Biology Test - 50

Plant tissues may be meristematic or permanent. 

• Permanent tissues may be simple, made up of a single type of cells (parenchyma, collenchyma and sclerenchyma) or complex, made up of cells of more than one type (xylem and phloem). Parenchyma cells are thin walled and have intercellular spaces. Collenchyma cells have thickenings of cellulose and pectin at the corners.
• Meristematic tissues are made up of continuously dividing cells and permanent tissues are made of non-dividing cells. They include Apical, intercalary and lateral meristems. One important characteristic of the rapidly dividing cell is the lack of vacuoles.

IVC is the highest oxygen concentration presents in fetal circulation.

Highly oxygenated blood from the placenta is carried to the fetus by the umbilical vein, which is shunted to the inferior vena cava (IVC). The relatively higher oxygenated UV blood does not completely mix with the blood returning from the fetal body in the inferior vena cava (IVC), and is preferentially streamed towards the left atrium (through the foramen ovale).

The most common substrate used in distilleries for the production of ethanol is molasses.

Molasses are used commonly in distilleries for ethanol production. Saccharomyces cerevisiae is an industrial yeast possessing most of the desirable fermentation characteristics like fast growth and fermentation rate, osmo-tolerance, high ethanol tolerance, ability to ferment molasses, and to ferment at elevated temperatures etc.

The ground tissue is all plant tissues except vascular and dermal tissues. The parenchymatous ground tissue serves in photosynthesis, food storage and healing and tissue regeneration. Collenchymatous ground tissue supports the young stem, roots and petioles. The sclerenchymatous ground tissue provides rigid support and protection to plant parts. The function of material transport is performed by the vascular tissue system which is not part of the ground tissue.

In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates, e.g.,aschelminthes such as round worm.

In predation, one species is benefitted where as the other is harmed. It is (+ –) type of populationinteraction

Griffith performed the transformation experiment in mice using the R and S strains of Streptococcus pneumoniae. S strain is generally pathogenic and R strain is non-pathogenic. However, the heat-killed S strain cannot cause the disease. So when R strain and heat-killed S strain bacteria were injected separately, the mice stayed alive. But when injected together, the mice died. This was because, R strain bacteria got “transformed” into S strains, and caused the disease. Heat-killed R strain does not affect the mice and the mice live.

At the end of first meiotic division, male germ cell differentiates into secondary spermatocyte.

During meiosis-I, primary spermatocyte is the main germ cell. It is diploid, (2n) with 44 + XY (total 46) chromosomes. It completes the first meiotic division (reduction division) leading to the formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each i.e., 22 + X or 22+ Y. So, at the end of first meiotic division, male germ cell differentiates into secondary spermatocyte.

Blue-green algae (BGA) are actually types of bacteria known as Cyanobacteria.

• They normally look green and sometimes may turn bluish when scums are dying.
• BGA is widely distributed all over the earth.
• While fixing carbon from CO₂, certain BGA can fix dinitrogen from the atmosphere and are called nitrogen-fixing BGA, including free-living and symbiotic forms.

Some green beetles appear among the red beetle because natural variations occur during sexual reproduction. Genetic variation is useful because it helps populations change over time. Variations that help an organism survive and reproduce are passed on to the next generation. Variations that hinder survival and reproduction are eliminated from the population. This process of natural selection can lead to significant changes in the appearance, behavior, or physiology of individuals in a population, in just a few generations. Once new alleles arise, meiosis and sexual reproduction combine different alleles in new ways to increase genetic variation.