TyroCity: Biology XII Notes

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.

Biology XII

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

Section A (Botany)

Section B (Zoology)

The Human Heart

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

Introduction:
The human heart is a hollow, cone-shaped muscular organ located between the two lungs above the diaphragm. Two-thirds of the heart is located to the left of the mid line of the body and 1/3 is to the right.
In heart, the apex points down and to the left. It is 5 inches (12 cm) long, 3.5 inches (8-9 cm) wide and 2.5 inches (6 cm) from front to back, and is roughly the size of one’s fist. The heart comprises less than 0.5 percent of the total body weight.

Internal Layers of Heart:

The heart has three layers. The smooth, inside lining of the heart, made of epithelial tissues, is called the endocardium. The middle layer of heart muscle is called the myocardium, which is made of cardiac muscles and important part of the heart. It is surrounded by a fluid filled sac call the pericardium, which is outermost part.

Test Tube Baby (IVF)

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

Introduction:
In vitro fertilisation (IVF) is a process by which an egg is fertilized by sperm outside the body: in vitro, in a highly sophisticated lab and in peer inspection of medical personals. It is a major treatment for infertility when other methods of assisted reproductive technology have failed.

Procedure/Method:
In vitro fertilisation could be performed by collecting the contents from a woman’s fallopian tubes or uterus after natural ovulation, mixing it with semen, and reinserting into the uterus. Here, the sperm and the egg are incubated together at a ratio of about 75,000:1 in the culture media for about 18 hours. The fertilized egg is passed to a special growth medium and left for about 48 hours until the egg consists of six to eight cells.
In gamete intrafallopian transfer, eggs are removed from the woman and placed in one of the fallopian tubes, along with the man’s sperm. This allows fertilisation to take place inside the woman’s body (may also be Surrogate Mother).

Advantages:

IVF may be used to overcome female infertility in the woman due to problems of the fallopian tube, making fertilisation in vivo difficult.
It may also assist in male infertility, where there is a defect in sperm quality, and in such cases intracytoplasmic sperm injection (ICSI) may be used, where a sperm cell is injected directly into the egg cell.
This is used when sperm have difficulty penetrating the egg, and in these cases the partner’s or a donor’s sperm may be used.

Disadvantages:

An expensive process
Chances of multiple births
May lead to production of many unwanted embryos
Legal case may arise among surrogate and genetic mother

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

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.

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.

Respiration

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

1. Mechanism of respiration:
Breathing or ventilation is the mechanical process of inhalation of fresh air (oxygen) and exhalation of foul air (carbon dioxide). It consists of the following two steps:

- Inspiration:
Process of inhaling air into the lungs is called inspiration. At first, the muscles between the ribs contract. When external muscles between these ribs contract, the ribs are pulled out and the chest cavity expands and secondly, a muscular partition wall between the chest cavity and the lower abdominal cavity, called diaphragm, contracts in such a way that it is brought down a little bit (Convexed). This also expands the chest cavity, called diaphragm, contracts in such a way that it is brought down a little bit. This also expands the chest cavity. Thirdly, there is a contraction of muscles of the stomach. All these events create a partial vacuum in the chest cavity and the atmospheric air rushes in the lung by respiratory passage.

- Expiration:
When the exchange of gases in the lungs has taken place, the air has to be expelled. Expulsion of the air from the lungs is called expiration. Reversal of events that had occurred in inspiration makes foul air go out of lungs in atmosphere.

2. Exchange of gases in lungs:
The air inhaled by inspiration comes to alveoli. All around the alveoli there is a network of blood capillaries. These capillaries are extremely fine tubes with only one layered wall. The deoxygenated blood collected from different parts of the body is at first brought to the heart, and from here pumped out to the lungs. This blood which may also be called venous blood is sent to the lungs where it has to pass through the network of capillaries around the alveoli. The oxygen from the alveolus diffuses out into the blood capillary due to difference in partial pressures of oxygen and is picked up by the hemoglobin molecules present inside the red blood corpuscles. Again, carbon dioxide, which is in greater amount in the venous blood, comes from the capillary into the alveolus.

Endocrine Glands and Exocrine Glands

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

The study of endocrine glands is called endocrinology. Thomas Addison is known as ‘The Father of Endocrinology’.

Endocrine Glands:

Endocrine glands are the ductless glands secreting hormones directly into the bloodstream and control long-term activity of target organ. They control, co-ordinate and influence various physiological activity of the body. The hormones are regulatory, metabolic and morphological in action. E.g. Pituitary gland, Thyroid gland, Parathyroid gland etc.

Chemical Composition of Hormones:

Hormones are of following chemical compositions:

a)Glycoprotein – Follical stimulating Hormone (FSH), Leutenizing Hormone (LH)

b)Proteinous – Insulin, Glucagon

c)Biogenic Amines (Containing NH2) – Thyroxin, Adrenaline

d)Steroids (containing fats) – testosterone, progesterone

Exocrine Glands:

Exocrine glands are the glands with ducts secreting enzymes. They secrete enzymes into the ducts and are present near to the site of action. The enzymes are exclusively proteinous. Their secretions may be released in or out (e.g., sweat) of the body. E.g. sweat gland, mammary gland, salivary gland etc.

Note: Glands like pancreas, testis and ovary are known as heterocrine glands because they act as exocrine as well as endocrine glands i.e. release hormones as well as enzymes, while the rest single- functioning glands are called holocrine glands.

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.

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.

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.