SSLC Biology

 

Chapter 1: Genetics of Life

Explain the basic structure of DNA.

Value Points:

• Strands: DNA has two strands, which are found in a double helical model.
• Nucleotide: The basic building block of DNA is the nucleotide.
• Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
• Formation of Strands: The strands of DNA are made up of sugar molecules and phosphate molecules.
• Formation of Rungs: The rungs of the DNA ladder are formed by nitrogenous bases.
• Nitrogenous Bases: The nitrogenous bases in DNA are Adenine, Thymine, Guanine, and Cytosine.

How is a chromosome formed?

Value Points:

• DNA and histone proteins are the primary components of a chromosome.
• Eight histone proteins come together to form a histone octamer.
• DNA strands wrap around this octamer to form a structure called a nucleosome.
• Numerous nucleosomes coil and condense to form chromosomes.
• Chromatids are the parts of a chromosome connected by a centromere.

Explain the stages of Protein Synthesis.

Value Points:

• Transcription: With the help of various enzymes, mRNA (messenger RNA) is formed from a specific nucleotide sequence (gene) in the DNA. The messages for protein synthesis are contained in the mRNA.
• Translation: Based on the messages in the mRNA that has reached the ribosome from the nucleus, tRNAs (transfer RNA) bring specific amino acids to the ribosome.
• rRNAs (ribosomal RNA), which are part of the ribosomes, combine the amino acids to synthesize protein.

What are the main postulates Gregor Mendel arrived at from the Monohybrid Cross?

Value Points:

• A character is controlled by two 'factors' (now known as genes).
• When a pair of contrasting characters is subjected to hybridization, only one character (dominant trait) is expressed in the first-generation offspring; the other (recessive trait) remains hidden.
• The trait that was hidden in the first generation reappears in the second generation.
• When gametes are formed, the factors determining a character segregate without blending with each other.
• The ratio of the dominant trait to the recessive trait in the second-generation offspring will be approximately 3:1.

Explain Non-Mendelian Inheritance patterns with examples.

Value Points:

• Incomplete Dominance: When the dominant allele is unable to completely mask the recessive allele, an intermediate trait is expressed. (Example: When a four o'clock plant with red flowers is crossed with one with white flowers, pink flowers are produced).
• Co-dominance: Both alleles express their traits simultaneously. (Example: The 'roan coat' pattern seen in some cattle and horses).
• Multiple allelism: A gene that determines a character has more than two alleles. (Example: The ABO blood group in humans is determined by three alleles: Iᴬ, Iᴮ, and i).
• Polygenic inheritance: More than one gene controls a single character. (Example: Skin color - variations in melanin production are caused by the action of multiple genes).

Chapter 2: Paths of Evolution

Explain Charles Darwin's 'Theory of Natural Selection'.

Value Points:

• Overproduction: Organisms produce more offspring than the environment can support.
• Variations: Organisms show differences from each other in most characteristics, such as size, immunity, and seed production. These variations can be favorable or unfavorable to the organism.
• Struggle for existence: The limitation of resources, including food, habitat, and mates, leads to competition among organisms.
• Survival of the fittest: Organisms with favorable variations survive the struggle for existence, reproduce more effectively, and create new generations.
• Natural selection: Favorable variations are passed on to the next generations. Over time, more variations accumulate, leading to the evolution of new species.

How do Lamarckism and Darwinism differ regarding the length of a giraffe's neck?

Value Points:

Lamarckism	Darwinism
The environment causes variations in organisms.	The environment selects favorable variations in organisms.
Early giraffes had short necks.	There were giraffes with varying neck lengths.
Long necks were formed by stretching the neck to get food.	In the competition for food, only giraffes with long necks survived.
Acquired traits were passed on through generations, forming a new species.	Only the favorable ones survived and evolved into a new species.

How does Molecular Biology provide evidence for evolutionary relationships?

Value Points:

• The sequence of nucleotides in an organism's DNA and the sequence of amino acids in its proteins can be compared with other organisms to determine evolutionary relationships.
• For example, the amino acids in the beta chain of human hemoglobin show zero difference from that of a chimpanzee, indicating a close evolutionary relationship between them.

What are the main functions of the Myelin sheath?

Value Points:

• Acts as an insulator, increasing the speed of message transmission.
• Provides nutrition to the neuron.
• Protects the axon from external injuries. (Note: The myelin sheath is produced by oligodendrocytes in the brain and spinal cord and by Schwann cells in nerves).

Compare the functions of the Sympathetic and Parasympathetic systems.

(The sympathetic system prepares the body for emergency situations; the parasympathetic system handles normal functions.)

Part/Organ	Sympathetic system	Parasympathetic system
Pupil of the eye	Dilates	Constricts
Heartbeat	Increases	Decreases
Bronchiole	Expands	Constricts
Digestion	Slows down	Stimulates
Adrenal gland	Increases hormone production	No direct influence
Urinary bladder	Retains urine	Empties

Chapter 3: Behind Sensations

List the layers of the eye and their main functions.

Value Points:

• Sclera: The outer layer; provides firmness and protection to the eye.
• Cornea: The transparent front part of the sclera; allows light to enter the eye.
• Choroid: The middle layer; provides oxygen and nutrients to the inner layer of the retina, and regulates temperature.
• Iris: Controls the size of the pupil; contains the pigment melanin.
• Lens: A convex lens; forms a small, real, and inverted image of the object on the retina.
• Retina: The inner layer; contains photoreceptor cells, where the image is formed.

What are the differences between Rod cells and Cone cells?

Value Points:

• Rod cells: Cylindrical in shape; more than 90 million in number; contain the pigment rhodopsin; help in seeing in dim light and recognizing black and white shades.
• Cone cells: Conical in shape; about 4.5 million in number; contain the pigment photopsin; help in seeing in bright light and recognizing colors.
• The components of both rhodopsin and photopsin include retinal, a substance formed from Vitamin A, and a protein called opsin.

Even though an image is formed in both eyes, how do we see objects as a single entity?

Value Points:

• Since each eye receives light from different angles, two slightly different images are formed on the retinas.
• Both these images are sent to the visual cortex in the brain via the optic nerve.
• The brain compares and combines (fuses) these images. This process is called binocular fusion.
• This helps provide 3D vision and understand how far or near objects are (depth perception).

Explain the process of hearing in the form of a flowchart.

Value Points:
Sound waves reach the Pinna → Auditory Canal → Tympanum (eardrum) vibrates → Ear Ossicles (Malleus, Incus, Stapes) vibrate → Oval Window vibrates → Perilymph in the cochlea moves → Basilar membrane is stimulated → Impulses are generated in the Hair cells of the Organ of Corti → Reaches the Brain via the Auditory Nerve → Sense of Hearing.

What is the role of the ear in maintaining body balance?

Value Points:

• The Vestibular system in the inner ear maintains body balance.
• It includes three Semicircular canals and the Vestibule (Utricle and Saccule).
• According to the rotating movements of the head, the endolymph in the canals moves and stimulates the hair cells there, generating impulses.
• These impulses reach the brain via the vestibular nerve and are integrated with impulses from the eyes and muscles to maintain balance. (The part of the brain that helps maintain body balance is the cerebellum).

Chapter 4: Chemoreception in Organisms

How do the 'Target cells' of hormones work?

Value Points:

• A cell on which a hormone acts is called a target cell.
• Each hormone has corresponding receptors in its target cells.
• Hormones combine with their receptors to form a hormone-receptor complex.
• This complex is what regulates the functions inside the cell.

How do the hormones insulin and glucagon regulate the level of glucose in the blood?

Value Points:

• When the level of glucose in blood increases:
  • Beta cells in the pancreas produce insulin.
  • Insulin speeds up the entry of glucose into cells.
  • Insulin accelerates the process of storing glucose as glycogen in the liver.
  • Result: The level of glucose in the blood decreases.
• When the level of glucose in blood decreases:
  • Alpha cells in the pancreas produce glucagon.
  • Glucagon converts the glycogen stored in the liver back into glucose.
  • It also converts amino acids into glucose.
  • Result: The level of glucose in the blood returns to normal.

How does the Adrenal gland help the body face emergency situations?

Value Points:

• The hormones epinephrine and norepinephrine are secreted from the adrenal medulla, the inner part of the adrenal gland.
• These hormones increase heart rate and blood pressure.
• They increase the level of glucose in the blood.
• They increase blood flow to the heart and muscles while decreasing blood flow to the skin and digestive organs.
• Through these physical changes, the hormones prepare the body to face emergency situations.

What is the role of the hormone Vasopressin (ADH) in maintaining water balance in the body?

Value Points:

• When the amount of water in the body decreases (for example, due to excessive heat and sweat), the production of vasopressin (ADH) increases.
• This accelerates the reabsorption of water in the kidneys.
• As a result, urine production decreases, and dehydration is prevented.

Chapter 5: Immunity and Healthcare

What are the differences between T lymphocytes and B lymphocytes?

Value Points:

• Formation: Both are formed in the bone marrow.
• Maturation: T lymphocytes mature in the thymus gland. B lymphocytes mature in the bone marrow itself.
• Function: T lymphocytes identify and destroy infected cells and cancer cells. B lymphocytes produce proteins called antibodies that act against antigens.

How do vaccines work in the body?

Value Points:

• The components in vaccines (pathogens or parts of them) act as antigens in our body.
• This stimulates our immune system to produce antibodies against the pathogens.
• These antibodies remain in the body and provide long-term protection from the disease.

How is Tuberculosis transmitted? What are its symptoms?

Value Points:

• Pathogen: Mycobacterium tuberculosis.
• Mode of transmission: By inhaling tiny droplets released into the air when a patient coughs, sneezes, or talks.
• Symptoms: A persistent cough for more than two weeks, fever, loss of appetite, weight loss, and fatigue. Sometimes blood may be seen in the sputum.

Explain the condition of Cancer, its causes, and treatment methods.

Value Points:

• Condition: When the control systems of the cell division process are damaged, abnormal and uncontrolled cell division occurs, and cells multiply. This condition, where cells can also spread to other parts of the body, is cancer.
• Causes: Genetic changes, environmental factors, viral infections, and lifestyle can cause cancer.
• Treatment methods: The main treatment methods are Surgery, Chemotherapy, Radiation therapy, Immunotherapy, Targeted therapy, and Hormone therapy.

Although antibiotics are effective, their irrational use is harmful. Give a reason.

Value Points:

• The unscientific use of antibiotics can lead to side effects such as stomach pain, vomiting, diarrhea, allergies, damage to the liver and kidneys, and the destruction of beneficial bacteria in the gut.
• The biggest concern is that bacteria develop resistance against antibiotics (Antibiotic resistance).
• This makes treatment more complex and can lead to the formation of multi-drug-resistant 'Superbugs' against which common antibiotics are ineffective.

Chapter 6: Biology and Technology

Define Biotechnology and Genetic engineering.

Value Points:

• Biotechnology: It is the technology of using living things or their parts to provide useful products and services for humans.
• Genetic engineering: The technology of creating desired characteristics in organisms by combining or removing genes.

Explain the components and working of Recombinant DNA Technology.

Components and Functions (Value Points):

• Restriction Endonuclease Enzyme: It is known as 'genetic scissors'. It is used to cut out a specific gene.
• Ligase enzyme: It is known as 'genetic glue'. It is used to join two cut DNA fragments together.
• Vector: Carriers that transport genes. Plasmids, the circular DNA in bacteria, are often used as vectors.
• Host cell: The cell into which the recombinant DNA is inserted.
• Working: The desired gene is combined with a vector (plasmid) to create recombinant DNA, which is then inserted into a host cell. The inserted gene functions within the host cell and produces the required products (for example, human insulin).

What is the function of Guide RNA and the Cas9 enzyme in CRISPR technology?

Value Points:

• CRISPR is a 'gene editing' technology.
• Guide RNA (gRNA): The guide RNA precisely identifies which part of the DNA needs to be cut.
• Cas9 enzyme: This acts as scissors, cutting the DNA segment identified by the guide RNA.

What is the basis of DNA fingerprinting? What are its uses?

Value Points:

• Basis: 99.9% of human DNA is identical. However, the remaining 0.1% of DNA is where differences between individuals are found.
• DNA fingerprinting is the technology of identifying individuals by analyzing the nucleotide sequence of their DNA.
• In the parts of DNA that do not code for proteins, certain sequences are repeated. The number and order of these repetitions vary in each individual. This uniqueness helps in identifying individuals.
• Uses: Identifying criminals, determining the biological relationship between parents and offspring, identifying missing persons in accidents or disasters, and detecting genetic diseases.

What is the Human Microbiome? Explain its importance.

Value Points:

• Microbiome: The Human Microbiome is the collection of microorganisms (including bacteria, fungi, and viruses) and their genes that live in and on the human body and interact with each other. Their number is about ten times the number of human cells.
• Main functions: Providing immunity, aiding digestion, and producing and absorbing vitamins.
• Importance (HMP): The Human Microbiome Project (HMP) has shown that symbiosis with microorganisms is essential for our health. The knowledge that changes in the balance of microorganisms in the body can also cause diseases has opened the way for new diagnostic methods.