Synthesis of DNA occurs in which phase of cell cycle

 # Synthesis of DNA occurs in which phase of cell cycle?

 A. Mitosis-M phase

B. Gap- G1 phase

C. Gap-G2 phase

D. Synthesis- S phase

The correct answer is D. Synthesis - S phase.

S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase. Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved. 

Entry into S-phase is controlled by the G1 restriction point (R), which commits cells to the remainder of the cell-cycle if there is adequate nutrients and growth signaling. This transition is essentially irreversible; after passing the restriction point, the cell will progress through S-phase even if environmental conditions become unfavorable.

A d-shell containing four unpaired electrons can exchange:

 # A d-shell containing four unpaired electrons can exchange:

A. four electrons 

B. three electrons

C. sixteen electrons 

D. six electrons

The correct answer is D. Six electrons.

Explanation:

A d-shell contains 5 orbitals in which 2 electrons can be accommodated for a maximum of 10 electrons.

When four of them are unpaired, the first unpaired electron can exchange with either of other three, making possible exchanges three, the second unpaired electron can then exchange with either of third and fourth (possible exchange with first already counted) and lastly the third unpaired electron can exchange with the fourth one, making a total of 3+2+1= 6 electron exchanges possible.

Now, Can you answer this one?

# A f-shell containing six unpaired electrons can exchange:

A. Three electrons 

B. Nine electrons

C. Twelve electrons 

D. Fifteen electrons

COMMENT YOUR ANSWER. 

Aeroplane flying at a constant velocity releases a bomb

 # An aeroplane flying at a constant velocity releases a bomb. As the bomb drops down from the aeroplane, 

A. it will always be vertically below the aeroplane

B. it will always be vertically below the aeroplane only if the aeroplane is flying horizontally

C. it will always be vertically below the aeroplane only if the aeroplane is flying at an angle of 45° to the horizontal

D. it will gradually fall behind the aeroplane if the aeroplane is flying horizontally

The correct answer is A. it will always be vertically below the aeroplane

The horizontal component of the velocity of the bomb is the same as the horizontal component of the velocity of the aeroplane in all cases. Hence, in all cases, the two have the same horizontal displacement in the same time.

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Cell inclusions / Ergastic substances

 Cell inclusions / Ergastic substances

• Non-protoplasmic, non-living, metabolically inactive substance formed due to  activity of protoplasm.

3 types

1. Reserve/storage food material:

• Carbohydrate, protein and lipid are reserve material.

Carbohydrate:

• Most abundant monosaccharide is glucose.

• Most sweetest carbohydrate is fructose, also present in honey, semen.

• Sugar present in fruits, honey and nectar is fructose

• Galactose is called nerve sugar.

• Inulin is the fructose units, present in Dahlia. Also, called Dahlia starch.

• Starch = Amylose + Amylopectin

• Aleurone grains are found in the endosoperm of cereals.

• Glycogen: in animal cells and fungi.

Note: Largest starch grain is found in Canna and smallest in rice.

Lipid:

• Cells contain unsaturated fattyacids like oleic acid (C17H33COOH), linoleic acid (C17H31COOH) and linolenic acid (C17H29COOH) 

• Phospholipids are amphipathic in nature

• Waxes are esters of monohydric alcohol and fatty acids.

Protein:

• The building block of protein is amino acid.

• Simplest amino acid is Glycine, most complex Tryptophan, first amino acid to be discovered is Asparagine.

• Sulphur contaning amino acids are cystein, cystine and methionine.

• Proteins are amphoteric in nature oxidized by putrefaction process.

• Most abundant protein is RUBISCO (RUBP-Carboxylase)

• Smallest protein is Adrenocorticotropic hormone (ACTH)

• Zeatin of Maize, Oryzenin of rice, Glutelin and Gliadin of wheat are protein.

2. Secretary products: enzyme, pigment and nectar are the secretary products.

Enzymes

• Term enzymes was coined by 'Kuhne'.

• Buchner reported zymase in yeast.

• Apoenzyme + cofactor = Holoenzyme (Conjugated enzyme) 

• Enzymes have cavity known as active site, where specific substrate is attached during reaction.

Nectar

• Mixture of sucrose, glucose and fructose.

• Attracts insects for pollination.

Pigments

• Yellow colour-xanthophyll, orange colour carotene

• Anthocyanin for purple and pink colours of flower, fruits etc.

3. Excretory products: These are waste of different metabolism and accumulated in 
old leaves, bark, etc. These includes.

A. Alkaloids:

• Nitrogen containing substances, found in storage organ in combination with organic acids.

• Waste of protein metabolism 

• Insoluble in water, sour in taste and poisonous. 

• Sometimes, used in medicine as well.

Examples:

Name of Alkaloid	Obtained From
Atropine	From roots of Atropa belladona
Quinine	From bark of Cinchona
Morphine	From latex of Papaver somniferum (opium or poppy)
Nicotine	From leaves of Nicotiana tabaccum (tobacco leaves)
Reserpine	From Roots of Rauwolfia serpentina [@ R = R] Useful in cure of snakebite
Ephedrine	From shoots of Ephedra (gymnosperm) → Found in sub–alpine climate. → Yaks take it as food
Ergotine	From fungi Claviceps purpurea (Ergot fungi): source of LSD.
Thein	From leaves of Tea (Thea sinensis)
Caffeine	From seeds of coffee (Coffia arabica).
Vasine	From leaves of Adhatoda vasica
Colchicine (is a mutagen)	From corm of Colchicum autumnale (Family- Liliaceae)

Note:

• Colchicine is also called as mitotic poison.

• Inhibits formation of spindle fibres.

• Disturb metaphase stage of cell division.

• Quinine, reserpine and atropine are used for treatment of malaria, high blood pressure and heart disease respectively.

B. Tannins:

• Degradation product of carbohydrates.

• Bitter in taste.

• Found in cell sap. 

• Its percentage is high in young fruits.

• Obtained from heartwood of Acacia catechu, leaves of tea, fruits of Emblica officinalis (amla).

• At maturity, tannin changes to sugar.

C. Latex:

• Yellow/white viscous fluid made of suspensions of main source of proteins, gums, etc. 

• Main source of commercial rubber production

• Latex of papaya contains enzyme papain.

• Papain helps in protein digestion.

• Latex of banana contains Tannins. 

D. Glucosides:

• Degradation products of carbohydrates.

• Control acidity and alkalinity of cell.

Eg: Digitoxin (useful in cure of heart diseases) → source plant → Digitalis purpurea, Saponin (from fruits of Sapindus)

E. Gums: Degradation products of cell wall or cellulose.

• Source of gum Acacia Senegal (Gum tree).

• Process of gum formation is called gumosis.

F. Essential oils:

• These oils evaporate in contact with air. Eg: Leaves of Ocimum, citrus.

G. Resin: Oxidation product of essential oils.

Types:

(i) Oleoresin: eg. Canada balsam → used as a mounting medium for preparation of permanent slide.

• Source plant of Canada balsam → Abies balsamea.

(ii) Gum Resin: Eg: Assafoetida (Hing)

• From roots of Ferula assafoetida.

H. Organic acids:

• Citric acid (in fruits of citrus)

• Malic acid (from apples)

• Oxalic acid (oxalis)

• Tartaric acid (fruit of Tamarindus).

I. Mineral crystals:

• Aggregate crystals of calcium oxalate

(i) Raphids: are needle shaped.

eg. Pistia, Eicchornia.

(ii) Sphaeroraphides/Druses: are star shaped.

eg. Colocasia, Dioscorea.

• Aggregate crystals of calcium carbonate (CaCO3) are called cystoliths → found in leaf cells of Ficus (Banyan tree).

• Crystals of silica → in leaf cells of grasses.

→ Petiole of Atropa belladona (Solanaceae)

→ Equisetum (Horse tail plant) is a pteridophyte.

Note:

• Chloroplast containing spores are found in Funaria, Equisetum.

• Cell walls of grasses and Equisetum are impregnated with silicon.

Which part of the ear translates waves into mechanical vibrations?

 # Which part of the ear translates waves into mechanical vibrations?

a. External ear.

b. Middle ear.

c. Inner ear.

d. Olfactory organ.

The correct answer is B. Middle ear. 

The external ear receives sound waves. The middle ear translates waves into mechanical vibrations. The internal ear receives the vibrations and changes them into specific impulses that are transmitted by the acoustic nerve to the brain. The olfactory organ is located in the olfactory epithelium. 

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Clear layer of cells in the epithelium

 # The clear layer of cells in the epithelium is referred to as which of the following? 

a. Basal layer. 

b. Spinous layer. 

c. Granular layer. 

d. Stratum lucidum.

The correct answer is D. Stratum lucidum.

The stratum lucidum (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin, which are found on the palms of the hands and the soles of the feet.

Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes. The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin. They are surrounded by an oily substance that is the result of the exocytosis of lamellar bodies accumulated while the keratinocytes are moving through the stratum spinosum and stratum granulosum.

The thickness of the stratum lucidum is controlled by the rate of mitosis (division) of the epidermal cells. Melanosomes in the stratum basale determine the darkness of the stratum lucidum.

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Most common type of cartilage:

 # Which is the most common type of cartilage? 

a. Hyaline. 

b. Elastic. 

c. Fibrous. 

d. Dense.

The correct answer is A. Hyaline Cartilage.

Hyaline cartilage is the most common type of cartilage.

The elastic cartilage has abundant elastic fibers in its matrix and functions in the epiglottis, in the cuneiform cartilage of the larynx, and in the auditory canal and tube.

Fibrous cartilage contains bundles of collagen fibers associated with either hyaline cartilage or dense regular connective tissue.

Dense cartilage is not a term associated with cartilage.

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Part of the neuron containing the nucleus

 # Which of the following part of the neuron contains the nucleus? 

a. Axon. 

b. Perikaryon. 

c. Dendrite. 

d. Myelin sheath

The correct answer is B. Perikaryon.

The axon conducts nerve impulses away from the nerve cell body.

The cell body or perikaryon contains the nucleus and the cytoplasm. (@ Peri- around, karyon- nucleus)

Dendrites receive impulses and conduct these impulses to the cell body.

Most axons outside the CNS are protected and insulated by a myelin sheath.

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Lining epithelium - simple cell type that lines the heart, blood, and lymph vessels

 # Which of the following is a simple cell type that lines the heart, blood, and lymph vessels? 

a. Squamous. 

b. Columnar. 

c. Cuboidal. 

d. Transitional.

The correct answer is A. Squamous. 

Squamous cells line the heart, blood, and lymph vessels. Columnar cells are located in most glands, small intestines, and respiratory passages. Cuboidal cells are located in the kidney, glands, and respiratory passages. Transitional cells are located in the urinary passages and bladder.

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Which of the following is an example of an agranulocyte?

 # Which of the following is an example of an agranulocyte? 

a. Neutrophil. 

b. Monocyte. 

c. Eosinophil. 

d. Basophil.

The correct answer is B. Monocyte. 

Three types of granulocytes exist: neutrophils, eosinophils, and basophils. Two types of agranulocytes are lymphocytes and monocytes.

@ BEN-G , i.e. Basophils, Eosinophils and Neutrophils are Granulocytes. 

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