TyroCity: Biology XII Notes

Chemical structure of DNA

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:
DNA is genetic material in most of organisms (exception: RNA virus). It is a double-helix and has two strands running in opposite directions. Each chain is a polymer of subunits called nucleotides (polynucleotide).

Chemical composition:
A DNA strand has a backbone made up of (deoxy-ribose) sugar molecules linked together by phosphate groups. The 3′ C of a sugar molecule is connected through a phosphate group to the 5′ C of the next sugar. This linkage is also called 3′-5′ phosphodiester linkage. All DNA strands are read from the 5′ to the 3′ end where the 5′ end terminates in a phosphate group and the 3′ end terminates in a sugar molecule.

Each sugar molecule is covalently linked to one of 4 possible bases (Adenine, Guanine, Cytosine and Thymine). A and G are double-ringed larger molecules (called purines); C and T are single-ringed smaller molecules (called pyrimidines).
In the double-stranded DNA, the two strands run in opposite directions and the bases pair up such that A always pairs with T and G always pairs with C. The A-T base-pair has 2 hydrogen bonds and the G-C base-pair has 3 hydrogen bonds.

Permanent Tisues

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:
They are the tissues that have lost the potentiality of cell division after gaining the maturity. They are of various types as described below:

A) Simple permanent tissue:
They are composed of similar types of cells having certain .This tissue consists of only one type of cells, e.g. parenchyma, collenchymas and sclerenchyma.

B)Complex permanent tissue:
They are composed of more than one type of cells but have common functions. They are of following types:

1)Xylem:

It is a complex tissue composed of several types of cells. The various constituent of xylem are :
(a) tracheids
(b) vessels
(c) fibres
(d) parenchyma cells

Tracheids and vessels are known as tracheary elements. Primary xylem develops from procambium during the development of plant. Secondary xylem is produced later by the activity of vascular cambium during secondary growth. The detailed structures of various elements of xylem are described below.

Tracheids:
These are elongated cells pointed at both ends. The end walls are imperforate. Tracheids are present in all groups of vascular plants.

Vessels:
The vessels are shorter and broader than tracheids. Their length varies from one to many cells. They are joined end-to-end form a long chain of cells. Vessels are also found in some pteridophytes.
Different types if lignin depositions are found in tracheary elements. Accordingly, they show the following types of thickenings: Annual: Both are found in protoxylem elements, Spiral Scalariform: Both are found in metaxylem., Reticulate, The tracheids show simple pit or bordered pit.

The main function of tracheids and vessels is conduction of water.

Xylem fibres (Wood Fibres):
The fibres are long cells with lignified secondary walls. They provide mechanical strength while and sometimes conduct organic food.

Xylem Parenchyma:
They are only living cells in xylem. These cells store stratch, oils and many ergastic substances. Some of the parenchyma becomes sclerified forming sclereids cells.

2)Phloem:
Phloem is composed of variety cell types like xylem. The constituent cells are:
(a) Sieve tube elements
(b) Companion cells
(c) Phloem fibres
(d) Phloem parenchyma

Primary phloem is produced by the procambium while the secondary phloem develops from the vascular cambium. It develops from the vascular cambium. The detailed structure of various phloem elements are given below.

Seive tube elements:
It includes sieve tubes with sieve plates and sieve cells. Both of these are thin-walled living cells. Sieve tube members are long slender tube-like joined end to end to form long tubular to form a long tubular channel. Seive plates are present at the end of the tube.

Seive cells:
These are elongated narrow cells with tapering ends. In these cells sieve areas occur all over the wall.

Companion cells:
All angiosperms have specialized parenchyma cells associated with the sieve tube elements. Usually, a single companion cell extends through the whole length of the sieve tube. These are living cells and its function is associated with sieve tube.

Phloem fibres:
It is the only dead tissue in xylem. These are found both in primary and secondary phloem. Fibres are invariably long and the walls are thick. The main function is mechanical support.

Phloem parenchyma:
These are living cells contain various substances, such as starch, tannins, crystal, etc. these cells are associated with fibres. The main functions are storage and translocation food.

HIV/AIDS

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:

Human immunodeficiency virus infection / acquired immunodeficiency syndrome (HIV/AIDS) is a disease of the human immune system caused by infection with human immunodeficiency virus i.e. HIV. The HIV was first isolated by Luc Montagnier and Robert Gallo. HIV cause AIDS by destroying T4 cells. Hence, this weakens the immune system and allows opportunistic infections.

Modes of Transmission:
HIV is transmitted by following main routes:

Sexual contact: By unsafe sex with infected persons
Exposure to infected body fluids or tissues like infected blood transfusions.
From mother to child during pregnancy, delivery, or breastfeeding, hence also called as vertical transmission).
Use of infected needles, syringes etc., esp. among drug addicts.

Symptoms of AIDS:

The Symptoms include:

Continuous fever and diarrhea for more than one month
Weight loss by more than 10%.
Many individuals develop an influenza-like illness or a mononucleosis-like illness 2–4 weeks post exposure while others have no significant symptoms.
Symptoms occur in 40–90% of cases and most commonly include fever, large tender lymph nodes, throat inflammation, a rash, headache, and/or sores of the mouth and genitals.
Gastrointestinal symptoms such as nausea, vomiting or diarrhea may occur
People with AIDS have an increased risk of developing various viral induced cancers including: Kaposi’s sarcoma, Burkitt’s lymphoma, primary central nervous system lymphoma, and cervical cancer.

Diagnosis of AIDS:

Western blot test
Ora quick method (by FDA)
Blood test
ELISA test

Treatments of AIDS:

Currently, there’s no treatment for AIDS but use of HAART drugs DLV, 3TZ, ATC etc. can prolong the life of patient.
Healthy life style and exercise can reduce the circulation of virus in the blood.

Preventions of AIDS:

Use of condoms during sex
Avoiding unsafe and multiple sex
Pregnant woman mustn’t give birth
Blood should be screened before transfusion
Materials should be sterilized before using
Sex education on school and university levels
Public awareness

Megagametogenesis

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Megagametogenesis is the process of formation of female gamete or egg from megaspores of plants. It occurs as follows:

Process:

The process takes place inside the ovule of a plant. The megaspore becomes larger and the nucleus of it undergoes mitosis three times until there are eight nuclei. These eight nuclei are then arranged into two groups of four. These groups both send a nucleus to the center of the cell which then becomes the polar nuclei (2n). The three cells left at the end of the cell near the micropylar become the egg apparatus with an egg cell in the center and two synergids. A cell wall forms around the other set of nuclei and forms the antipodal cells. The cells in the center develop into the central cell. This entire structure finally called as embryo sac.
Finally, the embryo sac contains seven cells, out of which one is diploid and the rest are haploid.

Light Reaction (Hill’s Reaction)

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:
Light reaction is the first step in photosynthesis occurring in grana of chloroplast and needs the utilization of light energy. It consists of following three phases:

(a) Photolysis of water:
The light energy trapped by chlorophyll molecule decomposes water into its constituent elements, called photolysis of water.
H2O →(←) 4H⁺ + OH^-
4OH^- → 2H2 + 4e^- +2O2

(b) Photo-phosphorylation:
The electrons produced during the photolysis of water pass via 2 photosystems (PS –I and II). Each photo system has its own trap center and a primary pigment molecule.
It is the process of synthesis of ATP from ADP using light energy.
ADP+ ip → (light) ATP

It is of further two types:

1)Non-cyclic photo-phosphorylation:

High energy electrons released from P680 of PS-II are accepted by primary electron acceptor. The electrons pass via a series of electron acceptor i.e. PQ- cytochorome complex- PC and finally to P700 of PSI.

Again, the electrons given out by P700 of PS-I are taken up by primary pigment molecule and are ultimately passed to NADP through Fd. The electrons combine with ions and reduce NADP to NADP H2.

The net result of non-cyclic photo phosphorylation is the formation of 1oxygen (as a waste), 2 NADP H2 and 1 ATP molecule.

2)Cyclic photo-phosphorylation:

High energy electrons expelled from P700 of PS-I are taken up by primary pigment molecule, when the pass through series of electron acceptors i.e. Fd-PQ-Cytochorome complex-PC and finally to the same pigment molecule from which they have been originated.

There is formation of 2ATP molecules at the end.

(c)Photo reduction:

Chloroplast contains naturally occurring electron acceptor NADP. With addition of H+ from photolysis, it is reduced to NADP H2.
NADP + 2 H⁺ + 2e^- →(light) NADPH2

Note: Light reaction is linked with dark reaction in a sense that the products i.e. ATP and of light reaction are used for carbon fixation in the dark reaction.

Amniocentesis

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:
Amniocentesis is the medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid from amniotic sac of pregnant woman is sampled, which contains fetal tissues, and the fetal DNA is examined for genetic abnormalities.
It was developed by Richard Dedrick, and can be used for prenatal sex discernment and hence this procedure has legal restrictions in some countries.

Procedure/Method:
A local anesthetic is given to the mother in order to relieve the pain felt during the insertion of the needle used to withdraw the fluid. Then a sterilized hypodermal needle is usually inserted through the mother’s abdominal wall, then through the wall of the uterus, and finally into the amniotic sac to take out amniotic fluid.
If used for prenatal genetic diagnosis, fetal cells are separated from the extracted sample. The cells are grown in a culture medium, then fixed and stained. Under a microscope the chromosomes are examined for abnormalities like Down’s syndrome, Sickel cell anemia etc. It is also used in detecting sex of baby.

Advantages:

i) Genetic diagnosis:

Down syndrome
Fragile X
Rare, inherited metabolic disorders
Neural tube defects

ii) Determination of sex of foetus.

Drawbacks:

Amniocentesis is performed between the 15th and 20th week of pregnancy; performing this test earlier may result in fetal injury
Complications of amniocentesis include preterm labor and delivery
Chance of infections and miscarriage
Ethical problems arise when parents decide for an abortion following the test results when there is a baby girl in the womb of mother
It is expensive process

Biology XII

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Section A (Botany)

Section B (Zoology)

Distribution of PINUS in Nepal

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Pinus is a gymnospermic plant which is found in arid places, slopes of hills. It is a xerophytic plant. In Nepal, two species of Pinus are found, namely- Pinus roxburghii and Pinus wallichiana. Their distribution is briefed below:

1)P. roxburghii :
It is a large tree, usually 10-20 m in height. It is mainly distributed in the main valleys of Himalayan’s. It is found at an altitude of 1200-2100 m above the sea level. The forests of Pinusroxburghii in Nepal are mainly concentrated in the south facing slopes of central and eastern Nepal. They are also found in northern Siwalik Hills.

2)P. wallichiana :
It is also a large tree, usually 20 m and above. It is found at an altitude of 1800-3300 m above the sea level. The extensive forests of Pinus wallichiana in association with Picea smithiana are found in the Karnali region of Nepal. They also extend to central Nepal in the Gandaki region.
In such a way, the species of Pinushave been distributed in Nepal.

Cancer

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:

Cancer is the uncontrolled growth of abnormal cells of body. The abnormal cells are termed cancer cells, malignant cells, or tumor cells. It is also called neoplasm.

Types of Cancer:
There are many of cancers, as follows:

Carcinoma: Cancer that begins in the skin or in tissues that line or cover internal organs.

Sarcoma: Cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.

Leukemia: Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.

Lymphoma and myeloma: Cancers that begin in the cells of the immune system.

Causes of Cancer:

Exposure of body to UV-radiation or X-rays for long.
Carcinogens like mustard gas, benzopyerene etc
Chewing tobacco and smoking causes lung and oral cancer.
Viruses can also cause cancer.

Symptoms of Cancer:
They are as follows:

May cause Fever (no clear infectious source, recurrent or constant)
There may be Fatigue (not relived by rest)
Person claims Weight loss (without trying to lose weight)
Pain (usually persistent)
Skin changes (coloration, sores that do not heal, white spots in mouth or on tongue, wart changes)
Change in bowel or bladder functions
Unusual bleeding (mouth, vaginal, and bladder) or discharge
There can be Persistent cough or change in voice
Lumps or tissue masses are seen

Diagnosis of Cancer:

Blood test for blood cancer
Bone marrow biopsy
CT scans and MRI
Analysis of molecular changes of cancerous cells

Treatment of Cancer:

Medicines like ABC etc
Interferon medicines

Prevention’s of Cancer:

Avoiding smoking tobacco.
Avoiding excess sunlight (by decreasing exposure or applying sunscreen) and many of the chemicals and toxins is an excellent way to avoid cancers.
Avoiding contact with certain viruses and other pathogens also is likely to prevent some cancers.
People who have to work close to cancer-causing agents (chemical workers,
X-ray technicians, ionizing radiation researchers) should follow all safety precautions and minimize any exposure to such compounds.
There are two vaccines currently approved by the U.S. Food and Drug Administration (FDA) to prevent specific types of cancer. Vaccines against the hepatitis B virus, which is considered a cause of some liver cancers, and vaccines against human papillomavirus types 16 and 18, which, according to the NCI, are responsible for about 70% of cervical cancer.

Mendel’s Law

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Q) What is law of independent assortment and how is it verified from Mendel’s Cross?
Ans: Mendel’s law of independent assortment states-“When two or more than two characters are inherited from parents to offspring, the inheritance of one character is not influenced by the other.”
This law is explained by Mendel’s Dihybrid Cross as follows:

Mendel’s Dihybrid Cross

Mendel crossed pure breeding plants with round seeds and yellow albumen to pure breeding plants with wrinkled seeds and green albumen. The F1 plants all had found seeds and yellow albumen and Mendel predicted that they would be heterozygous for both traits (RrYy).
He then did a self-cross of the F1 plants to produce the results shown as the F2. He obtained phenotypic ratio as 9:3:3:1 and genotypic ratio 1:2:1:2:4:2:1:2:1.s

Conclusion :
The production of different recombinants in F2 generation proved that the colour and shape of seed didn’t influence each other but assorted independently in F2 generation. Hence, it verifies the law.

Plant Anatomy

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Anatomy is the study of gross internal structure of an organism with. Plant anatomy deals with the study of internal structures of plants.

Plant Tissue:

Tissue is a group of similar (e.g. parenchyma) or dissimilar (e.g. xylem and phloem) cells with similar functions or functions having the common origin. In the higher plants like angiosperms, on the basis of their division of labors, there’re basically following three types of tissues:

1) Epidermal Tissue: They are distributed on outer region. They are protective in nature. E.g. epidermis.

2)Ground Tissue: They are distributed in cortex and pith region. They help in food synthesis, storage and also provide the mechanical support. E.g. parenchyma, collenchyma, sclorenchyma.

3)Vascular Tissue: They are distributed in stellar region. They help in food synthesis and translocation. They also help in conduction of water and minerals. E.g. xylem and phloem.

Plant Tissues are generally classified as follows:

1)Meristematic Tissue: They have the high potential of cell division and do not have fixed shape and size. Such tissues are always living. They later on modify into permanent tissue. They are distributed in growing regions like root and shoot tips, buds etc.

2)Permanent Tissue: They lack the potential of the cell division but have definite shape and size. Such tissues can be dead or living. They carry out various functions. They are widely distributed in the regions like cortex, pith and stale. E.g. parenchyma, xylem etc.

3)Secretory Tissue: They are the tissues secreting like enzymes and hormones which are used by plants. They also produce some other products like resin, gums, latex, essential oils which are also commercially important. E.g. Latic ferrous and grandular tissues etc.

Digestive System of man

Biology XII Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction:
Digestive system of man consists of alimentary canal and digestive glands. Different parts of it are explained below:

- Mouth:
The mouth is the beginning of the alimentary canal. In fact, digestion starts after eating food. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form and the body can absorb it.

- Pharynx:
The pharynx is the next destination for food you’ve eaten. From here, food travels to the esophagus or swallowing tube.

- Esophagus:
It is a muscular tube extending from the pharynx to the stomach. By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach.

- Stomach:
The stomach is a sac-like organ with strong muscular walls. Apart from holding the food, it’s also a mixer and grinder. It secretes acid and powerful enzymes that continue the process of breaking down the food. After it leaves the stomach, food is the consistency of a liquid or paste. From there the food moves to the small intestine.

- Small Intestine:
It is made up of three parts- the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen, it is 20 feet long. The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a compound that aids in the digestion of fat and eliminates waste products from the blood. Peristalsis (contractions) is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.

Digestive glands:

- Pancreas:
It secretes enzymes into the small intestine. These enzymes break down protein, fat, and carbohydrates from the food we eat.

- Liver:
The two of main functions of liver within the digestive system are to make and secrete bile, and to cleanse and purify the blood coming from the small intestine containing the nutrients just absorbed. It has 4 lobes- two large right and left lobes while two small caudate and quadrate lobes.