HRD Minister Ramesh Nishank announced a major CBSE syllabus reduction for the new academic year 2020-21 on July 7 which was soon followed by an official notification by CBSE on the same.

Considering the loss of classroom teaching time due to the Covid-19 pandemic and lockdown, CBSE reduced the syllabus of classes 9 to 12 with the help of suggestions from NCERT.

The CBSE syllabus has been rationalized keeping intact the learning outcomes so that the core concepts of students can be retained.

Deleted syllabus of CBSE Class 12 Biology

Mechanism of Urine Formation

The mechanism of urine formation involves the following steps:

Glomerular Filteration

Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers.

Blood is filtered in such a way that all the constituents of the plasma reach the Bowman’s capsule, except proteins. Therefore, this process is known as ultrafiltration.

Reabsorption

Around 99 percent of the filtrate obtained is reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport.

Secretion

The next step in urine formation is the tubular secretion. Here, tubular cells secrete substances like hydrogen ion, potassium ion, etc into the filtrate. By this process, the ionic, acid-base and the balance of other body fluids are maintained. The secreted ions combine with the filtrate and form urine. The urine passes out of the nephron tubule into a collecting duct.

Urine

The urine produced is 95% water and 5% nitrogenous wastes. Wastes such as urea, ammonia, creatinine are excreted in the urine. Apart from these, the potassium, sodium and calcium ions are also excreted.

Abscisic acid is the hormone which inhibits the plant growth, and also it is responsible for wilting of the leaves, germination of the seed, it is responsible for stimulating the closure of stomata in the epidermis and it also helps in increasing the tolerance of the plants to various stressful situations

• In diatoms the cell walls form two thin overlapping shells embedded with silica.
• diatoms have left behind large amount of cell wall deposits in their habitat, which accumulated over billions of years is referred to as ‘diatomaceous earth’ .
• Most of them are photosynthetic and are the chief ‘producers’ in the oceans.

A lichen, or lichenized fungus, is actually two organisms functioning as a single, stable unit. Lichens comprise a fungus living in a symbiotic relationship with an alga or cyanobacterium (or both in some instances). There are about 17,000 species of lichen worldwide.

Consciousness is the state of being aware of surrounding. It is defined by the ability of the organism to respond to the stimulus which is known as irritability. If an organism is able to respond to stimuli, that means it is aware. As irritability is defining the property of life, so consciousness can be considered as defining property of a living organism.

Metabolism is the ability to split the complex substance (catabolism) and convert them into simpler ones which further forms energy (anabolism). The energy helps to carry several metabolic and physiological function which makes metabolism an important and defining property of life.

Consciousness is the state of being aware of surrounding. It is defined by the ability of the organism to respond to the stimulus which is known as irritability. If an organism is able to respond to stimuli, that means it is aware. As irritability is defining the property of life, so consciousness can be considered as defining property of a living organism.

Metabolism is the ability to split the complex substance (catabolism) and convert them into simpler ones which further forms energy (anabolism). The energy helps to carry several metabolic and physiological function which makes metabolism an important and defining property of life.

Respiration is defined as a metabolic process wherein, the living cells of an organism obtains energy (in the form of ATP) by taking in oxygen and liberating carbon dioxide from the oxidation of complex organic substances.

Pace maker is a neuro muscular structure which produces and regulates cardiac impulses. Natural pacemaker is sino-atrial node (SA node).

The SAN is a patch of cardiac musculature tissue present in the right upper corner of the right atrium. It has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable. The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. 

Artificial pacemaker: is a medical device which uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart.

Sometimes the SAN i.e. pacemaker gets damaged and fails to generate cardiac impluses. This defect can be corrected by installing an artificial apparatus or pacemaker in the chest of the patient. Artificial pacemaker is connected to right ventricle. The apparatus stimulates the heart electrically at regular time intervals and maintains the heart beat.

The function of respiratory system is to breathe in oxygen for respiration (producing energy from food), and to breathe out carbon dioxide produced by respiration.

The major organs of respiratory system in human beings are: (i) Nose (ii) Nasal Passage (iii) Trachea (iv) Bronchi (v) Lungs and (vi) diaphragm.

In human beings, air is taken into the body through the nostrils, is filtered by fine hairs that line the passage. When air passes through the nasal passage, the dust particles and other impurities present in it are trapped by nasal hair and mucus so that clean air goes into the lungs. From here, the air passes through the throat and into the lungs. Trachea does not collapse even when there is no air in it because it is supported by rings of soft bones called cartilage.
Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli. The alveoli provide a surface where the exchange of gases can take place. The walls of the alveoli contain an extensive network of blood-vessels. When we breathe in, the ribs are lift up and the diaphragm flattens which increases the size of the chest cavity. Because of this, air is sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

Growth is defined as increase in the size and mass. It is not a defining property of life because even non living organism grows and increases in size and mass. For example, mountains can increase in height by accumulation of snow.

• Animals grow for a limited period of time after which their growth ceases and they ultimately die.
• Plant growth is unique because plants retain their capacity for unlimited growth throughout their life.
• This ability of plants is due to the presence of meristematic tissue at certain locations in their body.
• The cells of such meristems have the capacity to divide and self-perpetuate.

Reproduction is the ability to produce younger ones. It cannot be considered as a defining property of the living organism because in unicellular organism the increase in number of cells is considered as growth as well reproduction. Mule is a cross of female horse and a male donkey cannot produce fertile offspring though they are living.

Reduction divisions in the life cycle of a liverwort, a moss, a fern and a gymnosperm take place during the production of spores from spore mother cells. In case of an angiosperm, the reduction division occurs during pollen grain formation from anthers and during production of embryo sac from ovule.

In meiosis I, homologous chromosomes separate, while in meiosis II, sister chromatids separate.
Meiosis II produces 4 haploid daughter cells, whereas meiosis I produces 2 diploid daughter cells.
Genetic recombination (crossing over) only occurs in meiosis I.
If you didn't understand any of those difference or didn't notice them, it's okay, because I'm going to explain it below in detail:

Diploid Cells have two sets of chromosomes, while Haploid Cells have only one set of chromosomes. Here's how the chromatids and chromosomes split in meiosis, in terms of n.

The cell has 2 pairs of chromosomes after DNA replication, and 1 pair of chromatids is distributed to each cell during meiosis I. In meiosis II the daughter cells now have 1 chromatid each.

Hierarchical Classification is a system of grouping things according to a hierarchy, or levels and orders. ... The categorization of species is another example of hierarchical classification. At the very top is the kingdom which is the broadest category, followed by phylum, class, order, family, genus, and species. Hierarchy of categories refers to an arrangement of different taxonomic groups in a definite order from higher to lower categories. A category is called a taxon. The main aim of hierarchical taxonomy is to assign an organism an appropriate place within the systematic framework of classification.

• Ribosomes are the granular structures composed of ribonucleic acid (RNA) and proteins.
• The eukaryotic ribosomes are 80S, while the prokaryotic ribosomes are 70S, made up of two subunits.
• ‘S’ stands for the sedimentation coefficient, which is indirectly is a measure of density and size.

The Golgi is disassembled during prometaphase into vesicles, which are segregated in metaphase and then reformed during telophase. Mitochondria are fused in interphase, fragment during mitotic entry in prophase and begin to re-fuse during anaphase. Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells.