Biology Test - 1

PCT(Proximal convoluted tubule) is lined by a simple cuboidal brush border epithelium which increases the surface area for reabsorption. Nearly all of the essential nutrients and 70-80 percent of electrolytes and water are reabsorbed by this segment. Glucose is absorbed actively by PCT. It is reabsorbed using a cotransporter with sodium.

Transgenic animals serve as a model for human diseases. Today transgenic model exists for a disease like cystic fibrosis. Cystic fibrosis is a genetic, hereditary disease that affects the lungs and digestive system of humans.

The exchange of gases between the external environment and the lungs external respiration.

External Respiration is the exchange of gases between the external environment and the lungs. Inside the lungs, oxygen is exchanged for carbon dioxide waste through the process called external respiration. This respiratory process takes place through hundreds of millions of microscopic sacs called alveoli. Oxygen from inhaled air diffuses from the alveoli into pulmonary capillaries surrounding them. It binds to haemoglobin molecules in red blood cells and is pumped through the bloodstream. The carbon dioxide from deoxygenated blood diffuses from the capillaries into the alveoli and is expelled through exhalation.

Protein synthesis in a cell takes place in cytoplasm as well as in mitochondria. Protein synthesis takes place during the translation process inside the ribosomes. The ribosome is the protein factory of the cell. Ribosomes are found in both prokaryotic and eukaryotic cells. Ribosomes are also found in association with other cell organelles like mitochondria.  The ribosomes are synthesized in the nucleolus. Also, the ribosomes are found attached to the Endoplasmic Reticulum (ER) means they are found freely present in the cytoplasm. \(70\) S ribosomes are found in the matrix of the mitochondria of both the prokaryotic and the eukaryotic cells. This is because mitochondria are the powerhouse of the cell and the major site for aerobic respiration and ATP production.

A – Insects

B – Molluscs

C – Crustaceans

D – Other animal groups

Fertilization results in the formation of a zygote that takes place in the oviduct. This zygote then undergoes a series of changes before it actually gets implanted in the uterus. Zygote first undergoes cleavage and results in the formation of 16 cells known as a morula. This is a solid ball and is represented by figure a. The morula then enters the uterus and undergoes changes. The 16 celled morula further forms 32 cells and these then start arranging in two layers: outer trophoblast and inner embryonal mass. This also forms a cavity and is known as a blastocyst and the structure is known as a blastula. This now gets implanted in the uterus. Thus figure b is a blastocyst.

Drosophila flies with XXY genotype are females, but human beings with such genotype are abnormal males. It shows that Y-chromosome is male determinator in human beings.

In the case of mammals, sex is determined using sex chromosomes. The primary sex is determined by whether an organism has an XX or an XY karyotype. Females have two X-chromosomes in all their somatic cells whereas males have one X and one Y chromosome. Individuals with a Y-chromosome will develop into a male, independent of the number of X-chromosomes. But the individual without the Y-chromosome will develop into a female. In the case of secondary sex determination, the male or female sex is determined by the hormones produced by gonads.

In the case of Drosophila, the sex of an individual is not determined by the Y-chromosome. The genes present on the Y-chromosome are responsible for sperm formation in adults. Sex is determined by the balance of autosomal alleles and the X-chromosome. A normal diploid male contains two sets of autosomes and XY-chromosomes. A normal diploid female has 2 sets of autosomes and two X-chromosomes.

Drosophila flies with XXY genotype are females, but human beings with such genotypes are abnormal males. It shows that the Y chromosome is the male determiner in human beings.

The main feature of heterosis is:

The F1 hybrid obtained will exhibits superiority over both parents in yield, adaptation, quality and maturity because when two plants having different characters are crossed the F1 hybrid can acquire the superior desired characters of both the parents. For example, one parent has a higher yield while the other parent has greater disease resistance now the F1 progeny obtained may acquire both the characters and become superior.

Heterosis results in phenotypic superiority like increased height, yield and fertility but it is totally under genetic control because all these characters are expressed by the concerned genes only. The possible genetic causes of heterosis are: Partial to complete dominance, overdominance & epistasis. The superiority is reproducible in a specific environment only

Therefore, the correct answer is ''all of these''

Carrier ions like sodium ions facilitate the absorption of substances like amino acids and glucose.

Glucose and amino acids are co-transported along with sodium ions in the intestinal epithelium. The Na/Glucose co-transporter (SGLT \(1\)) facilitates glucose-coupled sodium absorption while amino acid-coupled sodium absorption occurs through the epithelial cells with the help of sodium/amino acid co-transporters. There are specific co-transporters for different classes of amino acids.

Formation of ribosomes is a function of the ''Nucleolus''.

The Nucleolus is a spherical and membrane-less structure so that the content of the nucleolus is continuous with the rest of the nucleoplasm. It is the site for active ribosomal RNA (rRNA) synthesis. Because of the production of ribosomes nucleolus is also called the ''ribosomal factory''

Nucleolus usually attached to chromatin (or chromosomes) at a specific site called the Nucleolar organizer region/NOR. The number of nucleolus in a nucleus is one. Onion cell has 4, and in oocytes of amphibians has 2000 nucleoli. The human cell has 5 nucleoli.