimination CBSE Class 11  Biology bowmans capsule

– The tubule continues with proximal convoluted tubule (PCT), Henle’s loop & distal convoluted tubule (DCT).

– Henle’s loop is hairpin-shaped. It has to descending and ascending limbs. – The DCTs of many nephrons open into a collecting duct.

The collecting duct extends from the cortex to the inner parts of the medulla. They converge and open into the renal pelvis through medullary pyramids in the calyces.

– Malpighian body (Renal corpuscle), PCT, and DCT are situated in the renal cortex. Loop of Henle dips into the medulla.

– The efferent arteriole forms a fine capillary network (peritubular capillaries) around the renal tubule.

A minute vessel of this network runs parallel to Henle’s loop forming a ‘U’ shaped vasa recta.

Types of nephrons

1. Cortical nephrons (85%): In this, the Henle’s loop is short and extends only very little into the medulla. Vasa recta is absent or highly reduced.

2. Juxtamedullary nephrons (15%): In this, Henle’s loop is long and runs deep into medulla. Vasa recta present.