NEET Part Test - 7 - NEET MCQ

Chromosomes appeared beaded during the leptotene stage of the prophase of meiosis I, also the longest stage of meiosis cell division.
Chromatin materials start condensing after that stage.

Pachytene: During the third substage of meiosis, the chromosomes continue to condense. Crossing over takes place at this stage and at each point of crossing over a chiasma is formed (singular: chiasma) between non-sister chromatids of homologous chromosomes.

Fig: Stages of Prophase I of Meiosis

Since, in mitosis the number of chromosomes in the parent and progeny cells is the same, it is also called as equational division.

The figure given above shows diakinesis phase of prophase of meiosis I as terminalisation of chiasmata is  visualized in it.

The lysosomes may be called "suicide bags’ of the cell in view of their autolytic role, or "disposal units’ of the cell because they digest the incoming food materials and remove the foreign bodies, toxic molecules, and debris, or "recyling centres" as they break down worn out cells cell organelles to component molecules for building organelles and cells.

Nucleolus is a dense, rounded, dark-staining, granular structure without a limiting membrane. It consists largely of RNAs and proteins. Nucleolus syntesizes and stores RNA. It also receives ribosomal proteins from the cytoplasm for storage. It forms ribosomal subunits by wrapping the RNAs with nitosomal proteins. The ribosomal subunits later have the nucleus through the nuclear pores.

Chloroplasts and mitochondria are semi-autonomous cell-organelles possessing their own DNA and proteins. In animals an individual gets mitochondria and mitochondrial. genes from its mother because the middle piece of a sperm that contains mltochondria does not enter the egg during fetilization. This inheritance pattern of mitochondrial genes is called uniparental inheritance or extra nuclear inheritance or maternal inheritance.

Dictyosome is a cup-shaped structure of flattened membranous vesicles found in plant cell. They modify proteins from the ER, and may also polymerise sugars to  polysaccharides. They then package these materials for delivery to destinations within the cell, for secretion, or for storage.

In most fungi the structural polysaccharide of cell wall is chitin. In plant cells cell wall is made up of cellulose.

Uracil nitrogenous base is produces nucleoside only with ribose sugar. This nucleoside is present only inside the RNA and absent in DNA.

Growth is defined as a permanent or irreversible increase in dry weight, size, mass or volume of a cell organ or organism. Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at curtain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate. The product, however, soon loses the capacity to divide and such cells make up the plant body. This form of growth wherein new als are always being added to the plant body by the activity of the meristem is called the open form of growth.

Development is the sequence of events that occur in the life history of a plant which includes seed germination, growth, differentiation, maturation, flowering, seed formation and senescence. The process of development is considered as the sum of growth and differentiation controlled by several intrinsic factors (including genetic and hormonal) and extrinsic factors (including light, temperature, water, oxygen, nutrients, etc).

Increase in growth per unit time is called as growth rate. The growth rate may be arithmetic or geometrical. Arithmetic Growth is a type of growth in which the rate of growth is constant and increase in growth occurs in arithmetic progression-- 2, 4, 6, 8, 10,12. Meristematic cells at the growing point divide in such a fashion that one daughter cell remains meristematic while the other grows and differentiates. the process continues. Mathematically, arithmetic growth is expressed as
L_t =L₀ +rt.
where L_t = length after time t, L₀   = length at the beginning, and r = growth rate. On plotting growth against time, a linear graph is obtained.

An embryo shows geometrical growth initially but later it passes into arithematic phase.

A meristematic tissue is a group of similar and immature cells that are in continuous state of division. These tissues are found in growing regions of plants. The chief characteristics of these tissues are:
(i) The cells may be round, oval, polygonal or rectangular.
(ii) They have thin cellulosic cell walls.
(iii) They do not have intercellular spaces.
(iv) They have dense cytoplasm with prominent nuclei.
(v) Vacuoles are absent or many small vacuoles may be present. The cells are in active state of metabolism.

The hepatic portal vein carries blood from the intestine to the liver before it is delivered to the systemic circulation.

Prehypertension is defined as a systolic pressure from 120–139 millimeters of mercury (mm Hg) or a diastolic pressure from 80–89 mm Hg.

(i) A microsporangium or future pollen sac is a cylindrical sac that appears circular in the transverse section. It consists of two parts, the outer wall, and central homogeneous sporogenous tissue. 
(ii) Microsporangial wall has four types of layers - epidermis, endothecium, 1−3 middle layers, and tapetum. 
(iii) The outer three layers perform the function of protection in the young anther and mechanism of dehiscence in the ripe anther. 

A stamen or male reproductive organ of a flower is made up of two parts- a stalk-like filament and a knob like terminal anther. Each anther has two lobes which are attached at the back by a sterile band called connective. When both the anther lobes are present, the stamen is called bithecous (or dithecous). A dithecous anther is tetrasporangiate having four microsporangia. Each lobe has two microsporangia separated by a strip of sterile tissue. When a single anther lobe is present, the stamen is termed as monothecous

The development of the male gametophyte in angiosperms is called as microgametogenesis. Pollen grain is the first cell of a male gametophyte. This cell undergoes only two divisions, with the result of first division two cells are formed - a large vegetative cell and a small generative cell. The second division is concerned with generative cell only. This division may take place either in pollen grain or in the pollen tube and gives rise to two male gametes.

• Having two antibiotic resistance genes in the same plasmid helps in identifying transformants.
• Transformants take up the plasmid and also integrate it into recombinant DNA.

Genetic engineering is the artificial synthesis, isolation, modification, combination, addition and repair of the genetic material (DNA) to alter the phenotype of the host organism to suit human needs. It is the manipulation of genes by man in vitro. Restriction endonucleases play major role in genetic engineering as they can cut DNA at specific sites.

CrylAb has been introduced in Bt corn to protect it from corn borer.

Bt toxin is obtained from Bacillus thuringiensis bacterium that can kill certain insects like tobacco budworm, armyworm, beetles and flies.

Cry gene is present in plasmid of bacterium. This gene can be easily separated from plasmid and included into another crops to provide resistance against pests and insects.

A collection of methods that allows the correction of a gene that has been diagnosed in a child/embryo is called gene therapy. It consists of various processes. In this, the defective genes are corrected and replaced with normal, healthy genes.

Biopiracy is the use of biological resources without proper authorization from country or people concerned without compensate payment.

The energy of light captured by pigment molecules called chlorophylls, in chloroplasts is used to generate high- energy electrons with great reducing potential. These electrons are used to produce NADPH₂ as well as ATP in a series of reactions called the light reactions because they require light.

The given molecule is adenylic acid. It is a nucleotide found in RNA. It is an ester of phosphoric acid with the nucleoside adenosine. It consists of a phosphate group, a pentose sugar ribose, and the nucleobase adenine.

Double helix model of DNA was proposed by James Watson and Francis Crick in 1953 based on X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin.