Biology: Topic-wise Test- 1 - NEET MCQ

The anther is the part of the stamen (male reproductive organ of a flower) responsible for producing pollen grains. Pollen grains contain the male gametes necessary for the fertilization of the ovules.

Size and shape of the cells vary with the functions they perform. In unicellular organism a single cell constitutes the entire organism. The components in all eukaryotic cells are more/less the same. Centrioles are present in animal cells but absent in plant cells.

Plasma membrane is a selectively permeable membrane and allows only those particles that protect the cell. Movement of air and water takes place through diffusion and osmosis respectively. Osmosis and diffusion are examples of passive transport. Active transport takes place through use of energy.

Plasma membrane is made of lipids and proteins. Lipids with hydrophobic and hydrophilic end are called amphipathic lipids. The plasma membrane is a lipid bilayer membrane. Integral proteins are not just present on the surface of the membrane but span along the entire width of the membrane.

Thus, light microscopes allow one to visualize cells and their larger components such as nuclei, nucleoli, secretory granules, lysosomes, and large mitochondria.

Mitochondria and chloroplast contain theirown genetic material. Genetic material is mainly present in nucleus of the cell but these two cell organelles also contain own genetic material.

Pleuro Pneumonia Like Organisms (PPLOs) are considered as smallest free living organism. It do not contain cell membrane or cell wall and present as fluid. It causes disease in plants.

Imparipinnate leaf is the pinnately compound leaf in which it has long terminal leaflet rather than a pair of leaflet and that terminal leaflet is called old pinnate or old leaf.

Cell cycle involves duplication of the genome, division of the parent cell into two daughter cells, synthesis of cell organelles for the daughter cells, but centrosomes are not degenerated.

Parietal:

• This type of placentation is found in the unilocular syncarpous ovary. In it, the ovule develops on the inner wall of the ovary or on the peripheral part.
• Ovary becomes bi or multilocular due to the formation a false septum.
• For example, Cucurbita, Argemone and Cruciferae family (Mustard). 

Axile:

• It is found in multicarpellary syncarpous gynoecium. The fusion margin of carpels grows inward and meets in the centre of the ovary.
• Thus, an axis forms in the centre of the ovary and the ovary becomes multi-chambered. The ovules are borne at the central axis.
• A number of these chambers are equal to the number of the carpel.
• For example,  Potato, China rose, Onion, Lemon, Orange, Tomato.

Some roots, called adventitious roots, arise from an organ other than the root—usually a stem, sometimes a leaf. They are especially numerous on underground stems, such as rhizomes, corms, and tubers, and make it possible to vegetatively propagate many plants from stem or leaf cuttings.

All cells are surrounded by a plasma membrane. The membrane is composed of a phospholipid bilayer arranged back-to-back. The membrane is also covered in places with cholesterol molecules and proteins. The plasma membrane is selectively permeable and regulates which molecules are allowed to enter and exit the cell.

Desmosomes (macula adherens) consists of intercellular thrckening matedals, disc-shaped intracellular thickening adjacent to each membrane with tonofibrils. These act as intercellular cementing material, adhere cells together at places like spot welding.

Morphological and biochemical studies indicate that plasma membranes (PM) are derived from nuclear membranes (NM) or endoplasmic reticulum (ER) via the Golgi apparatus (GA) by a process of membrane flow and differentiation.According to this concept, membranes are transferred and transformed along a chain of cell components in a subcellular developmental pathway.

A hemicellulose (also known as polyose) is a heteropolymer (matrix polysaccharide), such as arabinoxylans, present along with cellulose in almost all plant cell walls.While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength. It is easily hydrolyzed by dilute acid or base as well as a myriad of hemicellulase enzymes.

• The endoplasmic reticulum (smooth and rough) is an interconnected network of flattened, membrane-enclosed sacs or tube-like structure which are evenly distributed throughout the cytoplasm.
• It forms a continuous membrane system with the nuclear membrane which are the extensions of the infolded plasma membrane.

The Golgi apparatus plays a crucial role in the packaging and modification of proteins. Proteins synthesized in the rough endoplasmic reticulum are transported to the Golgi apparatus, where they are modified, sorted, and packaged into vesicles for transport to their destination within or outside the cell.

The synaptonemal complex (SC) is a protein structure that forms between homologous chromosomes (two pairs of sister chromatids) during meiosis and is thought to mediate chromosome pairing, synapsis, and recombination.

Telophase I, is followed by an interphase, called interkinesis, similar to the mitoticinter phase. During interkinesis the chromatin is partially uncoiled; however, there is no replication of the genetic material, because each chromosome already consists of two chromatids.

The two homologous chromosomes do not completely separate but remain attached together at one or more points as indicated by X arrangements known as Chiasmata.The displacement of Chiasmata is termed as terminalization.Terminalization is completed in Diakinesis stage.

Because during metaphase, all the chromosomes lined up on the metaphase plate and further proceeding anaphase. So it is easy to count them at that stage by counting the number of functional centromere. Because the number of chromosomes = count the number of functional centromere.

Lampbrush chromosomes are a special form of chromosome found in the growing oocytes (immature eggs) of most animals, except mammals. They were first described by Walther Flemming in 1882. Lampbrush chromosomes of tailed and tailless amphibians, birds and insects are described best of all.

Prophase I is divided into five sub-phases: leptotene, zygotene, pachytene, diplotene and diakinesis. Another sub-phase called preleptonema is sometimes recognized prior to leptonema.

Nucleoproteins are the conjugated proteins. These include ribonucleoproteins and occur in ribosomes. Deoxyribonucleoproteins occur in chromosomes.All proteins are formed in cytoplasm

Triglycerides (fats) can be hydrolyzed to produce glycerol and 3 fatty acids in the presence of acid and heat or with a suitable lipase enzyme under biological conditions.

Aspartic acid and glutamic acid are amino acids that have an additional carboxyl group that can release a proton and acquire a negative charge at the pH of body fluids.

The structure for hemoglobin is very similar to myoglobin except that it has a quaternary structure due to the presence of four protein chain subunits.Each protein chain subunit contains a heme group with the iron attached. Each hemoglobin molecule can bind to a total of four oxygen molecules.

It inhibits hexokinase from allosteric site and this process is known as competitive inhibition.

The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group. The two components are joined together by a glycerol molecule.

The protienous part of an enzyme is known as apoenzyme.