Cell The Unit of Life Test - 13

(i) Amphitrichous bacteria have flagella (single or multiple) extending from both ends of the cell.

(ii) Peritrichous bacteria have flagella projecting in all directions around the cell.

(iii) Atrichous bacteria lack flagella.

(iv) Lophotricous bacteria have a tuft of flagella located at the same point on the bacterial cell.

• The best understood are those of Drosophila, Chironomus, and Rhynchosciara.
• Thus Polytene chromosomes form when multiple rounds of replication produce many sister chromatids which stay fused together.

Microtubules are the largest type of filament, with a diameter of about 25 nanometers (nm), and they are composed of a protein called tubulin.

Actin filaments are the smallest type, with a diameter of only about 6 nm, and they are made of a protein called actin.

Recent researches suggest that peroxisomes have Actinobacterial origin.

(a) Peroxisome does not contain DNA. Most notably, they are surrounded by only a single membrane, and they do not contain DNA or Ribosomes.

(b) Like mitochondria and chloroplasts, however, peroxisomes are thought to acquire their proteins by selective import from the cytosol.

(c) But because they have no genome, all of their proteins must be imported.

(i) The chloroplast is a discoid plastid which contains chlorophyll (green pigment) within the thylakoid membranes of the organelle.

(ii) This organelle is present in the green parts of plants where photosynthesis takes place.

(iii) It is the main site of synthesis of glucose by the process called photosynthesis.

(iv) The chlorophyll pigment captures the sunlight and converts it into chemical energy and thus, helps in the process of photosynthesis.

• Most abundant water insoluble polysaccharide of plant cell wall is lignin. Lignin is a complex polymer of aromatic alcohols known as monolignols.
• It is most commonly derived from wood and is an integral part of the secondary cell walls of plants. Lignin fills the spaces in the cell wall between cellulose, hemicelluloses and pectin components, especially in xylem tracheids, vessel elements and sclereid cells.
• It is covalently linked to hemicelluloses and therefore, crosslinks' different plant polysaccharides, conferring mechanical strength to the cell wall and by extension the plant as a whole.

The chloroplasts are double membrane-bound organelle that is found in the cytoplasm. They have membrane-bound thylakoids in which the photosynthesis takes place.

The cytoplasm is thus separated from the intra thylakoid space by 3 membranes.

(i) The specialized DNA sequence that links a pair of sister chromatids where the spindle fibres are attached during cell division is known as a Centromere.

(ii) It is the lighter staining region on the chromosome of a cell which appears as a constriction.

(iii) They are also known as a primary constriction or kinetochore.

The shape of chromosomes is determined by the position of Centromere. The Centromere is the lighter staining region on the chromosome of a cell which appears as a constriction.

They are also known as a primary constriction or kinetochore. So, the correct answer is 'Centromere'.

Asafoetida is the dried latex (gum oleoresin) exuded from the rhizome or tap root of several species of Ferula, a perennial herb that grows 1 to 1.5 m tall.

Lysosomes are membrane-bound organelles which contain digestive enzymes that digest excess or worn-out organelles, food particles, engulfed viruses or bacteria, and macromolecules.

It is formed by the budding off from the trans-face of the Golgi network (sorting and modification of synthesized proteins).

Golgi apparatus is a cellular organelle which consists of folded and flattened membranes (cisternae) within the cytoplasm.

Cisternae are a flattened membrane disk-like structure (5-8 in number) in a Golgi apparatus.

The flattened and curved structure of the cisternae gives a definite polarity to the Golgi bodies.

Temperature, molecule size, molecule charge, and concentration gradients all affect the rate at which diffusion takes place.

Cell theory was proposed in 1838 by Matthias Schleiden and by Theodor Schwann. The cell theory says that: All organisms are composed of one or more cells. All cells come from pre-existing cells. All vital functions of an organism occur within cells. Cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

Several isozymes of malate dehydrogenase exist. There are two main isoforms in eukaryotic cells. One is found in the mitochondrial matrix, participating as a key enzyme in the citric acid cycle that catalyzes the oxidation of malate.

Anything less than a complete structure of a cell does not ensure independent living. Hence, cell is the fundamental structural and functional unit of all living organisms.

Mitochondria are double-membrane cell organelles with the outer membrane and inner membrane. Lysosome is a single membrane-bound vesicular structure. It contains many hydrolytic enzymes and commonly called as suicidal bag of the cells.

Ribosome is a granular structure, without membrane. It consists of RNA and proteins and is the protein builders or the protein synthesisers of the cell.

(i) The fungal cell wall is made up of chitin, glucans, and glycoproteins.

(ii) Chitin is an important structural element of fungal cell wall which is present in the form of N-acetyl glucosamine polymer of chitin.

(iii) It provides rigidity and structural support to the fungal cells.

(iv) The Chitinous cell wall also protects the cell from desiccation.

Pectic compounds are amorphous colloidal substances plastic and highly hydrophilic. The pectic substances constitute the intercellular substance that binds together the wall of individual cells. It also occurs associated with the cellulose in other wall layers, mainly the primary.